(GMAW) - TechAV

GAS METAL ARC WELDING

(GMAW)

Learner Guide

TABLE OF CONTENTS

INTRODUCTION PAGE 1 LEARNERS INSTRUCTIONS (HOW TO USE THIS PROGRAMME) PAGE 2 PROGRAMME 1 - THE GMAW PROCESS INTRODUCTION PAGE 3 RESOURCE NOTES PAGE 4 SELF-TEST NO. 1 PAGE 12 GLOSSARY OF TERMS PAGE 14 PROGRAMME 2 - EQUIPMENT PARTS AND FUNCTIONS PART 1 - EQUIPMENT PARTS AND FUNCTIONS PAGE 19 RESOURCE NOTES PAGE 20 SELF-TEST EXERCISE 2.1 PAGE 26 PART 2 - WELDING EQUIPMENT PREPARATION PAGE 28 SELF-TEST EXERCISE 2.2 PAGE 36 PRACTICAL EVALUATION - EXERCISE 2.2 PAGE 37 PROGRAMME 3 - WELDING PRACTICES AND PROCEDURES INTRODUCTION PAGE 38 RESOURCE NOTES PAGE 39 PART1 - BASIC SKILLS PAGE 39 PART 2 - PRACTICAL EXERCISES PAGE 44 PRACTICAL EXERCISE NO. 1 PAGE 49 EXERCISE NO. 2 PAGE 50 PRACTICAL EXERCISE NO. 2 PAGE 52 EXERCISE NO. 3 PAGE 53 PRACTICAL EXERCISE NO. 3 PAGE 55 EXERCISE NO. 4 PAGE 56 PRACTICAL EXERCISE NO. 4 PAGE 57 CONCLUSION PAGE 58 SOME USEFUL GMAW TIPS PAGE 59 WELDING CHART 1 PAGE 60

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GAS METAL ARC WELDING

INTRODUCTION This learning aid, consisting of your "Learners Guide" and video programmes, has been designed to assist you to learn the BASIC SKILLS and KNOWLEDGE involved in "Gas Metal Arc" welding processes. OBJECTIVES: (PURPOSE OF THIS MATERIAL) This series serves to assist you, the "Learner", in achieving a "Learnership" in any of the engineering fields where GMAW welding is stated as being a "unit of learning". PURPOSE STATEMENT (WHAT YOU WILL LEARN) During this learning programme you will learn:

o To describe basic GMAW welding processes. o To identify, by name, the equipment, components, accessories and consumables

used in typical processes. To set up and prepare for welding. To use GMAW equipment in flat weld position.

LEARNING ASSUMED TO BE IN PLACE (WHAT YOU SHOULD ALREADY KNOW / BE ABLE TO DO)

o A working knowledge of Industrial Safety and Arc welding PPE. o Identify common metals and "alloys". o An understanding of AC and DC current. o Use SMAW equipment.

LEARNING OUTCOMES (WHAT YOU WILL BE ABLE TO DO AFTER COMPLETING THE GMAW MODULE)

o Prepare a typical MIG/MAG welding unit for operation. o Produce "down-hand" welds, utilising both "Short-Circuit" and "Spray Transfer"

modes, on mild steel plates.


LEARNERS INSTRUCTIONS (HOW TO USE THIS LEARNING AID)

Step 1 - Read the Resource Notes and follow any written instructions. Step 2 - View the relevant video section (where applicable). Step 3 - Complete any "Self-Test Exercise" (as applicable). Step 4 - Perform a practical exercise (as applicable). Step 5 - Have your Mentor/Instructor assess your work.


PROGRAMME 1 THE GMAW PROCESS - AN INTRODUCTION

THE BASIC "GAS METAL ARC WELDING" PROCESS In this section you will learn:

o To describe the concept I principles of Gas Metal Arc Welding processes. o Describe/Identify by name, typical equipment constituting a GMAW system. o Explain in basic terms how MIG/MAG/FCAW processes operate. o Explain in basic terms the modes of metal transfer (Short arc, globular, spray and

pulsed).

BEGIN THIS SECTION OF LEARNING BY READING THE NOTES THAT BEGIN ON THE NEXT PAGE.


RESOURCE NOTES PROGRAMME 1

1. PRINCIPLES OF GAS METAL ARC WELDING Gas metal arc welding, or GMAW, is a welding process that involves the "continuous feeding" of filler material into a weld-pool. Gas Metal Arc Welding has become the most popular welding process, especially in fabrication industries. Although the majority of GMAW is performed "manually" (by hand skill) much is also performed using "robotic equipment" (Automobile manufacturing is a major user of such systems). In this series of programmes we will concentrate upon "manual practices". GMAW is a very easy process to operate, and anyone having had experience with other "traditional welding processes such as "gas welding" and "stick welding (Shielded Metal Arc) will find the GMAW process a "pleasure" to use! Although the term GMAW has been used several times already in this text, you will rarely hear this in the "work-place". Other common terms used to describe this process include:

o MIG or Metal Inert Gas. o MAG or Metal Active Gas. o FCAW or Fluxed Cored Arc Welding, also known as CO2 Welding.

These terms are based primarily on the method in which the weld pool (molten metal) is protected or "shielded" from the atmosphere. In order to understand these terms you need to first understand how a GMAW process works, in principle. There is a lot of science involved in welding, especially in the GMAW process, and more especially in the process of "metal transfer". We shall in this module explain those issues that affect the "weld quality" and the manner in which you, the welder, prepare and use the equipment. In this programme you will learn all that is necessary to understand the process, however let us start at the beginning and get to know what equipment is used in GMAW. 2. AN OVERVIEW OF BASIC GMAW EQUIPMENT The main parts of any GMAW system typically comprise the following:

o A "Power Supply" that delivers DC welding current at Constant Voltage. o A "Wire Feeder" -either fixed speed or variable speed. o Filler-wire, also called "electrode wire". This is a "consumable item". o Shielding gas -either "inert" or "active". This too is a "consumable item". o A "welding gun" and its connecting "power cable" and supply lines. o A work lead or "ground-lead" (cable). o Some systems include a "liquid cooling system" that cools the welding gun.


3. HOW DOES GMAW WORK? It is important that you understand the operating principles of your GMAW equipment as this knowledge will assist you to set-up and operate your equipment more efficiently. In any arc welding process metal parts are locally heated to "melting temperatures" using the "heat" generated from an electrical arc. Causing an electrical current to "jump across a gap" produces an ARC. In "arc welding", the arc is deliberately created between an "electrode" and the metal to be welded (base metal). It must be understood that an arc is established through voltage, but the "intensity' (heat power) is generated through current (amps). A welding machine or "power source" provides electrical energy to create an arc (electric equivalent of flame from a gas torch). The arc is directed onto the work (base metal) to be joined (welded) where the "heat energy" produces "local melting" of the metal. The arc is created at the tip of the electrode wire that is constantly being fed into the "weld pool". The electrode, in effect, "melts" into the weld adding "filler material" into the molten pool. In this regard the electrode is also the filler- material and is therefore a "consumable" item in the process. Electrodes are produced in the form of "wire" and supplied on reels or spools (Like fishing line). The wire is normally very thin, ranging in size (diameter) from about 0.76mm -2.38mm (0.030 inch -0.090 inch). In "common language" the electrode is known as "wire". There are many TYPES of wire in terms of the "material" from which they are produced and the "wire-size" or diameter. Note: It must be understood that when you put metal into a weld, the filler material must be "compatible" with (the same as or "similar to) the base metal. (Base metal is sometimes called the "parent metal"). You must be aware there are many types of metal and "alloys" on the general market and most of these need to be "welded" in fabrication processes. Selecting the correct "wire" for the type of


metal, and for the weld-process, is vital as a mistake could result in catastrophic damage, and possible loss of life. For this reason the "responsible welder" will seek advice on the correct wire type for any given task if he or she is in any doubt. As a rule the wire type is provided in a "welding specification" for a given task, and this in turn is given by the designing engineer or welding authority. The point being made is that you simply cannot use "any old wire type" for any job! Filler-wire (the electrode) is carried to the weld-zone via a "welding-gun" or torch. The welding gun is attached to the end of a cable assembly, sometimes known as a "conduit:'. The cable serves many functions and strictly speaking it is a combination" unit consisting of:

o A "liner" through which the electrode is fed. o A conductor wire or "electrode lead", through which the "welding current"

passes. o A "gas line" (or tube) through which the shielding gas flows. o "Signal wires" (or sensor wires) through which the gun "communicates" with

the welding machine. o And in some cases, "water lines" (hoses) through which "coolant' flows to

and from the welding-gun. This cable is connected to an adapter (socket) at the wire-feeder outlet. With the cable connected, and the machine is "powered up", upon operating the trigger on the welding-gun (depending on make, type and design) the welding machines' "contactor" is activated. A contactor is usually a "solenoid (or electronic) activated switch" that "connects the welding current to the welding terminals of the machine (In other words the welding -circuit is activated and the machine terminals are live!) At the same time other circuits are activated that do the following:

o Open the shielding gas valve (providing gas flow). o Open the coolant valve (providing coolant, where applicable). o Operate the "wire feeder motor" and thereby drive the electrode-wire

through the gun. In order for welding to happen the "welding circuit' must be "closed" (or completed). The circuit is complete as soon as an arc has been established. As already mentioned, an arc is the "source of "heat" in a weld-zone. The resultant heat causes local melting of the parent metal and the tip of the wire which "transfers" into the melted "weld pool". The manner in which the electrode I filler metal enters or "transfers" into the weld-pool is particularly important and we will deal with this in more detail when we describe "metal transfer modes" in the next section, but first a word about "shielding". Most metals will, especially when in their molten state, readily "react" with the gases in the atmosphere (notably with oxygen and nitrogen) to form "oxides" and


"nitrides". Simply stated, the result of this "chemical combination" results in the metal becoming "oxidised" or, in "welding language", porous. A "porous weld" is extremely weak and cannot be tolerated in any joint that will carry load (or stress), as the weld will fracture. To avoid "porosity" the weld zone must be protected or "shielded" from the atmosphere and this is part of the reason we need "shielding gas" in the system. In a pure Metal Inert Gas (MIG) process the shielding gas is an INERT gas, such as ARGON or HELIUM. Inert gases will not react (mix or combine) with heated metal (in the weld pool). Note: Argon is the most widely used gas type in MIG processes, mainly because helium is extremely costly. Shielding gas, supplied in pressurised cylinders, is forced through the welding gun and exits via a "gas nozzle" at the "nose" of the gun. This gas is directed onto (over) the weld pool where it surrounds the weld zone and "drenches" the hot metal. Atmospheric gases cannot penetrate the gas shield as a positive pressure is created in the gas envelope. (Gas shield pressure exceeds atmospheric pressure). Some "shielding gases" are "mixtures" of inert and reactive gases. The commonest reactive gas used is "carbon dioxide" (C02). The addition of a reactive gas into the "shielding gas cylinder' is not to improve shielding but to improve other factors such as "arc stability", weld penetration and various other factors that are far too technical to launch into right now! When a welding process makes use of "mixed gases", that include an active gas such as C02, then that process should technically be considered as Metal Active Gas (MAG) process. Note: This distinction varies according to countries and many (including South Africa) consider the MAG process to be one that uses purely "active gas", normally C02 , as the total means of "shielding". In contrast to MIG and MAG processes that use "solid wire electrodes", the FCAW process uses "hollow electrode wire" and the hollow "core" of the wire is filled with "flux". Flux is a mixture of various substances (chemicals and other compounds) which, when subjected to the heat of the welding process, release shielding gas and, in some cases, add elements into the weld that improve the quality of the weld material. The flux also acts to "clean" the metal surfaces during the process. Conventional FCAW electrodes do not generate sufficient shielding for the weld and additional shielding is provided, most usually, with carbon dioxide. Some flux-cored wires, known as "self-shielding electrodes", do not require additional shielding during the welding process. The most usual (common) gases used in GMAW processes are:

o Argon -a fully inert gas -commonly used for welding aluminium. o Helium -a fully inert gas -not commonly used alone, often mixed with argon

and CO2for high quality welds in stainless steel. Thick section aluminium (over 25mm) requires at least 75% helium 25% argon mix to achieve the desired heat input.

o Carbon Dioxide -Usually known by its "chemical designation, CO2'' This is a "reactive gas" that, if permitted, will combine "chemically" with the metal in


a weld-pool. This gas is used only with "ferrous metals" and, with the exception of FCAW welding, is mixed in small quantities with inert gases.

o Oxygen -a reactive gas and used only in minute quantities for purposes of improving arc stability and heat transfer when welding steel using "spray transfer". Oxygen is normally mixed with argon in quantities rarely exceeding 5% of total volume.

Note: Gas providers or suppliers usually have their own "brand names" for their "commercial gas mixes". Ask your gas vendor for the information regarding the proportions and suitability of gases for a particular application.

4. METAL TRANSFER MODES We move now to a topic that is often misunderstood namely, metal transfer modes, or "the way in which the electrode wire gets into the weld!" There are 3 "modes of transfer" namely:

o Short-Circuit transfer, sometimes called "dip transfer", "short arc transfer" and "buried arc".

o Globular transfer, and o Spray transfer.

4.1 SHORT CIRCUIT TRANSFER (SHORT ARC AND DIP TRANSFER) Short Circuit Transfer is the "preferred mode" for welding the following:

o Thin metal up to approximately 2 to 3mm thick. o Out of Position welding. o Filling large gaps. o Root runs in heavy gauge material (V-grooved).

The short circuit mode is considered to provide a "cool weld" owing to the "on and off' nature of the arc. In the short circuit mode the "cycle" begins when an arc jumps across the small gap between the electrode wire and the work (base-metal). An instant later the electrode-wire makes contact with the base metal or weld-pool as it is fed through the gun by the wire feeder, and a "dead short" occurs in the circuit. The welding machine (power source) tries to maintain the pre-set voltage and it does this by increasing the amperage (current). As a result of the increased current a "pinch force" is created at the electrode tip, and a small section of the wire fuses (breaks) off into the weld-pool. At this instant the "arc gap" is recreated between the electrode tip and the base metal and the arc is re-generated, due to the voltage returning to its set value. The electrode wire is then fed back into the weld pool creating a short circuit again, and so the cycle continues. This "cycle" of shorting, wire tip pinching off and the arc re-establishing happens between 80 and 200 times per second!


INDUCTANCE CONTROL With short circuit transfer, the current rise, at the time of the short circuiting occurring may take place too quickly causing the electrode tip to explode. Some power sources include "inductance control" in the form of "tapings" to which the "work lead" is attached. Increasing inductance, in "short circuit transfer mode", will prevent the electrode from exploding (spattering) as well as result in a more fluid weld pool. SLOPE ADJUSTMENT Slope adjustment, featured on some power sources, is used to alter the value of the maximum "short circuit current". When the slope is "increased" the maximum current is "decreased". The ultimate effect is the reduction of spatter. BURN BACK CONTROL In short circuit mode there is a chance that the wire will stick or "freeze" to the weld at the moment that the gun trigger is released when welding stops. (Releasing the trigger when set to the 2 times or "2T" trigger mode position, effectively stops the welding current, the gas flow and the wire feeder). Burn back control delays the current "contactor" from cutting• out for a fraction of a second after the wire feeder motor stops. In this way the wire tip will still be energised (although the feed has stopped) and the tip will burn back thereby preventing it from sticking to the work. Many modern machines incorporate automatic burn back control in the electrical circuit. Note that the welder (operator) could simply break the arc by pulling the gun away from the weld, but this action would remove the "post flow" of shielding gas from the weld pool and result in a "porous" crater at the end of the weld. SUMMARY (SHORT CIRCUIT) Short-circuit transfer will be achieved on carbon-steel typically using:

o Wire sizes ranging from 0.98mm to 1.2mm. o Voltage range of 15 to 20 volts. o Wire feed speeds between 2.5 to 10 metres per minute. o Current range -approximately 80 to 200 amps. o Argon + 5 - 10% C02 for steel thickness below 1. 75mm. o Argon + 15 - 25% C02 for thicker material.

4.2 SPRAY TRANSFER In "Spray Transfer" the electrode melts in the arc to form small droplets roughly the same diameter as the wire. These droplets are carried into the weld pool by electro- magnetic forces in a continuous stream or "spray". Spray transfer places a lot of heat into the base metal thereby making it more suitable for joints requiring deep penetration and for metal thickness of 6mm and greater.


It is however difficult to weld steel "out of position" with spray transfer owing to the "excessive fluidity" of the weld-pool and the risk of "spill over". Metals with good heat dissipation ("conductivity") such as aluminium, can be welded out of position using spray transfer. Spray transfer occurs, with carbon steel when:

o Welding voltage is set relatively high, typically 25 to 35 volts. o Wire size 0.98mm -1.2mm. o Wire feed speed between 9 to 14 metres per minute. o Current range -approximately 180 -380 amps. o Shielding-gas comprising at least 80% inert gas (Argon or Helium).

You will notice that a "long arc" is generated when spray transfer is used, owing to the relatively high voltage. 4.3 GLOBULAR TRANSFER Globular transfer occurs when the electrode (wire) tip melts in the arc to form a relatively large ball (or globule) that falls in a "random fashion" into the weld pool. Globular transfer occurs when the welding "voltage" is set higher than for "short circuit transfer" but too low for "spray transfer", in other words it is a "transitional" transfer-mode between dip and spray. 4.4 PULSED SPRAY In an effort to achieve a "spray transfer mode" using lower welding currents the manufacturers of welding "power sources" created welding machines called "pulsed- arc units". A pulsed-arc unit basically combines two power sources into one machine. One power source provides a "background current" which effectively keeps the wire tip in a "molten state". The other generates "peak-current pulses", that are higher than the "background current", at a "frequency of between 60 and several hundred times per second. Upon each "peak-pulse" a small droplet separates from the tip of the electrode-wire and is carried into the arc stream (sprayed) and deposited in the weld pool in a steady (constant rate) stream. Pulsed arc welding typically imposes welding currents of between 50 and 220 amps when using arc voltages of 23 -25volt thereby creating a "cooler weld" than conventional spray transfer, making it possible to weld thin gauge material. IN SUMMARY Keep the following facts in mind regarding metal transfer modes: It is the welding "voltage" that determines the arc length and it is the "wire feed speed' that determines the "welding current (amps)".


That the mode of metal transfer is the result of a combination of the following factors: o Wire size (diameter). o Wire feed speed (Current). o Welding voltage. o Type or mix of welding gas.

5. SAFETY AND PPE For most practical applications you must take the same precautions with GMAW welding processes as you would with SMAW (Stick welding) namely:

o Always wear a welding helmet (mask or hood) when welding or when observing a weld in progress. The visor must be fitted with at least a #12 shaded lens.

o When working in the "general area" of GMAW welding operations, always wear "flash goggles".

o Erect "welding screens" around the work area in order to protect those around you.

o Wear welding gloves. o Wear overalls and roll the sleeves down to protect against skin burns. o Wear a "welders apron" especially if you are doing "overhead welding". o Always work in a properly ventilated area. (Special safety precautions are

required if you have to weld in a "confined space"-see Tech A.V programme CS-1).

o Use a "fume extractor" when welding indoors or in a small workshop. o Take care when welding upon certain metals, notably those alloys containing

zinc, as fumes are "toxic". Many FCAW electrodes also emit toxic or "noxious" fumes (Always read the warnings given on the labels where applicable).

o Always adhere to mandatory safety rules applicable to your industry.

NOW VIEW VIDEO GMAW-1. THEN COMPLETE THE SELF• TEST EXERCISE ON THE FOLLOWING PAGE.



SELFTEST NO. 1 GMAW OPERATING PRINCIPLES

INSTRUCTIONS Complete the following exercise without reference to your notes or the video. When you have completed the exercise check your answers/responses by:

o Referring to the notes. o Reviewing the video material. o Asking your Instructor/Mentor.

QUESTION YES NO

1. What do the letters "GMAW" mean? ___________________________________________________________

2. What do the letters "MIG" mean? ___________________________________________________________

3. What does "MAG" mean? ___________________________________________________________

4. What is "FCAW"? ___________________________________________________________

5. What makes a GMAW process different from Shielded Metal Arc welding? ___________________________________________________________

6. What is the "primary reason" for a "welding gas" in most GMAW processes? ___________________________________________________________

7. Which part of the welding equipment supplies the "welding current"? ___________________________________________________________

8. Which part of the equipment moves the electrode to the welding gun? ___________________________________________________________


9. What 3 main types of "shielding gases" are used with MIG and MAG processes? i) _________________________________________________________ ii) _________________________________________________________ iii) _________________________________________________________

10. What are the 3 modes of metal transfer? i) __________________________________________________________ ii) _________________________________________________________ iii) _________________________________________________________

11. List 3 items of "personal protective equipment" that you should always use when welding. i) __________________________________________________________ ii) _________________________________________________________ iii) _________________________________________________________

THIS CONCLUDES PROGRAMME NO. 1.


GLOSSARY OF TERMS (RELEVANT TO PROGRAMME NO. 1) A brief explanation of certain "technical terms" or words that may appear in the text or be used in the video programme. A Active Gas: A gas that will combine easily or readily with molten weld material. Carbon Dioxide and Oxygen are active gases. Air Cooled Gun: A GMAW welding gun used mainly for light duty work, The nozzle and contact tip are cooled by the flow of air and "shielding gas" surrounding them, These guns are rarely used where the welding current exceeds 200 amps. Alloy: A pure metal that has been mixed, during the molten state, with other metals or metallic elements. Brass, for example, is an "alloy" of copper and zinc. Arc: The flow of electricity that jumps across a gap in an electric circuit. Argon: An "inert gas" found in the atmosphere. Automatic Welding: A welding process that is controlled "mechanically" using a "robot" or any other device other than a "human welder". B Background current: A relatively low current that remains on all the time during "pulsed spray transfer". The background current maintains a "continuous arc". Base Metal: Metal that is to be welded also called the "work". Bead: The shape of a finished fusion-weld. C Carbon Dioxide: Known as C02 by most welders, is a gas commonly used for "shielding" in GMAW processes. Carbon Steel: Steel that has been produced by adding small amounts of carbon to pure iron in the molten state. Circuit: The path through which "electrons" flow from a "source", through various electrical components and back to the "source". Constant Current (CC): The term used to describe a power source that delivers "near constant" amps" even if the circuit voltage fluctuates. Most SMAW machines are of the CC type. Constant Voltage (CV): Also known as "constant potential" is the term used to describe a welding machine that delivers "near constant volts" even if the "amperage fluctuates, Most GMAW welding machines are of the CV type. Consumable (welding): Any item in a welding process that is used in the creation of the weld and enters the weld-pool is considered to be a "welding consumable". The electrode in the GMAW process is the main "consumable" in such a process. Continuous Weld: A weld that is started and finished, in a single operation, without having to stop.


Current: The volume or flow of electrons that pass through an electrical circuit. Current is measured in Amperes or Amps. D Deposition Rate: The weight (mass) of material (filler) that is deposited into a weld over a given time period, normally expressed in Kg/Hr. Direct Current (DC): The flow of electrons in one direction only, for example from the negative to the positive connection of a power source. Duty Cycle: The amount of time, in a given period (usually 10 minutes), that a welding machine can operate, at its rated load (amps), without "overloading" or "overheating". E Electrode: The point to which the "welding current" is brought in order to generate the "arc" that generates the "heat" that melts the "base metal". An electrode may be made of the "filler material" required to create a "bead" in which case it is a "consumable electrode". In some cases the electrode may be "non-consumable", such as the "tungsten electrode" used in TIG welding. F Filler Metal: Metal or Alloy that is used to create the weld bead. Flash: The bright intense arc, generated in Arc-welding processes, as seen by the human eye. G Gas Metal Arc Welding (GMAW): the arc welding process that uses a continuously fed, consumable electrode in conjunction with a "shielding gas". (Also called MIG/MAG welding). Globular Transfer: The deposition of metal from an electrode (melting in the arc), in the form of large "blobs" of molten metal. H Helium: An inert gas which, like argon, is used to provide shielding in certain MIG welding processes. Generally associated with "critical welding", especially with Stainless Steel. I Inching: The term used to "advance" the electrode wire, in a "controlled manner" (little at a time). Inductance: An electrical term of complex meaning, but from a Welders' point of view it is a manner of controlling the "rate of increase" (rise) of a welding current to reduce excessive "spattering" when welding. Inert Gas: Gases such as Argon and Helium that do not react (cause change} in a weld.


Insulation: Any material that will not permit an electric current to pass through it. The handle surrounding the welding gun is made of "insulative-material". L Lead: The cable, wire or "conductor" that carries electricity. In welding terms this is usually the "work lead" that returns the electricity from the work back to the "power source". Liner: The flexible tube through which the electrode passes between a "wire feeder" and the "welding gun". M Metal Active Gas (MAG welding): The use of "mixed shielding gases", both active and inert, result in the term MAG. MAG welding normally involves the use a shielding gas containing mostly Argon plus around 15-25% C02 and very small amounts of Oxygen (2-5%). The MAG process is mainly restricted to the welding of steel (ferrous metals). Metal Transfer: The movement of metal from one surface to another. This can occur in various ways but it is mostly used to describe the "molten transfer" as in "fusion welding". N Nozzle: A metal or a ceramic tube or cup fitted to the end of a welding gun. The nozzle directs the flow of "shielding gas" onto the weld area. O Open Arc: Any arc that is VISIBLE is considered an "open arc". Open Circuit voltage: The voltage in a welding machine circuit when the machine is "powered up" but the arc has not been struck. Out of Position Welding: Welds made in the vertical, overhead or horizontal position. That is any position other than "flat" or "down-hand". Oxidation: The process in which Oxygen combines with a material or substance to form a chemical compound called an "oxide". (Normally associated with "burning" and "heating"). P Pinch Force: An electrical "force", associated with Short Circuit Transfer. It is a "magnetic force" that causes a droplet of metal to be "pinched off' at the end of the electrode during the short circuit phase. Porous / porosity: The presence of gas pockets or "holes" in a weld bead. Post Flow: The flow of shielding gas that continues for a short time after the welding current has been stopped. Normally required to prevent "oxidising" and "porosity" whilst metal is in the "molten state". Pressure Regulator: Device used to convert cylinder gas pressure to a usable "working pressure". Pulsed Spray transfer: Alternative mode of spray -transfer, where spray transfer is achieved with reduced current.


Pull Gun: A welding gun that has an in-built wire-feeder that pulls the electrode-wire through the gun cable. R Rated Output-Current: The maximum current or "load" that can be generated from a welding machine. Resistance: In electrical terms, the property of a material to "resist" (slow down) the flow of electricity through it. S Shielding (gas): The protection of a weld-pool and arc from the atmosphere. An "inert gas" is used to surround the weld-zone and prevent atmospheric gases (oxygen and nitrogen) from reacting with the heated surfaces. Short Circuit: An electrical term used to describe an electrical current moving directly to its source by bypassing the electrical devices in the circuit. Short Circuit Transfer: A term used to describe the manner in which filler material breaks away from the electrode when the electrode "shorts out" against the weld or the base metal. Slope: The electrical "losses", in terms of volts and amps, as a result of resistance in an electrical circuit. Stainless Steel: An alloy of steel with elements such as "chromium" that result in a product that can withstand "corrosion" and oxidation (rust). T Tap (or Tapping): An electrical connection point on a welding machine to which the work-lead may be attached. V Voltage: The "force" or "electrical pressure" in an electric circuit, that causes current to flow. Volt drop: The loss of "voltage" as a result of resistance in a circuit. (As in slope). Voltmeter: A device used to measure voltage. W Water-cooled gun: A welding-gun or welding torch that is cooled using liquid, normally water. Water-cooling prevents a gun from overheating especially when welding currents above 200 amps are generated. Weld: The mixing of two or more materials (metal or non-metal) using heat to bring them to a molten state where the elements "fuse" to become one. Weldment: An assembly of parts (pieces) that have been joined together by welding. Welding Station: The work area, including all the welding equipment, where a welding operation will be (is being) performed.


Wire: In GMAW terms this is the name used, by most "Welders", for the electrode-wire. Wire-Feeder: The device used to deliver the electrode-wire in a continuous action, to the weld area. Work piece: The material to be (being) welded.

NOW MOVE ON TO PROGRAMME 2: EQUIPMENT - PARTS, FUNCTIONS AND PREPARATION".


PROGRAMME 2 EQUIPMENT - PARTS, FUNCTIONS AND PREPARATION

PART 1 - EQUIPMENT PARTS AND FUNCTIONS In this section you will learn to identify by name, and describe the function/operation of:

o A GMAW power source (Typical). o A Wire feeder (Typical). o A welding gun (Typical). o Gas supply equipment. o Electrode wire(s).

BEGIN THIS SECTION OF LEARNING BY READING THE NOTES ON THE NEXT PAGE.



EQUIPMENT -PARTS AND FUNCTIONS 1. GMAW POWER SOURCE (AND WIRE FEEDER) Virtually all GMAW power sources ( "power supplies" or "welding machines") deliver a DC output, and are of the CONSTANT VOLTAGE type. The welding current is most commonly set to "Reverse Polarity" or DCEP (electrode positive). There are many and various makes, types and sizes of GMAW machines available and the selection of a machine is normally based on the nature of the work to be performed. Machines are generally rated in terms of their current output (welding current in Amperes). Typical (max) current ratings, for light to medium fabrication work would be 220 amps, 280 amps and 350 amps. Heavy-duty machines would typically achieve amperages above 380 often moving into the 600 amp (plus) range. For portability a welding machine is usually mounted upon a wheeled platform or "trolley" which usually accommodates (supports) the shielding gas cylinder. The controls on typical GMAW "welding set" normally include:

o An isolator switch -Power switch. o Voltage controls (Coarse and Fine) -for the "pre-setting of welding voltage. o A wire feeder control -to set the desired rate of "feed" of the electrode wire

into the weld pool. o A wire "inching control" -also called a "jog control"-used mostly when lacing

wire through the wire-feeder. o Gas "post flow" timer control -for setting the desired amount of gas

post - flow. o Burn-back control -a control that essentially prevents an electrode sticking to

the work when welding stops. ( effective when using short -circuit transfer). Depending on make, model and "price-range" you may find other controls or features, refer to the Operators manual to identify all the controls on your particular welding unit. 2. WIRE FEEDER The purpose of the wire feeder is to deliver "electrode wire" into the weld zone, via the welding gun, at a controlled rate. The rate at which wire is fed to the gun is stated in either "metres per minute", or "inches per minute". A controller dial (rotary switch) mounted on the "panel" offers the control over the delivery rate (wire feed speed).


The most "conventional" (non-digital) feeders offer speed ranges between 2 M/min (70 inches/min) and 20 M/min (700 inches/min). There are two basic types of controllers namely, step type and infinite control. • A step type normally has 10 positions (notches or clicks) and (turning the dial clockwise) each notch increases the feed speed by 2 metres per minute. (70 in/min). An infinite controller offers precise control between the minimum and maximum range. Electrode-wire is stored upon a spool (or reel) and this is mounted on a spindle, either within or just behind the wire feeder unit. The spool must always be "free to rotate" on the spindle. Electrode-wire is drawn off the spool by motorised "drive rolls". In essence the wire is "pinched" between two metal rollers (drive-rolls) which are powered by an electric motor. As the rolls turn they cause the "pinched wire" to be pulled off the spool and to be "pushed" into the "cable liner" that terminates in the welding gun. There may be one or two sets of "drive rolls" in a wire-feeder depending on the make and model. The electrode-wire enters and exits the drive rollers via "wire guides". Wire guides ensure that the electrode remains "rigid" as it passes through the rollers and prevents the wire from "buckling". The wire guides (plus the housing) on older machines have to be "set" (adjusted) to optimise the smooth movement of wire through the rollers and into the flexible cable. Most modern machines have "pre- set" drive rolls that require no adjusting other than "pressure" or tension upon the upper rolls . The pressure exerted upon the wire between the drive rollers must be adjusted, whenever a new spool is attached, to provide positive feed and minimum "slippage" between the wire and the roller surfaces. Drive-rolls are grooved to maintain wire- alignment, and to provide "grip" on the wire as it passes through.

WIRE - FEED MECHANISM OF THE "MIGATRONIC 505"


SPECIALISED EQUIPMENT Aluminium wire is very soft and is prone to sticking or jamming in a standard wire feeder. To get over this problem a second set of drive-rollers may be situated at the "gun end" of the cable. This design effectively provides a "push and pull" effort to the electrode-wire.

3. WELDING GUN (INCLUDING CABLE) The purpose of the welding gun is:

o Make electrical contact with the electrode. o Direct shielding gas to the weld. o Start and stop the welding operation.

There are various types, sizes and shapes of welding guns but essentially they all have the following features (Use a good diagram with labels):

o A body. o A "contact tube". o A nozzle.

o A trigger/switch The gun assembly is connected to the electrode cable. The

"combination cable" on the gun carries electricity, the electrode and hielding gas, as well as the electrode "liner" and "remote control wires".

(Note: Some gas hoses may be situated outside the cable housing).


The electrode cable is connected to the power source output-connector. When the trigger is depressed on the gun the system is activated. Upon action the electrode wire is fed, from the wire-feeder, through a wire-liner and on through the gun via a "contact tip". The contact-tip, itself an electrical conductor (copper), makes contact with the "electrode cable" within the body of the gun and this in turn makes an electrical connection with the electrode wire passing through it. (Liners can be removed and replaced fairly simply. When aluminium wire is fed through a cable then a "soft liner" is fitted. A soft liner is normally made from special "plastic material" called Teflon® ). On activating the trigger, shielding gas is also directed through the gun. Gas is directed to the weld-zone from the gun via a metal nozzle which maintains the correct gas envelope shape. In this way the gas also serves to cool the gun during operation. Both the nozzle and the contact tube are replaceable items as they do become contaminated and damaged through the effects of heat and "spatter" during a weld process. Contact tips must be matched (sized) according to the wire-size, and renewed when the bore becomes worn from the electrode-wire. 4. CABLE AND HOSE CONNECTIONS Various cables, hoses and other connections are involved in any typical MIG/MAG welding unit and these include:

o The Mains Power Cable -to supply shop power to the machine. o The Electrode cable -to supply welding current to the gun.


o A "Wire-Liner" that supports and insulates the "electrode-wire" between the wire feeder and the gun.

o A gas supply line -to connect the shielding gas from the gas bottle to the power source (welding machine).

o A gas feed line -to carry gas from the machine to the welding gun. o A remote connector -to connect the trigger switch to the machines' internal

electronics and the "contactor switch". o The wire feeder inter-connector cable ( for remote wire feeder). o The "work lead" also known as the "Ground cable", -that provides the

electrical "return path" for the weld current. 5. SHIELDING GAS EQUIPMENT Shielding gas, as supplied by your gas vendor, is contained within heavy steel cylinders, usually known as "gas bottles". The pressure within a freshly filled bottle is extremely high ( approx. 200kg/cm2) so that a large volume of gas can be stored. The pressure required to cause a "shielding envelope" around the weld-zone is approximately (1 bar) and this pressure is called the "working pressure". A gas "regulator", fitted to a "delivery valve" upon the bottle reduces cylinder-pressure to the desired "working pressure". A pressure gauge situated on the regulator shows the pressure of the gas contained within the bottle. The volume of gas, or the "flow rate", being delivered to the gun is controlled using a flow control-valve that is situated on the "down-stream" side of the regulator. 6. ELECTRODE WIRE (TYPES AND SIZES) As earlier mentioned there are many and various types of electrode wires used in GMAW processes. Selection of a suitable electrode is usually based on factors such as:

o Base metal type and composition. o Cleanliness of the base metal. o Type of shielding gas available. o Metal transfer mode required. o The welding position.

Note: Both MIG and MAG processes utilise "solid wire" electrodes and FCAW processes use "flux cored" or "hollow" electrode wire. The following tables offer recommendations as to the type of electrodes used typically for various metal types. Note that FCAW electrodes are limited to use on steel (including stainless) base material.


TABEL 1 GMAW (Solid Wire for MIG and MAG)

BASE METAL ELECTRODE TYPE Aluminium. ER1100, ER4043, ER5356. Copper and copper based alloys. ERCu, ERCuSi-A, ERCuAI-A1. Carbon steel. ER70S-3, ER70S-6. Low alloy steel. ER80S-B2, ER80S-D2. Stainless steel. ER308, ER308L, ER316, ER347. Nickel and nickel alloys. ERNi-1, ERNiCr-3, ERNiCrMo-3. Magnesium. ERAZ61A, ERAZ92A. Titanium. ERTi-1.

TABEL 2

FCAW (Hollow wire) BASE METAL ELECTRODE TYPE Carbon steel. E70T-1, E71T-1, E70T-2. Low alloy steel. E80T1-B2, E80T1-Ni2. Stainless steel. ERE308T-3, E308LT-3, E316LT-3, E347T-

3. It must be noted that "Flux Cored" electrodes are designed with the letter "T" in the identification code. For a full and complete explanation on electrode types and their suitability for various metals and alloys, refer to the following AWS references: TABLE 3

METAL TYPE AND PROCESS AWS REFERENCE Stainless steel - MIG/MAG. A5.9 Aluminium alloy - MAG. A5.10 Nickel alloy - MIG. A5.14 Carbon steel - MIG/MAG. A5.18 Magnesium alloys - MIG. A5.19 Carbon steel - FCAW. A5.20 Stainless steel - FCAW. A5.22 Low alloy steel - MIG. A5.28 Low alloy steel - FCAW. A5.29

NOW VIEW PART 1 OF VIDEO NO. 2. THEN COMPLETE SELF - TEST NO. 2.1 ON THE NEXT PAGE.



SELF TEST NO. 2.1 GENERAL EQUIPMENT AND CONSUMABLES

INSTRUCTIONS Complete the following exercise without reference to your notes or the video. When you have completed the exercise check your answers/responses by:

o Referring to the notes. o Reviewing the video material. o Asking your Instructor/Mentor.

QUESTION YES NO

1. MIG welding machines most usually deliver what (tick correct response): a) AC constant current. b) DC constant voltage. c) DC constant current.

2. What is the main purpose of a wire-feeder? ________________________________________________________

3. What purpose do the "grooves" in the drive-rolls serve? ________________________________________________________

4. The electrode-wire is guided through the gun-cable, by what? ________________________________________________________

5. Contact tips become worn because ...? ________________________________________________________

6. Why are contact tips available in various sizes? ________________________________________________________

7. What purpose does a "regulator" serve? ________________________________________________________

8. What purpose has a "flow-meter"? ________________________________________________________

9. What is "post flow"? ________________________________________________________


10. What is the main purpose of "post flow"? ________________________________________________________

NOW MOVE ON TO PART 2 OF THE PROGRAMME: "WELDING EQUIPMENT PREPARATION".


PROGRAMME 2 EQUIPMENT - PARTS, FUNCTIONS AND PREPARATION

PART 2 - WELDING EQUIPMENT PREPARATION In this section you will learn how to:

o Connect the power source to the wire feeder. o Prepare the gas supply to the welding station. o Prepare a welding gun and gun liner. o Prepare the wire feeder unit. o Connect the welding gun and feed the electrode to the contact tip. o Connect the work lead.

BEGIN BY READING THE NOTES ON THE NEXT PAGE.


IMPORTANT SAFETY NOTE: Make sure the machines' power switch is in the OFF position and that the machine is ISOLATED FROM THE MAIN SUPPLY before attempting any electrical connections or mechanical connections where rotating parts are involved! 1. CONNECT THE POWER SOURCE AND WIRE FEEDER No matter which equipment you use, an external wire feeder unit must be connected to the power source in some way. On our demonstration unit, this is achieved via an "inter ¬connecting combination cable". This cable supplies the electric current, the shielding gas, the control signals and in our example, the cooling water between these two units. Check the instruction manual of your particular equipment for details on how your units are connected.

2. SHIELDING GAS PREPARATION A standard (Industrial) cylinder is very heavy and MUST be positioned in an upright position and secured to prevent it toppling over. Assuming that you have to replace a gas cylinder, for whatever reason, then the procedure for preparing the gas supply in readiness for welding is as follows:

o Fit the regulator assembly. o Connect the delivery hose to the welding unit.

PROCEDURE Assuming that a new or refilled cylinder has been installed and secured to your welding station then proceed as follows:

o Remove the dust cover from the cylinders' "delivery valve". o Stand aside (not facing) the cylinder and blowout any possible dirt (dust etc) from

the valve by quickly opening then closing the delivery valve. o Attach the regulator assembly to the delivery valve. Use a correctly fitting spanner to

tighten the "bull nose connector nut". Do not use "makeshift tools such as pliers or a pipe-wrench as this will damage the hexagon. Make sure that the flow-meter sight glass is in an upright position when the connection has been secured.


o Attach the "supply hose connector" to the "outlet connector-nipple" on the regulator assembly. Again, use only the correct fitting spanner for this. If the hose has a "hose clamp" attached, then, using a screwdriver, check that the hose is secure by tightening the clamp-screw.

3. WELDING GUN 3.1 PREPARING THE WELDING GUN Welding guns contain wearing parts and it will be necessary to replace or repair them on occasion. The contact tip is the most usual part that will need replacement. During normal use with steel wire the contact tip will need replacement after about 8 hours of welding time owing to the wear factor. A worn contact tip will typically, upon inspection, present an elongated "bore" (oval). Another problem encountered with contact tips is "spatter deposits". Spatter, or "metal droplets" solidify on the tip resulting in "wire jams", and other problems. A contact tip is easily replaced simply by unscrewing it from the contact sleeve. A "spattered" contact tip may be cleaned using a small wire brush. The application, before use, of "spatter compound" (anti-stick) makes the task of spatter removal a lot easier. When fitting a contact tip, make sure that it is the correct size for the wire diameter selected. Gas diffusers should also be inspected for damage such as cracks and renewed if necessary. Nozzles that are badly damaged through heat erosion must also be renewed to ensure proper shielding of the weld. 3.2 WIRE LINER REPLACEMENT A "gun liner" or " wire liner" is a flexible tube, made usually of spring steel or Teflon, which houses and guides the electrode -wire through the gun cable and up to the contact tip. The gun or "wire-liner" will require replacement for the following reasons:

o When it is worn or "kinked" from continued use. o When a new wire size is fitted to the wire feeder. o When a soft liner is to be fitted (for aluminium wire).

The procedure for renewing a gun liner is (typically) as follows:


Disconnect the welding gun cable (conduit) from the wire feeder and lay the cable onto a clean surface. Remove the wire-liner retainer nut and withdraw the liner from the conduit. (If you intend to retain the liner then coil it neatly and store it in a protective packet). Select the new liner according to type and length. Remove the contact tip from the gun. Feed the new liner through the conduit allowing the "excess length" to protrude out of the gun. Fit and "hand tighten" the retainer nut (in the connector). Using sharp "side-cutters", cut off the excess liner leaving a 2-3mm protrusion from the contact-sleeve. Note: The small amount of protrusion left after trimming the liner will ensure that the liner "butts" against the contact-tip. Failure to allow for this will result in the wire becoming "fouled" as it enters the tip. Slacken or remove the retainer nut so that the liner can move into the contact sleeve. Refit the contact tip and assemble the "nozzle end" of the gun. (Do not forget to replace the gas-diffuser). Push the retainer nut upon the ferrule of the liner and force the liner into the conduit against its "spring tension". Connect and tighten the retainer using a properly fitting spanner. Store the gun until it is ready to be replaced onto the wire-feeder. Note: Always avoid creating sharp bends in the gun cable. Sharp bends can cause the wire liner to become "kinked", which in turn will restrict the smooth movement of the electrode wire to the contact tip, ultimately effecting the quality of the weld. 4. WIRE FEEDER 4.1 SELECTION AND PLACEMENT OF ELECTRODE "FILLER-WIRE" "Electrode" wire (filler) is available in standard "spools" or reels each designed to be accommodated upon the "spigot" of your wire feeder. (Sometimes a "spool adapter" is required). The type and size of wire is displayed on the manufacturers' label. The label should present the relevant AWS code or specification. Select the wire specified for your work.


The wire-reel, along with an adapter, is fitted onto the spindle in such a way that the wire is pulled off from the bottom of the reel. Take note of the precise mounting instructions offered by the machines' manufacturer. Make sure that the "reel retainer" is properly positioned to prevent the reel from working its way off the spindle. Make sure that the wire roll is clean before you feed it through the rollers. Dirt, dust and grit will cause accelerated wear to the drive-rolls, the wire-guides and the gun- liner. 4.2 FEEDING WIRE THROUGH THE DRIVE-ROLLS (TYPICAL PROCEDURE)

Safety Note: A/ways make sure that the machines' power switch is in the OFF position before feeding the wire into the drive rolls. Begin by (loosening) raising the upper roll (Unclip or release). Before feeding the fresh wire through, take the time to wipe clean the "drive-rolls" using a suitable solvent. Inspect the rolls for damage or wear. Report or replace damaged or worn rolls. Feed the wire, by hand, through the "inlet wire-guide" and pull it over the drive roll. Push the wire through the "delivery wire-guide". Make sure that the wire is settled within the "wire groove" (where applicable). Swing the upper roll back into place and latch the adjuster screw/handle into position. Tighten down the wire tension a little thus ensuring a slight "grip" (clamping force) on the wire. Note: On some machines the wire-guides and the drive rolls may require "aligning" to ensure that the wire takes a straight line through the mechanism. Where applicable (check Operators Instructions), slacken the "drive-housing screws" and manually manoeuvre the housing until the wire is not forced either up or down over the rolls. Retighten the housing screws and check that the wire runs without bending over the rolls. Check, (where applicable) from the "end view", that the wire grooves are aligned. Reset the rollers (according to instructions) so that the two grooves match. Poor alignment will result in various problems such as:

o Drive motor overloading. o Wire buckling and sticking in the gun liner. o Erratic feed speed and poor weld quality.

See diagram It "Alignment and Adjustment of Rolls and Guides" over the page.


ALIGNMENT AND ADJUSTMENT OF ROLLS AND GUIDES.

CORRECT ALIGNMENT OF ROLLS AND GUIDES.

CORRECT PRESSURE & ALIGNMENT.

WIRE BENT DOWN - ADJUST HOUSING - DOWN.

MISALIGNED ROLLS.

WIRE BENT UP - ADJUST HOUSING - UP.

WIRE LOOSE.


4.3 TENSIONING THE DRIVE ROLLS This step involves adjusting the top roll (pressure roll) to press against the electrode wire in order to provide a "slip free" feed of wire to the gun. Pressure is exerted onto the wire when the "pressure adjusting screw(s)", situated on the top roll(s) are tightened. 5. CONNECTING THE GUN AND FEEDING THE WIRE TO THE CONTACT TIP 5.1 CONNECTING THE WELDING GUN It is important that you make sure the gun -cable connector and the corresponding socket on the wire feeder unit, are correctly lined up, then guide the cable connector so that the electrode wire protruding from the wire-feeder, enters the wire-liner in the cable smoothly. Push the connector fully into position and then tighten the retainer nut by hand only. If the gun is water cooled, like it is on our demonstration unit, then connect these hoses now. These connectors and their corresponding couplings are usually colour coded, blue for cooling flow, red for the return flow. NB: Reversal of these connections will cause damage to the cooling system and the gun! 5.2 FEEDING THE WIRE TO THE CONTACT TIP In order to feed the electrode wire through the wire -liner and up to the contact tip within the gun, you will need to activate the wire feeder mechanism. Switch the unit on and then arrange the cable so that there are no sharp bends in it. Next, holding the gun pointed away from your body, or any metal objects, operate the jog switch on the wire-feeder unit. Continue operating the jog until the electrode-wire passes through the contact tip and out of the nozzle. If your machine does not feature a jog control, then operate the gun trigger until the electrode wire exits the gun. Caution: Remember that when activating the unit via the gun trigger, the electrode will be "LIVE." Be careful where you point the gun and 00 NOT touch the electrode while activating the trigger. Switch off the unit until you are ready to begin welding.


6. CONNECT THE WORK-LEAD This is not a complicated task but there are one or two considerations that you must keep in mind. 6.1 IDENTIFY THE CORRECT "INDUCTION TAPPING POSITION" When welding in the Short-Circuit transfer (Dip mode) it is advisable to fit the work lead to one of the inductance tappings. Selection of the inductance is made according to the wire size. As a rule, use the lowest value for wire sizes below 1.2mm. Use the second tapping for 1.2mm and 1.4mm etc. If during the welding process you find that the wire "pops" (explodes) with excessive "spatter and sparks" then move the work-lead to the next highest inductance tapping. 6.2 CONNECT TO A "GOOD GROUND" One of the most important considerations when performing any ARC weld is to ensure that the "Ground Clamp" makes proper "electrical contact" with your work. A bad contact results in excessive "volt drop" owing to the excessive "resistance" in the weld circuit. The ground clamp must be attached to a clean metal surface that is free of paint, oil, grease and surface impurities such as rust and "mill scale". As a general rule always attach the "ground clamp" as close as possible to the weld zone, in other words keep the distance as short as possible between the weld point and the ground clamp.

NOW VIEW PART 2 OF VIDEO GMAW 2. THEN COMPLETE SELF -TEST NO. 2.2 ON THE NEXT PAGE.



SELF TEST NO. 2.2 EQUIPMENT PREPARATION

INSTRUCTIONS

o Complete the following exercise without reference to your notes or the video. o Perform the tasks on the MIG/MAG equipment allocated to you by your Instructor:

1) Connect the wire feeder to the power-source ensuring that all connections are made correctly according to the manufacturers' recommendations. (Note: this task is applicable only to "remote wire feeders" not to "compact units"). 2) Fit and prepare the gas supply system to the unit including the installation of the regulator / flow-meter unit. 3) Dismantle the "nozzle end" of your welding gun and inspect all components. Reassemble the gun with the correct parts for the wire size selected by your Instructor. 4) Fit a "new" wire-liner to your gun cable (conduit). 5) Set up your wire-feeder unit beginning with the attaching of a "new" wire- reel. Feed the wire through to the contact tip and then, 6) Set the equipment into position at your welding bay and attach the work-lead to the welding bench.

CHECK YOUR WORK, UPON COMPLETION OF ALL TASKS, BY COMPLETING THE EVALUATION "CHECK LIST" ON THE FOLLOWING PAGE.


PRACTICAL EVALUATION - EXERCISE 2.2 INSTRUCTIONS Upon completion of the tasks on previous page check your work against the evaluation check-list below. (Note: Place a tick in the YES column if applicable, or place a cross (x) in the NO column where applicable).

TASK (CRITERIA) YES NO

1. All connections made correctly between power-source and wire feeder.

2. All "safety" precautions made whilst fitting the regulator.

3. Correct tools used when removing contact tip and wire liner retainer.

4. Correct wire-liner protrusion allowed at tip end, 2-3mm.

5. Correct drive-rolls and guides fitted for wire size.

6. Wire spool correctly installed on carrier, wire draw off bottom.

7. Gun cable correctly installed to wire feed adapter.

8. Wire fed through to the contact tip.

9. Drive rolls tensioned equally (if applicable).

10. All "safety" precautions made before working with the wire feeder.

11. Work lead connected to machine and to welding bench.

THIS CONCLUDES PROGRAMME GMAW-2. NOW MOVE ON TO PROGRAMME 3 ON THE NEXT PAGE.


PROGRAMME 3 GAS METAL ARC WELDING PRACTICES AND PROCEDURES

OBJECTIVES When you have completed this programme (module) you will be able to: 1. Prepare and use a MIG/MAG power source to produce "Short-Circuit Transfer Mode" welds on steel work pieces. 2. Prepare and use a MIG/MAG power source to produce "Spray Transfer Mode" welds on steel work-pieces.

NOW READ THROUGH THE NOTES THAT BEGIN ON THE NEXT PAGE.



PART 1 - BASIC SKILLS In this programme you will be shown how to put your GMAW welding equipment to practical use. In practice the welder normally does not have to make too many decisions regarding the "welding procedure" as this is normally the responsibility of the welding engineer. The "welders' responsibility" is to follow the procedures using the process and materials that the engineers have provided. In other words a welder has to know "how to weld" and his / her main responsibility is to produce a welded joint (or other task) that meets the required "standards". The aim of this training programme is to assist you in achieving "acceptable weld standards", and in order to achieve this, you will have to learn "basic skills" and "processes". The following points represent those deemed necessary prior to us moving onto actual "welding exercises". BASE METAL PREPARATION The most basic requirement for an "acceptable weld" is thorough cleaning of the base metal, no matter what metal you intend to weld. For demonstration purposes, the base metal that we shall use throughout this programme is "mild steel". Thorough cleaning involves the removal of all "surface impurities" such as rust, mill-scale, paint, grease, oil and even "dust". Every surface within the "weld-zone", including the "root faces" must be thoroughly clean. Aluminium and stainless steel should be treated in similar fashion but care must be taken to ensure that you use the correct type of grinding wheel rated for "stainless steel", never use a "steel rated wheel", especially upon aluminium. After sanding, wipe the weld zone surfaces with a clean cloth that has been dampened with acetone (See safety note below). It must be kept in mind that your metal welding-bench often forms part of the welding circuit. Your bench top must be clean and free of rust, paint, oil or any other substances that will cause "electrical resistance". The "work lead clamp" must be connected to a bright and clean portion of your bench. SAFETY NOTE Handle and apply all chemical cleaning-fluids according to the safety instructions on the manufacturers' label.


As a rule, avoid using fluids such as thinners, petrol, turpentine, and paraffin as these products, apart from their "flammable nature", leave residues on the metal, which in turn, will negatively affect the weld quality. SHIELDING GAS PREPARATION Adjusting the shielding-gas delivery flow-rate and post flow. The following procedure is typical for most GMAW equipment.

o Shut (close) the "flow-control valve" at the flow-meter. o Open the (cylinder) delivery-valve, slowly, by % turn maximum (see safety notes

below). o Ensure that there is adequate gas in the cylinder by observing the pressure gauge.

Minimum gas pressure should be above 1 bar (gauge). o Open the flow-control valve by about % turn. o Check between the delivery-valve and the input connection to the welding machine

for gas leaks. Rectify any leakage by securing the fitting, tightening clamps as necessary. Use a weak solution of "dish washing liquid" if necessary to detect leaks. Paint the solution onto connections and fittings and look for the "tell tale bubbles". Always wipe the area dry after checking to prevent dirt and dust from sticking to the parts.

SAFETY NOTES 1. Do not face the pressure gauge whilst opening the delivery-valve. Gauges have been known to burst when a sudden rush of pressure enters them. Serious face or eye injury may result from a busting gauge. 2. Do not neglect to repair a gas leak. Although MIG gases are non-toxic and non- flammable there is still the risk of "oxygen depletion" if you are operating in a small room (confined area). A further good reason to repair a leak is that you need all the gas at the "weld zone" and a leak will reduce the shielding effect. ADJUSTING THE GAS FLOW-RATE The volume of shielding gas that reaches the weld pool is controlled via the "flow control valve", situated below the glass sight tube of the "flow meter". In "metric countries" the volume of gas is measured in "Litres per minute" (Lpm). In "non metric countries" (USA) flow is measured in "cubic feet per hour" (cfh). The flow meter on your gas cylinder may display b9th standards. Note: 1 cfh = 0.442 Lpm In order to set the desired gas flow rate the gas must be flowing through the system (out of the gas nozzle). For this to occur the "gas control valve" situated within the power source unit must be "activated". In order to activate the gas control-valve the power source unit must be switched on.


The next step will depend on your machine design. o Machines with a "Gas Purge Button" To activate (open) the gas control valve, push

and hold in the "purge button". Gas will flow through the gun cable whilst the button is held.

o Machines without "Gas Purge Button" -simply operate the "gun trigger" momentarily (See note over the page). Gas will flow until the "post flow timer" cuts out. For this reason it may be necessary to set the post-flow control to "maximum" thus providing you with sufficient time to make the flow-rate adjustment.

Note: Make sure that the "trigger mode" is set for the 2T position (hold on / release off) or the wire feeder will continue to operate a "live electrode" from the gun. Whilst gas is actually flowing , manipulate the flow-control valve until the floating ball rises to the desired height in the "sight tube". To "read" the meter, observe the TOP of the ball and compare this to the graduated markings on the sight tube. Take the reading at "eye level in order to obtain accuracy. The actual figure (amount) of gas flow will of course vary according to conditions such as: Metal type, metal thickness, type of gas, type of electrode and even, the weather (such as welding outdoors when a wind is blowing). An "average" of between 11 and 15 Lpm is generally considered the "norm" for mild steel and stainless steel work up to 6mm thick. If you require accurate settings then you will need to consult the "welding procedure" for the work you are going. POST FLOW SETTINGS Once again this figure cannot be offered without the welding procedure. The main criterion is that sufficient post flow must continue to shield the weld at the end of a run to offer protection whilst the metal cools to the "colour" of the surrounding metal. (Of course with aluminium this is a bit of a problem because aluminium does not change colour when heated, and it takes a long time to cool as well!) As a "guide" allow 1 second of post flow for every 10 amps of current. Some machines provide fairly accurate "timer controls" and the post flow can be set to an actual value. Other machines may simply use a "Minimum/Maximum" control and the setting becomes a matter of "guess work and experience". Reference to the "operators manual" may provide information regarding the post flow time at Minimum and Maximum settings, leaving you to "figure out" the values in between! In the video demonstration we have such a unit and we have elected to set the timer control to its "halfway point" and, by literally "timing" the gas flow, using a stop watch, we have discovered that at this position (1/2 point) the post-flow operates for 15 seconds.


PREPARING THE WELDING GUN Prior to operating the welding gun there is one setting that needs to be made namely, the electrode-protrusion or "stick-out" as it is commonly known. Stick-out is the amount of electrode wire that should protrude from the contact-tip. This distance is important as it provides the correct conditions in which the electrode wire is pre-heated and it also produces the desired envelope of shielding gas over the weld-pool by ensuring that the gas-nozzle is maintained at the optimum distance from the work. When using "short circuit transfer mode" the electrode should "stick-out" beyond the nozzle by approximately 4 to 10 millimetres (6 -13mm from the contact-tip). For "spray transfer mode" the stick-out should be twice this distance, that is, between 13 and 26mm (10 -23mm from gas-nozzle) . In practice, the stick-out is set by operating the trigger (or the wire jog) until about 30mm of wire emerges from the tip, then, using your cutting pliers, snip the wire to leave the desired amount of protrusion. SAFETY NOTE Always point the nozzle away from your body, and away from others in the area to prevent injury from the piece of wire that flies off. HANDLING (CONTROLLING) THE WELDING GUN Getting the "feel" of holding, moving and manipulating the welding gun is a very important part of your training. Please note that instructions relating to left or right directions should be reversed for left handed Operators. Begin by getting yourself into a comfortable welding position. Arrange the welding-cable so that it is free of sharp bends, which will ensure that the wire feeds smoothly to the contact-tip. Hold the gun in a relaxed grip making sure that the trigger is in easy reach. You may find that you are "fighting" the gun in order to hold it in position owing to the weight of the cable. It is quite acceptable for you to support some of the cable weight (mass) by resting it on your arm, or across your lap if you are in a sitting position. For "flat position welding" you will find that controlling the gun will be made easier using the "two hand method" with the supporting elbow resting on the bench top. GUN (NOZZLE) ANGLES AND TRAVEL DIRECTION Most welds are made with the gun held at an angle of between 20 and 25 degrees off vertical. Travel may be made in the "forehand direction", or in the "back hand direction". Deeper weld-penetration is achieved using the backhand direction.


Whichever direction you decide to use keep in mind that the distance between the nozzle and the work must be maintained as steadily as you can, which is why we recommend the two handed support, especially during your earlier training. The main "skill" with gun handling is your ability to maintain both the nozzle angle and the "nozzle-to-work" distance. Both of these factors have a marked effect on the weld. Although small variances will be "tolerated" by the machine a large shift, specifically with the nozzle-to work distance, will cause major "fluctuations" with the welding current. Suffice. it to say that if you can maintain the "stick out" distance and follow the "guide line" (weld joint) during the welding process then you have achieved the ability to produce a weld. Naturally you will require time to practice the skill of manoeuvring your welding gun so, before we move on to the first welding exercise, that's what you should do, practice, after you have viewed Part 1 of the video.

NOW VIEW PART 1 OF VIDEO GMAW-3 AND THEN PRACTICE HANDLING THE GUN IN YOUR WORK PLACE. (NOTE: THERE IS NO TEST FOR THIS SECTION)

MOVE ON TO EXERCISE NO. 1 ON THE NEXT PAGE.



PROGRAMME 3 PART 2 - PRACTICAL EXERCISES

EXERCISE NO.1 - SURFACE STRINGER-BEADS USING SHORT-ARC TRANSFER In this exercise you will be shown the following:

o How to set the welding machines' parameters for "short-circuit transfer mode". o How to start the arc. o How to run a "surface bead". o How to complete a run (end off). o Inspect a weld bead.

In preparation for the exercise the following should be done: CLEAN AND PREPARE THE METAL WORK PIECE In this exercise we will be laying "surface runs" upon 3mm mild steel plate. Remove all surface impurities from the steel, using your angle grinder or other suitable method. Remember that you need to clean both sides of the plate. Failure to do this will result in a "high electrical resistance" between the work and the metal bench top, which in turn will result in problems when you attempt to strike the arc. The main purpose of this exercise is to enable you to experience the "feel" of actually running a weld bead. To assist in this we suggest that you scribe "guide lines" along the surface of your work piece. Use an angle grinder to produce the guide-lines. Space the lines about 25mm apart. ATTACH THE WORK-LEAD Not exactly a difficult task, but remember to connect the work-lead to a "shiny and clean" section of the work or the welding bench. Attach the lead as close as possible to the weld zone but not in such a way that it will interfere with your movement of the gun. If your welding machine has "inductance tappings" then attach the work-lead to one that suggested in the "Operators Manual" for the wire size that you are using. ADJUST THE SHIELDING GAS The volume or "flow rate" of Argon shielding gas should be set at approximately 12-15 "litres per minute" (Lpm) for most "steel applications". When you have completed the preparatory tasks then we can begin with the first objective, namely the machine settings required in achieving short circuit transfer (Dip). SETTING THE MACHINE (FOR SHORT CIRCUIT TRANSFER MODE) The (main) factors that determine any mode of transfer are:

o Welding voltage.


o Wire-feed speed, and o The type and mix of shielding-gas being used.

For convenience sake the following guides will assist you to establish the "optimum settings". SETTING GUIDE FOR O.98MM WIRE.

METAL THICKNESS (STEEL)

WIRE SIZE mm WELD VOLTS WIRE FEED RATE M/min

APPROX. AMPS

1.6mm 0.98 16-17 5-6 100-125 1.8mm (2 mm) 0.98 17-18 7-8 150-170 2.8mm (3 mm) 0.98 18 19 9-10 180-200 SETTING GUIDE FOR 1.2MM WIRE.



APPROX. AMPS

1.6mm 1.2 15 - 16 2 - 3 100 - 130 1.8mm (2 mm) 1.2 16 - 17 3.5 - 4 150 - 170 2.8mm (3 mm) 1.2 18 20 4.5 - 5 180 - 200 OVER 3mm 1.2 20 - 22 5.5 - 7 210 - 250 SETTING THE WELDING VOLTAGE In the video demonstration the wire size used is 0.98 mm therefore, according to the guides, we need to set the voltage to 18 as our starting point. It must be noted that voltage adjustments (controls) will vary depending on the type or make of machine you are using. Some machines make life easy by providing a scaled-control that is simply turned to the desired setting figure. More sophisticated machines may offer a "digital display'. Others, like the one in our video are more "challenging" in that you have to have to work out the voltages. There are two "stepped" voltage controllers on this machine. One is the "coarse setting control" and the other is the "fine setting control". Both controllers have six setting positions, beginning at number 1. The "minimum voltage" that this machine will deliver, according to the manufacturers' specification, is 17 volts. This means that if both voltage controllers are set to their minimum settings (No.1), then the "open circuit voltage" (voltage across the welding connections) will be 17 volts. We are told that each stepped increase (notch) of the coarse controller results in a 6 volt increase in OCV (open circuit voltage). We are also told that each "notch' of the fine controller increases the OCV by 1 volt.


Therefore, as we require 18 volts to begin our exercise, we need only set the fine control to position number 2 (ADDING 1 VOLT TO THE MINIMUM) and leave the coarse control at its minimum (No.1) setting. SETTING THE WIRE-FEED SPEED Very simply, rotate the wire-feeder controller to the desired feed speed. Once again it must be mentioned that controllers may vary according to make and model. You may also come across "imperial machines" where the feed rate is given in "inches per minute". CONVERSION To convert inches to metres multiply by 0.025. (Example: 300 inches per minute 300 x 0.025 = 7.5 m/min). At this point we can assume that we are ready to begin welding so let's get back into the welding position and get started. STARTING THE ARC Again we arrive at another point that requires more description than the action involved. We are now at the start of the weld and in "real life" everything will happen very quickly so let's describe the action. In the video demonstration we use the "forehand direction" and therefore we start the arc (strike) at the right hand edge of the work. Do not activate the trigger at this time, simply hold the gun at the correct angle, (20 -25°) and bring the electrode into contact with the base metal (On your guide line). Now lift the gun to create a gap of between 1 and 2 millimetres between the electrode and the work. Hold this position and drop your welding visor. This is where the two-hand support method becomes very practical. Naturally you need to develop the trick that all welders learn, that of being able to "flick" down the helmet / mask with a sharp nod of the head. Activate the trigger and the arc will start.


RUN A SURFACE BEAD As soon as the arc is established, a weld-pool will form. The size of the weld pool is your main point of reference. The aim is to keep the weld pool diameter constant at about 3 to 4 times larger than the electrode diameter and this involves moving the gun along the "guide line" at a steady pace. The gun must be moved along the work steadily keeping the electrode tip slightly ahead of the centre of the weld-pool (toward the front of the pool). If you allow the tip to trail the bead will grow very wide. A very reliable method of assessing whether your weld is going correctly is to LISTEN to the sound of the arc. The sound made by Short Circuit Transfer, if all is well, is similar to the sound of a piece of cloth being torn. Things are not going right if the sound is erratic and lots of "popping" and excessive spatter is generated. Heavy spatter (sparks) is caused when one or more of "several things" are wrong, for example:

o Poor electrical connection of the work lead. o Voltage too high. o Shielding gas flow too high, and ....... . o Wire protrusion, or "stick out" too long.

However the three MOST likely causes of excessive spatter, especially in your early attempts and these are:

o Voltage too high. o Shielding gas flow too high, and ....... . o Wire protrusion, or "stick out" too long.

STOPPING THE WELD When you come to the end of a weld run then move the gun (arc) back over the weld bead for a short distance and stop the weld current (switch off). When you run the arc back over the weld bead (selection 2) you are in effect filling the "crater". To avoid a "porous weld' the gas nozzle must be held over the weld pool until the gas "post flow' has stopped or the metal "colour" has returned to that of the surrounding material. WELD INSPECTION When you have made a few practice runs (surface beads) on practice plates then have a good look at the results (when the metal is cool enough to handle). A "stringer bead" should have the following "good features":

o Even and consistent width along its full length. o Approximately 2 to 3m of "reinforcement". o There should be no "undercutting" on the edges. o There should be a minimum of "spatter" surrounding the bead. o On the reverse side you should observe a narrow bead of "penetration".


SOME USEFUL TIPS One of the "difficulties" that most Learners experience when starting to use GMAW equipment is that of getting the two basic machine settings, voltage and wire feed speed, just right. As there are no "hard and fast rules" (as to the "correct settings") one has to rely on experience and, ones' natural senses. When you have set everything correctly and you have mastered the skill of maintaining the correct arc length then your sense of "hearing" will play a major role in assessing the machine settings. The sound of a "good short-circuit transfer (dip) can be likened to the rapid tearing of heavy cloth. If however the welding sounds like small "fire crackers" then something is wrong, especially if this is accompanied by an excess of "sparks" (spatter). Presuming that you are maintaining the proper arc length then, if spatter is excessive, try the following:

o Increase the inductance -by fitting the work-lead to another tapping point. o Increase the wire feed speed -do this in small stages (+/-1 m/min). o Reduce the voltage setting -do this in small increments of 1 volt at a time. o Try altering the gun angle between 20 and 25 degrees.

It should be noted that any alteration made should be done one at a time. Do not alter ALL the settings together as you will never know which setting made the difference, and you will probably never get the machine set correctly!

NOW VIEW VIDEO SECTION ON THIS EXERCISE. THEN PERFORM PRACTICAL EXERCISE NO. 1 ON THE NEXT PAGE.



PRACTICAL EXERCISE NO. 1 LAYING A BEAD ONTO STEEL PLATE USING "SHORT CIRCUIT TRANSFER MODE"

INSTRUCTIONS

o Obtain a piece of 3mm mild steel plate approximately 70mm x 150mm. o Clean both surfaces to remove all surface deposits, including rust and mill scale. o Scribe parallel "guide-lines", length-wise, onto the plate. o Set up your MIG machine with O.98mm steel wire then adjust all settings according

to the setting guides offered in the notes. o Run "surface-beads", following the guide-lines, along your practice plates in the

forehand position. o Try the same exercise using the back-hand position as well. o Examine your work on completion. o When you think you have mastered the skill of running a surface bead, using" short

circuit transfer", complete the evaluation Check-List below. SELF EVALUATION -CHECKLIST NO. 1 CRITERIA YES NO 1. The bead is straight (follows the guide line). 2. The bead is of uniform width (approximately 4-5mm wide). 3. The height of the bead, or "reinforcement", is approx. 2-3mm. 4. There is no "undercut" along the edges of the bead. 5. You have discussed any problems with your Instructor?

NOW MOVE ON TO EXERCISE NO. 2 ON THE NEXT PAGE.


EXERCISE NO. 2 BUTT-WELD USING SHORT-ARC TRANSFER

In this exercise you will be shown the following:

o Setting up 3mm MIs plate for a butt-joint weld. o Performing a single-sided weld using short-arc (dip) transfer mode. o Inspecting your weld.

INTRODUCTION The purpose of this exercise is to offer you the experience in using your GMAW equipment to join two pieces of metal using "dip transfer". This is probably the commonest type of operation you will experience in the work place. The task involves the following typical procedure: CLEAN AND PREPARE THE WORK

o Remove all traces of "oxide" and other substances from the weld-zone, as described earlier.

o Check that the edges to be welded are straight (square). o Set the pieces onto "backing plates" (or a raised welding platform). o Establish a "root gap" of approximately 2mm (use a piece of wire to "gauge" this).

WELD THE JOINT

o Tack the plates together at each end (tack welds are made in similar manner to a full weld).

o Check that the root gap is parallel after the first tack and , if necessary re-set it. o If required (and where possible) introduce a small "pre-set" (off-set) between the

two plates to allow for contraction of the weld and pull on the plates. o Set your work on backing plates to raise the bead area off the work bench surface. o Start the arc, on the right -hand end and on the surface of one of the plates in the

manner you have already learnt. o Draw the arc into the "root gap". o Maintain the gun angle and the arc length. o Establish a "correct weld-pool" and run the bead along the root in exactly the same

manner as you did with the surface weld (stringer). o At the end of the run, draw the arc back onto the bead for approximately 10 -20mm

and then stop the arc. o Hold the shielding gas on the weld until the "post flow" stops. o Wait until the work has cooled naturally (do not quench) and then inspect your

work.


INSPECT THE WORK A "satisfactory weld" will have the following features:

o Even and consistent width along the full length. o No undercutting on the edges (toe) of the bead. o Evenly spaced "C-shaped ripples". o A 1.5 - 2mm "raised weld-face" (Convex reinforcement). o On the reverse side there will be a thin and even bead of "penetration filler".

NOW VIEW THE VIDEO SECTION FOR THIS EXERCISE NO. 2 THEN COMPLETE PRACTICAL EXERCISE NO. 2 ON THE NEXT PAGE.



PRACTICAL EXERCISE NO. 2 WELDING A "BUTT-JOINT" USING "SHORT-CIRCUIT TRANSFER"

INSTRUCTIONS For this exercise you will require:

o 2 x Pieces of 3mm mild-steel flat plate cut to approximately 70mm x 150mm. o O.98mm (E70S-3) Electrode wire Procedure. o Set up your MIG machine as you did for exercise No.1 (Use same optimum settings). o Clean the weld-zone of both plates, including the root faces. o Set out you work onto backing-plates, so as to raise the weld-zone off the welding-

bench top. o Set a root gap of approximately 2mm making sure it is parallel. o Tack the plates at each end. o Pre-set the plates (work) to allow for "weld pull". o Run a stringer bead (no weaving) along the joint. o Fill the crater at the end of the run. o Examine your work. o When you think you have mastered the skill of performing the butt-weld, using"

short circuit" transfer, complete the evaluation Check-List below. SELFEVALUATION - CHECKLIST NO. 2 CRITERIA YES NO 1. The bead is of uniform width (approximately 4-5mm wide). 2. The height of the bead, or "reinforcement", is approx. 2-3mm. 3. There is no "undercut" along the edges of the bead. 4. There is a full bead of "penetration" visible on the underside of the weld. 5. You have discussed any problems with your Instructor?



EXERCISE NO. 3 SET UP MACHINE TO DELIVER "SPRAY TRANSFER MODE" AND RUN SURFACE BEADS

In this exercise you will be shown the following:

o How to set the welding machines' parameters for "spray-transfer mode". o How to produce surface beads on thick mild-steel plate using the "spray-transfer

mode". INTRODUCTION The primary purpose of this exercise is to offer you exposure to the "spray mode" of metal transfer. The 3 key factors that influence "spray mode" are: 1) Welding Voltage -normally higher than for Short-circuit transfer. 2) Wire feed speed (or welding current) -generally in excess of 250 amps. 3) Type of gas -must be at least 80% Argon. Spray transfer can be achieved using any size wire, however it is seldom necessary to go above 1.2mm in order to achieve the desired effects namely:

o Good weld penetration. o A smooth and even weld bead. o Good "deposition rate" (amount of filler material placed into the weld in a given

time). The weld bead is very "fluid" and for this reason spray-transfer is generally restricted to "flat position" welding. One of the primary applications for using Spray Transfer is for welding thick material (over 5mm). It is common practice for deep "V Groove" welds to have the "root run" welded using short -circuit transfer and the "capping runs" welded using spray transfer. SETTING UP YOUR EQUIPMENT TO PRODUCE SPRAY TRANSFER Use the setting guide below to adjust your machine to "optimum" spray-transfer conditions:

POWER SOURCE SETTINGS - MILD STEEL AND LOW ALLOY STEEL TRANSFER METHOD - SPRAY TRANSFER



APPROX. AMPS

OVER 5mm 0.98 24 - 28 10 - 17 200 - 250 OVER 5mm 1.2 24 - 30 5 - 10 200 - 320 OVER 5mm 1.6 24 - 32 4 - 8 250 - 450 Note: (Remember that the electrode "stick out" for spray -transfer is between 13 and 25mm ).


o Set your machines' voltage and wire feed speed, initially, to the "lower end" of the suggested figures given above (relative to the wire size).

o Use Welding Chart -1 (at end of this book) if you wish to check "amps / wire -feed" relationship.

STRIKING THE ARC AND RUNNING A BEAD There is very little difference in the procedure for striking the arc and running a bead compared to short circuit transfer. The welding-gun angle (nozzle angle) is exactly the same, namely between 20 and 25 degrees. To strike the arc, hold the electrode tip between 1 and 2mm above the base metal and then, with your visor down, press the trigger. A weld-pool will develop very quickly, so be ready to move off along your guide -line almost immediately. You will (no doubt) notice that the filler is deposited much faster than you experienced with "dip transfer", and you will have to travel faster in order to maintain the correct weld-pool size. You will also notice that the shape of the arc and the electrode tip is different to that of short ¬circuit transfer. The arc is more "bell" shaped and the electrode tip becomes very pointed. Listen to the "sound of the arc" while you weld. A good "spray" produces a "crisp" and even "crackling "sound. Spatter will be light and concentrated close to the arc zone. If the arc splutters and emits excessive "spatter" (sparks) then try the following (one at a time): 1) Increase the "nozzle-to-work distance", as you may have gone in too much and check your gun angle as you may be "leaning too much". 2) Assuming a correct nozzle distance, increase the voltage by ONE VOLT at a time, but never exceed the maximum suggested voltage. 3) Increase the wire -feed speed slightly. A very "quiet arc" (hissing sound) is an indication of excessive VOLTAGE. Higher than "normal" voltage will result in "undercutting" along the edges of the bead. Reduce the voltage by 1 VOL T AT A TIME until the arc has a "crisp, crackle sound" and spatter is "minimal". At the end of the run, draw the arc back onto the bead and stop the weld. Hold the nozzle over the "hot spot" until the post -flow timer stops the gas flow.

NOW VIEW THE VIDEO SECTION FOR THIS EXERCISE. THEN COMPLETE PRACTICAL EXERCISE NO. 3 ON THE NEXT PAGE.



PRACTICAL EXERCISE NO. 3 RUN SURFACE BEADS WITH "SPRAY TRANSFER MODE"

For this exercise you will require the following:

o Pieces of 8 mm mild-steel plate approximately 50mm x 150mm. o 1.2mm (E70S-3) Electrode wire. o Shielding gas mix containing at LEAST 80% Argon.

INSTRUCTIONS Follow the typical procedure to produce surface beads on your work-pieces:

o Set up your MIG machine to obtain "spray transfer". (use charts and tables as required).

o Clean the surfaces of your work plates. o Scribe "guidelines" along the plate surface. o Run surface beads along the guidelines using forehand or back hand direction. o Adjust, as necessary, the machine settings, until you achieve a "crisp crackle"

from the arc. o Examine your work. o When you think you have mastered the skill of producing surface beads with "spray

transfer", complete the evaluation Check-List below. SELF EVALUATION -CHECKLIST NO. 3 CRITERIA YES NO 1. The bead is straight (follows the guide line). 2. The bead is of uniform width (approximately 5-6mm wide). 3. The height of the bead, or "reinforcement", is approx. 2-3mm. 4. There is no "undercutting" along the edges of the bead. 5. You obtained a good "spray sound" from the arc. 6. Spatter is very light around the weld zone. 7. You have discussed any problems with your Instructor.



EXERCISE NO. 4 FILLET WELD WITH SPRAY TRANSFER

INTRODUCTION For purposes of demonstration we will use Spray Transfer mode to perform a "fillet weld". The primary reason for this exercise is to offer you experience in using spray transfer to effect an actual join. PROCEDURE

o Clean and prepare the weld zone of both work-pieces. o Set-up work-pieces in the normal manner for the joint on your welding bench. o Clamp the work or, if you prefer, tack weld in 3 places on back of the work. o Set your machine to produce "spray transfer" in the manner previously described. o Ensure that the shielding gas has been opened and adjusted to provide 12 -15 Lpm. o Introduce the nozzle to the weld zone at an angle of approximately 45°. o Use "back-hand" travel direction for best control and penetration. Begin the weld at

the left-hand side of the work (work from left to right across. o Your body if you are "right handed"). Reverse this action if you are left-handed. o Weld the full bead. o At the end of the run move the arc back onto the weld area for a short distance (1 0-

20mm) in order to fill the arc crater. o Hold the "post flow" gas on the bead until the metal cools and the post-flow gas cuts

out (10 -15 seconds). o Allow the material to cool naturally (do not quench) and then inspect your work.

INSPECT YOUR WORK The following features indicate that you have produced a satisfactory weld:

o The bead width is uniform and consistent for the full length. o The weld bead "legs" are evenly distributed between the horizontal and the upright

members. o There is no "undercut" along the bead. o The ripples are evenly spaced. o The "face" is slightly convex in shape. o There is no porosity at the end of the bead.

NOW VIEW THE VIDEO SECTION FOR THIS EXERCISE. THEN COMPLETE THE PRACTICAL EXERCISE NO. 4 ON THE NEXT PAGE.



PRACTICAL EXERCISE NO. 4 FILLET WELD USING "SPRAY TRANSFER" MODE

INSTRUCTIONS Follow the procedure below to produce a fillet-weld in a Lap -Joint. MATERIAL (CONSUMABLE)

o 2 Pieces of 8mm m/s plate, 50mm x 150mm (approximately). o Use 1 ,2mm solid filler wire (ER 70S -3). o Shielding gas -Argon (min 80%).

PROCEDURE

o Set up your MIG machine as you did for exercise NO.3 (for Spray Transfer). o Clean the weld-zone of both plates, including the edges. o Arrange the plates on your welding bench in the appropriate manner to create a

"Lap Joint". o Tack the plates at each end. o Check that the gap between the plates is closed and correct if necessary. o Turn work over and run a "back-hand" weld along the full joint. o Fill and shield the crater at the end of the bead. o Examine your work once it has cooled sufficiently. o When you think you have mastered the skill of producing a "Fillet weld", using

"Spray transfer", complete the evaluation Check-List below. SELF EVALUATION -CHECKLIST NO. 4 CRITERIA YES NO 1. The weld is "neat" in appearance. 2. The weld "legs" are evenly distributed between the horizontal and the

vertical surfaces.

3. Welding is uniform with no "overlapping" of the top edge. 4. The crater has been filled at end of the run. 5. You have discussed any problems with your Instructor?

YOU HAVE NOW COMPLETED THE PRACTICAL EXERCISES FOR THIS PROGRAMME. PLEASE COMPLETE THE PROGRAMME BY READING THE NOTES ON THE FOLLOWING PAGE.


IN CONCLUSION SHUTTING DOWN To conclude this basic GMAW series we must spend a few moments on the topic of how to correctly close down your equipment. The main focus is upon safety, however it is also a matter of "good working practice" to ensure that you leave your equipment in proper working condition and ready for the next operator who needs to use it. Follow the suggested routine for shutting down your equipment:

o Close the gas delivery valve. o Open the flow control valve and trigger the welding gun (this will "drain" the line). o Switch off the power at the isolation switch (on/off switch). o Switch off the machine from the shop "mains supply" point. o Set the voltage selectors back to minimum. o Set the wire feeder control back to "minimum". o Remove the work-lead from the work or bench and coil it neatly. Hang this on an

appropriate bracket as well. (Do not wrap leads and cables around the gas cylinder). o Clean the gun nozzle and contact tip. o Neatly coil the gun cable (conduit) and hang up on an appropriate hanger bracket.

Do not coil this item in such a way that tight bends are created. o Tidy up your work bench or work area. o Place all scrap and rubbish in the designated scrap collection receptacle. o Return any tools to their proper place of storage. o Clean your machine and park it in its designated area.

Note: It may be necessary. depending on the "rules" in your work place. to remove the welding cables (including the gun cable) from the machine. If this is the case then you will have to retract the electrode wire from the conduit in order to detach the gun cable. Remember to "snip off' the ball from the end of the wire before retracting as this will jam up in the contact tip. If your machine has a "reverse feed" control then run the wire feeder in reverse to extract the wire. Alternatively, with the power switched off, release the tensioner(s) on the top rolls and wind the reel back (clockwise), by hand, to draw the wire out of the conduit. Control the wire as it is drawn out and stop BEFORE it clears the drive rolls. If the wire is "hard" then remember that it will "spring off the reel" if you don't support the coil on the reel. Tie-off the free end by twisting round the reel cage (wire type).


SOME USEFUL GMAW TIPS

o When you have to weld a section of steel that has "mill scale" on it, and for whatever valid reason it cannot be removed, then use a shielding gas mix that contains at least 25% CO2and apply the "high end voltage setting". Also note that, owing to the high C02 content, you will not achieve "spray-transfer" but the "globular transfer mode".

o Remember that an increase in "wire feed speed" also increases the "welding current (amps). Too much amperage results in excessive heat generation and can cause "porosity" in a weld.

o When welding stainless steel do not impose a high feed-speed rate as this will overheat the metal. Overheating results in serious weakening of the "metal structure". (For best results use "pulsed welding" on stainless steel).

o When using CO2 as shielding with mild steel (carbon steels up to 6mm) use an electrode AWS rating of E70S-6.

o When welding steel, using an "argon based shielding gas" then use an electrode with an "AWS rating" of E70S-3. It is important that the metal is properly cleaned when using this electrode.

o Never use AWS E70-6 on galvanised (zinc coated) plate or "aluminised steel" as this will result in weld cracks.

o It is rarely necessary to exceed a wire size of 1 ,4mm for spray transfer mode. Large wire sizes are only suitable for "flat welds" (Down-hand) on material over 6.5mm thick and requires a welding power source capable of delivering high welding currents (typically in excess of 400 amps) with a high duty cycle capability and liquid cooled welding-gun.

o With both MIG and MAG welding the success of a weld is heavily dependent on the steady flow of shielding gas around the weld-pool. Welding in the open, on a windy day, can play havoc with your welds as wind, or strong draughts will blow the gas away from the weld resulting in porosity.

THAT COMPLETES THIS MODULE ON THE SUBJECT OF GMAW. ALWAYS WORK SAFELY AND REMEMBER "PRACTICE MAKES PERFECT".


WELDING CHART-1 WELDING CURRENTS / WIRE - FEED SPEEDS FOR CARBON - STEEL ELECTRODES

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(GMAW) - TechAV