MANUFACTURING PROCESS(BMFG 2323)

Lecture 4Joining Process & Equipment

(Solid-State Welding)

INTRODUCTIONINTRODUCTION

- Joining takes place without fusion at the interface of the two parts to be welded.- No liquid or molten phase is present in the joint.

- The processes are automated by using robotics, vision systems, sensors, and adaptive computer controls for cost reduction, consistency, reliability of weld quality, and higher productivity.- Solid-state welding involves one or more phenomena:

i) Diffusion.

ii) Pressure.

iii) Relative interfacial movements.

SOLID-STATE WELDINGSOLID-STATE WELDING

i) Diffusion- The transfer of atoms across an interface – applying external heat improves the strength

of the bond between the two surfaces being joined.- Heat may be generated internally by friction, electrical-resistance heating, and

externally by induction heating.

ii) Pressure- The higher the pressure, the stronger is the interface – due to occurrence of the plastic

deformation at the interface.

iii) Relative interface movements- When the movement of the contacting surfaces occur, even in a very small amplitudes,

this phenomena will disturb the mating surface, break up any oxide films, and generate new, clean surfaces and directly it improving the strength of the bond.

COLD WELDING (CW)COLD WELDING (CW)

- Pressure is applied to the work piece through dies or rolls.-Due to the involvement of plastic deformation, therefore at least one of the mating parts be ductile.-Before start the welding process, the interface is degreased, wire-brushed, and wiped to remove oxide smudges.-CW can be used to join small work pieces made of soft, ductile metals.-During the joining of two dissimilar metals, intermetallic compounds may form, which means it will produce a weak and brittle joint.

ROLL BONDING/WELDING (ROW)ROLL BONDING/WELDING (ROW)- The pressure which required for the welding process can be applied through a pair of

rolls.- The process can be carried out at elevated temperatures (eg: hot roll bonding).- Surface preparation is important for interfacial strength.- Ex: the cladding of pure aluminum over precipitation hardened aluminum-alloy sheet;

stainless steel over mild steel – for corrosion resistance.- A common application of roll bonding is the production of bimetallic strips for

thermostats.

- Other common application: the implementation of two layers of materials with different thermal-expansion coefficients.

- Bonding in only selected regions in the interface can be achieved by depositing a parting agent, such as graphite or ceramic, called stop-off. Schematic illustration of the roll

bonding or cladding process.

ULTRASONIC WELDINGULTRASONIC WELDINGOperations

- The faying surfaces of the two components are subjected to a static normal force and oscilating shearing stresses.

- The shearing stresses are applied by the tip of a transducer, and the frequency of the oscillation is generally in the range of 10 to 75kHz.

- The shearing stresses cause plastic deformation at the interface of the two components, breaking up oxide films and contaminants, thus allowing good contact and producing a strong solid-state bond.

- The temp. generated in the weld zone ranging from 1/3 to ½ of the melting point of the metals joined.

- Can be used on a variety of metallic and nonmetallic mtl’s. Typical use for joining plastics, packaging with foils.

ULTRASONIC WELDINGULTRASONIC WELDING(a) (b)

(a) Components of an ultrasonic-welding machine for making lap welds. The lateral vibrations of the tool tip cause plastic deformation and bonding at the interface of the workpieces.

(b) Ultrasonic seam welding using a roller as the sonotrode.

FRICTION WELDING (FRW)FRICTION WELDING (FRW)Operations

- The heat required for welding is generated thru’ friction at the interface of the two components being joined.

- One of the w/p components remain stationary while the other is placed in a chuck or collet and rotated at a high constant speed, can reached as high as 15 m/s.

- The rotating member must be clamped securely to the chuck to resist both torque and axial forces without slipping.

- The two members to be joined then are brought into contact under an axial force.

- After sufficient contact established, the rotating member is brought to a quick stop while the axial force is increased.

- The weld zone usually is confined to a narrow region; its size depends on the parameters such as:

i) Amount of heat generated.ii) Thermal conductivity of the materials.iii) Mechanical properties of the materials at elevated temperature.

- The shape of the welded joint depends on the rotational speed on the axial pressure applied and this need to be controlled to obtain a uniform and strong joint.

- The radially outward movement of the hot metal at the interface pushes oxides and other contaminants out of the interface.

- Can joint solid or tubular on variety of mtl’s; solid steel bars up to 100 mm in diameter and pipes up to 250mm outside diameter.

- The interface in FRW develops a flash by plastic deformation of the heated zone which can be easily removed by machining or grinding.

(a)

(b)

FRICTION STIR WELDING (FSW)FRICTION STIR WELDING (FSW)

The principle of the friction stir welding process. Aluminum-alloy plates up to 75 mm (3 in.) thick have been welded by this process.

- Heating interfaces is achieved through friction by rubbing two contacting surfaces.

- In FSW, the third body is rubbed against the two surfaces to be joined.

- Involved with low heat input, therefore, low distortion and little microstructural changes.

- No shielding gas are required.- A rotating nonconsumable probe is plunged

into the joint.- The contact pressures cause frictional heating,

raising the temperature ranging 2300 to 2600.- The probe which is located at the rotating tool,

forces heating and mixing of the material in the joint.

- Materials which can be weld: aluminum, copper, steel, titanium.

- Thickness of w/p which can be welded: 1mm to 50mm.

RESISTANCE WELDING (RW)RESISTANCE WELDING (RW)

-Heat required from electrical resistance across the two components to be joined.

-Not requiring consumable electrode, shielding gas as well as flux.

-Can weld either similar or dissimilar metals.

-The actual temperature rise at the joint depends on the specific heat and the thermal conductivity of the metals to be joined.

-The strength of the bond depends on surface roughness and on the cleanliness of the mating surfaces.

RESISTANCE SPOT WELDING (RSW)RESISTANCE SPOT WELDING (RSW)- The tips of the two opposing solid, cylindrical electrodes touch a lap joint of two sheet

metals, and resistance heating produces a spot welding.

- To get a strong bond in the weld nugget, pressure is applied until the current is turned off automatically and the weld has solidified.

- In the RSW, accurate control and timing of the electric current and of the pressure are essential.

- The size of the weld nugget can varied, sometimes up to 6 or 10mm, depending of the probes used.

- Currents range from 3000 to 40,000 A and the current level depends on the materials being welded as well as their thickness.

- Pressure are supplied through pneumatic system.

- Rocker arm type spot welding mc: used for smaller parts.

- Press type spot welding mc: Used for larger w/p.

RESISTANCE SEAM WELDING (RSEW)RESISTANCE SEAM WELDING (RSEW)

-RSEW is a modification of spot welding.-Electrodes are replace with rotating wheels or rollers.-Application: used to make the longitudinal (side) seam of cans for household products, mufflers, gasoline tanks and other containers.-By using AC power supply, the electrically conducting rollers produce a spot weld whenever the current reaches a sufficiently high level in the AC cycle.-With high enough frequency or slow enough traverse speed, the spot weld actually overlap into a continuous seam.-This will produce a joint that is liquid tight and gas tight.-In roll spot welding: current flows to the rollers intermittently, resulting in a series of spot welds at specified intervals along the length of the seam.-In mash seam welding: the overlapping weld are about one to two times the sheet thickness.-On the other hand, the welded seam thickness is about 90% of the original sheet thickness.

Resistance Seam WeldingResistance Seam Welding

RESISTANCE PROJECTION WELDING (RPW)RESISTANCE PROJECTION WELDING (RPW)

- In RPW, high electrical resistance at the joint is developed by embossing one or more projections on one of the surfaces to be weld.

- The projection can be in a form of round or oval for strength purposes.

- High temperature are generated at the projections, which are in contact with the flat matting part.

- The electrodes are large and flat and water cooled are provided to keep their temperature low.

- Weld nuggets are the same as in resistance spot welding.

- Material can be welded: from sheet metal until plates with different thickness; nuts and bolts are also can be welded to sheets and plates.

BRAZING & SOLDERINGBRAZING & SOLDERING

- Require low temperatures compared to welding process.-Filler metals are placed in or supplied to the joint and then melted by using external source of heat.-Once when it is solidified, a strong joint is obtained.-Temperature for solder < temperature for brazing; therefore the strength of soldered joint is much lower.

BRAZINGBRAZING

- It is a joining process where by the filler metal is placed between the contact surfaces or along the periphery of the components to joint them together.

- The heat that supplied just enough to melt the filler but not the components or base metal.

- Once when it become cool and solidified, the strong joint is obtained.- Filler metals that used typically melt above 4500, which is below the melting point of the

metals or w/p to be joined.- During the brazing operation, the external heat will melt the filler which fills the closely

fitting space or joint clearance at the interfaces.- Application: normally for repair work

Furnace BrazingFurnace Brazing

An example of furnace brazing: (a) before, (b) after. Note that the filler metal is a shaped wire.

Induction BrazingInduction Brazing

Schematic illustration of a continuous induction-brazing setup, for increased productivity.

Joint Designs Used in BrazingJoint Designs Used in Brazing

Joint designs commonly used in brazing operations. The clearance between the two parts being brazed is an important factor in joint strength. If the clearance is too small, the molten braze metal will not fully penetrate the interface. If it is too large, there will be insufficient capillary action for the molten metal to fill the interface.

Brazing DesignBrazing DesignExamples of good and poor design for brazing.

SOLDERINGSOLDERING

- In this operation, filler metal is called solder.- Using low temperature than brazing process.-The solder will fills the joint by capillary action between closely fitting or closely placed components.-The solders have low surface tension and high wetting capability.-Heat sources: from soldering irons, torches, or ovens.-Solders melt at a temperature that is eutectic point of the solder alloy.

Circuit board

Types of Solders and Types of Solders and their Applicationstheir Applications

TABLE 30.2Tin-lead General purposeTin-zincLead-silverCadmium-silverZinc-aluminumTin-silverTin-bismuth

AluminumStrength at higher than room temperatureStrength at high temperaturesAluminum; corrosion resistanceElectronicsElectronics

Joint Joint Designs Designs Used in Used in

SolderingSoldering

Joint designs commonly used for soldering. Note that examples (e), (g), (i), and (j) are mechanically joined prior to being soldered, for improved strength

ADHESIVE BONDINGADHESIVE BONDING- Can be in the form of liquid, paste, solution, emulsion, powder, tape and film.- When applied, adhesive typically are about 0.1 mm thickness.- An adhesive may require one or more of the following properties:

• Strength: shear and peel.• Toughness.• Resistance to various fluids and chemicals.• Resistance to environmental degradation, including heat and moisture.• Capability to wet the surfaces to be bonded.

Types of adhesives

1) Natural adhesives: such as starch, dextrin (a gummy substance obtained from starch), soya flour, and animal products.

2) Inorganic adhesives: such as sodium silicate, and magnesium oxychloride.3) Synthetic organic adhesives: which may be thermoplastics or thermosetting

polymers.

- Because of its strength, synthetic organic adhesives are the most important in manufacturing process, particularly for load-bearing applications.

TABLE 30.4Type Comments ApplicationsAcrylic Thermoplastic; quick setting; tough bond at room

temperature; two component; good solvent chemicaland impact resistance; short work life; odorous;ventilation required

Fiberglass and steel sandwich bonds,tennis racquets, metal parts,plastics.

Anaearobic Thermoset; easy to use; slow curing; bonds at roomtemperature; curing occurs in absence of air, will notcure where air contacts adherents; one component; notgood on permeable surfaces

Close fitting machine parts such asshafts and pulleys, nuts and bolts,bushings and pins.

Epoxy Thermoset; one or two component; tough bond;strongest of engineering adhesives; high tensile and lowpeel strengths; resists moisture and high temperature;difficult to use

Metal, ceramic and rigid plastic parts.

Cyanoacrylate Thermoplastic; quick setting; tough bond at roomtemperature; easy to use; colorless.

“Crazy glue.” ™

Hot melt Thermoplastic; quick setting; rigid or flexible bonds;easy to apply; brittle at low temperatures; based onethylene vinyl acetate, polyolefins, polyamides andpolyesters

Bonds most materials. Packaging,book binding, metal can joints.

Pressure sensitive Thermoplastic; variable strength bonds. Primer anchorsadhesive to roll tape backing material, a release agenton the back of web permits unwinding. Made ofpolyacrylate esters and various natural and syntheticrubber

Tapes, labels, stickers.

General Properties of the Adhesives

TABLE 30.4 (continued)Type Comments ApplicationsPhenolic Thermoset; oven cured, strong bond; High tensile and

low impact strength; brittle, easy to use; cures bysolvent evaporation.

Acoustical padding, brake lining andclutch pads, abrasive grain bonding,honeycomb structures.

Silicone Thermoset; slow curing, flexible; bonds at roomtemperature; high impact and peel strength; rubber like

Gaskets, sealants.

Formaldehyde: -urea -melamine -phenol -resorcinol

Thermoset; strong with wood bonds; urea isinexpensive, available as powder or liquid and requiresa catalyst; melamine is more expensive, cures with heat,bond is waterproof; resorcinol forms waterproof bondat room temperature. Types can be combined

Wood joints, plywood, bonding.

Urethane Thermoset; bonds at room temperature or oven cure;good gap filling qualities

Fiberglass body parts, rubber, fabric.

Water-base -animal -vegetable -rubbers

Inexpensive, nontoxic, nonflammable. Wood, paper, fabric, leather, dry sealenvelopes.

Adhesive Peeling TestAdhesive Peeling Test

Characteristic behavior of (a) brittle and (b) tough adhesives in a peeling test. This test is similar to the peeling of adhesive tape from a solid surface.

Joint Designs in Adhesive BondingJoint Designs in Adhesive Bonding

Various joint designs in adhesive bonding. Note that good designs require large contact areas between the members to be joined.

Configurations of Adhesively Bonded JointsConfigurations of Adhesively Bonded Joints

Various configurations for adhesively bonded joints: (a) single lap, (b) double lap, (c) scarf, (d) strap.

- Advantages of adhesive bondings:• It provides a bond at the interface either for structural strength or for non structural applications such as sealing, insulation, the prevention of electrochemical corrosion between dissimilar metals, and the reduction of vibration and of noise.• It distributes the load at an interface and thereby eliminates localized stresses that usually result from joining the components with mechanical fasteners, such as bolts and screws.• The external appearance of the bonded components is unaffacted.• Very thin and fragile components can be bonded without significant increase in their weight.• Porous materials and materials of very different properties and sizes can be joined.• Because it usually carried out at a temperature between room temperature and about 2000C, therefore there is no significant distortion of the components or change in their original properties.

-Limitation of adhesive bondings:• A limited range of service temperature.• Bonding time can be long.• The need for great care in surface preparation.• The difficulty of testing bonded joints nondestructively, particularly for large structures.

MECHANICAL FASTENINGMECHANICAL FASTENING

- Joined or fasten can be taken apart during the product’s service life.- The mechanical fastening method is preferred due to:• Ease of manufacturing.• Ease of assembly and transportation.• Ease of disassembly, maintenance, parts replacement, or repair.• Ease in creating design that require moveable joints, such as hinges, sliding mechanisms, and adjustable components and fixtures.• Lower overall cost of manufacturing the product.

Examples of rivets: (a) solid, (b) tubular, (c) split (or bifurcated), (d) compression.

RIVETSRIVETS

- It is a permanent or semi-permanent of mechanical joining.

Design Guidelines for RivetingDesign Guidelines for Riveting

Design guidelines for riveting. (a) Exposed shank is too long; the result is buckling instead of upsetting. (b) Rivets should be placed sufficiently far from edges to avoid stress concentrations. (c) Joined sections should allow ample clearance for the riveting tools. (d) Section curvature should not interfere with the riveting process.

Metal Stitching and a Double-Lock SeamMetal Stitching and a Double-Lock Seam

Various examples of metal stitching.

Stages in forming a double-lock seam.

Crimping

Two examples of mechanical joining by crimping.

Spring and Snap-In FastenersSpring and Snap-In Fasteners

Examples of spring and snap-in fasteners used to facilitate assembly.