Weld Joints

Manufacturing Processes for Engineering Materials, 5th ed. Kalpakjian Schmid 2008, Pearson EducationISBN No. 0-13-227271-7

Weld Joints

FIGURE 12.1 Examples of welded joints.

(a) Butt joint (b) Corner joint (c) T joint (d) Lap joint (e) Edge joint

Method Streng

th

Design

Var

iabilit

y

SmallP

arts

Larg

ePar

ts

Tolera

nces

Relibility

Eas

eof

Maint

enan

ce

Visua

lIns

pection

Cos

t

Arc welding 1 2 3 1 3 1 2 2 2Resistance welding 1 2 1 1 3 3 3 3 1Brazing 1 1 1 1 3 1 3 2 3Bolts and nuts 1 2 3 1 2 1 1 1 3Riveting 1 2 3 1 1 1 3 1 2Fasteners 2 3 3 1 2 2 2 1 3Seaming, crimping 2 2 1 3 3 1 3 1 1Adhesive bonding 3 1 1 2 3 2 3 3 2Note: 1, very good; 2, good; 3, poor.

TABLE 12.1 Comparison of various joining methods.


General Summary

Joining Skill Level Welding Current Distor- Cost ofProcess Operation Advantage Required Position Type tion EquipmentShieldedmetal arc

Manual Portableand flexible

High All ac, dc 1 to 2 Low

Submergedarc

Automatic High deposi-tion

Low tomedium

Flat andhorizontal

ac, dc 1 to 2 Medium

Gas metalarc

Semiautomaticor automatic

Works withmost metals

Low tohigh

All dc 2 to 3 Medium tohigh

Gas tung-sten arc

Manual orautomatic


Low tohigh

All ac, dc 2 to 3 Medium

Flux-coredarc


High deposi-tion

Low tohigh

All dc 1 to 3 Medium

Oxyfuel Manual Portableand flexible

High All 2 to 4 Low

Electronbeam, laserbeam



Medium tohigh

All 3 to 5 High

1, highest; 5, lowest

TABLE 12.2 General characteristics of joining processes.


Oxyfuel Gas Welding

FIGURE 12.2 Three basic types of oxyacetylene flames used in oxyfuel gas welding and cutting operations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing, flame. (d) The principle of the oxyfuel gas welding operation.

(a) Neutral flame (b) Oxidizing flame (c) Carburizing (reducing) flame

2100C(3800F)

1260C(2300F)

Inner cone3040 to 3300C(5500 to 6000F)

Outerenvelope

Outer envelope(small and narrow)

Inner cone(pointed)

Acetylenefeather

Bright luminousinner cone

Blueenvelope

(d)

Gas mixture

Welding torch

Flame

Solidifiedweld metal

Moltenweld metal

Filler rod

Base metal


Pressure Gas Welding

FIGURE 12.3 Schematic illustration of the pressure gas welding process; (a) before, and (b) after. Note the formation of a flash at the joint, which can later be trimmed off.

C2H2 + O2 mixture

Torch

Flame heatingof surfaces

Clamp

Upsettingforce

Torchwithdrawn

(a) (b)


Heat Transfer in Welding

Specific Energy, uMaterial J/mm3 BTU/in3

Aluminum and its alloys 2.9 41Cast irons 7.8 112Copper 6.1 87Bronze (90Cu-10Sn) 4.2 59Magnesium 2.9 42Nickel 9.8 142Steels 9.1-10.3 128-146Stainless steels 9.3-9.6 133-137Titanium 14.3 204

TABLE 12.3 Approximate specific energy required to melt a unit volume of commonly welded materials.

Heat input

Welding speed

Hl= eVI

v

v= eVIuA


Shielded Metal Arc Welding

FIGURE 12.4 (a) Schematic illustration of the shielded metal arc welding process. About one-half of all large-scale industrial welding operations use this process. (b) Schematic illustration of the shielded metal arc welding operation.

Welding machine AC or DC

power source and controls

Electrode

Electrode

holder

Arc

Solidified slag

Coating

Electrode

Shieldinggas

Base metal

ArcWeld metal

Work

Work

cable

Electrode

cable

FIGURE 12.5 A weld zone showing the build-up sequence of individual weld beads in deep welds.

7

1

2

8

5 4

6 3


Submerged Arc Welding

FIGURE 12.6 Schematic illustration of the submerged arc welding process and equipment. Unfused flux is recovered and reused.

Electrode-wire reel

Electrode cable

Voltage andcurrent control

Voltage-pickupleads (optional)

Ground

Wire-feed motor

Unfused-fluxrecovery tube

Flux hopper

Contact tube

Workpiece

Weld backing


Gas Metal Arc Welding

FIGURE 12.7 (a) Gas metal arc welding process, formerly known as MIG welding (for metal inert gas). (b) Basic equipment used in gas metal arc welding operations.

Shielding gas

Nozzle

Travel

Arc

Base metal Molten weld metal

Solidified weld metal

Wire guide andcontact tube

Shielding gasSolid wire electrode

Current conductor

WorkpieceGun

Feed control

Control system

Gas out

Gun control Gas in

Wire

Shielding-gas source

Wire-feeddrive motor

110 V supply

Voltage control

Contactor control

(a)

(b)

Welding machine


Flux-Cored Arc Welding

FIGURE 12.8 Schematic illustration of the flux-cored arc welding process. This operation is similar to gas metal arc welding.

Metal droplets covered withthin slag coating formingmolten puddle

Powdered metal, vapor-orgas-forming materials,deoxidizers and scavengers

Insulated extension tip

Current-carrying guide tube

Arc

Base metal

Arc shield composed ofvaporized and slag-formingcompounds protects metaltransfer through arc

Solidified slag

Molten slag


Moltenweld metal


Electrogas & Electroslag Welding

FIGURE 12.9 Schematic illustration of the electrogas welding process.

Welding wire

Drive rolls

Electrode conduit

Gas

Welding gun

Welding wireWater out

Water in Water in

Water out

Moveable shoeFixed shoe

Primary shielding gas

Supplementaryshielding gas

GasGas box

Water

Gas

Oscillator

FIGURE 12.10 Equipment used for electroslag welding operations.

Control panel

Wire reel

Wire-feed drive

Oscillation (optional)

Molten slag

Molten weld pool

Retaining shoe

Water in

Consumableguide tube

Water out

Work

Workpiece(ground) lead

Electrode lead

Power source


Gas Tungsten Arc Welding

FIGURE 12.11 (a) Gas tungsten arc welding process, formerly known as TIG welding (for tungsten inert gas). (b) Equipment for gas tungsten arc welding operations.

Electrical conductor

Tungsten electrode

Shielding gas

Arc

Travel

Filler wire

Molten weld metal

Gas passage

Filler rod

Cooling-watersupply

Inert-gassupply

Foot pedal (optional)

WorkpieceDrain

AC or DCwelder

(a)

(b)


Torch


Plasma Arc Welding

FIGURE 12.12 Two types of plasma arc welding processes: (a) transferred and (b) nontransferred. Deep and narrow welds are made by this process at high welding speeds.

Powersupply

Tungstenelectrode

Plasma gas

Shielding gas

(a) (b)

Powersupply

+

+


Weld Bead Comparisons

FIGURE 12.13 Comparison of the size of weld beads in (a) electron-beam or laser-beam welding with that in (b) conventional (tungsten arc) welding. Source: American Welding Society, Welding Handbook, 8th ed., 1991.

(a) (b)

FIGURE 12.14 Gillette Sensor razor cartridge, with laser-beam welds.

Laser welds


Fusion Weld Characteristics

FIGURE 12.15 Characteristics of a typical fusion weld zone in oxyfuel gas welding and arc welding processes.

Molten weld metal

Melting point of base metal

Temperature at which thebase-metal microstructureis affected

Originaltemperatureof base metal

Te

mp

era

ture

Originalstructure

Heat-affectedzone

Fusion zone(weld metal)

Base metal

FIGURE 12.16 Grain structure in (a) a deep weld and (b) a shallow weld. Note that the grains in the solidified weld metal are perpendicular to their interface with the base metal.

(a) (b)

FIGURE 12.17 (a) Weld bead on a cold-rolled nickel strip produced by a laser beam. (b) Microhardness profile across the weld bead. Note the lower hardness of the weld bead as compared with the base metal. Source: IIT Research Institute.

(a) (b)

145

155

260

330

355

0.1 mm

1 mm

0.43 mm

Hardness (HV)

Heat-affectedzone

Melt zone


Fusion Defects

FIGURE 12.19 Examples of various incomplete fusion in welds.

FIGURE 12.18 Intergranular corrosion of a weld joint in ferritic stainless-steel welded tube, after exposure to a caustic solution. The weld line is at the center of the photograph. Source: Courtesy of Allegheny Ludlum Corp.

Incomplete fusion in fillet welds.B is often termed !bridging"

B

Weld

Basemetal

(a) (b) (c)

Weld

Incomplete fusion from oxideor dross at the center of a joint,

especially in aluminum

Incomplete fusion in agroove weld

Weld


Defects in Welded Joints

FIGURE 12.20 Examples of various defects in fusion welds.

(c)

Good weld

(b)

Lack of penetration

Undercut

Porosity

Overlap

Underfill Crack

Inclusions

(a)

Incomplete penetration

Base metal

FIGURE 12.19 Examples of various incomplete fusion in welds.

Toe crack

Underbeadcrack

Toe crack

Base metal

Weld

Longitudinalcrack

LongitudinalcrackCrater

cracks

Weld

Basemetal

(a) (b)

Transversecrack

Transversecrack

Basemetal

Weld


Weld Crack

FIGURE 12.22 Crack in a weld bead, due to the fact that the two components were not allowed to contract after the weld was completed. Source: Courtesy of Packer Engineering.


Distortion in Welds

FIGURE 12.24 Residual stresses developed in a straight butt joint. Source: Courtesy of the American Welding Society.

(a) (c) (d)(b)

Transverse shrinkage

Angular distortion

Weld

Longitudinalshrinkage

WeldNeutral axisWeld

Weld FIGURE 12.23 Distortion and warping of parts after welding, caused by differential thermal expansion and contraction of different regions of the welded assembly. Warping can be reduced or eliminated by proper weld design and fixturing prior to welding.

Weld

Basemetal

(b)(a)

Residual stress

Compressive Tensile


Distortion of Welded Structures

FIGURE 12.25 Distortion of a welded structure. (a) Before welding; (b) during welding, with weld bead placed in joint; (c) after welding, showing distortion in the structure. Source: After J.A. Schey.

Rigid frame Hot zone (expanded)

No shapechange

Melt(pushedout)

Contraction

Internal(residual)tensilestress

Distortion

(a) (b) (c)


Tension-Shear Testing

FIGURE 12.26 (a) Types of specimens for tension-shear testing of welds. (b) Wraparound bend test method. (c) Three-point bending of welded specimens. (See also Fig. 2.21.)

(a) (b)

Longitudinaltension-shear

Transversetension-shear

(c)

Clamp

Roller

Weld

Side bend

Face bend

Root bend


Tension-Shear Test of Spot Welds

FIGURE 12.27 (a) Tension-shear test for spot welds; (b) cross-tension test; (c) twist test; (d) peel test.

Hole left in part

Button diameterindicates quality

(c)

(b)

(a)

(d)

1.

2.

3.

Raised nugget


Roll Bonding & Ultrasonic Welding

FIGURE 12.28 Schematic illustration of the roll-bonding, or cladding, process.

Rolls

Cladding metal

Base metal

FIGURE 12.29 (a) Components of an ultrasonic welding machine for lap welds. (b) Ultrasonic seam welding using a roller.

Mass

Anvil

Transducer DCpolarizationsupply

AC

powersupply

Direction ofvibration

(a)

Force

Couplingsystem

Tip

Workpiece

(b)

Transducer

Toolholder

Roller

Workpiece


Friction Welding

FIGURE 12.31 Shapes of the fusion zone in friction welding as a function of the force applied and the rotational speed.

Forceincreased

Beginning of flash

Flash

1.2.

3.

4.

Force

Speed

Sp

ee

d,

Fo

rce,

Up

se

t le

ng

th

Time

Force

Total upset lengthUpset le

ngth

FIGURE 12.30 Sequence of operations in the friction welding process. (1) The part on the left is rotated at high speed. (2) The part on the right is brought into contact under an axial force. (3) The axial force is increased, and the part on the left stops rotating; flash begins to form. (4) After a specified upset length or distance is achieved, the weld is completed. The upset length is the distance the two pieces move inward during welding after their initial contact; thus, the total length after welding is less than the sum of the lengths of the two pieces. If necessary, the flash can be removed by secondary operations, such as machining or grinding.

(a) High pressure or low speed

(b) Low pressure or high speed

(c) Optimum


Friction Stir Welding

FIGURE 12.32 The principle of the friction stir welding process. Aluminum-alloy plates up to 75 mm (3 in.) thick have been welded by this process. Source: TWI, Cambridge, United Kingdom.

Shouldered

non-consumable

tool

Weld

Probe


Resistance Spot Welding

FIGURE 12.33 (a) Sequence in the resistance spot welding operation. (b) Cross-section of a spot weld, showing weld nugget and light indentation by the electrode on sheet surfaces.

(b)

Electrode

Sheetseparation

Indentation

Heat-affected zone

Electrode tip

Weld nugget

Electrode

(a)

1. Pressure applied

2. Current on

3. Current off, pressure on

4. Pressure released

Lap joint

Weld nugget

Electrodes

FIGURE 12.34 Two types of electrode designs for easy access in spot welding operations for complex shapes.

(a) (b)

Workpiece

Electrodes

Workpiece


Seam & Resistance Projection Welding

FIGURE 12.35 (a) Illustration of the seam welding process, with rolls acting as electrodes. (b) Overlapping spots in a seam weld. (c) Cross-section of a roll spot weld. (d) Mash seam welding.

Electrode wheels

Electrode wheels

Weld Sheet

(b)(a) (c) (d)

WeldWeld nuggets

FIGURE 12.36 Schematic illustration of resistance projection welding: (a) before and (b) after. The projections on sheet metal are produced by embossing operations, as described in Section 7.5.2.

Flat electrodes

Sheet

Workpiece

Projections

Weldnuggets

Product

Force

Force

(a) (b)


Flash & Stud Welding

FIGURE 12.37 Flash welding process for end-to-end welding of solid rods or tubular parts. (a) Before and (b) after.

Arc

(a) (b)

FIGURE 12.38 Sequence of operations in stud arc welding, used for welding bars, threaded rods, and various fasteners on metal plates.

Weld

Push PushPull

Moltenweldmetal

ArcCeramicferrule

Stud

Workpiece(base metal)

1. 2. 3. 4.


Explosion Welding

FIGURE 12.39 Schematic illustration of the explosion welding process: (a) constant interface clearance gap and (b) angular interface clearance gap.

(a) (b)

Detonator Explosive Clad metal(flyer)

Constant-interfaceclearancegap

Base plate

Detonator Explosive

A

Buffer

Clad metal

Angular-interfaceclearance gap

Base plate

FIGURE 12.40 Cross-sections of explosion welded joints: (a) titanium (top) on low-carbon steel (bottom) and (b) Incoloy 800 (iron-nickel-base alloy) on low-carbon steel. The wavy interfaces shown improve the shear strength of the joint. Some combinations of metals, such as tantalum and vanadium, produce a much less wavy interface. If the two metals have little metallurgical compatibility, an interlayer may be added that has compatibility with both metals. {\it Source:} Courtesy of DuPont Company.

(a) (b)


Diffusion Bonding

FIGURE 12.41 Sequence of operations in diffusion bonding and superplastic forming of a structure with three flat sheets. See also Fig. 7.46. Source: After D. Stephen and S.J. Swadling.

Bonding pressure

Die

Stop off

Die

Gaspressurefor forming

1. Core sheet 2. Diffusion bonding

3. Superplastic forming 4. Final structure


Brazing & Braze Welding

FIGURE 12.43 The effect of joint clearance on tensile and shear strength of brazed joints. Note that unlike tensile strength, shear strength continually decreases as clearance increases.

(a) (b)

Basemetal

Base metal

Fillermetal

Torch

Flux

Brass filler metal

FIGURE 12.42 (a) Brazing and (b) braze welding operations.

Joint clearance

Jo

int

str

en

gth

Tensile strength

Shear strength

Base Metal Filler Metal Brazing Temperature (C)Aluminum and its alloys Aluminum-silicon 570-620Magnesium alloys Magnesium-aluminum 580-625Copper and its alloys Copper-phosphorus 700-925Ferrous and nonferrous alloys (except Silver and copper alloys, 620-1150

aluminum and magnesium) copper-phosphorusIron-, nickel-, and cobalt-base alloys Gold 900-1100Stainless steels, nickel- and cobalt- Nickel-silver 925-1200

base alloys

TABLE 12.4 Typical filler metals for brazing various metals and alloys.


Furnace Brazing & Brazed Joints

FIGURE 12.44 An application of furnace brazing: (a) before and (b) after. Note that the filler metal is a shaped wire.

(b)

Filler metal

Filler-metal wire

(a)

FIGURE 12.45 Joint designs commonly used in brazing operations.


Solder Joints

FIGURE 12.46 Joint designs commonly used for soldering.

(a) Flanged T (d) Line contact(b) Flush lap (c) Flanged corner

Boltor rivet

(e) Flat lock seam (f) Flanged bottom (g) Gull wing

Crimp

(h) Through hole (i) Crimped (j) Twisted

PC board Wire

Solder Typical ApplicationTin-lead General purposeTin-zinc AluminumLead-silver Strength at higher than room temperatureCadmium-silver Strength at high temperaturesZinc-aluminum Aluminum; corrosion resistanceTin-silver ElectronicsTin-bismuth Electronics

TABLE 12.5 Types of solders and their applications.


Soldering for Circuit Boards

FIGURE 12.47 Screening solder paste onto a printed circuit board in reflow soldering. Source: After V. Solberg.

Tensioned screen Screen material

Squeegee

Paste

Paste depositedon contact area

Emulsion Contact area

FIGURE 12.48 (a) Schematic illustration of the wave soldering process. (b) SEM image of a wave soldered joint on a surface-mount device. See also Section 13.13. Oil mixed in

Flux

Copper land

Copper land

Oil or air

Turbulent zone(oil prevents dross)

Turbulent zone(dross formedin air)

Plating or coating

Residues

(a) (b)

Wetted soldercoat


Adhesive Bonding

FIGURE 12.49 Various configurations for adhesively bonded joints: (a) single lap, (b) double lap, (c) scarf, and (d) strap.

(a)

Simple

Beveled

Radiused

(b)

Simple

Beveled

Radiused

(c)

Single taper

Double taper

Increased thickness

(d)

Single

Double

Beveled

FIGURE 12.50 Characteristic behavior of (a) brittle and (b) tough and ductile adhesives in a peeling test. This test is similar to peeling adhesive tape from a solid surface.

Peelingforce

(a) (b)


Properties of AdhesivesEpoxy Polyurethane Modified Acrylic Cyanocrylate Anaerobic

Impact resistance Poor Excellent Good Poor FairTension-shear 15-22 12-20 20-30 18.9 17.5

strength, MPa (2.2-3.2) (1.7-2.9) (2.9-4.3) (2.7) (2.5)(103 psi)

Peel strength, N/m < 523 (3) 14,000 (80) 5250 (30) < 525 (3) 1750 (10)(lb/in.)

Substrates bonded Most Most smooth, Most smooth, Most non- Metals, glass,nonporous nonporous porous metals thermosets

or plasticsService temperature -55 to 120 -40 to 90 -70 to 120 -55 to 80 -55 to 150

range, C (F) (-70 to 250) (-250 to 175) (-100 to 250) (-70 to 175) (-70 to 300)Heat cure or mixing Yes Yes No No No

requiredSolvent resistance Excellent Good Good Good ExcellentMoisture resistance Good-Excellent Fair Good Poor GoodGap limitation, mm None None 0.5 (0.02) 0.25 (0.01) 0.60 (0.025)

(in.)Odor Mild Mild Strong Moderate MildToxicity Moderate Moderate Moderate Low LowFlammability Low Low High Low LowNote: Peel strength varies widely depending on surface preparation and quality.

TABLE 12.6 Typical properties and characteristics of chemically reactive structural adhesives.


Rivets and Stapling

FIGURE 12.51 Examples of rivets: (a) solid, (b) tubular, (c) split, or bifurcated, and (d) compression.

(a) (b) (c) (d)

FIGURE 12.52 Examples of various fastening methods. (a) Standard loop staple; (b) flat clinch staple; (c) channel strap; (d) pin strap.

(a)

Standard loop

(b)

Flat clinch

(c) (d)

Nonmetal

Metal channel


Seams & Crimping

FIGURE 12.53 Stages in forming a double-lock seam. See also Fig. 7.23.

1. 2. 3. 4.

FIGURE 12.54 Two examples of mechanical joining by crimping.

(a) (b)


Snap Fasteners

FIGURE 12.55 Examples of spring and snap-in fasteners to facilitate assembly.

Sheet-metal cover

(d) (e) (f) (g)

Integrated snap fastenersSheet-metal cover

Deflected Rigid

Rod-end attachmentto sheet-metal part

(b)(a) (c)

Spring clip

Nut

Push-onfastener


Design Guidelines for Welding

FIGURE 12.56 Design guidelines for welding. Source: Bralla, J.G. (ed.) Handbook of Product Design for Manufacturing, 2d ed. McGraw-Hill, 1999.

(a) (b)

(c) (d)

(e) (f)

Poor

Burr

GoodPoor Good

Deburrededge

Load

Load

Cut notsquare

90

Surface to be machined


Weld Designs

FIGURE 12.58 Weld designs for Example 12.7.

Poor Good

FIGURE 12.57 Design guidelines for flash welding.

Continuousweld

(a)

Intermittentwelds

(c)

Double V groove

Weld Base metal

Single V groove

(b)

Moment, M 3M

Welds


Brazing Designs

FIGURE 12.59 Examples of good and poor designs for brazing.

Good Poor Comments

Too little jointarea in shear

Improved designwhen fatigueloading is a factorto be considered

Insufficientbonding


Design for Adhesive Bonding

FIGURE 12.60 Various joint designs in adhesive bonding. Note that good designs require large contact areas for better joint strength.

(d) Combination joints

Adhesive Adhesive

Rivet Spot weld

Good Very goodPoor

Adhesive

(a) (b) (c)


Design for Riveting

FIGURE 12.61 Design guidelines for riveting. Source: Bralla, J.G. (ed.) Handbook of Product Design for Manufacturing, 2nd ed. McGraw-Hill, 1999.

(c) (d)(b)

Poor

Good

(a)


Case Study: Monosteel Pistons

FIGURE 12.62 The Monosteel piston. (a) Cutaway view of the piston, showing the oil gallery and friction welded sections; (b) detail of the friction welds before the external flash is removed by machining; note that this photo is a reverse of the one on the left.

Oil gallery

Friction welds

(a) (b)

Documents

Weld Joints