Solid-State Welding Processes

Text Reference: “Manufacturing Engineering and T h l ” K l kji & S h id 6/ 2010Technology”, Kalpakjian & Schmid, 6/e, 2010

Chapter 31

Solid-State Welding ProcessesSolid State Welding Processes• Joining takes place without fusion at the g p

interface• No liquid or molten phase is present at the joint• Two surfaces brought together under pressure• For strong bond, both surfaces must be clean:

– No oxide films– No residues– No metalworking fluidsNo metalworking fluids– No adsorbed layers of gas– No other contaminants……

Solid State BondinggInvolves one or more of:

• Diffusion: the transfer of atoms across an interface– Facilitated by heat

• Friction• Friction• Electrical-resistance• Induction

P• Pressure:– The higher the pressure, the stronger the interface– May combine pressure & resistance heatingMay combine pressure & resistance heating

• Relative interfacial movements– Create clean surfaces– Even small amplitudes improve bond strength

Cold Welding• Pressure is applied to the workpieces

through dies or rollsthrough dies or rolls• Plastic deformation

R i t l t ( f bl b th)• Requires at least one (preferably both) mating parts be ductile

• Prepare surfaces by pre-cleaning• Best bond strength occurs with two similar g

materials

FIGURE 31.1 Schematic illustration of the roll bonding, or cladding, processprocess.

FIGURE 31.2 (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 workpiecesdeformation and bonding at the interface of the workpieces. (b) Ultrasonic seam welding using a roller as the sonotrode.

Ultrasonic Weldingg• Process is versatile and reliable• Used with wide variety of metallic & non-• Used with wide variety of metallic & non-

metallic materials– Including dissimilar metals (bimetallic strips)Including dissimilar metals (bimetallic strips)

• Useful for: – Joining plastics– Joining plastics– Packaging with foils– Lap welding of sheet foil thin wireLap welding of sheet, foil, thin wire– Seam welding if one material is:

• sheet, foil, polymer-woven materialp y

• Moderate operator skill

FIGURE 31.3 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

bro ght into contact ith the part on the left nder an a ial force (3) The a ialbrought into contact with the part on the left 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 p p g p gwelding after their initial contact; thus, the total length after welding is less than

the sum of the lengths of the two pieces. The flash subsequently can be removed by machining or grinding.

FIGURE 31.4 Shape of the fusion zones in friction welding as a function of the axial force applied and the rotational speedfunction of the axial force applied and the rotational speed.

Inertia Friction Welding• A modification of Friction Welding• The necessary energy is supplied by the kinetic• The necessary energy is supplied by the kinetic

energy of a rotating flywheel

Linear Friction Welding- Use linear reciprocating motion (not rotational)- Process suitable for welding square or

rectangular parts- Metals or plastics

FIGURE 31.5 The principle of the friction-stir-welding process. Aluminum-alloy plates up to 75 mm (3 in.) thick have been welded by y p p ( ) y

this process.

Resistance Welding (RW)Resistance Welding (RW)• The heat required for welding is produced by

means of electrical resistance across the two joining components

• Process does not require:Consumable electrodes– Consumable electrodes

– Shielding gasses– Flux

• Bond strength depends on surface roughness & cleanliness

• Requires specialized machinery (generally non-• Requires specialized machinery (generally non-portable)

• Many facilities now automated• Low operator skill level

FIGURE 31.6 (a) Sequence of events in resistance spot welding. (b) Cross section of a spot weld showing the weld nugget and the indentation(b) Cross section of a spot weld, showing the weld nugget and the indentation

of the electrode on the sheet surfaces. This is one of the most commonly used processes in sheet-metal fabrication and in automotive body assembly.

FIGURE 31.7 Two electrode designs for easy access to the components to be welded.

FIGURE 31.8 Spot-welded (a) cookware and (b) muffler. (c) An automated spot-welding machine. The welding tip can move in three principal directions. Sheets as large as 2.2 × 0.55 m (88 × 22 in.)three principal directions. Sheets as large as 2.2 × 0.55 m (88 × 22 in.) can be accommodated in this machine with proper workpiece supports.

Source: Courtesy of Taylor–Winfield Corporation.

FIGURE 31.9 Test methods for spot welds: (a) tension-shear test, (b) cross tension test (c) twist test (d) peel test (see also Fig 32 9)cross-tension test, (c) twist test, (d) peel test (see also Fig. 32.9).

FIGURE 31.10 (a) Seam-welding process in which rotating rolls act as electrodes. (b) Overlapping spots in a seam weld. (c) Roll spot welds ( ) pp g p ( ) p

and (d) Mash seam welding.

FIGURE 31.11 Two methods of high-frequency continuous butt welding of tubeswelding of tubes.

FIGURE 31.12 (a) Schematic illustration of resistance projection welding. (b) A welded bracket. (c) and (d) Projection welding of nuts or g ( ) ( ) ( ) j g

threaded bosses and studs. (e) Resistance projection welded grills.

FIGURE 31.13 (a) Flash-welding process for end-to-end welding of solid rods or tubular parts. (b) and (c) Typical parts made by flash p ( ) ( ) yp p y

welding. (d) and (e) Some design guidelines for flash welding.

FIGURE 31.14 The sequence of operations in stud welding commonly used for welding bars, threaded rods, and various fasteners onto metal g

plates.

FIGURE 31.15 The relative sizes of the weld beads obtained by tungsten arc and by electron beam or laser beam weldingtungsten-arc and by electron-beam or laser-beam welding.

FIGURE 31.16 Schematic illustration of the explosion-welding process: (a) constant-interface clearance gap and (b) angular-interface

clearance gap. (c) Cross section of explosion-welded joint: titanium g p ( ) p j(top) and low-carbon steel (bottom). (d) Iron–nickel alloy (top) and low-

carbon steel (bottom).

Diffusion Bonding• A process in which the strength of the joint results from

– diffusion (primarily), and– plastic deformation of the faying surfaces

• Diffusion is the movement of atoms across the interfaces• Temperatures about 0.5 Tm (absolute)• The bonded interface has the same physical & mechanicalThe bonded interface has the same physical & mechanical

properties as the base metal• Strength of bond depends on:

– PressurePressure– Temperature– Time (duration) of contact– Cleanliness of faying surfacesy g

• Bonding may be facilitated by use of a filler metal at the interface

• For some materials, brittle intermetallic compounds may form , p yat interface– Prevented by electroplating the surfaces

Diffusion Bondingg• Use high pressure autoclaves for complex parts• Suitable for joiningj g

– Dissimilar metals (most common)– Reactive metals (e.g. Titanium, Beryllium)

Metal matrix composite materials– Metal-matrix composite materials• An important PM sintering mechanism• Relatively slow process y p

– To allow time for diffusion• Automation enables economic production in

moderate volumes;moderate volumes; – Aerospace, nuclear, electronics

• Requires skilled operatorq p

FIGURE 31.17 Aerospace diffusion bonding applications.p g pp

FIGURE 31.18 The sequence of operations in the fabrication of a structure by the diffusion bonding and superplastic forming of three

originally flat sheets See also Fig 16 48 Sources: (a) After D Stephenoriginally flat sheets. See also Fig. 16.48. Sources: (a) After D. Stephen and S.J. Swadling. (b) and (c) Courtesy of Rockwell International Corp.

FIGURE 31.19 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;the friction welds before the external flash is removed by machining; note that this photo is a reverse of the one on the left.