Alternative Types of Welding

Cold welding

Cold welding, the joining of materials without the use of heat, can be

accomplished simply by pressing them together. Surfaces have to be well

prepared, and pressure sufficient to produce 35 to 90 percent deformation at

the joint is necessary, depending on the material. Lapped jointsin sheets and

cold-buttwelding of wires constitute the major applications of this

technique. Pressure can be applied by punch presses, rolling stands, or

pneumatic tooling. Pressures of 1,400,000 to 2,800,000 kilopascals (200,000

to 400,000 pounds per square inch) are needed to produce a joint in

aluminum; almost all other metals need higher pressures.

Friction welding

In friction welding two work pieces are brought together under load

with one part rapidly revolving. Frictional heat is developed at the interface

until the material becomes plastic, at which time the rotation is stopped and

the load is increased to consolidate the joint. A strong joint results with the

plastic deformation, and in this sense the process may be considered a

variation of pressure welding. The process is self-regulating, for, as the

temperature at the joint rises, the friction coefficient is reduced and

overheating cannot occur. The machines are almost like lathes in appearance.

Speed, force, and time are the main variables. The process has been

automated for the production of axle casings in the automotive industry.

Laser welding

Laser welding is accomplished when the light energy emitted from a

laser source focused upon a work-piece to fuse materials together. The

limited availability of lasers of sufficient power for most welding purposes

has so far restricted its use in this area. Another difficulty is that the speed

and the thickness that can be welded are controlled not so much by power but

by the thermal conductivity of the metals and by the avoidance of metal

vaporization at the surface. Particular applications of the process with very

thin materials up to 0.5 mm (0.02 inch) have, however, been very successful.

The process is useful in the joining of miniaturized electrical circuitry.

Diffusion bonding

This type of bonding relies on the effect of applied pressure at an

elevated temperature for an appreciable period of time. Generally, the

pressure applied must be less than that necessary to cause 5 percent

deformation so that the process can be applied to finishedmachine parts. The process has been used most extensively in the aerospace industries for joining

materials and shapes that otherwise could not be made—for example,

multiple-finned channels and honeycombconstruction. Steel can be

diffusion bonded at above 1,000 ° C (1,800 ° F) in a few minutes.

Ultrasonic welding

Ultrasonic joining is achieved by clamping the two pieces to be welded

between an anviland a vibrating probe or sonotrode. The vibration raises the

temperature at the interface and produces the weld. The main variables are

the clamping force, power input, and welding time. A weld can be made in

0.005 second on thin wires and up to 1 second with material 1.3 mm (0.05

inch) thick. Spot welds and continuous seam welds are made with good

reliability. Applications include extensive use on lead bonding to integrated

circuitry, transistor canning, and aluminum can bodies.

Explosive welding

Explosive welding takes place when two plates are impacted together

under an explosive force at high velocity. The lower plate is laid on a firm

surface, such as a heavier steel plate. The upper plate is placed carefully at an

angle of approximately 5° to the lower plate with a sheet of explosive

material on top. The charge is detonated from the hinge of the two plates, and

a weld takes place in microseconds by very rapid plastic deformation of the

material at the interface. A completed weld has the appearance of waves at

the joint caused by a jetting action of metal between the plates.