"Alternative Types of Welding"

"ULTRASONIC WELDING, COLD WELDING, FRICTION WELDING, LASER WELDING"

(ультрозвукове зварювання, холодне зварювання, зварювання тертям. )

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(1) Ultrasonic welding

1.Ultrasonic joining is achieved by clamping the two pieces to be welded between an anvil and a vibrating probe or sonotrode. 2.The vibration raises the temperature at the interface and produces the weld. 3.The main variables are the clamping force, power input, and welding time. 4.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. 5.Spot welds and continuous seam welds are made with good reliability. 6.Applications include extensive use on lead bonding to integrated circuitry, transistor canning, and aluminum can bodies.

(2) 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 joints in sheets and cold-butt welding 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.

(3) Friction welding

In friction welding two work pieces are brought together under loadwith one part rapidly revolving. Frictional heat is developed at the interfaceuntil the material becomes plastic, at which time the rotation is stopped andthe load is increased to consolidate the joint. A strong joint results with theplastic deformation, and in this sense the process may be considered avariation of pressure welding. The process is self-regulating, for, as thetemperature at the joint rises, the friction coefficient is reduced andoverheating 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.

(4) Laser welding

Laser welding is accomplished when the light energy emitted from alaser source focused upon a workpiece 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.

(5)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 mdeformation so that the process can be applied to finished machine 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 honeycomb construction. Steel can be diffusion bonded at above 1,000° C (1,800° F) in a few minutes.

(6)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.

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