Chapter 37 Flashcards
Solid state welding
Creates joints without melting of the workpiece of fillers.
Resistance welding
Heat and pressure are combined to induce coalescence. Electrodes are placed in contact with the material and electrical current is passed between them.
Pressure
Applied by the electrodes
Pros?
Rapid and economical. No filler required and no fluxes needed.
Heat in resistance welding
Obtained by passing a large electrical current through the workpiece for a short period.
Total resistance of electrodes consists of:
1) bull resistance of electrodes and workpieces 2) the contact resistance between the electrodes and workpieces 3) resistance between surfaces to be joined, faying surfaces.
Resistance between facing surfaces:
A function of 1) quality of surfaces, 2) the presence of contaminants, 3) pressure, 4) the contact area.
Pressure?
Too little causes high resistance and pitting or electrodes. Too high causes molten metal to be expelled. A moderate pressure should be used.
Temperature of welding?
Determined by the magnitude and duration of the welding current
What conditions are preferred?
High currents and short time intervals
Power supply?
High currents are generally required to produce a resistance weld
Resistance spot welding
Simplest and most widely used form of resistance welding. Provides a fast and economical means of joining materials.
Nugget
A satisfactory spot weld full of coalesced metal between faying surfaces
Spot welding equipment
Rocker arm machine
Larger spot welders?
Generally press type. Moveable electrodes are controlled by an air cylinder
Spot welding guns
For desired products that are too large to be manipulated and positioned on a welding machine.
Transguns
Welding transformer has been integrated into the welding gun. Transguns offer reduced power losses and enchanted process efficiency.
Electrodes
Electrodes should never melt, and should have a composition that does not allot to the material being welded
What metals can be used in spot welds?
Virtually all metals can be used.limit on metal thickness is 3 mm.
Resistance seam welding
The seam could be an overlapping series of spot welds.
Second type of resistance seam welding
Resistance butt welding. Produced butt welds between thicker metal plates. Used mostly for pipes and tubes.any combination of metal can be welded.
Projection welding
Produces many spot welds at once
How does projection welding work?
A simple is embossed into the workpieces and then pressure and current are applied. Multiple dimples can be used to enable multiple welds. Spot welding machines can be changed to projection welding machines.
Capacitor discharge stud welding
A chest of current from an electrostatic site system melts the projection and the pieces are pushed together.
Advantages of resistance
Rapid, equipment automated, conserve materials, minimal distortion, not required skilled operators, dissimilar metals may be joined, reliability.
Limitations of resistance?
High cost, lap joints are limited, accès to both sides of joint is required for pressure, skilled maintenance is required to service the machine, clean surfaces are necessary, impose heavy electrical load.
