This document discusses resistance welding, specifically spot welding and seam welding. It explains that resistance welding uses electrical current to generate heat and join metal pieces. For spot welding, current is applied through electrode tips that hold the metals under pressure. Spot welding is used extensively in automotive and aerospace industries. Seam welding is a continuous version of spot welding that produces leak-proof seams, such as for fuel tanks, by overlapping spot welds. Key factors in resistance welding include current, time, pressure, and electrode material and design.

1. 115 April 2020 Dr.Abhishek Sharma
By
Dr. Abhishek Sharma
Metal Joining (Resistance Welding)
KME-403
Unit - IV
GL BAJAJ INSTITUTE OF TECHONOLOGY & MANAGEMENT

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Resistance Welding:
• Resistance welding is accomplished when current is caused to flow through electrode tips and
the separate pieces of metal to be joined.
• The resistance of the base metal to electrical current flow causes localized heating in the joint,
and the weld is made.
• The weld is made by a combination of heat, pressure and time.
• The pressure exerted by the tongs and electrode tips, through which the current flows, holds the
parts to be welded in intimate contact before, during and after the welding current time cycle.
• The required amount of time current flows in the joint is determined by material thickness and
the type, the amount of current flowing, and the cross sectional area of welding tip contact
surface.
In resistance welding actual nugget is
formed internally, unlike that in other
welding methods like TIG, MIG.
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• Spot welding in particular has been used extensively in the automotive industry.
• For the joining of steel and in the aerospace industry for airframe components in aluminum
alloys.
• Seam welding is used in the production of thin sheet, leak-tight containers such as fuel tanks.
Principle of Resistance welding:
• The basic formula for heat generation may be stated:
H = I2Rt
H is Heat, I2 is welding current squared and t is the time for which current flows.
Spot Welding
• The resistance spot weld nugget is formed when the interface of the weld joint is heated due to
the resistance of the joint surfaces to electrical current flow.
• The current must flow or the weld cannot be made.
• Pressure of electrode tips on the workpiece holds the part in close and intimate contact during
the making of the weld.
Spot Welding Time Cycle:
• SQUEEZE TIME − Time between pressure application and weld.
• HEAT OR WELD TIME − Actual Welding Time.
• HOLD TIME − Time that pressure is maintained after weld is made.
•OFF TIME − Electrodes separated to permit moving of material for next spot.
5 April 2020 Dr.Abhishek Sharma

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➢ Copper is the base metal normally used for
resistance spot welding tips.
➢ The purpose of electrode tips is to conduct the
welding current to the workpiece.
➢ To be the focal point of the pressure applied.
➢ To the weld joint, to conduct heat from the work
surface, and to maintain their integrity of shape and
characteristics of thermal and electrical conductivity
under working conditions.
Resistance Welding Machines:
➢ AC or DC supply may be used.
➢ The frame solutions for resistance welding machines can vary greatly.
➢ In larger welding units and automated production, welding force is created by means of
pneumatic and hydraulic cylinders.
➢ The cooling of transformers and contactors is usually separate from the other cooling circuit.
➢ Equipment manufacturers usually state the minimum cooling water circulation.
➢ Inadequate cooling damages the heat balance of the joint and wears the electrodes quickly.
5 April 2020 Dr.Abhishek Sharma

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Seam Welding
➢ Seam Welding replaces spot welding for producing continuous leak proof joints for use in
sheet metal containers like petrol tanks etc.
➢ In practice it is a continuous type of spot welding, where spot welds overlap each other to the
desired extent.
➢ Electrodes used are in form of copper wheels or rollers.
➢ One or both the wheels are powered.
➢ Pressure is applied in the same way as in spot welding.
➢ For producing gas tight seam, the welds should overlap 15 to 20% of nugget dia.
➢ While for maximum strength overlap dia should be 40 to 50%.
➢ Size of nugget depends on weld time for given welding speed and current and the amount of
overlap depends upon the off time.
➢ As the electrodes rotate, the work is moved b/w them and current is supplied in pulses during
the weld time.
➢ Weld time is adjusted to be long enough to produce a spot weld in a metal of given thickness
and desired overlap.
5 April 2020 Dr.Abhishek Sharma