Spot Welding

Questions and Answers

Copper is a very conductive material and therefore can require different procedures. It can be resistance welded to similar materials. Factors that will be present are:

• Currents will be high to generate heat.

• Projections may be a good design idea to concentrate heat in a small area.

• Resistance brazing may be a method to simplify the attachment.

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Sometimes increasing the current and weld time seems to hit a wall as far as nugget growth goes. It is very difficult to grow a nugget larger than the face size of the electrode.

A method that some find successful to increase the face size is to use weld impulses. At the end of the weld cycle schedule an off period of one or two cycles then repeat the weld schedule. The length of the impulses may need to be adjusted to prevent overheated and expulsion.

Multiple impulse Pulsation Welds

A larger electrode face size is also an option. This will require a completely new weld schedule. The larger weld face will encourage a larger weld nugget.

Reference: RWMA – Resistance Welding Manual 4th Edition

Nugget diameters are published for various materials and thicknesses in many locations.

The American Welding Society AWS C1.1 - “Recommended Practices for Resistance Welding” is one of these. Weld schedules including nugget diameters are listed for various materials. How to measure a nugget is also shown in the AWS C1.1 standard.

This blog also describes the method to measure a nugget:

HOW DO YOU MEASURE WELD NUGGETS?

WHAT IS THE FORMULA TO CALCULATE NUGGET DIAMETER IN RESISTANCE WELDING?

Weld Nugget

There is no formula to calculate a weld nugget.

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Yes, resistance welding electrodes should always be water cooled.

The water for the electrodes should come directly from the water manifold. The flow rate should be optimally 5.5 L/minute (1.5 gallons/minute) at a water temperature of 18 – 29 deg C (65 – 85 deg F). Flow should never be less than 2 L/minute (0.5 gal/minute). Additional flow and water specifications can be found in AWS Standard - J1.2 “Guide to Installation and Maintenance of Resistance Welding Machines” Water flow tubes should be located within 6 mm (¼ inch) of the hole bottom. This prevents steam pockets from forming. Water flow on the exit side should be monitored with flow indicators or gauges.

                     Water Flow Indicator                                            Relative Resistances of a spot weld1

               FLOW INDICATOR                                       PROPERLY LOCATED WATER TUBES

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This question was generated after the person read the article in this blog:

“IS THERE A MINIMUM SPACING BETWEEN SPOT WELDS”
 Shunting Current 3

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