Spot Welding

Questions and Answers

Pulses are used in resistance welding to help grow the nugget size without overheating the part. It is difficult to grow a nugget as large as the electrode face diameter or larger without being inventive with the weld schedule. Pulses or impulses are one means of obtaining nugget growth without overheating the part. There is always one or two off/cool cycles between each pulse.

Multiple impulse Pulsation Welds

 

Additional information on pulsation can be found in another article in this blog:

WHEN USING PULSATION IS THE SECOND PULSE SET HIGHER OR LOWER THAT THE FIRST PULSE?

Reference: RWMA - Resistance Welding Manual 4th Edition

 

 

WHEN USING PULSATION IS THE SECOND PULSE SET HIGHER OR LOWER THAT THE FIRST PULSE?Reference: RWMA - Resistance Welding Manual 4th Edition

On all welders the tongs should mate at the weld surface when the electrodes are attached. Altering the bend without or with heat might be a solution. Keep in mind the heat may anneal the tongs and reduce their strength. Good quality equipment has adjustments for alignment.

This is a machinery design/warranty issue not a resistance welding issue. It is not in the scope of this blog.

Many components in a resistance welding machine should see 4-6 L per minute (1-1.5 gal/min) of water. This is a very high necessary flow of cool water. The specifications for this water can be found in:

AWS Specification AWS J1.2 Guide to Installation and Maintenance of Resistance Welding Machines

Proper sizing of the electric, air and water for a welder installation is very important. It should be done by professionals. The machine manufacturer may provide specifications for the installation. Contact local qualified installers.

This subject is beyond the scope of the blog.

  Water Manifold

Reference: American Welding Society - AWS J1.2 Guide to Installation and Maintenance of Resistance Welding Machines

An inquiry came in after reading about PCT, It asked when does current flow? To clarify current flows during weld time. Be it AC, DC or MFDC equipment.  Weld time is when the current is ON. The current is on the length of time T of PCT. The amplitude of the current is C of PCT. By now you know that the pressure or force is P of PCT.

  Spot Weld Schematic


To see and understand this better please view another article in this blog:

HOW ARE PRESSURE CURRENT AND TIME USED IN RESISTANCE WELDING?

Reference: RWMA Resistance Welding Manual 4th Edition

The answer is yes. One could, but it is not recommended. Stainless requires relatively high forces and pure copper without alloy strengthening additives does not have the strength at the temperature generated to hold up. Mushrooming will occur quickly. Weld nugget failure will be frequent and require constant electrode dressing and attention.

My answer is no don’t use pure copper. In another blog article electrode selection for stainless steel was addressed:

WHAT IS THE PROPER ELECTRODE MATERIAL FOR SPOT WELDING STAINLESS STEEL?

Stainless Steel weld schedules are available in:
AWS Specification C1.1 Recommended Practices for Resistance Welding
In this specification the data necessary to dial in a good starting weld schedule is available

Reference: AWS Specification C1.1 Recommended Practices for Resistance Welding
                  RWMA Resistance Welding Manual 4th Edition

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