How can heat cause smaller nuggets as I weld?

If the weld equipment is not properly cooled especially the electrodes weld failure is likely to occur. Poor cooling at the electrodes can cause them to mushroom prematurely which reduces the current density at the weld face and the nugget size will reduce. Poor cooling can be caused by low flow, warm water, improperly located cooling tubes, clogged/restricted tubes and no flow.

The first check is the outbound side of the electrode water. Determine the flow rate and the outbound water temperature. Do not burn yourself. Water or the components shortly after a weld should not be too hot to touch and never be less than 0.5 gal/minute flow. The desired water flow is 1.5 gal/minute. The water temperature should be at ground water temperature or good water tower temperatures 18-29 deg C (65-85 deg F). Next check the electrode holder water tube location. It should be within ¼” of the electrode inner face to prevent steam pockets from forming.

Water Flow Indicator                                 Relative Resistances of a spot weld1              

              FLOW INDICATOR                                    PROPERLY LOCATED WATER TUBES

If all of these are good then start to check the other components in the machine for heat buildup. Any copper component that gets hot will carry less current and therefor reduce the current to the spot weld. Cooling is necessary for all components of the system from the electrodes to the pads on the transformer and the transformer itself.
Make sure that there is water flow on the outbound side of all components. Sometimes lines can get plugged with debris and need to be cleaned out. Be sure that all electrical connections are tight and clean. Frequently connections are silver plated to reduce corrosion and resistance.
If all check out good then the next step is to use a secondary current meter and force gauge. Use both to insure that each weld is being made with the proper force and current. Reference your original set up information sheet for the job for the proper values. If not take appropriate action.

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Reference: AWS J1.2:2016 - Guide to Installation and Maintenance of Resistance Wedling Machines

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