Must I have full force before current is applied?

Squeeze is the first segment of the weld schedule. It’s function is to apply force on the work pieces to bring them together. This pressure under the face of the electrode in turn makes good electrical contact and controls and contains the resultant weld nugget during the weld and hold portion of the weld cycle. If current is applied prematurely before the proper force has been reached these functions will be compromised and expulsion and poor nuggets should be expected.

The problems that arise by firing the current early are that parts are not in intimate contact to each other or the electrodes. Current will flow as an arc or as expulsion from the contact surface or part interface until the force has built up. Part or all of the nugget material will have been expelled and is not available for weld nugget formation and weld strength. Obviously safety is an issue. Electrode wear and sticking to the work piece is likely. Machine maintenance will be necessary to clean up the expulsion. Rejects and rework will be high.

Some machines are slower than others in their application of force. With time cylinders or actuators can fail and not reach the desired force or start to stick and take longer. All of these are issues that must be watched for in set up or preventive maintenance programs.

The squeeze cycle is an important portion of the weld schedule. Make sure that the welder reaches the desired level of force on the part before you initiate the current.

Reference: RWMA - Resistance Welding Manual 4th Edition 

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