How are force and pressure related?

Pressure and Force are frequently  confused in resistance welding. They are related terms. The force applied produces pressure at the face of the electrode. For example approximately 1600 lb-force will produce 32,000 psi/pressure on a ¼” electrode face.

Usually weld schedules call out the force in pounds-force or newtons for proper welding. To obtain this force one using an air cylinder, one would adjust a pressure regulator which is labeled in pressure units like (psi). There normally is a conversion chart supplied by the machine manufacturer which will tells you the pounds force generated at the weld head for the pressure setting at the regulator.

Pressure Regulator                     Machine Force Chart

Air Pressure Regulator                                                          Typical Machine Pressure/Force Chart

If you use servos the equipment will also have to be set up to give the set down and desired force on the part.
In all cases the final test is to use a calibrated force gauge to determine that you are getting the proper force at the weld.  The next step is to record same on your set up sheet along with all of the other set up parameters related to "PCT" pressure, current and time.

Ref: RWMA Resistance Welding Manual 4th Edition

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