Force is the "P" in PCT - Pressure Current and Time.The Force component of a weld schedule is required to hold the two work pieces being welded together during the welding operation. This prevents any arcing due to the parts being loose. If not held tightly molten material would be expelled during the weld operation. It also provides a forging action as the weld solidifies and cools. This forging action greatly improves the final weld strength.
Air pressure is the reading on the pressure regulator that you set in order to deliver the desired force to the electrodes on the part being welded. Air volume is the ability to deliver this air and force within the time desired by the weld schedule. If the air manifold feeding the resistance welder cannot fill the cylinder in the squeeze time of the weld cycle you will be welding at a low force and in an uncontrolled condition.
Some resistance welding applications call out forces above the limits of tapered electrodes. The RWMA Manual Fig 18.3 shows force vs taper. It shows that above 2400 Lbs force tapers are not viable. Above this force specially designed High Pressure/High Force Electrodes must be used. These electrodes can be straight shanks, threaded or flanged electrodes. They are available from several manufacturers. Contact your electrode supplier for assistance.
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.
Aluminum welds have a narrow plastic range and a very high thermal expansion and contraction. This combination may be the cause for voids in the resultant weld nugget. Application of an increased secondary force near the end of the weld cycle is commonly used to forge the part in its plastic state and close these voids.
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