When a job is set up properly and the electrodes and water cooling are maintained it is still possible to have weld variation during a production day. It is very common that the line voltage at most production plants can vary during the day because of the demand on the Utility Company. The problem could be your feed to your plant or the Utility Company's main grid.
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.
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.
Force is used for two main reasons. One is to contain the weld nugget and prevent expulsion and the other is to strengthen the weld by forging the solidifying weld nugget. It is easy to see that if welding force is changed these actions will be affected to some degree. Expulsion could increase or decrease and the resultant weld strength could also increase or decrease.
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