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.
Spot welding can decrease in weld size as you weld across the part. One cause for this is increasing magnetic material in the throat of the welder as you move across the part. Most parts are low carbon steel which is a magnetic material. In AC welding applications, if after each weld more material is moved into the throat of the machine, the weld current will decrease.
METAL IN THE THROAT CAUSES IMPEDANCE TO INCREASE
Cracks appearing in the parent material around the weld nugget can be caused by several issues. They are:
High Weld Force – can fracture the parent material with excessive forging action.
Insufficient Cooling – Over heating can cause excessive stresses from expansion and contraction along with the forging action.
Metallurgy of Material Welded – Some materials become brittle at the temperatures experienced in resistance welding.
Low weld strength can be caused by anything which retards weld nugget growth or formation. It can also be caused by the condition of the materials being welded.
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