The Effect of Electrode Force on Weld Quality
Why correct pressure is as important as current
When we think about resistance welding, we generally focus on current and time. However, there is a third parameter equally critical that is frequently ignored: electrode force. Incorrect force can cause anything from material expulsion to weak welds, regardless of how good your electrodes are.
What Happens with Insufficient Force?
When force is too low, contact resistance is high and heat is generated too quickly. This causes:
The metal melts before the parts are well compressed. The liquid metal "explodes" outward, creating spatter and leaving craters in the weld.
The expulsion of molten metal erodes the electrode surface. An electrode that should last 5,000 welds can degrade in 1,000 if there is constant expulsion.
Without uniform contact, heat is distributed irregularly. This produces weld nuggets of different sizes and unpredictable mechanical strengths.
What Happens with Excessive Force?
Contact resistance decreases so much that not enough heat is generated to properly melt the metal.
The electrode mark penetrates too deeply into the material, weakening the sheet and creating aesthetic problems.
Excessive force accelerates electrode "mushrooming," especially at high temperatures.
Finding the Right Balance
Low Carbon Steel
350-500 pounds per spot (1.5-2.2 kN) for 0.8-1.2mm sheets. Adjust proportionally according to thickness.
Coated Steels (Galvanized)
Increase 10-20% over bare steel. The coating requires more pressure to displace it and achieve metal-to-metal contact.
AHSS (Advanced High-Strength)
Follow steel manufacturer specifications. Generally require higher forces and Class 3 electrodes due to their higher hardness.
Problem Signs
If you see constant expulsion → increase force. If welds fail peel tests → it may be excessive force (or insufficient current).
Having problems with expulsion or weak welds?
Our engineering team can help you optimize your process parameters.