The resistance made when the electrode touches the workpiece is created by:
• Composition of the workpiece
• Surface condition of the workpiece – rough, smooth, clean, dirty
• Conductivity or resistivity of workpiece surface
• Composition of the electrode
• Surface condition of the electrode – rough, smooth, clean, dirty
• Conductivity or resistivity of the electrode surface
• Pressure or force of the electrode on the workpiece
Sandblasting has a dramatic affect upon the surface condition of the workpiece. Depending upon the media used for sand blasting the surface resistance can be a problem?
If glass beads or aluminum oxide were used and have become imbedded in the surface of a soft workpiece, surface resistance may have risen. These or any resistive material may migrate to the electrode face during welding and form an increasing resistive layer. Nugget formation will change and the operation will be inconsistent.
Electrode pickup from the sandblasted surface could be the culprit. What was meant to be a surface cleaning operation became a contamination source.
Yes, sandblasting can be a problem with the wrong material combinations. Make sure that the electrodes are dressed frequently as needed to prevent this problem. Or alter the sandblast process or media.
Hand Held Pneumatic Dresser
Reference: RWMA – Resistance Welding Manual 4th Edition