Re: MFDC welding.
Nice to see someone interested in this subject!
There are a few things you can do to improve the efficiency. If the welds are good and there is no spatter, it is a sign that it is efficient.
One simple method is dressing the electrode tips regularly. By "scraping" off the residue from past welds this process lowers the resistance and keeps the cross section of the electrode tips consistent from weld to weld. This means the current density is also consistent and it is easier to tune the program as the parameters in a way that avoids expulsions. How often you need to use the tip dresser depends on the materials welded. Galvanised steel or aluminium leave more residue.
Ensuring correct fit up of the parts before welding will prevent gaps between the steel sheets. This means the force on the surfaces between the sheets will be consistent and you don't need to use a higher force than necessary. If you set the force higher to compensate for parts with a gap, the parts that fit correctly (no gap) will conduct electricity too good and have a smaller spot. (This is often a problem with high strenght steel and ultra high strength steel, like those used in the "safety" frame of a car body. The B-pillar with the multiple layers of metal is especially tricky to weld, even with a robot.)
There are monitoring systems for the weld quality from a number of vendors. These will tell you if the weld was good or not. A better solution is to use a weldtimer that adjust the current during the weld process. By monitoring the current, voltage and resistance during the weld it figure out how much current it should put out.
[ September 29, 2005, 03:57 AM: Message edited by: c-h ]
