Projection Welding
Questions and Answers
The 70% value in a resistance welding standard/specification is typically associated with the projection welding of coined/forged/solid weld nuts. For context, the embossed/stamped projection welding requirements detailed in both the RWMA Manual, and the AWS C1.1, only state what sort of weld strength is required, not the required weld size.
Over time individual manufacturers performing projection welding developed standards based on nugget size as an alternative to pulling tensile tests. To be more specific, the 70% value is typically applied to the size of the weld in relation to the projection when subjecting the part to destructive evaluation. For the record, some standards use a value of 80%.
One cannot calculate the welding parameters (squeeze, weld, hold – force & amperage). A very similar question was recently answered for 4MM wire.
CAN THE BUTT END OF A 4MM (0.156”) MILD STEEL WIRE BE PROJECTION WELDED AT 90 DEGRESS TO A PIECE OF 4MM (0.156”) MILD STEEL WIRE?
The process is very doable but the parameters are likely not published. They cannot be calculated. One will need to either consult the literature for similar operational data or do trial and error.
Another article in this blog describes the steps one must follow to do the trial and error:
“HOW DO YOU DEVELOP A PROJECTION WELDING PROCESS?”
This outlines the processes to develop a schedule and the important factors to consider in setting up the equipment:
FORCE APPLICATION AND FOLLOW-UP
ALIGNMENT
PROJECTION SHAPE, SIZE & CONSISTENCY
ELECTRODE MATERIAL AND CONFIGURATION
A “T” weld is not a cross wire weld. It is a projection weld similar to an elongated projection weld. The most important factor will be the cut off of the wire end. Secondly, fixturing it to maintain its perpendicularity as force is applied. Good tooling and maintenance can make this work and many good welds will be produced.
Reference: AWS C1.1 Recommended Practices for Resistance Welding
AWS J1.3 Specification for Materials Used In Resistance Welding Electrodes and Tooling
AWS J1.2 Guide to Installation and Maintenance of Resistance Welding Machines
Yes, projection welding is very common with wire. Cross wire welding is done every day to make fencing and grating.
Burrs in projection welding be it Capacitive Discharge, AC or MFDC resistance welding are caused by several factors. One is the inability to contain the molten weld nugget as it is forms. Another is the weld interface may have been overheated. A very important factor is that the full force must be maintained on the projections as they collapse. Pressure/force is a factor in each of these considerations. To reduce the burrs and weld flash/expulsion that creates this condition one must look at the basics of force application.
Material at 0.250” (6.4 mm) is generally beyond the limits for resistance spot welding. This question did not define the shape of this bar (round or square). The possibility of using a resistance welding process is viable on this bar with either shape if projection welding is used.
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