Page 44 - MetalForming May 2014

The Secrets to Successful
Resistance Fastener Welding
Follow the advice offered here to successfully projection-weld nuts and studs and avoid cold welds and thread distortion.
For the most part, the resistance- projection-welding (RPW ) process is very similar to the spot-welding process. During spot welding, the size of the contact surface of the electrode cap determines current flow, while during RPW current flow is directed by the projections of the fas- tener. While AC and DC power sources suit RPW of fasteners, the choice of AC or DC depends on workpiece-material composition along with projection size and torque requirements.
Common Projection- Welding Challenges
While the basic process for the pro- jection welding of nuts and studs may be simple, when fabricators fail to fol- low a few standard guidelines, several problems may occur. For instance, you might develop weld spatter in the threads, or experience hole misalign- ment. Cold welds and thread distortion also may occur.
Undetected, these problems can easily result in lost production time
Stephen Andrassy is national sales man- ager at Dengensha America, Bedford, OH: 440/439-8081, www.dengensha.com
BY STEPHEN ANDRASSY
and scrapped parts, which will end up cost- ing manufacturers money that cannot be recouped until the issues are corrected. The good news: By fol- lowing just a few sim- ple recommendations, fabricators can avoid these problems and successfully—and profitably—projection- weld nuts and studs.
Simple Setup Guidelines
42 MetalForming/May 2014
www.metalformingmagazine.com
RPWofanutorstud
occurs in three distinct
phases. First, the upper
electrode of the weld-
ing machine holds the
fastener projections in
place to the stamped
metal part. The machine then applies current and begins to heat the projec- tions to the prescribed welding tem- perature. Finally, force applied to the electrode causes the heated projections to rapidly collapse, and fusion of the two takes place. To achieve a success-
To achieve a successfully projection-welded part, the welding machine must be correctly sized for the particular fastener being welded. The frame of the machine and the electrode assembly must be rigid to avoid flexure and misalignment under load. Shown: a single-point projection-welding system combining a pedestal welder and nut/bolt feeder.
fully projection-welded part, adhere to the following guidelines.
First, ensure that the welding machine is correctly sized for the par- ticular fastener being welded, and that the required welding conditions fall within the normal operating range of