Page 36 - MetalForming March 2017

Recipe for
Resistance
Spot-
Welding
Success
Here’s a quick “cooking class” for resistance welding, honing in on pressure, current and time. Without an understanding of these variables and their relation to one another, weak or inconsistent welds, or complete weld failure, often will result.
BY RAY MICHELENA
Properly applied, the resistance spot-welding (RSW) process provides a fast, reliable and cost-effective means for joining sheetmetal. However, although RSW has been used in manufacturing for decades, the process still is not well understood outside of the automotive industry.
RSW is unique because it provides a high-speed joining method using a forged weld joint created through the appli- cation of accurately controlled electric heat and force, without the addition of filler metal. The process looks simple, but fabricators must fully understand the process variables in order to achieve the desired result: a weld stronger than the parent material. In fact, often the welds must be cos-
Ray Michelena is an AWS-certified resistance-welding tech- nician with more than 20 yr. of experience with resistance welding. As a resistance-welding seminar instructor and serv- ice tech with T.J. Snow (www.tjsnow.com), he travels regularly to metalworking plants nationwide.
To consistently produce high-quality resistance spot welds, fabri- cators must carefully control the process variables—pressure, current and time.
metically appealing as well as strong, which presents addi- tional challenges to welding-machine setup personnel.
A Review of Critical Process Variables
Fabricators must control three main variables to suc- cessfully create resistance welds: pressure (forging force), current (the amount of welding amps used), and time (the duration of current flow)—PCT. Without understanding the importance of these variables and their relation to one another, weak welds or weld failure often results. Unfortu- nately, the RSW process often gets blamed for these problems, in some cases causing users to adopt a more expensive and slower joining method, such as arc welding, riveting or adhe- sive bonding.
A recent visit to a customer’s plant illustrates how improp- er RSW machine setup can lead to weak or failed welds. In this case, the setup tech assumed that a long weld time would result in stronger welds. However, we proved other- wise.
Why won’t a long-duration weld time produce a better
34 MetalForming/March 2017
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