Resistance Spot Welding is a commonly used practice in several HVAC and Metal Fabrication shops. A recent article in the July issue of MetalForming by Tom Snow of T.J. Snow Company Inc. makes reference to spot welding to being much like a recipe from a cook book. The ingredients, in this case being secondary amps, weld duration, and forging pressure all need to be mixed in the right quantity to provide the desired results.
Key considerations to keep in mind:
- Choose a machine that can provide optimal strength welds which would be Class A welds while keeping 25 percent of the capacity of the welder in reserve at the welders most demanding application.
- Keep in mind the material thickness and type of material you are planning to weld and at what speed you want the machine to weld.
- Most Resistance Spot Welders are rated at a 50 percent duty cycle however some KVA ratings can be in flated by using a duty cycle less than 50 percent so be sure to ask if what you are being quoted on meets these standards to ensure you are comparing, ” apples with apples”.
- Be sure to consider a machine that fits your applications needs as a spot welders that is oversized can be just as a problematic as a machine that is undersized for the application.
- Rocker-arm style machines are the most common as they are the most cost effective solution. However their rocker style can allow for the tips to skid which leads to the spot arms to not being perfectly aligned. In applications that call for a low-marking show surface a linear press style spot welder will be a better fit for this application.
- Using a specialized resistance welding amp meter to measure the secondary RMS welding current delivered to the tips along with a weld force gauge will help ensure proper set up for each application. A tensile tester can also help in testing spot welds. The tensile tester is designed to pull small weld samples to failure. The shear strength of a good spot weld should be more than the shear strength of the material being welded together.
- Use the correct tips and holders for the application. An offset top holder and straight tips can be more cost effective in the long run than using more expensive offset electrodes.
- “Dress” your tips frequently – most spot weld quality issues can be traced back to the tips being worn.
- To achieve good quality spot welds be sure to use good quality steel. High Carbon content can cause issues just as well inconsistent coating thickness. ( ie. Galvanized)
- Schedule regular maintenance for your spot welder to prevent significant breakdowns.
The full article can be found at the following link – http://metalformingmagazine.com/magazine/article.asp?iid=114&aid=9505