What should you know about arc welding processes? https://www.zupyak.com/p/3513812/t/what-should-you-know-about-arc-welding-processes The first layer is the perfect foundation for your welded parts. The first layer has a big job to do to make your welding process successful. Note that welding can never be 100% predictable. That’s why the primary layer of the arc welding plays a crucial role in optimizing MIG welder.