Projection Welding

I did projection welding of 4.5 mm thk sheet to a bracket of 2 mm thk with three projections of 5 mm dia & 1.5 mm height.

As per RWMA data, thk is usually limited to appx 6 mm.

I don't think there is a hard and fast rule on this. You should try it and test the results. In general, when the thickness ratio of two projection welded parts becomes very large, the projection should be located on the thicker of the two parts for best heat balance. You can also use longer weld time and optimize electrode material selection to improve heat balance. Your objective should be to optimize weld parameters so that the hottest part of the weld is at the weld interface.

There is no maximum sheet metal thickness. You can projection weld to any thickness providing you have the heat required. Testing is a sure way to go about making sure you are successful. There are minimum thickness requirements, but no Max. Good luck,