I have a part that consistently gives me trouble in obtaining a good weld. One of the parts is an un-heat-treated stamping of mild steel ~.08" thick, while the other part is a turned part case hardened .002-.005" deep 83-93 HR15N. An edge of the stamped part is to be welded to the bottom of a slot machined across the face of the turned part. After doing a destructive test on the welded assembly I often see no evidence of any material pulled from the heat-treated part, and very little force is required to break the weld joint. Does the fact that one of the parts is case hardened make it more difficult to get a good weld joint than if both parts were "soft"?

There are also some issues with the geometry of the parts that I think might be working against me. Since I can't provide any type of a drawing or picture here, I'll try to describe the geometry as best I can in words. The edge of the stamped part that gets welded has two v-shaped points that are meant to make contact with the bottom of the slot. Also, the bottom of the slot is a curved surface, not flat. The turned part also has a hole through the center of it. I think one of a few things happen when the weld is made that may contribute to a bad weld. It's also possible that each of these scenarios has occurred at one time or another, and not just one of them all the time.

1. Since the bottom of the slot is curved, rather than the points of the teeth contacting the bottom of the slot, the stamped part makes contact along some length of its edge causing the energy to be dissipated over some distance rather than at one point.

2. The edges of the v-shaped teeth are making contact along the diameter of the hole, rather than the points contacting the bottom of the slot.

3. The face of the stamped part makes contact with the wall of the slot and a very weak weld occurs here rather than on the edge of the stamped part.

I would greatly appreciate if some of you could share your thoughts on this problem. Please let me know if there is any additional information I can provide.

-- Joe Werner (jwerner@southco.com), August 01, 2002

Answers

Several problems could exist with your application, including geometry, material, plating, part thickness and position. It is difficult to troubleshoot your exact application via description. I would suggest you submit sample parts to be welded to a development lab for setup, design, and equipment suggestions. Many vendors (including mine) do this free of charge. Kurt Tolliver Unitek Miyachi Corp.

-- Kurt Tolliver (kurt@unitekmiyachi.com), August 02, 2002.