We are resistance Welding Stainless Steel to copper that is Nickel Plated. We perform the welding of a thermistor to a housing that contains a lead frame. There are two spot welds that we perform per part. The welds we are making are approximately 3/16" apart. We are getting defects where weld splatter is going from one contact to the other. This is causing a short across our thermister. We perform each weld at seperate times, but we are making contact to to the each leadframe contact at the same time. Is there a way to reduce weld splatter to eliminate this defect.

-- Kevin Blakelock (g12680@email.mot.com), June 23, 2001

Answers

Dear Kevin

In order to help, I need to know your present equipment set-up. Please add the following information. What type welding equipment are you presently using? Is it single phase AC, single phase DC, Capacitor Discharge, Inverter type, etc? What are your present weld parameter settings? What is your electrode geometry, and material?

-- Bob Balla (bobballa@tjsnow.com), June 25, 2001.

We are using a Unitek Equipment Inverter Welder. The electrode that we are using is flat faced, rectangular in shape with length of .150" and width of .100".

The parameter settings are: Force = 5 ~ (20 lbs) Squeeze Time = 50ms Upslope Time = 80ms Upslope Current = 0.1kA Weld Time = 45ms Hold Time = 50ms Monitor = 3 to 7.0kW

-- Kevin Blakelock (g12680@email.mot.com), June 27, 2001.

Subject: Welding of a thermistor to housing Stainless Steel to copper that is Nickel Plated Two spot welds approx. 3/16” apart. Weld defects where weld splatter is going from one contact to the other. Reduce weld splatter to eliminate weld defect.

Dear Kevin

Just recently, we were contacted by another manufacturer who was experiencing problems with arcing at the end of the weld cycle when welding Ni plated metal. It appears to be a two (2) fold problem. One is variations in the coating thickness, and the second would possibly be the length of the hold time. At the end of the weld cycle the stainless steel may become too soft to properly support the Ni plating and the electrode will sheer the Ni plating. The stainless steel then may spit out through the break in the plating. If the electrode is withdrawn immediately after the welding energy has been released, the Ni may not break and therefore the expulsion may disappear.

It appears that the welding energy heats the material from the center (joint) out. Variation in electrode shape and material may produce some acceptable manufacturing solutions. A metallurgist has suggested spherical radius on the electrode in the past, as recommended by a reference book.

Should this information help solve your problems, or should you continue to experience problems please keep us informed.

Bob

-- Bob Balla (bobballa@tjsnow.com), June 27, 2001.