Weldbonding surface preparation

Important Processing Issues. As with conventional adhesive bonding, there are several important issues that cannot be overlooked with weldbonding. Two of the most important issues are joint design and surface preparation. 

The surface preparation method must be carefully considered, especially if the completed weldbond is to have long-term durability to hostile environments. The surface preparation should provide an optimal surface for both adhesion and welding. Thus, the choice of surface treatment is crucial, and there can be a conflict of requirements. The spot welding process requires a low electrical surface resistance, and many adhesive surface preparation processes provide a high surface resistance because of oxide layer buildup. When it is impossible to harmonize on a surface treatment, current practice tends to favor treatments that yield good weld nuggets at the expense of the adhesive bond. 

To assess the advantages of the weldbonded joint, one must look at the properties of the spot weld alone, the adhesive bond alone, and compare these to the properties of the weldbonded joint. One must also be aware of the physical and environmental effects on the joint. Studies show that weldbonded joints can be stronger than joints that are only spot welded or only adhesively bonded. However, metal thickness, surface preparation, adhesive flow and cohesion, and weld quality can influence the results. 

Kizer, J.A., Development of weld-thru weldbond process surface preparation. Proceedings of the 5th National SAMPE Technical Conference, Vol. 5, Kiamesha Lake, New York, pp. 124-130, October 9-11,1973. 

Russell, W.J. and W.C. Tanner, Component Parts Assembly with Joints Adhesive-Mechanical, Part 1. Surface Preparation of Aluminum for Weldbonding, Picatinny Arsenal Technical Report (PATR) 4610, AD 919 514L, February 1974. 

Lockheed workers Kizer and Grosko have studied weldbonding using four different surface preparation techniques on aluminum. A technique developed for aluminum by the Northrop Grumman Corporation for the Air Force follows. It was found to be superior to the previously recommended FPL etch plus 60-min dichromate seal. 

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