Hybrid Induction Welding for Steel Pistons

Manufacturers are moving from aluminum to steel in the production of pistons for light vehicle diesel engines to take advantage of the cost, mass, durability, and heat tolerance properties of steel. Steel pistons are assembled from two pieces, crown and skirt, joined at the cross section of the crown where the cooling gallery is located. This process requires simultaneous welding of two concentric surfaces. Until now this has been done by friction welding; twisting the surfaces together until a bond has been established by inertia. However, friction welding creates bulge, flash and debris in the cooling gallery; and it is not feasible for smaller bore sizes where curl on the mated surfaces obstructs the gallery.

To solve these problems Federal Mogul Powertrain has developed a hybrid induction welding technique (HIW), wherein the concentric surfaces are heated by electrical induction and then mated in a brief back-and-forth rotation. This process minimizes bulge and flash, leaving a clean unimpeded cooling gallery, with flexibility in the choice of steel material combinations. Engine efficiency is improved by two to five percent.

Market acceptance has been exceptional.