Machining Bimetals

Bimetal components put hard materials in select wear areas surrounded by or mixed with softer alloys. They are gaining popularity in the automotive industry and elsewhere, and they pose special machining challenges. The CBN inserts that are so productive cutting alloys with greater than 50 Rc hardness can fracture if they hit softer materials. PCD inserts able to machine abrasive aluminum suffer excessive wear cutting ferrous metals.

Machining bimetals productively calls for refined machining routines developed by the user, tool supplier and machine vendor. In one application, the hard powder metal composite alloy described earlier was hot isostatically pressed onto a less costly 316 stainless steel substrate. A helically interpolated tool path programmed into the machine control applied optimum feeds and speeds to machine the powder metal zone first, then the backing.

To machine bimetal cylinder blocks productively, automakers must contend with both abrasive aluminum alloys and cast iron cylinder liners. The design of the part means hard iron wear zones cannot be isolated from the soft aluminum. However, machine programs providing very low speeds and very light depths of cut enable abrasion-resistant PCD inserts to machine both aluminum and iron without frequent tool changes.