Coated tools produce more powder-metal parts

Ridgway, PA--Add long-term wear resistance to tooling made from a steel that combines high strength and fracture toughness, and what do you get? In the case of Alpine Pressed Metals, you get 100 times more productivity.

Alpine faced the usual severity challenge of powder-metal parts manufacturing--the effect on tooling of high press loads and the abrasive wear encountered in high-speed powder-metal compaction. The solution: a switch from conventional tool steels to AerMet(TM)-for-Tooling alloy, a specialty grade developed by Carpenter Technology Corp. (Reading, PA).

To obtain longer wear, Jim Paladino, Alpine engineering manager, turned to Metalife Industries (Reno, PA), a specialist in industrial chrome plating. Metalife applied a thin coating to Alpine's tools in two stages. First, a chrome film was bonded molecularly to the metal substrate. Then, in what's called a polyseal process, a melted polymer compound was added for lower friction. "The results have been spectacular," says Paladino.

Alpine's problem started with an inner bottom punch used to make iron-base powder-metal bushings for the seat adjustment in automobiles. The bushing measures 0.900 inch long, and has a 0.650-inch OD, a 0.400 ID, a key on the OD, and a 25-degree taper across the face. Two 30-ton compacting presses turn the parts out at the rate of 700 to 800 per hr. Pressure applied during the procedure averages 32 tons psi during each compacting stroke.

Initially, the punches consisted of AISI Type S7, AISI Type D2, and 4% vanadium powder metallurgy cold-work tool steels. The punches warped in heat treatment, making it impossible to grind relief in the punch ID. Worse, they would break near the top end, sometimes after making as few as 1,000 pieces.

"We couldn't get any repeatability," Paladino recalls. "It was like a crapshoot. We wanted to produce 150,000 to 250,000 parts a week, but never knew what to expect."

Alpine asked Dietech Tool & Die Co. (St. Mary's, PA) to make its punches from the AerMet alloy. Working from 1 1/4-inch bar stock, Dietech lathed the tools close to size, then heat-treated them in accordance with Carpenter's specifications. Next, the punches were double-aged, finish-ground, and face-detail-burned on a CNC/EDM machine; polished; and then delivered to Alpine.

With the new punches, Alpine eliminated all breaking problems and distortion. However, to make certain they could withstand all service conditions, Alpine had them coated by Metalife with a chrome solution held at 136F, resulting in an initial plating hardness of Rockwell C72 to 74. At last count, Paladino reports the company has produced more than one million bushings with the tools--and they have yet to show any signs of wear.