A manufacturer of specialty cold formed products claims it can fabricate high quality stainless steel parts, cost effectively, that can be cold headed and subsequently machined or fabricated from the same feed stock. Typically, most stainless steels with excellent heading characteristics do not machine well when secondary fabrication is required. Similarly, a stainless alloy designed to provide exceptional machining properties is not a likely candidate for cold heading. Ready Rivet & Fastener found that it could get superior cold forming and machinability performance from a single stainless grade used to mass produce ball studs for an automotive application. The shop increased productivity and tool life by using 302HQ-FM® stainless, an alloy developed by Carpenter Technology Corporation. Originally, Ready Rivet tried making the ball studs from the conventional 302HQ stainless steel, with little or no success. A Carpenter metallurgist, suggested that the shop try 302HQ-FM stainless, a modification of Carpenter Stainless Custom Flo 302HQ. This variation of the alloy has excellent cold headability, plus machinability approaching that of Type 303 stainless. It was designed primarily for cold headed parts that needed to be drilled, slotted, broached or otherwise machined. Ready Rivet made its ball studs by starting with 0.315â? round Type 302HQ-FM stainless heading wire in annealed condition. Using a cold header, the shop cut the heading wire to 0.680â? lengths and extruded down to 0.235â?. The part was then upset in two blows to form a 0.470â?. washer about one third up the length of the stud. After the cold headed studs were cleaned in a washer, they underwent secondary fabrication on a Towa shaving machine. They were fed into the machine, chucked and spun at high speeds. Two carbide form tools, on opposite sides, plunged into the headed studs to form a 5/16â?ball on one end and cut a neck from 0.320â? down to 0.155â?. After passivating, the parts exhibit the bright finish required for the application. Carpenter 302HQ-FM stainless has a machinability rating of about 75% of Carpenter Project 70+® stainless Type 303 in conventional cutting type applications. Due to its low work hardening rate, this stainless grade is superior to Project 70+ stainless Type 303 in roll threading and cold form tapping machining operations. Typical analysis of the alloy is: carbon 0.06 percent max., manganese 2.00 percent max., phosphorous 0.040 percent max., sulfur 0.14 percent max., silicon 1.00 percent max., chromium 17.50 percent, nickel 10.00 percent, copper 1.75 percent, balance iron.
