EVOLUTIONARY CUTTER DOUBLES THROUGHPUT

How often have you throttled back on the milling rate for fear of workpiece “liftoff”?

Ron Newsome recently faced precisely that dilemma, on a hard-to-fixture military hatch retainer milled from solid 4140 steel hardened to Rc 33. He is a tooling engineer at LT Enterprises (LTE), Fairfield, OH, a busy contract machine shop with a good aerospace and defense clientele. His solution not only sped up milling of that part by 2 ½ to 1. It also led to a projected 40% plant-wide reduction in milling costs – even on the easier parts.

“Liftoff may be a good thing in the aerospace business, and out on the launching pad, but not here on the shop floor,” says Mr. Newsome,.

Previously, Ron ran the part a bit slowly so the part wouldn’t pull out of the fixture because of the cutting forces. LTE was satisfied with how the job was running, until Ingersoll’s Tom Craze spotted a better way during one of his weekly walk-throughs. That was in July, ’08. Craze suggested the brand-new Ingersoll EVO TEC milling cutter, which features an extremely free-cutting but robust presentation geometry pressed into a very stocky tangential insert body. “Tom was sure we could run faster with no part liftoff. He’s been right before, so we decided to give it a try.”

Debut Application for New Cutter
The LT job represented one of the first applications for Ingersoll’s EVO TEC family of milling cutters, commercialized only in April, 2008. It includes facemills and endmills that use the same inserts, and which combine the best elements of tangential cutter design (fig 1) with extremely high insert rakes (fig 2), secure seat pockets (fig 3) and robust edge design (fig 4).

Founded in 1982 as a real mom and pop shop, LT Enterprises today runs 24/7 in a busy 40,000 sq-ft plant with 70 employees. Their air conditioned facility specializes in precision contract machining and water jet cutting for aerospace, medical and military markets.

LT produces about 12,000 of the hatch retainers/yr on a CAT 50/50 horizontal machining center, in 400-500-pc lots every few weeks. Although the workholding fixture provides four-point clamping, the part is L-shaped with a slender cross section at some points, and about 60% of the original stock is machined away. This severely limits the choice of clamping locations. “As the operation progresses, the pullout forces move around and shift in direction, Newsome explains. “Some of them are twisting forces because of the L-shape. Liftoff aside, the unsupported slender sections are prone to vibration during the cut.” The problem was so serious that Newsome even considered sequencing between two fixtures to get a better grip in the later