ShopSolutions Case Histories of Manufacturing Problem Solving Tangential Milling Secures Roughing Process T
o solve a production problem in a high-volume setting, R.H. Sheppard Inc. (Hanover, PA) found that tangen- tial milling improves process security for a difficult
rough-milling operation. The lesson here is that you don’t have to settle for the first thing that works better. Dig deeper for what’s best. That’s why manufacturing engineers at R.H. Sheppard spent almost a year working to fix a tool wreck problem in a rough-milling operation. Rather than settle on the first new tool that could marginally improve things, they dug deeper to uncover the single best solution from among more than eight tool- ing providers. The result: no more tool wrecks or their associated production stoppages—plus an unexpected 30–40% bump in throughput. Together, these gains helped the company con- tain costs and improve delivery performance for demanding customers. The annualized sav- ing exceeds $100,000, offsetting higher energy and other indirect costs that are beyond the company’s control.
R.H. Sheppard is a leading first-tier supplier of OEM power steering components for trans- portation industries worldwide. The Hanover, PA, plant has 160 employees and runs 20 hours a day, four days a week, 50 weeks a year. Annual volume for the workpiece in ques- tion, a power steering housing made of ductile cast iron, is 100,000.
The housing in question is essentially an 8 ½" (216-mm) long casting with a 3.937" (100-mm) bore diameter that is machined in a manually fed multipart setup on a horizontal CNC machine. The operator loads holemaking operations. The operation that caused the problem, which occurs twice in an 18-step process, is rough-milling the mating surfaces on both ends. Since the parts are run four-up, it is by definition an interrupted cut. With the previous radial cutter, an insert
Key to the gain was the switch to tangential milling with an S-MAX face mill from Ingersoll Cutting Tools (Rockford, IL) that features a stronger cutting geometry. The previous cutter was a conven- tional mill, with inserts oriented radially. In tangential milling, the insert lies flat in the pitch circle, presenting its strongest cross section to the main cutting force. Size for size, the cutter body is stronger, and, according to Allen Smith, R.H. Shep- pard manufacturing superintendent, “the selected inserts also are larger and more robust.”
Ingersoll’s Randy Bohm (left) and R.H. Sheppard’s Allen Smith examine the 6" (152-mm) tangential S-MAX face mill that delivered process security for the punishing job of rough-milling power steering housings made of ductile cast iron.
edge would spontaneously rupture, starting the chain reaction leading to irreparable damage to the cutter itself. The damaged insert doesn’t take off its share of material, which overloads the next insert to failure—all in a split second. If the operator can’t shut down quickly enough, the excessive cutting forces over- load the entire cutter body to the point where insert seats break out or the cutter gets bent out of shape.