An ongoing project at the Chrysler Kenosha (Wisconsin) Engine Plant has been to find ways to optimize machining—cutting cycle times, costs, and payback times. Some of this work is being accomplished through the participation of suppliers. Sandvik Coromant Co. (Fair Lawn, NJ) introduced its CoroMill 331 cutters for use in gangs on a number of Chrysler's transfer lines. An early advantage over previous approaches appeared in maintenance, for when the arbors arrive from production, the arbor assembly remains intact with cutters maintained fully set-up. Accuracy, ease of insert indexing and reliability have contributed to increased performance, not only in production but in tool-grind, as well.
Bearing Cap Slitting.
CoroMill 311 side and facemills are now being used in slitting bearing cap loaves. Special 9-in. versions of the cutter in a gang of seven saw parts off nodular SG iron, pearlitic 250HB. The cutter thickness is 0.280-in. with 18 inserts per cutter. Tool life per edge-set of grade 3015 inserts has increased from 1,400 parts to 3,400. Tool-grind time has fallen from 140 minutes to 20. Cutting speed is 132 sfm, feed is 7.125 ipm, axial depth of cut is 4-in. The number of parts machined per year is 300,000, which translates into a savings of $164,500 annually over previous methods.
Engine Bulkhead Milling.
In a present transfer line configuration, half-side facemilling of bulkheads is being performed using two gangs of four 7-in. diameter CoroMill 331 cutters. Part material is low-tensile cast iron, 180HB. Standard cutters with WM/3015 inserts are used in two gangs in two operations. Tool life per cutting edge-set is 20,000, with tool-grind time down from 400 minutes to 20. Cutting speed is 300 sfm, feed is 6 ipm, axial depth of cut is 0.12 in. and radial depth of cut is 0.75 in. The number of parts machined at present is 125,000 a year. Annual cost savings: $17,770.
Just being set up, and justified on the two previous examples, is a new bulkhead milling line which will employ gangs of 11 CoroMill 331 6- and 6.75-in. diameter cutters, to perform the entire bulkhead machining process in a single operation. Cutting speed will be 649 sfm and feed of 12 ipm. Results and savings? Too soon to tell, but both Chrysler and Sandvik are looking for good things.
A growing trend in engine manufacture is to produce aluminum blocks with cast-iron sleeves. Remarks Ed Oles, a scientist at Kennametal Inc. (Latrobe, PA), "On the one hand, you have the fuel-saving low weight of aluminum combined, on the other, with cast iron's ability to resist wear and dissipate heat. But finish milling the block presents its own unique combinations: namely a number of tough machining challenges that include interrupted cutting, varying workpiece hardness and abrasiveness, and the cycle stresses characteristic of milling operations."
Oles admits that conventional coated and uncoated milling inserts can do the job. However, polycrystalline diamond (PCD) cutting tools, like KCD25, offer longer tool life and higher cutting speeds, and thus greater productivity. Further, he adds, additional efficiencies come from the use of carbide inserts coated with a thin film of diamond, because they offer multiple cutting edges and chip control geometries not available in solid or brazed-tipped PCD tools.
Valenite Inc. (Madison Heights, MI) offers a new solution to high speed milling of aluminum and other non-ferrous materials. Dubbed the MasterMill High Velocity Aluminum (HVA) system, it uses a modular design that allows all cutter bodies from 3 to 12 in. to use four different standard cartridge styles. "The HVAs are a perfect solution to rough and finish milling the ever-growing number of automotive aluminum components—engines, headers, rocker arms, and so on," says Valenite's Tom Howes. "In addition, HVA is ideal for milling the fastest growing metallurgical segment, magnesium." The 7075-T6 aluminum bodies are hardcoated to 60 Rc and are rated for speeds up to 13,500 rpm (10,611 sfm; table speed 270 ipm, at 0.005-in. per tooth). Further, the new cutters feature Valenite's effective high-velocity, high-pressure through-the-spindle coolant delivery system.
Lots of Slots.
According to Pat Cline, manufacturing manager, Iscar Metals Inc. (Arlington, TX), the new PVD TiCN coated IC328 easily tackles high-impact, un-interrupted slot milling. "The parting of a crankshaft connecting rod made of 280HB cast steel," he says, "is an excellent example of economy and efficiency. Tailor-made inserts GSFP, 5.98 mm wide, PVD coated, on a special 160 mm diameter cutter, improved tool life from 700 parts to 3,500 parts, with one set of the new inserts, at a cutting speed of 85m/min."
Mitsubishi Materials USA (Garden Grove, CA) has launched a new grade—UE6005—that's been used with good results in machining crankshafts. The grade starts with a carbide substrate, then coated with TiCN and Al2O3. The result is a tool that resists flank wear, cratering, and plastic deformation in cutting steels and cast irons.
In the crankshaft turning operation, the new grade was tested against an existing tool. The cast iron crank (180-230 Brinell) was cut at 574 sfpm, 0.020 ipr and a 0.236-in. depth of cut. The existing tool was producing 75 parts per corner. With the UE6005, there were increases in both the sfpm and ipr rates; the depth of cut remained the same. And the average number of parts per corner was boosted to 150.
Die Work Considerations.
Tom Piper, applications manager, Dapra Corp. (Bloomfield, CT), says a major issue in mold and die work is turnaround—getting from initial design, through prototype, to actual dies and molds, to finished parts. An impediment: in the process is "benching"—the need for and practice of hand rework, finishing, and polishing of the dies. "This is particularly important in metal stamping—hoods, doors, trunk lids, and such," Piper says. "If you can do away with benching, you can go right from machining the stamping die to the stamping press." Although the right cutting tool is certainly important—which means not only the proper geometry and coating to handle the material being machined, but the ability to run for an extended period of time so that the job can be done without too many tool changes—Piper points out that the tool paths must be programmed properly in order to achieve the eliminatin of benching. In other words, the tool is just one part of a larger system.
Speaking of tools, however, Carboloy has launched a new product for die and mold shops. "What's important about this new copy milling cutter isn't so much the interchangeable head and indexable inserts," according to Derek Giles, manager, Rotating Product, Carboloy Inc. (Detroit, MI). "We feel this will be significant to die and mold shops because of its ability to machine vertical walls. With traditional ball nose endmills the tool holder can rub against the wall. Not so with this tool. The tip of the insert extends outward beyond the line of the shank, thus eliminating the potential for the toolholder to make contact with the wall."