Tool Shop Reduces Machining Time on Large Molds
High-Speed Spindle Permits Greater Mold Detail and Efficiency
Penco Tool, Inc., a 30-year-old mold-making job shop headquartered in Ashtabula, Ohio, specializes in building large compression and injection molds for OEMs in the plastics and fiberglass industries. During the last two years, the firm has saved bench time and quickened its finishing operations on these molds by using a versatile, high-speed electric spindle system with three different machine tools.
In many cases, the company says, the spindle is used instead of EDM to cut narrow grooves and finish small radii. "It's helped in the area of mold detailsmall radii and fillets where you can't use larger cutters," says owner James Cufr.
With a workforce of about 30 people, Penco serves product manufacturers located primarily in northeastern Ohio. Some of the firm's customers, however, are located throughout the eastern United States. According to Mr. Cufr and co-owner Brian Lewis, customers for the company's large mold capabilities are concentrated in industries that include trucks, satellite TV, recreational vehicles, snowmobiles, outboard motors, and automotive. "We handle molds up to 40,000 lbs.," said Mr.Cufr.
Tooling Capabilities and Equipment
Penco Tool works with several software programs for tool design, including AutoCAD 13C4-CAD, CADKEY version 7.5-CAD, and SurfCAM version 7.2. In addition to compression and injection molds, the firm's tooling capabilities include punches and dies, die-cast dies, and specialty machining. Penco also has outsource capabilities for gages, fixtures, and secondary and prototype tooling at its 18,400-square-foot plant in Ashtabula.
The company's extensive equipment list encompasses large CNC milling machines, horizontal boring mills, gun drills, EDM equipment, and a wide variety of grinders. Typically, large molds are rough-machined on one of the large CNC milling machines; the company then uses EDM and bench finishing to add finishing details.
But about two years ago, Penco acquired a Precise High-Speed Electric Spindle System to take over some of its finishing operations. According to Mr. Cufr, the company is currently employing the spindle instead of EDM to cut grooves in a mold used to create reinforcing ribs on the back of satellite dish antennas. Mr. Cufr also said that the spindle can reduce or eliminate some bench work, thereby speeding up the finishing process and providing repeatability.
"We bought it so we could put more detail in radial corners and save benching time, and we wanted to increase production with high-speed machining," he said.
The spindle system used by Penco Tool features a 2.7-hp (2.0 kW) Precise PKZ 25 fixed centerline spindle, reported to be capable of speeds of up to 25,000 rpm. With the spindle, the company uses a Precise PCF 310 solid-state frequency converter and a Precise 7136 coolant system.
A Yoneda YD1220F, a Makino FDX2NC, and a Lagunmatic Vertical Machining Center (VMC) are among the CNC milling machines on which the spindle system is used. The self-contained system is mounted in a cabinet that can be rolled up to any one of the three CNC milling machines. Because it is easily installed in a matter of minutes, it eliminates the need to change a setup when working on the same part.
According to Mr. Cufr, setup and takedown can be accomplished in as little as 15 to 20 minutes. The fixed centerline spindle design maintains the machine centerline. As a result, CNC program adjustments are only needed to adjust the "Z" axis for spindle height.
Most molds are machined from P-20, which is pre-hardened to 28 to 32 Rockwell. Occasionally, however, some H-13 material (Rockwell 40) is used.
Typically, carbide end mills are used for standard materials. For tool steel, Penco uses carbide, coated with titanium nitride or titanium carbon nitride. Sizes range from about 1/16-inch (the common size) to 1/4-inch diameter. Smaller diameters can be used because, Mr. Cufr notes, the only limitation seems to be the maximum feed rate of the machine.
With the smaller-diameter mills, the high spindle speed reportedly provides the most effective cutting speed (sfm) to achieve optimum productivity and finish. Mr. Cufr said that a typical 1/8-inch-diameter carbide end mill, in a rib-cutting setup, runs at 11,000 rpm and feeds at 150 ipm.
Greater Efficiency and Accuracy
Another advantage of using the spindle, according to operator Brian Van Loocke, is that it is more efficient than the machine's main spindle in many operations. It can also improve accuracy, he said. "When you run the main spindle at very fast speeds, it heats up, so we have to adjust for the change in dimensions," said Mr. Van Loocke. "It also costs a lot more to run a 35-hp spindle when the Precise spindle will handle the cut," he explained.
Mr. Cufr said that the high-rpm finishing gives more precision and a better surface with less bench work. Typically, a 0.002-inch depth of cut is used. "We're able to get the detail a lot easier and better," he explained. "In rib patterns approximately 1/8-inch wide, we can reduce machine time by two-thirds and cut bench time in half. In the long run, the biggest benefit is the quality we get."
Mr. Cufr points out that Penco's sales have tripled in the six years since he and Mr. Lewis bought the company. He attributes the growth of the company largely to the addition of more computers and investments in productivity-enhancing equipment, such as the Precise spindle system.
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