May 2011 / Volume 63 / Issue 5|
Maximizing global competitiveness
By CTE Staff
R.P. Machine Enterprises Inc., Statesville, N.C., markets reconditioned gear production machines and provides technical services, including CNC retro- fitting, custom gear cutting and general machining. The company’s Alpha Group consists of Alpha Machining and Grinding Inc. (AMG), which performs precision grinding, machining and sawing, and Alpha Workholding Solutions (AWS), which designs, manufactures and sells permanent workholders, permanent electromagnetic workholders and magnetic lifting devices.
AMG produces several lines of midsize to large Blanchard-ground and machined steel plates. One line, machined from mild steel, includes versions from ½" to 1" thick, 24" to 72" long and 24" wide. AMG mills pockets, slots and the plate perimeters, and drills holes in the plates. Annual plate production volume is in the thousands.
Courtesy of Alpha Machining and Grinding
To reduce costs and improve productivity, AMG addressed every aspect of the production process. “We have set up a better mousetrap than most folks,” said Marty Murawski, AMG general manager.
One effort targeted reduction of setup and clamping time when milling. The shop began using the A-Pod milling magnet system from AWS to boost productivity and cut costs by saving the time and expense of designing, building and changing fixtures for different-size plates.
“It also benefits us if our customer redesigns a product family. Instead of making costly changes to or scrapping a fixture, we merely rearrange the magnets,” Murawski said. “In the entire plant, I’d be hard pressed to find three or four hard fixtures, and those are for nonmagnetic stainless steel or aluminum parts.”
The A-Pod system consists of portable, round magnetic poles 3.8" in diameter and 2.8" tall, which each create 1,450 lbs. of vertical clamping force. Unlike traditional electromagnets, A-Pod permanent electromagnets require only a short charge of electricity to activate or deactivate grip, assuring workholding security if power fails.
Murawski noted that the magnetic force penetrates upward only about 0.3" into the workpiece, so chips don’t stick to the top or in pockets and slots, eliminating the possibility of chip recutting. Machining time is greatly reduced as well, because the entire plate periphery can be milled without stopping to reposition workholding clamps.
The A-Pod magnets bolt into and slide along the T-slots of the machine table for positioning. When Greg Thibodeau, operations manager, looked to streamline part changeover, AMG manufactured a subplate for the table of the gantry mill where the plates are machined. The subplate is drilled and tapped 1" on center with 3⁄8" holes to match the bolt hole on each A-Pod magnet. AMG bolts the magnets to the subplate in a pattern that enables all plate sizes to be machined without changing the workholding setup. Depending on the plate being milled, eight to 24 magnets are employed.
After workholding issues were addressed, Thibodeau consulted Dick Hagenbuch, sales engineer for manufacturing services company Turning Concepts, Matthews, N.C., to find ways to speed up the plate machining operations. Hagenbuch suggested application of Gorilla Mill endmills from CGC Tools Inc., Waukesha, Wis. Gorilla Mills combine variable flute spacing with variable helix angles to minimize harmonics that generate vibration. According to CGC Tools President Kevin Cranker, the resulting smooth cutting action permits milling at higher feed rates and extends tool life.
For pocket and slot milling, Thibodeau replaced 4-flute, ½"-dia., 1¼" length of cut, variable-spacing-only, solid-carbide endmills with similar-sized tools from Gorilla Mill. For peripheral milling where chip clearance is less of an issue, 5-flute Gorilla Mills are applied.
Thibodeau said the new mills run at a 25 percent higher feed rate than the previous tools, reducing cycle time 25 to 30 percent. Applying the Gorilla Mills improved tool life, Hagenbuch said, adding “We’ve been able to reduce the cost per cubic inch of metal removal to a degree the shop didn’t think possible.”
The savings resulting from AMG’s improvement efforts enabled the shop to secure a 3,000-per-year-plate-production program that one of its customers was subcontracting to an offshore supplier.
Regarding AMG’s ongoing process improvement, Thibodeau said: “Through continuous improvement, you can do more with the same amount of equipment and sometimes fewer people. You continuously improve your process, your tooling and the education and ability of your people, which in turn makes them productive and proud.”
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