June 2011 / Volume 63 / Issue 6|
Taming tough machining operations
By CTE Staff
The products made by Genesis Attachments are literally mechanical beasts, designed to quickly chew up and spit out tons of concrete, steel and other materials derived from recycling and demolition operations.
Components for such equipment can also be a beast to machine. The jaws used on Genesis shears, for example, are produced from Weldox or Hardox proprietary high-strength steels supplied by SSAB, Stockholm, Sweden.
Located in Superior, Wis., Genesis has 130 employees working out of a 55,000-sq.-ft. shop. The company now cranks out a shear every 16 hours using four vertical machining centers, four horizontal machining centers and two turning centers—quite an increase compared with the one shear per month rate when it was established 14 years ago.
Courtesy of Genesis Attachments
Scott Woerle, machine shop supervisor, credits lean manufacturing efforts during the past 7 years for much of the productivity increase. “We’ve done a lot of work with University of Wisconsin-Stout’s Northwest Wisconsin Manufacturing Outreach Center,” Woerle said. “That includes training in basic lean principles, value-stream mapping, 5S and cellular flow. Last year we ran 20 Kaizen events throughout the shop, and we expect to do 12 to 14 this year.”
Genesis tracks safety, quality, delivery and cost metrics, and results have been impressive. The number of OSHA events has been reduced 50 percent, and quality-related costs have been cut in half. Efforts to reduce machine shop costs have focused on cutting machining time for operations with the longest cycle times.
Shear jaw production begins with plasma or oxy-fuel cutting of shapes from plate up to 3" thick. “Shapes are burned, welded, chamfered and vibratory finished before they hit the machine shop,” Woerle said. “At that point we begin machining pockets in the jaw, chin plate and any other parts required for the jaw assembly. The machined components then go back to the fab shop for welding.”
Produced by rough and finish milling, the pockets, which can be as large as 8" wide × 48" long × 2¾" deep, have tolerances of ±0.002". For upper-jaw component milling, Genesis previously applied cutters tooled with button inserts at surface speeds of 30 to 35 ipm. Machining time was 12 to 13 hours.
The company experienced significant productivity gains when it switched to F2330 high-feed endmills from Walter USA LLC, Waukesha, Wis. “Now we run at 100 to 200 ipm, depending on the part,” Woerle said. “Chip load per insert is 0.045" to 0.060". We cut more than 2 hours of milling time per part with this approach.”
Tool life has increased, and tool costs have decreased. “Instead of buying a big, heavy round insert, we’re buying smaller inserts at a greatly reduced cost,” Woerle said.
He pointed out that the high-speed approach to rough milling is also much more in line with current machining technology. “We were beating up our machines taking those large DOCs, so reducing the stress on them is a big benefit,” Woerle said.
Shear components also require drilling 24 to 30 holes on mounting flanges. Previously, holemaking in the laminated high-strength material required spot drilling and pecking using spade drills run at 65 sfm and 2.5 ipm. “We couldn’t use indexable drills because of the lamination—the two pieces of material welded together were just too tough for indexable tools to handle,” Woerle said.
Genesis worked with Walter to switch the process to its Xtra-tec insert drills. The impact on productivity was immediate and dramatic: Per-hole machining time decreased from 80 to 12 seconds. The holemaking parameters are 272 sfm and 0.010 ipr. Total holemaking time was cut from 18 to 6 minutes for a typical part. Holes are from 20mm to 30mm in diameter and are a minimum of 4 diameters deep.
Woerle expects to continue working with Walter to improve productivity. “Our next project involves use of live tooling on our new CNC turning center, which incorporates quick-change tooling to reduce setup,” he said. “It’s an ongoing effort, and technical support from [Walter sales engineer] Doug Krueger and use of Walter’s new Multiply tech service program have been key factors in our success.”
Multiply is designed to transfer technical expertise across planning, manufacturing and logistics, maintenance and training sectors to help shops pool resources to increase productivity. CTE
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