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March 2008 eNews

Vincent Precision Machining cuts setup time to less than a minute

HDL vises with ductile iron bodies improve VMC ‘in-the-cut’ time

Using five new vises in a new setup instead of two has resulted in a huge savings of time for Vincent Precision Machining, Medota Heights, MN.

Five Kurt HDL double station vises mounted side-by-side on a new Bridgeport VMC 1000 XP³ vertical machining center (VMC) allow Vincent Precision to set up in less than a minute per part compared to more than five minutes per part for its 420 stainless steel medical components.

Previously using double station vises with aluminum bodies, Vincent Precision’s workholding upgrade to new Kurt HDL vises provided workholding rigidity that assured repeatable precision part after part while the setup eliminated expensive scrap parts.

“We struggled through two different workholding setups which did not have the needed rigidity and holding power for these difficult to machine stainless steel medical parts,” says Bill Ehnstrom of Vincent Precision Machining. “During heavy milling operations, parts tended to creep upward and out of alignment within the vise jaws. Small chips got imbedded between the part and vise jaws causing all kinds of problems. We couldn’t operate our new Bridgeport VMC to its full potential on this part project so we looked for a better workholding solution.”

Vincent Precision Machining is a new company start-up with Ehnstrom its owner/operator. An applications engineer with a strong background as a machine tool salesman and a machining center operator, Ehnstrom saw a need in the Upper Midwest’s medical device industry for top quality precision machining work at competitive prices. Specializing in high speed 3-D machining and hard milling to 65Rc using a new Kitamura 2XiF machining center with two Kurt 3600V vises, Ehnstrom recognized that workholding often holds the key to both high quality and a fair profit. He called in his local Kurt sales representative, Mike Neeley, for his workholding recommendations on his new Bridgeport VMC.

Vises provide rigidity

The workholding challenge was a 1½" x 1" x ¾" 420 stainless steel medical device component machined with a series of recessed flat and contoured surfaces inside a center slot. The goal was to produce these components to tight tolerances with a near-perfect finish to avoid secondary operations. Quantity requirements for these parts averaged 250 a week, which was a stretch for the previously tested dual-twin-station vise setup. Instead of two vises, Neeley recommended five side-by-side mounted Kurt HDL vises on the Bridgeport’s generously large 1,200 x 600mm (47.2 x 23.6in.) worktable. For some machining centers, five ductile iron vises would prove too heavy. This model Bridgeport, however, has a table load capacity of 900kg (2000 lbs) and easily accommodated the vises, which weigh less than 100lbs each.

“It’s very hard and difficult to machine 420 stainless material with the many complex features we required,” Ehnstrom notes. “The Kurt HDL vises with their ductile iron bodies gave us the rigidity needed. That plus the machine table and base are all iron castings so everything from the vise clamping stations down to the floor is solid iron. What can be more solid and rigid than that?”

The base of all Kurt HDL vises are made of durable 80,000psi ductile iron which provides rugged strength, rigidity and long-term accuracy while absorbing vibration especially when machining extra hard material such as 420 stainless steel.

Using changeable iron jaws machined to the medical components outer contours, the Kurt HDL vises in effect become custom fixtures using a standard model vise base. The beauty of this set-up is that the parts “nest” inside the machined jaws so when the vise is clamped up, all outer surfaces are held tightly. There’s no chance of part misalignment or chatter even at highest speeds. When the part run is completed, jaws can be replaced with others for different jobs. The jaws themselves relocate quickly and precisely without special alignment tools.

“Part loading and unloading is really fast, less than a minute,” says Ehnstrom. “The parts position quickly within the jaw plate’s machined pockets. There’s no alignment needed. When the part is machined, less than a half turn of the vise screw releases it. There’s no wasted motion or heavy labor needed with this set-up. Before with the aluminum body vises, part loading took several minutes. Now with these HDL vises, it takes just seconds plus the five vises handle 20 parts where before the two vises handled only eight parts. These vises have an enclosed design, which makes it easier to blow out chips and coolant with an air hose. The five-vise set-up also frees me for a full half hour to work on other projects while the machine cycles through all 20 clamping stations.”

Five machining operations

Each vise on the worktable holds the components for a different series of milling operations done at cutting speeds up to 350SFM. This is well within the range of XP3 capabilities, which has a rapid traverse rate of 43/43/36/min (1690/1690/1410 ipm). Spindle travel from part to part is minimal. Premium toolholders and high performance solid carbide end mills are used for all of the milling operations. When complete, each machined component has a 16mil surface finish, tolerances of ±0.0005" on bores with no secondary operations needed.

Several features of the Kurt HDL vise design help expedite Ehnstrom’s process for reduced cycle time while maintaining quality. With a 533.400mm length (21") and 152.400mm width (6"), the vises are very compact and position within 25.40mm (1") of each other so that less spindle travel is required, part-to-part, to get into and around parts for complex machining operations. With clamping force up to 5556lbs at 70foot-lbs of input torque, these vises provide repeatable accuracy to 0.001 inch, well within Ehnstrom’s tolerance requirements.

Ehnstrom also likes the quick-change jaw features of the HDL vises. A half turn of the vise hex key and the stationary jaw lifts off the vise body. The quick change jaws self-align allowing fast and accurate setup on the next job.

“The best machining center is only as good as the workholding used,” Ehnstrom concludes. “I tried three different vise setups and learned that when machining very hard materials, rigidity makes the key difference. To get that rigidity, ductile iron is the only way to go.

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