Case Study 33
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Find 5 new engineering developments every day in elements related to facilities, products and processes in your organization and assess their use. Best Practices in #IndustrialEngineering
Industrial engineers have to first know alternatives to produce to specification. Then ways to increase productivity of the best alternative.
Hard Milling - Productivity Improvement Using Tool Clamping Solution
A combination of toolholding used to get the most performance from its small-diameter tools.
Impact Forge in Columbus, Indiana, faced a toolholding challenge. The shop runs small tools at long overhang lengths on jobs that involve not just restricted tool access, but also hard material.
The application is machining forging dies. that have been repaired through flood welding. Process engineering programmer has to develop process plan for material with hardness reaching as high as 50 Rc.
Roughing and finishing occur on Okuma horizontal machining centers. Roughing is done using a 1-inch diameter end mill in a setscrew holder. Finishing the fine details of the dies calling for end mills as small as 0.030 inch in diameter. Deep cavities and small relief angles for the cavity walls require a toolholder slender enough to let these small tools get close to the walls to do their work.
Slender shrink-fit toolholders were first tried. The shrink-fit holder uses thermal expansion and contraction. The holder is heated to open the bore, which then shrinks during cooling to clamp around the tool. The shrink fit’s clamping force is proportional to the amount of expansion and contraction, which is proportional to the size of the bore. As the tool holding bores are small in case of small tools, the clamping force was small. The shrink-fit holders are not able to clamp the the tiny tools if the cutting force became too high at the high speeds used. The toolholder became the limiting factor for productivity of the machine.
Search for the solution to the problem led to the trial using the “Tribos” system from Schunk (Morrisville, North Carolina). The proprietary tool clamping system uses metal spring-back to clamp the tool in a way that is similar to shrink fit, except that it uses mechanical force to open the bore instead of heat. The other part of solution was to hold the Tribos extension within a hydraulic toolholder. The shop used “Tendo” hydraulic toolholders, also from Schunk. A hydraulic toolholder uses hydraulic pressure to deliver its force. The toolholder contains a reservoir of hydraulic fluid. By tightening a screw, the user applies pressure to this fluid, and that pressure is in turn distributed around the metal sleeve, or bush, that holds the tool’s shank. The compression of this flexible bush clamps the tool. In addition, the hydraulic fluid provides vibration damping as a secondary benefit. This damping for the tool life improvement according to shop's process planners.
The Tribos toolholder’s bore has a natural shape that is considerably distorted from being a perfect circle. Instead, the shape has three lobes. The clamping device applies force to the toolholder to push this shape closer to being a circle and the tool can be inserted. Releasing the force then lets the toolholder spring back, concentrically clamping the tool.
With this tool clamping and holding solution, the shop was able to run one of the 0.030-inch Melin ballnose tools in 50 Rc steel at 8,500 rpm, 20 ipm and 0.003-inch depth of cut. The parameters were used and productivity improved substantially.
https://www.mmsonline.com/articles/hard-milling-with-tandem-toolholding
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8 Oct 2015
MAPAL HiTECO CO., Ltd.
https://www.productivity.com/
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