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MILLING


T


Get with the Program


imes change. That tired adage is applicable to most machining operations, but especially so with cutter toolpaths. In yesterday’s programming world, milling cutters used wide radial depths of cut and shallow axial engagement to remove metal, like scraping your fi nger across the icing on a birthday cake. The result was high heat in the cut, heavy spindle loads, and cutters that wore out quickly, leaving much of the tool length unused. There’s a better way. Designed originally for cutting heat-resistant super alloys and for hardened steels, today’s CAM developers employ a variety of catchy and proprietary names to describe toolpaths the complete opposite of yesterday’s “hog it and hope” approach. Most employ a phenomena known as chip thinning, which relies on shallow cutter engage- ment—often no more than 10—15% of the tool width—to produce a C-shaped chip that starts out thick but tapers as the cutter exits the workpiece; pressed fl at, the chip profi le resembles an icicle. Since each fl ute is engaged far more briefl y than with conventional cutting, there’s less heat generated and tool life


improves dramatically. Rubbing and tool pressure is likewise reduced. This results in surprisingly high feed rates, often 10 times that of yesterday’s outdated methods. The best part of this approach is that greater axial depths of cut are possible; often the cutter’s entire fl ute length can be engaged, making the most of solid carbide end mills and indexable shell cutters. There’s more. Constant cutter engagement maintains consistent tool pressure through the toolpath, eliminating the bumps in the road that can easily break a cutting tool. Slicing techniques clean out pocket corners using bite-sized pieces, avoiding broken tools and the general unpleasantness that comes when tools get buried between intersecting walls. Smoother cuts, less wear and tear on machine tools, predictable processes and more parts out the door—these are just a few of the benefi ts that come with modern metal removal techniques. If you’re still programming in the ’90s, you should take a hard look at a new CAM system. Your bottom line will thank you.


applicable here as they are with indexable tools. Nor are solid- carbide tools limited to hogging operations. A number of cutting tool manufacturers now offer high-helix end mill designs with six or more fl utes per tool. These make short work of fi nishing and superfi nishing operations, and are also effective in constant cut- ter engagement, high-feed milling (HFM) applications.


CoroMill 419 uses a 19° lead angle to reduce forces on the machine, enabling the application of higher feed rates.


94 AdvancedManufacturing.org | May 2016


Keep it Quiet in There With the increased popularity and use of fi ve-axis ma- chining, tools have to reach farther than ever before to clear fi xtures, clamps, and vises. Moldmaking operations require cutters that can dive deep into cavities, often while machining hardened steel at feed rates and spindle speeds that would have been laughable 20 years ago. Multi- axis aerospace parts have complex shapes and are made of robust materials such as titanium and Inconel, metals notorious for high cutting pressures, premature tool wear, and chatter. Built up edge on the cut- ting tool, material inclusions in castings and forgings, and interrupted cuts such as a cross hole in a bore also introduce vibration into the machining process, an unpleas- ant condition that can quickly escalate into scrap parts and total tool failure. The best way to avoid these noisy situations is with a rigid setup. Stub tools up as much as possible, employ carbide tool shanks and make sure workholding offers no chance of part movement or fl ex. When this isn’t enough, however, a more


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