Rough and tough - high-efficiency roughing versus high-speed roughing

Author / Editor: Al Whatmough, CAM Product Manager from Autodesk / Barbara Schulz

USA – A modern high-speed machining strategy for roughing on machines capable of running complex NC files at high speeds, or adaptive clearing, maintains a constant radial tool engagement throughout the entire cut. Larger axial depth of cut can be taken, while simultaneously maintaining a high feed rate.

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When machining moulds with complex 3D shapes, a step-up functionality will give roughed stock a consistent stock allowance.
When machining moulds with complex 3D shapes, a step-up functionality will give roughed stock a consistent stock allowance.
(Source: Autodesk)

A common joke that persists in the industry is that you can tell a good machinist from an average machinist by his or her toolbox. However, what is not a joke is that a good machinist can hear the difference between a high-quality and poor-quality cut from across the shop floor. This is especially true when the machinist is performing traditional roughing operations. The associated cutter paths often contain variable chip loads, varying stepovers and, too often, full-diameter-width cuts. Using the right roughing strategy can clear large quantities of material effectively.

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Traditional roughing passes are characterised by using a series of offset radial passes. These passes are calculated by offsetting a planar cross-section of the CAD geometry and stock model when necessary, then merging and trimming the two together. With this approach, regardless of the offset stepover value used, the tool will see increased cutter engagement at every internal corner or when driving into slots. These internal corners and slots are where cutter forces spike and when the tool is most prone to breakage. In order to operate at a high feed rate while using traditional roughing strategies, the programmer needs to take a shallow axial depth of cut. This can create other tool issues, as he is now overusing the bottom of the cutter rather than the whole flute length. This causes the tool to store more heat in the bottom versus spreading it out along the whole flute, causing premature wear.

In contrast, a modern high-speed machining strategy for roughing on machines capable of running complex NC files at high speeds, or adaptive clearing, maintains a constant radial tool engagement throughout the entire cut. Constant radial tool engagement eliminates spikes in the cutting forces and allows the programmer to take a larger axial depth of cut, while simultaneously maintaining a high feed rate and extending tool life.

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