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Schneeberger tool grinding software offers strategies for all tools
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May 2007
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Schneeberger has developed software to permit the easy grinding of even the most complex tools.
“One size does not fit all” says Chris Harford, general manager of Leicestershire-based Schneeberger. “The grinding strategy has to be suited to the particular type of tool to be manufactured in order to create the tool integrity, long life and precision required in high quality tooling. The cutting strategy which should be employed varies according to the number of cutting edges, flute depths and flute cutting angles. If form consistency is important, yet another strategy should be used – depending on the penetration depth of the flute from the cutting edge, for instance, requires defined contact grinding in the radius by means of pitch correction. In addition, the ratio of radius to slot depth (v=R/Tn) plays an important role”.
Cutting strategies are defined according to tool specification, for instance corner radius milling cutters whose radius edge is not affected by the run in of the slot shape and are standard tools with a standard helix angle up to 30 degrees, slot cutting angle between 0 and 10 degrees, slot depth (v) of between 0 and 0.5mm, those with a slot depth (v) of between 0.5mm and 1mm, or corner radius milling cutters with a helix angle of more than 35 degrees, slot cutting angle of between –8 and 16 degrees, a slot depth (v) between 0.5 and 1 mm. For this category radius edge correction to ensure specific positioning needs to be carried out.
The grinding strategy within Schneeberger’s easy to use proprietary software is selected according to the cutting out of end cutters. It maybe based on straight cutting out, with the machining space of the end cutter made at the defined orthogonal cutting angle by plunging the wheel straight in, or by cutting out with a movement along the course of the cutting edge and with helix pitch correction to give the radius a guaranteed true shape. In the case of tools subjected to extreme loads in the end-face region and with small helix angles, the grinding strategy involves straight cutting out with a defined orthogonal cutting edge where the straight machining face covers the entire radius region. This ensures the entire radius region is corrected by a plane cutting out surface to maximise the lip angle of the cutting edge in the radius region.
Another areas of difficulty is the grinding of multi-pitch helical milling cutters (end mills with various spiral pitches) since four-flute spiral cutters with two different spiral leads have become commonplace because differing pitches result in more stable milling due to the changing direction of normal force from tooth to tooth and minimise the chattering common with higher feed rates. The Schneeberger proprietary software allows the operator to programme multi-pitch helical cutters as a cylindrical cutter using the “multi-spiral milling cutter” option in the software. Primary cut is performed by the pitch of flute one, secondary cut by that of flute 2. The flutes with the steeper pitch are prevented from running into the back of the following flute by defining the rotary offset. With unequal pitch it is sufficient to define the offset via the pitch angle. The software assumes that the two different pitches are distributed in each case over the central and secondary cutting. The pitches themselves need not be known. The software ensures similar cutting conditions for all cuts on the periphery. Multi-spiral milling cutters with corner chamfers and corner radii can be ground using the same software option.
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Author
Andrew Allcock
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