Why mould makers can’t treat cutting tool choice in isolation

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Cutter grades, geometries, materials and sizes

Many cutting tool manufacturers develop cutting tool grades and geometries for specific materials. In mould machining, those materials are typically P20 steels, CPMV 10 and powdered metals. It is therefore critical to select the grades and geometries best-suited to the particular material being machined to avoid premature tool failure. Additionally, matching cutting tool to material increases performance and predictability, resulting in fewer tool changes, fewer rejects and reduced re-working.

If the material used is 52 HRC or softer, general-purpose solid carbide tools work well. For materials harder than that, solid carbide end mills with different geometries and coatings such as aluminium titanium nitrate (designed for extremely hard materials) should be used. It is worthwhile remembering that for solid carbide tooling there are special blends of coatings, unique to individual tooling manufacturers, available. For indexable insert cutters, insert geometries and coatings for hard milling will work for extremely hard powder metals. And the different insert grades and chip grooves available on today’s indexable insert cutters make it possible for machining harder mould materials.

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Once cutter types are determined, proper cutter radii sizes must be selected. Cutter radii must be smaller than inside mould corner radii. If the radius of a tool matches the radii of a mould’s corner, a hard stop will occur. For the finishing process, smaller diameter solid carbide cutters are recommended.