Ninety-degree milling: Part 3- Tool-diameter areas

International Metalworking News for Asia presents the third and final part of Sandvik Coromant's full-length article on ninety-degree milling, which was first featured in the magazine's August issue to help provide solutions to a multitude of metalworking operations, manufacturers in Asia perform.

Endmilling operations have been largely dominated by two somewhat overlapping application areas as regards tool types - indexable insert cutters and solid carbide cutters. These areas have been segregated mainly by tool-diameter, operation type and the component finish required. Indexable insert endmills have no upper diameter limit but, through physical reasons, have a lower diameter limit - often 12 mm. Solid carbide endmills, on the other hand, can be of diameters down to tenths of a mm but today usually have a competitive upper diameter-limit round 25mm.

As regards type of operation and finish, indexable insert cutters are flexible, high-metal-removal-rate tools, well suited for most operations while solid carbide cutters have close tooltolerances and can provide high finishes and accuracy, especially at large axial depth of cut thanks to long radial cutting edges.

While a solid carbide tool is one, complete precision tool, integrated from shank to cutting edge, an indexable insert tool is made up of two tool elements which should now be seen as a possibility for broad variation and optimisation possibilities. In between the two areas provided by the indexable insert and solid carbide tools, there is a potential area for an alternative tool solution which overlaps both. One that provides both cutting edge indexability and the benefits of solid carbide tooling for small to medium size endmill diameters - 10 to 25mm.

Exchangeable tool heads
The concept of an endmill with cutting heads (316) that can be exchanged on a tool shank provides a good combination of what different ninety-degree cutter types have to offer. The intermediate tool - diameter area in question (10 to 25 mm) lends itself particularly to this concept. The conventional solid carbide endmill remains a good solution where a long radial edge is needed for large axial depths of cut, especially for semi-finishing to super-finishing operations. The indexable insert endmill remains the best for highproductive roughing to semi-finishing operations. A modern exchangeable-head
endmill has an important complimentary position offering several advantages.

Exchangeable-head cutters have the advantages of solid carbide tooling, without having long, spiral chip-channels which result in a relatively weak tool-core. But they also have some of the advantages of the indexable cutter without the need for loose parts in a seat with clamping screw or mechanism. If a solid carbide endmill breaks, it represents a substantial tool cost because the whole tool has to be replaced - the exchangeable head costs considerably less. Solid carbide tools are reground, representing loss of tool diameter, position and costs, whereas the small tool-head is used once, exchanged for a new one, and recycled when worn out.

Versatility is a big advantage of these cutters because changing tools is easy and quick in the machine or in the tool-room and the tool precision ensures cutting edge position. The quality of the coupling, however, is decisive to handling and cutter capability. The balance between tool accessibility and stability is easily optimised with exchangeablehead endmills through selecting the most suitable tool shank for either long tool reach or to high rigidity with minimallength tool shank. The potential metal
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