Titanium machining with optimised insert

Some materials are particularly difficult to cut. Titanium alloys and highly heat-resistant superalloys, for example, are both subcategories within the ISO-S group of materials. On closer examination, however, these types of material behave completely different from each other under machining conditions. Walter is expanding its range of indexable inserts suitable for Asian manufacturers’ turning applications by adding a new selection of optimised geometries.
 In practice, titanium and superalloys are often machined by one and the same type of insert. Here, the use of cutting tool materials and geometries proven in the machining of ISO-M materials - stainless and acid-proof steels - is not at all uncommon. "While it is possible to machine difficult-to-cut materials using a combination of solutions in this way," explains Stefan Lenischenko, tool developer at Walter in Tübingen, "these are merely compromise solutions that fall well short compared with other options available to us today. For maximum performance and a long tool life, the best insert solutions are the ones that have been optimised either for titanium alloys or for superalloys." For steel and cast iron, universal indexable inserts may be cost-effective to use, but, in the area of ISO-S-materials, special solutions pay dividends.

Requirements
 These two material subgroups do have a few things in common. They tend to gum up and promote a built up edge. They are poor thermal conductors, which results in most of the heat from cutting flowing into the cutting edge. That's about it. The specific properties of these materials mean that titanium alloys and superalloys produce completely different chip shapes on the tool cutting edge and are susceptible to different types of wear.
Titanium alloys are prone to crater wear caused by diffusion. Carbide particles migrate into the chip and the indexable insert is eroded and weakened in the machining zone. Very hard forged skins and high strengths increase the risk of spalling and plastic deformation on the cutting edge. In addition, the material has a low modulus of elasticity, which increases the tendency to oscillate. With build-up on the cutting edge, the cutting edge erupts even more quickly.
All these phenomena are exacerbated in line with the percentage of beta-stabilising elements in the alloy microstructure. If the widely used material Ti6Al4V, which contains both alpha and beta elements, were already difficult enough to machine, the new material Ti-5553, a commercially pure beta alloy, is even more unyielding. Cutting speeds generally have to be reduced by half. Yet, properties that give the machinist cause to worry are welcomed by the structural engineer: the extremely high strength of the material makes it ideal for aircraft landing gear parts and load-bearing structural components. "The trend towards beta titanium materials was a crucial motivation for us to bring Sky?tec? indexable inserts onto the market," explains Gerd Kussmaul, product manager at Walter. "Conventional indexable inserts are usually unable to meet the high requirements for performance and tool life."
From lightweight to heavy-duty components: the machining of superalloys is also often hindered by the formation of forged skins, but also by the material's susceptibility to cold work hardening. In addition, the extremely high cutting forces intensify the problem of an overloaded cutting edge. With forged components, as typically used for engine parts in the aviation industry, the depth of cut varies. In such cases, it is difficult to select the appropHombre