According to aircraft manufacturers, the number of workpieces using titanium alloys has more than doubled. With the increasing demand for titanium alloy workpieces, Ti6Al4V alloys with high temperature resistance and emerging Ti5553 (Ti-5Al-5Mo3Cr) materials have become more and more important.
With the increasing use of titanium alloy materials, tools and their application technology have also received greater challenges. For example, the processing of aerospace workpieces is very characteristic: the workpiece wall is thin and the shape is complex; the deep cavity milling process has many processes. In addition, in the high-end motorcycle and medical device manufacturing industry, titanium alloy is also often used in the manufacture of small workpieces such as connectors.
The following three factors seriously affect the tool life of titanium alloy processing: very low heat conduction (Ti6Al4V=7.56W/mK; steel Ck45=51.9W/mK), relatively low elastic modulus (Ti6Al4V=110kN/mm2; steel Ck45 = 210kN / mm 2 ) and a clear trend in rubber properties. The cutting edge is mainly concentrated on the cutting edge and is not carried away by iron filings like machining steel. Due to the relatively shallow depth of cut, it is necessary to be able to carry extremely high thermal and mechanical loads in a small area of the population. This determines that coolant processing must be used. The lower modulus of elasticity of the material is very likely to cause vibration, and it also has a clear tendency to rubber properties, which tends to cause built-up edge of the cutting edge. Therefore, the cutting speed must be greatly reduced.
Processing problem: Ti5553
The emergence of the new material Ti5553 made processing worse. Ti6Al4V is a balanced alpha-beta micro-structured alloy (alpha = hexagonal microcrystalline structure, beta = central tetragonal microcrystalline structure), while Ti5553 is a structure close to beta but higher order. The structure not only makes the alloy more resistant to heat, but also makes the material more difficult to cut, and the Ti5553 has a resistance strength close to 900 N/mm2.
In this regard, Walter's rotary tool development manager Josef Giessler stressed: "Professional titanium machining requires an optimized tooling solution." When machining a diameter of 20~25mm/, a solid carbide tool is usually used. In order to reduce vibration and reduce the occurrence of built-up edge, the design of the tool is extremely important. The polished sign-off surface can bring excellent chip removal. The use of AlCrN coating and internal cooling can greatly improve the quality and efficiency of titanium alloy processing. .
This solution has been adopted by Walter Prototyp: the Duo Protostar Ti40/Ti45 solid carbide milling cutter has the above characteristics.
In a project by Airbus, the Ti40 tool increased the machining life of a Ti6Al4V material workpiece by a factor of two. The maximum cutting capacity is 80cm3/min (Vc=25m/min) and the diameter of the HSS-E tool is 32mm. A new generation of hard tools created a benchmark in the case of 25mm machining diameters, reaching 160~200cm3 minutes (Vc=50-60m/min). For the HSS overall milling cutter, its development has reached a relative stage high.
Walter's experts conducted further experiments on the processing of the Ti5553 with the aim of determining how the new generation of tools can handle more complex machining.
The material used for this time has a tensile strength of 1400 N/mm2 and a Brinell hardness of 430. The test tool is Prostar Ti40 with a diameter of 16 mm and z=4. The cutting data is significantly lower than that of Ti6Al4V.
Processing of Ti5553 materials requires a reduction in cutting speed of approximately 50% (medium processing conditions). The groove milling reduces more speed, while the side milling reduces the speed less. For large-scale machining, it is necessary to use a tool that can be converted into a blade for processing large workpieces or a metal removal rate. Large tools such as tools can be used. It has been very similar to the development of solid carbide tools in the past two years. The main direction is also how to process difficult-to-machine materials, that is, on the (ISO-S) material group containing titanium alloy materials. Walter's flagship product for difficult-to-machine materials is now Tiger.tec (PVD-Tiger) with PVD alumina coating. Two other materials (WSM35 with high wear resistance coating and WSP45 with strong wear) have also been introduced to the market.
Another project developed in parallel with PVD-Tiger was designed to accommodate the machining of aerospace workpieces, the G77 geometry, which is also suitable for titanium alloy processing applications. Its biggest feature is a 20 degree front angle and a special micro-groove. Siegfried Bohnet said: "We are now combining a variety of technologies, such as Tiger.tec? Tiger technology, PVD coating, high positive groove and special blade fillet." The technology will form a new Blade ADGT (for square shoulder milling cutters, corn milling cutters) or RO.X (round blade cutters). Now, this series of new products has become the backbone of aerospace or titanium alloy processing applications.
