Thermal softening of Heat Resistant Super Alloys

Thermal softening of Heat Resistant Super Alloys

Softening heat resistant alloys with heat

Excellent performance when machining heat resistant alloys

We are currently developing Ceramic End Mills capable of cutting materials at super-high speeds that existing cemented carbide end mills cannot match. To perform at these super-high speeds when machining heat resistant alloys, the end mills need to have outstanding resistance to the heat generated during this process. When cemented carbide end mills are used to machine heat resistant alloys it is necessary to reduce the heat generated to maintain tool life. This means that cutting speed is limited to around 70 m/min. However, with ceramic end mills the cutting speed can be 500 m/min or higher. This causes materials to be softened with the heat generated by machining. Although it sounds contradictory, heat resistant alloys soften at around 1,000 degrees C because bearing and tensile strengths are lowered in this temperature zone. While cemented carbide end mills cannot work at such high temperature, ceramic end mills can. This new ceramic end mill delivers outstanding performance when machining materials even whilst generating extremely high heat that produces red-hot chips (see photo 1).

Photo 1: Machining with ceramic end mills. INCONEL® is a registered trademark of Huntington Alloys Canada, Ltd.

Excellent efficiency and tool life

Ceramic end mills machine heat resistant alloys in a completely different way than cemented carbide end mills. In fact, rather than "machining," it may be more accurate to describe the mechanism as "scarfing." The edge of the tool welds slightly but does not suffer significant damage because ceramics have outstanding resistance to the heat generated during machining. Therefore, compared with cemented carbide end mills, ceramic end mill tool life is significantly longer. Furthermore, cemented carbide end mills commonly break in the early stages of machining, but ceramic end mills can process up to 35 m (see Fig. 1). Cemented carbide end mills are not designed for such high-efficiency cutting at high speed, but ceramic end mills are, which gives them a distinct advantage (see Fig. 2). However, when using ceramic end mills the emphasis is placed on the challenging requirements of the machine tool. This is because of the speed required to generate the heat needed to soften materials without causing abrasion or other damage. Therefore, machine tool spindles must be capable of handling high revolutions and it is for this reason machining with ceramic end mills requires the best quality machine tools.

Hiroshi Watanabe Solid tool R&D Centre

Further utilisation of ceramic end mills

I was involved from the early stages of product development and soon realised it was a challenge to identify the ideal machining conditions. Unfortunately repeated breakage and abrasion damage prevented sufficient product evaluation. However, with commitment towards finding the best ways to exert the potential performance of ceramic end mills, continued testing meant that the answers were finally found.