Of difficult-to-machine materials curves

By Niraj M Wanikar, Chief Editor, CNCTimes.com, 2016-07-26 13:15:00

Engines in aircrafts, exhaust gas turbines in automobiles or knee joints in medical technology: In numerous applications, materials are used which are difficult to process using conventional milling methods. In this case, trochoidal milling is the ideal solution. Users can significantly reduce processing times, while ensuring high quality and process reliability. A machining workshop held by LMT Tools and Coscom has shown which tools are suitable for trochoidal processing and what requirements must be met by the machines.

Trochoidal milling is experiencing a comeback. The foundations for this milling method with the circular feed motion were laid already decades ago. But it is only through the combination of high-performance tools and machines with the appropriate CAM software that users can benefit from the complete performance potential of this procedure. This applies especially to materials which are particularly challenging for conventional slot and edge milling tools. Stainless steels, for example, tend to be adhesive and very tough. Nickel-base alloys additionally show a high machining energy and resilience. In the case of hardened tool steels, the extremely high mechanical strength leads to fast wear and tear of conventional cutters. Titanium, on the other hand, only has a low thermal conductivity, which means that during processing the thermal load must be as low as possible. All of these materials are widely used, for example in the automotive industry, in the aerospace industry, for structural and small-series components in mold and die making or in medical technology.

Prerequisites for trochoidal milling
With difficult-to-machine materials, users can optimally benefit from trochoidal milling. In a joint machining workshop held in early 2016 in Schwarzenbek, LMT Tools and the CAD/CAM specialist Coscom showed how this can be done. Clemens Mohr, Head of Training Center LMT Tools, summarized the technical requirements: “First of all, customers require a CAM programming system with a software module for trochoidal milling. The machine tool used should have fast controls and high traveling speeds. Generally, the machine should be equipped with an internal coolant or air supply at the machine spindle. The geometry of the workpieces must be suitable for processing, i.e. it must show high edges and slots. Everything else is a question of the right tool.”

Tools for special challenges
In a live demonstration, Clemens Mohr presented the suitable tool solutions. The DHC (Different Helix Cutter) end mills by LMT Fette were at the center of attention. These solid carbide end mills are suited e.g. for trochoidal processing of tempering steels and stainless steels. Due to the different angles of twist, users can achieve high cutting depths and high feed performances at optimum running smoothness. The DHC HARDLINE end mill is the first choice when it comes to trochoidal milling of particularly hard materials. Its resistant cutting material allows processing of high-strength materials up to 1600 N/mm² or hardened tool steels of 45 to 60 HRC. In the case of superalloys on the basis of nickel or titanium, the DHC INOX end mill has proven to be efficient. Its cutting material and nanocrystalline PVD coating ensure maximum performance and low wear and tear, even at extreme cutting values.

Practical example: trochoidal milling of cold work steel
An internal experiment carried out by LMT Tools and Coscom has demonstrated the possibilities of trochoidal milling. For this purpose, a workpiece made of high-strength cold work steel of 60 HRC was processed using an end mill of the DHC HARDLINE series (material 1.2379/X155CrVMo12-1). The experts first tried to mill the slots in the workpiece conventionally at a cutting speed of vc = 80 m/min and a cutting depth of ap = 4 mm. However, the cold work steel could not be successfully processed in this way because the cutting edge was destroyed by the excessive heat after only a short time. As an alternative, the employees programmed the trochoid milling movement in their CAM system. This proved to be highly successful: The DHC HARDLINE reached a cutting speed of up to vc = 180 m/min at a cutting depth of ap = 16 mm.

“Examples such as this internal experiment show that trochoid milling opens up new paths for processing difficult materials,” said Mohr. “For this purpose, we closely cooperate with CAM partners such as Coscom. This way, we are able to offer our customers a complete solution for their milling strategy – including suitable tools and a perfectly tailored programming system.”

http://www.lmt-tools.com/in-kurven-durch-schwer-zerspanbare-werkstoffe/?bpid=453&hltags=403&cHash=c63ebed34ded883b0c397e9c2c723971

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