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Shine with speed - High feed hard turning

October 2017
Author: SUMITOMO ELECTRIC Hartmetall GmbH
Company: SUMITOMO ELECTRIC Hartmetall GmbH
Shine with speed - High feed hard turning

In order to produce good surfaces during hard turning, generally low feed rates are used, which usually means a relatively long machining time per workpiece. However, because of increasing productivity is required, Sumitomo has now developed the HFT system for high feed turning, which can reduce machining times by a factor of 6 to 10. At cutting speeds of up to 150 m/min and a cutting depth of 0.15 mm ap, as an example of a workpiece made of case-hardened steel with a hardness of about 60 HRC, the values appear to be more common for hard turning. The difference is then made by the comparatively high feed rate f of 1.2 mm per revolution. This gives productivity a big boost. With a downstream finishing pass with reduced feed rate, almost glossy surfaces are obtained.

The new high-feed turning requires very rigid machine and tool conditions. This means that a very stiff and vibration-damping machine is required, which also has sufficiently high torques. The very stiff monoblock tool holders from Sumitomo are also matched to this, so that this stiffness is maintained up to the cutting edge. The ingenious plate seats of the tools transfer the cutting forces, which are higher by a factor of 2 to 3, optimally and without vibrations into the machine. The cutting edges themselves consist of an octagonal insert with a full CBN coating on the entire plate surface. The plate is therefore unusually robust and can be used both in dry machining and under emulsion, which makes its application range very universal. Here too, stiffness and optimum chip flow are just as important as the optimum use of CBN cutting material. For this reason, a tool insert with eight cutting edges was chosen, which reduces the number of required inserts and thus the tooling costs for the customer. The cutting edge geometry offers a so-called wiper geometry, which is provided with a drag edge that smoothes the surface of the workpiece after the actual cut. This guarantees long tool life, high cutting speeds and glossy surfaces.


The high feed turning process is feasible on simple standard machines and can therefore be used by many customers without any major investment. Up to now, very good results have been achieved not only in high-alloyed and hardened steels, but also in materials that are difficult to machine, such as titanium alloys or Inconel.

The process works not only for external machining, but also for internal machining of medium and large diameters. A typical example is the inner bore of a planetary gear wheel, where the surface quality and desired oil grooves are important. The interrupted cut due to the oil drilling process can be mastered well with Sumitomo CBN plates. Compared to normal hard turning, productivity has been increased sixfold.

Another practical example is a hinge pin with a large bore and a flat surface. This results in a severely interrupted cut, which has caused high cutting consumption during the previous hard machining. Up to now, only 3 - 5 workpieces could be processed per cutting edge. The inserts used had only two cutting edges, which meant high tooling costs and frequent tool changes. With the new tools and the high feed-rate turning process, 35 - 40 workpieces can now be produced per cutting edge. The machining process is 10 times faster, which dramatically increases productivity by 92%. With the eight cutting edges, an incredible number of 320 workpieces can now be produced with only one insert. The economic viability of the process is beyond question.

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