High speed machining

from Wikipedia, the free encyclopedia

The term high-speed machining ( HST ; English High Speed Cutting , HSC) referred to in the metal processing , a cutting procedure in which the cutting parameters ( cutting speed and feed rate ) can be applied several times higher than conventional, to the removal rate to optimize maximum.

history

As early as 1925, Carl J. Salomon was concerned with high cutting speeds and registered a patent in which he showed that after the parabolic increase in the cutting temperature with increasing cutting speed, the temperature falls again when the apex is reached, despite the increase in speed. Accordingly, it would be possible, for example, to cut steel at a cutting speed of 42,000 m / min or more with ordinary tools made of high-speed steel without damaging the cutting edges. However, Salomon has never proven this experimentally. It was not until the 1950s that Salomon's theory was essentially confirmed in the former Soviet Union and at Lockheed in the USA. At Lockheed, for example, steel was machined at a cutting speed between 40,000 and 50,000 m / min in the translational cutting direction using HSS tools.

The most important results of investigations with ultra-high cutting speeds of up to 60,000 m / min can be summarized in four points: The HSS tools withstood the high loads unscathed, tool wear was very low, the surface qualities achieved were good and the metal removal rates exceeded conventional processes by Factor 240.

The speeds used in the tests are still far from possible with today's high-speed machining in the industrial environment, but the results form the basis for machining at high speeds. The speeds achieved today are around 5000 m / min with aluminum, around 2000 m / min with steel or around 8000 m / min with plastic.

The HSC was first used in the aviation industry . An extreme amount of machining is required to manufacture lightweight components that are typical for aviation, such as frames . The machining costs of some components reach over 90% of the total component costs. With regard to this problem, a significant cost reduction was only possible in the form-giving production. As an alternative to metal-cutting shaping, reshaping or primary shaping has not been able to establish itself because of the often only small quantities or production-related problems .

application areas

The areas of application of HSC technology are primarily where high demands are made on cutting performance and surface quality, i.e. especially in tool and mold making . Another typical application in mold making with complex three-dimensional contours are e.g. B. Blow molds for plastic bottles. The design, the defined filling quantity and the requirements of the blow molding systems require the highest levels of precision and surface quality.

Advantages and disadvantages

advantages

The special thing about HSC is a metal removal rate that is up to 30% higher, feed rates 5 to 10 times higher and cutting forces up to 30 times lower. This enables thin-walled workpieces to be machined . The surface quality increases, which can result in savings in otherwise subsequent grinding operations. A distortion caused by heating during the machining process is also prevented because the cutting speed is greater than the heat conduction speed and therefore the heat remains in the chip .

Hardened materials up to a hardness of 69 HRC can be machined, which in most cases eliminates hardening after milling and thus the risk of hardening distortion.

There are great savings potentials compared to conventional production in both pre-roughing (due to high cutting performance) and finishing (due to high surface quality ).

disadvantage

With high speed cutting, the extreme speeds result in a considerably increased need for shielding the work area, as even the smallest fragments or chips can develop enormous flight speeds, which under certain circumstances exceed those of projectiles from firearms . Furthermore, there is a higher wear of the tool and thus a reduction in service life , which is put into perspective by the increased metal removal rate. There are also high demands on the balancing of the tools, since otherwise extreme forces arise which, on the one hand, can lead to tool breakage and, on the other hand, would put a heavy load on the spindle bearings. Due to the extreme speeds and loads on the work spindle, expensive and time-consuming maintenance and regular replacement of the work spindle may also be necessary because of the relatively high wear.

Tools

Milling cutters that are suitable for HSC are usually made of fine and finest-grained solid carbide , mostly coated with a hard material and have a special cutting edge geometry . In addition, found as cutting materials and polycrystalline cubic boron nitride (CBN) and polycrystalline diamond (PCD) application.

In mold making , any contours are produced by machining the contours with round indexable inserts (form R) with small distances between the milling paths.

In order to enable precise machining at high rotational speeds, the tools are directly driven by motor spindles .

See also

swell

  1. Patent application DE523594 : Method for processing metals or materials with similar behavior when processing using cutting tools. Registered on February 27, 1925 , published on April 27, 1931 , applicant: Krupp AG, inventor: Carl J. Salomon.
  2. Werner Degner, Hans-Dieter Lutz, Erhard Smejkal: Spanende Formung , Carl Hanser Verlag, 2002, ISBN 3446221387 , pages 139-140.