Teamwork for a perfect cutting edge

By Niraj M Wanikar, Chief Editor, CNCTimes.com, 2016-04-04 16:26:00

In the production grinding and sharpening of tools, undercuts, free-form surfaces, new materials, and tolerances of only a few thousandths of a millimeter place high demands on the used clamping devices. They significantly influence the tool geometry and the quality of the surface, as well as the reliability and cost effectiveness of the grinding process. This situation increases the demand for versatile precision clamping devices, which enable an unmanned grinding process even in the case of small batch sizes.
A technological highlight is the fully automatic SCHUNK PRISMO3 tool grinding toolholder, which was developed especially for fully automated grinding processes. With a high repeat accuracy of ≤ 0.005 mm and run-out accuracy of ≤ 0.01 mm at an unclamped length of 45 mm it steplessly clamps diameters from 3 bis 20 mm, without the use of intermediate sleeves or modifications to the toolholder. During the clamping process the tool shank is automatically centered in the toolholder.
Since the X-axis always remains unchanged, regardless of the tool diameter, which means all chuck jaws remain in the identical axial position, it is possible to machine a broad range of drilling, reaming, and milling tools also in small quantities without reprogramming the L1 dimension, in unmanned operation, and in any sequence whatsoever. The expense of additional programming and the danger of a crash due to unnoticed axis misalignment are therefore eliminated. Hard-coated chuck jaws ensure a long life and high process reliability in 24/7 operations.
An optimized contour assures that the grinding wheel can run out unimpeded, even in demanding operations. Nevertheless, if the jaw set is ever damaged, it can be replaced as a unit. The engineering design, the base sleeve, and the robust construction give the toolholder its exceptionally high rigidity. Its sturdy jaw guidances prevent the grinding discs from swinging up and almost completely eliminate axial eccentricity. In order to prevent dirt accumulation and to permanently maintain the high precision, the toolholder is flushed with clean oil during the grinding operation.
Compact dimensions of 125 mm x 125 mm leave ample space for the tools, grinding process, and loading. The mechanical high-end toolholder is especially suitable for use in sharpening applications, since it is compatible with virtually all interfaces - from axial clamping cylinders to radial front-end chucks. It is even possible to implement custom machine interfaces.
Resilient polyamide gripper fingers
In developing the toolholder, the engineers utilized the entire range of SCHUNK competence, from the clamping technology to the gripping systems. For the loading process, for example, the innovative family-owned company developed additively manufactured polyamide fingers, which ensure reliable and gentle holding with a simultaneous compensating effect during loading. At the moment when the tool is transferred to the toolholder the fingers prevent over-definition, which ensures exact centering. The resilient fingers were designed for universal use, so that the same pair of fingers can be used for handling of different tool diameters. The fingers are lightweight, extremely wear-resistant and exceptionally adaptable.
Hydraulic expansion technology is becoming the standard
There are good reasons why SCHUNK has established a long-standing reputation as a leading supplier of clamping devices for tool grinding applications. The company bundles decades of experience in hydraulic expansion toolholding technology and has developed an extensive range of specialized products for tool grinding. The precision toolholders are available in the TENDO SDF-WZS SK 50 version which is certified to DIN 69871 and also with numerous other interfaces. As opposed to collet-style holders the power-operated hydraulic expansion toolholders have no openings or gaps that are susceptible to dirt accumulation.
They are insensitive to grinding particles and therefore require exceptionally little maintenance. The enormous diversity of the product spectrum ensures process stability in use of the toolholders on all relevant grinding machines. They are often recommended and even required by the machine manufacturers. Compared to conventional toolholders the hydraulically clamped SCHUNK TENDO WZS tool grinding toolholders are optimized for the special requirements of tool grinding and they also enable ten times more clamping cycles than conventional tool mountings.
The biggest advantage: the tool shank is clamped with no moving parts. Instead it is held evenly and fully by means of pressure build-up in an expansion chamber that extends around the entire shank. The pressure is controlled to ensure precise holding without excessive stress on the hydraulic expansion system. The expansion takes place only in the flexible area of the inner chamber. Changing the tool takes only seconds with an Allen key. One only has to turn the clamping screw to dead stop; over-tightening of the clamping sleeve is not possible.
To enable grinding processes with maximum efficiency, SCHUNK offers the tool grinding toolholders both in a manual version and as power-operated toolholders for automated machine loading. This is achieved by manually inserting the tools in high-precision SCHUNK intermediate sleeves or in special tool extensions with a gripper collar, then placing them in a storage rack, from which the machine automatically changes them into the hydraulic expansion toolholder on the machine spindle. This is where the high repeat accuracy and low susceptibility to dirt accumulation are especially advantageous. In addition, it is possible to use the same toolholder for diverse clamping diameters.
Unhindered access for the grinding wheel
Due to a 25° bevel on the nose, SCHUNK tool grinding toolholders have a much slimmer interfering contour than other hydraulic toolholders. Its run-out and change repeat accuracy < 0.003 mm assure a consistent removal of material during the grinding process and increase process safety with the grinding of serial tools. In addition, the hydraulic system damps vibrations and thereby assures an outstanding surface quality.
The excellent retention of shape and dimensional accuracy on the cutting edge increase the service life of tools by up to 75%. With the grinding toolholders, shank tools with a diameter of up to 32 mm can be clamped with a depth of up to 95 mm. SCHUNK also produces customized grinding toolholders with hydraulic expansion technology, for example for clamping of grinding wheels or cylindrical milling cutters. Intermediate sleeves expand the clamping options and ensure high versatility, in addition to automated loading. The simple handling, the sealed clamping screw and the long service life make SCHUNK hydraulic expansion toolholders affordable aids for grinding work.
Hydraulic expansion toolholders can be combined with 100 mm SCHUNK tool extensions of the SCHUNK TRIBOS series. Its slim interfering contour assures that the grinding wheel can run out unimpeded, even in the case of long cutting edges. With minimal interfering contours the hydraulic expansion toolholder aligns the extension optimally with the tool blank, while simultaneously damping the vibrations from the grinding process. This increases the precision on the sharp cutting edge, and achieves very exact tool geometries. For standard tool lengths, excellent run-out and repeat accuracies between 0.003 and 0.006 mm can be achieved on the sharp cutting edge.
SCHUNK’s patented polygonal clamping technology, the use of which is established especially in high-precision machining applications, ensures very precise tool clamping. SCHUNK TRIBOS extensions are suitable for all clamping diameters form 0.5 mm to 20 mm. To change tools a defined force is applied to the extension by means of a hydraulic clamping device. The clamping process can be repeated several thousand times with no fatigue or loss of the excellent run-out and repeat accuracy.

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