HSK Force Gage

CAT/DIN/BT Force Gage

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Reprint from the journal 10 - 2002

 Hard turning and grinding of HSK tool holders.

Author: Rudolf Beyer E-Mail: beyer@konradin.de

The vertical pickup lathe V300 from Index is a recent acquisition of the grinding department of Bilz Werkzeugfabrik in Ostfildern, Germany. Upgraded to a turn-grind center with counter spindle, this lathe allows to hard-turn a wide range of HSK63 toolholding fixtures with high precision and to finish grind them size-controlled on the outside and inside with high process safety.

Finding a lathe in the grinding department is not something that you would normally expect. But Johann Zauner, the foreman in charge of the grinding department at the tool manufacturer Bilz in Ostfildern, which forms part of the LMT group, is convinced, following the successful commissioning of the V300, that this vertical machining center is at the right place in his grinding department. The reason is that this single turn-grind center at Bilz combines four individual machining steps, for which different production machines used to be necessary in order to achieve the hard machining of toolholding fixtures with HSK63 interface: centering, external grinding, hard turning and bore grinding. The advantages of the solution now found are obvious: minimum space requirement, shorter throughput and non-productive times and, most importantly: higher and consistent production quality through constant temperature conditions and the elimination of chucking operations.

Hard turning of the HSK side

The machining sequence at the Bilz toolholding fixtures is as follows: Soft machining takes place on an Index G300 lathe. After hardening, the pre-machined blanks are placed on pallets of the V300 infeed belt, picked up there by the main spindle, clamped and then transferred to the working area. After that, a Renishaw touch probe in the lower turret first measures the shoulder position. This is followed by finish hard turning of the inner contour and of the taper face at Vc = 150 m/min and f= 0.1 mm/rev.

External grinding

The next step is rough grinding of taper and shoulder in a single operation by means of plunge grinding. Then the grinding wheel is dressed path-controlled, using a diamond dressing plate mounted on the main spindle. This is followed by finish

grinding. The flat shoulder is finish ground by pendulum grinding, while the taper is finish ground by an oscillating movement  with path control. This is done by using a special 2-layer fused corundum grinding wheel. Grinding master Johann Zauner appreciates being able to apply to the V300, not only his knowledge of the right grinding wheel, but also his additional grinding know-how, which he acquired during his 30 years of working at Bilz. This knowledge comes in handy because the grinding cycles stored in the Siemens 840D Control of the V300 are basically the same as those normally used in the programming of cylindrical surface grinding. What impresses him most are the grinding results obtained, which right from the start are just as good as the ones from previous productions. Johann Zauner: „The V300 has a very rigid basic structure.

Using the same feed rates as in the standard cylindrical surface grinding machine, allows us to reach Rz precisions of 2, a roundness of <1µm and a form tolerance of <1µm. There are absolutely no chatter marks.“

In-process gauging

After the external cylindrical surface grinding, the spindle carrier transports the part to the left to a gauging station arranged outside the working area, in which the HSK taper is gauged. If the measures are correct, the workpiece is then transferred to the counter spindle. If any deviation is detected, the taper is automatically reground.

Transfer to the counter spindle

Prior to being transferred to the counter spindle, the part is thoroughly cleaned with coolant nozzles directed at the target. The workpiece is clamped into the counter spindle in the HSK toolholding chuck - exactly as it will be later in the machining center. When empty, the HSK toolholding fixture is covered with a rotating lifting cylinder to protect it from soiling.

Hard turning of the rear side

First the gripper grooves and the front nominal diameter are hard turned. The tools necessary for this are attached to the periphery of the main spindle and are adjustable. The different tools are rotated into their working position by means of the C-axis. Next, the toolholding bore is hard turned, with a grinding allowance of 0.05 mm, using an adjustable boring bar attached to the spindle support. This is followed by finish turning of the bore of tolerance H7. The finishing is done by the machine with such process safety that this tolerance is safely maintained, no regauging being necessary.

Transfer to the counter spindle

Prior to being transferred to the counter spindle, the part is thoroughly cleaned with coolant nozzles directed at the target. The workpiece is clamped into the counter spindle in the HSK toolholding chuck - exactly as it will be later in the machining center. When empty, the HSK toolholding fixture is covered with a rotating lifting cylinder to protect it from soiling.

Hard turning of the rear side

First the gripper grooves and the front nominal diameter are hard turned. The tools necessary for this are attached to the periphery of the main spindle and are adjustable. The different tools are rotated into their working position by means of the C-axis. Next, the toolholding bore is hard turned, with a grinding allowance of 0.05 mm, using an adjustable boring bar attached to the spindle support. This is followed by finish turning of the bore of tolerance H7. The finishing is done by the machine with such process safety that this tolerance is safely maintained, no regauging being necessary.

External grinding

Internal grinding

The rear part of the bore, which forms the shrink fit of the tool, is a different story. This part must be ground due to the narrow tolerances. To this end, the internal grinding spindle necessary for the next operation has been attached to the spindle support.
Its internal grinding pin is first dressed by means of a diamond attached to the counter spindle and then used to finish grind the pre-turned toolholding bore. The bore dimension is checked by means of a pneumatic plug gauge attached to the upper support of the main spindle. The turn-grind center installed at Bilz is, by the way, a prototype machine, which was presented by Index for the first time at the EMO 2001 for the combined processes in hard machining. That's why the employees at Bilz appreciate the support they have received from the Index specialists, for whom this new center is a pilot project. For 2 1/2 months, the machine has been running under production conditions, yielding an estimated reduction in costs per part of 10 to 15 %. Since the production process always takes place under identical temperature conditions, which is not the case for single machines, the form and position tolerances of the workpieces are better at the first go than they used to be. Despite that, Manfred Zauner has already found new potential for improvement. Since the coolant warms by 4 to 5° over the course of the day, which results in the loss of the calibration measure of the gauging systems, his idea is that in the future the coolant should be cooled. He also plans to increase the clamping power of the collet chuck, so as to be able to transfer even more power. In addition, in the future, the external grinding spindle will be mounted at an angle of 30° instead of 15°, in order to optimize shoulder grinding. The grinding experts at Bilz would like to replace the 40,000 rpm internal grinding spindle with one of higher speed because the cutting speed for small bores is not sufficient in terms of the number of revolutions.

Internal grinding spindle Grinding master Johann Zauner: "At first, we grinders were skeptical but then pleasantly surprised, especially by the ease of operation via the control."

User
Bilz, a company of the Leitz Metalworking Technology Group, together with its subsidiaries in England, Italy, France, India, Brazil and the US, is the leading manufacturer of clamping tools for the areas of thread-cutting and highperformance tools. The company has set new standards over the last few years by developing a thermogrip shrink-fit clamping system.
Bilz Werkzeugfabrik GmbH & Co. KG, Germany
Tel. +49 (711) 34801-67, Fax +49 (711) 34801-88

INDEX-Werke GmbH & Co. KG Hahn & Tessky 73730 Esslingen, Germany Tel. +49 (711) 3191- 0 www.index-werke.de 
INDEX Corporation Noblesville, IN 46060, USA Tel. +1 (317) 770- 6300 www.index-usa.com

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