EP0012799B1 - Lapping device for annular workpieces - Google Patents

Description

The invention relates to a device for lapping the outer peripheral surface of ring-shaped workpieces, according to the preamble of claim 1 (GB-A-1 125 079).

During lapping, the workpiece slides with its surface to be lapped on the corresponding counter surface of the lapping tool, the loosely applied lapping agent between the two parts causing the grinding effect. The abrasive grains contained in the lapping agent slide and roll between the two surfaces and thus have a rubbing and pressing effect on both. A part of the body is embedded and held in the tool and also in the workpiece and then has a sharp and cutting effect on the counterpart. The auxiliary substances contained in the lapping agent, such as fat, oil or other liquids, support this effect. The amount of material removed by this process is the desired grinding, while the amount of material removed on the tool is the undesired tool wear.

Closed hollow bodies (bushes) are used as tools for circular lapping. For the reasons mentioned above, these are exposed to a relatively large amount of wear. Furthermore, lapping clips or rings are used for circular lapping, which are moved back and forth on the rotating workpiece (lapping, basics and practical application by Walter Lätzig, Carl Hanser - Verlag, Munich, 1950, pp. 85, 87 and 98-99, Fig. 83, 84, 85, 98).

Lapping clips essentially consist of a clip jaw with a bore which corresponds to the workpiece diameter and at least one slot pointing in the radial direction. By screwing the lapping clip can be adjusted as required during lapping. The lapping ring consists of a rigid slotted ring, the axial length of which is approximately V4 smaller than the workpiece length, a holder that surrounds the slotted ring and adjusting screws that are arranged on the outer circumference of the holder. If it would be necessary to line up several clips or rings axially, great difficulties would arise in the readjustment, since each clip or ring would have to be readjusted individually. It would therefore depend entirely on the sensitivity of the person who is adjusting the clips or rings. Since the workpieces are often packaged with axial play in order to achieve a slightly spherical contour when lapping the outer circumferential surface, it would be pure coincidence to find a workpiece that jams when adjusting the clips or rings and to correspondingly clamp the associated clip or ring to solve.

GB-A 1125079 also discloses a lapping tool for machining bores, in particular cylinder liners. This tool, which is made of gray cast iron, has a continuous slot running in the axial direction. The cut, one-piece hollow body is then expanded and then subjected to a heat treatment. After the tool is compressed again, it is inserted into the hole and then lies under full radial tension on the surface to be machined. This device for lapping leaves something to be desired in terms of its production costs and its readjustability.

According to the problems described above when lapping circular workpieces, in particular piston rings, combined into a package, the invention is based on the object of constructively improving the device in question in such a way that a targeted delivery option of the device is achieved essentially over the entire service life for wear compensation, the hollow body used as a lapping sleeve being easier to manufacture and adjust.

To solve this problem, the characterizing features of claim 1 are proposed. The axially stacked, self-tightening parts can be easily removed from the reject of the current production. For this purpose, piston ring blanks or other ring blanks can be used, for example, which are already ground to the axial height, but are no longer suitable for further processing due to irregularities (edge breakouts, inclusions in the structure, etc.). These rings are packaged and - if not already done - then slit in the axial direction. The slotted rings are spread out over a mandrel and clamped axially between two supporting bodies in the form of tensioning washers. If necessary, the ring package is then machined on the inner circumference in order to strive for a defined inner diameter. The exact diameter is achieved by inserting a caliber mandrel into the ring package, which is now axially relaxed again, in that the self-tightening rings rest on the outer circumferential surface of the caliber mandrel. In this state, the rings are firmly clamped axially again, and a bushing with the precisely aimed inside diameter is created. In order to facilitate the introduction of the ring package to be machined and the caliber mandrel, at least one of the clamping disks can preferably be provided with a centering cone.

According to the invention, there are several options for arranging the slotted rings axially one above the other. Starting from a conventional ring stack with axially superimposed butt joints, there is also the possibility of placing the rings axially on top of one another in such a way that the butt joints are offset from one another in the circumferential direction. Another constructive possibility Accordingly, the rings can be arranged axially in such a way that they are entangled at their abutting points, that is to say that the abutting end of the one ring adjoins the abutting end of the following ring. For this purpose, a spring washer is required, which is profiled on its end face facing the rings so that the first ring can be clamped with an overlapping joint.

If there are signs of wear on this sleeve made of individual rings, a new adjustment is made by inserting the caliber mandrel and axially releasing the ring pack. Due to their radial self-tensioning, the rings attach themselves to the outer circumferential surface of the caliber mandrel and are then axially clamped again between the spring washers. In contrast to the closed lapping sleeve, the use of self-tightening individual rings automatically compensates for the wear occurring differently in both the axial and circumferential directions along the inner surface of the sleeve. The ring package can be readjusted as often as the self-tensioning of the rings provides. It is advantageous to see that the use of reject rings makes it possible to manufacture an adjustable lapping sleeve at a significantly lower price than if a closed, non-adjustable sleeve were already purchased.

In principle, it is of course also possible to apply the invention to the lapping of the inner peripheral surfaces of workpieces, in particular of packaged piston rings. In this case, slotted external clamping rings could be used, which are inserted in a packaged, axially clamped manner into a calibrated measuring sleeve, rest axially relaxed on their inner circumferential surface and then clamped axially again in order to then have the exact outside diameter.

• In der Zeichnung ist eine Läppvorrichtung 1 dargestellt, die sich aus den folgenden Teilen zusammensetzt: den beiden Spannhalbschalen 2, 3, den Spannringen 4, 5, den Zentrierringen 6, 7 und dem Ring 8 zur Sicherung gegen Verdrehung, der mittels eines Zentrierstiftes 9, welcher in den Zentrierring 6 eingreift, seine Aufgabe erfüllt. Der Hohlkörper (Läppbüchse) ist anhand von 3 Varianten 10, 11 und 12 dargestellt, die jeweils aus einer Vielzahl geschlitzter Teile, z.B. Kolbenringe hergestellt wird. Variante 10 zeigt, dass die Kolbenringe 13 derart axial übereinander angeordnet sind, dass die Stossstellen 14 einen axial durchgehenden Schlitz 15 bilden. In Variante 11 sind die Stossstellen 16 der Kolbenringe 17 in Umfangsrichtung gegeneinander versetzt. Nach der Variante 12 werden Kolbenringe 21 mit einander überlappender Stossstelle 18 bzw. 19 verwendet, wobei letzteres am Stossende 20 des nächsten Kolbenringes 21 anliegt. Der erste Kolbenring stützt sich dabei auf einer axialen Anschlagfläche 23 des Spannringes 5 ab. Um so eine durchgehende Büchse zu erhalten, ist der Spannring mit einer in Umfangsrichtung ansteigenden Spannfläche 25 ausgebildet. Die Läppbüchse, die aus einer der drei dargestellten Varianten gebildet sein kann, wird durch die Spannringe 4, 5 axial festgespannt. Nachdem die Büchse aufgrund von Verschleisserscheinungen ihrer Aufgabe nicht mehr gerecht werden kann, wird der Kaliberdorn 24 eingebracht. Um dies zu erleichtern, weist der Spannring 4 einen Zentrierkonus 22 auf. Ist der Dorn eingebracht, wird der Spannring 4 gelöst, und die Kolbenringe legen sich aufgrund ihrer radialen Selbstspannung an der Umfangsfläche des Kaliberdornes 24 an.

The invention is illustrated in the drawing using an exemplary embodiment and is described in more detail below:

• In the drawing, a lapping device 1 is shown, which is composed of the following parts: the two clamping half-shells 2, 3, the clamping rings 4, 5, the centering rings 6, 7 and the ring 8 for securing against rotation, which by means of a centering pin 9, which engages in the centering ring 6, does its job. The hollow body (lapping sleeve) is shown using 3 variants 10, 11 and 12, each of which is made from a large number of slotted parts, for example piston rings. Variant 10 shows that the piston rings 13 are arranged axially one above the other in such a way that the abutment points 14 form an axially continuous slot 15. In variant 11, the joints 16 of the piston rings 17 are offset from one another in the circumferential direction. According to variant 12, piston rings 21 with an overlapping joint 18 or 19 are used, the latter abutting the joint end 20 of the next piston ring 21. The first piston ring is supported on an axial stop surface 23 of the clamping ring 5. In order to obtain a continuous bush in this way, the clamping ring is designed with a clamping surface 25 that rises in the circumferential direction. The lapping sleeve, which can be formed from one of the three variants shown, is axially clamped by the clamping rings 4, 5. After the bush can no longer fulfill its task due to signs of wear, the caliber mandrel 24 is inserted. In order to facilitate this, the clamping ring 4 has a centering cone 22. If the mandrel is inserted, the clamping ring 4 is released and the piston rings rest on the circumferential surface of the caliber mandrel 24 due to their radial self-tension.

After the alignment and axial tensioning of the piston rings forming the lapping tool, the caliber mandrel is then moved out and the workpiece, for example in the form of a piston ring package 26 to be lapped on the outside, can then be axially inserted into the tool.

Claims (4)

1. A device for lapping the outer peripheral surface of annular workpieces (26), in particular the running surface of piston rings assembled together in stacks, consisting of a hollow piece (13, 17, 21), slotted axially and self- tensioning, used as a lapping sleeve, whereby the hollow piece (13, 17, 21) consists of several parts and can be clamped axially between a tool holder in the form of two clamping discs (4, 5) and is readjust- able radially inwards through its inherent tension after release to compensate for wear.

2. A device in accordance with Claim 1, whereby at least one of the clamping discs (4, 5) has a centering taper (22).

3. A device in accordance with Claims 1 and 2, whereby the slotted parts (17) are located axially upon each other such that their gap positions (16) are offset to each other in the peripheral direction.

4. A device in accordance with Claims 1 and 2, whereby the parts (21) are so arranged axially that they are staggered in the region of their gap positions (18, 20) and that at least one of the clamping discs (5) on their front surface is turned towards the slotted parts (21) such that it provides a firm hold to the gap position (23) of the first hollow piece (21).

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