Spanzange

Abstract

Guide bushing for guiding a bar to be machined in a lathe, with - a collet chuck (10) axially displaceably mounted in a collet chuck holder, which has a plurality of radially movable jaws (20a, 20b) which, with their clamping surfaces (30a, 30b), form a common receptacle for guiding the bar to be machined in the lathe, wherein a blind hole (50) is provided in at least one jaw (20a, 20b) from the outer surface (40a, 40b) of the jaw (20a, 20b) opposite the clamping surface (30a, 30b) in the direction of the clamping surface (30a, 30b), with a blind hole bottom bounded on one side by the clamping surface (30a, 30b) and on the other side by the blind hole (50), which, through wear of the clamping surface (30a, 30b), is configured to form a through hole indicating the wear of the collet chuck (10), and - a device communicating with the blind hole bottom of the collet (10), which is designed to supply the blind hole (50) with compressed air, to detect the air pressure in the blind hole (50) and, in the event of the formation of the through hole created by wear of the blind hole bottom, to detect the drop in air pressure and to issue an alarm signaling the wear of the collet (10).

Description

[0001] The invention relates to a collet chuck with a plurality of radially movable jaws, which, with their clamping surfaces, form a common receptacle for guiding a bar to be machined in a lathe.

[0002] Collets are known, for example, from DE 101 38 330 A1.

[0003] Guide bushings and collets are used to hold, guide, and support the material bar being machined on Swiss-type lathes during the machining process. This allows for the production of very long and slender workpieces with tight machining tolerances. Variations in the diameter of the material bar can be compensated for with such guide bushings, and bars of different diameters can be machined using the same guide bushing.

[0004] On Swiss-type lathes, the workpiece is machined by pushing the material bar through the guide bushing with a feed movement of the headstock in the Z-direction, while the infeed movement of the machining tool, in its basic function, occurs exclusively in the X-direction. The collet is opened and closed pneumatically, with the opening, closing, and feed movements typically defined in the machine's part production program.

[0005] During material processing, the collet is closed and exerts a clamping force on the material bar, particularly during the feed movement, as required for the respective processing step.

[0006] The feed motion of the workpiece in the closed position of the collet generates a frictional force on the internal guide surfaces of the collet, which are referred to below as clamping surfaces. This force results, on the one hand, from the clamping force required to guide and hold the workpiece during machining, and on the other hand, is further increased by the cutting pressure of the machining tools. This frictional force leads to frictional wear of the clamping surfaces and thus to a decrease in the precision of holding and guiding the workpiece, resulting in a loss of machining precision.

[0007] This process is gradual, resulting in a decrease in the dimensional accuracy of the workpieces until the tolerance is exceeded. This is usually detected through random checks during production, and the collet is then replaced.

[0008] However, this approach has the disadvantage that quality losses are detected too late, workpieces are manufactured close to the tolerance limit, or even scrap is produced, resulting in unplanned downtime.

[0009] The object of the invention is therefore to find a solution for the timely detection of wear of the collet chuck during operation.

[0010] This problem is solved according to the invention by the guide bushing with the features of claim 1.

[0011] The basic idea of ​​the invention is to equip a collet chuck, which is known per se, with a wear indicator. In particular, the solution according to the invention utilizes the fact that wear causes material to be worn away, especially on the inside of the collet chuck segments, i.e., in the receptacle for the material rod.

[0012] Specifically proposed are one or more, particularly radially oriented, bores at the front end of the collet jaws, each designed as a blind hole extending from the outside inwards to near the inner wall of the jaws. The remaining dimension between the deepest point of the blind hole and the inner contour of the jaws is dimensioned to correspond to the maximum permissible wear. If material is worn away from the inside of the jaws, a perforation forms at the end of the blind hole, transforming it into a through hole. This inward perforation indicates the wear limit, allowing the affected collet to be removed from the production process before defective parts are manufactured.

[0013] According to the invention, the described blind holes are remotely monitored. For this purpose, it is preferably proposed to align the blind holes in the jaws with channels in the collet chuck in a rotationally secure manner. If compressed air is directed into the blind holes via the channels, a wear-related breakthrough leads to a pressure drop and, according to the invention, triggers a signal.

[0014] According to the invention, a guide bushing for guiding a bar to be machined in a lathe is provided, comprising a collet axially displaceable in a collet chuck, the collet having a plurality of radially movable jaws which, with their clamping surfaces, form a common receptacle for guiding the bar to be machined in the lathe, wherein a blind hole is provided in at least one jaw, guided from the outer surface of the jaw opposite the clamping surface towards the clamping surface, with a blind hole bottom bounded on one side by the clamping surface and on the other side by the blind hole, which, through wear of the clamping surface, is configured to form the through hole indicating wear of the collet, and a device communicating with the blind hole bottom of the collet is proposed, which is used to supply the blind hole with compressed air,is designed to detect the air pressure in the blind hole and, when a through hole is formed by wear of the blind hole bottom, to detect the air pressure drop in order to issue an alarm signaling the wear of the collet.

[0015] The thickness of the blind hole base therefore corresponds to the predetermined maximum permissible wear of the clamping surfaces of the jaws, which is captured by creating a through hole from the blind hole through abrasion.

[0016] The blind hole is preferably arranged radially, so that a blind hole bottom with a precisely defined thickness can easily be manufactured.

[0017] The invention will be explained in more detail below with reference to a particularly preferred embodiment illustrated in the accompanying drawings. The drawings show: Fig. 1 a longitudinal section through a particularly preferably designed collet according to the invention; and Fig. 2 a further longitudinal section through the particularly preferred collet chuck in a detail view.

[0018] Fig. Figure 1 shows a particularly preferred embodiment of a collet chuck according to the invention in a longitudinal section. In the example shown, the collet chuck 10 has three radially movable jaws 20a, 20b, of which two jaws 20a, 20b are visible in the sectional view. As is known, the three jaws 20a, 20b, with their clamping surfaces 30a, 30b, form a common receptacle for guiding a bar to be machined in a lathe. Furthermore, the receptacles 60 for fastening spring elements arranged between the jaws 20a, 20b are visible in one jaw 20b.

[0019] According to the invention, at least one jaw 20a, 20b is provided with a blind hole 50 extending radially from the outer surface 40a, 40b of the jaw 20a, 20b opposite the clamping surface 30a, 30b in the direction of the clamping surface 30a, 30b, wherein the bottom of the blind hole is bounded on one side by the clamping surface 30a, 30b and on the other side by the blind hole 50. The thickness of the bottom of the blind hole corresponds to the predetermined maximum permissible wear-related material loss, which results in the formation of a through-hole indicating the wear of the collet 10.

[0020] Fig.Figure 2 shows a further longitudinal section through the particularly preferred collet in a detailed view, from which it can be seen that the blind hole bottom has a small thickness, corresponding to the maximum permissible wear for the use of the collet 10. If the blind hole bottom is completely worn away by wear of the clamping surfaces 30a, 30b, this wear can be detected by identifying a through hole instead of a blind hole, and the collet 10 can be replaced.

Claims

[1] Guide bush for guiding a bar to be machined in a lathe, with - a collet chuck (10) mounted axially displaceably in a collet chuck holder, said collet chuck having a plurality of jaws (20a, 20b) which are radially movable relative to one another and which, with their clamping surfaces (30a, 30b), form a common holder for guiding the bar to be machined in the lathe, wherein a blind hole (50) is provided in at least one jaw (20a, 20b) which extends from the outer surface (40a, 40b) opposite the clamping surface (30a, 30b) of the jaw (20a, 20b) in the direction of the clamping surface (30a, 30b) and has a blind hole base delimited on the one hand by the clamping surface (30a, 30b) and on the other hand by the blind hole (50), said blind hole base being designed to cause the formation of a through hole indicating wear of the collet chuck (10) as a result of wear of the clamping surface (30a, 30b), and - a device communicating with the blind hole base of the collet (10), which is designed to pressurise the blind hole (50) with compressed air, to detect the air pressure in the blind hole (50) and, when the through hole is formed due to wear of the blind hole base, to output an alarm signalling the wear of the collet (10).

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