Collet chuck

Abstract

A collet chuck (1), comprising: a mandrel (5) on which a frustoconical, tapered outer surface (55) is formed at a tip section and which is fixed in a central position; a first collet (6) which is positioned outside the mandrel (5) in which a cylindrical collet main body section is divided in the circumferential direction, and an intermediate claw (63) formed on each tip section of the collet main body section has a tapered inner surface (65) which is formed on an inner side in sliding contact with the tapered outer surface (55) of the mandrel (5); a second collet (7) positioned outside the first collet (6), in which a cylindrical collet main body section is divided circumferentially, a clamping claw (73) formed on each tip section of the collet main body section having an inner sliding contact surface (75) which is in sliding contact on an inner side with an outer sliding contact surface (67) formed on an outer side of the intermediate claw (63), and a clamping surface (77) formed on an outer side of the clamping claw (73) is brought into contact with a workpiece (W); and a collet holding element that absorbs a force in an axial direction and keeps the first collet (6) movable in the axial direction.

Description

Technical area

[0001] The present invention relates to a collet chuck that prevents the workpiece from being pulled in. State of the art

[0002] A machine tool for machining a workpiece uses a clamping device to grip the workpiece. A collet chuck is used as the clamping device for gripping an internal diameter hole in a workpiece. In this chuck, a mandrel is inserted into a collet that has radial slots extending from its center. The collet chuck expands and contracts the clamping jaws of the collet in a radial direction through the tapered surfaces of both the mandrel and the collet, which are in sliding contact with each other due to the relative movement of the mandrel and the collet in the axial direction. For example, the following patent reference 1 discloses a collet chuck of a type in which one side of the mandrel moves in an axial direction. The cylindrical collet has six radial slots and six circumferentially oriented, expandable and contractable clamping jaws.

[0003] The collet chuck has a tapered inner surface, and the tip section of a drawbar (referred to in this description as the mandrel) has a tapered outer surface that slides in contact with the tapered inner surface of the collet chuck. In a fixed collet chuck with a fixed collet side, the tapered outer surface retracts when the mandrel is pulled axially. At this point, the tapered inner surface of the collet is forced outward, and each collet jaw expands to be pressed against the inner diameter hole of the workpiece to clamp the workpiece. Meanwhile, the collet chuck includes a retracted collet for pulling the collet side, and as the workpiece is drawn in, the collets expand through the tapered surface of the mandrel to clamp the workpiece. Patent literature

[0004] Patent Literature 1: JP-2017 - 217 744 A Summary of the invention: Technical problem

[0005] With a retracted collet chuck, the collet retracts while the jaws are pressed against the workpiece. Therefore, when clamping a workpiece with a relatively thin wall thickness, the workpiece is pulled in together, resulting in further deformation. Since the mandrel moves instead of the collet, a fixed collet chuck can clamp the workpiece without pulling it. However, the fixed collet is shaped such that the outer taper of the mandrel increases in diameter towards the tip. Consequently, when the collet is pulled out of the collet chuck body, the outer taper of the mandrel remains stuck, and the design does not allow for easy component replacement. Furthermore, because the centrally positioned mandrel moves, the centering accuracy is inferior to that of a retracted collet chuck with a fixed mandrel.

[0006] Therefore, it is an object of the present invention to provide a collet chuck with double collets in order to solve this problem. Solution to the problem

[0007] A collet chuck according to one aspect of the present invention comprises a mandrel on which a frustoconical, tapered outer surface is formed at a tip section and which is fixed at a central position, a first collet positioned outside the mandrel in which a cylindrical collet body is divided circumferentially, and an intermediate claw formed on each tip section of the collet body section having a tapered inner surface which is in sliding contact on an inner side with the tapered outer surface of the mandrel, a second collet positioned outside the first collet in which a cylindrical collet body is divided circumferentially, a clamping claw formed on each tip section of the collet body section having an inner sliding contact surface,which is in sliding contact on an inner side with an outer sliding contact surface formed on an outer side of the intermediate claw, and a clamping surface formed on an outer side of the clamping claw is brought into contact with a workpiece, and a collet holding element that absorbs a force in an axial direction and keeps the first collet movable in the axial direction. Advantageous effect of the invention

[0008] If, according to the configuration above, the collet chuck retaining element absorbs a force in the axial direction and moves the first collet in the axial direction, since the tapered inner surface of the intermediate claw formed on the first collet slides on the tapered outer surface of the mandrel fixed at the central position, and the intermediate claw widens in the radial direction depending on the tapering angle, and in addition the inner sliding contact surface of the clamping claw is in sliding contact with the outer sliding contact surface of the intermediate claw, the clamping claw is pushed outwards and widens, it is possible to clamp a workpiece without moving the workpiece in the axial direction. Brief description of the drawings Fig. Figure 1 is a cross-sectional view showing one embodiment of a collet chuck. Fig. Figure 2 is a simplified cross-sectional view showing the state of a clamping mechanism when the clamping mechanism is relaxed. Fig. Figure 3 is a simplified cross-sectional view that represents the state of a clamping mechanism when the clamping mechanism is tensioned. Description of embodiments

[0009] An embodiment of a collet chuck according to the present invention is described below with reference to the drawings. A machine tool is equipped with a spindle device for gripping and rotating a workpiece, and various clamping devices are mounted on the spindle device according to a target workpiece and machining operations. One of the clamping devices is a collet chuck that grips the inner diameter hole of a workpiece from the inside. Fig. Figure 1 is a cross-sectional view showing a collet chuck of the present embodiment. The collet chuck 1 is mounted on the rotating spindle 80 and forms the spindle assembly of the machine tool. Accordingly, the center line O of the collet is superimposed on the axis of rotation of the spindle 80.

[0010] In the collet chuck 1, the base block 3 is stacked axially onto the end of the spindle 80 and fixed with screws, and the main body block 4 is further stacked axially onto the base block 3 and fixed with screws. In the collet chuck 1 of the present embodiment, a double collet chuck mechanism is mounted on the main body block 4. In the collet chuck 1, the cylindrical mandrel 5 is fixed in the central position, the axially movable first collet 6 is located outside the mandrel 5, and the fixed second collet 7 is also located outside the first collet 6.

[0011] The spindle 80 of the spindle device is rotatably mounted on a bearing and configured to rotate in response to the power output of a servo motor. The drawbar 81 is inserted axially into the center hole of the spindle 80 of the hollow shaft and connected to a piston rod of a coaxially arranged hydraulic cylinder. In the collet chuck 1, the actuating rod 11 is installed coaxially with the mandrel 5 in a central position and connected to the drawbar 81. Therefore, the collet chuck 1 is configured such that the actuating rod 11 is displaced axially by the actuation of the hydraulic cylinder. The left side of the collet chuck 1 in the drawing is the rear side, and the same direction is the retraction direction of the actuating rod 11 by the hydraulic cylinder.

[0012] The actuating rod 11 is inserted into the cylindrical retracting element 12, and the radially projecting flange section 111 is brought into contact from the front with the stepped section 121 formed on the inside of the retracting element 12. As the actuating rod 11 moves backward, the retracting element 12 is pulled backward over the flange section 111, which is engaged with the stepped section 121. Simultaneously, the retracting element 12 is biased forward by the spring 15 and is configured to be displaced forward as the actuating rod 11 moves forward.

[0013] The cylindrical retaining element 16 is positioned between the base block 3 and the spindle 80 such that the flange sections of the retaining element 16 are integrated in such a way that they engage with one another. The retaining element 16 holds the insertion element 12 and the drawbar 81 slidably and is fixed to the base block 3 by screws. Therefore, a collet chuck retaining element, which moves the insertion element 12 in the forward / backward direction via the actuating rod 11 connected to the drawbar 81, is configured in the hollow section formed in the spindle 80, the base block 3, and the main body block 4.

[0014] In the insertion element 12, the connecting section 123 is formed radially on the outside of the stepped subsection 121 and is connected axially to the first collet 6. Several connecting sections 123 are formed at equal intervals around the circumference, pass through through holes formed in the flange subsection 51 of the mandrel 5, and are fixed to the flange subsection 61 of the first collet 6 with screws. Meanwhile, the flange subsection 51 formed at the rear end of the mandrel 5 is fixed to the main body block 4 with screws.

[0015] In the first collet 6, several radial slots are formed in a cylindrical collet body, and the intermediate jaws 63 are formed on each tip section of the collet body, which is subdivided circumferentially by the slots. A frustoconical, tapered outer surface 55, the diameter of which decreases towards the front, is formed on the tip section of the mandrel 5, and the tapered surfaces of the intermediate jaws 63 of the first collet 6 are in contact with the tip section of the mandrel 5. On the inside of the intermediate jaw 63, a tapered inner surface 65 corresponding to the angle of the tapered outer surface 55 is formed, and the tapered inner surface 65 slides on the tapered outer surface 55 in a state in which it is in contact with the tapered outer surface 55, as shown.The inside of the intermediate claw 63 of the first collet 6 is a tapered surface which is inclined in the axial direction, but on the opposite outside an outer sliding contact surface 67 parallel to the center line O is formed.

[0016] The flange section 71 of the second collet 7, located outside the first collet 6, is fixed to the main body block 4 by screws. In the second collet 7, several slots are formed in a cylindrical section of the main body at equal intervals to those in the first collet 6, and the clamping claw 73 is formed on each end section of the main body, which is subdivided circumferentially by the slots. On the inside of the clamping claw 73, an inner sliding contact surface 75 is formed parallel to the center line O such that it is in contact with the outer sliding contact surface 67 of the intermediate claw 63, and on the outside, a clamping surface 77 is formed parallel to the center line O so that it is pressed against the inner diameter hole of the workpiece W. The receiving block 8 is fixed to the flange section 71 of the second collet 7 by screws.

[0017] Next are in the Fig. 2 and Fig. Three simplified cross-sectional views are shown, illustrating the clamping mechanism of the collet chuck 1. In particular, the Fig. 2 a state in which the clamping mechanism is relaxed, and the figure shows the state in which the clamping mechanism is clamped. The operation of the collet chuck 1 is described below with reference to the Fig. 1 described. The collet chuck 1 clamps and releases the workpiece W by actuating a hydraulic cylinder which actuates the drawbar 81. In the normal state, the drawbar 81 is in a forward-moved position and the collet is in the relaxed state, as described in the Fig. 2 shown.

[0018] The workpiece W is attached to such a collet chuck 1. The workpiece W is a thin-walled cylindrical component with flanges, and the cylindrical section of the workpiece is fitted into the clamping jaw 73 of the second collet 7, with the flanged sections resting against the mounting surface of the holding block 8. When the workpiece is clamped, the hydraulic cylinder is actuated, and the actuating rod 11, integrated with the draw rod 81, is pulled backward. The actuating rod 11 is configured to use the preload force of the spring 15 to pull the retracting element 12 by means of the flanged section 111, which is hooked onto the stepped section 121. Therefore, the first collet 6, which is connected to the retracting element 12, moves backward by a certain distance.

[0019] The first collet chuck 6 moves backwards, as indicated by the arrow in the Fig. 3 is shown, and the intermediate claw 63 widens according to the taper angle as the tapered inner surface 65 slides on the tapered outer surface 55 of the mandrel 5. Since the intermediate claw 63 is in contact with the clamping claw 73 of the second collet 7 on the outside as the intermediate claw 63 slides on the tapered outer surface 55 of the mandrel 5, the clamping claw 73 is displaced to be pushed outwards, as indicated by the white arrows. The workpiece W is clamped such that the cylindrical section of the workpiece is gripped from the inside by the widened clamping claws 73.

[0020] When the hydraulic cylinder is actuated in the reverse direction and the actuating rod 11 is pushed forward via the pull rod 81, the released retracting element 12 moves forward due to the preload force of the spring 15 and is positioned by impacting the flange section 111. To move the retracting element 12 forward, the intermediate claw 63 of the first collet 6 is disengaged from the Fig. 3 shown position in the Fig. 2 position shown is moved so that the clamping jaws 73, which are pressed outwards, are moved inwards and pulled together, and the workpiece W is released and clamped.

[0021] Since the clamping mechanism in the collet chuck 1 of the present embodiment comprises the double collets of the first collet 6 and the second collet 7, the second collet 7, which is in contact with the workpiece W, does not move in the axial direction, and it is possible to avoid pulling the workpiece W during clamping. Because the workpiece W is no longer pulled in, even a workpiece with a relatively thin wall thickness is not deformed by the clamping, and the problem of reduced machining accuracy by the machine tool can be solved.

[0022] Since, in the collet chuck 1 of the present embodiment, the intermediate jaws 63 and the clamping jaws 73 are displaced along the tapered outer surface 55 of the mandrel 5, which is fixed in the central position, the centering accuracy is high and precise clamping can be carried out, so that the intermediate jaws 63 and the clamping jaws 73 are coaxial with the centerline O of the workpiece W. Furthermore, since in the collet chuck 1 of the present embodiment the tip section of the mandrel 5, on which the tapered outer surface 55 is formed, has a frustoconical shape with a diameter that decreases towards the front, the first collet 6 and the second collet 7 can be easily removed.

[0023] Although one embodiment of the present invention has been described, the present invention is not limited to this embodiment and various modifications can be made without deviating from its core.

[0024] For example, it has been described that the collet chuck 1 of the embodiment has a design in which the first collet 6 is pulled in to clamp a workpiece, but it can also have a design in which the angles of the tapered outer surface 55 and the tapered inner surface 65 are changed to clamp a workpiece by extrusion. List of reference symbols

[0025] 1: Collet chuck, 3: Base block, 4: Main body block, 5: Mandrel, 6: First collet, 7: Second collet, 8: Mounting block, 11: Actuating rod, 12: Draw-in element, 15: Spring, 16: Retaining element, 51: Flange section, 55: Tapered outer surface, 61: Flange section, 63: Intermediate claw, 65: Tapered inner surface, 67: Outer sliding contact surface, 71: Flange section, 73: Clamping claw, 75: Inner sliding contact surface, 77: Clamping surface, 80: Spindle, 81: Drawbar, 111: Flange section, 121: Stepped section, 123: Connecting section, O: Center line, W: Workpiece

Claims

[1] A collet chuck (1) comprising: a mandrel (5) on which a frustoconical, tapered outer surface (55) is formed at a tip section and which is fixed in a central position; a first collet (6) which is positioned outside the mandrel (5) in which a cylindrical collet main body section is divided in the circumferential direction, and an intermediate claw (63) formed on each tip section of the collet main body section has a tapered inner surface (65) which is formed on an inner side in sliding contact with the tapered outer surface (55) of the mandrel (5); a second collet (7) positioned outside the first collet (6), in which a cylindrical collet main body section is divided circumferentially, a clamping claw (73) formed on each tip section of the collet main body section having an inner sliding contact surface (75) which is in sliding contact on an inner side with an outer sliding contact surface (67) formed on an outer side of the intermediate claw (63), and a clamping surface (77) formed on an outer side of the clamping claw (73) is brought into contact with a workpiece (W); and a collet holding element that absorbs a force in an axial direction and keeps the first collet (6) movable in the axial direction. [2] The collet chuck (1) according to claim 1, wherein the tapered outer surface (55) of the mandrel (5) and the tapered inner surface (65) of the first collet (6) are inclined surfaces such that the diameters of the surfaces decrease towards the front. [3] The collet chuck (1) according to claim 1 or 2, wherein the outer sliding contact surface (67) formed on the intermediate claw (63) of the first collet (6) and the inner sliding contact surface (75) formed on the collet (73) of the second collet (7) are surfaces that are parallel to a center line (O).

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