WO2023110091A1

WO2023110091A1 - Hydraulic clamping device, system and method

Info

Publication number: WO2023110091A1
Application number: PCT/EP2021/085986
Authority: WO
Inventors: Niclas Rosberg; Conny Johansson
Original assignee: ETP Transmission AB
Current assignee: ETP Transmission AB
Priority date: 2021-12-15
Filing date: 2021-12-15
Publication date: 2023-06-22
Anticipated expiration: 2024-06-15

Abstract

A hydraulic clamping device (14) configured to releasably secure a tool shaft (16) comprises an outer sleeve (141) having an outwardly conical surface (142), which tapers in a direction from a first end of the outer sleeve (141) towards a second end of the outer sleeve (141), an inner sleeve (143, 148) having an inwardly facing surface (144), an annular pressure chamber (145) extending axially along a substantial portion of the inwardly facing surface (144), the pressure chamber (145) containing a pressurization medium, and a piston (146), which is axially exposed at the first end of the outer sleeve (141) and which is configured to pressurize the pressure chamber (145). Further disclosed is a system (1) comprising a hydraulic clamping device (14) and a method for providing a hydraulic chuck.

Description

HYDRAULIC CLAMPING DEVICE, SYSTEM AND METHOD

Technical field

The present document relates to a hydraulic clamping device, to a system comprising such a hydraulic clamping device and to a method of providing a hydraulic chuck.

The concepts disclosed in the document find particular use in chucks for holding rotating tools, such as drill tools or milling tools or for holding a rotating workpiece. The concepts are also applicable to static applications, i.e. where a workpiece is rotating and the tool is held static, or is only translated.

Background

Collet chucks, or mechanical chucks, are used in machines to provide a mechanical connection between a collet and a tool shank. This type of chucks may be defined in standards to provide a possibility of changing tools and the ability to correspond to different machines.

A collet is a part of a chuck that forms a collar around an object to be held and exerts a strong clamping force on the object when it is tightened, usually by means of a tapered outer collar. The collet usually comprises a sleeve of spring steel with two or more longitudinal slits extending from a first axial end of the sleeve almost to a second axial end of the sleeve, so as to divide the sleeve into two or more jaws, which can move radially inwardly when engaged by the tapered outer collar.

As a non-limiting example, the ISO 15488:2003 standard defines collets with 8° setting angle for tool shanks and defines the dimensions of the collets, corresponding holders and nuts.

While there are many advantages with collet chucks, it would be desirable to have a collet that provides an even more accurate grip of the workpiece. The jaws’ ability of moving independently in connection with each other can create a risk for each independent piece having a malfunction or gripping the workpiece differently due to how the workpiece is introduced into the collet. The outcome of this could lead to the workpiece not being fully centred.

Hydraulic chucks are used in high precision tools such as drills, reamers, mills and grinding tools. This technique presents a greater precision due to the integrated pressuring mechanism in the collet.

However, a downside of hydraulic chucks is that each hydraulic chuck is designed for only one tool diameter, or a very limited range of tool shaft diameters.

Hence, there is a need for increasing the precision of existing chucks, and preferably without increasing the cost of the chuck too much. There is also a need for facilitating chuck replacement, e.g. for shifting between different tool shaft diameters.

Summary

It is an object of the present disclosure to provide a hydraulic chuck, which can be manufactured at reduced cost. Particular objects comprise improving the precision, tool mounting repeatability and vibration damping properties of a chuck.

The invention is defined by the appended independent claims, with embodiments being set forth in the dependent claims, in the following description and in the appended drawings.

According to a first aspect, there is provided a hydraulic clamping device configured to releasably secure a tool shaft, the clamping device comprising an outer sleeve having an outwardly conical surface, which tapers in a direction from a first end of the outer sleeve towards a second end of the outer sleeve, an inner sleeve having an inwardly facing surface, an annular pressure chamber extending axially along a substantial portion of the inwardly facing surface, the pressure chamber containing a pressurization medium, and a piston, which is axially exposed at the first end of the outer sleeve and which is configured to pressurize the pressure chamber. The outwardly conical surface may be formed in accordance with a standard such as ISO 15488:2003, or in accordance with a company standard. Typical taper angles of such standards may be 4 or 8 degrees.

The inwardly facing surface effectively provides a nominal diameter for a tool shaft or workpiece that is to be held by the clamping device.

The piston may be movable along an axial direction, between a clamping position, wherein the pressure chamber may be in a pressurized state, and a release position, wherein the pressure chamber may be in an unpressurized state.

The pressurized state is a state when there is a higher pressure in the pressure chamber than the pressure in the pressure chamber at the unpressurized state.

The piston may be essentially annular.

Furthermore, the piston may be axially movable in a piston space which is in fluid communication with the annular pressure chamber.

The piston space a may be formed between the inner sleeve and the outer sleeve. In particular, the piston space a may be axially open at the first end of the outer sleeve.

The piston space may present a piston movement limiting arrangement, for limiting a movement of the piston in an axial direction.

The movement limiting arrangement may be formed as a step or the like, against which the piston may strike, such that the piston’s axial movement inwardly into the device may be limited.

At least one of the sleeves may present a piston stroke reference surface, for limiting a movement of the piston in an axial direction.

The annular pressure chamber may have an axial length, which is sufficient for securing a tool shaft or work piece in the clamping device.

The axial length may be about 1 .5-3.5 times a tool space diameter, preferably about 2-3 times said tool space diameter.

A taper angle of the outwardly conical surface can be about 2° to about 10°, preferably about 2° to about 8°. The taper angle is the angle that is created at the intersection by the conical surface and the axial direction of the device.

The inner sleeve and the outer sleeve can be made in one piece of material.

The annular pressure chamber may be formed radially between the inner sleeve and the outer sleeve.

The outwardly conical surface and the inwardly facing surface may overlap axially. Alternatively, the annular pressure chamber may be formed at least partially axially outside of the outer sleeve. Hence, a pen type chuck may be provided.

The clamping device may comprise an intermediate sleeve, with the pressure chamber being situated radially between the intermediate sleeve and the inner sleeve.

Furthermore, at least one of the inner sleeve and the intermediate sleeve may extend axially beyond the first end of the outer sleeve.

According to a second aspect, there is provided a system comprising a chuck body having, at a first axial end thereof, an axially open receptacle for receiving a collet, a device as claimed in any one of the preceding claims, wherein the device is receivable in the receptacle, and a cap member, such as a chuck nut, which is engageable with the chuck body, such that axial displacement of the cap member causes movement of the piston.

The receptacle may have an inwardly conical surface, wherein the inwardly conical surface tapers in a direction from the first axial end towards a second end of the chuck body.

The system may further comprise a machine connection, such as a machine taper, a spindle or a flange at the second end of the chuck body.

The system may further comprise a piston abutment surface, which may be arranged on the cap member or on a separate part which may be engageable with the cap member such that displacement of the cap member causes displacement also of the piston abutment surface.

According to a third aspect, there is provided a method of providing a hydraulic chuck, comprising providing a chuck body having, at a first axial end thereof an axially open receptacle for receiving a collet, providing a hydraulic clamping device, arranging the device such that it is received with the second end inwardly in the receptacle, providing a cap member, movably connecting the cap member to the first end of the chuck body, and displacing the cap member such that the cap member engages the piston and causes the piston to move axially inwardly towards the second end.

The method may further comprise removing a mechanical collet from the receptacle prior to said arranging the device such that it is received with the second end inwardly in the receptacle.

The method may further comprise inserting a tool into the inner sleeve when the piston is in a release position prior to said displacing the cap member.

The machine tool can be a drill, a grinder, a mill or a lathe.

Brief Description of the Drawings

Fig. 1 is a schematic view of the system according to the present concept.

Fig. 2 is a schematic exploded view of the hydraulic chuck according to the present concept.

Fig. 3 is a schematic view of the hydraulic clamping device when in an unpressurized state.

Fig. 4 is a schematic view of the hydraulic chuck when in a pressurized state.

Fig. 5 is a schematic view of the a pen chuck in a pressurised state.

Detailed Description

Fig. 1 schematically illustrates a system 1 including a hydraulic clamping device 14. The system 1 comprises a chuck body 13 having, at a first axial end, an axially open receptacle having an inwardly conical surface 131 , for receiving the clamping device 14.

At a second axial end of the chuck body 13, a machine taper 12 is connected. The machine taper 12 forms a male taper, which tapers away from the chuck body 13 and is sized and adapted for being able to be received in a female machine taper arranged in the machine 11 .

A chuck nut 15 is engageable at the first axial end of the chuck body 13 for holding the clamping device 14 in place and for activating the clamping device 14. The chuck nut 15 can be engaged to the chuck body 13 by means of a threaded connection.

The clamping device 14 can receive, and secure by means of the chuck nut 15, a machine tool 16 in the clamping device 14. The machine tool 16 may be a drill tool or milling tool. However, it is also possible to use the present invention for holding a workpiece that is to rotate, such as would be the case in a lathe.

Fig. 2 schematically illustrates an exploded perspective view of the chuck body 13, the clamping device 14 and the chuck nut 15. The chuck body 13 comprises the clamping device 14, which is receivable with its second end inwardly in the axially open receptacle of the chuck body 13.

A piston 146, and optionally a seal 147, are arranged at the first end of the clamping device 14.

A chuck washer 17 may be provided, having a piston abutment surface 171 that is arranged to abut or engage the piston 146. The chuck nut 15 can be connected or connectable to the chuck washer 17. In some embodiments, the chuck nut and the chuck washer 17 can be integrated with each other, such as being formed in one piece of material or being permanently attached to each other.

Fig. 3 schematically illustrates the clamping device 14 comprising an outer sleeve 141 having an outwardly conical surface 142, that is sized and adapted for being received by the receptacle of the chuck body 13.

An inner sleeve 143 is provided having an inwardly facing surface 144, defining the tool space with the nominal diameter B for holding the machine tool 16.

An annular pressure chamber 145 is formed radially between the inner sleeve 143 and the outer sleeve 141 and extends axially along a substantial portion of the inwardly facing surface 144. The pressure chamber 145 contains a pressurization medium.

The inner and outer sleeves may conventionally be formed from separate sleeves which are connected, such as welded or soldered, at axial end portions thereof. Alternatively, the inner and outer sleeves may be formed in one piece by additive manufacturing, followed by grinding and/or polishing for those surfaces for which dimensions and/or surface quality are critical.

A wall thickness of the outer sleeve 141 may be thicker in a radial direction than a wall thickness of the inner sleeve 148. Hence, the pressure chamber may be positioned closer to the inwardly facing surface 144 than to the outwardly conical surface 142.

The piston 146 is axially movably arranged in a piston space 1463, which may be formed as an annular space or as one or more cylindrical spaces that is/are in fluid connection with the pressure chamber 145. The piston space may provide an axial stroke A.

The piston 146 is axially exposed at the first end of the outer sleeve 141 and is configured to pressurize the pressure chamber 145 by moving in its piston space 1463. In fig. 3, the piston is in a release position, i.e. the piston is at its axially outermost position.

For limiting the movement of the piston 146, the clamping device 14 may have a piston movement limiting arrangement 1461 in the piston space 1463 and/or a piston stroke reference surface 1462 formed on at least one of the sleeves 141 , 143, 148. As illustrated, the piston movement limiting arrangement 1461 may be formed as a step by both the outer sleeve 141 and the inner sleeve 143, against which the piston 146 and/or the seal 147 will strike, to limit their movement.

The seal 147 may be situated adjacent to the piston 146 in the piston space 1463, between the piston 146 and the piston movement limiting arrangement 1461. As illustrated, the seal 147 may be formed as a separate part. However, the seal 147 can be integrated with the piston 146.

The piston movement limiting arrangement 1461 may comprise a step, against which the piston 146 may strike when it reaches its limit position. Fig. 4 is a longitudinal sectional view of the chuck in a pressurized state, i.e. with the piston 146 in its axially innermost position.

The chuck comprises the chuck body 13, receiving the clamping device 14 such that the inwardly conical surface 131 of the chuck body 13 is arranged with the outwardly conical surface 142 of the clamping device 14.

The chuck nut 15 is threadingly connected with the chuck body 13, such that it can assume a continuum of axial positions along the axial direction of the chuck. Hence, the axial position of the piston 146 can be continuously adjusted between its end positions, as illustrated by figs 3 and 4, by turning the chuck nut 15, while an abutment surface of the chuck nut 15 or of the washer 17 presses against the piston 146.

The clamping thread 151 has threads on both the chuck nut 15 and the chuck body 13 to enable the axial movement of the chuck nut 15 over the chuck body 13.

The chuck washer 17 may be exposed to the chuck nut 15 and can be tightened or untightened in different axial positions when the chuck nut 15 is moved.

On operation of the chuck nut 15, the chuck washer 17 thus causes the annular piston 146 to be axially displaced, while bearing on the annular seal 147 to build up or to release a pressure difference in the pressure chamber 145.

In the closed position showed in figure 4, the chuck washer 17 has struck against the outer sleeve 141 of the clamping device 14, thus limiting the movement of the piston 146 and preventing overpressure in the chamber 145.

Fig. 5 is a longitudinal sectional view of a pen chuck, i.e. a chuck in which the portion which holds the tool extends axially beyond the portion of the chuck that is being held by the chuck body 13.

Hence, as described with reference to figs 2-4, the clamping device 14 is fixed into the chuck body 13 and has a chuck nut 15, a chuck washer 17 (which is optional), an integrated chuck washer and piston 146 and a seal 147 (which is optional and/or may be integrated with the piston) that are operable to provide a pressure difference in the pressure chamber 145. The piston 146 is thus movable in a piston chamber corresponding to that of figs 2-4 and in fluid connection with the pressure chamber 145.

In any of the embodiments, an additional o-ring 1471 may be provided for additional sealing between the seal 147 and the connection to the pressure chamber 145.

As illustrated in fig. 5, an integrated chuck washer and piston 146 may be caused to strike against the piston stroke reference surface 1462.

However, an intermediate sleeve 149 is provided, radially inwardly of the outer sleeve 141 and the pressure chamber 145 is formed between the intermediate sleeve 149 and the inner sleeve 148.

The intermediate sleeve 149 and the inner sleeve 148 extend axially beyond the first end of the outer sleeve 141 . Hence, at least part, possibly all, of the pressure chamber 145 is formed axially beyond the first end of the outer sleeve 141 .

The inner, intermediate and outer sleeves 141 , 148, 149 may conventionally be formed from separate sleeves which are connected, such as welded or soldered, at axial end portions thereof. Alternatively, at least two of the inner, intermediate and outer sleeves 141 , 148, 149 may be formed in one piece by additive manufacturing, followed by grinding and/or polishing for those surfaces for which dimensions and/or surface quality are critical.

Hence, while as illustrated in figs 2-4, the opening to the tool space essentially coincides with the first end of the outer sleeve 141 , as illustrated in fig. 5, the opening to the tool space is shifted axially outwardly, beyond the first end of the outer sleeve. However, the mounting and operation of the clamping device 14 remains the same.

In some embodiments, the chuck nut may be provided as a cap member having a central hole for the tool. The cap member may be axially displaceable relative to the chuck body under the influence of one or more axially extending bolts. Hence, the chuck nut does not need to have an internal thread that engages an external thread on the chuck body, but instead, e.g., one, two or three axially extending bolts may connect the cap member to the chuck body, whereby the cap member engages the piston so as to cause it to move axially as the bolts are tightened or released.

Threaded portions of the bolt or bolts may engage axially open threaded holes in the chuck body, while bolt heads engage the cap member. The cap member may comprise a skirt portion, which may extend axially so as to partially overlap the chuck body.

Claims

1 . A hydraulic clamping device (14) configured to releasably secure a tool shaft (16), the clamping device (14) comprising: an outer sleeve (141) having an outwardly conical surface (142), which tapers in a direction from a first end of the outer sleeve (141 ) towards a second end of the outer sleeve (141 ), an inner sleeve (143, 148) having an inwardly facing surface (144), an annular pressure chamber (145) extending axially along a substantial portion of the inwardly facing surface (144), the pressure chamber (145) containing a pressurization medium, and a piston (146), which is axially exposed at the first end of the outer sleeve (141) and which is configured to pressurize the pressure chamber (145).

2. The device (14) as claimed in any one of the preceding claims, wherein the piston (146) is movable along an axial direction, between: a clamping position, wherein the pressure chamber (145) is in a pressurized state, and a release position, wherein the pressure chamber (145) is in an unpressurized state.

3. The device (14) as claimed in any one of the preceding claims, wherein the piston (146) is essentially annular.

4. The device (14) as claimed in any one of the preceding claims, wherein the piston (146) is axially movable in a piston space (1463) which is in fluid communication with the annular pressure chamber (145).

5. The device (14) as claimed in claim 8, wherein the piston space (1463) presents a piston movement limiting arrangement (1461), for limiting a movement of the piston in an axial direction.

6. The device (14) as claimed in any one of the preceding claims, wherein at least one of the sleeves presents a piston stroke reference surface (1462), for limiting a movement of the piston (146) in an axial direction.

7. The device (14) as claimed in any one of the preceding claims, wherein the annular pressure chamber (145) has an axial length, which is sufficient for securing a tool shaft (16) in the clamping device (14).

8. The device (14) as claimed in claim 7, wherein the axial length is 1 .5-3.5 times a tool space diameter (B), preferably 2-3 times said tool space diameter (B).

9. The device (14) as claimed in any one of the preceding claims, wherein a taper angle of the outwardly conical surface (142) is about 2° to about 10°, preferably about 2° to about 8°.

10. The device (14) as claimed in any one of the preceding claims, wherein the inner sleeve (143, 148) and the outer sleeve (141 ) are made in one piece of material.

11. The device (14) as claimed in any one of the preceding claims, wherein the annular pressure chamber (145) is formed radially between the inner sleeve (143) and the outer sleeve (141 ).

12. The device (14) as claimed in any one of the preceding claims, wherein the outwardly conical surface (142) and the inwardly facing surface (144) overlap axially.

13. The device as claimed in any one of claims 1 -10, wherein the annular pressure chamber is formed at least partially axially outside of the outer sleeve (141 ).

14. The device (14) as claimed in claim 13, further comprising an intermediate sleeve (149), wherein the pressure chamber (145) is situated between the intermediate sleeve (149) and the inner sleeve (148).

15. The device (14) as claimed in claim 12 or 13, wherein at least one of the inner sleeve (148) and the intermediate sleeve (149) extends axially beyond the first end of the outer sleeve (141 ).

16. A system (1) comprising: a chuck body (13) having, at a first axial end thereof an axially open receptacle for receiving a collet, a device (14) as claimed in any one of the preceding claims, wherein the device is receivable in the receptacle, and a cap member, such as a chuck nut (15), which is engageable with the chuck body (13), such that axial displacement of the chuck nut (15) causes movement of the piston (146).

17. The system (1 ) as claimed in claim 16, wherein the receptacle has an inwardly conical surface (131 ), wherein the inwardly conical surface (131 ) tapers in a direction from the first axial end towards a second end of the chuck body (13).

18. The system (1 ) as claimed in claim 16 or 17, further comprising a machine connection at the second end of the chuck body (13).

19. The system as claimed in any one of claims 16-18, further comprising a piston abutment surface (171 ), which is arranged on the cap member or on a separate part (17) which is engageable with the cap member such that displacement of the cap member causes displacement also of the piston abutment surface.

20. A method of providing a hydraulic chuck, comprising: providing a chuck body (13) having, at a first axial end thereof an axially open receptacle for receiving a collet, providing a hydraulic clamping device (14) as claimed in any one of claims 1-15, arranging the device (14) such that it is received with the second end inwardly in the receptacle, providing a cap member, such as a chuck nut (15), movably connecting the cap member to the first end of the chuck body (13), and displacing the cap member such that the cap member engages the piston (146) and causes the piston to move axially inwardly towards the second end.

21. The method as claimed in claim 20, further comprising removing a mechanical collet from the receptacle prior to said arranging the device (14) such that it is received with the second end inwardly in the receptacle.

22. The method as claimed in claim 20 or 21 , further comprising: inserting a tool (16) into the inner sleeve (143, 148) when the piston (146) is in a release position prior to said displacing the cap member.