Tool coupling between a toolholder and a machine spindle

Abstract: The invention relates to a tool coupling for machine tools. The coupling comprises a draw bar (20) which carries a shaft portion (12) of a tool holder (13) by means of a radially expandable locking element (24) that is releasably provided around the draw bar. The shaft portion (12) is carried by the provision of a radially extending integral shoulder (21) on the draw bar, said shoulder comprising a bevelled face (30) and a radially outer surface (31) which upon relative axial movement between the draw bar and the locking element forces the latter radially outwards into locking engagement with a complementarily designed annular recess (18) in the shaft portion (12) so as to provide firm clamping thereof.

Description: The present invention relates to a tool clamping device for machine tools, comprising a draw bar that is axially displaceable inside a machine spindle and a locking element arranged in cooperation with said draw bar, said device carrying a toolholder by exercising a relative movement between the draw bar and the locking element thus effecting a lateral displacement of said locking element into locking engagement with the shaft portion of said toolholder (see e.g. EP-A-0291 048). There is an increased demand for tool clamping devices that are reliable in tooling machines. Usually the tool is carried by a conical portion which is aimed to centralize the tool in the spindle and to absorb the radial and axial forces that are acting on the tool. There is also an increased demand for devices that enable tool changes to be made automatically in tooling machines. It is therefore a purpose of the present invention to provide a tool clamping device that enables transmission of much larger tensile forces than what is possible with other commercially available devices. It is another purpose of the invention to provide a tool clamping device which requires less space than those hitherto available. It is another purpose of the invention to provide such a clamping device that enables a short axial displacement of the clamping sleeve in connection with change of tools. It is yet another purpose of the invention to provide a clamping device that consists of a few details thus enabling simplified construction of the device. These purposes are met with a tool clamping device having the features of claim 1. The invention will now be described more in detail in connection with the preferred embodiment illustrated on the enclosed drawings. Fig. 1 shows a longitudinal section of a tool machine spindle and a clamping device arranged therein according to one embodiment of the invention, and more specifically, to the right of the centre line, the device is in its clamped position and to the left of the centre line, the device is in its released position. Fig. 2 shows an axial section of another embodiment of the clamping device of the invention wherein the clamping sleeve is axially slotted and composed of vulcanized rubber and metal segments. Fig. 3-5 shows sectional views of possible embodiments of locking elements forming part of the clamping device shown in Fig. 2. In the Figures there is shown a portion of a tool machine spindle 10. The spindle 10 is power operated in a conventional way and therefore the means that are used are not shown. A shaft portion 12 of a toolholder 13 which is symmetrical about the central axis 11 is received in a corresponding cylindrical bore 14 in the machine spindle 10. The shaft portion 12 is intended to carry a tool (not shown) at one end thereof. The shaft portion 12 is at its opposite end provided with a cylindrical hole 15 confined by a radial bottom surface 16 and an axially extending hole wall 17 in which an annular recess 18, semi-circular in cross-section, is provided. As shown in Fig. 3-4 the recess 18 could alternatively have a formation differing from semi-circular. As shown in Fig. 3 the annular recess can be smoothly rounded whilst extending axially. In Fig. 4-5 there is shown an embodiment where the annular recess 18 has a downward smoothly rounded portion which is elongated but confined axially upwards by an upper radial shoulder 19. A clamping device which carries the shaft portion 12 and the toolholder 13 is provided inside the machine spindle, said clamping device comprising a draw bar 20 the lower end of which is provided in form of a radially extended shoulder portion 21. Between a radially provided surface 22 on the spindle, intended for axial abutment, and the shoulder 21 on the draw bar 20 a sleeve 23 is provided concentrically around the bar 20, the lower portion of said sleeve 23 being in shape of an annular flange 24 with a circularly rounded profile. When the draw bar is subjected to forces in F₁-direction the annular flange 24 is forced radially outwards, due to the shoulder 21, and further into engagement with the recess 18 in the shaft portion 13. This is made possible due to the fact that the sleeve 23 is manufactured of spring steel in a thin section and by having provided a number of axially extending slots around its circumference, said slots extending upwardly from the flange 24 and up to a rear point 25 on the sleeve 23 where the rear portion 26 of said sleeve is somewhat broader in its section than the remainder portion of the sleeve. This rear portion 26 has an even thickness and is received with clearance fit in a corresponding recess 27 in the spindle whilst being in abutment against an O-ring 28 located against radial surface 22, said O-ring acting as a tolerance absorbing element. The force that is applied to the draw bar 20 is transferred to the shoulder portion 21 by means of the contact that is applied by the annular flange 24 of said sleeve 23 on to the shaft portion 12 in the point 29. There is consequently no transmission of the force F₁ to be applied on the draw bar 20. The shoulder portion 21 which forces the flange 24 radially outwards and into the annular recess 18 comprises a bevelled surface 30, inclined in relation to the central axis 11, and a radially outer surface 31 that preferably has a circularly rounded formation. The bevelled surface 30 is intended to act as a sliding surface and the outer surface 31 is intended to represent an abutment for the flange 24 of the sleeve 23. It is important that the outer surface 31 has a smoothly rounded profile which as closely as possible matches the profile of said annular flange 24. This ensures the establishment of largest possible contact surface which enables a desirable low surface pressure. It is equally as important that said outer surface 31, said annular flange 24 and the annular recess 18 are made of a hardened material which makes it easier to maintain desired dimensional limitations of the device. In Fig. 2 there is shown an alternative embodiment of the device in which the clamping sleeve 23 again comprises a lower end portion in the form of a circular extension 24 that is integral with the remainder of said sleeve whereas the upper portion thereof comprises a number of slots distributed around the periphery of the sleeve in which rubber or any other synthetic material is vulcanized. In addition thereto rubber portions 32 are firmly vulcanized on to the outer surface of said clamping sleeve along a portion of its length and also provided as rear end portions arranged in abutment with an abutment surface 33 provided radially. This enables the synthetic portion 32 to be expandable when the force F₁ is exerted to the draw bar 20 in order to have the shaft portion 12 firmly secured to the machine spindle 10. The synthetic material or the rubber will contract the sleeve when the draw bar is subjected to the force F₂. In order to have the draw bar 20 in Fig. 1-2 subjected to a good centering and guidance axially in the hole 15 the outer mantle surface of the shoulder portion 21 has been formed as a cylindrical guiding surface 34 aimed to be guided with clearance fit towards the axially extending hole wall 17 in the hole 15. When there is a need for change of tools the draw bar 20 is activated by a press force F₂ sufficiently large so as to press the bar 20 and its shoulder portion 21 to the position shown to the left of the centre line 11. The diameter of the flange 24 is selected such that the shaft portion 12 can be released axially from the draw bar 20 to enable desired exchange of tools. As appears from Fig. 1 and 2 the shoulder portion 21 of said draw bar 20 is brought to a position where its end surface comes to abutment with the bottom surface 16 of said hole 15 when the force F₂ acts upon the draw bar so that it is brought to its release position as shown to the left of the centre line 11 whereby the draw bar 20 acts as a pushing-out member. In Fig. 5 there is shown an alternative embodiment wherein the annular recess 18 has the same formation as in Fig. 4. Hence, the axial abutment for the locking member 24 is provided by a radial abutment 19 whereas the interior surface of the lower portion of the clamping sleeve 23 comes into surface contact with the abutment surface 31 on the shoulder 21, said surface 31 being located outwardly of bevelled surface 30 whilst inclined in relation to the centre line 11. The lower end portion of the locking member 24 is made in the form of a radial support surface 35 which is brought in contact with a radial surface 36 on the draw bar 20 which is oriented parallel with an upper support surface 37 intended for abutment against the radial abutment surface 19. Due to the provision of an axially slotted clamping sleeve as aforesaid wherein rubber segments are vulcanized between metal segments it is ensured that during clamping there is established an elastic outbending radially and that fatigue failure of the material due to outbending of the metal segments is limited to the rubber material in the vulcanized part. Vulcanization by means of rubber can serve the purpose of a collapse-promoting element, i.e. promotes contraction of the sleeve, and to serve as a tolerance absorbing unit. Due to the fact that no force transmission occurs when said locking sleeve 23 is subject to a relative movement in relation to the locking recess its requirements of tolerance and surface finish are very low and therefore it is not necessary to perform any grinding of tool. The tool clamping device has been described when used in a machine spindle with a rotary tool. It is to be understood however that the invention is also useful for the purpose of connecting a stationary turning tool with a correspondingly matching tool machine.

Claims: Tool clamping device for machine tools comprising a draw bar (20) that is axially displaceable inside a machine spindle (10) said draw bar being provided with a radially extending shoulder portion (21) at one end, and a locking element (24) arranged concentrically around said draw bar for the purpose of carrying a shaft portion (12) of a tool holder by exercising a relative movement between the draw bar and the locking element, thus effecting a lateral displacement of said locking element (24) into locking engagement with the shaft portion (12) of said tool holder, characterized in that the shoulder portion of said draw bar is provided as a radially forged shoulder (21) comprising two distinct surface portions (30, 31), and that the locking element consists of a radially expandable clamping sleeve (23) provided around said draw bar provided with an integral annular flange (24) which is received in a cylindrical hole (15) in the shaft portion jointly together with the shoulder portion (21) whereby the draw bar (20) is provided with an inclined bevelled face (30) so as to exert a radial force outwards on to said flange (24) so that the latter, upon axial clamping of said draw bar, is forced into final abutment with a radially outer surface (31) on said draw bar whilst simultaneously engaging with a correspondingly designed annular recess (18) provided in the shaft portion (12) for the clamping thereof, whereby said outer surface (31) has a profile which matches the profile of said flange (24). Tool clamping device as defined in claim 1, characterized in that the clamping sleeve (23) is radially expandable by being provided with axially extending slots distributed around its circumference, said slots extending along a major portion of the length of said sleeve. Tool clamping device as defined in claim 1 characterized in that the annular recess (18) is provided with circular cross-section, and that the annular flange (24) has a corresponding formation. Tool clamping device as defined in claim 1, characterized in that the annular flange (24) of the clamping sleeve and the shoulder portion (21) of said draw bar are received in a counterbore (15) of such depth that the end surface of the draw bar comes into abutment with the radial bottom surface (16) of said counterbore (15) when the draw bar is displaced into its release position. Tool clamping device as defined in claim 2, characterized in that the rear portion of said sleeve (23) has a number of axial slots around its circumference in which portions (32) of rubber or other synthetic material is vulcanized whereby said rubber portions (32) also extend axially beyond said sleeve so as to provide a rear end portion for abutment against a radially provided surface (22) in the spindle (10). Tool clamping device as defined in claim 1, characterized in that the rear portion (26) of said sleeve (23) has a wider cross-section than the remainder of the sleeve whilst being received with clearance fit in a corresponding recess (27) in the shoulder in axial abutment with an O-ring (28) of rubber. Tool clamping device as defined in any of the claims 1-6, characterized in that the integral shoulder (21) of the draw bar (20) is received in a cylindrical hole (15) of such diameter that the clamping sleeve (23) becomes radially expandable in the annular space between the hole wall (17) and the mantle surface of the draw bar. Tool clamping device as defined in any of the claims 1-7, characterized in that the outer mantle surface of the shoulder (21) is in the shape of a cylindrical guiding surface (34) provided to be slidable with clearance fit towards the hole wall (17). Tool clamping device as defined in any of the claims 1-8, characterized in that the flange (24) and the annular recess (18) are axially elongated whilst having a smoothly rounded mantle surface. Tool clamping device as defined in any of the claims 1-9, characterized in that the annular recess (18) is elongated and comprises an axially forward rounded portion and a rear end portion in the form of a radial shoulder (19) whereby the flange (24) has a complementary shape. Tool clamping device as defined in claim 10, characterized in that the abutment surface (31) that is located outwardly of the bevelled surface (30) is inclined whereby the interior surface of the lower portion of the annular flange (24) is provided at a correspondingly inclined angle. Tool clamping device as defined in claim 11, characterized in that the abutment surface (31) is inclined at an angle in relation to the centre line (11) that is smaller than the inclination angle of the radially inner bevelled face (30). Tool clamping device as defined in claim 9, characterized in that the lower and upper end portions of the annular flange (24) are in the shape of radially provided surfaces (35) and (37) respectively, the lower radial surface (35) being arranged for abutment against a radial surface (36) on the draw bar (20) whereby the radial surface (36) on said draw bar is located adjacent to and intersects with the axially extending guide surface (34) on said draw bar.

Inventors: TJERNSTROEM ERIC, TJERNSTROEM, ERIC, Tjernström, Eric
Applicants: SANDVIK AB, SANDVIK AKTIEBOLAG
Application year: 1990
Main classification: B23B31
IPC codes: B23B31