Cutting tool holder

Abstract: A tool holder (1) comprises a house and a clamping mechanism (15, 23, 31, 32) provided therein, said clamping mechanism including a male member (15) adapted to engage in a female-like opening (12) in a tool (2). The male member (15) is movable to and fro between clamping and releasing positions by means of a piston device (14) that separates inner and outer hydraulic medium chambers (19, 20). A passage (36) extends through the piston device (14), said passage (36) emerging in said two chambers, a valve (37) being provided in said passage (36), in order to open the passage when the hydraulic pressure in the outer chamber (19) rises to a set limit value so as to maximize the force that clamps the tool.

Description: Technical Field of the Invention This invention relates to a holder adapted for detachable mounting of cutting tools, said holder comprising a house having a first end to which a tool is adapted to be detachably mounted and a clamping mechanism provided in said house, said clamping mechanism including a male member adapted to engage in a female-like opening in the tool, said male member being movable to and fro between an inner end position, where the tool is clamped relative to the house, and an outer end position, where the tool is releasable from the house, more precisely by means of a piston device that is movable to and fro in a cavity within the house, said piston device separating outer and inner chambers to and from which a hydraulic medium may be fed in order to move said male member towards one of said end positions, the piston device comprising a spigot, that extends from a piston of the piston device and is adapted to contact and move relative to the male member to cause the male member to move between the inner end and outer end positions. Background of the Invention Tool holders of the kind defined above are frequently present in automatic machines for metal cutting, i.e. turning, milling, drilling and the like. A benefit with this type of holder is that it allows quick and simple tool exchanges. However, a problem in connection with previously known tool holders is the adjustment of the pressure of the hydraulic medium, usually oil, that is fed into one of the chambers of the house in order to either clamp the tool or push out the same. The adjustment of the pressure is especially tricky as regards the hydraulic medium that is fed into the outer chamber in connection with clamping of the tool. If the tool is clamped by an excessively large force the components included in the clamping mechanism may be damaged or at least, in the long run, be worn out too quickly. Therefore, it is desirable to limit the pressure of the hydraulic medium that is fed to the outer chamber to a maximum value. A theoretically feasible solution of the problem mentioned above would be to provide an external pressure adjusting system in the hydraulic system of the automatic machine itself, i.e. to provide, in one way or another, a fine adjustment of the pressures to both of the hydraulic medium chambers of the tool holder. However, this is for several reasons no attractive problem solution. Since the pressure adjustment in such a case would take place at a distance from the tool holder, unavoidable pressure variations in the hydraulic system as a whole (as a consequence of the fact that other functions in the machine is activated or inactivated) may lead to the consequence that the outer chamber will not safely operate with a certain maximum pressure. Further, a remote controlled pressure adjusting system would run a risk that individual operators could too easily change the working pressures in the respective chambers in an uncontrolled way that is not always desired. Objects and Features of the Invention The present invention aims at obviating the problems mentioned above and providing an improved tool holder. Thus, a primary object of the invention is to provide a tool holder that independently of any pressure variations being present in the hydraulic system as a whole, always guarantees that the hydraulic pressure in the outer chamber is maximised to an upper limit value. A further object is to provide a tool holder in which the adjustment of the hydraulic pressure calls for certain measures, more precisely in order to eliminate the risk that individual operators change the pressure in an uncontrolled manner. Still a further object of the invention is to provide a tool holder that realizes the desired pressure adjusting function via structurally simple and cheap means. According to the invention, at least the primary object of the invention is attained by means of the features defined in claim 1. Furthermore, preferred embodiments of the invention are defined in the dependent claims. Brief Description of the Appended Drawings In the drawings: Figure 1 is a perspective longitudinal section through a holder according to the invention, where a cutting tool applied in the holder is partly shown in view, partly in section, Figure 2 is a longitudinal section through a piston device included in the tool holder, said piston device being designed in accordance with the principles of the invention, Figure 3 is a longitudinal section through the tool holder according to figure 1 and 2, the upper half of the section illustrating a first mode of function in which the tool is releasable from the holder, while the lower half illustrates a second mode of function in which the tool is clamped in the holder, Figure 4 is a partial rear longitudinal section through a holder according to a second, alternative embodiment of the invention, and Figure 5 is a longitudinal section, corresponding to figure 3, said section showing a third alternative embodiment of the invention. Detailed Description of Preferred Embodiments of the Invention In figures 1-3 reference numeral 1 generally designates a tool holder in which a tool, designated 2, may be detachably mounted. The holder 1 is in the shape of a cylindrical house that on one hand is composed of a rear part constituting a cylindrical tube 3 and an end wall 4, and on the other hand of a front part comprising a flange 5 and a tube socket 6 extending rearwardly from the flange 5, said tube socket 6 being connected with the cylindrical tube 3 via a thread coupling 7. In the flange 5, that may be fixed in an adherent machine by means of screws 8 (see figure 3), a central hole 9 is recessed, said hole 9 serving as grip for the tool 2. Apart from a head 10, the tool 2 comprises a part 11 in the shape of a short tube piece, said part 11 extending rearwardly from the head 10 and defining a female-like opening 12 that emerges rearwardly. In practice the external envelope surface of the tube piece 11, as well as the internal surface of the hole 9, may have a polygonal cross sectional shape and an axially tapering shape. Such tools are commercially available under the trade name COROMANT CAPTO™. As is evident from figure 1 the tool 2 is equipped with at least one cutting insert 13. Within the house of the holder two components are provided, said components being axially movable to and fro, more precisely a piston device 14 and a male member designated by 15. As is evident from figure 2 the piston device 14 includes, on one hand, an actual piston 16 and, on the other hand, a spigot 17 projecting from one side of the piston 16. The piston 16 divides a cavity 18 within the house into a frontal or outer chamber 19, on one hand, and a rear or inner chamber 20, on the other hand. Oil or another suitable hydraulic medium may be fed into respectively out of said chambers via first and second passages 21 and 22 respectively. The male member 15 has a rotationally symmetrical shape and engages a number of tangentially separated fingers 23 that are mounted in a ring 24 and may, with their thickened outer portions, engage in a groove 25 at the inner side of the tube piece 11. In the area of an intermediate section, the male member is sealed, via a sealing ring 27, against a sleeve 26 provided in the house. In a hydraulic respect the outer chamber 19 is defined between, on one hand, said sealing ring 27 and, on the other hand, an analogous sealing ring 28 at the periphery of the piston 16. At its rear end the sleeve 26 has a conical, rearwardly widening surface 29 against which conical surfaces 30 partially abut, said surfaces 30 being provided at tangentially separated driving bodies 31. Rear, planar end surfaces of these driving bodies abut a ring 32 included in the male member 15. Internal conical surfaces 33 of the bodies 31 abut a conical surface 34 on the spigot 17 of the piston device, said conical surface 34 converging in a rearward direction. Between the conical surface 34 and the piston 16 itself, the spigot 17 has a waist portion 35 of reduced diameter. Between the waist portion 35 and the conical surface 34 there is a second conical surface 34' having an essentially larger cone angle than the conical surface 34. The male member 15, the fingers 23, the driving bodies 31 and the spigot 17 together form the main components of a clamping mechanism by means of which the tool 2 may be either clamped in the house of the tool holder or released therefrom. More precisely, the clamping is effected in the state shown in the lower half of figure 3. In this state the piston device has been displaced, by feeding of hydraulic oil to the outer chamber 19, to an inner end position in which the conical surfaces 34 and 34' have drawn the driving bodies 31 and urged them outwards to radially outer end positions. At the same time as the bodies 31 move axially rearwards, the ring 32 is driven and thus the entire male member 15. When the male member approaches its inner end position the thickened, free end portions of the fingers 23 engage the groove 25 at the inner side of the tube piece 11 are firmly urged into the groove by means of a thickened, partly conically shaped end portion 15' (see figure 1) of the male memeber. In such a way the fingers lock the tool relative to the holder. Oil is fed into the inner chamber 20 via the passage 22 (simultaneously as the oil from the chamber 19 returns to the reservoir via the passage 21) when the tool is to be released and pushed out of the holder. In doing so, the male member will be moved to an outer end position (as shown in the upper half of figure 3), more precisely by abutting the free end surface of the piston spigot 17 against an analogous rear end surface of the male member. Hereby, the ring 32 drives the driving bodies 31 in the axial direction and the conical surfaces 29, 30 effectuate a movement of said bodies also in the radial direction, more precisely in a direction towards the centre. When the male member 15 is moved to its outer end position the fingers 23 are elastically deflected, radially inwards towards the centre and said fingers are released from the engagement in the groove 25. This means that the locking of the tool relative to the holder ceases and the tool is pushed out of the holder in one piece to subsequently be removed from the holder by hand. So far described the shown tool holder is previously known in all essential aspects. Significant for the present invention is that a passage 36 (see figure 2) extends through the piston device 14 and includes a valve having the function to open the passage when the hydraulic pressure in the outer chamber 19 increases to a set limit value. In the embodiment according to figures 1-3 the valve is constituted by a ball 37 that is loaded by a pressure spring 38, e.g. a helical pressure spring. The ball abuts a seat 39 that is provided in the transition between a narrow, outer passage section 36' and a wider passage section 36''. Thus, the valve constitutes a pressure restriction valve with a check valve function. In accordance with a preferred embodiment of the invention the spring 38 cooperates with means for adjustable setting of the spring force thereof. Thus, figure 2 shows how the rear or inner end of the spring 38 abuts an externally threaded sleeve 40 that is in engagement with an internal thread 41 in the passage 36. In the example, the sleeve 40 has a groove for a driver that may be inserted into the passage in order to bring the sleeve to rotate and hence be displaced axially in either direction in order to alternatively increase or decrease the spring force. This means that the ball 37, serving as valve body, is urged against the associated seat with a force that will be overcome when the hydraulic pressure in the chamber 19 reaches the desired value. Reference is now being made to figure 4 showing an alternative embodiment of the tool holder according to the invention. In a known way the piston device in this case includes not only the spigot 17 projecting ahead of the piston 16, but also a spigot 17' projecting in a rearward direction relative to the piston. Said spigot 17' extends through a through-going hole 42 in the end wall 4' of the cylindrical house. The free, projecting end of the spigot 17' is thus located outside of the house of the holder, and thereby the spigot may be coupled to a measuring device or a sensing device by means of which it can be determined whether the male member of the clamping mechanism is in its outer or inner end position. As regards the embodiment according to figure 4 the central oil passage 36 is divided into one or more radial passages 43 that emerge in the envelope surface of the rear spigot 17', preferably close to the piston 16. In its inner end position, shown in figure 4, the piston 16 abuts an annular abutment surface 44, inside of which a recess 45 is provided in the end wall 4'. The branch passages 43 are located in such a way that they emerge in this recess when the piston device assumes its inner end position. In this example the oil passage 22 is L-shaped and provided in the end wall 4' itself. As is evident from figure 4 the ball 37, serving as a valve body, is, in this embodiment, located between the spring 38 and the sleeve 40, a seat for the ball being provided in the sleeve itself. Also in this case the adjustment of the spring force is effected by screwing of the sleeve 40, although said sleeve 40 abuts the ball that in its turn abuts the spring. The embodiment according to figure 5 differs from the embodiment according to figures 1-3 essentially only in the respect that the valve spring 38 works with a force that is set once and for all. Thus the spring and the ball 37 are secured in the adherent passage by means of an elastic washer 46 that is fixed by snapping against an abutment shoulder in a rear end portion of the passage. A basic advantage of the tool holder according to the invention is that the pressure adjustment, more precisely the determination of a maximum pressure present in the outer hydraulic chamber, takes place within the tool holder itself and not by means of adjusting devices that are spaced from the tool holder. Among other things, this means that sufficient pressure adjustment may be effected in an exact way without depending on possible pressure variations in the hydraulic system as a whole. Furthermore, the risk of non-authorised adjustments of the working pressure of the tool holder is eliminated. Feasible Modifications of the Invention The invention is not limited to the embodiments described and shown in the drawings only. Although it is preferred to locate the overflow passage between the two hydraulic chambers centrally in the piston device, it is thus also possible to locate the passage and the adherent check valve in a non-centric position in the piston device. The passage must not necessarily extend axially through the piston device. Thus, it is only essential that the passage extends through the spigot and at its opposite ends emerges in the respective chambers and allows liquid flow between said chambers when the valve is opened. Although a spring-loaded ball is exemplified in the drawings also other, arbitrary valve designs are feasible. The valve body may for instance be in the shape of a cone. The invention is neither limited to the type of tool holder that is marketed under the trade name COROMANT CAPTO™, but may be used in connection with any tool holders of the type defined in appended claim 1.

Claims: A holder for detachable mounting of cutting tools, comprising a house having a first end to which a tool is adapted to be detachably mounted, and a clamping mechanism provided in the house, the clamping mechanism including a male member (15) adapted to engage in a female-like opening (12) in the tool (2), the male member (15) being movable between an inner end position in which the tool is clamped relative to the house, and an outer end position in which the tool is releasable from the house, the male member (15) being movable by a piston device (14) that is movable in a cavity (18) within the house, the piston device (14) separating outer and inner chambers (19, 20) to and from which a hydraulic medium may be fed in order to move the male member towards one of the inner end or outer end positions, the piston device (14) comprising a spigot (17), the spigot (17) extending from a piston (16) of the piston device (14) and being adapted to contact and move relative to the male member (15) to cause the male member to move between the inner end and outer end positions, characterized in that a passage (36) extends through the piston (16) and the spigot (17), the passage (36) emerging in the two chambers (19; 20), a valve (37) being provided in the passage (36), in order to open the passage when the hydraulic pressure in the outer chamber (19) rises to a set limit value so as to limit hydraulic pressure for clamping the tool. A holder according to claim 1, characterized in that the valve, in a known way, comprises a ball-shaped or cone-shaped valve body (37) that is loaded by a pressure spring (38). A holder according to claim 2, characterized in that the spring (38) co-operates with means (40) for adjustable setting of the spring force thereof. A holder according to claim 3, characterized in that the means is constituted by an externally threaded sleeve (40) that engages an internal (41) thread in the passage (36). A holder according to claim 4, characterized in that the valve body (37) is provided between the spring (38) and the sleeve (40), the sleeve (40) having a seat for the valve body. A holder according to any one of the preceding claims, characterized in that the passage (36) extends axially and centrally through the piston device. A holder according to claim 5 and 6, characterized in that the piston device, apart from an actual piston (16), comprises two spigots (17, 17') that project axially from opposite sides of the piston (16), a first one of the spigots (17) being positioned in the outer hydraulic medium chamber (19) and being designed to cooperate with the clamping mechanism, while a second spigot (17') being accessible from the outside of the house by projecting through a hole (42) in a rear end wall (4') of the house, characterized in that the central passage (36) divides into one or more radial passages (43) that emerge in the rear spigot (17') in an area behind the actual piston (16).

Inventors: ASBERG MATS, ASBERG, MATS
Applicants: SANDVIK AB, SANDVIK AKTIEBOLAG
Application year: 1999
Main classification: B23B29
IPC codes: B23B29, B23B31