Spacer element for cutting tool

Abstract: A cut-off tool comprises a thin holder plate (1) of steel, and a cutting insert (2) of cemented carbide. The holder plate (1) has an outwardly opening, insert-receiving recess (5) defined by a bottom wall (6), an inner wall (7) and an upper wall (8) which is part of an elastically movable clamping arm (9) serving to retain the insert in the recess. The insert has both upper and lower grooves of V-shaped cross-section, which are adapted to cooperate with analogous V-shaped ridges associated with the recess. Between the insert (2) and the bottom wall (16) of the recess, there is provided a dismountable spacer element (3) of cemented carbide, which has on its upper side a V-ridge (21) for engaging a corresponding V-groove in the underside of the insert. The spacer element is maintained in place, on the one hand, by means of a countersunk connecting device in the area of the outer end of the bottom wall and, on the other hand, by means of a male-female connection between the inner wall (7) of the recess and a rear end of the element.

Description: This invention relates to a tool for cut-off or similar turning operations of the type comprising a holder in the form of a comparatively thin plate or plate-like part of a first material, such as steel, a cutting insert of a second, harder material, such as cemented carbide, said holder plate having, in at least one free end thereof, an outwardly opening recess substantially defined by a bottom wall, an inner or rear wall, and an upper wall which is part of an elastically movable clamping arm formed in the plate and serving to retain the insert in the recess, the insert having both upper and lower grooves or, alternatively, ridges of substantially V-shaped cross-section, which are adapted to cooperate with ridges of analogous V-shaped cross-section or, alternatively, grooves provided in conjunction with the recess, and, provided between the insert and the bottom wall of the recess a dismountable spacer element or anvil seat having on its upper side a ridge of V-shaped cross-section or, alternatively, a groove for engaging a corresponding V-groove or V-ridge in the underside of the insert. (cf. US-A-35 43 363) Background of the Invention Since cemented carbide is a relatively expensive material and since the inserts, when worn-down, must be scrapped and exchanged at relatively short intervals, it is a general ambition to make the inserts for the above-mentioned tools as small as possible. Especially during intense processing of the workpieces involved, large amounts of heat are generated in the cutting edge portion of the insert and conducted through the remainder of the insert. Since the inserts are small and, in conventional cut-off tools, are applied directly against the bottom wall of the recess in the holder plate, only a minor portion of the heat will be emitted into the ambient atmosphere before the heat reaches, in particular, the underlying bottom wall of the recess in the holder plate. This means that the temperature in the portion of the holder plate adjacent the bottom wall of the recess will rise to such a level that the steel material of this plate portion is liable to considerable plastic deformation. This, in turn, may result in that the cutting edge is moved out of its initial or reference position, accurately fixed in relation to the plate. This may entail considerable practical inconveniences, not only in the form of dramatically deteriorated measurement accuracy in the processed workpiece, but also, for example, in that the cutting edge, in the final phase of a cut-off operation, will not hit the centre of the rotating workpiece. In serious cases, the plastic deformation and the consequential displacement of the insert may give rise to tool breakage as well. Summary of the Invention The present invention aims at overcoming the above-mentioned drawbacks inherent in prior-art cut-off tools and providing a tool in which the risk of plastic deformation in the insert holder plate is minimised or eliminated while maintaining the setting accuracy of the cutting edge. A basic object of the invention thus is to make more efficient the removal of the heat generated in the area of the cutting edge of the insert in order to prevent the temperature in the surrounding portions of the holder plate from reaching such levels that there is an obvious risk of plastic deformation of the steel material. Another object of the invention is, while eliminating such risk of deformation, to ensure safe retention of the insert in the desired initial position also under severe and/or intense processing conditions. Yet another object of the invention is to eliminate or minimise the risk of the occurrence of mechanical damage to the insert holder plate in those cases where the insert proper is damaged, e.g. by crack formation or chipping, so as to ensure longer service life of the insert holder plate. According to the invention, these objects are achieved by means of a tool having the features of claim 1. According to another aspect, the invention also relates to a spacer element or anvil seat intended for the tool described above. A basic object of the invention according to this aspect is to provide a spacer element which is capable not only of abducting heat before this reaches the insert holder plate, but also of firmly retaining the insert in its initial reference position. A further object is to provide a spacer element which is easy to dismount and exchange. According to the invention, these objects are achieved by means of the spacer element defined in claim 8. Description of the Prior-Art The measure of providing a simple spacer plate between a cemented carbide insert and an insert holder in the form of a tool shank is previously known in connection with conventional turning tool holders. Further, from EP 0 088 426 and DE 31 19 834, it is previously known in connection with cut-off tools to arrange the insert in a special, detachable, substantially U-shaped insert which, in turn, is applied in the recess of the insert-holder plate. In these cases, the U-shaped insert must however be made of a relatively elastic material, more specifically steel, which has considerably poorer heat-resisting properties than the cemented carbide from which the spacer plate according to the invention is made. Moreover, US 3,543,363 discloses a cut-off tool in which a special spacer element or anvil seat comprising an insert-receiving seat of V-shaped cross-section is disposed between the insert and the bottom wall of the recess in the holder plate. In this case, the anvil seat is however permanently connected to the holder plate, more specifically by gluing or brazing the underside of the anvil seat to the bottom wall of the recess. Also, the anvil seat does not have the explicit function of making the removal of heat from the insert more effective (the US publication is completely silent on the material of which the anvil seat is to be made). This means that simple and quick dismounting and remounting of the anvil seat is not possible. Moreover, the simple glue or solder layer between the anvil seat and the bottom wall of the recess provides no reliable retention of the anvil seat and the insert placed thereon, especially not when the insert is subjected to lateral stresses. Brief Description of the Drawings In the drawings, FIG. 1 is a partial perspective view of a tool embodying the invention with an insert and a spacer element or anvil seat mounted in place. FIG. 2 is a similar perspective view showing the tool without insert and spacer element, and with a clamping screw also removed, FIG. 3 is an enlarged perspective view of an insert for the tool, FIG. 4 is a perspective, exploded view showing a spacer element with the associated locking or connecting screw, FIG. 5 is an enlarged, vertical cross-section of the spacer element and the associated locking screw in locking position, FIG. 6 is a perspective view illustrating on an enlarged scale the inner wall of the insert-receiving recess, and FIG. 7 is a partial side view showing the insert and the spacer element when mounted in the tool. Description of the Preferred Embodiment The cut-off tool illustrated in Fig. 1 comprises a holder, generally designated 1, a cutting insert 2, as well as a spacer element or anvil seat 3. Moreover, a clamping screw is designated 4. The holder 1 has the shape of a relatively thin plate or plate-like part, which is made of steel or equivalent material. In practice, the holder plate often has a rectangular, elongate form and is provided, in at least one of its opposite ends, with an outwardly opening recess 5 (see also Fig. 2), which is substantially defined by a bottom wall 6, an inner or rear wall 7, and an upper wall 8 which is part of an elastically movable clamping arm 9 formed in the plate and serving to retain the insert in the recess. In the embodiment exemplified in the drawings, the plate 1 has a slot 10 which is terminated at its inner end by a through hole 11 extending transversely of the plane of the plate. The slot 10 serves to impart to the clamping arm 9 appreciable elasticity although the length of the clamping arm, counting from the rear wall 7 of the recess 5, is relatively limited. By being elastically yieldable, the arm 9 can be pivoted in known manner downwards towards the bottom wall of the recess by means of the clamping screw 4. The insert 2 shown in Fig. 3 is a body made of cemented carbide, which has at its front end a main cutting edge 12, adjacent to which chip-breaking surfaces 13 are formed on the upper side of the body. In the area behind this chip-breaking part of the insert body, there is formed a groove 14 of substantially V-shaped cross-section. This groove, which is divided into front and rear portions 14' and 14'', respectively, is defined by two flank surfaces 15, 15', between which there is a central groove portion 16 having a concavely rounded shape. The portion 14'' of the groove located adjacent the rear end of the insert passes via an upset line 17 into a front portion 14' having the same cross-sectional shape as the rear portion, but making an obtuse angle with the rear portion, as seen in the longitudinal extent of the insert body. In practice, the rear portion of the V-groove may be substantially parallel to the underside of the insert body or make an extremely small angle therewith (e.g. in the order of 0.1-2), while the front portion 14' extends obliquely downwardly-forwardly at an angle of 3-10, suitably 5-7, relative to the underside. Also in its underside, the insert body 2 in this case has a groove 18 of V-shaped cross-section. In practice, the grooves may have one and the same V-shape on the upper side and on the underside. Although, in the illustrated embodiment, the cutting edge 12 extends at right angles to the longitudinal extent of the insert, the location and the shape of the cutting edge may vary most considerably. Thus, the insert may be designed with circular or partially round cutting edges. Moreover, in the case of a straight cutting edge, it may also be inclined relative to the longitudinal extent of the insert. Characteristic of all the embodiments is however that the length of the cutting edge or its extent transversely of the longitudinal axis of the insert, is at least slightly larger than, respectively, the thickness of the holder plate 1 and the width of the portion of the insert itself located behind it such that the insert and the holder plate can be accommodated in a groove made by the cutting edge in a workpiece. Fig. 4 illustrates a spacer element or anvil seat according to a preferred embodiment of the invention. This element consists of a substantially flat body 3 which, in the illustrated Example, has a basic rectangular shape. Like the insert 2, the body 3 is made of cemented carbide or other equivalent material having higher heat resistance than steel. In the area of the front end of the body, there is provided a through hole 19 for a locking or connecting screw, generally designated 20. In this case, the upper side of the spacer element or body 3 is designed as a ridge 21 of V-shaped cross-section, which is defined by two inclined flank surfaces 22, 22', between which there is a longitudinal central portion 23 having a convexly rounded shape. The rounded central portion 23 has a larger diameter than the central portion 16 in a cooperating V-groove, such that there exists between the respective central portions a clearance of crescent-shaped cross-section. At its rear end, the spacer body 3 has a female groove 24 extending vertically from the upper side to the underside of the body. In the illustrated embodiment, the underside 25 of the body is in the form of a planar, substantially rectangular surface to be applied against the similarly planar surface forming the bottom wall 6 of the recess 5 in the holder plate. In addition to a threaded shank 26, the locking screw 20 has a thickened head 27, the lower portion 28 of which is tapered, suitably conically, towards the threaded shank. In the upper face of the screw head, there is, for example, a starformed seat 29 for receiving a key wrench. As appears from Fig. 5, the hole 19 is defined at the top by a cylindrical surface 30 of a relatively large diameter, which passes at the bottom into a rotationally symmetric surface 31 having a diameter which decreases successively downwards. The surface 31 is however not conical, but arched. The threaded shank 26 of the screw 20 is to be screwed into an internally threaded hole 32 in the insert holder plate 1. The hole 32, opening into the bottom wall surface 6 (see Fig. 2), is located centrally in the plate 1 relatively close to the front short end of the insert holder plate. According to a preferred embodiment of the invention, the distance between the centre of the hole 32 and the inner wall 7, against which the rear short end of the spacer element 3 is applied, is slightly shorter than the distance between the centre of the hole 19 and said rear short end. As a result, the screw 20, when being tightened, will exert, by its substantially conically tapering head, a force on the spacer element 3, which is directed in the longitudinal extent thereof and which urges the spacer element most forcefully against the inner or rear wall 7 of the recess. The difference in distance mentioned above may be relatively small and, in practice, amount to one or some tenths of a millimetre. In practice, the actual contact between the rear end of the spacer element 3 and the inner wall 7 of the recess 5 takes place between the female, vertical groove 24 and a male projection 33 (see Fig. 6) on the inner wall 7, the projection 33 and the groove-shaped recess 24 together forming a male-female connection between the spacer element and the insert holder plate. The projection 33 may be implemented in many different ways. It is however preferred, as shown in Figs 2 and 6, to design it as a ridge of substantially V-shaped cross-section and of the same basic design as the ridge 21 formed on the upper side of the spacer element 3. Thus, the V-ridge 33 is defined by two flank surfaces 34, 34' and an intermediate, convexly rounded central portion 35. A V-ridge of this type is also designed on the underside of the clamping arm 9, i.e. the upper wall 8 of the recess 5, for cooperating with the V-groove 14 on the upper side of the insert 2. By designing the V-ridge on the underside of the clamping arm 9 and the V-ridge forming the projection 33 with the same cross-sectional shape, it is convenient, in the making of the insert holder, to use one and the same form cutter for providing these two details, more specifically in a continuous working operation. In the area below the V-ridge 33, there is a transverse recess 36 ensuring that the lower, inner edge portion 37 of the spacer element 3 (see Fig. 1) comes clear of the insert holder plate. Also in the area above the V-ridge 33, there is a similar recess 38 extending a certain distance along the underside of the clamping arm and serving to ensure that the upper, rear edge portion of the insert 2 similarly comes clear of the insert holder plate. The V-ridge (not shown) which is formed on the underside 8 of the clamping arm 9 extends - when the insert 2 is in place and the clamping screw 4 is tightened-substantially parallel to the bottom wall surface 6 and hence substantially parallel to the rear portion of the V-groove 14 on the upper side of the insert 2. At its free, outer end, the clamping arm 9 passes into a slightly downwardly-directed nose 39, as shown in Fig. 6. Also this nose portion 39 has on its underside a V-shaped ridge of the type described above, which is intended to engage in the front portion 14' of the upper V-groove of the insert. The inclination between the V-ridge on the underside of the nose 39 and the V-ridge located behind it on the underside of the clamping arm is substantially equal to the inclination between the front and rear portions 14' and 14, respectively, of the upper V-groove in the insert. In the working position in which the insert is in place and the clamping screw 4 is tightened, the forwardly-downwardly inclined outer portion of the V-ridge on the underside of the clamping arm will thus engage in the similarly forwardly-downwardly inclined, countersunk front portion 14' of the V-groove in the insert so as to provide positive locking of the insert in a position in which it is prevented with high reliability from being pulled out of the recess 5 in the axial direction. Operation and Advantages of the Invention The spacer element or anvil seat 3 shown in Fig. 4 is mounted in the recess 5 of the insert holder plate by engaging the V-ridge 33, acting as a male projection, with the female groove 24 in the rear end portion of the spacer element, and tightening the screw 20 in the hole 32. As earlier pointed out, the screw 20 will apply, when being tightened, to the spacer element 3 an axially directed force ensuring a distinct engagement between the V-ridge 33 and the groove 24. This interaction between, on the one hand, the male-female connection 33-24 located at the inner end of the spacer element and, on the other hand, the locking screw 20 located in the area of the outer end of the spacer element provides a substantially immovable retention of the spacer element in an accurately defined position in relation to the rest of the insert holder plate. Once the spacer element is mounted in place, the insert 2 is applied in the tool. This is done by pushing the insert in under the clamping arm 9 while the clamping screw 4 still is but loosely inserted in the associated threaded hole. The clamping screw is then tightened until the final clamping force is achieved, the arm 9 clamping the insert in the position shown in Fig. 1. This is a well-defined position in relation to the insert holder 1 itself. Thus, the front transverse surface 40 (see Fig. 6) of the clamping arm 9 forms a stop which engages the similarly inclined surface 41 on the insert 2 (see Fig. 3), which means that the insert cannot be pushed further inwards than the position in which said surfaces contact each other. Extraction of the insert is prevented, as earlier pointed out, by the cooperation between the V-ridge on the underside of the nose portion 39 of the clamping arm 9 and the front, inclined portion 14' of the V-groove on the upper side of the insert. Lateral movements of the insert are prevented by the cooperation of, on the one hand, the V-grooves 14, 18 on the upper and lower sides of the insert and, on the other hand, the V-ridge on the underside of the clamping arm 9 and the V-ridge 21 on the upper side of the spacer element. In the working position, the insert will thus be immovably retained in the desired reference position, not only in connection with simple cut-off operations, but also in connection with other operations in which the insert is subjected to both lateral forces and forces of extraction, such as groove turning, contour turning and undercutting. An essential advantage of the inventive tool is that the spacer element 3, made of cemented carbide, has considerably higher heat resistance than the steel in the insert holder plate 1. This means that heat generated in the area of the cutting edge 12 of the insert will be removed not only via the insert itself but also via the spacer element. In this manner, it is ensured that the temperature in the insert holder plate will not rise to such a level that a considerable plastic deformation of the steel will take place. Thus, the insert will not run the risk of being moved out of its reference position initially fixed in relation to the insert holder. Another advantage of the spacer element 3 is that it makes it possible to increase the life of the insert holder, for instance by reducing the risk of mechanical damage to the insert holder. If the insert is damaged, e.g. by chipping or crack formation, this need in fact not result in subsequent damage to the insert holder plate itself thanks to the provision of the spacer element or anvil seat as an extra safety component between the insert and the subjacent portion of the insert holder plate. If, therefore, the spacer element is damaged as a result of damage to the insert, it will be necessary only to replace the spacer element, whereas not the entire insert holder. Exchanging the spacer element is also very easy to do, since only a simple locking screw need be removed for releasing the spacer element. Conceivable Modifications of the Invention It goes without saying that the invention is not restricted only to the embodiment described above and illustrated in the drawings. Thus, it is conceivable, for instance, to replace the locking screw with other connecting means between the spacer element and the insert holder plate, e.g. a pin. Instead of a planar underside, the spacer element may have an underside of V-shaped cross-section (either a ridge or a groove) for cooperating with a bottom wall 6 (either a groove or a ridge) of analogous V-shaped cross-section. Also, the design of the male-female connection between the rear end of the spacer element and the inner wall of the insert-receiving recess may deviate from the design exemplified in the drawings, e.g. by designing the male element on the rear end of the spacer element and the female element in the inner wall 7. It should also be pointed out that the insert holder plate 1 need not in itself form a shank, as is the case in the embodiment shown in the drawings. Thus, the insert holder plate need only form a minor portion of the tool and, for instance, be disposed transversely of a thicker shank. Although the embodiment shown in the drawings includes an insert whose V-formation consists of precisely a groove on both the upper side and the underside for cooperating with analogous V-ridges on the underside of the clamping arm and the upper side of the spacer element, respectively, it is also possible to design at least one and preferably both of the V-formations on the insert as ridges to cooperate with analogous V-grooves on the underside of the clamping arm and in the upper side of the spacer element, respectively.

Claims: A tool for cut-off or similar turning operations, comprising a holder in the form of a comparatively thin plate or plate-like part (1) of a first material, such as steel, a cutting insert (2) of a second, harder material, such as cemented carbide, said holder plate (1) having, in at least one free end thereof, an outwardly opening recess (5) substantially defined by a bottom wall (6), an inner or rear wall (7), and an upper wall (8) which is part of an elastically movable clamping arm (9) formed in the plate and serving to retain the insert in the recess, the insert having both upper and lower grooves (14, 18) or, alternatively, ridges of substantially V-shaped cross-section, which are adapted to cooperate with ridges of analogous V-shaped cross-section or, alternatively, grooves provided in conjunction with the recess, and, provided between the insert (2) and the bottom wall (6) of the recess (5) a dismountable spacer element or anvil seat (3) having on its upper side a ridge (21) of V-shaped cross-section or, alternatively, a groove for engaging a corresponding V-groove (18) or V-ridge in the underside of the insert, characterised in that said spacer element (3) is made of a material, especially cemented carbide, which has a higher heat resistance than the material of the plate (1), and in that said spacer element (3) is maintained in place, on the one hand, by a countersunk connecting means (20) in the area of the front or outer end of the bottom wall (6) and, on the other hand, by a male-female connection (33, 24) between the inner wall (7) of the recess (5) and a rear or inner end of the element (3). A tool as claimed in claim 1, characterised in that the upper side of the spacer element (3) is designed as a V-ridge (21) for engaging in a V-groove (18) in the underside of the insert (2). A tool as claimed in claim 1 or 2, characterised in that underside of the spacer element is designed as a ridge of substantially V-shaped cross-section, or alternatively a groove, which is adapted to cooperate with a groove of analogous V-shaped cross-section, or alternatively a ridge, in the bottom wall of said recess (5). A tool as claimed in any one of the preceding claims, characterised in that said male-female connection comprises a female groove or seat (24) in the rear end of the spacer element (3), and a male projection (33) on the inner wall (7) of the recess (5). A tool as claimed in claim 4, characterised in that the male projection is a ridge (33) of substantially V-shaped cross-section being equal to the V-shape of a ridge formed on the underside of the clamping arm (9) and adapted to cooperate with the upper V-groove (14) of the insert (2). A tool as claimed in any one of the preceding claims, characterised in that the connecting means comprises a screw (20) having a head (27) which in the transition to a threaded shank (26) has a downwardly, suitably conically tapering contact surface (28) for cooperating with a countersunk seat surface (31), located on a level below the upper side of the spacer element (3), in a through hole (19) provided therein, said seat surface similarly tapering downwards in the hole, and an internally threaded hole (32) provided in the holder plate (1) and opening in the bottom wall (6) of the recess (5) being located at least slightly closer to the inner wall (7) of the recess (5) than said through hole (19) in the spacer element, whereby tightening of the connecting screw (20) applies to the spacer element a force urging the rear end thereof most forcefully against said inner wall (7). A tool as claimed in claim 1, characterised in that the underside (25) of the base element (3) is planar and adapted to engage a similarly planar surface (6) forming the bottom wall of the recess (5). A spacer element or anvil seat for an insert in a cut-off tool, comprising a body (3) which is provided on an upper side thereof with a ridge (21) of V-shaped cross-section, or alternatively a groove, for engaging a corresponding V-groove or alternatively a ridge in the underside of the insert, characterised in that said body (3) is made of a material having a higher heat resistance than steel, especially cemented carbide, said body being provided, on the one hand, in the area of a front end with a through hole (19) for a countersunk connecting means and, on the other hand, in the area of a rear end with one (24) of a pair of male and female elements (33, 24) being part of a male-female connection for mechanical interconnection of the spacer element and the tool. A spacer element as claimed in claim 8, characterised in that there is provided at the rear end of the body (3) a groove, preferably a groove (24) of V-shaped cross-section, which forms the female element of said male-female connection.

Inventors: GUSTAFSSON LARS-ERIK, GUSTAFSSON, LARS-ERIK
Applicants: SANDVIK AB, SANDVIK AKTIEBOLAG
Application year: 1993
Main classification: B23B27
IPC codes: B23B27