TOOL FOR CHIP REMOVING MACHINING

Abstract: The present invention relates to a tool, a tool body and a tool tip for chip removing machining, wherein the tool in operative position preferably rotates about its longitudinal center axis. The tool comprises a tool body (12), a tool tip (10) and a pull rod, said tool body having a front surface and the tool tip having an end surface provided to detachably face each other. The body has a shank portion (40). The tool tip consists of injection molded cemented carbide and comprises a central blind hole (14) that cooperates with the means for retention, and at least one cutting edge (19). The blind hole and the cutting edge are integral with the tool tip (10). The cutting edge extends from the tool periphery to the area of the axis (22) of rotation of the tool. The front surface (24) and the end surface (16) comprise cooperating projections (30) and recesses (26), which are provided to substantially alone transfer cutting forces directed towards the shank portion appearing during machining. The cooperating projections (30) and recesses (26) are substantially X-shaped.

Description: Tool for chip removing machining Background of the invention The present invention relates to a tool for rotary, chip removing machining, comprising a tool body, a tool tip and means for retention. The tool body has a front surface and the tool tip has an end surface provided to detachably facing each other. The body has a shank portion. The invention also relates to a separate tool tip and a tool body. Prior art It is previously known to use interchangeable cutting edges on different types of tools for chip removing machining. This technique has however its practical limitation for strength reasons in milling and drilling tools which rotate around a longitudinal axis. Through DE-A-1 950 718 is previously known a tool with a detachable tool tip anchored in a body by means of a central screw. In that known tool lips transfer torque created during drilling, to the tool body. Such a tool suffers from a number of drawbacks, such as the tool tip can not have central cutting edges, since the screw occupies the central portion and the tool tip is forced to contain less amount of cemented carbide in order to accommodate the screw and therefore propensity for crack formation increases. In addition tolerance problems arise in connection with the known tool since a tangential gap must exist between cooperating lip and recess, and therefore the tip will rotate somewhat relative the tool body at the start of a machining operation. Objects of the invention One object of the present invention is to provide a design of milling and drilling tools with interchangeable cutting edges, whereby said design eliminates problems according to known technique. Another object of the present invention is to provide a rigid tool preferably for drilling or milling where the tool tip has a wedging cooperation with the tool body such that the clamping force increases with increasing feed force. Another object of the present invention to provide a rigid tool preferably for drilling or milling where the tool tip easily can be exchanged. Another object of the present invention is to provide a tool and a tool tip manufactured of injection molded cemented carbide. Still another object of the present invention is to provide a tool and a tool tip where the movement of the tool tip relative to the tool body is made impossible also after wear of the tool body. These and other objects have been achieved by a tool, a tool body and a tool tip such as defined in the subsequent claims with reference to the drawings. Description of the drawings Fig. 1 shows a drilling tool according to the present invention, in a side view. Fig. 2 shows a tool tip according to the present invention in a perspective view. Fig. 3A shows the tool tip in a side view. Fig. 3B shows an enlarged part of the tool tip in Fig. 3A. Fig. 4 shows the tool tip in a top view. Fig. 5 shows the tool tip in a bottom view. Fig. 6 shows a cross-section according to line VI-VI in Fig. 4. Fig. 7A shows a tool body according to the present invention in a perspective view. Fig. 7B shows a part of the tool body in cross section. Detailed description of the invention The embodiment of a tool according to the invention shown in Fig. 1 is a so called helix drill, which comprises a tool tip 10, a pull rod, not shown, a drill body 12 and a nut, not shown. The tool tip 10 is provided with at least one cutting edge 19 at the end facing away from the drill body 12, which is given different design depending of the area of application. In this manner the cutting edge or the cutting edges is/are substantially straight and parallel with the longitudinal center axis of the tool tip when its an end mill while the cutting edges are circular when its a ball nose end mill. The forward end of the tool tip 10 shows in the figures a cutting edge 19 for drilling. The appearance and the area of application for the tool can vary in several ways. The tool tip 10 is performed in hard material, preferably cemented carbide and most preferably in injection molded cemented carbide and comprises two upper clearance surfaces 1 5, an end surface 16 as well as them uniting first 1 7 and second 18 curved surfaces, Figs. 2-6. All these surfaces and associated edges are performed in the same material, i.e. preferably in injection molded cemented carbide. The lines of intersection between the second curved surfaces or the chip flutes 18 and the clearance surfaces 15 form main cutting edges 19, preferably via, reinforcing chamfers. The cutting edge extends from the tool periphery to the area of the tool axis of rotation 22. The lines of intersection between the first curved the surfaces 1 7 and the chip flutes 18 form secondary cutting edges 20. The chip flute can alternatively be adapted for a drill body with straight chip flutes. The tool tip preferably also comprises a coring-out surface 21 , which extends to the center of the tool tip and which forms an angle, Fig. 6, with the tool axis of rotation 22. The biggest diameter of the tool is defined by the diametrical distance between the radial extreme points of the secondary cutting edges 20. The height of the tool tip is substantially the same as said biggest diameter, in order to minimize the wear from chips on the joint between the tool tip and the drill body. The biggest diameter of the end surface 16 is preferably less than the biggest diameter of the tool, in order to provide clearance during machining. Flushing holes 23, substantially parallel to the rotational axis 22, run through the tool tip from the end surface 16 to the orifice in each upper clearance surface 15. The flushing holes are provided on a line L which crosses the rotational axis 22 and on each side of the axis 22. The end surface 16 is provided with a number of from each other separate, substantially identical lips 30. The lips 30 are preferably four and consist of two pairs of lips 30A and 30B substantially forming an X, wherein each pair is arranged on a line L1 and L2, respectively, substantially perpendicular to the axis 22, Fig. 5. The imaginary lines L1 and L2 intersect the axis 22 and extend on each side of the line L. The line L1 forms an acute angle α with the line L and the line L2 forms an acute angle β with the line L1. Each lip 30 comprises a planar, axial ly external surface 31 , which connects to two convex flanks 32A, 32B. Each flank is defined, in the cross section according to Fig. 3B, by a radius R1 , the center of which preferably is provided radially and axially beyond the lip. The radius R1 is about 1 to 1 ,5 mm. The lips 30A are oblong and extend radially inwardly from the first curved surface or the envelope surface 1 7 a distance towards a central recess or blind hole 14. The distance between the flanks 32A, 32B diminishes successively in direction towards the axially external surface 31 . The lip has a height h and a biggest width w. The height h is maximum 1 mm and the width w is 0.6 to 2 mm. The number of lips 30 depends indirectly of the diameter of the tool tip, said number varying between 2 and 6 lips. At the end facing towards the drill body 12 the tool tip is equipped with the end surface 16, which is provided with the blind hole 14, which in the shown embodiment comprises a threaded recess 34 as well as an entering surface 35, Fig. 6. A pull rod which shall cooperate with the tool tip should exhibit a threaded portion 36 at the end facing against the tool tip, which portion is intended to cooperate with the blind hole 14. In operative position the threaded recess 34 cooperates with the threaded portion 36 of the pull rod. A further externally threaded portion should be arranged at the other end of the pull rod, to cooperate with a cylindrical nut, not shown, provided with a key grip. The drill body is according to Fig. 7A provided with flush channels 23A, which follow the protruding lands of the drill along a helical path at substantially constant distance from the rotational axis 22. The drill body has screw-shaped chip flutes 18A or straight chip flutes and these can extend along the entire body or along a part thereof. The drill body 12 is provided with a front surface 24 at the end facing towards the tool tip 10, which surface during mounting is arranged close to the end surface of the tool tip 10, but preferably does not contact this. The biggest diameter of the front surface is smaller than the biggest diameter of the tool tip, but preferably the same as the smallest diameter of the tool tip. A central channel 37 is provided in the drill body 12. The channel 37 extends through the entire body and terminates centrally in the front surface 24 of the drill body. The front surface is provided with a number of from each other separate, identical recesses or grooves 26A, 26B, which in cross-section describes a substantially V- shaped or trapezoidal path, Fig. 7B. The grooves are oblong and extend along essentially the entire front surface, except for intersecting the channel 37. Each groove forms an acute angle with an imaginary line through the centers of the flushing holes 23A. The grooves 26A, 26B substantially form an X in the front surface 24, wherein the smallest included acute angle β is about 50 to 70°. Each groove 26A, 26B coincide with an imaginary line L1 and L2 respectively, substantially perpendicular to the axis 22. The imaginary lines L1 and L2 intersect at the axis 22 and define the acute angle β. Each groove 26 has two flanks 28A, 28B, which, via a sharp or rounded transition, connects to the bottom 27. The flanks form an acute angle ε with each other. The angle ε lies within the interval of 40° to 80°, preferably 55° to 60°. The front surface 24 is provided at each side of the groove 26. The front surface connects to the associated flank via an obtuse inner, soft or sharp, transition. The number of grooves 26, which depends of how the end surface of the tool tip is formed, is consequently the same as the number of lip pairs which the end surface has, and therefore the number is chosen in the interval of 2 to 6 grooves. The groove has a depth d, and a biggest width z. The lip height is 50 % to 95 % of the depth of the groove 26 and biggest width w of the lip is bigger than the biggest width z of the groove. This implies at mounting that a gap arises between the external surface 33A and the bottom 27 when mounting the tool tip in the tool body. The gap makes sure that the flanks engage with each other and that the bottom does not support the cutting insert, and therefore tilting is avoided. A corresponding gap thereby arises also above the front surface 24. The lips and the grooves form, in mounted condition, a joint with a number of wedging connections which entail an increase in the frictional force with increasing feed force. Another advantage with said wedging effect is that it allows some obliquely positioning of the lips and the grooves relative each other in connection with the start of the mounting, whereby these are guided correctly by their geometries at continuous compression. The joint is placed such that it mostly will be situated in the drilled hole during the drilling. The ends of a lip pair or a groove should be as far from each other as possible for best transfer of torque. Mounting of the tool tip 10 on the drill body 12 is done as follows. The pull rod is brought into and through the central hole 37 of the drill body 12 until the nut, which is connected with the axially rear end of the pull rod, abuts against a contact surface. The forward portion of the pull rod thereby projects centrally from the front surface 24. Then the threaded portion 36 is brought into the blind hole 14 and the tool tip is rotated and is screen onto the pull rod. Then the lips 30A, 30B of the tool tip are brought by hand into contact with the groove of the front surface. During rotation of the nut the tool tip 10 will be firmly drawn against the front surface, i.e. the position according to Fig. 1 has been achieved. In this position the end surface 16 will not abut against the front surface 24 since a gap L3 is provided therebetween. The gap L3 is of the magnitude of 1/100 - 10/100 mm for avoiding tilting of the tool tip relative to the tool body. The tool tip 10 is now anchored in the drill body 12 in a satisfactory manner. The pull rod is in this position substantially intended to retain the tool tip during extraction of the tool from the machined hole while the lips and the grooves receive the forces and torque which are created by chip removing machining. However, the force from the pull rod is large enough to counter act loose fit at the joint between the tool tip and the body at extraction. The lips and the grooves does not intersect the chip flutes 18, 18A. In this connection should be noted that the combination of the lips/grooves and the threaded connection between the tool tip and the pull rod serves three purposes, namely to place the tool tip 10 in a centered position (with a run out of truth measure of less than 0.02 mm) in the drill body at mounting; to transfer torque and to ensure at application of the cutting tool that the tool tip 10 is always held in its fixed position. A drill according to the present invention contains much cemented carbide as well as it unloads the pull rod both radially and axially. After mounting the lips 30 and the grooves 26 will form line-shaped contact surfaces. The contact surfaces of the lips and the grooves substantially lie in a common plane. The height of the profile is maximum 20 % of the height of the tool tip. Since the major portions of the front surface 24 and the end surface 16 are substantially planar they will be separated by the distance L3 in the mounted position. The tool tip 10 can be detachably connected to or be disconnected from the front surface 24 when the end 36 of the pull rod is unscrewed, i.e. when the end is activated from a first axially forward position to a second axially rear position. When the tool tip 10 shall be exchanged the process of mounting is reversed, whereby the tool tip 10 can be removed from the drill body 12 and be exchanged. For the above described the embodiment applies that the tool tip has a wedging cooperation with the tool body such that the clamping force or the frictional force, i.e. the resistance against radial motion of the part relative to the body, increases with increasing feed force. In addition the means for retention is provided to influence the tool tip in the same direction as the feed force during drilling, i.e. the pull rod draws the tool tip axially rearwards substantially in the same direction as the feed force acts. It is understood that the geometries of the cooperating lips and grooves can be varied within the spirit of the present invention without departing from the scope of the claims. Consequently the geometries may assume most cross sections of conventional threads (however with a degree of overlap of maximum 95%), for example trapezoid shape on both cooperating surfaces. The invention is serviceable also with milling cutters. The tool tip is preferably coated with layers of for example Al 2 0 3 , TiN and/or TiCN. In certain cases it can be well-founded to coat the cutting edges with super hard material such as PCD. It is also possible to utilize other clamping means than a central pull rod. For example, it is the possible to maintain the tool tip by means of a wedge, movable perpendicularly to the rotational axis and influencing on a pull rod. Furthermore shall be noted that the above described embodiments relate to tools which rotate relative to its longitudinal axis or to the workpiece center axis and that the means for retention rotates with the tool. The embodiments can be used also as stationary but then in combination with a rotating work piece. The invention is in no way limited to the above described embodiments but may be varied freely within the scope of the appended claims.

Claims: Claims 1. Tool for relative to a work piece, rotary chip removing machining, including a tool body (12), a tool tip (10) and means for retention (36), said tool body having a front surface (24) and the tool tip having an end surface (16), said surfaces facing each other in mounted position, said body having a shank portion (40) and an axis of rotation (22), characterized in that the tool tip consists of injection molded cemented carbide and comprises a central blind hole (14) that cooperates with the means for retention (36), and at least one cutting edge (19), said blind hole and said cutting edge being integrated with the tool tip (10), said cutting edge extending from the periphery of the tool to the area of the axis of rotation (22) of the tool and in that the front surface (24) and the end surface (16) comprise cooperating projections (30) and recesses (26), which are provided to substantially alone transfer cutting forces directed towards the shank portion during machining and in that the projections (30) and recesses (26) are arranged on imaginary lines (L1,L2) which form an acute angle (β) with each other. 2. Tool according to claim 1, characterized in that the cooperating projections (30) and recesses (26) consist of at least two pairs of lips (30A,30B) and at least two grooves (26A,26B), which are provided radially outside the rotational axis (22), for mutual wedging cooperation. 3. Tool according to claim 2 or 3, characterized in that the lips (30A,30B) and the grooves (26A,26B) form line-shaped contact surfaces and in that major portions of the front surface (24) and the end surface (16) are substantially planar and separated by a distance (L3) in a mounted position. 4. Tool according to claim 1, 2 or 3, characterized in that the tool is elongated and in that the tool tip (10) is provided to be detachably connected to or be removed from the front surface (24) when the means for retention is activated from a first axial position to a second axial position. 5. Tool according to claim 4, characterized i n that the projections are formed by wedge-shaped lips (30) which extend along a part of the diameter of the end surface (16) and in that the recesses are formed by wedge-shaped grooves (26) which extend along substantially the entire lateral direction of the tool body and in that flush channels (23,23A) are provided radially outside the central hole (14,37). 6. Tool according to anyone of the preceding claims, characterized i n that a gap (p) is provided between an external surface (31) of the lip and a bottom (27) of the groove and in that each lip in cross section describes a truncated ballistic shape while the grooves describe a substantially trapezoidal path in cross-section and in that the height (h) of the lip is 50 % to 95 % of the groove depth (d) and in that the number of cooperating groove and lip pairs is equal, namely from 2 to 6 pieces. 7. Tool tip for rotary chip removing machining, wherein the tool tip (10) has a circular basic shape and has at least one cutting edge (19), which is integral with the tool tip (10), which at the end facing away from the cutting edge is provided with an end surface (16) comprising projections (30A,30B), said tip having an axis (22) of rotation, characterized in that the tool tip consists of injection molded cemented carbide and comprises a central blind hole (14) that cooperates with a means for retention, at least one cutting edge (19), said blind hole and said cutting edge being integrated with the tool tip (10), said cutting edge extending from the periphery of the tool to the area of the axis (22) of rotation of the tool and in that the end surface (16) of the tool tip comprises projections (30), the flanks (32A,32B) of which are intended to constitute the lower abutment surfaces of the cutting insert and in that the projections (30) are arranged on imaginary lines (L1,L2) which form an acute angle (β) with each other. 8. Tool tip according to claim 7, characterized i n that the projections are shaped in the form of lips (30), the flanks (32A,32B) of which are convex, said lips extending along a part of the end surface and which are arranged at a distance from the blind hole (14), which is concentric with the axis (22) of rotation of the tool and in that the blind hole comprises a threaded portion (34). 9. Tool body for a tool for rotary chip removing machining, comprising a shank portion (40), chip flutes (23,23A), a front surface (24) as well as means for retention, said body having a center axis (22), characterized i n that the front surface (24) has recesses (26A,26B), said recesses being provided to constitute the only abutment means of the tool body and in that the front surface (24) has a central recess wherefrom a free end of the means for retention is provided to project and in that the free projecting end surface of the means for retention is threaded and in that the recesses (26) are arranged on imaginary lines (L1,L2) which form an acute angle (β) with each other. 10. Tool body according to claim 9, characterized i n that the recesses consist of grooves (26A,26B), which in cross-section describes a substantially V-shaped or trapezoidal path.

Inventors: KARLSSON RONNY, WAGNER OLLE, KARLSSON, RONNY, WAGNER, OLLE
Applicants: SECO TOOLS AB
Application year: 1997
Main classification: B23B51
IPC codes: B23B51