CUTTING TOOL ASSEMBLY

Abstract: Tool system using replaceable cutting inserts and the insert for use in the systems wherein the tool holders have wedge shaped recesses for holding the inserts which are also wedge shaped and have shoulder means thereon that maintains the distance the cutting edge of the insert extends from the holder predetermined during operation of the system.

Description: This invention relates to a cutting tool assembly for use in machine tools for machining grooves and the like and more particularly to such machine cutting tools for use where it is necessary to maintain the accuracy of the depth of cut. Once the machine tool has been set up for a particular operation the accuracy of the depth of cut depends on maintaining a constant distance between the cutting edge and a fixed point on the tool holder. Where the cutting tool uses an insert special steps have been taken in the prior art to assure the accuracy and constancy of the depth of cut. The steps include forcing the cutting inset to abut the same surface on the cutting tool holder at all times. Clamp means of various kinds are used to hold the cutting tool insert against the abutting means. The clamping arrangements, however, complicate the tools, take up valuable space, make the tooling more expensive and also add to the difficulties of using the inserts in the tool. Accordingly, in recent years tool insert systems have been provided which do not require clamping. Such tool insert systems, however, are not amenable to precision usage. The distance that the cutting inserts in such systems extend beyond the holders varies with characteristics, such as the feed rate and the material being cut. The prior art inserts that are held without clamping means are held either by spring forces such as that shown in the system disclosed in US-A-3,785,021 or the insert is held by the geometry of the insert in relation to the geometry of the holder. This type of self-gripping is shown in Belgian Patent BE-A-853,475. When using spring forces for maintaining the insert in the holder without clamping means as disclosed in the U.S. patent, it is possible theoretically, to maintain the distance that the insert extends beyond the holder constant. In pratice, however, the spring element in the body of the holder which holds the cutting insert in place is the weak point of the tool. While working with the tool, the cutting forces negatively affect the stability of the clamping system such that it is not possible to make true precision cuts. In the present applicants' own published German Specification DE-U1-8001813, and also in an article in Werkstatt und Betrieb III (1978)5 entitled "Abstechwerkzenge mit selbstklemmenden auswechselbaren Hartmetall-Schneidplatten" is described and shown a self-gripping cutting tool assembly of the kind comprising a tool holder; a pair of rigid gripping jaws formed integrally as one piece in an edge portion of said tool holder; a pair of longitudinally directed jaw edges which are directed at an acute angle to each other and which define between them an open-ended, wedge-shaped recess of said holder which opens out towards the edge of the tool holder; a cutting insert comprising a pair of longitudinally directed insert edges which are directed at an acute angle to each other and which define between them a wedge shaped body portion of said insert; a leading end of said insert being formed adjacent the wider end of said body portion and having formed thereon a cutting edge; and an opposite rear end of said insert being formed adjacent the narrower end of said body portion. It is definitely not possible to make precision cuts with the prior art systems which use geometrical configuration for retaining purposes. More particularly the geometrical configuration in the prior art systems use recesses defined by jaws in the tool holder. The jaws are at a first angle and abut clamping surfaces on the inserts which are at slightly larger angles. Thus as the cutting forces act on the cutting insert during the cutting operation the insert is forced further into the jaw until equilibrium is reached and the insert is locked in place. However, since the equilibrium point can vary, it has not been possible to use such tools for precision work. Accordingly there is a long-felt need for cutting inserts that are maintained in the tool holders by the geometrical configurations and that can be used for precision work. It is an object of the present invention to provide a new and improved precision groove cutting tool system in which the above-referred to disadvantages are substantially reduced or overcome. According to the present invention there is provided a tool holder, a pair of rigid gripping jaws formed integrally as one piece in an edge portion of said tool holder; a pair of longitudinally directed jaw edges which are directed at an acute angle to each other and which define between them an open-ended wedge-shaped recess (16) of said holder which opens out towards the edge of the tool holder; a cutting insert having a pair of substantially planar side walls, first and second (a pair) longitudinally directed insert edges acting as clamping surfaces respectively defined between adjacent pairs of edges of said planar side walls and which are disposed at an acute angle to each other so that the first clamping surface has one end where it is relatively further from the second clamping surface than it is at its opposite end whereby said clamping surfaces define a wedge-shaped body portion of said insert; a leading relief surface of the insert defined between a pair of leading edges of said side walls and between a leading extremity of said second clamping surface and a cutting edge formed on a leading end of the insert adjacent a wider end of the body portion, an opposite rear end of said insert being formed adjacent a narrower end of said body portion; and chip shaping means, formed adjacent to said cutting edge; said insert being inserted into said recess and being frictionally retained between said jaws as a consequent a relative resilient outwardly directed displacement of said jaws, resilient displacement of said jaws being maintained during the entire frictional retention of the insert in the recess; characterised in that an abutment shoulder is formed adjacent to said one end of the first of said clamping surfaces so that, when the insert is inserted into the recess to a predetermined extent and is frictionally retained therein with said insert frictionally engaging said jaw edges, said abutment shoulder abuts an exposed end of one of said jaws so as to limit the extend of insertion of said insert into said recess. Another preferable feature provides for the abutment shoulder to have a characterised surface into which the abutting surface of the holder meshes to maintain the stability of the cutting insert during the operation of the system. Not only is the stability maintained but it is reinforced by the meshing and characterized shapes of the holder and the cutting insert. Such characterized shape can for example be an extended V meshing into an inverted V. Yet another preferable feature of the present invention is to provide spring detent means as a safety factor to assure that the "self-grip" tool insert will not inadvertently come out of the holder. It should be noted that if such spring means are used, the configuration of the portion of the insert receiving the spring means is such that the spring means has no influence on the location of the insert. Still another preferable feature of the present invention is that the system is usable in stationary tools as well as in rotary tools. The system retains the cutting insert located and held with sufficient stability to withstand the vibrations caused by the additional forces generated by means for controlling the form and the flow of the chips. Brief Description of the Drawings The operation and utilization of the present invention will become more fully apparent from the description of the preferred embodiments taken in conjunction with the accompanying drawings, in which: Fig. 1 is a pictorial showing of a rotary tool holder and self-gripping, shoulder equipped cutting inserts; Fig. 2 is a portion of the rotary tool holder of Fig. 1 wherein one embodiment of the geometrical configuration of the interacting recess and cutting insert are shown; Fig. 3 is a pictorial showing of a portion of the rotary tool of Fig. 1 with yet another geometrical configuration shown; Fig. 4 is a stationary tool holder using the "self-grip" configuration having a shoulder equipped cutting insert; Figs. 5, 6 and 7 show different chip control configurations that can be used with the inventive system; and Figs. 8 and 9 show the use of spring-like detents in the recesses of the rotary tool holder and a matching groove in the shoulder equipped insert for receiving the detent. General Description The cutting tool 11 shown in Fig. 1 includes a rotary tool holder 12 having a centrally disposed mounting aperture 13. Peripherally mounted are shown a plurality of cutting inserts such as insert 14. The cutting inserts are configured to be held in the holder in cooperation with the shape of the recess 16 without any clamping means. It is noted that the cutting insert 14 has a shoulder 17 which abuts against portion or top jaw 18 of the recess 16. Angularly disposed from top jaw 18 is a bottom jaw 19. At the rear of the recess 16, there is an aperture, such as aperture 21 for use in removing the inserts. In the partial view of Fig. 2 the recess 16 is shown as being defined by the jaws 18 and 19 which have clamping surfaces 23 and 24 respectively. The surfaces 23 and 24 are shown as having inverted V shapes. The front portion 26 of the top jaw 18 also has a characterized shape as shown as an inserted V shape with the apex extending outwardly. Surface 26 is the shoulder abutting surface of the holder. The cutting insert 14 also is shown as including a pair of substantially planar side walls 14a, a cutting edge 27, a top clamping surface 28, a bottom clamping surface 29 a relief surface 30 defined between a pair of leading edges of the side walls 14a, and between a leading extremity of the bottom clamping surface 29 and the cutting edge 27, and a holder abutting characterized surface 31. In this cas it is a V shaped surface with the apex of the V jutting inwardly so that the shoulder 17 of insert 12 abuts with the shoulder abutting surface 26. Similarly the top and bottom jaws clamping surfaces 28 and 29 are characterized to match the surfaces 23 and 24. Thus those surfaces also are V shaped with the apex of the V inclined inwardly. The insert is also shown with means 32 for controlling the shape of the chips generated during the cutting operation. More particularly, upwardly protruding sections 33 and 34 are shown slightly removed from the cutting edge 27 and at the side boundaries of the top surface of the cutting insert. In Fig. 3 the system is very similar to that shown in Fig. 3 with the exception that the surfaces 36 and 37 of the jaws are each shown as having the apex of the V inclined inwardly. Ths shoulder abutting surface 42 is also shown as an inverted V, that is a V with the apex inclined inwardly. The holder abutting surface 41 on the cutting insert 14 is an inverted V with the apex inclined outwardly. Different shapes can be used at the abutting surfaces within the scope of the invention. The key thing is that the shapes conform one to the other and aid in stabilizing the insert. The shoulder also assures that the cutting depth is precise. It should be understood that while Figs. 1 to 3 are concerned with a rotary tool system, the system is just as effective in stationary tools. In Fig. 4 the stationary tool system 46 is shown. The sytem includes the tool machine shown only in part as 47 and 48 into which is clamped a tool holder 49 by clamp means 51 actuated by clamping screw 52, for example. One end of the tool holder includes a recess defined by top jaw 53 and bottom jaw 54. An aperture 56 is also included for use in removing a cutting insert such as insert 14. The abutting surfaces of the insert conform to the jaw surfaces of the tool holder 49. The insert 14 includes a shoulder 17 having a characterized shape shown as holder abutting surface 31 which matches with shoulder abutting surface 58 on the holder. The insert 14 is shown as having a cutting edge 27 and it is shown without any chip control means. It should be understood that the chip control means can also be used with the stationary tool systems shown in Fig. 4. Within the confines of the present invention it is possible to use different chip control configurations. These different configurations are shown in Figs. 5, 6 and 7. The shape of the chip determined by the respective configurations is shown in the three figures generally strengthen the chip by putting a stress on the chip and narrow the width of the chip. The narrower width is particularly pointed out in Fig. 7a which shows the chip within the groove being cut. Fig. 5 is very similar to the showing of the inserts of Figs. 2 and 3 where there are a pair of protrusions 33 and 34 spaced apart from each other on both sides of the cutting surface of the insert 14. The cutting edge 27 is slightly in front of the protusions. This assures that the protrusions which are spaced back from the cutting edge control the chip shape after the cuts but while the chip is still hot and maleable. In Fig. 6 the insert cutting edge 27 has a chip control protrusion 61 which is slightly removed by space 63 from the cutting edge. It is located approximately in the middle of the top surface 62 of the cutting insert 14 The configuration of Fig. 6 generates a spine down to the middle of the chip and thereby rigidizes the chip and also decreases the width of the chip. The showing of the cutting insert 14 in Fig. 7 also shows a shoulder 17 such as shown in Fig. 2. Therein the shoulder 17 is shown as having a characterized holder abutting surface 31 which is V shaped having the apex on the inward side of the V. The chip control configuration includes a protruding central rib 61 and two small side protrusions 64 and 66. The protrusions are also all three slightly removed from the cutting edge 27. Means are provided for assuring that even under the worst conditions the insert 14 is not inadvertently removed from between the jaws. More particularly a spring detent 68 shown in Fig. 8a fits into a groove such as groove 69 in insert 14 shown in Fig. 9a. The detent extends in Fig. 8a from the top jaw surface. Similarly a detent 71 is shown extending from the bottom jaw surface of a rotary holder. The groove 72 in Fig. 9b receives the detent. It should be understood that while Figs. 8a and 8b show a rotary tool holder the same principle is applied to the stationary tool holder and as a matter of fact the detent and groove arrangement are shown at 76 in Fig. 4. The shape of the groove and the meshing spring detent are such that the detent groove arrangement has no bearing on the location of the insert. When the insert is being forced out, the detent and the groove cooperate to resist the removal of the insert. The tool system provided assures that the insert will only go into the recess defined by the jaws up to the shoulder. This maintains the spacing between the cutting edge and the holder constant and thus enables precision machining with a "self-gripping" type insert. The insert is placed into the recess in either a rotary tool or a straight tool holder and the machining forces push the insert into the recess until the shoulder abuts the holder. The angle of the recess is generally smaller than used in holders for inserts without shoulders. It is retained and maintained in a stable position and the geometrical configuration is such that the shoulder abuts the holder without undue stresses being placed on the holder by the wedge-shape of the insert even when the tolerances of the system are at their extremes. Up to this present system, tool engineers have refrained from using shoulders on "self-grip" tool holder systems. The shoulders are after all contrary to the logic of such systems. "Self-grip" or "wedge-shaped" tool holder systems depend on an equilibrium of forces for retaining the tool insert in the recess of the holder without fracturing the holder. The force P resulting from the action of the cutting surface and the work piece must be at least equal to the sum of: 1) the vector force R resulting from the resilient forces acting normal to the clamping surfaces of the insert tending to force the insert out of the recess and 2) the friction force F between the clamping surfaces and the jaw-resisting movement of the insert. The force R increases as the insert is forced deeper into the recess and therefore at some point before fracture of the tool holder the forces must reach equilibrium so that the cutting can be accomplished. The forces R and F are both trigonometrical functions of the wedge angle (sine and tangent respectively). It is known that a smaller wedge angle gives more effective grip by the jaws. The smaller angle however, also increases the strain tending to fracture the holder about the recess. Thus too small an angle can result in fracturing the holder. Also the smaller angle enables further longitudinal movement of the insert in the recess. It was thought that a shoulder on the insert would tend to prevent the insert from being forced into a holder to the equilibrium point or else the equilibrium point would be reached prior to the shoulder abutting the holder. in either case the shoulder, it was thought, would not enable precision work. Thus shoulders have not been used in the prior art and the problem of using "self-grip" systems for precision work remained. The problem is solved in the present system by using smaller wedge angles (6°-12° on this system compared to 8°-15° on the prior systems) which enables smaller forces to move the insert into the holder up to the shoulder. At the same time the shoulder prevents the insert from being driven into the recess far enough to fracture the holder. The system is designed to take into account the tolerances so that at the minimum height of the insert the friction force F is sufficient to at least equal the force R to hold the insert in its place. Also at the maximum size of the insert and minimum size of the recess the angle is such that the insert does not exert a fracturing force on the holder. The force P is countered by the shoulder. Thus the system insures that the insert is self-gripped, the shoulder abuts the holder, and the system can be used for precision slotting. Another advantage provided by the system is that the cutting edge of the insert can be aligned with the top surface or upper face of the holder. Thus the possibility of collision between the chip and the holder is practically non-existent. While the principles of the invention have been described above in connection with specified apparatus and applications, it is to be understood that this description is made by way of example only and not as a limitation on the scope of the invention.

Claims: A cutting tool assembly comprising: a tool holder (12, 4,9), a pair of rigid gripping jaws (18, 19) formed integrally as one piece in an edge portion of said tool holder; a pair of longitudinally directed jaw edges (23, 24, 63, 54) which are directed at an acute angle to each other and which define between them an open-ended wedge-shaped recess (16) of said holder which opens out towards the edge of the tool holder; a cutting insert (14) having a pair of substantially planar side walls (14a), first and second (a pair) longitudinally directed insert edges acting as clamping surfaces (28, 29) respectively defined between adjacent pairs of edges of said planar side walls (14a) and which are disposed at an acute angle to each other so that the first clamping surface has one end where it is relatively further from the second clamping surface than it is at its opposite end whereby said clamping surfaces define a wedge-shaped body portion of said insert; a leading relief surface (30)) of the insert defined between a pair of leading edges of said side walls (14a) and between a leading extremity of said second clamping surface (29) and a cutting edge (27) formed on a leading end of the insert adjacent a wider end of the body portion, an opposite rear end of said insert being formed adjacent a narrower end of said body portion; and chip shaping means (33, 34) formed adjacent to said cutting edge (27); said insert (14) being inserted into said recess (16) and being frictionally retained between said jaws as a consequent a relative resilient outwardly directed displacement of said jaws (18, 19), resilient displacement of said jaws being maintained during the entire frictional retention of the insert (14) in the recess (16); characterised in that an abutment shoulder (31) is formed adjacent to said one end of the first (28) of said clamping surfaces (28, 29) so that, when the insert (14) is inserted into the recess (16) to a predetermined extent and is frictionally retained therein with said insert (14) frictionally engaging said jaw edges (23, 24, 53, 54), said abutment shoulder (31) abuts an exposed end (26) of one of said jaws so as to limit the extent of insertion of said insert into said recess. A cutting tool assembly as claimed in claim 1 characterised in that said tool holder is a rotary tool holder (12). A cutting tool assembly as claimed in claim 1 characterised in that said tool holder is a stationary tool holder (49). A cutting tool assembly as claimed in any preceding claim characterised in that means (68, 69, 76) are provided for ensuring that said insert (14) is not inadvertently removed from said recess. A cutting tool assembly as claimed in claim 4, characterised in that said means for ensuring that the insert (14) is not inadvertently removed comprises spring detent means (68). A cutting tool assembly as claimed in claim 5 characterised in that groove means (69) are provided in said cutting insert (14) for receiving said spring detent means (68). A cutting tool assembly as claimed in any preceding claim characterised in that said angle is between six and fifteen degree inclusive. A cutting tool assembly as claimed in any preceding claim characterised in at said cutting insert (14) has top cutting surface means (32) including said chip shaping means (33, 34), clearance side means extending from said top cutting surface means, a cutting edge (27) formed at the junctures of said top cutting surface means (32) and said clearance side means, land surface means between said cutting edge means and said chip shaping means, and said chip shaping means comprising rib means (33, 34) on said top cutting surface means extending from said land surface means longitudinally away from said cutting edge (27). A cutting tool assembly as claimed in claim 8 characterised in that said rib means comprises a pair of oppositely disposed spaced apart ribs (34). A cutting tool assembly as claimed in claim 9 characterised in that said rib means comprises single rib means (61) between opposite sides of said top cutting surface means. A cutting tool assembly as claimed in claim 8 characterised in that said rib means comprises a pair of oppositely disposed spaced apart side ribs (64, 66) and a central rib (61) between said side ribs. A cutting tool assembly as claimed in any preceding claim wherein said top and bottom jaws (18, 19) and said top and bottom clamping surfaces (28, 29) have meshing concave and convex surfaces (23, 24; 28, 29 respectively). A cutting tool assembly as claimed in any preceding claim characterised in that said shoulder (31) and recess (16) are adapted to maintain the cutting edge of the insert (14) aligned with the top surface of said holder (12). Use of a cutting insert in a cutting tool assembly as claimed in claim 1, the said cutting insert (14) having two separate longitudinally directed clamping surfaces (28,29) which are disposed at an acute angle to each other so that each of them has one end where it is relatively further from the other clamping surface than it is at its opposite end, the insert (14) having a pair of substantially planar side walls (14 a ), a cutting edge (27) which is remote from the said opposite ends of the clamping surfaces (28,29), and chip shaping means (33,34) adjacent to the cutting edge (27), characterised in that an abutment shoulder (17) is formed on and adjacent to the said one end of one (28) of said clamping surfaces (28,29) and protrudes therefrom.

Inventors: PANO, JOSEPH
Applicants: ISCAR LTD.
Application year: 1982
Main classification: B23B27
IPC codes: B23B27, B23D13, B23D61, B23C5