TOOL HOLDER FOR CUTTING INSERTS

Abstract: The invention concerns an arrangement for fastening cutting inserts (1) on a holder (2) for the chip forming machining of metals. The bottom surfaces of the inserts include one or more grooves (3), which extend mainly in the longitudinal direction of the holder and/or substantially at right angles to the axis of rotation of the workpiece. The holding surfaces of the holder (5) are designed with one or more corresponding ribs (7), which are intended to engage in the said grooves (3). The underside of the insert features primary support surfaces (10) which extend substantially at right angle to the said grooves and the holder features secondary contact surfaces (11) which extend substantially at right angles to the ribs, whereby the primary support surfaces are brought into engagement with the secondary support surfaces. Hence enabling the insert to withstand radial forces.

Description: Tool Holder for Cutting Inserts The present invention relates to an arrangement for the fastening of cutting inserts for the chip forming machining of metals. Different cutting inserts and indexable inserts are fastened on tool holders in several different known ways. One of the most common is that the insert has a central through hole and that the insert pocket in the holder has a threaded hole. A locking screw is inserted into the centre hole of the insert and is screwed into the hole in the holder with a suitable torque, a shim with a centre hole is often placed between the insert and the bottom support surface. Usually, the insert pocket also comprises two internal, substantially perpendicular abutment surfaces, or three abutment points, for abutting against two of the insert ' s side surfaces. The disadvantage with this design is that a certain amount of play can easily occur after a period of use. A further drawback is that the screw can easily be tightened excessively, thereby damaging the screw or causing it to break. Other known insert holders have a clamp or similar fastening arrangement, which presses upon the upper surface of the insert in order to clamp it in the insert pocket. The clamping force can be regulated by a screw. Such designs may, for instance, be used to fasten cutting inserts which have no centre hole, which is the case for, among others, grooving and parting inserts. In order to avoid play and in general to attain a more stable fastening of a cutting insert, designs have been suggested according to which the lower surface of the cutting insert and the bottom support surface of the insert pocket have been formed as ribbed surfaces which are intended to match each other. Such designs are disclosed in US-A-2 140 941 and US-A-2 453 464. However, a drawback with these embodiments is that they necessitate a considerable amount of grinding of the ribbed surfaces of either the cutting insert or the holder, or both. A further drawback is that, even if the insert has been secured in a direction perpendicular to the ribs by means of a stop face behind the insert, a vertical play can occur just as easily with these designs as with those with two completely CONFIRMATION planar abutment surfaces, particularly in machining operations with a tendency to vibration. In addition there are a number of disadvantages associated with the use of a stop surface for the insert behind said insert. For example it is only possible to mount inserts which are precisely suited to the length in question. In addition the shape of such a stop surface must be adapted to the geometry of the insert. The said surface must not, for example, damage the cutting edge which is turned away from the workpiece. Furthermore such a stop surface can, to a certain extent, limit the accessibility of the insert and holder to the workpiece. A system for clamping inserts on a holder is described in WO-A-95/29026, which is so arranged that it includes parallel grooves on the underside of the insert and ribs on the holder, whereby the ribs fit into the grooves. The insert is screwed fast in the holder, whereby a wedge action is created between the ribs and grooves. This wedge action and the friction between the flank surfaces of the ribs and grooves stabilize the insert even to a significant degree in a radial direction, but when cutting forces are large this clamping action is not entirely reliable, and for this reason a rear stop surface must be utilized on occassions. Thus a primary object of the present invention is to design a clamping system comprising an insert and a holder so that the use of a rear stop surface can be avoided. A secondary object of the present invention is to design a clamping system in such a way that, the same holder can receive several inserts with different basic geometries. A third object of the invention is to optimize the accessibily of the insert and holder with regard to the workpiece. A further object of the invention is to design a clamping system which can in an optimal manner absorb both radial and axial cutting forces. These and other objects have been achieved by designing a clamping system which features those characteristics which are given in claim 1 . In order to clarify but in no way limit the invention it will now be described in more detail with reference to the attached drawings. These are presented in short here: Figure 1 shows an insert and a holder in accordance with the invention, shown straight from above. Figure 2 shows an insert and holder according to fig. 1 straight from the side. Figure 3 shows a holder according to figs. 1 and 2 separately without insert, in perspective obliquely from above. Figure 4 shows the holder according to fig. 3 straight from above. Figure 5 shows the holder according to fig. 3 straight from the side Figure 6 shows an insert in accordance with the invention, in perspective obliquely from below. Figure 7 shows the insert according to fig 6, straight from below. Figure 8 shows the insert according to fig. 6, straight from the side Figure 9 shows another insert according to the invention, straight from above. In figs. 1 and 2 an insert is designated in general by 1 and a holder in general by 2. The cutting insert is in most cases manufactured in coated or uncoated cemented carbide. The geometry of the cutting insert ' s basic shape is not an essential characterization of the invention, not least of all because one of the main aims with the invention is that different inserts can be assembled in the same holder. Thus the insert according to figs. 6-8 represents an implementation of the invention. Characteristic for all the cutting inserts according to the invention is however, that they feature one or several grooves 3, the flank sides 3a, 3b, of which act as contact surfaces for the flank surfaces 7a,7b, on an equivalent number of ribs 7. The said grooves run mainly in the longitudinal direction of the holder 2, and/or mainly perpendicular to the workpiece ' s axis of rotation. In fig. 6 an insert is shown with only one groove 3, but the insert can even have several grooves (and the holder an equivalent number of ribs), in accordance with the above mentioned patent publication WO-A-95/29026, which is herewith incorporated into this patent application by means of this reference. A substantially planar surface 4, connects to the two sides of the said grooves, which when in the assembled condition form an air surface, since a gap "s" (see figs. 1 and 2) then exists between the surface 4, and the opposite, substantially planar bottom surface 5, in the holder. The gap "s" can suitably be between 0,02 and 0,03mm. The planar surface 4, is bordered by, among things, four flanks 6, which extend mainly parallel to the grooves 3. In the same way as the flank surfaces of the grooves 3a, 3b, these flank surfaces 6, also act as support surfaces for the equivalent support surfaces 8, in the insert holder, which later form flank surfaces for the raised parts 9a, 9b, in the holder. When the insert is mounted, it will consequently only rest against the flank surfaces 7a, 7b, and 8, of the holder. No contact occurs between the the tops of the ribs and the bottoms of the grooves as represented by gap "t" in figure 1 . Suitable values for the angle of the flank surfaces 7a, 7b, (respectively 3a, 3b,) relative to the bottom surface are to be found between 50° and 70°, preferably between 55 and 65 . Accordingly, since the insert only rests on the flanks 7a, 7b and 8, a clamping wedge function between the ribs and grooves becomes possible. In addition the slight surface roughness of the direct pressed ribs has a positive effect on the clamping function. An important characteristic of the invention in question is however the aim to ensure definitely and constantly that the insert is not displaced in a radial direction which is achieved by arranging flank or support surfaces 10, which are substantially aligned axially to the workpiece plus substantially perpendicular to the grooves 3. The support surfaces 10, are intended to lie against the opposite surfaces 1 1 , in the tool holder. The matching surfaces 1 1 , equivalent support surfaces 12, on the raised part 9b, are however not intended to function as support surfaces, which is illustrated by the gap "u" in figure 2. The width of the flanks 10 which is limited by the proturbence of the planar surface 4, is accordingly somewhat narrower than the equivalent groove between flank surfaces 1 1 and 12. A suitable value for the gap "u " is between 0,05 and 1 mm. The insert illustrated in figs. 6-8 features two operative cutting edges 1 3. After a cutting edge has been worn out the insert can be loosened and turned half a revolution in order to index forward the other cutting edge. The insert is clamped in the holder with the help of a locking screw which is not shown, which is fed through the smooth hole 14, and is screwed tight into the threaded hole 1 5, in the holder. When the insert is indexed, its other two flanks 10, will act as support surfaces against the holder ' s support surfaces 1 1 . As can be seen from figs. 3 and 4, the threaded hole 15, in the holder is positioned in line with the rib 7. The reason for placing the hole on a rib instead of, for example, between two ribs, is naturally because the insert could break if it was exposed to a force between the two support lines. In cases where the insert has several ribs 7, in order to impart a symmetrical clamping force on the insert on both sides of the central rib, the insert and holder are designed with an uneven number of grooves and ribs. In order to improve the cutting economy when machining with inserts according to this invention they can also have a design with four operative cutting edges 1 3, as shown in fig. 9. This insert can rest against the holder as shown in figs. 3-5 in the same way as the insert as shown in figs. 6-8. The one groove 3, will accept the rib 7, of the holder, whilst the groove 3 " , which is at right angles to this groove will be empty and open against the bottom surface 5. A couple of the flank surfaces 10, (e.g. those maked 10, in fig. 9.) will function as support surfaces against the support surfaces 1 1 , of the holder, whilst the four flank surfaces 6, will act as support surfaces against surfaces 8, of the insert holder. When the insert is indexed a quarter turn, surfaces 6, and 10, will change places with each other and groove 3 ' will accept rib 7. A number of advantages have been obtained via the axially aligned, interactive support surfaces 10 and 1 1 . The size and shape of different inserts need not have an influence on the design of the holder since the holder need not include a rear support surface for the insert. In other words one obtains a greater degree of freedom when designing an insert. With these inserts it can also be difficult to design a functionally acceptable support surface, for example because of the different radial reliefs. In addition the holders can be given a more pliant and slimmer design, without any abutment surfaces behind the insert. As has been mentioned above, an insert according to the invention in question is well equipped to absorb both axial and radial forces. Bearing this in mind, it should be pointed out finally that advantage can be taken of this by designing double functional inserts in accordance with figs. 6-8. Because of the straight front edge 1 3, on these inserts and the curved side edges 16, which border it on both sides this insert can be used for facing and even for axial copying, plus use for the turning of radii. Hence a large number of different contours can be generated.

Claims: CLAIMS 1 ) An arrangement for the fastening of a cutting insert (1 ) on an insert holder (2) for the chip forming machining of metal, whereby the bottom surface of the insert incorporates one or several grooves (3), which extend substantially in the longitudinal direction of the holder and/or substantially at right angles to the workpieces axis of rotation, and the holding surface (5) of the holder is formed with one or several equivalent ribs (7), which are intended to fit into the said grooves (3), characterized in, that the underside of the insert even features primary support surfaces (10) which are substantially at right angles to said grooves and the holder features secondary support surfaces (1 1 ) which are substantially at right angles to the said ribs, whereby the first support surfaces are brought to rest against the secondary support surfaces, thereby making the insert well able to withstand radial cutting forces. 2. An arrangement according to claim 1 , wherein the underside of the insert apart from one or several grooves (3) even features side flank surfaces (6), which are substantially parallel to the said grooves and which are intended to rest against the equivalent side flank surfaces (8) on the holder. 3. An arrangement according to claims 1 and 2, whereby the insert rests in the holder only against the flank surfaces (3a, 3b) of said grooves and on the said side flanks (6). 4. An arrangement according to any of the above claims wherein the flanks of the ribs and grooves (3a, 3b, 7a, 7b) plus even the surfaces of the side flanks (6, 8) feature an angle between the holder surface on the holder of between 50° and 70°. 5. An arrangement according to any of the above claims wherein the cutting insert even features one or several other grooves (3 ), which are substantially at right angles to the said grooves (9). 6. An insert for chip forming metal machining including a bottom surface which is formed with one or several mutually, substantially parallel grooves (3), characterized in, that the bottom surface also includes flank surfaces (10) which are substantially at right angles to the said grooves (3), which said flank surfaces are intended to rest against the equivalent flank surfaces on the holder in order to insure that the insert can withstand radial forces. 7. An insert according to claim 6, which even includes one or more additional grooves (3 Λ ) which are substantially at right angles to the said grooves (fig. 9).

Inventors: LARSSON BERNT, LARSSON, BERNT
Applicants: SANDVIK AB, SANDVIK AKTIEBOLAG (PUBL)
Application year: 1998
Main classification: B23B27
IPC codes: B23B27