Indexable cutting insert and holder therefor

The present invention relates to a turning insert for milling heads, with two mutually parallel chip surfaces with the same geometric shape, and perpendicular thereto two clearing surfaces forming side surfaces, which with the chip surfaces form the main edges, at each end of the insert between the two side surfaces two uniform end clearing surfaces. in relation to the intermediate center plane of the chip surfaces inclined as much in the opposite direction ooh as with each chip surface forming a side edge, the end of the clearing surfaces with the chip surfaces forming a shorter and a longer edge, the shorter edge forming side edges.

Such tools are known from DT-OS 1 552 544, wherein the main edges and the side edges of the inserts are arranged so that the chips generated by the tool roll upwards outwards from the work surface, which has a favorable effect on the work by removing the chips from the workpiece the shortest way.

However, the known device has the disadvantage that the same main edges and side edges on the inserts are always in the working position, so that in order to maintain the performance they often have to be sharpened. Due to the complicated position of the edges, the grinding of such face mills is cumbersome and time consuming. Depending on the lifespan of the edges

7110492-1 natural limits the life of the cutter is between two grindings in an unfavorable relation to the time of a grinding.

An object of the invention is to remove the disadvantages of the known cutters by finding such a shape on the milling head and the inserts clamped therein that the service life of the cutter between the grinding times is increased several times. By using so-called indexable inserts, the invention is characterized mainly in that the geometric basic shape of the indexable insert is a parallel epiped, whose cross section has a greater height than width, and whose longitudinal edges form the main edges and narrow sides of the chip surfaces. This design of the inserts makes it possible to insert four different main edges into the cutter one after the other without the need for grinding.

Suitably, the end flap surfaces enclose end surfaces forming between them from the parallelepiped shape. The advantage of this is a side surface running through, a center hole arranged at right angles to them for receiving a fastening screw, which can be screwed into a threaded hole in the milling head.

The invention is described below with reference to the accompanying drawings, in which Fig. 1 is a view obliquely from above of an end face cutter with indexable inserts according to the invention, one of the inserts being removed from its position, Fig. 2 a perspective view on a larger scale of an insert, Fig. 5 a section along the line III - III in Fig. 2, Fig. 4 is a partial view of Fig. 1 seen from above, Fig. 5 is a side view of the portion V - 7 in Fig. 4, Fig. 6 is a section along the line VI - VI in Fig. 5 and Fig. 7 is a partial view of the cutter and a workpiece along the line VII - VII in Fig. 5 when milling a workpiece, the cutter being inverted in relation to the positions according to Figs. 4 and 5.

In the cutter, the inserts 15 are inclined at an angle b to the milling plane in radially outwardly inclined cutting positions in the rotatable milling head 10. The inserts can. of course also used on cutters of other kinds. The inserts are inserted in the cutting positions 9 on the milling head at equal angular distances along the periphery, so that when rotating around the shaft 11 and setting against the workpiece each insert loosens a chip and all the inserts together leave a smooth working surface. Each insert is designed as a flat, substantially rectangular prism of suitable material, eg tungsten carbide, with two parallel side surfaces 16 and 17 and parallel upper surface 18 and lower surface 19. In the embodiment according to Figs. 1, 2, 4 and 5, the side surfaces 16 and 17 perpendicular to the upper surface 18 and the lower surface 19, and on the short ends of the insert different inclined, preferably flat end clearance surfaces 21 and 22 are arranged.

The intersection between the upper surface 18 and the side surfaces 16 and 17 forms the main edges 23 and 24, and the intersection between the lower surface 19 and the side surfaces 16 and 17 forms main edges 25 and 26. The surface areas 23a and 24a adjacent to the edges (Fig. 2) to the upper surface 18 form the

7110492-1 actual chip surfaces after the main edges, and corresponding chip surfaces 25a and 26a are formed along the main edges 25 and 26 to the lower surface 19. Each insert thus has four different main edges 25 - 26, which depending on their wear can be inserted in position in the milling head 10. For each and one of these main edges forms the connecting areas on the side surfaces 16 and 17 when the cutting positions 9 in the milling head are correctly arranged, the clearance of the working main edge required for a correct work of the milling cutter.

According to the most characteristic feature of the invention, the end clearance surfaces 21 and 22 on the short ends of the insert are separated from each other by end surfaces 27 and 28, which are perpendicular to both the side surfaces 16 and 17 and to the chip surfaces 18 and 19, but run approximately diagonally so that the end clearance surfaces 21 and 22 a trapezoidal shape. A slightly shorter edge, which is formed at the intersection between the end release surface 21 and the lower surface 19, gives a side edge 29 to the main edge 25 and adjoins it at an obtuse angle in the tip 50. The second end release surface 22 gives at the intersection with the upper surface 18 a side edge 52 and forms with the main edge a tip 55. The main edge 24 with its side edge 52 thus lies diagonally obliquely against the main edge 25 with its side edge 29. In the same way the end surface 28 25 and the side edge 29 of the main edge 25.

To form the clearance required for milling behind the side edges 29 and 52, the end release surfaces 21 and 22 are inclined inwards, so that the edges 54 and 55 of the trapezoidal side surfaces are longer than the side edges.

The inserts 15 according to the described embodiment are fixed in the cutting positions 9 in the milling head 10, each cutting position having a base surface 56 and two side walls 57 and 5 placed at an angle thereto and opposite each other. a chip space 59 formed. The side walls 57 and 58 are flat, the wall 57 being perpendicular to the base surface 56 approximately in the radial plane of the milling head, while the side wall 58 is perpendicular to the base surface and partly to the wall 57. The three surfaces together form directional surfaces for the inserts 15, which are clamped down and in the clamped position, the end surface 27 abuts the side wall 58 and the lower surface 19 against the side wall 57.

In this clamping position on the insert 15 shown in Fig. 1, the rear, upper main edge 24 lies above the upper edge of the side wall 57 », while the rear, lower main edge 26, which rests on the base surface 56, lies freely against a groove 42 in the side wall 57. This avoids that the currently not working edge can be accidentally damaged.

Mounting of the indexable inserts 15 in the milling head 10 takes place as follows.

In each base surface 56, a threaded hole 45a is provided; whose axis 46 is inclined at an angle c to the base surface. In this hole the screw 41 is threaded through the hole 45 of the insert 15, which goes perpendicular to the side surfaces 16 of the insert and

7110492-1 and has a recess 44 on each side of the screw head 43. When threading the screw with a tool fitting in a driver 43a in the screw, the screw bends as soon as the conical head 43 penetrates the recess 44 in the insert, as shown in Fig. 6, the sides of the insert being pressed against the side walls 37 and 38 and against the base surface 36. When the screw head 43 is completely penetrated into the recess 44, the upper surface of the screw is lower than the side surface 16 or 17 of the insert and holds the insert with great force and in a precise working position at the cutting position 9.

Of course, the insert 15 can be attached in another way as long as it is ensured that it rests well against the surfaces 36, 37 and 38.

Figs. 1 and 7 show how the inserts 15 are so clamped that their main edges, for example 23 according to Figs. 1, 5 and 6, always tilt the angle b towards the plane of rotation. The base surface 36 is inclined backwards in the rotation direction so much that the active main edge, in this case 23, has a larger radius of rotation within the area a than all other edges in this area. As a result, the surface area 25a of the edge 23a on the insert has a negative rake angle but acts through the slope b with a positive slope and stress, so that the chips cut by the main edges curl outwards, ie away from the working surface. Release and rake angles for the main edges 23 - 26 inserted in the working position in the inserts depend on the desired angle b and on the material in the workpiece and in the milling head. Due to the conformal shape, the edges have positive values ​​that are best suited for the milling work.

Since all four edges of the inserts are equally placed in the milling head, it is clear that the same working result is obtained after each edge and insert change. For replacements, it is only necessary to loosen the screw that holds the insert, and after turning or replacing the insert, tighten again with the screw.

All edges of the inserts 15 can be sharpened without changing the overall width and length. The side edges 29 and 32 are sharpened only by grinding the trapezoidal end release surface 21 and 22. For sharpening the main edges 23 - 26, it is only necessary to grind the adjacent surface areas 23a - 26a of the chip surfaces 18 and 19.