Milling cutter and cartridge therefor

The present invention relates to a milling cutter for chip machining of metal workpieces and a cartridge therefor. The milling cutter comprises a milling cutter body rotatable about its longitudinal axis and a plurality of insert-­equipped cartridges mounted around the periphery thereof. Each cartridge is located in a recess in the periphery of said milling cutter body. The cartridge is intended to be secured in said recess by suitable clamping means.

A milling cutter of the aforesaid type is disclosed in DE-A1-3125185 wherein each cartridge is adjustable radially and axially by wedge means. Two wedge means are associated with each cartridge. A screw which extends through the cartridge and into the milling cutter body is arranged to absorb the forces caused by said cartridge and by wedge means during the rotation of the milling cutter. During the milling operation a higher rotation speed is applied which may result in an out-hurling force of 200 kg applied upon a body of for instance 30 g. This means that the screw that is holding the cartridge and the wedge will be subjected to large bending moments during the milling operation. The risk for tool failure will increase with increased usage time. Further, there is a risk that the adjustment of the insert in the cartridge might be changed during a working operation. Also, it becomes less economical and more complicated to arrange a wedge arrangement for each cartridge.

The present invention aims to provide a solution to the above related problems.

The invention will now be described more in detail with reference to the attached drawings.

• Fig. 1 shows one embodiment of a milling cutter body according to this invention as seen in a perspective view.
• Fig. 2 shows a plan view of the milling cutter shown in Fig. 1
• Fig. 3 shows a side view of the milling cutter shown in Fig. 1
• Fig. 4 shows a cross-section along the line IV-IV in Fig. 3.
• Fig. 5-7 show a cartridge designed according to this invention as seen in plan view, in side view and in end view respectively.
• Fig. 8 shows a partial view of the milling cutter shown in Fig. 1.
• Fig. 9 shows an alternative embodiment of the milling cutter of the invention.
• Fig. 10 shows a perspective view of the milling cutter of Fig. 1.

Fig. 1 to 4 show a milling cutter body 10 having a multiplicity of peripheral recesses 11 for the receipt of insert-equipped cartridges. The milling cutter body is arranged to rotate around the central axis CL in the direction R. The recesses 11 are evenly distributed around the periphery of the body 10; in this case there are four of them. Each recess consists of a rear supporting surface 12, as seen in rotary direction R, and a forwardly located support surface 13 which are connected by a substandially partly cylindrically shaped recess 14. This recess 14 can alternatively have other shapes, for instance oval shape, rectangular shape or other.

The support surfaces 12 and 13 are essentially planar and parallel. In the preferred embodiment of the invention these surfaces 12 and 13 are inclined also in relation to the central axis CL. The rear support surface 12 as well as the recess 14 extend from the underneath side 10A of the milling cutter body at least to an upper shelf 10B of said cutter body. The recess 14 is approximately perpendicularly oriented in relation to the underneath side 10A of the milling cutter. The forwardly located support surface 13 has a shorter dimension in the axial direction of the milling cutter than the rear support surface 12. The forwardly located support surface 13 is arranged on one or several arms 15 that are integral with the milling cutter body 10; in this case two of them are arranged. The support surface 13 is connected forwardly, in the rotary direction R, to a concave chip space 16 via a protruding end face portion 17. Each arm 15 is provided with a recessed smoothly curved portion 18 proximate the underneath side 10A of the milling cutter in order to facilitate chip removal.

Two holes 19 and 20 are provided in the arms 15 and in said rear support surface 12 whilst each bore being oriented along a common centre line therein, said centre line preferably being oriented perpendicularly to the rear support surface 12. This centre line can alternatively be oriented at an obtuse or acute angle from said support surface 12. The hole 20 in said arm is non-threaded and extends forwardly into a recessed portion 21 in said chip space 16 via a plane shoulder 22. The arms 15 are separated from each other by means of a slot 30. The shoulders 22 are mainly plane parallel in relation to the support surface 13. The recess 21 is arranged for the purpose of facilitating chip removal and the mounting of the cutter. The holes 19 provided in the rear support surface 12 are threaded. The smallest thickness t of the arm 15, measured between the chip space 16 and the recess 14 (Fig. 8) is less than the smallest distance a between the support surfaces 12 and 13. The distance a is substantially smaller than the diameter of recess 14. The inner angle between the forwardly located support surface 13 and the chip space 16 around the end face portion 17 is max 10 degrees. The forwardly located support surface 13 is mainly parallel with the shoulder 22.

In Fig. 5-7 is shown an insert-equipped cartridge 23 designed to be attached to the above described milling cutter body. A cutting insert 24 is located in a seat in the cartridge by means of a screw. The insert could be made of cemented carbide, ceramics or any other type of hard metal which comprises a body with one or several tips with cutting edges of diamond or cubic boron nitride. The cartridge 23 has a plane edge surface 25 which is provided as an abutment surface for an adjustment device. The cartridge has two non-­threaded holes 26 for the receipt of thread sections. The cartridge is preferably made of steel and includes a number of clearance faces for avoiding occurrence of traces from the workpiece during the milling operation. The cartridge has a rear surface 27 and a front surface 28 which are planar and parallel. The holes 26 are mainly oriented perpendicularly from the surfaces 27, 28. The cartridge 23 can be made of steel, directly pressed from powder material or ground from a steel blank. Instead of designing the insert 24 as aforesaid one corner might be made of ceramics, cubic boron nitride or diamond and being brazed on to the cartridge or sintered into the latter.

The forwardly located support surface of the milling cutter can alternatively be inclined in relation to the rear support surface 12 as shown in Fig. 9 which shows a cross section between the arms 15. In one case the support surfaces 12 and 13′ diverge radially outwardly as shown in enlarged scale whereby a more evenly distributed clamping force can be exerted on the plane parallel cartridge. In that case the angle β obtained is 1° or less. In the other case the surface 12 and 13˝ converge radially outwards as shown in enlarged scale and provide an angle δ of about 5° whereby the cartridge might be wedgingly clamped during mounting without assistance of the screws 29. The cartridge is at least partially wedge shaped whereby the nose of the wedge is directed radially outwards so that the resistance towards out-hurling can be improved. The mounting of the cartridge 23 in the milling cutter body 10 is described in the following by reference to primarily Fig. 8 and 10. The insert-equipped cartridge 23 is manually entered into the recess 11 along and proximate the recess 14 until the cartridge reaches an approximately correct position. The arms 15 could eventually be prestressed somewhat by means of the screws 29 in connection with the mounting of the cartridge so that the distance between the surfaces 12 and 13 decreases and so that the angle between these surfaces increases. The cartridge is thereafter pushed by hand radially outwards so that it wedgingly fits between the forward support surface 13 and the rear support surface 12. Thereafter an ajustment device (not shown) is inserted which brings about a wedging action from the underneath side in the recess 14 with the purpose of forcing the cartridge radially outwards so as to position and adjust the insert angularly. Another or the same adjustment device (not shown) will exert displacement of the cartridge axially to its desired position. When the cartridge has reached this position screws 29 are inserted in case the arm 15 is not prestressed through the holes 20 and 26 and threadably tightened into the bores 19 in the rear support surface 12. When each screw 29 is tightened the arm 15 is caused to clamp the cartridge firmly against the support surface 12. If, for some reason, the cartridge is being displaced before tightening the screw 29 the latter is loosened whereby the position of the cartridge can be adjusted due to the fact that the screw is located with a loose fit in the bore 26 of the cartridge. In the preferred embodiment the cartridge 23 is provided with two holes which improve the possibilities of reaching a stable and tilt-free clamping of the cartridge than compared with a cartridge having just one hole.

When dismounting the milling cutter the screw 29 is removed and the cartridge 23 is pushed inwards towards the recess 14 whereby the clamping pressure around the cartridge ceases and the cartridge is released. Alternatively the clamping pressure around the cartridge ceases entirely at the same time as the screw becomes loose whereby the cartridge can be dismounted. Hence, the invention relates to a milling cutter having recesses for the receipt of cartridges. The milling cutter lacks adjustment devices and the out-hurling force exerted to each cartridge can be minimized. The screw that exerts pressure from the arm towards the cartridge is supported on both sides of said cartridge and the screw can therefor not be bent. The radially inner surface of the cartridge is not in abutment with any other surface during the milling operation. In case it is not desirable to have a radially adjustable cartridge the cartridge 23′ might be designed for abutment against the recess 14 according to the dashed line 25′ in Fig. 8. The milling cutter is relatively cheap and simple to produce.