Side-milling cutter

[0001] The invention relates to a side-milling cutter for the chip-removal machining of cylindrical contours on a workpiece, especially of eccentrically disposed cylindrical contours on a workpiece rotatable about a longitudinal axis like a crankshaft, having a multiplicity of peripherally arranged cutting inserts on a disk-shaped tool carrier and inclined at an axial inclination angle, of which a part of the inserts are used for cheek and undercut machining and are radially clamped and another part of the inserts are used for pin outer diameter machining and are tangentially clamped on the tool carrier.

[0002] In WO 96/39269, a method for the chip-removal machining of cylindrical correctors and a device for carrying out this method are described. The cited method uses a so-called cut division in which, in the production of the final contour which can be to the final dimensions or can still have a certain amount to be removed and which can be taken off by grinding or polishing, tools are used which are fitted with cutting inserts disposed one after another or which can simultaneously engage with the workpiece. In the case of a crankshaft, the cheeks are machined and undercuts are formed and the pins of the crankshaft or the formation of a half crankshaft cheek control with an undercut or a diameter portion can be formed with a first tool and a second undercut and the remaining portion of the diameter with a second tool into which the machining is subdivided. The subdivision enables a variation of the bearing width within certain limits. Preferably the machining is carried out by so-called high speed milling in which the tool is driven with a constant high or variable speed. In high-speed milling, a cutting speed of more than 160 m/min is used. The chip thickness is in the range of 0.05 to 0.1 mm. The length of the tool carrier over which the corresponding cutting insert is engaged relative to its total length is selected to be as small as possible. With this feature, surface quality can be achieved that is so high that the preliminary grinding or additional pretreatment required prior to the heat treatment as additional process steps can be completely eliminated. With the method described in WO 96/39269 it was proposed to provide different tools with turning cutting plates for cheek machining on the one hand or for pin machining and for undercutting on the other. All of the cutting inserts used had positive rake angles whereby the cutting insert settings with respect to the workpiece were such that the effective rake angle varied between 5 and 15, preferably 5 to 5 and/or had a positive axial rake angle (back rake angle) up to 10.

[0003] In a there described special embodiment, a side-milling cutter had two types of cutting plates of which one type were radially clamped to the tool carrier and the second type were tangentially clamped to the tool carrier or tool receiver.

[0004] If the side-milling cutter has on its cylindrical peripheral surface two rows of tangentially clamped cutting plates disposed next to one another in the case of finishing inaccuracy or with a divided tool, a step can develop with position inaccuracies of the machine tool by means of which, in the overlap region of the machined workpiece an undesired sharp edged setback can arise. To prevent this over-cut, WO 96/39269 has proposed a cutting insert whose rake surfaces in the region of a cutting corner and the main cutting edge are beveled or set in a region extending over both neighboring main cutting edges. Such cutting inserts enable the formation of clean transitions in the overlap region, for example in the production of the pin surfaces of a crankshaft lifter pin.

[0005] In WO 96/39260, radially clamped cutting inserts have been illustrated for forming an undercut in a crankshaft.

[0006] In DE 197 39 300 A1, a cutting insert has been described for the cutting of structural shapes, especially for milling of profiled cuts in rotating workpieces like crankshafts. These cut inserts have a substantially cubical base body with at least two useful cutting edges, two mutually parallel, planar side faces traversed by a fastening bore, two base surfaces which at their opposite ends each form a cutting edge which has an arc shape corresponding to the profile to be cut and is bounded by a rake surface. The free surface between two opposite cutting edges should at least partly be formed as circularly concave. Because of the concave-free area configuration, there is a clearance angle enlargement and a greater clearance space open toward the middle of the clearance surface whereby a desired tilt of this cutting insert relative to the workpiece is enabled.

[0007] It is an object of the present invention to further develop a side-milling cutter of the type described at the outset so that softer cutting during machining is ensured.

[0008] This object is achieved with a side-milling cutter according to claim 1 or 3.

[0009] With the side-milling cutter according to claim 1, which additionally achieves the object of enabling the greatest possible number of cutting tools to be mounted on the provided cylindrical periphery of the side-milling cutter, the tangentially clamped cutting inserts are at an axial inclination angle of 2510, preferably at an inclination angle of 20 to 30. Seen opposite the mill rotation direction, the rearmost cutting corner of such a cutting insert lies at a straight line perpendicular to the direction of rotation of the side mill cutter which is spaced from the leading cutting edge of the subsequent radially clamped cutting insert by a distance of 5 mm, preferably 2 mm and extending into negative values.

[0010] With side mill cutters known from the state of the art, the setting of the axial angle is limited to small values in order to keep the spatial requirements of the tangentially clamped and preferably square rake surfaces on the cutting inserts on the periphery as small as possible since a tilting around an axial angle requires a respective spacing from the next following radially clamped cutting insert taking into consideration the enlarged rake chamber formed on the tool carrier. With the selected axial angle inclination for the tangential cutting insert, it is however possible to swing the rearmost cutting corner to the cutting insert inwardly so that its spacing, measured by means of a straight line lying perpendicular to the milling direction, from the cutting edge of the next following radially clamped cutting insert can be reduced preferably from less than 2 mm to even negative values. By negative spacing values an arrangement is understood for the tangentially clamped cutting inserts in which the rearmost cutting edge is spatially located behind the cutting edge of the next following radial cutting insert. With the chosen arrangement it is possible to increase the number of useable cutting inserts on the tool carrier. Preferably the side mill cutter has, as seen in the direction of cutting, an alternating sequence of tangentially and radially clamped cutting inserts on the cylindrical periphery of the tool carrier or, as stated otherwise, radially clamped cutting inserts along the edges of the side mill cutter cylinder which respectively (left as well as right) is spatially disposed ahead of a respective tangentially clamped cutting insert. The two rows thus formed of tangentially clamped cutting inserts have cutting inserts which, depending upon the row with which they are associated, have a tilt about an axial angle in the opposite sense from another cutting insert of the other row.

[0011] For the machining of cylindrical surfaces without undercuts, the objects are achieved further with the side mill cutter according to claim 3. By contrast with the embodiment described above, a portion of the tangentially clamped cutting inserts can be omitted as will be apparent from the description of FIGS. 4 and 5. In this arrangement there is a spacing of the rearmost cutting corner of such cutting inserts as taken along a straight line which is perpendicular to the cutting direction of the side mill cutter, from the reading cutting edge of the next following radially clamped cutting insert of a distance of 10 mm, preferably 5 mm to negative values.

[0012] Further features of the invention are described in the dependent claims 4 to 6. Thus preferably the tangentially clamped cutting inserts are so arranged that the shortest distance of the cutting edges which are inactive during machining or their extensions which are turned toward the edges of the side mill cutter cylinder, to the next following cutting corner of the subsequently arranged radially clamped cutting insert in the cutting direction is selected 1 mm. Through this feature it is ensured that a sufficient place for the requisite rake chamber remains ahead of the radially clamped cutting insert and chip running off from it does not collide with the inactive cutting edge toward the rake chamber of the tangentially clamped cutting insert or can damage this cutting edge. This is especially of significance for so-called turning cutting plates which respectively have four useable cutting edges. a preferred measure for the axial inclination angle of the tangentially clamped cutting inserts is 25.

[0013] According to a further feature of the invention, the cutting regions of two successive tangentially clamped cutting inserts overlap slightly.

[0014] With the side mill cutter according to the invention, cutting speeds of 160 m/min and greater chip thicknesses of 0.1 mm to 0.25 mm can be removed.

[0015] An embodiment of the invention is illustrated in the drawing. It shows.

[0016] FIG. 1 a schematic elevation of an apparatus for machining crankshafts,

[0017] FIG. 2 a plan view of a part of a side-milling cutter according to the invention with a cylindrical periphery on which cutting inserts are attached,

[0018] FIG. 3 a perspective partial elevation of the side-milling cutter of FIG. 2 according to the invention,

[0019] FIG. 4 a plan view of a part of a further side-milling cutter according to the invention having a cylindrical periphery to which cutting inserts are attached and

[0020] FIG. 5 a perspective partial elevation of the side-milling cutter of FIG. 4.

[0021] In FIG. 1 an apparatus 100 for the chip-removing machining a crankshaft 10 has been shown purely schematically. The crankshaft 10 is so engaged in drivable rotatable clamping chucks 13 and 14 with its ends 11 and 12 that it is rotatable about its central axis. For machining disk-shaped high-speed cutting tools 15 and 16 are used which can be rotated via corresponding drives 17, 18, whereby each drive 17, 18 is mounted on a support 19, 20 so that the tool can be adjusted toward an axis of the workpiece. Furthermore, in the illustrated apparatus two orthogonal rotary mills 21, 22 are disposed which are also rotatable by corresponding drives 23, 24. Each orthogonal rotary mill 21, 22 is mounted on a support with a respective pair of slides 25, 26; 27, 28 so that an adjustment of each orthogonal rotary mill 21, 22 relative to the rotating crankshaft is possible. With the illustrated apparatus the simultaneous machining of four lifter bearing locations of the crankshaft is possible.

[0022] In order to carry out the chip-removal machining of a crankshaft lifter bearing located outside the eccentrically arranged rotational center of the workpiece 10, the side-milling cutters 15 or 16 must be driven about their central axes with constant or variably higher speeds so that cutting inserts arranged on their peripheries are displaced past the machining locations of the workpiece with a higher cutting speed. The machining of crankshafts is described in greater detail in WO 96/39269 to which reference is made.

[0023] Each of the side-milling cutters 15, 16 is provided on its cylindrical outer periphery with cutting inserts 29-32 which are there clamped and of which the cutting inserts 29, 30 are respectively radially clamped and the cutting inserts 31 and 32 are respectively tangentially clamped. By rotation of the side-milling cutters in the direction of the arrows 33 which have been shown, the advantageously selected small cutting arcs engage one after the other the respective active cutting edges of the cutting inserts.

[0024] Where an axial inclination angle 25 of the cutting inserts 31 in the clockwise sense is selected, the tangentially clamped cutting inserts 32 are tilted about the inclination axis by 25 in counterclockwise sense. As a result, the respectively rearmost cutting corners 34 or 35 of the cutting inserts 31 or 32 are tilted inwardly, so that a measure of the spacing a shown in FIG. 2, between the straight line 36 at the cutting corner 34 which is perpendicular to the cutting direction 33 and the cutting edge 37 of the next-following cutting insert 29, can be a5 mm, preferably a2 mm.

[0025] Optionally, the illustrated rear cutting corners 34 or 35 can also be located rearwardly of the cutting edges of the next following radially clamped cutting insert in space. The distance b of the illustrated (inactive) cutting edge 38 to the next lying cutting edge 37 or its end point amounts to at least 0.5 mm.

[0026] With the side-milling cutter according to FIG. 2, the simultaneous formation of two undercuts by the cutting inserts 29 and 30 and the machining away of a cylindrical surface by the cutting inserts 31 and 32 is possible. The cut regions of the two offset rows of tangentially clamped cutting inserts 31 and 32 overlap each other slightly.

[0027] The tangentially clamped inserts visible in FIG. 3 have additionally along their respective cutting edges, notches 39 which are basically known from the state of the art. These notches are effective in that during the machining instead of a wide chip, a plurality of smaller chips are produced corresponding to the number of notches. In general the tangentially clamped cutting insert correspond to the tangentially cutting inserts illustrated in WO 96/39269. The radial cutting inserts have a configuration which corresponds to those described in DE 197 39 300 A1.

[0028] In the embodiment illustrated in FIG. 4, the cutting inserts 29 and 30 are radially clamped. These cutting inserts serve primarily for machining the cheeks, but however do not project beyond the tangentially clamped cutting inserts 31 and 32 so that they cut in part the pin outer diameter in the edge regions. By contrast to the embodiment illustrated in FIGS. 2 and 3, in the respective alternating sequence there are two left and right radially clamped cutting inserts and only one tangentially clamped cutting insert, whereby the successive tangentially clamped cutting inserts 31 and 32 are inclined in opposite senses at an axial inclination angle of preferably 25. The spacing a can here be selected to be somewhat greater and can amount to up to 10 mm. The spacing b can also be selected to be correspondingly greater by comparison to the embodiment illustrated in FIG. 2. Otherwise the same reference characters have been used for identical parts to those of FIG. 2 and reference is made to the description of them.

[0029] The tangential cutting inserts 31 and 32 have their configurations as described in WO 96/39269 as a consequence of which reference is made to that disclosure.