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1. US20090080991 - Tool

Anmerkung: Text basiert auf automatischer optischer Zeichenerkennung (OCR). Verwenden Sie bitte aus rechtlichen Gründen die PDF-Version.

[ EN ]
      The invention relates to a disk-shaped or bar-shaped tool for machining, in particular for cutting profiles on a workpiece such as a crankshaft that is rotated during machining, having a plurality of tangentially and a plurality of radially mounted indexable inserts.
      When manufacturing a crankshaft, the crankshaft is cast with certain dimensions in order to be able to perform subsequent machining operations with sufficient certainty. Tools for single- or double-rotation lathing are known from the prior art. In lathing, a linear lathing tool is pressed radially against the tool that is to be machined. In double-rotation lathing a plurality of successive cutting inserts are mounted on a reference circle circumference of a disk-shaped tool holder, and the cutting inserts project gradually and continuously more along a first segment of the disk circumference. This tool is pivoted in the radial direction against the rotating tool along a reference arc as is known in principle from EP 0 313 644 B1 or EP 0 286 771 A1. These tools use two geometrically different cutting inserts for shaft lathing and for finishing the undercut. Tools of the above-described type are shown and described for instance in DE 100 27 945 A1. In order to be able to provide a thinner cut during cutting and to be able to mount the greatest possible number of cutting tools on the side-lathing cutter, it is suggested that the tangentially mounted cutting inserts be mounted at an axial angle of inclination of 150 to 350 and that the rearmost cutting corner, seen opposite the lath rotation direction, is on a straight line perpendicular to the direction of rotation of the side-lathing cutter, which is spaced from the leading cutting edge of the subsequent radially mounted cutting insert by a distance of no more than 5 mm, preferably no more than 2 mm and extending into negative values.
      When machining crankshafts, for instance for producing the crank pins using a double-rotation lathing method, and when the cutting operation begins immediately on the raw cast surface of crankshaft, the indexable inserts disposed on the tool are under extreme stress so that there is relatively high wear. In addition to the service life for the individually used indexable inserts, the costs are also largely a function of how many indexable inserts must be used per tool.
      It is the object of the present invention to create a tool that permits cost-effective precutting of a crank pin for a crankshaft so that in the subsequent cutting process by means of a double-rotation lathing method only a minimum finish-machining amount must be removed, with which the double-rotation lathing tool used for the finish machining is less stressed, and whose service life is thus significantly improved. Furthermore, the new tool should have as many effective cutting edges as possible for a minimum number of indexable inserts used. Use of the indexable inserts should be flexible, i.e. it should be possible to use them for other cutting operations as well.
      This object is attained using the tool in accordance with claim 1.
      In accordance with the invention, at least a part of the tangentially mounted indexable inserts has a cutout that, in the tangentially mounted indexable insert, extends into a portion of the support face and into a portion of the radially situated face, and into which an upper rear portion of a radially mounted indexable insert projects whose upper front section radially projects with regard to the face. Using this measure it is possible to attain a particularly high number of effective cutting edges on the tool. While in the cutting insert arrangements in accordance with the prior art the radially mounted indexable inserts were mounted one after the other, alternately with the tangentially mounted indexable inserts, in accordance with the invention a radially mounted indexable insert and a tangentially mounted indexable insert can be mounted “in a line” so that when cutting crankshafts both cutting inserts can machine the crank pin base and the lateral surface of the crank pin simultaneously. This saves an additional operation and consequently also saves machining time.
      Further embodiments of the invention are described in the subordinate claims.
      Thus the width of the cutout is preferably no more than one-third of the width of the face and/or no more than one-half the height of the tangentially mounted indexable insert. Using these dimensions take into account that the cutout must not weaken the tangentially mounted indexable insert; on the other hand, a cutout that is too small in volume would create only a relatively small space for receiving the rear portion of the radially mounted indexable insert, and this could entail the risk that the radially mounted indexable insert is too weak in terms of dimensions in the area of the active cutting edges. Likewise, the width of the cutout is selected to be no more than one-half the thickness of the radially mounted indexable insert.
      In order to render usable the greatest possible number of cutting edges, the tangentially mounted indexable insert has a respective cutout on each of its diametrically opposite sides.
      Preferably the tangentially mounted indexable insert has two largely parallel broad faces through which a fastening bore passes and four adjacent lateral faces, specifically two at least largely parallel faces spaced apart from one another and two longitudinal faces disposed on opposite sides. The intersections of the broad faces with the longitudinal faces and the intersection of the broad faces with the transverse faces and also the transition area from the longitudinal face to the face, which is rounded (convex), form cutting edges. Preferably the tangentially mounted indexable insert also has eight usable cutting corners, each on the edge of the rounded transition area from the face to the broad face.
      In accordance with another embodiment of the invention, each broad face has two subfaces that are slightly angled to one another, preferably at an enclosed angle >170°, preferably >175°, and furthermore the subface closer to toward the tool center is preferably smaller than the subface extending toward the edge.
      The result is that a relatively thin cut can be made in the crank pin center because the cutting inserts are slightly angled there.
      With respect to the radially mounted indexable inserts, preferably an embodiment in accordance with claim 9 or 10 is used. According to these, at least one part of the radially mounted indexable inserts has two largely parallel broad faces through which a fastening bore passes and that are joined on opposite sides at least by faces that in cross-section are at least partially convex, preferably semicylindrical and whose side edges are embodied as cutting edges. Preferably a base body that has a fastening bore and that expands to the center extends between the faces.
      Preferably the tangentially-mounted and the radially mounted indexable inserts are mounted in a cassette, which facilitates their flexibility with respect to the design (setting of crank pin width, etc.) and also facilitates rapid exchangeability, specifically by switching cassettes.
      In accordance with another embodiment of the invention, all indexable inserts are produced from a hard metal or a cermet body that has been produced using powder metallurgy by pressing and then sintering without intermediate processing. Where required the indexable inserts can also be coated, the composition of the coatings used being selected in a manner known per se in accordance with the prior art.
      Additional advantages and embodiments are described in the following using the drawings. Therein:
       FIG. 1 is a sectional view of a lathed crank pin;
       FIG. 2 is a perspective elevation of a-radially mountable cutting insert;
       FIG. 3 is a perspective elevation of a tangentially mounted indexable insert;
       FIG. 4 is a perspective elevation of the indexable inserts in accordance with FIGS. 2 and 3 for illustrating the “interfit” of the two indexable inserts;
       FIG. 5 is the partial perspective view of an inventive tool.
       FIG. 1 shows by way of example a section through a part of a crankshaft in which the side cheeks 10 are to be cut as well as the crank pin 11 and the undercuts 12. In this drawing the finish-machining amount that typically has to be removed using double-rotation-lathing are also provided as an example.
      In order to obtain the cross-sectional shape shown in FIG. 1, two or three types of indexable inserts are used in the cassette of a tool holder in accordance with FIG. 5 for precutting, and these indexable inserts will be discussed in greater detail in the following. FIG. 2 shows an indexable insert 13 that can be mounted to extend radially and that has two parallel broad faces 14 and 15 through which passes a mounting bore 16 and that meet at opposite ends at semicylindrical faces 17 whose side edges 18 and 19 serve as cutting edges. The above-described at least largely semicylindrical faces 17 are situated at opposite ends of a base body 20 that is rhomboidal and that broadens toward the center in order to create a large enough space for the fastening bore 16. The four cutting edges 18 and 19 of this cutting body can be used successively by turning the indexable insert.
       FIG. 3 shows a tangentially mountable indexable insert 21 that has two largely parallel broad faces through which a fastening hole 22 passes, and four adjacent lateral faces, specifically two at least largely parallel transverse faces 23 and 24 that are spaced apart from one another, and two longitudinal faces 25 and 26 disposed on opposite sides. The broad faces are slightly angled to one another and each are formed by two subfaces 27 and 28 forming between them an angle of about 175°. Like the edges where the faces 23 and 24 intersect the longitudinal faces 25 and 26, the edges where the subfaces 27 and 28 intersect the two longitudinal faces 25 and 26 form cutting edges, their transition areas being rounded so that cutting corners 29 are formed there having adjacent linear cutting edges approximately at a right angle of 90° to one another. In the embodiment shown in FIG. 3, there is a total of four rounded cutting corners 29 that are formed diametrically opposite one another. If the sharp corners 30 are also embodied as rounded cutting edges, eight usable cutting corners 29 result.
      In accordance with the invention, the indexable insert 21 has, on diametrically opposite sides, cutouts 31 whose width is slightly larger than the width of the indexable insert 13 at each end face 17 so that the indexable insert 13 can assume the position shown in FIG. 4 in which the rear portion of one of the faces engages in the cutout 31, as shown. The front part 32 with exposed cutting corner sections there can be used for lathing side walls of a crank pin on crankshafts. The cutting edge 33 of the tangentially mounted cutting insert (or, when the direction of rotation is reversed, the opposite cutting edge 34) is used for machining the crank pin base 11. The tool used for this is seen in FIG. 5, in which another cutting insert 35 is also mounted radially and, if the indexable insert 21 is also provided with rounded cutting corners on the corners 30, can also comprise the indexable insert shown in FIG. 3. If the tool shown in FIG. 5 is used for precutting, only a minimum finish-machining amount of the crankshaft must be removed during final machining so that the significantly more expensive final double-rotation lathing tool is stressed much less and thus its service life is extended. The tool shown in FIG. 5 possesses a great number of effective cutting edges in the smallest possible space, the indexable inserts being used being those in accordance with FIGS. 2 and 3, i.e. in some circumstances, in other cutting operations. The crank pin width that can be produced can be varied by varying the overlap area of the indexable inserts 21 in the tool in accordance with FIG. 5 (on opposite sides).
      The indexable inserts shown in FIGS. 2 and 3 can be mounted without washers or calibration pieces. All indexable inserts are advantageously produced using powder metallurgy from hard metals or cermet and do not undergo any mechanical post-processing after sintering apart of course from coating by means of PVD or CVD.
      As was already mentioned to a certain degree, a particularly high number of effective cuts results from the principle of inserting the indexable insert 13 into the cutout of the indexable insert 21. Any bearing width required in practice, that is, from about 18 to 27 mm, can be produced by mounting the indexable insert 21 in a cassette. Since the precutting process can be done at relatively high speeds and only a small finish-machining amount must be machined in the subsequent double-rotation lathing process, and some cutting processes have been included during precutting, 4 to 6 seconds of machining time per unit can be saved in the entire cutting process. Since in addition the double-rotation lathing process employed for finish machining can be performed more rapidly, overall less cassettes per tool are used, which increases the service life for the final machining tool.