Drill with coolant channels and method for its manufacture

Abstract: A spiral drill and a method to manufacture a spiral drill with two indexable inserts and two coolant channels (23, 24) wherein the coolant channels located in the holding shank part extend either parallel to the center line at different distances from said center line, or extend conically in relation to said center line, where the middle portion has been twisted while in heated condition to form spirally curved coolant channels (17, 18) and where the exit channels at the tip have been drilled after twisting, and where the exit openings (21,22) are located at different distances from the center line.

Description: The present invention relates to a spiral drill with indexable inserts comprising a holding shank, a nose portion with insert pockets for the receipt of a central insert and a peripheral insert and a spiral part which comprises two spirally curved ribs with a coolant channel provided into each such rib. The invention relates also to a method for manufacture of drills. A basically similar method is known from WO-A-9 413 422 representing the closest prior art. In spiral drills it is possible to supply liquid through coolant channels to openings near the cutting edges, which facilitates chip formation and lowers friction in the flutes. In order not to lower the torsion stiffness and give an undesirable coupling between axial force and torsion angle, the drill can often be made with two spiral coolant channels as shown in the patents SE 335 111 and EP-A-118 035 located between the flutes in the ribs where they are least detrimental to the strength. Those patents also show how a drill can be made from a such a spiral part joined to a separately made shank part with different location of coolant channels. It is also known through patent SE 194 706 to make drills with indexable carbide inserts in pockets on a steel body, where it has been made possible to utilize a limited number of insert sizes for a large number of drill diameters by using two or more unsymmetrically located indexable inserts, one of which is a center insert close to the center line of the drill and one of which is a peripheral insert close to the periphery of the drill. The invention concerns a spiral drill with coolant channels which to the larger part of their length are placed where they detract as little as possible from the strength and stiffness of the drill, and near the cutting edges are adapted to the location of the inserts. This problem is solved according to method claim 1 and device claim 6. Accordingly straight coolant channels are drilled in a cylindrical drill blank from the shank part but not through to the tip end such that said channels are located at different distances from the centre of said blank. The blank is then locally heated and twisted by a predetermined angle. After twisting, the flutes, the insert pockets, the cutting tip and straight exit portions are machined, said exit portions being provided to meet the coolant channels whereby at least one of the exit portions of the cooling channels is drilled as a conical channel. During this machining the cooling channels in the shank part are used as angle reference. This makes it possible to locate the exit openings at optimal positions relative to the insert pockets without regard to the spiral channel location in the cross-section. In accordance with the invention, the cooling channels are drilled at an oblique angle in relation to the central axis of the drill blank such that they terminate at different distances from the central axis at their exit openings. The insert pockets are unsymmetrically located, one near the center and one near the periphery. In order to achieve the best effect of the coolant, the exit openings should be located at same position as the following insert and thus one exit opening should be located closer to the center and one closer to the periphery, which is accomplished by drilling the exit channels in connection with the machining of the insert pockets. The invention is described in detail with reference to the figures, where figure 1 shows a drill which is not part of the invention, figure 2 a cross-section of the drill, figure 3 a drill blank for the drill of figure 1 prepared for twisting, and figure 4 a drill blank, before twisting, according to the invention. A drill according to the invention comprises a shank part (15), a spiral part with two ribs (11, 12) separated by two flutes (29, 30) and a tip where one center insert (13) and one peripheral insert (14) are fastened with screws to pockets machined at the ends of the ribs (11,12). To give the drill a well defined axial position when mounted in a machine, it can be made with a flange (16) between the shank part and the spiral part. Within each rib (11, 12) there is a coolant channel (17, 18) spirally curved with the same curvature as the rib, and continuing in the shank part (15) as a straight channel (23, 24) at varying distances R 1 and R 2 from the center line all the way to the end face (31) of the shank part. These channels (23, 24) have a straight extension whilst diverging towards the drill tip at an angle (α) all the way to the end face (31) of the shank part. The size of said angle (α) ought to vary in the range 1,5-4,0° for drills of the diameter 30-60 mm, and 0,3-2,5° for the diameter 13-30 mm. The spiral coolant channels (17, 18) end at terminal points (19, 20) within the ribs (11, 12) near the tip. In accordance with one embodiment of the invention conically extending exit channels lead to exit openings (21, 22) in the tip end face behind the inserts. The exit openings are not symmetrically located, but the exit opening (21) on the rib (11) carrying the center insert (13) is located radially farther from the center line to cool and lubricate the following peripheral insert (14). Preferably the exit channel in the rib carrying the center insert is made with a larger cross-section than the other exit channel. Alternatively it could be advantageous in some cases to provide the exit channel on the rib carrying the center insert with a smaller cross-section than the other exit channel. A drill according to figure 1 is manufactured from cylindrical drill blank with two straight parallel axial channels to be made into coolant channels (23, 24) running at different distances from the center line (CL) of the drill blank. The method of manufacture is thereafter the same as already disclosed in Swedish patent 9203716-7 corresponding to WO-94/13 422 . After twisting the drill blank is reduced to its final diameter, and the flutes (29, 30) machined. By using the channels (23, 24) as a reference, it is ensured that the spiral flutes will not be located in too close proximity from the cooling channels (17, 18). The pockets for the inserts (13, 14) are then machined and conically extending exit channels are drilled from the exit openings (21, 22) to the terminal points (19, 20), with the exit openings (21, 22) located at different radial distances from the center line. In accordance with an alternative embodiment the cooling channels (17, 18) could, for certain drill diameters, be allowed to be terminated directly at the drill tip end portion. Thanks to the above outlined arrangement of having the cooling channels located at different distances from the center line of the drill blank it becomes easier to locate the cooling channels and their exit openings such that more space can be provided for the chip flutes (29, 30). This enables greater flexibility so as to adapt the location of the holes for various types of chips depending upon which type of material in the workpiece to be subject of machining. In accordance with one embodiment the size of one of the cooling channels could be larger than the other one when there is a need for enlarged coolant supply such as in the proximity of the centrally located insert.

Claims: A method for the manufacture of a spiral drill with coolant channels and pockets for two indexable inserts (13, 14), comprising the steps of: a) drilling in a cylindrical blank two straight holes spaced at different radial distances from a center line of the drill, the holes communicating with a first end face of the cylindrical blank and extending to a second end face of the blank whilst diverging towards the drill tip at an angle (α) all the way to the end face (31); b) heating at least a middle portion of the blank; c) gripping first and second ends (15, 25) of the blank with chuck devices; d) applying a torque to the chuck devices to twist the middle portion by a predetermined angle to reform the holes into spirally curved channels (17, 18) such that each channel is spaced from a centerline of the drill by a distance which becomes larger toward the second end face; and e) machining spiral flutes, a tip end face, and insert pockets in the blank subsequent to step d), the tip end face being machined in the second end face, and the insert pockets being machined in the tip end face. The method according to claim 1, wherein step a) comprises drilling the two holes such that each hole forms an acute angle with the centerline of the bore drill, the angle being in the range of 0.3 to 4°. The method according to claim 2, wherein the angle is from 1.5 to 4°. The method according to claim 2, wherein the angle is from 0.3 to 2.5°. The method according to claim 1, wherein step a) comprises drilling the holes such that each hole extends to the first end face. A spiral drill for indexable inserts, comprising: a rear shank part (15), a front tip with a pocket for a center insert (13) and a pocket for a peripheral insert (14), said pockets being spaced by different respective distances from a centerline of the drill; a spiral part extending between the rear shank part (15) and the tip, the spiral part having two spirally curved ribs, each rib having a spiral coolant channel (17, 18) disposed therein; the spiral coolant channels being spirally curved with the same curvature as the ribs, said cooling channels communicate with exit openings located at different distances from the central axis at the front tip of the drill, each channel communicating with a rear end of the drill and extending to the front tip characterized in that the coolant channels are diverging towards the drill tip at an angle (α) all the way to the end face (31) and that each coolant channel (17, 18) is spaced from a centerline of the drill by a distance which becomes larger towards the front tip and in the shank part the coolant channels are straight and located at different radial distances from the center line (CL).

Inventors: TUKALA TOMMY, TUKALA, TOMMY
Applicants: SANDVIK AB, SANDVIK AKTIEBOLAG
Application year: 1996
Main classification: B23P15
IPC codes: B23P15, B23B51