SPIRAL DRILL WITH COOLANT CHANNELS AND METHOD TO MANUFACTURE A SPIRAL DRILL

Abstract: A spiral drill and a method to manufacture a spiral drill with two indexable inserts at different distances from the center line and two coolant channels, where the coolant channels (23, 24) run parallel to the center line within the shank part, and where the spiral part has been twisted while heated to form spirally curved coolant channels (17, 18), and where 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: SPIRAL DRILL WITH COOLANT CHANNELS AND METHOD TO MANUFACTURE A SPIRAL DRILL Background Spiral drills comprise a spiral part with cutting edges at a tip end, and a shank part which to at least some extent i bounded by cylindrical surfaces. With spiral drills for metal drilling it is of great importance that no chips are packed in the spiral flutes, since even a small counter pressure from adhering chips will seriously disturb the chip formation and lead to greatly increased feed and cutting forces, as well as slower feed rate. To facilitate the chip flow through the spiral flutes these should be made with a spacious cross section shaped to avoi pressing the chips against the wall of the hole. It is also suitable 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 t lower the torsion stiffness or give an undesirable coupling between axial force and torsion angle, the drill can be mad with two spiral coolant channels as shown in the patents SE 335 111 and DE 33 04 277, located between the flutes in the ribs where they are least detrimental to the strength and stiffness. Those patents show how a drill can be made from 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 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 to a smaller part near the cutting edges are located in relation to the location of th inserts to give optimal cooling and lubricating effect. Description of the invention Previously known drills with spiral coolant channels have had channels continuing through the whole spiral part with constant position relative to the cross-section, whether they were made by twisting of a milled blank, forging or extrusion. In some cases where the the drill blanks were forged, the channels were made before forging, filled with substance with low melting-point and either not continued through the tip end face, or plugged at the end with a meta with high melting-point. According to the invention coolant channels are drilled in cylindrical drill blank from the- shank part but not through to the tip end. The spiral part of the blank is then locall heated and twisted a predetermined angle. After twisting, the flutes, the insert pockets and other surfaces of the ti are machined using the channels at the shank part as an angle reference, and straight exit channels are drilled fro exit openings in the tip face to meet the coolant channels. This makes it possible to locate the exit openings at optimal positions relative to the inserts without regard of the spiral channel location in the cross-section. The insert pockets are unsymmetrically located, one near th center and one near the periphery. For best lubrication and cooling, the exit openings should be located at the same radius as the midpoint of the following insert, and thus on exit opening should be located closer to the center and one closer to the periphery, which is accomplished by drilling the exit channels after machining of the insert pockets. The invention is described in detail with reference to the figures, where figure 1 shows a drill according to the invention, figure 2 an axial view of the tip end of the drill and figure 3 a drill blank prepared for twisting. A drill according to the invention comprises a shank part (15), a spiral part with two flutes (29,30) and two ribs (11,12) 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 constant distance from the center line all the way to the end face (31) of the shank part. The spiral coolant channels (17,18) end at terminal points (19,20) within the ribs (11,12) near the tip. Straight exit channels lead from the terminal points to exit openings (21,22) in the tip end face behind the inserts. The exit openings are not symmetrically located, but the exit openin (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) , and the exi opening (22) on the rib (12) carrying the peripheral insert (14) is located closer to the center line to cool and lubricate the following center insert (13) . A drill according to the invention is manufactured from a cylindrical drill blank with two straight parallel axial channels to be made into coolant channels (23,24) running from an end face (31) to terminal points (19,20) within the blank near the other end (25) which is to become the tip end. The drill blank is mounted in two chucks, one of the chucks (27) holding what is to be the shank part (15) and the other chuck (28) holding a part of the blank near the end (25) to become the tip end. The drill blank is heated between the chucks by an induction coil (26) or other suitable means, whereupon the drill blank is twisted a predetermined angle with the chucks. The grip of the chucks must be stable enough to avoid any twisting of those parts of the drill blank held within the chucks. The portions of the channels (17,18) located between the chucks will become spirally curved, and the position of the terminal points (19,20) will be well defined relative to the straight channel parts (23,24). After twisting the drill blank is reduced to its final diameter, and the flutes (29,30) machined. By using the straight parts of the channels (23,24) as an angle reference, the flutes can be made to follow the coolant channels (17,18) at an appropriate distance. The pockets fo the inserts (13,14) are machined and straight exit channels are drilled from the exit openings (21,22) to the terminal points (19,20), with the exit openings located at different radial distances from the center line.

Claims: CLAIMS 1. Spiral drill with indexable inserts, comprising a shank part (15), a tip with pockets for a center insert (13) and peripheral insert (14) , and a spiral part with two spirally curved ribs (11,12) with a coolant channel (17,18) in each rib, said coolant channels being spirally curved with the same curvature as the ribs, running at constant distance from the center line and being continuous with straight channels (23,24) parallel to the center line in the shank part, c h a r a c t e r i z e d by each spirally curved coolant channel being continued by a straight exit channel from a terminal point (19,20) near the tip to an exit opening (21,22) on a tip face of a rib, said exit openings located at different radial distances from the center line. 2. Spiral drill according to claim 1, c h a r a c t e r i z e d by the exit opening (21) on the same rib (11) as the center insert (13) being located farther from the center line than the exit opening (22) located on the same rib (12) as the peripheral insert (14) . 3. Method for manufacture of spiral drills with coolant channels and two indexable inserts, c h a r a c t e r i z e d by the steps of: - drilling in a cylindrical blank two parallel holes (23,24 at the same distance from the center line, said holes extending from one end (31) of the cylindrical blank to terminal points (19,20) within the blank near its other end - heating at least the middle portion of the blank; - gripping both end portions of the blank with chuck devices; - applying torque to the chuck devices to twist said middle portion a predetermined angle to form said parallel holes within the middle part into spirally curved channels (17,18) ; - machining spiral flutes, tip end face and insert pockets with the parallel holes (23,24) at the end face (31) as an angle reference; - drilling exit channels from exit openings (21,22) at the tip end face to said terminal points (19,20), said exit openings being located at different radial distances from the center line of the drill. 4. Method according to claim 3, c h a r a c t e r i z e d by the grip of the chuck devices about the end portions (15,25) of the drill blank being stable enough to avoid twisting of said end portions.

Inventors: ERIKSSON KENT, KARLSSON LEIF, TUKALA TOMMY, ERIKSSON, KENT, KARLSSON, LEIF, TUKALA, TOMMY
Applicants: ERIKSSON KENT, KARLSSON LEIF, SANDVIK AB, TUKALA TOMMY, ERIKSSON, KENT, KARLSSON, LEIF, TUKALA, TOMMY
Application year: 1993
Main classification: B23B51
IPC codes: B23B51, B23P15