Patent Publication Number: US-7594784-B2

Title: Cutting tool

Description:
CONTINUING APPLICATION DATA 
   This application is a continuing application of International Patent Application No. PCT/EP2004/008987, filed on Aug. 11, 2004, which claims priority from Federal Republic of Germany Patent Application No. 103 37 203.2, filed on Aug. 13, 2003. International Patent Application No. PCT/EP2004/008987 was pending as of the filing date of this application. The United States was an elected state in International Patent Application No. PCT/EP2004/008987. 

   This invention relates to a drilling tool with two drill bits located on its opposite ends, wherein the drilling tool has a first drill bit and at least two forward cutting edges, a second drill bit and at least two rear cutting edges, and chip flutes ( 8 ,  9 ) that run from each of the forward cutting edges to a rear cutting edge, as described in the introduction to Claim  1 . The term “drilling tool” as used here means a drill that is designed for the creation of a boring with a constant diameter, as well as, for example, a stepped drill or a combination drill and countersink tool. 
   A drilling tool of the type described above is known, for example, from DE 1 752 616 A1. This double-tipped drilling tool is manufactured from an extruded profile, which is divided into individual small rods. As a result of the extrusion process, the chip flutes of the drilling tool have an unvarying profile over its length. 
   A drilling tool, in particular one that is used for machining metal workpieces, frequently has at least one replaceable cutting insert. The base body, to which the cutting insert can be fastened, can therefore be used beyond the useful life of the cutting insert. Drilling tools with replaceable cutting inserts, however, are typically limited to larger diameters. As a rule, one-piece drills are used for drilling smaller-diameter borings, for example up to 10 mm. In spite of the fact that they can generally be re-ground and re-used, their useful life is significantly shorter than that of a drill with a replaceable cutting insert or a plurality of replaceable cutting inserts. 
   The object of the invention is to indicate a drilling tool which has a particularly long useful life, in particular also at tool diameters up to 10 mm. 
   The invention teaches a drilling tool that has the following characteristics. The drilling tool has a drill bit on each end, whereby each drill bit has at least two cutting edges. Spiral chip flutes extend continuously from the cutting edges on the one drill bit to the cutting edges on the other drill bit. In the vicinity of the drill bits, each of the at least two chip flutes corresponding to the number of cutting edges per drill bit have in themselves an asymmetrical shape. As a result of the asymmetrical configuration of each chip flute, these tools are particularly well suited for a cutting geometry with controlled chip formation that is particularly advantageous for metal-removing operations. The asymmetrical profile of the chip flutes makes a transition, not later than toward the middle of the drilling tool, into a symmetrical profile, so that as the chip flutes proceed further toward the second drill bit, they once again assume a non-symmetrical shape, which is preferably the same as the shape at the first drill bit. As a variant from this configuration, the geometry of the second drill bit can also differ from the geometry of the first drill bit, and/or can also have an at least slightly different diameter, whereby in each case an asymmetrical profile of each chip flute is present in the areas adjacent to the drill bits and a symmetrical chip flute profile is present in an area that lies in between. The useful life of the drilling tool, which is also called a drill below, is therefore extended to almost twice that of a conventional drill that has only one drill bit. 
   The drilling tool, regardless of whether it is made out of a single material or of a plurality of different materials, is preferably provided so that it cannot be disassembled, for example for the extraction of a cutting insert. Possible materials that can be used as materials for the drill are all the materials or material combinations, with or without coatings, that are used in the prior art for conventional borers that have a single drill bit. If the drill bits are formed by separate tool bits, the bits are preferably permanently connected with the base body of the drilling tool, for example by soldering, whereby the tool bits are preferably made from a material that is harder than the material of the base body. In this embodiment, too, the chip flutes extend over the entire drilling tool, including the base body. 
   In one preferred configuration, the drilling tool has cooling channels which each extend from one drill bit to the opposite drill bit. 
   Each cooling channel is thereby associated with an individual cutting edge on each drill bit, whereby the function of the inlet and outlet openings of the cooling channels is interchangeable. 
   In the vicinity of the drill bits, the drilling tool has a shape, for example, that corresponds to one of the twist drills known from EP 0 249 104 A1, DE 100 275 544 A1 or DE 199 55 172 A1. Twist borers of this type are characterized by, among other things, good pipe tapping properties and possible high feeds while still achieving a long useful life. 
   The drilling tool, together with a chucking device, preferably forms a drilling device having the following characteristics. One part of the chucking device is a chucking sleeve which has an internal profiling that matches at least in part the shape of the chip flutes of the drill and thus makes possible a particularly precise chucking. In this case, preferably at least one opening cross section of the chucking sleeve at least in part matches the shape of the chip flutes. As a result, a penetration of chips into the chucking sleeve is prevented. Furthermore, an inner profiling of the chucking sleeve, which extends over the overall length, i.e. at least the major portion of the length of the chucking sleeve and matches the geometry of the drilling tool, makes possible a reliable chucking of the drilling tool, which is comparable to the chucking of a conventional drilling tool on the shank of a part of the tool without flutes. 
   Alternatively to the configuration disclosed herein above, a conventional draw-in collet chuck without internal profiling is also suitable for chucking the drilling tool, provided that the expansion capability of the collet is large enough to bridge any potential jumps or transitions in the diameter of the borer. 
   In accordance with one preferred development of the chucking device disclosed herein above, a sealing washer is provided that interacts with the chucking sleeve, and in particular is inserted in it or pushed over it, and by means of which an improved seal with respect to coolant-lubricant can be achieved. The sealing washer is preferably located on the side of the chucking sleeve facing the rear drill bit. As a result, no coolant lubricant or practically no coolant lubricant that is introduced into the drilling tool gets into the chucking sleeve or outward between the drill and the chucking sleeve. The term “rear drill bit” in this context means the drill bit that under current operating conditions is not being used for chip removal. The sealing washer located in this area also provides mechanical protection for the rear drill bit, which may be damaged, for example, by the vibrations that occur during chip removal operation. 
   To be able to insert the chucking sleeve easily into a conventional chuck, e.g. a hydraulic expansion chuck, the chucking sleeve preferably has a constant outside diameter. The material for the chucking sleeve, which in this case is also called a chucking shank, is preferably plastic or another flexible material such as rubber. The inside surface of the chucking sleeve is preferably configured so that the chucking sleeve simultaneously performs the function of a sealing washer. In this configuration, the drill is provided so that it can be screwed into the chucking shank. The chucking shank can either have a constant inner profiling over its entire length or can be provided with a blind hole to receive the drilling tool. When the chucking shank is realized with a blind hole, cooling lubricant can be fed to the drilling tool from outside. Likewise, however, it is also possible, instead of the blind hole, an area with a smaller inside diameter is provided through which coolant lubricant can also be fed in axially to the drill. 
   The advantage of the invention is, among other things, that a drill with two bits and continuous chip flutes can be used by means of a chucking sleeve coordinated with it, can be used in the same manner as a conventional borer that has only one bit, whereby in comparison to a conventional drill, there are no restrictions on its use, e.g. with regard to the maximum drilling depth. 

   
     Several exemplary embodiments of the invention are described in greater detail below with reference to the accompanying drawings, in which: 
       FIGS. 1   a ,  1   b  to  FIGS. 5   a ,  5   b  each show, in schematic sections, an exemplary embodiment of a drilling tool with two drill bits, 
       FIGS. 6 and 7  each show a schematic side view of an additional exemplary embodiment of a drilling tool with two drill bits, 
       FIGS. 8   a ,  8   b  different cross sections of the drilling tool illustrated in  FIG. 6 , 
       FIGS. 9   a ,  9   b  a chucking sleeve for a drilling tool with two drill bits and continuous chip flutes, 
       FIGS. 10   a  to  10   c  a sealing washer for a chucking sleeve as illustrated in  FIGS. 9   a ,  9   b,    
       FIGS. 11   a ,  11   b , an arrangement with a chucking sleeve as illustrated in  FIGS. 9   a ,  9   b  and a sealing washer as illustrated in  FIGS. 10   a  to  10   c,    
       FIGS. 12   a ,  12   b  an arrangement with an expansion chuck, a chucking sleeve as illustrated in  FIGS. 9   a ,  9   b , a sealing washer as illustrated in  FIG. 10   a  to  10   c  and a drill with two drill bits, 
       FIG. 13  an expansion chuck with a chucked borer, 
       FIG. 14   a ,  14   b  a plastic shank that can be chucked in an expansion chuck as illustrated in  FIG. 13 , 
       FIGS. 15   a ,  15   b  a drill in a plastic shank in different arrangements, and 
       FIGS. 16   a ,  16   b  show a drill in a plastic shank in an alternative embodiment. 
   

   Parts in the different figures that are identical, analogous or perform the same function are identified using the same numbers in all the figures. 
     FIGS. 1   a  and  1   b  to  5   a  and  5   b  each show an exemplary embodiment of a drilling tool  1  that has two drill bits  2 ,  3 . Each drilling tool  1  is realized in one piece and has a first area A adjacent to the first drill bit  2 , a contiguous middle area B and a rear area C that is adjacent to the second drill bit  3 . In the exemplary embodiments illustrated in  FIGS. 1   a  and  1   b  to  4   a  and  4   b , a reduced diameter D 2  in the middle area B is smaller than the tool diameter D 1 . Consequently, in particular in the particularly preferred exemplary embodiment illustrated in  FIGS. 2   a  and  2   b , a set of different tools can each have different tool diameters D 1 , which are dictated in each case by the outer areas A, C of the drilling tool  1 , but identical reduced diameters D 2 . All the tools of the set are thus suitable for the same chucking device. The cutting edges of each drilling tool  1  are identified by the reference numbers  4 ,  5 ,  6 ,  7 , and the corresponding chip flutes by the reference numbers  8 ,  9 . In each of the exemplary embodiments illustrated in  FIGS. 1   a  and  1   b  and  2   a  and  2   b , there are also four guide faces  10 . Two cooling channels  11  are shown simply by way of example in the exemplary embodiment illustrated in  FIGS. 5   a  and  5   b , which are preferably also present in all the other exemplary embodiments. 
     FIGS. 6 and 7  illustrate the shape of the chip flutes  8 ,  9  which extend over the entire length of each drilling tool  1 . While in the exemplary embodiment illustrated in  FIG. 6 , the drilling tool  1  is realized in one piece, for example, and is made of carbide coated using the CVD (Chemical Vapor Deposition) method, in the exemplary embodiment illustrated in  FIG. 7 , two tool bits  12 ,  13 , which can, for example, be coated or uncoated tungsten carbide, are permanently connected with a base body  14  which forms the middle area B of the drilling tool  1 , in particular by soldering to the base body  14 . 
     FIGS. 8   a  and  8   b  show two different cross sections of the drilling tool  1  illustrated in  FIG. 6 . In the vicinity of the maximum tool diameter D 1 , the drilling tool  1  has the asymmetrical profile of the chip flutes  8 ,  9  illustrated in  FIG. 8   a , which is optimized for the cutting method and chip formation. In this case, each chip flute  8 ,  9  is asymmetrical in itself, whereby the shape of the first chip flute  8  is the same as the shape of the second chip flute  9 . On the other hand, in the vicinity of the reduced diameter D 2 , as illustrated in  FIG. 8   b , the cross section of each chip flute  8 ,  9  is symmetrical overall in comparison to the outer areas A, C of the drill  1 . The chip flutes  8 , which are thereby optimized in terms of chip transport, have a constant cross section in the entire middle area B. The transition between the area of each chip flute  8 ,  9  that faces the drill bits  2 ,  3  and is in itself asymmetrical, and the middle, symmetrical area of each chip flute  8 ,  9  is continuous, i.e. without edges or discontinuities. 
     FIGS. 9   a  and  9   b  show a chucking sleeve  15  which is suitable for a drilling tool of the type illustrated in  FIG. 6  or  7 , for example. The chucking tool  15  is assembled from a cylinder body  16  and a cover  17 , which has an opening cross section  18  that approximately matches the shape of the chip flutes  8 ,  9 . The opening cross section  18 , on the guide faces  10 , has coordinated flutes  19 , which are indicated as dotted lines in  FIG. 9   a  as a portion of an inner profiling, and are continued into the cylinder body  16 . 
     FIGS. 10   a  to  10   c  illustrate a sealing washer  21  which is made of an elastomer, which has an edge segment  22  in the shape of a cylinder jacket, and a sealing surface  23  bordered by said edge segment and matching the cross section of the chip flutes  8 ,  9 . 
   The function of the clamping sleeve  15  and of the sealing washer  21  is illustrated in greater detail in  FIGS. 11   a ,  11   b ,  12   a  and  12   b . In the figures, the drilling tool  1  is chucked in an expansion chuck  24  by means of the chucking sleeve  15 , in which the sealing washer  21  is inserted on the side facing away from the drill bit  2  used for the chip removal. The drilling tool  1  can be chucked in axially different positions in the expansion chuck  24 , which can also theoretically be replaced by another type of chuck, such as a draw-in collet chuck. In general, the cutting edges  4 ,  5  which are used during the cutting operation are also called the forward cutting edges, and the cutting edges  6 ,  7  that are located on the inactive drill bit  3  that is kept in reserve are called the rear cutting edges. The cooling lubricant that is fed inside the expansion chuck  24  to the drilling tool  1  can flow at most only in a small proportion through the chip flutes  8 ,  9 , and is thereby conducted through the cooling channels  11 , which are not visible in this exemplary embodiment, to the drill bit  2 . 
     FIG. 13  shows, in an illustration that is analogous to  FIG. 12   b , a dual-bit drilling tool  1  chucked in an expansion chuck  24 . Instead of the chucking sleeve  15  in  FIG. 12   b , however, a plastic shank  25  is used. The plastic shank  25  is shown in isolation in a schematic side and front view in  FIGS. 14   a  and  14   b . The front view ( FIG. 14   b ) shows that the cross section of the plastic shank  25  is theoretically identical to the cross section of the sealing washer  21  ( FIGS. 10   a  to  10   c ), i.e. it has an opening surfaces that matches the cross section of the drill  1 . To make it easier to screw the drill  1  into the plastic shank  25  and in particular to make the plastic shank  25  suitable for use with drills  1  of a different diameter, slots  26  in the axial direction are provided over slightly more than one-half of the length of the plastic shank  25 . The plastic shank  25  illustrated in  FIGS. 14   a  and  14   b  is realized for a drilling tool  1  with a twist angle of 30 degrees of the chip flutes. The slots  26  are unnecessary in some cases, in particular if the plastic shank  25  is provided only for one specific drill diameter. 
     FIGS. 15   a  and  15   b  show the longitudinal section of the plastic shank  25 . These figures, also show, as indicated by the double arrow, that the plastic shank  25  can be optionally located on each of the two sides of the drilling tool  1 . In that case, one of the drill bits  2  is approximately flush with the end surface of the plastic shank  25 . In a variant of the illustrated exemplary embodiment, the drill can also be axially shifted to any position inside the shank. 
     FIGS. 16   a  and  16   b  show, in views that are similar to  FIGS. 15   a  and  15   b , a drilling tool  1  held in a plastic shank. In contrast to the plastic shank  25  illustrated in  FIGS. 13 to 15   b , the plastic shank  25   a  shown in  FIGS. 16   a  and  16   b  does not have a constant inside diameter, but a tapered diameter  27 . When the drilling tool  1  is screwed all the way into the plastic shank  25   a , its bit  2  is in contact against a peripheral step  28  which separates the tapered segment  27  from the remaining, untapered inner wall  29  of the plastic shank  25   a . In contrast to the exemplary embodiments illustrated in  FIGS. 13 to 15   b , the drill bit is thereby at some distance from the end surface of the plastic shank  25 . The tapered segment  27  can be used to feed coolant lubricant to the drilling tool  1 , and therefore forms a coolant lubricant channel, if necessary. If there is no need to feed in a coolant lubricant, the plastic shank  25   a  can be completely closed at the point of the tapered segment  27 .