Abstract:
Proposed is a drilling tool for drilling in solid material, having a base body (1) containing chip flutes (5, 5a) and at least two interchangeable inserts (3, 3a) at the face of the base body (1). The inserts are arranged on the base body at different radial distances such that their working ranges partially overlap. The blades (12) of the inserts (3, 3a) are formed by two cutting edges (8, 9) which together form an obtuse angle, that is the point angle (11). The face (13) of the blades (12) has parallel profile ribs (14, 14a) which act as runners and which in the region of the cutting edges (8, 9), aligned in the direction of chip removal, extend radially inwards over a curved course relative to their installed position, toward a flank region (17) of the insert (3, 3a) near the drilling tool axis (7).

Description:
This is a divisional application of U.S. Ser. No. 08/849,518, filed on Jun. 9, 1997, now U.S. Pat. No. 5,967,710 which is based on International Patent Application No. PCT/EP95/04872, filed on Dec. 11, 1995 and which claims priority from Fed. Rep. of Germany Patent Application Nos. P 44 44 022.7 and 195 38 391.5. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a drilling tool for drilling holes in solid metal, with a base body which contains at least one chip flute, with at least one replaceable cutting insert on the end surface of the base body located in a recess on the end of a chip flute, and with a blade which is preferably formed by two cutting edges which form an obtuse point angle with one another. 
     2. Background Information 
     In general usage, such drilling tools are also designated indexable insert drills. 
     During drilling work with such indexable insert drills, the chips are basically removed from the cutting edges after they have been bent into a curved shape. The curvature of the chip is caused by the different cutting speeds at individual points or areas of the cutting edges. Basically, the chips flow radially inward from the wall of the boring toward the axis of the drilling tool. 
     Such drilling tools of the prior art are equipped with replaceable cutting inserts, the faces of which carry chip shaping steps. The chip shaping steps on the faces are oriented approximately parallel to the major cutting edges (European Patent No. 0 181 844 B1), even if the chip shaping steps are hump-like structures in the manner of spot-like projections which project from the rake faces (U.S. Pat. No. 4,215,957 A). The chip shaping is conventionally also achieved by placing obstacles in the path of the chip as it is being removed. As a result of these obstacles, the chip is plastically deformed and immediately deflected in a new direction. 
     OBJECT OF THE INVENTION 
     The object of the invention is to provide a drilling tool of the type described above with chip shaping devices which promote the removal of the chips via the chip flutes. 
     SUMMARY OF THE INVENTION 
     The invention teaches that this object can be accomplished if the rake face of the blades contains chip shaping ribs located next to one another which act in the manner of runners for the chips, which chip shaping ribs, in the vicinity of the blade or of the cutting edges are oriented approximately perpendicular to the cutting edges, and from there the chip shaping ribs extend in the direction of chip removal with a curved profile with regard to their installed position radially inward toward a flank area of the insert, which flank area is close to the axis of the drilling tool. The reset replaceable inserts are each located in the end of a recess on the end surface of a drill base body, and are realized so that their chip surfaces contain chip shaping ribs which are located next to one another which act like runners on which chips slide. In the vicinity of the cutting edges of the indexable insert, the runners are oriented approximately perpendicular to the cutting edges, and from there run approximately in the chip removal direction on a curved path relative to their installation position, radially inward toward a flank area of the insert. The curved path of the chip shaping ribs or grooves is thereby selected so that it corresponds largely to the natural or optimal removal direction of the chip. This chip removal direction is not maintained with absolute reliability during drilling. Various factors which are due to changing advance speeds, the material of which the workpiece is made, etc., can cause the chip to deviate from its ideal removal direction, with the consequence that the chip spiral formed is not removed correctly from the chip space, and in particular can generate a great deal of friction. The chip shaping ribs claimed by the invention prevent this undesirable effect by promoting the removal of the chips along a curved path which runs radially inward toward the axis of the drill. The chip shaping ribs force the chips being removed to travel in the direction in which they are being removed from the cutting edges. In particular, the chip shaping ribs or grooves reflect the shape of the chips, which results in practically an automatic guidance. An additional advantageous effect of this shaping of the chip in the manner of a piece of corrugated sheet metal lies in its stiffening action which is effective in the longitudinal direction of the chip. The stiffening action of the spiral-shaped chips results in increased uniformity of the chip shaping, and thus an improvement of the chip removal from the boring, as a result of a more uniform removal of the chip. The subsequent chips, to some extent, push the previously-formed chip out of the hole. A jamming of these relatively large chip spirals between the body of the drilling tool and the wall of the hole is almost impossible. 
     The chip shaping ribs are preferably curved continuously toward the area in which they end. Such a configuration guarantees that the sliding movement of the chip on the chip shaping ribs and in the chip shaping grooves between the ribs takes place with as little friction and resistance as possible. The chip shaping ribs preferably run up to the flank area which flank area lies radially inward with regard to their installed position and close to the axis of the drilling tool, and there they run with an orientation which is approximately perpendicular to the axis of the drilling tool. Consequently, the chip is guided practically over the entire width of the insert which extends radially in relation to the axis of the drilling tool. It is thereby guaranteed that the chip impacts the interior wall of the chip flute exactly at a specified angle, and can then be removed with as little friction as possible. 
     The chip shaping ribs are formed by recesses or chip shaping grooves which are located next to and at some distance from one another, whereby the chip shaping ribs have a cross section which is curved in the form of a circular arc or an ellipse. This configuration meets the requirement for removal of the chips with the least friction possible. The chip shaping ribs can also have a somewhat trapezoidal-shaped cross section, whereby the flanks of the trapezoid can be slightly concave. As a result of this shape, and in particular as a result of the relatively sharp edge formed by the peak surface of the chip shaping ribs and a concave flank, the form-fitting engagement between the chip and the face, and thus the automatic guidance, of the chip is improved. 
     It is advantageous if the recesses or chip shaping ribs interrupt the cutting edges of the cutting insert. The copy of the chip shaping ribs or of the chip shaping troughs which lie between them in the back surface of the chip removed from the material to be worked then occurs practically simultaneously with the chip formation or chip removal. On account of the fact that at this point, the material can still be deformed plastically to a major extent, there is a significantly greater conformation to the chip shaping ribs on the back surface of the chip, whereby the form-fitting engagement between the chip and the chip shaping ribs, and consequently the automatic guidance of the chip, is improved. It is also advantageous if the chip shaping grooves also interrupt the near flank area of the insert which is radially inward in the installed position. The chip can then slide out of the insert into the chip flute area without resistance. 
     The advantage of a concave trough in the face of the insert is that the chips which are formed during the chip removal process are shaped by the concave trough or by the groove shape of the insert so that they impact the wall of the chip flute at an obtuse angle. As a result of the trough shape of the insert, the chips are already shaped so that the diameter of the chip spiral can fit easily into the volume of the chip space available. In cooperation with the automatic guidance of the chip as disclosed by the invention, an optimal removal of the chip from the chip space can therefore be guaranteed. 
     In many cases, and even in the majority of cases, it may be appropriate to curve the chip shaping ribs and grooves to an even greater extent than is necessary for the unimpeded removal of the chip. In other words, the chips are decelerated to a greater extent by the chip shaping ribs or grooves in the area closer to the axis of the drill than in the area which lies farther outward. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The object of the invention is explained in greater detail with reference to the embodiments illustrated in the accompanying figures. 
     FIG. 1 shows the point end of a drilling tool as claimed by the invention with two replaceable inserts, in a perspective view, 
     FIG. 2 shows an indexable insert as shown in FIG. 1, in a perspective view on a larger scale, 
     FIG. 3 shows a drilling tool as shown in FIG. 1 in perspective, to schematically illustrate the formation of a chip in the effective cutting range of the reset insert, 
     FIG. 4 shows an additional embodiment of an insert, in an overhead view, 
     FIG. 5 shows a view of the insert shown in FIG. 4, in the direction indicated by the Arrow V, 
     FIG. 6 shows a cross section along Line VI--VI in FIG. 4, 
     FIG. 7 shows a view along Arrow VII in FIG. 4, and 
     FIG. 8 shows a trigonal insert as claimed by the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The drilling tool consists essentially of the base body 1 with inserts 3, 3a located in the vicinity of the drill tip 2 and realized in the form of replaceable cutting inserts. The inserts 3, 3a are inserted in recesses 4, 4a, in which recesses they are fastened, e.g. by means of a screw. For this purpose, the inserts have a central fastening hole 6. The inserts are at different radial distances from the longitudinal center axis of the base body 1, and the working ranges of the two cutting inserts 3, 3a are adjacent to one another, and overlap to some extent. The longitudinal center axis forms the axis 7 of the drilling tool. The inserts 3, 3a can have a rectangular, approximately square outline (FIGS. 1 and 4), but they can also be trigonal inserts (FIG. 8). One characteristic common to both shapes of inserts is the presence of two cutting edges 8, 9 which project vertically in cross section, and which run together into a cutting tip 10, enclose an obtuse angle 11, and together form the blade 12 of the insert. Of course, inserts with a simpler basic geometry can also be used, such as inserts with square, triangular and rhombic outlines, in which the blade does not consist of a plurality of partial blades. 
     The face 13 can be flat or--in a preferred form--can have a curved groove, or--in particular on trigonal inserts--it can have a spoon-shaped trough. The invention teaches that the face 13 corresponding to each blade 12 contains chip shaping ribs 14 which are located next to one another and function as runners on which chips slide, e.g. as a result of an appropriate pattern of ribs and grooves. The profile ribs 14 are characterized by a special curved shape. In the vicinity of the cutting edges 8, 9, the chip shaping ribs first run approximately perpendicular, i.e. at an approximately right angle to the cutting edges 8, 9 (see Line 22 in FIG. 2). From there they are bent radially inward in the chip removal direction, namely toward the drilling tool axis of the drilling tool. 
     As noted above, the chip shaping ribs 14 are formed by making trough-shaped recesses, namely chip shaping grooves 15, in the face 13. The curve of the profile grooves 15 is selected so that the chip shaping ribs 14 which remain projecting vertically between them have the curve claimed by the invention. As shown in FIGS. 1-3, the chip shaping grooves 15 end at some distance in front of the blade 12 or the cutting edges 8 and 9. Between the end of each of the chip shaping grooves 15 and the blade 12, there are respective webs 16. The advantage of this configuration is that it simplifies the manufacturing process. The width of the webs 16 must be as small as possible, to make it possible for the chip material removed from the workpiece to flow into the chip shaping grooves. When the chip is formed, the workpiece material is still in a state in which it can more easily be deformed plastically than is the case as its distance from the cutting site increases. Therefore, the smaller the width of the webs 16, the closer the ends of the chip shaping grooves are to the chip in the plastically deformable area. For reasons of stability, there are natural limits regarding the reduction of the width of the webs 16. In the flank area 17 close to the axis 7 of the drilling tool, the chip shaping ribs 14 are oriented approximately perpendicular to the axis 7 of the drilling tool or to the lateral edge 18 of the flank area 17. Between the blade 12 in the operating position and the flank area 17 close to the axis of the insert 3, the rib curve therefore extends with a preferably uniform curvature between its two rib ends. In the flank area 17, the chip shaping troughs 15 do not end in front of the lateral edge 18, but continue through the lateral edge. The lateral edge thereby has a wavy profile in the area where the chip shaping groove 15 emerges. This configuration guarantees that the chip can be removed without resistance and can arrive in the vicinity of the chip flute of the drilling tool. 
     To further promote the curved removal path of the chips, the cutting angle of a cutting edge 8 or 9 preferably increases positively as the distance from the drill axis 17 increases. As a result, there is a reduced deformation of the chip caused by pressure in the radially outer areas of the blade. This different degree of pressure deformation over the chip width as a whole promotes the shaping of the chip into a spiral. The formation of a chip spiral 19 is illustrated schematically in FIG. 3. This figure also shows that the chip shaping ribs 14 and the chip shaping grooves 15, on the back surface 20 of the chip spiral 19 facing the face 13, are reproduced to a certain extent in the manner of a corrugation 21. 
     FIGS. 4 to 7 show an insert 3b as claimed by the invention which has a curved face 13 and which extends in a curved shape from the blade 12 to the lateral edge 18. As described above with reference to the insert 3, 3a in FIGS. 1 to 3, it is conventional on indexable inserts of the type in question to have a second blade 12 and second chip shaping ribs 14 and chip shaping grooves 15 in a symmetrical arrangement, whereby in this case there is a dyad axis of symmetry which is formed by the longitudinal center axis 23 of the fastening boring 6. The essential difference between this insert 3b and the one illustrated in FIGS. 1 to 3 is that the chip shaping grooves 15 interrupt the blade 12. The blade 12, when viewed in the direction indicated by the Arrow VII in FIG. 4, or in the direction of the longitudinal dimension of the insert 3b, therefore has a somewhat corrugated profile. The blade 12, 12&#39; accordingly has concave grooves 24 which are separated from one another by the chip shaping ribs 15. The result of this configuration is that the negative copy of the chip shaping ribs 14 and chip shaping grooves 15 occurs directly during the chip formation, because there is no web between the blade 12 and the chip shaping groove 15. The chip spiral 19 is removed from the workpiece material from the very beginning with a corrugated rear surface 20 (as shown in FIG. 3). The chip shaping ribs 14 and chip shaping grooves 15 are in this embodiment more clearly reflected in the shape of a corrugation 21 on the rear surface 20 of the chip spiral than is the case in the embodiment illustrated in FIGS. 1-3. The form-fitting engagement between the rear surface 20, the face 19 and the chip shaping ribs 14 and chip shaping grooves 15, and thus the automatic guidance of the chip spiral 19, is more pronounced. The chip shaping properties and in particular the automatic guidance in the direction of chip removal are even more strongly pronounced with the insert 3b. 
     FIG. 8 shows a trigonal insert 30. Such trigonal inserts have a total of 3 blades 31a, 31b and 31c, each of which is formed by cutting edges 8, 9 which are vertical in cross section. The trigonal insert 30, on its face 13, next to the above-mentioned curved chip shaping ribs 35, has three radial ribs 32a, 32b, 32c, each of which extends along the connecting line between a corner 33 of the insert and the center of the trigonal insert. At least one of the profile ribs 35 located in the vicinity of the radial ribs 32a, 32b and 32c merges into a radial rib 32a, 32b, 32c. Corresponding to the cutting edge 8a are a total of three chip shaping ribs 35, whereby the two which are next to the insert corner 33a merge into the radial rib 32a. Of the chip shaping ribs 35 corresponding to the blade 31c and the cutting edge 9c, only the chip shaping rib 35 which is next to the insert corner 33a merges into the radial rib 32a. There are corresponding conditions in the face areas which correspond to the insert corners 33b and 33c. Except for the chip shaping ribs which are respectively closest to each of the insert corners 33a, 33b, 33c, all the chip shaping ribs 35 and the radial ribs 32a, 32b and 32c merge into the positioning hole 6 or they extend to the edge of the boring 6. In contrast to the insert illustrated in FIGS. 1 or 4, the grooves located between the chip shaping ribs 35 are wider and less trough-shaped. The configuration is designed so that if the chip shaping ribs 35 and the radial ribs 32 are ignored, the outer surface or the face 13 is a continuous surface, possibly with a concave groove, or is spoon-shaped. 
     The purpose of the radial ribs 32 is to remove a chip which has been cut off by the blade, such as the blade 31, from the workpiece, and to move in the direction of the arrow 34 on the radial rib 32a, in the manner of a chip guide, away from the face 13. The chip is thereby prevented from coming into contact laterally with a chip shaping rib of the blade 31c which is next to the axis 7 of the drilling tool in the installed position, and thereby being deflected in an uncontrolled manner from the optimal chip removal direction. The formation of a chip spiral can also be achieved, when a trigonal insert is used, by a face 13 which is concave or has a groove so that it is spoon-shaped. 
     One feature of the invention resides broadly in the drilling tool for drilling holes in solid metal--with a base body 1 which contains at least one chip flute 5, 5a,--with at least one replaceable cutting insert 3, 3a on the end surface of the base body 1 located in a recess 4, 4a on the end of a chip flute 5, 5a, and--with a blade 12 which is preferably formed by two cutting edges 8, 9 which form an obtuse point angle 11 with one another, characterized by the fact that the rake face 13 of the blades 12 contains chip shaping ribs 14, 14a located next to one another which act in the manner of runners for the chips, which chip shaping ribs, in the vicinity of the blade 12 or of the cutting edges 8, 9, are oriented approximately perpendicular to the cutting edges, and from there the chip shaping ribs extend in the direction of chip removal with a curved profile with regard to their installed position radially inward toward a flank area 17 of the insert 3, 3a, which flank area 17 is close to the axis 17 of the drilling tool. 
     Another feature of the invention resides broadly in the tool characterized by a constant curvature of the chip shaping ribs 14, 14a toward their tapered terminal area. 
     Yet another feature of the invention resides broadly in the drilling tool characterized by the fact that the chip shaping ribs 14, 14a extend with a continuous curved path radially inward to the flank area 17 of the insert 3, 3a, where they are oriented perpendicular to the axis 7 of the drilling tool. 
     Still another feature of the invention resides broadly in the drilling tool characterized by the fact that the chip shaping ribs 14, 14a are formed by recesses or chip shaping grooves 15 which are located next to and at a distance from one another. 
     A further feature of the invention resides broadly in the drilling tool characterized by the fact that the chip shaping ribs 14, 14a are realized so that in cross section, they have approximately the shape of a circular arc or ellipse. 
     Another feature of the invention resides broadly in the drilling tool characterized by the fact that in cross section, the chip shaping ribs 14, 14a have the shape of a trapezoid, the flanks of which are concave. 
     Yet another feature of the invention resides broadly in the drilling tool characterized by the fact that the chip shaping ribs 15 interrupt the blade 12, 12&#39;. 
     Still another feature of the invention resides broadly in the drilling tool characterized by the fact that the chip shaping grooves 15 interrupt the lateral edge 18 which defines the flank area 17 of the insert 3, 3a. 
     A further feature of the invention resides broadly in the drilling tool characterized by at least two chip shaping ribs 14, 14a which are located next to one another and correspond to a blade 12. 
     Another feature of the invention resides broadly in the drilling tool characterized by the fact that the rake faces 13 of the inserts 3, 3a are concave. 
     Yet another feature of the invention resides broadly in the drilling tool characterized by the fact that the curvature of the chip shaping ribs 14, 14a is greater or less than the curvature of the unhindered or optimal chip removal path. 
     Still another feature of the invention resides broadly in the drilling tool characterized by the fact that the insert is a trigonal insert 30 which has a central fastening hole 6, on the face 13 of which there are three radial ribs 32a, 32b, 32c:--each of which runs along the connecting line between one corner 33a, 33b, 33c of the insert and the center of the trigonal insert 30,--and into which at least one of the chip shaping ribs 14 next to a corner 33a, 33b, 33c of the insert merges. 
     A further feature of the invention resides broadly in the drilling tool characterized by the fact that at least the chip shaping ribs 14 which do not merge into a radial rib 32a, 32b, 32c extend to the central fastening hole 6. 
     Another feature of the invention resides broadly in the drilling tool characterized by the fact that the cutting angle of a cutting edge 9 which is farther from the axis 7 of the drilling tool has a greater positive component than the cutting angle of a cutting edge 8 of the same insert 3, 3a which lies closer to the axis 7 of the drilling tool. 
     The invention as described hereinabove in the context of the preferred embodiments is not to be taken as limited to all of the provided details thereof, since modifications and variations thereof may be made without departing from the spirit and scope of the invention. 
     
         ______________________________________NOMENCLATURE______________________________________1               Base body2               Drill tip3               Insert3a              Insert3b              Insert4, 4a           Recess5, 5a           Chip flute6               Fastening boring7               Axis of boring tool8               Cutting edge9               Cutting edge10              Cutting tip11              Point angle12              Blade13              Face14              Chip shaping rib15              Chip shaping groove16              Web17              Flank area18              Lateral edge19              Chip spiral20              Rear surface21              Corrugation22              Line23              Longitudinal center axis24              Trough30              Trigonal insert31a             Blade31b             Blade31c             Blade32a             Radial rib32b             Radial rib32c             Radial rib33a             Insert corner33b             Insert corner33c             Insert corner34              Direction of arrow35              Profile ribs______________________________________