SINGLE-LIP DRILL HAVING TWO LONGITUDINAL GROOVES IN THE RAKE FACE

Abstract

The invention relates to single-lip drills in which two longitudinal grooves are formed in the rake face. They are arranged in the longitudinal direction of the tool, spaced apart from one another by a ridge and favor chip breaking.

Claims

1. A single-lip drill comprising a drill head, the drill head having an axis of rotation, a drilling diameter and a cutting edge, a rake face being assigned to the cutting edge, longitudinal grooves running parallel to each other being provided in the rake face, and a ridge being provided between the inner longitudinal groove and the outer longitudinal groove, characterized in that the ridge opens out into the cutting tip.

2. (canceled)

3. (canceled)

4. The single-lip drill according to claim 12 or 3, characterized in that the longitudinal grooves are arranged symmetrically or geometrically similar in cross section to the ridge.

5. The single-lip drill according to claim 1, characterized in that the longitudinal grooves have the shape of a first straight line and a tangentially adjoining curved line in a cutting plane running orthogonally to the axis of rotation of the deep hole drill, that the first straight line and the rake face form an angle (α), and that the curved line intersects the rake face at an angle (β).

6. The single-lip drill according to claim 1, characterized in that the longitudinal grooves have the shape of a first straight line and an adjoining second straight line in a sectional plane running orthogonally to the axis of rotation of the deep hole drill, that the first straight line and the rake face form an angle (α), and that the second straight line and the rake face form an angle (β).

7. The single-lip drill according to claim 5, characterized in that the angle (α) is less than or equal to 30° and/or that the angle (α) is greater than or equal to 10°.

8. The single-lip drill according to claim 5, characterized in that the angle (α) is less than or equal to 25° and/or that the angle (α) is greater than or equal to 15°.

9. The single-lip drill according to claim 5, characterized in that the angle (α) is equal to 20°.

10. The single-lip drill according to claim 5, characterized in that and the angle (β) is less than or equal to 60° and/or that the angle (β) is greater than or equal to 20°.

11. The single-lip drill according to claim 5, characterized in that the angle (β) is less than or equal to 50° and/or that the angle (β) is greater than or equal to 35°.

12. The single-lip drill according to claim 5, characterized in that the angle (β) is equal to 45°.

13. The single-lip drill according to claim 1, characterized in that the longitudinal grooves have the shape of a segment of a circle, an isosceles triangle or a non-isosceles triangle in a sectional plane running orthogonally to the axis of rotation of the deep hole drill.

14. The single-lip drill according to claim 1, characterized in that a distance (L.sub.1) of the cutting tip and the ridge from the secondary cutting edge is greater than 0.2 times the diameter (D). (L.sub.1>0.2×D)

15. The single-lip drill according to claim 1, characterized in that a distance (L.sub.1) of the cutting tip and the ridge from the secondary cutting edge is less than 0.36 times the diameter (D). (L.sub.1<0.36×D)

16. The single-lip drill according to claim 1, characterized in that a distance (L.sub.1) of the cutting tip and the ridge from the secondary cutting edge is 0.25 times the diameter (D).

17. The single-lip drill according to claim 1, characterized in that a distance (S.sub.1) between an edge of the outer longitudinal groove and the secondary cutting edge is at least 0.05 mm.

18. The single-lip drill according to claim 1, characterized in that the ridge has a width (B) at its highest point, and that the width (B) is a maximum of 0.4 mm.

19. The single-lip drill according to claim 1, characterized in that the sum of a width (B.sub.33.1) of the inner longitudinal groove and a width (B.sub.33.2) of the outer longitudinal groove is greater than 0.4×the diameter (D) of the deep hole drill.

20. The single-lip drill according to claim 1, characterized in that the drill head is at least partially provided with a hard material coating.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In the drawings:

[0034] FIGS. 1 and 2 show a single-lip drill (prior art);

[0035] FIG. 3 shows a view from the front of the single-lip drill according to FIG. 1;

[0036] FIG. 4 shows a single-lip drill according to the invention in a top view;

[0037] FIG. 5 shows a single-lip drill according to the invention in a view from the front; and

[0038] FIGS. 6 to 8 show sections through different shapes of longitudinal grooves according to the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] In all figures, the same reference signs are used for the same elements or components. FIG. 1 shows a single-lip drill 1. A central axis 3 is at the same time also the axis of rotation of the single-lip drill 1 or of the workpiece (not shown) when the drill is set in rotation during drilling.

[0040] A diameter of the single-lip drill 1 is denoted by D. The single-lip drill 1 is composed of three main components, specifically a drill head 5, a clamping sleeve 7 and a shank 9. This structure is known to a person skilled in the art and is therefore not explained in detail.

[0041] A bead 11 is provided in the shank 9 and the drill head 5. The bead 11 has a cross section approximately in the form of a segment of a circle (see FIG. 3) having an angle usually of approximately 90° to 130°. The bead 11 extends from the tip of the drill to in front of the clamping sleeve 7. Because of the bead 11, the drill head 5 and shank 9 have a cross section approximately in the shape of a segment of a circle with an angle of usually 230° to 270° (a supplementary angle to the angle of the bead 11).

[0042] A cooling channel 13 extends over the entire length of the single-lip drill 1. At one end of the clamping sleeve 7, coolant or a mixture of coolant and air is conveyed under pressure into the cooling channel 13. The coolant or the mixture of coolant and air exits back out from the cooling channel 13 at the opposite front end 15, the end face of the drilling tool. The coolant has a plurality of functions. On the one hand, it cools and lubricates the cutting edge and the guide pads. In addition, it conveys the chips produced during drilling out of the borehole via the bead 11.

[0043] The front end 15 is shown slightly enlarged in FIG. 2. Elements of the drill head 5 are explained in more detail on the basis of this figure.

[0044] In single-lip drills 1, a cutting edge 17 usually consists of an inner cutting edge 17.1 and an outer cutting edge 17.2. A cutting tip has the reference character 19. As is usual with single-lip drills, the cutting tip 19 is arranged at a radial distance from the central axis 3. The inner cutting edge 17.1 extends from the central axis 3 to the cutting tip 19. The outer cutting edge 17.2 extends from the cutting tip 19 in the radial direction to the outer diameter D of the drill head 5 and terminates at a secondary cutting edge 21. There are also known bevels that are flattened at the tip. In this case, a theoretical cutting tip 19 is obtained by extending the inner cutting edge and the outer cutting edge to their theoretical intersection, which serves as a reference point for the longitudinal grooves. Grindings are also known which have the contour of a circular arc (radius grind). Then the forwardmost point of the drilling tool is the “cutting tip.”

[0045] A distance between the cutting tip 19 and the secondary cutting edge 21 is denoted by L.sub.1 in FIG. 2. The bead 11 is delimited by a flat rake face 23 and a flat wall 25. The rake face 23 and the wall 25 form an angle of approximately 130°. In the embodiment shown, the rake face 23 extends through the central axis 3.

[0046] In FIG. 3, the central axis 3 is shown as “X”. The straight bead 11 is also clearly visible. It is defined by a rake face 23 and a wall 25. The rake face 23 and the wall 25 form an angle of approximately 130°. In the embodiment shown, the rake face 23 extends through the central axis 3. However, this does not have to be the case. The rake face 23 can run slightly below or slightly above the central axis 3. As a rule, the distance between the rake face 23 and the central axis 3 is less than 0.1 mm, preferably less than 0.05 mm. A rake face plane 27, indicated by a dot-dashed line, likewise extends through the central axis 3. The rake face plane 27 is a geometric definition which is not always and readily visible on the single-lip drill. The rake face plane 27 is defined in that it extends parallel to the rake face 23 and through the central axis 3. When the rake face 23 extends through the central axis 3, the rake face plane 27 and the rake face 23 coincide and the rake face plane 27 can be seen.

[0047] In FIG. 3, the inner cutting edge 17.1 can be seen as a line between the central axis 3 and the cutting tip 19. Correspondingly, the outer cutting edge 17.2 can be seen as a line between the cutting tip 19 and the secondary cutting edge 21. When viewed from the front, the inner cutting edge 17.1 and the outer cutting edge 17.2 coincide with the rake face 23. For the sake of clarity, reference signs 17.1 and 17.2 do not appear in FIG. 3.

[0048] In FIG. 3, two outlet openings of the cooling channel 13 are shown.

[0049] A plurality of guide pads 29 and 31 are formed on the drill head 5, distributed over the circumference. The guide pad 29 and the rake face 23 form the secondary cutting edge 21 where they intersect. This guide pad is referred to below as a circular grinding chamfer 29. The circular grinding chamfer 29 and the guide pads 31 have the task of guiding the drill head 5 in the bore.

[0050] In FIGS. 4 to 7, embodiments of deep hole drills according to the invention are shown in a view from the front or as a partial section along the line C-C (see FIG. 4).

[0051] According to the invention, two longitudinal grooves 33, namely an inner longitudinal groove 33.1 and an outer longitudinal groove 33.2, are provided in the rake face 23. A ridge 35 is formed between the inner longitudinal groove 33.1 and the outer longitudinal groove 33.2. The highest point of the ridge 35 lies in the rake face 23 or slightly below it. In numbers: The ridge 35 is a maximum of 0.1 mm, but preferably less than 0.05 mm, below the rake face 23. The term “slightly below” is to be understood in such a way that when the longitudinal grooves 33.1, 33.2 are ground into the rake face 23 in the region of the ridge 35, a maximum of 0.1 mm is removed from the rake face 23. It can be seen from FIG. 4 that the longitudinal grooves 33.1 and 33.2 are made in sufficient length in the rake face 23 of the drill head 5, so that they are retained even after repeated resharpening by resetting the cutting edge 17.

[0052] As can be seen from FIGS. 4 and 5, there is a distance S.sub.1 between the outer longitudinal groove 33.2 and the secondary cutting edge 21. This means that a narrow strip of the rake face 23 remains between the outer longitudinal groove 33.2 and the secondary cutting edge 21. As a result, the secondary cutting edge 21 is not weakened by the outer longitudinal groove 33.2. The strip with the width S.sub.1 also has a positive effect on the load-bearing capacity and the service life of the cutting edge corner.

[0053] The mode of operation of the longitudinal grooves during chip formation and chip forming is explained with reference to FIG. 5. The shaping of the longitudinal grooves 33.1 and 33.2 according to the invention means that the chip, which is cut by the outer cutting edge 17.2, begins to flow on the straight line 37 in the direction of the ridge 35. As soon as it flows over the curved line 39 or the associated curved surface in the outer longitudinal groove 33.2 in the direction of the ridge 35, the chip is bent over and rolled up. This reshaping process leads to breaking of the chip generated by the outer cutting edge 17.2. In a corresponding manner, the same process also takes place in the region of the inner longitudinal groove 33.1.

[0054] The majority of the cutting process takes place in the radially outer region of the outer cutting edge 17.2 (where it is formed by the straight lines 37 and the flank face). There the chip is cut, it flows over the flat region of the outer longitudinal groove 33.2 represented by the straight line 37 in FIG. 5 in the direction of the ridge 35; i.e., radially inwardly. The curved surface of the outer longitudinal groove 33.2 represented by the curved line 39 rolls the flowing chip in and leads to its breaking off.

[0055] The two curved arrows (without reference symbols) in FIG. 5 illustrate this situation. It was possible to verify the processes described above in real bores by recording with a high-speed camera.

[0056] FIG. 6 shows a further embodiment of a deep hole drill according to the invention. FIG. 6 shows a partial section along the line C-C from FIG. 4. In this embodiment, the inner longitudinal groove 33.1 is designed in cross section as a continuously curved line, for example as a segment of a circle. The same applies to the outer longitudinal groove 33.2. In this embodiment, the inner longitudinal groove 33.1 and the outer longitudinal groove 33.2 are geometrically similar. This means that in cross section both have the shape of a curved line or a segment of a circle. However, a width B.sub.33.1 of the inner longitudinal groove 33.1 is smaller than a width B.sub.33.2 of the outer longitudinal groove 33.2. In this embodiment, the tip 19 or the ridge 35 is located at D/3 from the outer diameter of the drilling tool or the secondary cutting edge 21. Correspondingly, the ridge 35 is only D/6 away from the central axis 3 or axis of rotation of the drilling tool. It is also possible to move the tip 19 and the ridge 35 outwardly, so that the width B.sub.33.1 of the inner longitudinal groove 33.1 is greater than the width B.sub.33.2 of the outer longitudinal groove 33.2.

[0057] A further embodiment of longitudinal grooves according to the invention is shown in FIG. 7. In this embodiment, the longitudinal grooves 33 have the shape of a non-isosceles triangle in cross section. These triangles are formed from a first straight line 37 and a second straight line 41. The angle α is shown between the first straight line 37 and the rake face 23. The second straight lines 41 form the angle β with the rake face 23. The value ranges for the angles α and β are named in the claims and in the introduction to the description.

[0058] In this embodiment of the longitudinal grooves 33 according to the invention, the dressing of the grinding wheel is somewhat easier. In practice, a small radius will appear after a short time at the intersection of the first straight line 37 and the second straight line 41. This rounding is due to the wear of the grinding wheel at the lowest point of the longitudinal grooves 33.

[0059] A further embodiment of longitudinal grooves 33.1 and 33.2 according to the invention is shown in FIG. 8. In this embodiment, the inner longitudinal groove has the shape of a segment of a circle in cross section, while the outer longitudinal groove 33.2 has the shape of a non-isosceles triangle which is formed by the straight lines 37 and 41.

[0060] It is of course also possible for the inner longitudinal groove 33.1 to have a triangular cross section, while the outer longitudinal groove 33.2 is designed as a circular arc-shaped longitudinal groove or as shown in the embodiment according to FIG. 5.

[0061] All embodiments have in common that a considerable part of the rake face is designed as a longitudinal groove, which is reflected in the fact that more than 40% (in some versions even 80% or more) of the rake face is removed by grinding in the longitudinal grooves 33. Only the ridge 35 remains, the width B of which is a maximum of 0.4 mm. At the outer edge, that is to say where the secondary cutting edge 21 is located, a narrow strip of the rake face 23 can remain, the width S.sub.1 of which, however, is only a few tenths of a millimeter. The width can also depend on the diameter and be 0.1×D.

[0062] In the following, some terms are briefly explained and defined.

[0063] The overall shape of all cutting and non-cutting faces at the end face of the drill head is referred to as the nose grind. This also includes surfaces that do not directly adjoin the cutting edges, for example surfaces for directing the coolant flow or additional flank faces, to allow the drill to cut cleanly. The nose grind determines the shaping of the chips to a large extent and is matched to the material to be machined. The aims of the matching are, among other things, shaping chips that are as favorable as possible, a high machining speed, the longest possible service life of the drill, and compliance with the required quality characteristics of the bore such as diameter, surface or straightness (center deviation).

[0064] To increase the service life, the drill head can be provided with a coating as wear protection, mostly from the group consisting of metal nitrides or metal oxides; the coating can also be provided in a plurality of alternating layers. The thickness is usually approx. 0.0005 to 0.010 mm. The coating is carried out by means of chemical or physical vacuum coating processes. The coating can be provided on the circumference of the drill head, on the flank faces or on the rake faces, and in some cases the entire drill head can also be coated.

[0065] Single-lip drills are single-edged deep hole drills. Single-lip drills are long and slender and have a central axis. The rake face thereof is flat; hence they are also referred to as “straight grooved” tools. They are used to create bores that have a large length to diameter ratio. They are mainly used in industrial metal working, such as in the production of engine components, in particular in the production of common rails or gear shafts.

[0066] Single-lip drills are usually used in a diameter range of approx. 0.5 to 50 mm. Bores having a length of up to about 6,000 mm are possible.

[0067] The length to diameter ratio (L/D) of the bore is usually in a range from approx. 10 to over 100; however, it can also be approx. 5 and up to about 250.

[0068] Single-lip drills are characterized by the fact that a high-quality bore can be produced in one stroke. They can be used in machine tools such as lathes, machining centers or special deep drilling machines.

[0069] The machining process is performed by means of a movement of the drill relative to the workpiece in the direction of rotation about a common central axis, and a relative movement of the drill toward the workpiece in the direction of the common central axis (feed movement). The rotational movement can be caused by means of the drill and/or the workpiece. The same applies to the feed movement.

[0070] The flank face is the surface at the tip of the drill head that is opposite the machined workpiece surface.

[0071] Guide pads are arranged on the circumference of the drill head to support the cutting forces in the drilled bore which arise during cutting. Guide pads are cylinder segments having the diameter of the drill head; they abut the wall of the bore during the drilling process. Radially recessed segments having a smaller diameter are arranged on the drill head, between the guide pads in the circumferential direction, such that a gap is formed between the bore wall and the drill head. The gap is used to collect coolant for cooling and lubricating the guide pads.

[0072] There are different arrangements of guide pads; the design depends on the material to be machined. The first guide pad, which adjoins the rake face counter to the direction of rotation of the drill, is referred to as the circular grinding chamfer.

[0073] Coolant or a mixture of coolant and air (minimum quantity lubrication) is conveyed through the cooling channel to lubricate and cool the drill head and the guide pads as well as to carry the chips away to the tip of the drill head. Coolant is supplied under pressure to the rear end, passes through the cooling channel and exits at the drill head. The pressure depends on the diameter and length of the drill.

[0074] By adapting the pressure of the coolant, single-lip drills can drill very small and very deep bores in one go.

[0075] During the drilling process, the deviation [mm] of the actual drilling central axis from the theoretical drilling central axis is regarded as the center deviation. The center deviation is an aspect of the bore quality. The aim is to achieve the smallest possible center deviation. In the ideal case, there is no center deviation at all.

[0076] Regrinding can allow a single-lip drill that has become blunt to be usable again. Regrinding means readjusting/grinding the worn part of the drill head mostly on the end face until all worn regions (in particular of the rake face and flank face) have been removed and a new, sharp cutting edge has been formed. The nose grind then reverts to its original shape.

[0077] The line of contact (edge) between the rake face and the circular grinding chamfer is referred to as the secondary cutting edge. The point of intersection between the outer cutting edge and the secondary cutting edge is referred to as the cutting corner.

[0078] The drill head has a cutting edge, which can be divided into a plurality of cutting edge portions and a plurality of stages. The cutting edge is the region that is involved in the machining. The cutting edge is the line of intersection of the rake face and the flank face. The cutting edge is usually divided into a plurality of straight partial cutting edges.

[0079] The rake face is the region on which the chip is discharged; it can also consist of a plurality of partial surfaces.

[0080] A chip-forming device is a recess machined into the rake face, extending parallel to the cutting edge and directly adjoining the cutting edge. In other words: There is no rake face between the cutting edge and the chip-forming device.

[0081] A chip divider constitutes a “break” in the outer cutting edge, which reduces the width of the chips.