DRILLING TOOL

Description

[0001] The present invention relates to a drilling tool having the features of the preamble of claim 1.

[0002] Typical drilling tools have a shank section and a cutting section. The cutting section typically has two helical chip flutes that serve to remove chips. Coolants and lubricants can be supplied, in particular, via cooling channels that run along the cutting edge of the tool.

[0003] Between each chip flute there is a web, the outer surface of which forms the cutting back.

[0004] Drilling tools typically have two main cutting edges located on one end of the tool. Peripheral cutting edges are located on the webs.

[0005] The loads on the main cutting edges and the cutting edge corner are very high, especially when machining hard, abrasive materials such as cast iron.

[0006] There are current approaches to reducing stress on the main cutting edge by extending the main cutting edge through a curved path. A small tip angle also results in longer main cutting edges than a large tip angle.

[0007] EP1622735 B1 discloses a drilling tool for machining cast materials, wherein a main cutting edge is continuously convex, at least in sections, in an axial direction starting from the cutting edge. The resulting extension of the main cutting edge leads to a reduction in the load per unit of main cutting edge length and thus to a robust main cutting edge.

[0008] DE102012002050 (A1) shows a drilling tool according to the preamble of claim 1: with a first chamfer on the peripheral cutting edge on a first diameter and on the cutting back a guide chamfer which determines the drilling diameter with respect to the direction of rotation after the first chamfer and is offset by an angle with respect to the first chamfer.

[0009] DE10144241 (A1) shows a drill with a secondary cutting edge featuring a rounded chamfer. Following this, rounded chamfers are formed on the back.

[0010] The object of the present invention is to provide an improved drilling tool, in particular an improved drilling tool for machining cast materials. In particular, the invention is directed to a drilling tool for machining wear-prone materials, in particular for machining cast iron materials.

[0011] The problem is solved by a drilling tool having the features of claim 1. Preferred developments are laid down in the dependent claims.

[0012] By having the features of claim 1, a drilling tool with improved service life, good guidance and low friction is created.

[0013] The main cutting edge does not extend radially to the drill diameter, but merges into the peripheral cutting edge along a transition zone. A first chamfer is formed on the peripheral cutting edge at a first diameter, which is smaller than the drill diameter. The chamfer on the peripheral cutting edge is ground with a clearance angle. This means that there is a defined clearance angle at this first chamfer. A particular advantage of the peripheral cutting edge with a clearance angle compared to a circular design is that the peripheral cutting edge has a cutting effect and generates little friction and therefore little force.

[0014] Thus, the peripheral cutting edge, with its first chamfer, acts as a pre-cutter to a first diameter that does not yet correspond to the drill diameter, i.e., is smaller than it. Only the circularly ground guide chamfer on the back of the cutter cuts the bore wall to the drill diameter. In other words, the cylindrical back of the guide chamfer is at the drill diameter. Only the guide chamfer on the back of the cutter determines the drill diameter.

[0015] This significantly reduces the load on the main cutting edge, and especially on the cutting edge corner, i.e., the transition from the main cutting edge to the peripheral cutting edge. This is because, particularly at the transition from the main cutting edge to the peripheral cutting edge, the loads from machining overlap at the bottom of the hole and at the wall of the hole. With the drilling tool according to the invention, the loads are at least partially decoupled and distributed locally.

[0016] With the drilling tool according to the invention, the main cutting edge, after the transition from the face of the drilling tool into the so-called diameter area, does not have to also cut the bore wall to the bore diameter. This is done by the guide lands on the cutting edge back.

[0017] The guide chamfer is offset from the first chamfer by an angle of 20° to 40°. When viewed in cross-section, the guide chamfer follows the first chamfer on the cutting edge after 20° to 40° in the direction of rotation. In particular, the guide chamfer is offset from the first chamfer by an angle of 30°±5°, more preferably by an angle of 30°±2°. This offset is close enough for immediate re-cutting to the drill diameter and also close enough for effective support of the drilling tool. The tool is unsupported only over a relatively small angular range. A guide close to the peripheral cutting edge prevents chatter.

[0018] At the same time, the guide chamfer is sufficiently spaced to form a sufficiently large auxiliary chip groove for the chips accumulating on the guide chamfer.

[0019] An auxiliary chip groove is formed in front of the guide land, relative to the intended direction of rotation of the drilling tool. The auxiliary chip groove is a radial recess formed in the back of the cutter in front of the guide land, creating additional chip space. This additional chip space in front of the guide land is particularly helpful for removing the material removed by the guide land and for facilitating the formation of the rake angle of the guide land.

[0020] In particular, the auxiliary chip groove extends to a diameter of 85% to 90% of the drill diameter. For example, for a drilling tool with an 8.5 mm drill diameter, the auxiliary chip groove was designed to extend to a diameter of approximately 7.5 mm. This depth corresponds to approximately 88% of the drill diameter.

[0021] The difference between the first diameter at the first chamfer, i.e. at the circumferential cutting edge, and the drill diameter is preferably present over a grooved length and, more preferably, constant in amount over the length of its formation.

[0022] According to the invention, the clearance angle at the first chamfer, i.e., the chamfer on the peripheral cutting edge, is between 5° and 15°. More preferably, the clearance angle is 10° ± 2°.

[0023] Preferably, the clearance angle facet extends over an angular range between 8° and 16°, in particular over an angular range of 12° ± 2°. The extent is apparent from a cross-sectional view. The swept angular range is a measure of the width of the clearance angle facet.

[0024] In particular, the clearance angle facet is flat. However, it can also be slightly concave or convex.

[0025] Preferably, the guide chamfer has a rake angle—in terms of magnitude—between 2° and 8°. The rake angle can take negative or positive values. The magnitude (also: "absolute value") in the mathematical sense is usually expressed by the operators ||. The magnitude of the rake angle, i.e. | rake angle | , is preferably between 2° and 8°. More preferably, the magnitude of the rake angle is 5°±2°, in particular 5°±1°.

[0026] Especially for small diameters (typically ∅ < 6 mm) of the drilling tool, the rake angle can also take on negative values.

[0027] A rake angle is determined between a rake face and a tool reference plane. By convention, a rake angle of 0° is considered negative.

[0028] The guide chamfer has a rounded surface, which allows it to support the drilling tool with minimal friction and also smooths the workpiece surface. In addition, the guide chamfer is designed to cut across the rake angle. Due to its arrangement and special design, the guide chamfer therefore performs several functions.

[0029] Preferably, the width of the guide chamfer is between 0.025 and 0.125 times the bore diameter. This ratio applies provided that a certain absolute width of the guide chamfer is not undercut. A suitable minimum value for the absolute width of the guide chamfer can preferably be set at 0.20 mm.

[0030] A guide chamfer that is too narrow causes the drilling tool to chatter and is not robust.

[0031] For friction reasons, it is also advisable not to exceed a certain absolute width of the guide chamfer. It is best if the absolute width of the guide chamfer remains below 3.0 mm. A guide chamfer that is too wide results in an excessively large contact area with the bore wall, thus causing more friction and higher forces.

[0032] Preferably, no further chamfer or web is formed on the cutting back behind the guide chamfer with respect to the direction of rotation, since additional friction is detrimental and undesirable.

[0033] Preferably, the difference between the first diameter and the bore diameter is between 0.025 mm and 0.065 mm. Further preferably, the difference between the first diameter and the bore diameter is 0.045 mm ± 0.010 mm, in particular 0.035 mm ± 0.02 mm.

[0034] The difference between the first diameter and the drill diameter is the amount that the guide lands on the circumference together remove. Thus, for a two-flute drill, if the difference between the first diameter and the drill diameter is, for example, 0.030 mm, each of the two guide lands on the circumference removes 0.015 mm, or half of 0.030 mm.

[0035] Too large a difference would require excessive material removal per guide land. Too small a difference is complex to manufacture and does not effectively decouple the main cutting edge from the peripheral cutting edge. An absolute value of the difference between the first diameter of 0.045 mm ± 0.01 mm has proven particularly advantageous.

[0036] Preferably, the difference between the first diameter and the drill diameter from the beginning of the peripheral cutting edges exists over the entire grooved length.

[0037] Further preferably, the difference between the first diameter and the drill diameter is constant over the entire grooved length.

[0038] Preferably, the drilling diameter of the drilling tool tapers from the tip toward the shaft. This reduces friction in the drilled hole. The taper is typically between 0.002 mm and 0.05 mm per 10 mm of length. Particularly preferably, the taper is 0.03 mm per 10 mm of length.

[0039] The taper is typically formed during the cylindrical grinding of a blank. Thus, the taper is also present on all chamfers with a cylindrical grind. To clarify: this means that the drill diameter determined by the guide chamfers is not a constant size over the length of the drill bit, but rather decreases according to the degree of the taper.

[0040] The difference between the initial diameter and the bore diameter discussed above is maintained even with a taper. Otherwise, the initial diameter and the bore diameter would converge.

[0041] Particularly for longer tools, for example, tools with a length ≥ 6 x D, it can be provided that the cutting guide chamfer extends only over a portion of the grooved length. Thus, it can be provided that the guide chamfer, viewed from the tip, extends only up to a first length of 2 x D to 4 x D. Particularly preferably, the guide chamfer extends up to a first length between 3.2 x D and 3.8 D, in particular by 3.5 x D.

[0042] This refinement is, of course, also feasible for shorter drilling tools, but is particularly useful for longer tools. It has the advantage of reducing friction with the bore wall. After all, the drilling diameter in a workpiece is already created by the section with the cutting guide lands, and the adjacent section of the drilling tool without guide lands is free.

[0043] It can be provided that the guide chamfer is formed along a first length, which is followed by a second length in the direction of the shaft, along which a further guide chamfer is formed on the peripheral cutting edge instead of the first chamfer (with clearance angle grinding). The further guide chamfer has a round grind.

[0044] The first and second lengths are sections of the grooved length. Chip grooves are inserted along the grooved length.

[0045] The cutting guide lands on the cutting edge of the cutter fulfill their function primarily in the longitudinally front area of ​​the drilling tool (i.e. close to the tip). As a result, the guide lands on the cutting edge tend to lose their function as diameter-cutting lands as the distance from the tip increases. According to the further development, the cutting guide lands on the cutting edge of the cutter taper off after an initial length. To ensure that the tool is still guided, a further guide land with a round grind is formed along a subsequent second length on the peripheral cutting edge instead of the first land with a flank grind previously formed there. This ensures that the drill is always guided by a fully round guide land.

[0046] Preferably, there is an overlap area where the transition from the guide bevel on the cutting back to the guide bevel on the peripheral cutting edge occurs. The overlap area can, for example, be a quarter of the length x D. A smooth taper of the guide bevel on the cutting back is advantageous.

[0047] This advanced training is particularly interesting for drilling tools for deep holes, for example grooved lengths greater than 6 x D, where D is the drill diameter.

[0048] If the first, sharply ground guide chamfer on drilling tools for deep holes were to be formed over the entire grooved area, there would even be a risk that the drill would "hook" on the diameter under unfavorable operating conditions, damaging the hole surface and / or even breaking the drilling tool.

[0049] The drill diameter is always determined by a fully circular guide land. Along the first length, with guide lands on the cutting edge, the drill diameter is determined by these cutting guide lands. Along the axially adjacent second length, the guide lands formed directly on the peripheral cutting edge are aligned with the drill diameter.

[0050] In this refinement, the drilling tool preferably tapers from the tip toward the shaft. Therefore, the drilling diameter of a tapered drilling tool is not a constant.

[0051] The main cutting edge has several main cutting edge sections.

[0052] There is a point thinning in an area close to the center. A preferably straight main cutting edge section adjoins this radially outward.

[0053] This is followed by a transition area along which the main cutting edge merges into the peripheral cutting edge. The transition area can be designed, for example, as a chamfer or, preferably, as a radius transition.

[0054] A radius transition is advantageous over sharp-edged transitions in that it is more robust against chipping and wear.

[0055] Particularly preferred is a radius for the radius transition between 0.028 x D and 0.088 x D with bore diameter D. More preferably, the radius for the radius transition is 0.058 ±0.005 x D.

[0056] Preferably, the main cutting edge has a straight main cutting edge section. "Straight" means that the main cutting edge section in question forms a straight line in a side view.

[0057] An alternative design for the main cutting edge section located between the point thinning and the transition area can be curved, particularly convex. Such crowned designs of the main cutting edges have been proposed for cast iron drills, as they increase the length of the main cutting edge.

[0058] However, compared to curved cutting edges, straight cutting edges offer better cutting performance. Furthermore, the shape of the hole base of non-straight cutting edges can be detrimental to subsequent operations.

[0059] Preferably, the drilling tool has a tip angle between 130° and 140°, more preferably a tip angle of 135° ± 2°.

[0060] A tip angle of the mentioned size, especially around 135° ± 2°, gives the drilling tool particularly balanced properties: at smaller tip angles, a center of the drilling tool becomes sensitive, at larger tip angles the cutting edge corners become more susceptible to chipping.

[0061] In the context of a chamfer design, a round grind means that the back of the chamfer forms a cylindrical section. Another term for this type of grinding is "fully round" or cylindrical. In the case of the guide chamfer discussed here, the back forms a cylindrical section with the bore diameter as the diameter. Typically, a round-ground chamfer simply retains the outer surface of a round-ground blank, while the remaining geometries of the tool are created by machining (grinding).

[0062] Preferably, the peripheral cutting edge and the cutting edge formed on the guide land are continuous across their respective extensions. This means that the cutting edge is preferably free of notches, waves, roughing profiles, or other interruptions. This refinement emphasizes a design of the drilling tool such that the cutting land on the cutting edge removes a uniformly thin chip in one uninterrupted cut.

[0063] Although explained predominantly in the singular in the explanations, it is of course preferred and the rule that in the case of multi-groove tools, the first chamfers or the guide chamfers on all peripheral cutting edges and cutting backs are designed as described.

[0064] In particular, the drilling tool is designed as a shank drill.

[0065] The drilling tool is preferably made of a composite material comprising at least one hard material and at least one binder phase. In particular, the tool is made of hard metal. Hard metal (English: "hard metal") cemented carbide ) is understood here to mean a composite material in which hard particles, which may be formed in particular by carbides, carbonitrides, and / or oxocarbonitrides of the elements of groups IVb to VIb of the Periodic Table of the Elements, are embedded in a ductile metallic matrix, which may be formed in particular from Co, Ni, Fe, or an alloy thereof. In most cases, the hard particles are at least predominantly formed by tungsten carbide, and the metallic matrix consists essentially of cobalt.

[0066] The drilling tool is preferably designed as a solid carbide drill and is preferably constructed in one piece. Alternatively, the tool can be assembled from two or more sections, for example, by sintering together.

[0067] Coolant channels can preferably be formed inside the drilling tool.

[0068] Protection is also sought for the use of the drilling tool for machining wear-prone materials, particularly cast materials. "Wear-prone" means that the materials in question are particularly difficult to machine and, in particular, cause abrasive wear on tools. For the purposes of the application, "cast materials" refers to metallic cast materials, particularly difficult-to-machine iron cast materials such as gray cast iron or compacted graphite cast iron. Examples of spheroidal graphite cast iron include the materials EN-JS1030 and EN-JS1070. Example:

[0069] The invention will be illustrated by an example with specific dimensions, which are by no means limiting. The tool demonstrated excellent service life and low wear when machining cast materials (here using the example of EN-GJS-700-2 / GGG-70 0.7070). On a solid carbide drilling tool with a nominal diameter of 8.5 mm, the diameter adjacent to the peripheral cutting edge was set to 0.03 mm smaller than the nominal diameter. The clearance angle of the first chamfers located on the peripheral cutting edges was selected to be 10° ± 1°. The width of the first chamfers, designed as flat facets, was 0.64 mm ± 0.1 mm. The fully rounded guide chamfers on the cutting edge are at the nominal diameter. For the two-flute drilling tool in the example, this resulted in the guide chamfers being designed such that they each remove 0.015 mm of material from the bore wall on the circumference.The guide chamfers were each arranged 30° offset from the peripheral cutting edges.

[0070] The fully rounded guide lands on the cutting edge backs had a rake angle of +5°±1°. The width of the guide lands was 0.64 mm. When measuring the width of the fully rounded guide lands, the chord length was determined as the width. The transition from the main cutting edge to the peripheral cutting edge was designed as a radius transition with a radius of 0.5 mm ± 0.05 mm.

[0071] The tip angle was 135° ±1°, the helix angle 30°.

[0072] The grooved length was 61 mm, which is about 7 x D.

[0073] Further advantages and benefits of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying figures. The figures show: Fig. 1: a drilling tool in a side view in a first embodiment Fig. 2: a detail of a drilling tool according to a further embodiment Fig. 3a, 3b Cross sections of a drilling tool of Figure 2 Fig. 4 a drilling tool in a further embodiment Fig. 5 a cross section of a drilling tool Figure 4

[0074] Figure 1 shows a side view of a drilling tool 1 according to the invention in a first exemplary embodiment. The drilling tool 1 has an overall length divided into a grooved length LN and a shank section of length LS.

[0075] The drilling tool 1 has a longitudinal drill axis L around which the drilling tool 1 is rotatable. This drilling tool 1 is designed for clockwise rotation in the direction of rotation R. Directions along or parallel to the longitudinal drill axis L are referred to as "axial," while directions perpendicular to it are referred to as "radial."

[0076] The drilling tool 1 of this embodiment has two flutes 4 that are twisted at a helix angle relative to the drill's longitudinal axis L. Such a two-flute configuration is preferred.

[0077] The chip flutes 4 are each spaced apart from a web 5. A cutting edge 6 is formed on a lateral surface of a web 5. In the exemplary embodiment, spiral-shaped coolant channels K are formed in the webs 5. Two main cutting edges 2 are formed on a tip S (also: face) of the drilling tool 1, each of which merges into a peripheral cutting edge 3 along a transition region 9. The transition region 9 is designed here as a radius transition, which is advantageous for preventing chipping at cutting edge corners.

[0078] A first chamfer 7 with a clearance angle grind is formed on each of the peripheral cutting edges 3, wherein the peripheral cutting edges 3 are located at a diameter D1 which is smaller than the bore diameter D.

[0079] On the cutting backs 6, a guide chamfer 8 with a round grind is formed which determines the drilling diameter D.

[0080] Theoretically, the special design of the cutting lands 6, namely the formation of a first chamfer 7 with a clearance angle grind on a diameter D1 and - behind it in the direction of rotation R - a guide chamfer 8 with a round grind defining the bore diameter D, could only take place on one cutting land 6, or could be different on the cutting lands 6, but it is particularly preferred that the cutting lands 6 are the same with regard to the design of the first chamfers 7 and the guide chamfers 8.

[0081] As can be seen, the first chamfers 7 and the guide chamfers 8 spirally follow the course of the chip flutes 4. In other words, the first chamfers 7 and the guide chamfers 8 extend at the same angle to the drill's longitudinal axis L as the helix angle β. Thus, the guide chamfers 8 maintain the distance to the peripheral cutting edges 3 and the first chamfers 7, respectively.

[0082] The first chamfer 7 and the guide chamfer 8 are formed along a first length L1 from the tip toward the shaft. In the present embodiment, the first length L1 corresponds essentially (over approximately 90%) to the entire grooved length LN, except for a length of the tip S and a length of a run-out region of the grooves 4.

[0083] As shown here and preferably, the guide chamfer 8 is positioned immediately behind the area of ​​the tip S of the drilling tool 1 so that the cutting edge corner is effectively protected.

[0084] Figure 2shows a section of a drilling tool 1 according to the invention in a side view in an enlarged representation of the area of ​​the tip S. In this exemplary embodiment, too, coolant channels K run spirally in the webs 5 and open at the tip S.

[0085] In the present embodiment, the drilling tool 1 has a tip angle WT of 135°. A tip angle WT between 130° and 140° is favorable, more preferably a tip angle of 135° ± 2°. This choice gives the drilling tool particularly balanced properties with regard to the length of the main cutting edges 2, the robustness of the cutting edges, and the required machining forces.

[0086] The main cutting edges 2 each merge into a peripheral cutting edge 3 along a transition area 9.

[0087] Two chamfers are formed on each of the webs 5, or more precisely, on the circumferentially formed cutting edges 6: a first chamfer 7 with a clearance angle is formed on each of the peripheral cutting edges 3. Behind, i.e. following, the circumferential direction R, a guide chamfer 8 with a round ground surface is formed on the same web 5, defining the drill diameter D.

[0088] The conditions are even better shown in the following sections.

[0089] Figures 3a and 3b show cross-sections of a drilling tool 1 according to the invention at the same axial position within the first length L1, viewed from the face S toward the shaft. The same sections are shown, only slightly rotated (approximately 10°) relative to each other to clarify the geometric conditions. Figures 3a and 3bthus show the same elements. For clarity, not all elements that occur multiple times are provided with reference symbols.

[0090] The drilling tool 1 has two chip flutes 4, each spaced apart from a web 5. Coolant channels K run in the webs 5. The webs 5 preferably extend over more than 90°, considering the angular range swept between the peripheral cutting edge 3 and the end of the cutting land 6. In the present example, the webs 5 sweep approximately 100°. This results in the so-called groove / back ratio. Preferably, the groove / back ratio, i.e. the ratio of an arc sweeping over the grooves to the arc sweeping over the backs, is 40:60, more preferably 30:70. This expresses that the cutting lands 6 preferably make up at least 60% of the cross-section in radians.

[0091] A first chamfer 7 is formed on each cutting edge 6, which is assigned to the peripheral cutting edges 3. The first chamfer 7 has a

[0092] Clearance angle grinding with a clearance angle α. The clearance angle grinding forms a clearance surface, preferably a flat clearance angle facet.

[0093] The clearance angle α is preferably between 5° and 15°. In the illustrated embodiment, the clearance angle α is 10°, which is a particularly preferred choice.

[0094] At an angle Ω relative to the direction of rotation R, behind—i.e., following in the circumferential direction—the circumferential cutting edge 3, the guide chamfer 8 begins with a rounded grind. The angle Ω is preferably between 20° and 40°, and in the present embodiment, 30° is particularly preferred.

[0095] Because the peripheral cutting edges 3 are located on a first diameter D1, which is smaller than the bore diameter D, and the subsequent, cutting guide lands 8 with a round ground define the bore diameter D, the peripheral cutting edges 3 act as pre-cutters. Only the guide lands 8 with a round ground on the back of the cutter cut a bore wall to the bore diameter D. This relieves the peripheral cutting edges 3 and results in a particularly cleanly machined bore wall. The relief of the peripheral cutting edges 3 is particularly important in a front area of ​​the drilling tool 1, where forces overlap on the main cutting edges 2 and the peripheral cutting edges 3.

[0096] A width b U of a first chamfer 7 is preferably between 0.025 and 0.125 times the drilling diameter D. In the present exemplary embodiment, the width b U of a first chamfer 7 is 7.5% of the drilling diameter D, i.e. 0.075 x D.

[0097] With respect to the direction of rotation R, an auxiliary chip groove 10 is formed in front of the guide chamfer 8. The auxiliary chip groove 10 particularly advantageously allows for the formation of a grinding surface on the guide chamfer 8, which is designed to cut. The auxiliary chip groove 10 serves to collect and remove chips removed by the cutting guide chamfer 8.

[0098] The auxiliary chip groove 10 extends radially up to a recess radius r F . In particular, the auxiliary chip groove 10 extends up to a diameter of 85% to 90% of the drill diameter D. In other words, the recess radius r F is preferably between 85% and 90% of half the drill diameter D. This ensures sufficient clearance of the guide chamfer 8 for attaching the rake angle as well as space for chip collection.

[0099] The guide chamfer 8 has a rake angle γ that is preferably between 2° and 8°. In the present embodiment, the rake angle γ is particularly preferably 5°.

[0100] The guide chamfer 8 has a rounded surface, which allows it to advantageously support the drilling tool 1 and also smooths the workpiece surface. The back of the guide chamfer 8 thus lies on a cylinder with the diameter D of the drilling diameter.

[0101] In addition, the guide chamfer 8 is designed to cut over a (here positive) rake angle γ.

[0102] A width b F of the guide chamfer 8 is preferably between 0.025 and 0.125 times the bore diameter D. In the present exemplary embodiment, the guide chamfer 8 has a width b F of 7.5% of the bore diameter D, i.e. 0.075 x D.

[0103] Figure 4shows a side view of a further embodiment of the invention. Shown here is a drilling tool 1 for deep holes, with a fluted length LN of greater than 6 x D, where D is the drill diameter. The drilling tool 1 is not shown in its entire length, as indicated by the interrupted lines. Over the first length L1, the first chamfers 7 and the guide chamfers 8 are designed as previously described. According to the further development according to Figure 4 It is provided that the cutting guide bevels 8 taper off after the first length L1. A typical extension of the first length L1 is 2 x D to 4 x D. Particularly preferably, the length L1 with guide bevels 8 extends between 3.2 x D to 3.8 D, in particular around 3.5 x D.

[0104] To ensure continued tool guidance, a further guide chamfer 11 with a round grind is formed along a second length L2 on the peripheral cutting edge 3, instead of the first chamfer 7 with a flank grind previously formed there. The further guide chamfer 11 formed on the peripheral cutting edge 3 is located on the bore diameter D. Thus, a change in guidance occurs from the guide chamfers 8 to the further guide chamfer 11.

[0105] The shape of the chamfer on the peripheral cutting edge 3 changes from the first chamfer 7 with flank grinding to a further guide chamfer 11 with circular grinding.

[0106] Preferably, there is an overlap region between the first length L1 and the second length L2, in which the transition from the guide bevel 8 on the cutting edge to the secondary guide bevel 11 on the peripheral cutting edge 3 occurs. The overlap region can, for example, be a quarter x D long.

[0107] Figure 5 shows a cross section of the drilling tool 1 according to Figure 4 in the region of the second length L2. The further guide chamfers 11 are formed on the peripheral cutting edges 3 and are located at the bore diameter D. A width of the further guide chamfers 11 is preferably in the region of the guide chamfers 8 of the first length L1.

[0108] The further guide bevels 11 are in particular not designed to be cutting. In the section of the Figure 5It also shows how the aforementioned flute / back ratio is determined. An arc BN in degrees sweeping over the chip flute 4 indicates the proportion of chip flute 4. An arc BR in degrees sweeping over the cutting back 6 indicates the proportion of cutting back 6. Together, the sections add up to 180°. The proportions expressed as a percentage result in the flute / back ratio, which in this preferred example is approximately 40:60. List of reference symbols:

[0109] 1Drilling tool / 2Main cutting edge / 3Circular cutting edge 4Chip groove / 5Web / 6Cutting back 7First chamfer 8Guide chamfer 9Transition area 10Auxiliary chip groove 11Further guide chamfer

Claims

1. Drilling tool with - a drill longitudinal axis (L) about which the drilling tool (1) is rotatable in a direction of rotation (R) and along which drill longitudinal axis (L) a fluted length (LN) extends - at least two main cutting edges (2) and at least two peripheral cutting edges (3), with a main cutting edge (2) transitioning into a peripheral cutting edge (3) along a transition area (9) - at least two flutes (4), which are each spaced from a web (5), - a land (6) formed on a lateral surface of a web (5), wherein along the fluted length (LN), at least in sections, a first chamfer (7) with a clearance angle cut is formed on the peripheral cutting edge (3), which peripheral cutting edge (3) is formed on a first diameter (D1), which first diameter (D1) is smaller than the bore diameter (D), characterized in that - on the cutting land (6), with respect to the direction of rotation (R), after the first bevel (7), a margin (8) with a circular grind is formed, determining the drill diameter (D), offset by an angle of 20° to 40° relative to the first bevel (7), wherein an auxiliary flute (10) is formed before the margin (8) with respect to the direction of rotation (R), - and wherein the first chamfer (7) has a clearance angle (α) of between 5° and 15°.

2. Drilling tool according to claim 1, wherein a width (bu) of the first bevel (7) is between 0.025 and 0.125 times the drilling diameter (D)3. Drilling tool according to one of the preceding claims, wherein the margin (8) has an amount of a rake angle between 2 and 8 .

4. Drilling tool according to one of the preceding claims, wherein a width (bF) of the margin (8) is between 0.025 and 0.125 times the drilling diameter (D).

5. Drilling tool according to one of the preceding claims, wherein a difference between the first diameter (D1) and the drilling diameter (D) is between 0.025 mm and 0.065 mm6. Drilling tool according to one of the preceding claims, wherein the margin (8) is formed along a first length (L1), which first length (L1) is smaller than a grooved length (LN) of the drilling tool (1).

7. Drilling tool according to one of the preceding claims, wherein the margin (8) is formed along a first length (L1), which is adjoined in the direction of the shank by a second length (L2), along which, instead of the first margin (7) on the peripheral cutting edge, a further margin (11) with a round cut is formed.

8. Use of a drilling tool according to one of the preceding claims for machining cast materials.