Drill cutting head and exchangeable head drill comprising such a drill cutting head
The drill cutting head design with inner and outer web thinnings addresses the challenge of maintaining strength and easy entry, ensuring accurate hole drilling with reduced wear and improved durability.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- SANDVIK COROMANT
- Filing Date
- 2024-12-20
- Publication Date
- 2026-06-25
AI Technical Summary
Existing drill cutting heads face challenges in maintaining strength at the drill tip while ensuring easy entry into the workpiece, leading to issues such as deviation from the intended hole path, wear, and reduced durability due to weak central edges and web thinning designs.
A drill cutting head design featuring inner and outer web thinnings that create a dual function of rake and secondary clearance surfaces, allowing for a shorter central edge without compromising strength, with main cutting edges that include inner and outer cutting edge sections and a helical chip flute for efficient chip removal.
The design enhances the drill's ability to enter the workpiece accurately, maintaining hole circularity and reducing wear, while requiring lower torque and feed force, thus improving the quality and durability of the drilling process.
Smart Images
Figure EP2024088098_25062026_PF_FP_ABST
Abstract
Description
[0001] A DRILL CUTTING HEAD AND AN EXCHANGEABLE HEAD DRILL COMPRISING SUCH A DRILL CUTTING HEAD
[0002] TECHNICAL FIELD OF THE INVENTION
[0003] The present invention relates to a drill cutting head and an exchangeable head drill. The drill cutting head and drill are primarily intended for, but not limited to, machining in workpieces of metal material.
[0004] BACKGROUND OF THE INVENTION AND PRIOR ART
[0005] Drill cutting heads for chip removing machining generally have a forward-facing cutting end forming a drill point. For a twist drill, a rearward-facing mount end configured for mounting in e.g., a machine spindle, a driving sleeve, a chuck, a socket or another type of fixture is generally provided. For exchangeable drill heads for drill tools, the axially rearward-facing mount end may comprise a mounting region configured to be mounted e.g., in a forward-facing mounting or fixture region, or drill cutting head seat, of a drill tool body. In this disclosure, the term drill cutting head will refer to both kinds.
[0006] In the forward-facing cutting end, two or more cutting edges are typically provided. From each cutting edge, a helical chip flute extends in a peripheral envelope surface in a rearward direction. The chip flutes are configured for conducting chips away from the cutting edges during machining. The cutting edges may be straight or may follow a curved line from a central edge provided at a centre point of the front end to the peripheral envelope surface.
[0007] The central part of the cutting end may comprise a web thinning region for each chip flute to make the drill pointier. The central edge is often called chisel edge and is normally straight, and short compared to the main cutting edges. The drawbacks with a pointy drill with a short chisel edge is that it becomes weaker and thus prone to wear or even breaking. On the other hand, a longer chisel edge may be stronger but may also have more difficulties entering the workpiece and requires more feed force and more torque to rotate the drill.
[0008] A drill with a web thinning area is known from W02020070737A1 . The web thinning area make the tip stronger with the disadvantage that it remains comparatively dull and with a relatively long center edge. Other drills with web thinnings of various designs are already known through EP3981529A1 , US201 8 / 0257151 A1 , US2023 / 0150039A1 and US2004 / 0151553A1 .
[0009] SUMMARY OF THE INVENTION
[0010] An object of the present invention is to provide a drill cutting head of the type defined in the introduction being improved in at least some aspect with respect to such drill cutting heads already known, for example through said documents. A special object of the invention is to provide a drill cutting head which can improve the quality of the drilled hole, e.g., improving the circularity of the hole cross section and follow the intended path through the workpiece, while at the same time maintaining strength in the drill tip region.
[0011] A drill that has difficulties entering the workpiece is likely to move off centre and enter the workpiece at an angle. This is bad for the quality of the hole, which may then deviate from its nominal circular cross section, be drilled in the wrong place, extend in the wrong direction or extend through the workpiece forming a non-cylindrical hole, e.g. like a cone. It may also be bad for the drill as it wears more quickly, both the on the cutting edge and the periphery of the drill. These tendencies are worse for drills that have an extended length L in relation to their diameter D, e.g., L > 5 x D, as they are weaker due to the reduced stiffness. Web thinnings have been applied to drill cutting heads already known, for instance through said documents, with improved capabilities to correctly enter the workpiece but also with various negative consequences, such as a weaker drill in the region of the drill tip, as end results. There is a contradiction in achieving a drill that simultaneously has strong main cutting edges in the central part of the drill and easily enters the workpiece.
[0012] According to a first aspect of the invention, this objective is achieved by means of a drill cutting head comprising:
[0013] - an axially rearward-facing mount end,
[0014] - an axially forward-facing cutting end for cutting a hole with a diameter D in a workpiece,
[0015] - a central rotational axis extending from the mount end to the cutting end,
[0016] - a peripheral envelope surface formed at the radially outer regions of the drill cutting head,
[0017] - a central edge which attaches to the central rotational axis,
[0018] - at least two main cutting edges which each extends radially outward from a respective radially outer end of the central edge, and which each have a clearance side and a rake side, wherein a pair of the at least two main cutting edges consists of a rotationally trailing main cutting edge and a directly rotationally leading main cutting edge, wherein
[0019] - each main cutting edge comprises a radially inner cutting edge section and a - relative to the inner cutting edge section - radially outer cutting edge section, wherein the inner cutting edge section is connected to and creates an obtuse angle with the central edge, - the clearance side of each main cutting edge comprises at least a primary clearance surface located directly behind the main cutting edge in a direction of intended rotation of the drill cutting head,
[0020] - the rake side of each main cutting edge comprises
[0021] - a chip flute which is formed in the peripheral envelope surface, located directly in front of the main cutting edge in the direction of intended rotation of the drill cutting head and configured for conducting chips away from the main cutting edge, which chip flute extends rearward from the cutting end towards the mount end of the drill cutting head,
[0022] - an outer web thinning extending between said chip flute and the primary clearance surface of the leading main cutting edge with which the respective main cutting edge as trailing main cutting edge forms a said pair of main cutting edges, and
[0023] - an inner web thinning which forms an inner rake surface for the inner cutting edge section of the respective main cutting edge, wherein the inner web thinning has a first short end portion and an opposite second short end portion, as well as a first long side portion and an opposite second long side portion interconnecting the first and second short end portions and arranged to provide the inner web thinning with an elongated shape in a top view having a longitudinal extension measured from the first to the second short end portion.
[0024] The drill cutting head of the embodiments of the present invention is characterized in that the inner web thinning of the rake side of each main cutting edge borders the inner cutting edge section of the main cutting edge by the first short end portion, borders the respective outer web thinning by the first long side portion and borders the primary clearance surface of the leading main cutting edge with which the respective main cutting edge as trailing main cutting edge forms a said pair of main cutting edges by the second long side portion.
[0025] The “pair of edges” should be seen as a way of distinguishing between the main cutting edges and make it clearer where the structural features of the drill cutting head are located. In any pair of subsequent main cutting edges, the leading edge is rotationally ahead of the trailing edge, i.e. in front of the leading edge in a direction of intended rotation of the drill cutting head and by any number of main cutting edges on the drill cutting head, each main cutting edge will form part of two different said pairs, or more specifically, it will be a trailing cutting edge for the main cutting edge in front of it and a leading cutting edge for the main cutting edge behind it in the direction of intended rotation. This is also the case by only two main cutting edges, as in the embodiments shown, where each main cutting edge constitutes the leading cutting edge in one pair each, with the other as trailing cutting edge.
[0026] Thanks to the inventive design of the inner cutting edge section and the inner web thinning, the central edge can be shortened without losing the strength necessary for a stable entry into the workpiece, which creates an improved center portion, or tip region, of the drill that is pointy at entry and strong immediately after entry. The inner cutting edge section also creates a very short central edge but at the same time also creates a longer edge to actually generate a chip, which the central edge does not.
[0027] The inner web thinning of one main cutting edge may further have the function of a secondary clearance surface for the rotationally leading main cutting edge. Thanks to the dual function of the inner web thinning, forming both a rake surface for one inner cutting edge as well as secondary clearance surface for the rotationally leading main cutting edge, a drill point geometry is created that is both strong and can easily enter the workpiece as it creates a very short central edge.
[0028] The central edge is the axially most forward part of the drill and enters the workpiece first. If the central edge does not pierce the workpiece in a good way the drill may start to drift off centre, i.e. it does not find the center. The longer the drill is in relation to its diameter D, the worse this problem becomes. If this happens, the drill may enter the workpiece at the wrong angle and the linear extension of the hole will not be as intended. It may also cause the hole to deviate from its nominal circular cross section. As the drill then progresses through the workpiece at the wrong angle, the periphery of the cutting end and support surfaces of the drill envelope are pushed against the hole wall, something that causes significant wear. All in all, an incorrect entry into the workpiece may be detrimental to the quality of a drilled hole.
[0029] Thanks to the inner web thinnings also having the function of secondary clearance surfaces, the clearances are improved without having to increase the primary clearance angles or shortening the primary clearance surfaces, which also strengthens the main cutting edges.
[0030] The drill cutting head according to the invention may be in the form of a solid twist drill in a single piece, or in the form of an exchangeable head mountable on a drill tool body. The drill cutting head may e.g. be manufactured from cemented carbide with an added wear resistant coating as an option. In the present invention, the drill cutting head that may be a twist drill or exchangeable head comprises an axially rearward-facing mount end. For a solid twist drill, the mount end may e.g. be formed as a straight or tapered shank adapted to be mounted in a support body, e.g. a chuck or tool holder. For an exchangeable head, the mount region comprises an interface adapted to be mounted in a support body, e.g. a jaw-like forward-facing drill cutting head seat of a drill tool body, which may comprise a screw or a bayonet connection to securely clamp the exchangeable head.
[0031] The present invention comprises an axially forward-facing cutting end and a central rotational axis extending between the mount end and the cutting end. The cutting end comprises at least two main cutting edges that extend from a central edge that intersects the central rotational axis. The main cutting edges extend radially outward from the central edge along the transition between the clearance side and the rake side. The exact geometric properties of the main cutting edges may vary depending on the material of the workpiece to be machined. The geometric properties of the main cutting edges may also vary to compensate for the fact that the cutting speed varies with the radial distance from the central rotating axis.
[0032] For each main cutting edge, the drill cutting head comprises a chip flute, normally a helical chip flute, configured for conducting chips away from the main cutting edge, and which is formed in the peripheral envelope surface and extend rearward from the cutting end.
[0033] For each main cutting edge, the drill cutting head also comprises a clearance side which comprises at least a primary clearance surface. The primary clearance surface is directly behind the cutting edge in the rotational direction. A clearance surface is meant to create room behind the cutting edge so the axial feed of the drill into the workpiece does not cause the area behind the cutting edge in the rotational direction to make contact with the bottom of the hole. This means that the feed rate and the clearance angle have to be adapted to one another. A larger clearance angle allows for a higher feed rate. When increasing the clearance angle, the cutting edge gets weaker. The most critical place along the main cutting edge in terms of clearance is closest to the center.
[0034] For each main cutting edge, the drill cutting head comprises an outer web thinning, which extends between the chip flute of the rake side of the respective main cutting edge and the primary clearance surface of the rotationally leading main cutting edge. The outer web thinning reduces the width of the drill core, or the so-called web, at the cutting end and thus makes the cutting end pointier.
[0035] The inner web thinning and the outer web thinning each comprises a respective rake surface for the associated main cutting edge. The inner web thinning creates the rake surface of the inner cutting edge section. This section extends radially outward from the central edge. The outer web thinning makes out the rake surface for an intermediate cutting edge section. The intermediate cutting edge section extends radially outward from the inner cutting edge section. The chip flute comprises the rake surface of the outer cutting edge section. The outer cutting edge section extends radially outward from the intermediate cutting edge section. Transitions between subsequent main cutting edge sections create obtuse angles in the main cutting edge as measured behind this, in the primary clearance surface thereof in a top view. The inner cutting edge section is preferably the shortest, whereas the outer cutting edge section is preferably the longest.
[0036] In the embodiments of the present invention, each inner web thinning is situated such that it extends between the associated outer web thinning and the primary clearance surface of the rotationally leading main cutting edge, thereby separating the two. Expressed alternatively, each inner web thinning extends as a transition radially outwards between the outer web thinning and the primary clearance surface of the rotationally leading main cutting edge. The inner web thinning may comprise the rake surface for the inner cutting edge section at the same time as being a secondary clearance surface for the rotationally leading main cutting edge. The positioning of the inner cutting edge section and of the inner web thinning in conjunction with the outer web thinning has been shown to have positive effects on the drill cutting head performance.
[0037] In the embodiments of the inventions, the inner web thinning and inner cutting edge section, apart from making the drill point sharper, also increase the clearance without weakening the respective main cutting edge.
[0038] According to an embodiment, the inner web thinning, when seen in a top view perpendicular to the central rotational axis, extends radially outward from the central edge so that the maximum radial extension is contained in a circle with the origin in the central rotational axis and the diameter of 0.1xD-0.4xD, or more preferably 0.15xD-0.35xD.
[0039] In an embodiment of the present invention, each outer web thinning is delimited by the inner web thinning and the chip flute of the associated main cutting edge and at least the primary clearance surface of the leading main cutting edge.
[0040] The length of the central edge as well as the width of the web of the drill influence the behaviour of the drill. In the present invention the features of the inner web thinning allow the central edge to be shorter than normal without weakening the drill point as it also creates a larger drill point angle. According to an embodiment, the total width of the web is 0.05xD-0.15xD (as an imaginary circle intersecting the respective transitions between the inner and intermediate cutting edge sections), or 0.25xD-0.35xD if measured between the transitions between the intermediate and outer cutting edge sections.
[0041] According to an embodiment, each inner web thinning creates an inner rake surface for the associated inner cutting edge section which is strongly negative and thereby an unusually short central edge, and the drill point achieves a surprising combination of strength, incisiveness and wear resistance.
[0042] The power requirements on the machine are also kept low due to the moderate torque and feed force required to rotate and feed the drill through the workpiece. A shorter central edge may normally create clearance issues, but this is avoided in the present invention. The rake angle of the inner rake surface is preferably less than -30 degrees.
[0043] According to an embodiment, the drill cutting head of the present invention may have a rake angle of the intermediate rake surface which is also negative, and preferably less negative than the rake angle of the rake surface of the inner cutting edge section. More preferably it is between -30 and 0 degrees.
[0044] The rake angle referred to in the present invention is defined as the angle between a tangent to the rake surface and a line parallel to the rotational axis of the drill cutting head.
[0045] The rake surface of the outer cutting edge section is preferably the largest of the rake surfaces. As opposed to the rake surfaces of the inner and intermediate cutting edge sections, the rake surface of the outer cutting edge section has a positive rake angle. According to an embodiment of the invention the transition between the inner cutting edge section and the intermediate cutting edge section for each main cutting edge is within an imaginary circle perpendicular to, and with origin in, the central rotational axis and with a diameter in the range of 0.05xD to 0.15xD.
[0046] According to another embodiment of the invention the transition between the intermediate cutting edge section and the outer cutting edge section for each main cutting edge is within an imaginary circle perpendicular to, and with origin in, the central rotational axis and with a diameter in the range of 0.25xD to 0.35xD.
[0047] According to another embodiment of the invention at each main cutting edge an angle between the inner and intermediate cutting edge sections is 130-165 degrees measured behind the cutting edge in a direction of intended rotation of the drill cutting head, inside the associated primary clearance surface in a top view.
[0048] According to another embodiment of the invention the inner web thinning of the rake side of each main cutting edge is arranged to have the longitudinal extension in a first end region closest to the first short end portion directed towards the leading main cutting edge with which the respective main cutting edge as trailing main cutting edge forms a said pair of main cutting edges, as seen in top view.
[0049] According to another embodiment of the invention the inner web thinning of the rake side of each main cutting edge is further arranged to have the longitudinal extension in a second end region closest to the second short end portion directed away from said leading main cutting edge, as seen in top view. According to another embodiment of the invention the first long side portion of each inner web thinning is curved in the direction of intended rotation of the drill cutting head, as seen in top view.
[0050] According to another embodiment of the invention the second long side portion of each inner web thinning is curved in the direction of intended rotation of the drill cutting head, as seen in top view.
[0051] According to another embodiment of the invention a length of each inner web thinning measured along the longitudinal extension from the first to the second short end portion is between 0.05-0.25xD, preferably between 0.1 -0.2xD, as seen in top view.
[0052] According to another embodiment of the invention a width of each inner web thinning measured between the first and second long side portions perpendicular to the longitudinal extension is not greater than 0.1 xD, preferably not greater than 0.05xD, as seen in top view.
[0053] According to another embodiment of the invention a surface area of each inner web thinning is not greater than 0.2 times, preferably not greater than 0.15 times, more preferred not greater than 0.1 times the surface area of a primary clearance surface, as seen in top view.
[0054] According to another embodiment of the invention, by the inner web thinning of the rake side of each main cutting edge the first short end portion only borders the inner cutting edge section of the main cutting edge, the first long side portion only borders the respective outer web thinning and the second long side portion only borders the primary clearance surface of the leading main cutting edge with which the respective main cutting edge as trailing main cutting edge forms a said pair of main cutting edges.
[0055] According to another embodiment of the invention an axial cross section of each inner web thinning presents a concave surface shape.
[0056] Further advantages as well as advantageous features of the invention will be apparent from the following detailed description of embodiments thereof.
[0057] DESCRIPTION OF THE DRAWINGS
[0058] Embodiments of the invention will in the following be described by means of example with reference to the appended drawings, in which:
[0059] Fig 1 is a top view of a drill cutting head according to a first embodiment of the invention, with an enlarged view of a region of the drill tip,
[0060] Fig 2 is a top view of a drill cutting head according to a second embodiment of the invention, with an enlarged view of a region of the drill tip,
[0061] Fig 3 is a side view of a top part of the drill cutting head of Fig 1 seen substantially parallel to an inner cutting edge section,
[0062] Fig 4 is a side view of a top part of the drill cutting head of Fig 1 seen substantially perpendicular to an inner cutting edge section,
[0063] Fig 5 is a perspective view of the drill cutting head of Fig 2 seen substantially parallel to an inner cutting edge section, and
[0064] Fig 6 shows a drill tool body as well as a drill tool body with a drill cutting head mounted so as to together form a drill according to the invention.
[0065] DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0066] A drill cutting head 1 according to two different embodiments of the invention is shown in a top view toward the axially forward-facing cutting end 5 in figures 1 and 2. Throughout the drawings, the same reference numbers are used for similar or corresponding elements at both embodiments shown.
[0067] The drill cutting head 1 comprises an axially rearward-facing mount end 2 and an axially forward-facing cutting end 5 for cutting a hole with diameter D in a workpiece of metal as well as a central rotational axis C extending from the mount end 2 to the cutting end 5 and defining a longitudinal extension and axial direction of the drill cutting head 1 . The cutting end 5 comprises two main cutting edges 6a-b which each extends radially outward from a respective radially outer end of the central edge 7, which central edge attaches to or intersect the central rotational axis C around which the drill rotates in a direction of intended rotation R.
[0068] Each main cutting edge 6a-b comprises a radially inner cutting edge section 16a-b and a - relative to the inner cutting edge section - radially outer cutting edge section 20a-b, wherein the inner cutting edge section 16a-b is connected to and creates an obtuse angle with the central edge 7. Each main cutting edge 6a-b further comprises an intermediate cutting edge section 18a-b interconnecting the inner 16a-b and outer 20a-b cutting edge sections in such a way that the inner, intermediate and outer cutting edge sections are connected to and follow each other, in that order, from said respective radially outer end of the central edge radially outward towards the envelope surface 22.
[0069] A pair of the at least two main cutting edges consists of a rotationally trailing main cutting edge 6a-b and a directly rotationally leading main cutting edge 6a- b.
[0070] For each main cutting edge 6a-b, the drill cutting head 1 comprises a rake side and a clearance side. The clearance side of each main cutting edge comprises a primary clearance surface 10a-b located directly behind the main cutting edge in the direction of intended rotation R of the drill cutting head and extending over the cutting end from the envelope surface 22 to the central edge 7.
[0071] The rake side of each main cutting edge 6a-b comprises a helical chip flute 8a- b configured for conducting chips away from the main cutting edge 6a-b, and which is formed in a peripheral envelope surface 22 and extend rearward from the cutting end 5 towards the mount end 2. The helical chip flute is located directly in front of the main cutting edge in the direction of intended rotation R of the drill cutting head 1 .
[0072] The rake side of each main cutting edge 6a-b further comprises an outer web thinning 14a-b extending between said chip flute 8a-b and the primary clearance surface 10a-b of the leading main cutting edge 6a-b with which the respective main cutting edge 6a-b as trailing main cutting edge 6a-b forms a said pair of main cutting edges 6a-b, that is, the outer web thinning 14a of the rake side of the main cutting edge 6a extends between the chip flute 8a and the primary clearance surface 10b of the other main cutting edge 6b, as an explanatory example.
[0073] The rake side of each main cutting edge 6a-b further comprises an inner web thinning 13a-b which forms an inner rake surface 17a-b for the inner cutting edge section 16a-b of the respective main cutting edge 6a-b. The inner web thinning has a first short end portion 23a-b and an opposite second short end portion 24a-b, as well as a first long side portion 25a-b and an opposite second long side portion 26a-b interconnecting the first and second short end portions and arranged to provide the inner web thinning 13a-b with an elongated shape in a top view having a longitudinal extension measured from the first 23a-b to the second 24a-b short end portion.
[0074] The inner web thinning 13a-b of the rake side of each main cutting edge 6a-b borders the inner cutting edge section 16a-b of the main cutting edge by the first short end portion 23a-b and extends radially therefrom forming a transition between the associated outer web thinning 14a-b and the primary clearance surface 10a-b of the rotationally leading main cutting edge. More specifically, the inner web thinning is formed between said outer web thinning and primary clearance surface to entirely separate them. The inner web thinning borders said outer web thinning by the first long side portion 25a-b and borders said primary clearance surface 10a-b by the second long side portion 26a-b. More specifically, the first short end portion only borders said inner cutting edge section, the first long side portion only borders said outer web thinning and the second long side portion only borders said primary clearance surface.
[0075] Each main cutting edge 6a-b extends in a transition between a respective rake side and clearance side. The inner web thinning 13a-b comprises the rake surface 17a-b of the inner cutting edge section 16. The outer web thinning comprises an intermediate rake surface 19a-b for the intermediate cutting edge section 18a-b. The chip flute 8a-b comprises an outer rake surface 21 a-b for the outer cutting edge section 20a-b.
[0076] Accordingly, the drill cutting head 1 comprises two main cutting edges 6a-b as well as, for each cutting edge, an inner web thinning 13a-b that extends radially outwards from the central edge 7 and the respective inner cutting edge section 16a-b in the shape of at least essentially a curved rectangle. It extends between the outer web thinning 14a-b of the rotationally trailing main cutting edge and the primary clearance surface 10a-b of the rotationally leading main cutting edge 6a-b, bending in the opposite direction to the direction of intended rotation R by the first long side portion 25a-b and the second long side portion 26a-b being curved in the direction of intended rotation, as seen in top view.
[0077] A length of each inner web thinning 13a-b measured along the longitudinal extension from the first 23a-b to the second 24a-b short end portion is between 0.05-0.25xD, preferably between 0.1 -0.2xD, as seen in top view. A width of each inner web thinning measured between the first 25a-b and second 26a-b long side portions perpendicular to the longitudinal extension is not greater than 0.1 xD, preferably not greater than 0.05xD, as seen in top view. In the embodiment shown in figs 1 and 3-4 the width of each inner web thinning is essentially constant along the entire longitudinal extension thereof, whereas in the embodiment shown in figs 2 and 5 the width of each inner web thinning is varying along the longitudinal extension, and more specifically larger in a center region than in first and second end regions (further described below). These different designs of each inner web thinning may be suitable for different specific applications, such as for machining in various materials and / or at certain feed rates, to mention a few examples. A surface area of each inner web thinning is not greater than 0.2 times, preferably not greater than 0.15 times, more preferred not greater than 0.1 times the surface area of a primary clearance surface 10a-b, as seen in top view.
[0078] By this design and positioning of the inner web thinning 13a-b of the rake side of each main cutting edge 6a-b this is arranged to have the longitudinal extension thereof in a first end region closest to the first short end portion 23a- b directed towards the leading main cutting edge 6a-b with which the respective main cutting edge as trailing main cutting edge forms a said pair of main cutting edges, and to have the longitudinal extension thereof in a second end region closest to the second short end portion 24a-b directed away from said leading main cutting edge, as seen in top view. This is clearly shown in the figures 1 and 2, where the longitudinal extension of each inner web thinning 13a in an first, initial, end region is directed towards and in a second, final, end region is directed away from the leading main cutting edge 6b, as an explanatory example.
[0079] As a result of this design and positioning of the inner web thinning 13a-b of the rake side of each main cutting edge a drill point geometry is created that is both strong and can easily enter the workpiece as it creates a very short central edge without the need to reduce the material thickness too much in the drill point region, thereby maintaining the strength of the cutting edges in that region.
[0080] The long side portions 25a-b, 26a-b are curved both radially and axially. Hence, an axial cross section of each inner web thinning 13a-b presents a concave surface shape. The radially inner, first short end portion 23a-b of the inner web thinning 13 borders the inner cutting edge section 16a-b and its surface adjacent to the inner cutting edge section constitutes the inner rake surface 17a-b. Seen in relation to the main cutting edge 6a-b for which an inner web thinning 13a-b comprises an inner rake surface, it is on the rake side and thus has the function of a web thinning. Seen in relation to the other, rotationally leading main cutting edge (for which the same inner web thinning 13a-b does not comprise a rake surface), the same inner web thinning is on the clearance side and constitutes a secondary clearance surface for that main cutting edge 6a-b.
[0081] As seen in the figures 1 -5, the main cutting edge sections 16a-b, 18a-b, 20a-b extend both in a straight and curved manner. For each main cutting edge section 6a-b the inner cutting edge section 16a-b is straight both seen in an axial and radial view, whereas the intermediate cutting edge section 18a-b is curved both radially and axially. The outer cutting edge section 20a-b is curved radially but not axially. An angle between the inner and intermediate cutting edge sections is 130-165 degrees measured over the transition between these cutting edge sections and behind the cutting edge in a direction of intended rotation R of the drill cutting head 1 , i.e. inside the associated primary clearance surface 10a-b in a top view.
[0082] For a drill cutting head 1 according to the first embodiment shown in figs 1 , 3 and 4 with D = 18.00 mm, the central edge 7 is 150 pm and the inner cutting edge section 16a-b is 0.53 mm. The intermediate cutting edge section 18a-b extends over about 2.45 mm. The inner web thinning 13a-b has a maximum radial extension (measured perpendicular to the central rotational axis C) of 2.8 mm, which is equivalent to 0.15xD. The web of the drill cutting head is 1 .10 mm, equivalent to 0.06xD. The outer cutting edge section 20a-b is 6.05 mm.
[0083] With reference to figures 3 and 4, the drill point of the drill cutting head 1 can be seen in two different views. In figure 3, the drill cutting head 1 is seen from a view roughly parallel to the inner cutting edge section 16a-b. In this view, the radial angles between the respective cutting edge sections 16a-b, 18a-b, 20a-b are decreasing moving toward the central rotational axis C and in the view in figure 4, which is roughly perpendicular to the inner cutting edge section 16a-b, the axial angles are increasing.
[0084] With reference to figures 1 -5, the rake angle of the inner rake surface 17a-b is negative. The rake angle of the intermediate rake surface 19a-b is still negative but less negative than that of the inner rake surface. The rake angle of the outer rake surface 21 a-b is positive.
[0085] The drill cutting head 1 further comprises an engagement structure 15a-b (see figs 2 and 5) configured to provide engagement surfaces for a locking tool for facilitating locking and / or unlocking of the drill cutting head to and / or from a drill cutting head seat 3 in a drill tool body 4 (see figs 5-6). At the embodiment shown in figs 2 and 5 the drill cutting head 1 comprises two such engagement structures, one arranged at each clearance side of the two main cutting edges 6a-b. Here, the engagement structures are formed as recesses in the cutting end 5 side of the drill cutting head, which may be engaged by a locking tool, such as a locking key, to lock or unlock the drill cutting head to or from a said seat 3. Such engagement structures could however also be male structures on the cutting end or holes in the envelope surface (which is the case at the cutting head of the embodiment in figs 1 and 3-4, although not shown), through the drill cutting head 1 , to mention a few examples. Engagement structures in the form of holes could be engaged by a locking tool in the form of a locking key or by a locking screw. Such engagement structures may be more favorably provided thanks to the material thickness in certain parts of the drill cutting head, in turn thanks to the design and positioning of each inner web thinning.
[0086] Fig 6 shows an exchangeable head drill 1 1 for chip removing metal machining according to the invention. The exchangeable head drill comprises a drill tool body 4 shown on its own in fig 5, which is provided with a jaw-like drill cutting head seat 3, often referred to as insert seat, in a front end thereof, and a drill cutting head 1 according to the invention arranged in the drill cutting head seat 3.
[0087] The invention is of course not in any way restricted to the embodiments described above. On the contrary, many possibilities to modifications thereof will be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention such as defined in the appended claims.
[0088] That a part is “connected to” another part should in this disclosure be interpreted as that the parts could be directly interconnected, or connected to each other via a third part. The main cutting edges of a drill cutting head according to the invention could in this way include more than three cutting edge sections, arranged between and interconnecting any two of the three cutting edge sections described.
Claims
CLAIMS1 . A drill cutting head (1 ) for chip removing metal machining comprising:- an axially rearward-facing mount end (2),- an axially forward-facing cutting end (5) for cutting a hole with a diameter D in a workpiece,- a central rotational axis (C) extending from the mount end (2) to the cutting end (5),- a peripheral envelope surface (22) formed at the radially outer regions of the drill cutting head (1 ),- a central edge (7) which attaches to the central rotational axis (C),- at least two main cutting edges (6a-b) which each extends radially outward from a respective radially outer end of the central edge (7), and which each have a clearance side and a rake side, wherein a pair of the at least two main cutting edges consists of a rotationally trailing main cutting edge (6a-b) and a directly rotationally leading main cutting edge (6a-b), wherein- each main cutting edge (6a-b) comprises a radially inner cutting edge section (16a-b) and a - relative to the inner cutting edge section (16a-b) - radially outer cutting edge section (20a-b), wherein the inner cutting edge section (16a-b) is connected to and creates an obtuse angle with the central edge (7),- the clearance side of each main cutting edge (6a-b) comprises at least a primary clearance surface (10a-b) located directly behind the main cutting edge (6a-b) in a direction of intended rotation (R) of the drill cutting head (1 ),- the rake side of each main cutting edge (6a-b) comprises- a chip flute (8a-b) which is formed in the peripheral envelope surface (22), located directly in front of the main cutting edge (6a-b) in the direction of intended rotation (R) of the drill cutting head (1 ) and configured for conducting chips away from the main cutting edge (6a-b), which chip flute (8a-b) extends rearward from the cutting end (5) towards the mount end (2) of the drill cutting head (1 ),- an outer web thinning (14a-b) extending between said chip flute (8a-b) and the primary clearance surface (10a-b) of the leading main cutting edge (6a-b) with which the respective main cutting edge (6a-b) as trailing main cutting edge (6a-b) forms a said pair of main cutting edges (6a-b), and- an inner web thinning (13a-b) which forms an inner rake surface (17a-b) for the inner cutting edge section (16a-b) of the respective main cutting edge (6a-b), wherein the inner web thinning (13a-b) has a first short end portion (23a-b) and an opposite second short end portion (24a-b), as well as a first long side portion (25a-b) and an opposite second long side portion (26a-b) interconnecting the first (23a-b) and second (24a-b) short end portions and arranged to provide the inner web thinning (13a-b) with an elongated shape in a top view having a longitudinal extension measured from the first (23a-b) to the second (24a-b) short end portion, characterized in that the inner web thinning (13a-b) of the rake side of each main cutting edge (6a-b) borders the inner cutting edge section (16a-b) of the main cutting edge (6a-b) by the first short end portion (23a-b), borders the respective outer web thinning (14a-b) by the first long side portion (25a-b) andborders the primary clearance surface (1 Oa-b) of the leading main cutting edge (6a-b) with which the respective main cutting edge (6a-b) as trailing main cutting edge (6a-b) forms a said pair of main cutting edges (6a-b) by the second long side portion (26a-b).
2. A drill cutting head (1 ) according to claim 1 , characterized in that each main cutting edge (6a-b) further comprises an intermediate cutting edge section (18a-b) interconnecting the inner (16a-b) and outer (20a-b) cutting edge sections in such a way that the inner (16a-b), intermediate (18a-b) and outer (20a-b) cutting edge sections are connected to and follow each other, in that order, from said respective radially outer end of the central edge (7) radially outward towards the envelope surface (22).
3. A drill cutting head (1 ) according to claim 2, characterized in that at each main cutting edge (6a-b) an angle between the inner (16a-b) and intermediate (18a-b) cutting edge sections is 130-165 degrees measured behind the cutting edge (6a-b) in a direction of intended rotation (R) of the drill cutting head (1 ), inside the associated primary clearance surface (10a-b) in a top view.
4. A drill cutting head (1 ) according to any of the preceding claims, characterized in that the inner web thinning (13a-b) of the rake side of each main cutting edge (6a-b) is arranged to have the longitudinal extension in a first end region closest to the first short end portion (23a- b) directed towards the leading main cutting edge (6a-b) with which the respective main cutting edge (6a-b) as trailing main cutting edge (6a-b) forms a said pair of main cutting edges (6a-b), as seen in top view.
5. A drill cutting head (1 ) according to claim 4, characterized in that the inner web thinning (13a-b) of the rake side of each main cutting edge (6a-b) is further arranged to have the longitudinal extension in a second end region closest to the second short end portion (24a-b) directed away from said leading main cutting edge (6a-b), as seen in top view.
6. A drill cutting head (1 ) according to any of the preceding claims, characterized in that the first long side portion (25a-b) of each inner web thinning (13a-b) is curved in the direction of intended rotation (R) of the drill cutting head (1 ), as seen in top view.
7. A drill cutting head (1 ) according to any of the preceding claims, characterized in that the second long side portion (26a-b) of each inner web thinning (13a-b) is curved in the direction of intended rotation (R) of the drill cutting head (1 ), as seen in top view.
8. A drill cutting head (1 ) according to any of the preceding claims, characterized in that a length of each inner web thinning (13a-b) measured along the longitudinal extension from the first (23a-b) to the second (24a-b) short end portion is between 0.05-0.25xD, preferably between 0.1 -0.2xD, as seen in top view.
9. A drill cutting head (1 ) according to any of the preceding claims, characterized in that a width of each inner web thinning (13a-b) measured between the first (25a-b) and second (26a-b) long side portions perpendicular to the longitudinal extension is not greater than 0.1 xD, preferably not greater than 0.05xD, as seen in top view.
10. A drill cutting head (1 ) according to any of the preceding claims, characterized in that a surface area of each inner web thinning (13a-b) is not greater than 0.2 times, preferably not greater than 0.15 times, more preferred not greater than 0.1 times the surface area of a primary clearance surface (10a-b), as seen in top view.1 1. A drill cutting head (1 ) according to any of the preceding claims, characterized in that by the inner web thinning (13a-b) of the rake side of each main cutting edge (6a-b) the first short end portion (23a-b) only borders the inner cutting edge section (16a-b) of the main cutting edge (6a-b), the first long side portion (25a-b) only borders the respective outer web thinning (14a-b) and the second long side portion (26a-b) only borders the primary clearance surface (1 Oa-b) of the leading main cutting edge (6a-b) with which the respective main cutting edge (6a-b) as trailing main cutting edge (6a-b) forms a said pair of main cutting edges (6a-b).
12. A drill cutting head (1 ) according to any of the preceding claims, characterized in that an axial cross section of each inner web thinning (13a-b) presents a concave surface shape.
13. A drill cutting head (1 ) according to any of the preceding claims, characterized in that the inner web thinning (13a-b) of the rake side of each main cutting edge (6a-b) entirely separates the respective outer web thinning (14a-b) and the primary clearance surface (10a-b) of the leading main cutting edge (6a-b) with which the respective main cutting edge (6a-b) as trailing main cutting edge (6a-b) forms a said pair of main cutting edges (6a-b).
14. A drill cutting head (1 ) according to any of the preceding claims, characterized in that the drill cutting head (1 ) further comprises an engagement structure (15a-b) configured to provide engagement surfaces for a locking tool for facilitating locking and / or unlocking of the drill cutting head (1 ) to and / or from a drill cutting head seat (3) in a drill tool body (4).
15. An exchangeable head drill (11 ) for chip removing metal machining comprising a drill tool body (4) provided with a drill cutting head seat (3) in a front end thereof, characterized in that the exchangeable head drill(1 ) further comprises a drill cutting head (1 ) according to any of the claims 1-14 arranged in the drill cutting head seat (3).T1