Power skiving tools and resharpenable cutting inserts for power skiving tools

Abstract

The present invention relates to a cutting insert (1) for a power skiving tool. The insert (1) comprises a first side (2) including a rake face (5), a second side (3) opposite the first side (2), a peripheral surface (4) extending between the first side (2) and the second side (3), the peripheral surface (4) including a relief surface (6) including a first minor relief surface (61), a second minor relief surface (62) and a corner minor relief surface (63), and a cutting edge (7) arranged at the intersection between the relief surface (6) and the rake face (5), the cutting edge (7) comprising a first relief edge (71), a second relief edge (72) and a nose edge (73), the cutting edge (7) being arranged or substantially arranged in a first plane (P) and having a cutting edge contour. At each point on the cutting edge (7), the relief surface (6) has a positive nominal relief angle (α) for each of the first minor relief surface (61), the second minor relief surface (62), and the corner minor relief surface (63), and has a maximum value (α) at ​​a first point (P1) along the nose edge (73). max ). The relief surfaces (6) are further arranged such that, when viewed in a cutting plane passing through the cutting insert (1) and parallel to the first plane (P), the intersection formed by the cutting plane on the one hand and the first minor relief surface (61), the second minor relief surface (62) and the angular minor relief surface (63) on the other hand has a contour that is identical or substantially identical to the cutting edge contour. The invention also relates to a power skiving tool comprising such a cutting insert.

Description

[Technical field]

[0001] The present invention relates to a cutting insert for a power skiving tool according to the preamble of claim 1, more particularly to a cutting insert for a power skiving tool used for gear machining, including machining of teeth or splines in metal workpieces. The present invention also relates to a power skiving tool body arranged to receive such a cutting insert. [Background technology]

[0002] Power skiving is a type of chip-removing machining method that utilizes a combination of rotary and linear motion between the milling tool and the workpiece. The method is used, inter alia, in connection with the formation of teeth, splines, etc., allowing internal as well as external machining. The method itself has been known for some time and utilizes chip-removing gear shaping, offering considerable advantages compared to traditional tooth formation methods of the type based on linearly reciprocating cutting members to remove material layer by layer while forming slots that ultimately form full-depth grooves.

[0003] In contrast to such gear forming, power skiving requires minimal tool readjustment in that the tool is held at constant rotation during planetary relative motion to the workpiece while a linear axial feed motion is imparted to the tool to remove only one fragment of chip from each groove made. In such a method, all grooves are machined to a particular depth, and as such, to a moderate depth, before the tool needs to be readjusted to accommodate the increased radial feed.

[0004] Power skiving tools using replaceable cutting inserts have been known for some time. An example of such a power skiving tool is disclosed in EP2845675. For cutting inserts used for metal cutting, the tool life of power skiving cutting inserts is limited. Even if the use of replaceable cutting inserts is cost-effective, cutting inserts are still expensive, especially when made of cemented carbide and of large dimensions, such as cutting inserts used for machining splines or teeth in the module range above 5 according to ISO standard DIN3960 for gears and ISO standard DIN5480 for splines, because only cutting inserts need to be discarded when cutting edge is damaged.

[0005] Therefore, there is a need for power skiving cutting inserts that can be used for an increased period of time before being discarded to improve manufacturing economics. Summary of the Invention

[0006] It is an object of the present invention to alleviate the shortcomings of the prior art and to provide an improved cutting insert which can be reused many times resulting in improved manufacturing economies, and to provide a cutting tool therefor.

[0007] According to a first aspect of the invention, said object is achieved by means of a cutting insert having the features defined in claim 1.

[0008] The cutting insert according to the present invention therefore comprises: - a first side including a rake face; - a second side opposite the first side; and - a peripheral surface extending between the first side and the second side, the peripheral surface including a relief surface including a first minor relief surface, a second minor relief surface and a corner minor relief surface, the corner minor relief surface being positioned between the first minor relief surface and the second minor relief surface forming a continuous transition between the first minor relief surface and the second minor relief surface; a cutting edge disposed at an intersection between a relief surface and a rake surface, the cutting edge comprising a first relief edge, a second relief edge and a nose edge, the first relief edge being disposed at the intersection between a first minor relief surface and the rake surface, the second relief edge being disposed at the intersection between the second minor relief surface and the rake surface, the nose edge being disposed at the intersection between the minor relief surface and the rake surface, the first and second relief edges extending from respective end points of the first and second relief edges to the nose edge, the cutting edge being disposed or substantially disposed in a first plane and having a cutting edge contour; Equipped with.

[0009] At each point of the cutting edge, the relief faces are arranged such that a nominal relief angle for each of the first minor relief face, the second minor relief face, and the angular minor relief face is positive and has a maximum value at a first point along the nose edge. The relief faces are further arranged such that when viewed in a cutting plane that passes through the insert and is parallel to the first plane, an intersection formed by the cutting plane on the one hand and the first minor relief face, the second minor relief face, and the angular minor relief face on the other hand has a contour that is identical or substantially identical to the cutting edge contour.

[0010] The cutting insert is replaceable and can therefore be mounted on and removed from the insert seat of the power skiving tool body. The inventors have discovered that when using the cutting insert shape as defined above, the cutting edge profile remains the same after regrinding the insert using a simple face grinding procedure, i.e. without the need for any further machining operations. This results in a regrindable power skiving cutting insert with increased overall tool life.

[0011] The cutting insert is preferably a coated carbide insert for power skiving of metal workpieces.

[0012] The first side and the second side may be parallel or substantially parallel to one another. Stated alternatively, the cutting insert may have a uniform thickness or a substantially uniform thickness.

[0013] As used herein, when a feature is described as "nominal", "nominal" refers only to the cutting insert itself, i.e., when the cutting insert is not coupled to the tool body, whereas the same feature, when termed "functional", refers only to the assembled state of the tool, i.e., when the cutting insert is mounted in its seat in the tool body.

[0014] The relief face and the rake face can form an acute tool angle at each point of the cutting edge. This is the case when no additional cutting edge reinforcement is applied. However, when the rake face includes a reinforcing land, such as a negative land, i.e., when the cutting edge is formed at the intersection between such a reinforcing land and the relief face, the tool angle between the rake face and the relief face can be obtuse.

[0015] A "cutting edge" should be understood to include all portions of the blade that are meant to engage in cutting action with a workpiece during the power skiving process. Thus, the "end points" of each of the first and second relief edges are not necessarily characterized by a particular physical attribute, and are not necessarily visually distinguishable from adjacent points on the blade, but merely refer to the furthest points along the respective relief edges that may be in cutting engagement with a workpiece during use of the power skiving tool. The cutting edges preferably consist of a first relief edge, a second relief edge, and a nose edge.

[0016] The invention may be most useful when machining splines or teeth in module ranges above 5, such as module ranges of 5-20, 5-15, or 7-12. The large dimensions of the cutting inserts required for such modules mean that each cutting insert will be expensive, thereby increasing the value of cutting inserts that are easily regrindable. Thus, by way of example, the cutting insert may be of a size used to manufacture splines having an overall height of 5 mm or more, or gear teeth having an overall height of 11.25 mm or more.

[0017] The first relief edge meets the nose edge at a first transition point. The nose edge adjacent to the first transition point on the side of the first transition point may be convexly curved and have a first radius of curvature. The first relief edge adjacent to the first transition point on the side of the first transition point may comprise either a first convexly curved round section or a straight section adjacent to the first convexly curved round section of the first relief edge, the first convexly curved round section of the first relief edge having a second radius of curvature, the second radius of curvature being greater than the first radius of curvature, for example at least 5 times or at least 10 times greater than the first radius of curvature. According to some embodiments, the first radius of curvature is less than 5 mm. In the same manner, the second relief edge meets the nose edge at a second transition point. The nose blade adjacent to the second transition point on the side of the second transition point may be convexly curved with a third radius of curvature. The second relief blade adjacent to the second transition point on the side of the second transition point may comprise either a first convexly curved round section or a straight section adjacent to the first convexly curved round section of the second relief blade, the first convexly curved round section of the second relief blade having a fourth radius of curvature, the fourth radius of curvature being greater than the third radius of curvature, for example at least 5 times or at least 10 times greater than the third radius of curvature. According to some embodiments, the third radius of curvature is less than 5 mm.

[0018] Each of the first and second relief edges may comprise a plurality of convexly curved sections having different radii of curvature. According to some embodiments, for each relief edge, the first of the convexly curved sections starting from the end point of the relief edge has the smallest radius of curvature. For each relief edge, the convexly curved section following the first convexly curved section, and each subsequent convexly curved section as it progresses towards the nose edge, may have a larger radius of curvature than the preceding convexly curved section.

[0019] The relief surfaces are preferably arranged so that the intersection formed by the cutting plane on the one hand and the first, second and corner minor relief surfaces on the other hand is identical or substantially identical to the cutting edge contour for a number of cutting planes through the insert that are parallel to the first plane, for example in all such cutting planes. However, this feature is not necessarily realized for all such cutting planes. For some cutting planes through the insert that are parallel to the first plane, for example cutting planes close to the second side, the contour of the intersection formed by the cutting plane on the one hand and the first, second and corner minor relief surfaces on the other hand may differ from the cutting edge contour. However, the contour should be identical or substantially identical to the cutting edge contour for all or at least most of the second planes in the area of ​​the cutting insert adjacent to the first side that corresponds to the maximum regrind depth.

[0020] Thus, according to some embodiments, the cutting plane is positioned at any distance from the first plane up to at least 0.3 mm, at least 0.5 mm, at least 1.0 mm, at least 1.5 mm, at least 2.0 mm, at least 2.5 mm, or at least 3.0 mm.

[0021] To restore the shape of the worn cutting edge, the first side may need to undergo a face grinding operation to a depth of approximately 0.3 mm, which is the accepted standard for maximum permissible flank wear in power skiving. Such a face grinding operation removes the worn parts of the rake face and the flank face. Prior to the face grinding operation, the insert may undergo a coating stripping operation, i.e., a process in which the remnants of the initial coating are removed by a special operation, such as a chemical operation. Following the face grinding operation, the insert may be coated again. Thus, to allow at least one re-grinding operation, a cutting plane parallel to the first plane and passing through the insert, located within 0.3 mm of the first plane, may form an intersection with the first minor flank face, the second minor flank face and the corner minor flank face, having a contour identical or substantially identical to the cutting edge contour. To allow for even greater re-sharpening depths, e.g., to compensate for greater tool wear that may occur due to local chipping of the blade, and / or to allow for multiple re-sharpening operations, a cutting plane through the insert that is parallel to the first plane and positioned within a distance from the first plane that is greater than at least 0.5 mm, at least 1.0 mm, at least 1.5 mm, at least 2.0 mm, at least 2.5 mm, or at least 3.0 mm, can form an intersection with the first minor relief surface, the second minor relief surface, and the corner minor relief surface that has a contour that is identical or substantially identical to the cutting blade contour.

[0022] As a further example, at least any cutting plane through the insert that is parallel to the first plane and positioned between the first plane and a central plane of the cutting insert positioned halfway between the first side and the second side can form an intersection with the first minor relief surface, the second minor relief surface, and the corner minor relief surface that have a contour that is the same or substantially the same as the cutting edge contour.

[0023] An imaginary reference line can be drawn in the first plane extending through the first point and perpendicular to a tangent to the cutting edge at the first point.

[0024] The first point at which the nominal clearance angle has its maximum value can often be considered the apex of the cutting edge profile and can correspond to the radially most distant point of the cutting edge relative to the central axis of the power skiving tool when the cutting insert is mounted in the seat of such a power skiving tool. A tangent to the cutting edge at this point can be oriented perpendicular or substantially perpendicular to the approximate longitudinal direction of the extension of the cutting insert, i.e., the direction in which the cutting insert has its maximum length. The reference line can therefore extend parallel to such longitudinal extension of the cutting insert or can coincide with such longitudinal extension.

[0025] According to some embodiments of the invention, both the first and second relief edges converge toward such a reference line when viewed in a direction from their respective end points toward the nose edge. Each relief edge may converge toward the reference line along its entire extent of its extension from its end point to the nose edge.

[0026] Furthermore, according to some embodiments of the present invention, the first and second clearance edges are asymmetric with respect to such reference line.

[0027] The cutting insert is particularly suitable for use in power skiving tools because it enhances the use of a wider variety of tip attachment angles and differently shaped tooth profiles. In contrast to other tooth milling processes, the power skiving process may not be able to provide the desired tooth profile in the workpiece if the relief cutting edge is symmetrical, particularly when cutting involute teeth. By imparting this asymmetric shape to the relief edge, it is easier for the individual cutting inserts to enter and exit the grooves made in the workpiece.

[0028] According to some embodiments of the present invention, the cutting insert may include a through hole extending between the first side and the second side.

[0029] Thereby, the cutting insert can be fixed in the insert seat of the power skiving tool body by a fastening element extending through the hole. For example, the fastening element can be a screw, the threads of which are arranged to engage with a threaded hole in the insert seat.

[0030] Thus, the bottom surface of the insert seat of the power skiving tool body may be provided with a threaded hole to facilitate mounting of the cutting insert using a fastening element such as a screw.

[0031] The through hole in the cutting insert can have two sections of different diameters, and the interface between them forms a support surface, such as a funnel-shaped, approximately conical cross section, that is arranged to be engaged by the head of a screw inserted through the hole to fasten the insert in the seat. The through hole can be formed such that the support surface or the funnel-shaped section is located at a depth greater than the maximum regrind depth of the cutting insert. For example, the support surface of the funnel-shaped section may be located at a hole depth corresponding to half the total length of the extension of the through hole or more. This may allow the insert to be regrind multiple times without affecting the engagement between the screw and the screw hole in the insert seat.

[0032] The through hole may be positioned such that a reference line passing through the first point, perpendicular to a tangent to the first point, is contained in a first plane and intersects or substantially intersects the center of the through hole.

[0033] The through hole can extend through the cutting insert in a central region of the insert, such as halfway across the maximum width of the insert, the width being measured in a direction perpendicular to a reference line.

[0034] According to some embodiments of the invention, the nominal clearance angle decreases along at least a major portion of each of the first and second clearance edges in a direction away from the nose edge, and may decrease along the entire extent of extension of one or both clearance edges from the nose edge to their respective end points.

[0035] The clearance angle may decrease continuously all along the cutting edge in such a direction, however, it is also possible for the clearance angle to be constant along a portion of the cutting edge, such as along a section of the cutting edge having a straight contour, or even to increase, such as along a section of the cutting edge that is concavely curved.

[0036] According to some embodiments of the invention, the portion of each of the first and second relief edges along which the nominal relief angle decreases in a direction away from the nose edge corresponds to at least 70% of the total length of extension of the respective relief edge.

[0037] According to some embodiments of the present invention, the maximum nominal clearance angle α max is in the range of 5-25°, 10-20°, or 12-17°.

[0038] Maximum nominal relief angle α max If the nominal clearance angle α is less than 5°, the cutting process may not be optimal because the cutting insert cannot be fitted to the cutting tool body with a proper chip mounting angle. max If is greater than 25°, the face grinding operation of the rake face will cause small chipping of the blade in the area around the first point (where the nominal relief angle has its maximum) when the grinding direction is unfavourable. According to some embodiments, the maximum value of the nominal relief angle is in the range of 10-20°. The cutting insert is preferably coated, the presence of a coating may have the undesirable effect of reducing the nominal relief angle close to the cutting blade, which further has the effect of reducing the functional relief angle as well. The maximum value of the nominal relief angle α max It has been observed that if the nominal relief angle α is less than 10°, when the insert is coated, the nominal relief angle along parts of the first and second relief edges may become too small, which may result in a more frequent need for regrinding of the insert. maxIt has also been observed that when the nominal clearance angle is equal to or less than 20°, a stable regrinding process is achieved without the need for quality control of the cutting edge. According to some embodiments, the best performance and quality of the regrinding insert is observed with a maximum nominal clearance angle in the range of 12-17°. Thus, by way of example, the maximum nominal clearance angle may be 15° or substantially 15°.

[0039] The nose blade profile, when viewed in a first plane, may be defined by one or more convexly curved rounded sections.

[0040] For example, the nose blade profile may be formed by a single convexly curved rounded section. The nose blade profile may be formed by multiple sections with different radii of curvature. The nose blade profile may be smooth without sharp corners. However, for some tooth profiles to be produced, the nose blade profile may be formed by short sections with a very small radius of curvature with portions between them including one or more sections (which may be almost straight sections) with a very large radius of curvature, resulting in a profile with a rather angular appearance. If the tooth profile to be produced has a flat bottom, the nose blade may have a concavely shaped section at the front.

[0041] The contours of the first and second clearance edges, when viewed in the first plane, may be defined, at least in their major part, by one or more convexly curved rounded sections.

[0042] By way of example, the profile of each of the relief edges may be formed only by convexly curved rounded sections. However, the profile may also comprise straight and / or concave portions. For example, for a particular tooth profile to be machined, such as a so-called semi-topping tooth profile, a part of the relief edge located near the end point may have a profile formed by one or more concavely curved rounded sections.

[0043] According to some embodiments of the invention, regardless of whether the relief edge also comprises a straight section and / or a concavely curved rounded section, the convexly curved rounded section of the relief edge profile may have an increasing radius of curvature along the respective relief edge in a direction from an end point of the respective relief edge towards the nose edge.

[0044] The nominal relief angle (α) at ​​any second point along the cutting edge is the maximum nominal relief angle (α max ) and the acute angle (θ) between a tangent to the cutting blade at the second point and a tangent to the cutting blade at the first point. For example, the nominal relief angle (α) at ​​any second point along the cutting blade can be a function of: α = arctan(tan α max cosθ) can be determined as, where α m ax is the relief angle at the first point and θ is the acute angle between a tangent to the cutting edge at the second point and a tangent to the cutting edge at the first point.

[0045] Such a shape of the relief surface has a maximum relief angle α max This can be achieved when designing a cutting insert based on a desired cutting edge profile by projecting the cutting edge profile along a path in the direction of a projection vector that is inclined at an angle corresponding to, where the projection vector is perpendicular to the first plane and is further included in a plane that contains the reference line.

[0046] According to some embodiments, the cutting insert is indexable and comprises a further cutting edge arranged in the first plane, both cutting edges having the same or substantially the same cutting edge contour and arranged opposite each other.

[0047] Thereby, the cutting insert can be mountable in the insert seat of the power skiving tool either in a first position where one of the cutting blades is active, or in a second position where the other cutting blade is active. In other words, the cutting insert can be a dual-position indexable insert, whereby the cutting insert can be used in two different positions before being re-ground, thus further increasing the usable time.

[0048] For such dual-position indexable cutting inserts, the datum lines as defined above may pass through both points of each cutting edge where the nominal clearance angle has a maximum value, or alternatively, corresponding datum lines may be drawn through each of those datum lines' respective points where the nominal clearance angle has a maximum value, and may be, for example, parallel to each other, although they may not necessarily be coaxial, when extending in a direction perpendicular to a tangent to such points.

[0049] According to some embodiments, the second side of the cutting insert may include one or more engagement structures arranged to engage with complementary engagement structures on the bottom surface of the insert seat to position the cutting insert in the insert seat and to prevent movement of the cutting insert in the plane of the bottom surface of the insert seat of the power skiving tool body.

[0050] For example, the one or more engagement structures may include one or more grooves and the complementary engagement structure may include one or more protrusions, or the one or more engagement structures may include one or more protrusions and the complementary engagement structure may include one or more grooves, and the one or more grooves or one or more protrusions in the one or more engagement structures included on the second side of the cutting insert are positioned to cooperate with the one or more protrusions or one or more grooves of the complementary engagement structure on the bottom surface of the insert seat.

[0051] The groove or grooves and the corresponding protrusion or protrusions may include at least two separate grooves / protrusions that extend transversely to each other, preferably perpendicular to each other. For example, the first groove can extend in the second surface of the cutting insert in a first direction, such as a direction parallel to the reference line as defined above, while the second groove can extend in a direction perpendicular to the first direction. The cooperating protrusions formed on the bottom surface of the insert seat of the power skiving tool on which the insert is mounted can be arranged in a corresponding manner. When the insert is two-way replaceable, preferably the reference lines of the cutting blades are coaxial with each other and parallel to the first groove arranged on the second surface.

[0052] According to a second aspect, the present invention relates to a power skiving tool comprising a tool body having a peripheral edge located in a first reference plane extending perpendicularly to a central axis and rotationally symmetric about the central axis. The edge comprises a plurality of tangentially spaced seats on which a cutting insert as described herein is mounted. Each seat is arranged on the tool body such that an intersection line between a first side of the cutting insert mounted in the seat and a second reference plane that includes the central axis of the tool and a first point of the cutting edge forms a radial angle with the first reference plane, the radial angle corresponding or substantially corresponding to a maximum value of the nominal clearance angle of the cutting insert.

[0053] When the cutting insert is mounted in the insert seat, the cutting insert may be chip mounted transversely to a first reference plane. The transverse angle is the angle between the first reference plane and a line extending perpendicular to the intersection line between the first side and the second reference plane on the first side of the insert. Such a transverse angle may be in the range of 5 to 40 degrees, for example.

[0054] With this setup, the radial angle corresponds to the maximum value of the nominal clearance angle, and not only does the cutting edge profile remain the same after regrinding the insert, but the cutting diameter also remains unchanged. The only parameter of the cutting tool that changes by regrinding the insert is the effective "length" of the power skiving tool, i.e., its extension along the central axis. However, this change is easily compensated for in the machine and does not affect the shape of the machined teeth on the workpiece.

[0055] On the other hand, this tool configuration does not have a clearance angle designed into it. In other words, if such a power skiving tool is used in a conventional power skiving setup, the functional clearance angle when machining the workpiece will be zero. Therefore, to compensate for this and to create the required clearance angle, such a tool is preferably applied with its central axis offset relative to the central axis of rotation of the workpiece.

[0056] In the following, example embodiments will be described in more detail with reference to the accompanying drawings. [Brief description of the drawings]

[0057] [Figure 1] FIG. 2 is a perspective view of a cutting insert according to an embodiment of the present invention. [Diagram 2] 2 is a different perspective view of the cutting insert shown in FIG. 1; FIG. [Diagram 3] FIG. 2 is a side view of the cutting insert according to FIG. [Figure 4] 2 is a plan view of the cutting insert according to FIG. 1 when viewed from above, perpendicular to the first side 2. FIG. [Diagram 5] FIG. 4 is a cross section VV in FIG. [Figure 6] FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. [Figure 7] FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. [Figure 8]FIG. 8 is a cross-sectional view taken along line VIII-VIII in FIG. [Figure 9] FIG. 9 is a cross-sectional view taken along line IX-IX in FIG. [Figure 10] FIG. 10 is a perspective view of a power skiving tool according to an embodiment of the present invention, comprising a plurality of cutting inserts as shown in FIGS. 1 to 9. [Figure 11] FIG. 11 is a side view of the tool according to FIG. [Figure 12] FIG. 11 is a plan view of the tool according to FIG. 10 when viewed from below. [Figure 13] FIG. 13 is a cross-sectional view taken along line XIII-XIII in FIG. 12. [Figure 14] FIG. 14 is a cross-section taken along line XIV-XIV in FIG. [Figure 15] FIG. 11 is a partially exploded perspective view of the tool according to FIG. [Figure 16] FIG. 2 is an enlarged cross-sectional view of the tool and the insert taken in a plane perpendicular to a first surface of the insert. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] All figures are schematic, not necessarily to scale, and only generally depict parts that are necessary to explain the respective embodiment, other parts may be omitted or only suggested. Unless otherwise indicated, like numerals refer to like parts in different figures.

[0059] 1 to 9 show a cutting insert 1 according to an embodiment of the present invention.

[0060] The cutting insert 1 comprises a first side 2, a second side 3 and a peripheral surface 4. The first side 2 comprises a rake face 5 and the peripheral surface 4 comprises a relief surface 6 comprising a first minor relief surface 61, a second minor relief surface 62 and a corner minor relief surface 63. At the intersection between the relief surface 6 and the rake face 5 a cutting edge 7 is formed comprising a first relief edge 71, a second relief edge 72 and a nose edge 73. The first relief edge 71 is disposed at the intersection between the rake face 5 and the first minor relief surface 61, the second relief edge 72 is disposed at the intersection between the rake face 5 and the second minor relief surface 62 and the nose edge 73 is disposed at the intersection between the rake face 5 and the corner minor relief surface 63. The cutting insert further comprises a through hole 8, which extends between the first and second sides along an axis A, which is also the central axis of the through hole 8. The cutting edge 7 is disposed in a first plane P that is perpendicular to the axis A. The cutting edge 7 has a particular cutting edge profile in the first plane P, as best seen in FIG. 4. The nominal relief angle α of each of the first minor relief surface, the second minor relief surface, and the angular minor relief surface is positive and has a maximum value α at a first point P1 along the nose edge. max The electrodes are arranged so as to have

[0061] As further shown in FIG. 4, a reference line RL can be drawn in the first plane P, which extends through the first point P1 and is perpendicular to the tangent t1 to the cutting blade at the first point P1. According to this embodiment, the reference line RL intersects the central axis A of the through hole 8 and extends through a corresponding first point of the other cutting blade 9, which also has a maximum value of the nominal clearance angle. The cutting blades 7, 9 are located on the opposite side of the blade, which is defined by the transition between the first side 2 and the peripheral surface 4. The cutting blades 7, 9 are rotationally symmetrical at 180° from each other with respect to the central axis A of the through hole 8, which is also the central axis of the cutting insert. Furthermore, the cutting insert has a rotational symmetry of 180° with respect to the central axis A.

[0062] The first relief edge 71 and the second relief edge 72 extend from their respective end points 711, 721 to the nose edge 73. Each of the relief edges 71, 72 converges towards the reference line RL when viewed in a direction from their respective end points 711, 721 towards the nose edge 73. According to this embodiment, the profile of each relief edge 71, 72 in the first plane P comprises a plurality of convexly curved rounded sections. The convexly curved sections have different radii of curvature, the first section starting from the end point of the relief edge having the smallest radius of curvature of the sections defining the respective relief edge. For each relief edge, the section following the first section and each subsequent section as it progresses towards the nose edge may have a larger radius of curvature than the preceding section. According to this embodiment, the transition from each relief edge 71, 72 to the nose edge 73 corresponds to the point where the convexly curved section with the smaller radius of curvature begins. The profile of the nose blade 73 also includes several convexly curved sections of different radii of curvature.

[0063] The first relief edge 71 meets the nose edge 73 at a first transition point 712. The nose edge 73 on the side of the first transition point 712 adjacent to the first transition point 712 is convexly curved and has a first radius of curvature. The first relief edge 71 on the side of the first transition point 712 adjacent to the first transition point 712 comprises a first convexly curved rounded section and has a second radius of curvature. The second radius of curvature is significantly larger than the first radius of curvature. In the same manner, the second relief edge 72 meets the nose edge 73 at a second transition point 722. The nose edge 73 on the side of the second transition point 722 adjacent to the second transition point 722 may be convexly curved with a third radius of curvature. On the side of the second transition point 722 and adjacent to the second transition point 722, the second relief edge 72 has a first convexly curved rounded section having a fourth radius of curvature, the fourth radius of curvature being significantly larger than the third radius of curvature.

[0064] As best seen in FIG. 4, the first relief edge 71 and the second relief edge 72 are asymmetric with respect to the reference line RL.

[0065] As described above, the nominal relief angle α reaches a maximum value α at the first point P1. max The nominal clearance angle decreases when moving along the cutting edge away from the first point P1. In this embodiment where the nose edge and clearance edge are simply formed by convexly curved rounded sections, the nominal clearance angle decreases continuously along the cutting edge 7 in the direction from the nose edge all the way towards the end points 711, 721 of the clearance edges 71, 72 respectively.

[0066] Maximum relief angle α at first point P1 max is shown in Fig. 7, which shows a cross-sectional view of the cutting insert 1 in a section through the first point P1 along the reference line RL as indicated in Fig. 4. According to this embodiment, the maximum clearance angle α max is 15°.

[0067] The relief angle α at any other point P2 along the cutting edge 7 is the maximum relief angle α max and the angle θ between the tangent t2 to the cutting edge 7 at the second point P2 and the tangent t1 to the cutting edge 7 at the first point P1, as shown in FIG. 4. Specifically, the nominal relief angle α at point P2 can be a function of: α = arctan(tan α max cosθ) is determined as, where α max is the relief angle at the first point P1, and θ is the acute angle between a tangent t2 to the cutting edge 7 at the second point P2 and a tangent t1 to the cutting edge 7 at the first point P1.

[0068] Figures 8 and 9 show two other cross sections through the cutting insert 1 along lines VIII-VIII and IX-IX in Figure 4, respectively, and show that, depending on the angle θ, the nominal clearance angle α decreases when approaching the end point 711, as discussed above.

[0069] When viewed in a cutting plane that passes through the cutting insert 1 and is parallel to the first plane P, the intersection formed by the cutting plane on the one hand and the first minor relief surface 61, the second minor relief surface 62 and the corner minor relief surface 63 on the other hand has a contour that is identical to the cutting edge contour. This is shown in Figs. 5 and 6, which show cross sections along lines VV and VI-VI in Fig. 3, respectively. Thus, if all material between the first plane P and such cutting plane is removed (e.g. by grinding), the reground cutting edges 7', 9', 7", 9" will have exactly the same contour as the original cutting edges 7, 9. The total length of the reground first side of the insert, as measured along the reference line RL, will be less than the corresponding length of the original first side 2. However, the relief surface 6 is shaped in such a way that the cutting edge contour is not affected by this.

[0070] In FIG. 3, the distance from the first plane P to the cutting plane shown in FIG. 6 corresponds to the maximum available grinding depth. In all cutting planes parallel to the first plane P in this area, the contour formed by the intersection between such cutting planes on the one hand and the first minor relief surface 61, the second minor relief surface 62 and the corner minor relief surface 63 on the other hand will have a contour that is identical to the cutting edge contour. This also applies to cutting planes located further away from the first plane P at a distance greater than the maximum grinding depth. Nevertheless, it may be inappropriate to regrind the cutting insert beyond the defined maximum grinding depth, for example due to the requirement to maintain sufficient strength and robustness of the cutting insert. In this example embodiment, the maximum grinding depth is 3 mm. It is therefore possible to regrind the cutting insert 10 times, if each regrind involves removing material to a depth of 0.3 mm.

[0071] 10 to 16 show a power skiving tool according to an embodiment of the invention. The power skiving tool comprises a tool body 10 having a rotationally symmetric peripheral edge 11, which is located in a first reference plane RP1 (FIG. 11) extending perpendicularly to the central axis C. The edge 11 comprises a number of tangentially spaced seats 12 (FIG. 15) on which the cutting insert 1 is mounted by means of a screw 13. A line of intersection 14 (FIG. 13) between a first side 2 of the insert 1 and a second reference plane RP2, which contains the central axis C of the tool and a first point P1 of the cutting edge of the insert, forms a radial angle γ with the first reference plane RP1. The radial angle γ can be considered as the functional rake angle of the power skiving tool and according to the invention is determined by a maximum value α of the nominal clearance angle of the cutting insert 1. max Therefore, the maximum nominal clearance angle α max According to this embodiment, where the angle γ is 15°, the insert is radially tip mounted with a corresponding angle γ of 15°.

[0072] For each cutting insert, the first point P1 is located at the apex of the cutting edge profile. When the cutting insert 1 is placed in the power skiving tool body 10, the first point P1 of each cutting insert 1 is located at the greatest distance from the central axis C, i.e., it is the point of the power skiving tool located at the radially outermost location. The nominal clearance angle α maxcorresponds to the radial angle γ, so that at this location the part of the relief surface 6 adjacent to the cutting edge 7 will be oriented parallel or substantially parallel to the central axis C. As can be seen in FIG. 13, the functional relief angle formed initially appears to be zero, but increases therefrom. This is because each cutting insert 1 is not only tip-mounted radially to the tool body 10, but also laterally. Thus, as can be seen in FIG. 14, a transverse angle β is formed between the first reference plane RP1 and a line extending perpendicular to the intersection line 14 on the first side of the insert 1. In this embodiment, the transverse angle β is 25°. FIG. 16 further illustrates the orientation of the insert relative to the tool body, showing a cross section through a power skiving tool similar to that shown in FIG. 13, in a cutting plane extending at an angle of 25° to the central axis C perpendicular to the first surface 2 of the cutting insert 1.

[0073] In this connection, it should also be mentioned that the illustrated embodiment of the cutting insert 1 is of uniform thickness (if one disregards the engagement structures 15 at the second side 3 of the insert). In other words, the second side 3 is arranged in a plane parallel to the first side 2. For this reason, the chip attachment of the cutting insert is provided not only laterally (angle β) but also radially (angle γ) by the seat 12 of the tool body which is formed with a bottom surface inclined at a respective angle with respect to the reference plane RP1.

[0074] Power skiving tools are usually applied with a central axis that is inclined tangentially to the rotation axis of the workpiece, but not inclined radially. Therefore, when applying the tool according to the invention in such a manner, the functional clearance angle is zero. Therefore, in order to provide the necessary clearance and to prevent friction with the workpiece, the power skiving tool according to the invention is preferably applied with a central axis offset from the rotation axis of the workpiece.

[0075] Now, with reference to Fig. 2 and Fig. 15, the interface between the cutting insert and the insert seat will be described. The second side 3 of the cutting insert 1 comprises an engagement structure 15 extending across the second side. The engagement structure 15 comprises so-called cross serrations, either in the form of grooves or protrusions in the cutting insert, for engagement with a corresponding number of protrusions or grooves in the insert seat 12. According to this particular embodiment, each engagement structure formed on the second side 3 of the cutting insert 1 consists of two protrusions extending in parallel such that a groove is formed between them. The engagement structures, while being oriented perpendicular to each other, form a cross-shaped configuration. Each one of the two engagement structures 15 is interrupted by a through hole 8. In other words, the centrally located groove of each engagement structure 15 consists of two sections spaced apart from each other via the through hole 8 and positioned in line with each other.

[0076] The complementary engagement structures 17 on the bottom surface of the seat 12 also extend perpendicular to each other while forming the same kind of cross-like configuration as the cross-configuration of the engagement structures 15 of the cutting insert 1. Each complementary engagement structure 17 comprises a central protrusion arranged to cooperate with a corresponding groove of the engagement structure of the insert.

[0077] It should further be pointed out that all protrusions and grooves have chamfered or inclined sides, thereby ensuring that the protrusions are pressed into the grooves in conjunction with the fixing of the cutting insert by tightening the screw 13.

[0078] Using the described fastening means, the cutting insert 1 by the simple measure of fastening the screw 13 is positioned in a very precisely defined position from which it cannot be displaced by angular displacement or in any other way.

[0079] Furthermore, since no part of the peripheral surface 4 of the insert 1 is used as a support surface for fixing the insert in the seat 12, the insert can be reground without affecting the interface between the insert and the seat.

Claims

1. A cutting insert (1) for a power skiving tool, comprising: a first side (2) including a rake face (5); a second side (3) opposite said first side (2); a peripheral surface (4) extending between the first side (2) and the second side (3), the peripheral surface (4) including relief surfaces (6) including a first minor relief surface (61), a second minor relief surface (62) and a corner minor relief surface (63), the corner minor relief surface (63) being positioned between the first minor relief surface (61) and the second minor relief surface (62) and forming a continuous transition between the first minor relief surface (61) and the second minor relief surface (62); a cutting edge (7) disposed at an intersection between the relief surface (6) and the rake surface (5), the cutting edge (7) comprising a first relief edge (71), a second relief edge (72) and a nose edge (73), the first relief edge (71) being disposed at an intersection between the first minor relief surface (61) and the rake surface (5), and the second relief edge (72) being disposed at an intersection between the second minor relief surface (62) and the rake surface (5); a cutting edge (7) disposed at an intersection between the corner minor relief surface (63) and the rake face (5), the nose edge (73) being disposed at the intersection between the corner minor relief surface (63) and the rake face (5), the first and second relief edges (71, 72) extending from end points (711, 721) of the first and second relief edges (71, 72) to the nose edge (73), the cutting edge (7) being disposed or substantially disposed in a first plane (P) and having a cutting edge contour; Equipped with At each point of the cutting edge (7), the relief surface (6) has a nominal relief angle (α) of each of the first minor relief surface (61), the second minor relief surface (62), and the corner minor relief surface (63) that is positive and has a maximum value (α) at ​​a first point (P1) along the nose edge (73). ｍａｘ ) and The cutting insert (1) is further characterized in that the relief surface (6) is arranged such that, when viewed in a cutting plane that passes through the cutting insert (1) and is parallel to the first plane (P), an intersection formed by the cutting plane on the one hand and the first minor relief surface (61), the second minor relief surface (62), and the corner minor relief surface (63) on the other hand has a contour that is identical or substantially identical to the cutting edge contour.

2. 2. The cutting insert of claim 1, wherein the cutting plane is positioned at any distance from the first plane up to at least 0.3 mm, at least 0.5 mm, at least 1.0 mm, at least 1.5 mm, at least 2.0 mm, at least 2.5 mm, or at least 3.0 mm.

3. 3. The cutting insert according to claim 1 or 2, wherein each of the first and second relief edges (71, 72) approaches a reference line (RL) included in the first plane (P) when viewed in a direction from the respective end points (711, 721) of the first and second relief edges (71, 72) toward the nose edge (73), the reference line (RL) extending through the first point (P1) and perpendicular to a tangent (t1) to the cutting edge at the first point (P1).

4. The cutting insert according to claim 3, wherein the first and second clearance edges (71, 72) are asymmetric with respect to the reference line (RL).

5. The cutting insert according to claim 1, further comprising a through hole (8) extending between the first side (2) and the second side (3).

6. 2. The cutting insert according to claim 1, wherein the nominal relief angle (α) decreases along at least a major portion of each of the first and second relief edges (71, 72) in a direction away from the nose edge (73).

7. The maximum value of the nominal relief angle (α ｍａｘ 2. The cutting insert according to claim 1, wherein the angle θ is in the range of 5 to 25°, 10 to 20°, or 12 to 17°.

8. The cutting insert according to claim 1 , wherein the contour of the nose edge (73) is formed by one or more convexly curved rounded sections when viewed in the first plane (P).

9. 2. The cutting insert according to claim 1, wherein the contour of each of the first and second clearance edges (71, 72) is formed, at least in its main part, by one or more convexly curved rounded segments when viewed in the first plane (P).

10. The nominal relief angle (α) at ​​any second point (P2) along the cutting edge (7) is equal to the maximum value of the nominal relief angle (α ｍａｘ 2. The cutting insert according to claim 1, wherein the cutting insert is a function of the distance (t2) between the cutting edge (7) at the second point (P2) and the acute angle (θ) between the tangent (t1) to the cutting edge (7) at the first point (P1).

11. The nominal relief angle (α) at ​​any second point (P2) along the cutting edge (7) is: α=arctan(tanα ｍａｘ ・cosθ) is determined as, where α ｍａｘ 2. The cutting insert according to claim 1, wherein θ is a relief angle at the first point (P1), and θ is an acute angle between a tangent (t2) to the cutting edge (7) at the second point (P2) and a tangent (t1) to the cutting edge (7) at the first point (P1).

12. 2. The cutting insert according to claim 1, wherein the cutting insert (1) is indexable and comprises a further cutting edge (9) arranged in the first plane (P), both cutting edges (7, 9) having identical or substantially identical cutting edge profiles and arranged opposite each other.

13. 2. The cutting insert according to claim 1, wherein the second side (3) comprises one or more engagement structures (15) arranged to engage with complementary engagement structures (17) on a bottom surface of the insert seat (12) to position the cutting insert in the insert seat (12) of the power skiving tool body (10) and to prevent movement of the cutting insert in the plane of the bottom surface of the insert seat (12).

14. 14. The cutting insert according to claim 13, wherein the one or more engagement structures (15) comprise one or more grooves and the complementary engagement structure (17) comprises one or more protrusions, or the one or more engagement structures (15) comprise one or more protrusions and the complementary engagement structure (17) comprise one or more grooves, and the one or more grooves or the one or more protrusions on the one or more engagement structures (15) included on the second side (3) of the cutting insert (1) are arranged to cooperate with the one or more protrusions or the one or more grooves of the complementary engagement structure (17) on the bottom surface of the insert seat (12).

15. A power skiving tool comprising a tool body (10) positioned in a first reference plane (RP1) extending perpendicular to a central axis (C) and having a peripheral edge (11) that is rotationally symmetric about said central axis (C), said edge (11) comprising a plurality of tangentially spaced seats (12), wherein a cutting insert (1) according to claim 1 is mounted on each one of said plurality of seats (12), and each seat (12) of said plurality of seats (12) is mounted on said seat (12). The cutting insert (1) is arranged in the tool body (10) such that an intersection line (14) between the first side (2) of the cutting insert (1) and a second reference plane (RP2) including the central axis (C) of the power skiving tool and the first point (P1) of the cutting edge (7) of the cutting insert (1) forms a radial angle (γ) with the first reference plane (RP1), and the radial angle (γ) is greater than or equal to the maximum value (α) of the nominal relief angle of the cutting insert (1). ｍａｘ ) power skiving tools that are compatible or substantially compatible with

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