End mill and method for machining a workpiece with an end mill

Abstract

The invention relates to an end mill (1) comprising a shank (2) which can be rotatably driven about a longitudinal axis (L) of the end mill (1) and which is designed for being received in a rotating tool holder of a machine tool, and comprising a tool head (3) which is rigidly connected to the shank (2) and has a milling section (4) with at least one geometrically defined cutting edge (7) over its circumference around the longitudinal axis (L), characterised in that the tool head (3) has an abrasive section (5) with abrasive grains (17), made of an abrasive material with geometrically undefined cutting edges, over its circumference about the longitudinal axis (L) and bonded in a bonding matrix (18).

Description

[0001] End mill and method for machining a workpiece with an end mill

[0002] Description

[0003] The invention relates to an end mill with a shank that can be driven in rotation about a longitudinal axis of the end mill and is designed for reception in a rotating tool holder of a machine tool. The end mill further comprises a tool head rigidly connected to the shank and having at least one milling section that has at least one geometrically defined cutting edge around its circumference around the longitudinal axis.

[0004] Such a tool is known from DE 103 18 948 A1, wherein the tool is designed as a combined drilling, roughing, and finishing tool. A drilling tool is driven in rotation along a rotational axis and has cutting edges for machining material exclusively at the tip, i.e. on the front side in the direction of the longitudinal axis. The cutting edges at the tool tip also run along a cone to make drilling easier when starting the drilling process, since only the tip of the tool comes into contact with the workpiece to be machined. This shape of the cutting edges also improves chip removal. Drilling tools do not have any cutting edges over the circumference around the longitudinal axis. Only helical grooves are provided, which serve to transport the resulting chips out of the drilled hole. A drilling tool therefore has a single machining direction in the direction of the longitudinal axis, which is also the rotational axis.

[0005] Unlike a drilling tool, a milling tool has one or more cutting edges around its circumference along its longitudinal axis. A milling tool can also have secondary cutting edges at the tool tip. In milling tools, the secondary cutting edges at the tool tip are usually arranged in a plane perpendicular to the longitudinal axis in order to form a flat surface parallel to the feed direction when the feed direction is transverse to the longitudinal axis. A milling tool can therefore machine material in various directions. The main working direction is transverse to the longitudinal axis.

[0006] The combination tool according to DE 103 18 948 A1 is a combination of a drilling tool and a milling tool. The tool has cutting edges at the tip arranged along a conical surface and cutting edges arranged along the circumference of the longitudinal axis. The cutting edges extend helically around the circumference.

[0007] The cutting edges of the tool can be provided with a wear-resistant coating over a section in the longitudinal direction, which can comprise, for example, nanocrystalline diamonds or other hard materials. This coating leaves the shape of the geometrically defined cutting edges unchanged, while the coating provides increased wear protection. This means that the tool can be used for different machining steps on the same workpiece made of a single material without having to change tools between machining steps. For example, a first section can be designed as a roughing section in order to remove a large amount of material in a short time at high feed rates. A second longitudinal section of the tool can be designed as a finishing tool, with which smooth surfaces can be achieved at low feed rates.The roughing section can have serrated cutting edges, which are also coated as described above to increase the tool's service life. To machine, for example, a plate-shaped workpiece, the tool is first arranged longitudinally such that the roughing section is aligned transversely to the plate-shaped workpiece, with the longitudinal axis of the tool aligned transversely to the plane of the plate-shaped workpiece. The tool is then moved at a high feed rate towards the plane of the plate-shaped workpiece in order to machine material over the circumference of the milling tool with the main cutting edges. For the finishing process, the tool is then moved axially such that the finishing section of the tool is aligned transversely to the workpiece, so that in the subsequent machining step the workpiece can be machined at a low feed rate.DE 10 2013 000 942 A1 discloses a milling tool with a rotating tool head, wherein at least one cutting edge is provided in the region of a peripheral surface of the tool head. An abrasive is arranged on the peripheral surface of the tool head adjacent to the at least one cutting edge in the direction of rotation. The at least one cutting edge and the region provided with the abrasive thus completely overlap along their axial extent.

[0008] Problems arise with conventional tools when plate-shaped workpieces are made of different materials, each comprising a layer of ductile material and a layer of a brittle and resistant material. In this case, tools with geometrically defined cutting edges wear faster in the brittle and more wear-resistant layer of the workpiece, requiring the tool to be replaced, even if the cutting edge sections that machine the ductile layers of the workpiece are less worn and could still be used for machining. When using tools with geometrically undefined cutting edges, they quickly become clogged in the area of ​​the ductile material layers of the workpiece, significantly reducing the tool's service life compared to the areas where the brittle layers are ground.

[0009] The object of the present invention is to provide a tool with which plate-shaped workpieces made of layers of different materials can be machined, wherein the tool has improved wear resistance and thus an increased service life.

[0010] The object is achieved according to the invention by an end mill comprising a shaft that can be driven to rotate about a longitudinal axis of the end mill and that is designed for reception in a rotating tool holder of a machine tool, and a tool head rigidly connected to the shaft with at least one milling section that has at least one geometrically defined cutting edge around its circumference about the longitudinal axis. The tool head has a grinding section that has abrasive grains made of an abrasive material with geometrically undefined cutting edges bound in a bond matrix around its circumference about the longitudinal axis and that is arranged at a distance from the milling section in the direction of the longitudinal axis.

[0011] This makes the end mill suitable for machining layers of different materials in a layered workpiece in a single machining step. It is an end mill that has a grinding section, and can therefore also be described as a combination tool for milling and grinding. The geometrically defined cutting edges of the milling section are particularly well suited to machining ductile materials such as plastic, non-ferrous metals, aluminum and even steel. The geometrically indeterminate cutting edges of the grinding section are particularly suitable for hard and brittle materials such as silicon carbide, silicon, glass and ceramics. The geometrically defined cutting edges would wear out faster when machining hard and brittle materials than the geometrically indeterminate cutting edges of the grinding section, since the abrasive grains have a higher strength than the base material of the milling section.On the other hand, the geometrically indeterminate cutting edges of the grinding section would quickly become worn when machining soft and ductile materials and would require either extensive cleaning or replacement. The combination of a milling section and a grinding section therefore ideally enables the machining of plate-shaped workpieces with layers of different materials in a single machining step.

[0012] For this purpose, the grinding section is arranged at a distance from the milling section in the direction of the longitudinal axis. This also includes an arrangement in which the milling section and the grinding section are directly adjacent to one another. The milling section and the grinding section are arranged circumferentially around the longitudinal axis without overlapping. In the circumferential direction, only one of the two sections per section, i.e., the milling section or the grinding section, is in machining engagement with the workpiece to be machined. This does not preclude the possibility of another section being arranged between the milling section and the grinding section, which combines the features of the milling section and the grinding section.

[0013] The milling section can have exclusively geometrically defined cutting edges. In addition to the geometrically indeterminate cutting edges, the grinding section can also have geometrically defined cutting edges or a corresponding contour. However, it is also possible for the grinding section to have exclusively geometrically indeterminate cutting edges.

[0014] In one embodiment, it is provided that the grinding section is arranged axially between the shaft and the milling section.

[0015] A further milling section can be arranged between the grinding section and the shaft, which has at least one geometrically defined cutting edge along its circumference around the longitudinal axis. Thus, the grinding section is arranged between two milling sections and is particularly suitable for plate-shaped workpieces that have two outer layers of a ductile material and a layer of a brittle material arranged between them, such as semiconductor chips.

[0016] In an exemplary embodiment, the grinding section is formed by a grinding wheel formed from the abrasive grains bonded in the bond matrix, the milling section is formed by a milling shaft, for example, made of a metallic material such as hard metal, and the grinding wheel and the milling shaft are rigidly connected to one another by a material fit or a force fit. Furthermore, the grinding wheel and the shaft can also be rigidly connected to one another by a material fit or a force fit.

[0017] Between the grinding wheel and the shaft, a further milling shaft, for example made of a metallic material such as hard metal, which forms a further milling section, can be arranged, wherein the further milling shaft can be rigidly connected to the grinding wheel on the one hand and to the shaft on the other hand in a material or force-fitting manner.

[0018] The grinding wheel can be shaped in such a way that its outer contour corresponds to the contour of the grinding sections in such a way that it continuously continues the geometrically determined cutting edges of the grinding sections.

[0019] According to a further exemplary embodiment, the grinding section is formed by a cylindrical section with an outer peripheral surface, wherein the bond matrix with the abrasive grains accommodated therein is applied to the outer peripheral surface.

[0020] The cylindrical portion may be formed by an outer circumferential groove.

[0021] In all embodiments, the bond matrix can be a metallic, ceramic, or synthetic resin-based bond matrix. The abrasive grains can be completely encased in the bond matrix. The abrasive grains can have an average grain size of at least 15 μm. The abrasive material from which the abrasive grains are made can be, for example, cubic boron nitride (CBN), diamond, corundum, zirconium corundum, ceramic corundum, or silicon carbide.

[0022] The object is further achieved by a method for machining a workpiece with a previously described end mill, wherein the workpiece has several flat layers of different materials. The method comprises the following steps:

[0023] - Aligning the end mill such that the longitudinal axis of the end mill is arranged transversely to the planes of the layers,

[0024] - Aligning the end mill such that the milling section is arranged in the axial direction in a plane of a first position and the grinding section is arranged in the axial direction in a plane of a second position of the workpiece, and

[0025] - machining the workpiece with the rotating end mill in a feed direction parallel to the planes of the layers.

[0026] In one embodiment of the method, the milling section can be aligned axially in the plane of the first bearings made of a ductile material, such as plastic, non-ferrous metal, aluminum, or synthetic resin. Furthermore, the grinding section can be aligned axially in the plane of the second layer made of a brittle material, such as silicon carbide, silicon, glass, or ceramic.

[0027] Exemplary embodiments are explained in more detail below with reference to the figures. Figure 1 shows a perspective view of the end mill,

[0028] Figure 2 is an enlarged perspective view of a tool tip of a first embodiment of an end mill,

[0029] Figure 3 is an enlarged perspective view of a tool tip of a second embodiment of an end mill,

[0030] Figure 4 shows a partial longitudinal section of an end mill according to the first or second embodiment,

[0031] Figure 5 shows an enlarged longitudinal section of the end mill according to Figure 4 in the area of ​​the tool tip,

[0032] Figure 6 shows an enlarged partial cross-section of a grinding wheel of the end mill according to Figure 5,

[0033] Figure 7 shows a partial longitudinal section of a third embodiment of an end mill,

[0034] Figure 8 shows an enlarged longitudinal section of the end mill according to Figure 7 in the area of ​​the grinding section, and

[0035] Figure 9 is a view showing the arrangement of the end mill according to Figure 1 relative to a plate-shaped workpiece for machining.

[0036] Figure 1 shows an end mill 1 in a perspective view. The end mill 1 has a shank 2 and a tool head 3. The end mill 1 and the shank 2 can be driven to rotate about a longitudinal axis L of the end mill 1. For this purpose, the shank 2 is designed to be received in a rotating tool holder (not shown here) of a machine tool. The tool head 3 is rigidly connected to the shank 2. The shank 2 and the tool head 3 can be made in one piece from a common tool blank. Alternatively, the shank 2 and the tool head 3 can be made from different tool blanks that are subsequently rigidly connected to one another. The tool head 3 has a milling section 4, a grinding section 5 adjoining this in the longitudinal direction, and a further milling section 6 adjoining the grinding section 5 in the longitudinal direction.The milling section 4, the grinding section 5, and the further milling section 6 are arranged axially separated from one another in the direction of the longitudinal axis L, i.e., they do not overlap in the circumferential direction. In the exemplary embodiment shown, the grinding section 5 is located between the milling section 4 and the further milling section 6, with the further milling section 6 being arranged directly adjacent to the shaft 2. In principle, it is also conceivable for only one milling section 4 and one grinding section 5 to be present. Furthermore, it is also conceivable for several milling sections and several grinding sections to be arranged alternately next to one another along the longitudinal axis L.

[0037] In the illustrated embodiment, the milling section 4 is arranged at the tool tip 9 facing away from the shaft 2. It is also possible for the grinding section 5 to be arranged at the tool tip 9.

[0038] The two milling sections 4, 6 each have several geometrically defined cutting edges 7, 8 extending helically over their entire circumference. Geometrically defined cutting edges are characterized by the fact that the number of cutting edges, their path, and the geometry of the cutting edges in the cross-section (cutting wedge) are predetermined and clearly defined.

[0039] The grinding section 5 has abrasive grains bound in a bond matrix around its entire circumference around the longitudinal axis L. These grains consist of an abrasive material with geometrically indeterminate cutting edges. Geometrically indeterminate cutting edges are characterized by the fact that the number of cutting edges, their course, and the geometry of the cutting edges in the cross-section (cutting wedge) are not predetermined and not clearly defined. Abrasive grains consist, in particular, of cubic boron nitride (CBN), diamond, corundum, zirconium corundum, ceramic corundum, or silicon carbide.

[0040] Figure 2 shows an enlarged view of the tool head 3 in the region of the tool tip 9 of a first embodiment of the end mill 1 according to Figure 1, wherein corresponding components are provided with the same reference numerals. The first embodiment of the end mill 1 has a grinding section 5 which has exclusively geometrically undefined cutting edges, i.e. essentially forms a cylindrical outer peripheral surface. The grinding section 5 is formed by a grinding wheel 12 formed from the abrasive grains bonded in the bond matrix. The milling section 4 and the further milling section 6 form exclusively geometrically defined cutting edges 7, 8. In the exemplary embodiment shown, the grinding section 5 is located between the milling section 4 and the further milling section 6. The milling section 4 is arranged at the tool tip 9.

[0041] Figure 3 shows an enlarged view of the tool head 3 in the region of the tool tip 9 of a second embodiment of the end mill 1 according to Figure 1, wherein corresponding components are provided with the same reference numerals. The second embodiment of the end mill 1 has a grinding section 5 which forms geometrically undefined cutting edges and is additionally shaped such that geometrically defined cutting edges 10 are formed. The grinding section 5 is formed by a grinding wheel 12 formed from the abrasive grains bonded in the bond matrix. Just as in the first embodiment, the grinding section 5 is located between the milling section 4 and the further milling section 6. The geometrically defined cutting edges 7, 8, 10 can be aligned with one another in the axial direction.

[0042] Figures 4 and 5 show different views of a partial longitudinal section of the first and second embodiments. It can be seen that the milling section 4 is formed by a milling shaft 11. The further milling section 6 is formed by a further milling shaft 13. The two milling shafts 11, 13 are designed as separate components. In the exemplary embodiment shown, the further milling shaft 13 is connected integrally, i.e. in one piece, to the shaft 2. The further milling shaft 13 can alternatively be designed as a separate component from the shaft 2, which is rigidly connected to the shaft 2 in a material-locking or form-fitting manner, for example by soldering. This has the advantage that the further milling shaft 13, like the milling shaft 11, can be made from a hard metal, whereas the shaft 2 can be made from a steel material.The grinding wheel 12 is located between the milling shank 11 and the further milling shank 13 and is rigidly connected to them by a material or force fit. For example, the grinding wheel 12 can be glued or soldered to the two milling shanks 11, 13. So that the milling shanks 11, 13 and the grinding wheel 12 can be connected to one another centered to the longitudinal axis L, the milling shanks 11, 13 each have central centering projections 19, 20 pointing towards the grinding wheel 12, which each penetrate into a centering recess 21, 22 of the grinding wheel 12. In principle, it is also conceivable for the milling shanks 11, 13 to have no centering projections and the grinding wheel 12 accordingly to have no centering recesses.

[0043] For production, it is possible to first form a tool blank with geometrically defined cutting edges 8. Subsequently, the tool tip 9 is cut off. The grinding wheel 12 can then be rigidly connected between the milling shank 11 formed by the cut-off and the further milling shank 13.

[0044] Alternatively, a tool blank can initially be used for production in which no geometrically defined cutting edges are yet formed. The tool tip 9 is then separated or provided as a separate component. The grinding wheel 12 is then arranged between the two milling shanks 11, 13 and rigidly connected to them. Subsequently, the geometrically defined cutting edges can be ground continuously across the two milling sections 4, 6 and the grinding section 5.

[0045] As schematically shown in Figure 6, the grinding wheel 12 has a metallic, ceramic, or synthetic resin-based bond matrix 18 in which abrasive grains 17 are bonded. The abrasive grains 17 consist of an abrasive material with geometrically undefined cutting edges.

[0046] Figures 7 and 8 show different views of a third embodiment of the end mill 1 according to Figure 1, wherein corresponding components are provided with the same reference numerals. The grinding section 5 is formed by a cylindrical section 14 with an outer peripheral surface 15. The outer peripheral surface 15 is coated with abrasive grains 27 received in a bond matrix 28. The outer peripheral surface 15 is formed by an outer peripheral groove 16, which is located between the milling section 4 and the further milling section 6. In this embodiment, the milling sections 4, 6, the grinding section 5 and the shaft 2 are manufactured starting from a common tool blank.

[0047] The abrasive grains 27 are accommodated in the bond matrix 28 and protrude outwardly from it or can also be enclosed by it. The bond matrix 28 is an electrochemical, e.g., galvanic bond matrix made of a nickel material, for example. The abrasive grains 27 can be made of the same material as those of the first two embodiments. For machining, the abrasive grains 17 have geometrically undefined cutting edges in the form of edges 29.

[0048] Figure 9 shows the orientation of the end mill 1 when used to machine a workpiece 23. The workpiece 23 is a plate-shaped component, such as a semiconductor chip. The workpiece 23 consists of a first layer 24, a second layer 25, and a third layer 26, with the second layer 25 being arranged between the first layer 24 and the third layer 26. The first layer 24 and the third layer 26 are made of a ductile or soft material, such as plastic or synthetic resin. The second layer 25 arranged between them is made of a brittle material, such as silicon carbide or silicon.

[0049] To machine the workpiece 23, the end mill 1 is aligned such that the milling section 4 is arranged in the axial direction along the longitudinal axis L in a plane of the first layer 24 or overlaps therewith. Furthermore, the grinding section 5 is arranged in the axial direction in a plane of the second layer 25. The further milling section 6 is arranged, at least in regions, in the axial direction in a plane of the third layer 26. To machine the workpiece 23, the end mill 1 is moved transversely to the longitudinal axis L in the direction of arrow P while being driven to rotate about the longitudinal axis L. The geometrically defined cutting edges 7, 8 can thus machine the ductile material. To machine the brittle material of the second layer 25, the geometrically undefined cutting edges of the grinding bodies of the grinding section 5 are used. Thus, the appropriate section of the end mill 1 is used for each material of the individual layers 24, 25, 26.

[0050] List of reference symbols

[0051] 1 end mill

[0052] 2 shaft

[0053] 3 tool head

[0054] 4 Milling section

[0055] 5 Grinding section

[0056] 6 further milling section

[0057] 7 geometrically determined cutting edges

[0058] 8 geometrically defined cutting edges

[0059] 9 Tool tip

[0060] 10 geometrically determined cutting edges

[0061] 11 Milling shank

[0062] 12 grinding wheels

[0063] 13 additional milling shaft

[0064] 14 cylindrical section

[0065] 15 Outer peripheral surface

[0066] 16 Outer circumferential groove

[0067] 17 abrasive grain

[0068] 18 Bonding matrix

[0069] 19 Centering projection

[0070] 20 Centering projection

[0071] 21 centners recess

[0072] 22 centners recess

[0073] 23 Workpiece

[0074] 24 first layer

[0075] 25 second layer

[0076] 26 third layer

[0077] 27 Abrasive grain 28 Bond matrix

[0078] 29 edge

[0079] P Arrow

Claims

End mill and method for machining a workpiece with an end mill Claims 1. End mill (1) comprising a shaft (2) which can be driven to rotate about a longitudinal axis (L) of the end mill (1) and which is designed for this purpose to be received in a rotating tool holder of a machine tool, and a tool head (3) which is rigidly connected to the shaft (2) and has a milling section (4) which has at least one geometrically defined cutting edge (7) over its circumference around the longitudinal axis (L), characterized in that the tool head (3) has a grinding section (5) which has abrasive grains (17) made of an abrasive material with geometrically indeterminate cutting edges, bound in a bond matrix (18) over its circumference around the longitudinal axis (L), and which is arranged at a distance from the milling section (4) in the direction of the longitudinal axis (L).

2. End mill (1) according to claim 1, characterized in that the milling section (4) has exclusively geometrically determined cutting edges (7).

3. End mill (1) according to claim 1 or 2, characterized in that the grinding section (5) has exclusively geometrically indeterminate cutting edges (7).

4. End mill (1) according to one of claims 1 to 3, characterized in that that the grinding section (5) is arranged axially in the direction of the longitudinal axis (L) between the shaft (2) and the milling section (4). End mill (1) according to one of claims 1 to 4, characterized in that a further milling section (6) is arranged axially in the direction of the longitudinal axis (L) between the grinding section (5) and the shaft (2), which further milling section has at least one geometrically defined cutting edge (8) over its circumference around the longitudinal axis (L). End mill (1) according to one of claims 1 to 5, characterized in that the grinding section (5) is formed by a grinding wheel (12) formed from the abrasive grains (17) bound in the bond matrix (18), that the milling section (4) is formed by a milling shaft (11), and that the grinding wheel (12) and the milling shaft (11) are rigidly connected to one another by a material fit or a force fit.End mill (1) according to claim 6, characterized in that the grinding wheel (12) and the shaft (2) are rigidly connected to one another by a material fit or a force fit. End mill (1) according to claim 6 or 7, characterized in that a further milling shaft (13) is arranged between the grinding wheel (12) and the shaft (2). End mill (1) according to claim 8, characterized in that the further milling shaft (13) is rigidly connected to the grinding wheel (12) on the one hand and to the shaft (2) on the other hand by a material fit or a force fit. End mill (1) according to one of claims 1 to 5. characterized in that the grinding section (5) is formed by a cylindrical section (14) with an outer peripheral surface (15), and in that the bonding matrix (18) with the abrasive grains (17) accommodated therein is applied to the outer peripheral surface (15). End mill (1) according to claim 10, characterized in that the cylindrical section (14) is formed by an outer peripheral groove (16). A method for machining a workpiece (23) with an end mill (1) according to one of the preceding claims, wherein the workpiece (23) has a plurality of flat layers (24, 25, 26) of different materials, comprising the steps: Aligning the end mill (1) such that the longitudinal axis (L) of the end mill (1) is arranged transversely to the planes of the layers (24, 25, 26), Aligning the end mill (1) such that the milling section (4) is arranged in the axial direction in a plane of a first layer (24) and the grinding section (5) is arranged in the axial direction in a plane of a second layer (25) of the workpiece (23), and machining the workpiece (23) with the rotationally driven end mill (1) in a feed direction (P) parallel to the planes of the layers (24, 25, 26). Method according to claim 12, characterized in that the milling section (4) is aligned in the axial direction in the plane of the first layer (24) made of a ductile material (e.g., plastic, non-ferrous metal, aluminum, synthetic resin), and the grinding section (5) is aligned in the axial direction in the plane of the second layer (25) made of a brittle material (e.g., silicon carbide, silicon, glass, ceramic).

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