END MILL

Abstract

The present invention relates to a left-hand rotating end mill (1) with a shank (10) and a cutting head (20) having a number of left-hand spiral cutting edges (50) spaced apart from one another by flutes (30), wherein the cutting edges (50) are divided into cutting edge segments (60) at least over a portion of their length by a number of right-hand spiral dividing grooves (40). The cutting head (20) is divided into a shank-side cutting step (22) and an end-side cutting step (24) adjoining the shank-side cutting step (22) via a transition section (23), the end-side cutting step having a smaller cutting diameter than the shank-side cutting step (22).

Description

[0001] The invention relates to a milling cutter for machining layered composite materials, e.g. fiber-reinforced plastics (FRP) such as carbon- or glass-fiber-reinforced plastics (CFRP / GFRP), as well as for stripping wires.

[0002] Fiber-reinforced plastics are relatively difficult to machine due to their multiphase structure. For example, when milling a fiber-reinforced plastic (FRP) panel, delamination of fiber composite layers or fiber protrusions on the two panel surfaces are frequently observed. Therefore, the economical machining of modern fiber-reinforced plastics, especially in series production, requires adapted tool designs that reliably prevent delamination or fiber protrusions on a machined FRP component. Examples of such adapted tools include end mills designed as compression cutters, in which opposing axial cutting forces are generated through a special cutting element design.At the point where the fibers of a milled fiber-reinforced composite (FRP) material, which are conventionally created by these cutting forces, meet, these fibers are compressed and ultimately separated. This prevents delamination or fiber protrusion on the two plate surfaces.

[0003] From US patent 9,174,287 B2, a right-handed end mill for milling layered composite materials, e.g., glass fibers, is known. The end mill has a shank and a cutting head with a plurality of right-handed main flutes with a positive rake angle and a plurality of left-handed auxiliary flutes with a positive rake angle, the number of main flutes and the number of auxiliary flutes differing. The cutting head has a constant outer diameter along its entire axial length. The end mill also has several end cutting edges. The auxiliary flutes act as divider slots for the main flutes and divide the main cutting edges extending along the main flutes into a plurality of main cutting edge segments. An auxiliary cutting edge segment extending along the auxiliary flute is connected to the end face of each main cutting edge segment by forming the corresponding auxiliary flute.

[0004] Overall, the end mill described in US 9,174,287 B2 features a multitude of circumferential cutting segments, each containing a main cutting segment and an auxiliary cutting segment located on the tool's outer diameter. This design allows for the generation of opposing axial cutting forces, which can counteract delamination when machining layered composite materials. US 9,174,287 B2 specifies an alternative embodiment in which the end mill can be a left-hand rotating tool with left-hand helical main flutes and right-hand helical auxiliary flutes.

[0005] A disadvantage of the end mill of US 9 174 287 B2 is that the tool's applications are limited to milling layered composite materials due to the special design of the cutting edges.

[0006] German patent application DE 10 2019 213 976 A1 discloses a circumferential milling tool for stripping an insulating layer from a wire, also known as a hairpin, with a substantially rectangular cross-section. The milling tool is designed as a profile tool, meaning that the effective outer contour equipped with circumferential cutting edges is adapted to the outer contour of the workpiece W to be machined. For this purpose, the cutting area equipped with circumferential cutting edges has a step that divides the milling tool into a first end-face section with a cylindrical outer contour or surface with a first diameter, and a second shank-side section separated by the step, with a cylindrical outer contour or surface with a second diameter that is larger than the first diameter.The outer contour of the step, which forms a transition from the first section to the second section, is adapted to the outer contour, in particular to the edges of the rectangular cross-section, of the wire, thus ensuring that the wire has an undamaged, clean surface after stripping. The circumferential cutting edges are continuous and extend from one end face of the tool into the second section on the shaft side.

[0007] Starting from an end mill as known from US 9,174,287 B2, the invention is therefore based on the objective of creating an end mill that is suitable for milling layered composite materials, e.g. fiber-reinforced plastics (FRP) such as carbon or glass fiber reinforced plastics (CFRP / GFRP), as well as for stripping wires, in particular so-called hairpin wires, which are used in the area of ​​the stator windings of electric motors and generators, and which thus offers more application possibilities.

[0008] This problem is solved by an end mill with the features of claim 1. Advantageous or preferred embodiments are the subject of dependent claims.

[0009] An end mill can be left-hand rotating and have a shank and a cutting head with a number of left-hand helical cutting edges spaced apart by flutes, wherein the cutting edges are divided into cutting edge segments by a number of right-hand helical dividing grooves over at least a portion of their length. The cutting head can be divided into a shank-side cutting step and a face-side cutting step, connected to the shank-side cutting step via a transition section, with a smaller cutting diameter than that of the shank-side cutting step.

[0010] Each cutting edge segment has a circumferential main cutting edge that extends in the direction of travel from a corner of the cutting edge segment located at the end face to a corner of the cutting edge segment located at the shank face. The main cutting edge of each cutting edge segment corresponds to the line of intersection between the rake face and the back or a clearance face of the cutting edge segment. In a cross-sectional view viewed along the axis of rotation of the end mill, the rake face and the back or clearance face of the cutting edge segment form a cutting wedge in a manner known to those skilled in the art.

[0011] Unlike the end mill described in US 9,174,287 B2, the cutting head of the end mill is divided into a shank-side cutting step and a face-side cutting step, connected to the shank-side cutting step via a transition section. The face-side cutting step has a smaller cutting diameter than the shank-side cutting step. The cutting edges or segments formed on the transition section allow the end mill to be used for machining and stripping corners or edges of wires with a rectangular cross-section. Two end mills can be used, arranged so that their axes of rotation are parallel but offset, and the faces of the end mills point in opposite directions.The end mills can be positioned against opposite sides of the wire, allowing the transition sections of the end mills to simultaneously machine two diametrically opposed corners or edges of the wire when the end mills, rotating around their axis of rotation, are moved relative to the wire. To machine or strip the remaining two diametrically opposed corners or edges of the wire, the two end mills simply need to be repositioned relative to the wire.

[0012] It has been found that the end mill can achieve good surface finishes when machining layered composite materials, e.g., CFRP materials, by milling with the end-face cutting edge and the shank cutting edge. Further areas of application for the end mill according to the invention include the machining of plastics and easily machinable, soft metals, for example, copper or aluminum. Furthermore, due to the transition section between the shank cutting edge and the end-face cutting edge, the end mill is also particularly suitable for removing or stripping relatively soft insulation material from a metal wire, especially a rectangular one, so that the wire has a clean and undamaged surface after stripping. The function of the transition section is, of course, not limited to stripping the corners or edges of a wire.For example, the transition section can also be used for milling special contours in a workpiece. The end mill is therefore a combination tool that offers a wide range of applications.

[0013] In another embodiment, the dividing grooves terminate in the area of ​​the end-face cutting step or at the transition section.

[0014] Depending on the intended use of the end mill, a rasp geometry created by dividing the cutting edges (spaced apart by flutes) into cutting edge segments using right-hand spiral dividing grooves is not necessary. If the dividing grooves taper off in the area of ​​the face cutting edge or at the transition section, faster and therefore more economical production of the end mill is possible.

[0015] In an alternative embodiment, the dividing grooves run out in the area of ​​the shank-side cutting step.

[0016] This allows the rasp geometry to be formed on the shank-side cutting edge as well. If the dividing grooves taper off in the area of ​​the shank-side cutting edge, especially if the chip flutes extend over the entire axial length of the shank-side cutting edge, the manufacturing process of the end mill can be simplified.

[0017] In another embodiment, the groove base of the divider slots has a larger diameter than the groove base of the clamping slots. The ratio between the diameter of the groove base of the clamping slots and the diameter of the groove base of the divider slots can be between 0.5 and 1.1. In particular, the groove base of the clamping slots can have a diameter of 6 mm and the groove base of the divider slots can have a diameter of 7.6 mm.

[0018] Since the function of the indexing grooves is primarily limited to forming the rasp geometry by dividing the cutting edges, and the material removed by the main cutting edges of the cutting edge segments is carried away via the flutes, the stability of the end mill can be increased by having the groove base of the indexing grooves lie on a larger diameter than the groove base of the flutes. Compared to indexing grooves whose groove base lies on a smaller diameter, the core of the end mill has a higher strength due to the greater amount of material.

[0019] Alternatively, the groove base of the divider grooves can also be on the same diameter as the groove base of the clamping grooves.

[0020] If the groove base of the divider slots has the same diameter as the groove base of the clamping slots, the manufacturing process or the formation of the clamping slots and the divider slots can be simplified by means of a grinding wheel.

[0021] In another embodiment, the cutting edges have rake surfaces with positive rake angles. The positive rake angle can be between 5° and 15°, and in particular 10°.

[0022] The rake angle is typically defined as the angle between a tool reference plane and the rake face. A positive rake angle ensures that the cutting edge segments of the end mill do not peel or scrape the material being removed, but rather cut it cleanly. It has been found that this end mill cutting edge geometry achieves good surface finishes both when machining layered composite materials, such as CFRP, and when removing relatively soft insulation material from a metal wire, particularly hairpin wires. When milling fiber-reinforced layered composite materials, the positive rake angle allows the fibers contained within the layer to be cut cleanly and is therefore less likely to be torn out of the composite, thus counteracting fiber delamination or fiber protrusions at the milled edges.The positive rake angle generates low cutting forces and a good surface finish, and has a positive effect on tool load. When stripping wires, the positive rake angle allows for gentle removal of the insulation material from the wire beneath the insulation layer. When machining relatively soft insulation materials, the positive rake angle enables a smooth cut and reduces material buildup on the cutting edge.

[0023] In a further embodiment, a front-facing dividing groove surface forming the cutting edge segment has a positive flank angle. The flank angle can be between 9° and 19°, and in particular 14°.

[0024] Even though the main cutting edges of the cutting segments, each extending from a face-end cutting segment corner to a shank-end cutting segment corner, perform the majority of the machining work and the removed material is primarily carried away via the chip flutes, the face-end cutting segment corner also generates a force on the workpiece that has a different direction than the force generated by the main cutting edge, e.g., perpendicular to the force generated by the main cutting edge. The face-end cutting segment corner can remove a small amount of material into the dividing groove. The positive flank angle, which can range between 9° and 19°, and is particularly 13°, can contribute to good surface quality in the same way as a positive rake angle of the rake faces, both when machining layered composite materials, e.g.,to be achieved with CFRP materials, as well as in the removal of relatively soft insulating material from a metal wire.

[0025] In another embodiment, the helix angle of the divider slots is greater than the helix angle of the clamping slots. Particularly good surface qualities are achieved both when machining layered composite materials and when removing insulating material from wires when the helix angle of the clamping slots is between 25° and 35°, particularly 30°, and the helix angle of the divider slots is between 35° and 45°, particularly 40°.

[0026] In another embodiment, the cutting head of the end mill is designed to cut at the face.

[0027] The end cutting edges of the end mill enable it to create countersinks in a workpiece by plunging the end mill in the direction of the axis of rotation.

[0028] In another embodiment, the number of flutes can be less than the number of divider slots. If the number of flutes is between 12 and 14, in particular 13, and the number of divider slots is between 16 and 18, in particular 17, a very good compromise is achieved between simple and fast manufacturing of the end mill and a sufficiently large number of formed cutting edge segments for material removal.

[0029] In another embodiment, the cutting edges or cutting edge segments have clearance surfaces, in particular angled clearance surfaces.

[0030] The clearance faces reduce friction between the end mill and the material being machined or removed, thus increasing the cutting speed. This reduced friction leads to less heat generation and ultimately to a longer tool life. If the clearance faces are angled, the first clearance angle of a first clearance face section can be between 8° and 12°, particularly 10°, and the second clearance angle of a second clearance face section can be between 13° and 17°, particularly 15°.

[0031] Compared to a clearance surface with a constant clearance angle, a smoother transition can be achieved by angling or staggering the clearance angle, for example, through the first and second clearance surface sections. The wedge angle of the cutting edge segments is larger, which improves the stability of the cutting edge segments. This contributes to a longer tool life and extended service life.

[0032] In another embodiment, the divider slots are narrower than the clamping slots.

[0033] If the cutting edges or cutting edge segments have clearance faces, the main cutting edges of each cutting edge segment, which run at a helix angle (left-hand helix), perform the majority of the material removal compared to the end-face cutting edge segment corner. This ensures that the removed material primarily collects in the main flutes and not in the divider grooves. The divider grooves, which are narrower than the flutes, primarily serve to divide the cutting edges of the end mill into cutting edge segments. The wider flutes can easily collect the removed material and channel it towards the shank.

[0034] In a further embodiment, each cutting edge segment has a main cutting edge extending from an end-face cutting edge segment corner to a shaft-face cutting edge segment corner, wherein a length of the main cutting edge measured in the direction of the chip groove is longer than a length of the clearance face measured in the direction of the divider groove.

[0035] The end mill with its relatively long main cutting edges and relatively shorter clearance surfaces functions as a rasp and delivers very good surface qualities, especially when removing insulating material from a wire.

[0036] In another embodiment, the transition section has an angle between 50° and 70°, preferably between 55° and 65°, in particular 60°, to an axis of rotation of the end mill.

[0037] If the transition section has an angle between 50° and 70°, preferably between 55° and 65°, particularly 60°, to an axis of rotation of the end mill, a continuous and stable transition is created between the shank-side cutting edge and the face-side cutting edge. The angle of the transition section is preferably adapted to the geometry of the workpiece to be machined. Furthermore, a second transition section can be provided between the shank-side cutting edge and the shank, which can form a continuous and stable transition from the shank-side cutting edge to the shank with a larger diameter. The second transition section can have an angle between 10° and 20°, particularly 15°.

[0038] In another embodiment, the groove base of the clamping grooves is defined by a radius.

[0039] The groove base of the chip flutes forms a transition zone between the rake face of a main cutting edge of the associated cutting edge segment and the leading edge of a cutting edge segment in the direction of rotation of the end mill. If the groove base of the chip flutes is defined by a radius, e.g., R0.42, the chips produced during machining can be reliably removed without jamming. The groove base of the indexing slots can also be defined by a radius, e.g., R0.1.

[0040] In another embodiment, the cutting head is flat on the front side and has a chamfer.

[0041] The chamfer formed on a circumferential end face of the end mill, which, when viewed from the side, preferably runs at an angle of 45° to the end face, forms a lead-in and enables the end mill to be brought safely up to a workpiece without tilting.

[0042] In a separately claimed embodiment, the end mill can be right-handed and have a shank and a cutting head with a number of right-handed helical cutting edges spaced apart by flutes, wherein the cutting edges are divided into cutting edge segments by a number of left-handed dividing grooves over at least a portion of their length. The cutting head can be divided into a shank-side cutting step and a face-side cutting step adjoining the shank-side cutting step via a transition section, the face-side cutting step having a smaller cutting diameter than the shank-side cutting step. In this embodiment, both the rake angles and the flank angles of the dividing grooves can be positive. The end mill of this embodiment can have all the other features mentioned above, in particular those of claims 2 to 11.

[0043] The features discussed above and others will be explained in more detail below using the accompanying figures and an example of an embodiment of an end mill. Fig. Figure 1 shows a side view of an end mill in a first embodiment, Fig. Figure 2 shows a front view of the end mill from Fig. 1, Fig. 3 shows a detailed view of A from Fig. 2, Fig. Figure 4 shows a detailed view of a face cutting edge of the end mill. Fig. 1, Fig. 5 shows a detailed view B from Fig. 4, Fig. Figure 6 shows a detailed view of a face end section of the end mill made of Fig. 1 with a chamfer, and Fig. Figure 7 shows another detailed view of the end-face cutting edge of the end mill. Fig. 1.

[0044] The figures are purely schematic and serve solely to aid in understanding the revelation. The relative sizes of the elements depicted in the figures have been adjusted to make the revelation more comprehensible.

[0045] The Fig. Figures 1 to 7 show an embodiment of an end mill 1 in the form of a combination tool, suitable for milling layered composite materials, e.g., fiber-reinforced plastics (FRP) such as carbon- or glass-fiber-reinforced plastics (CFRP / GFRP), as well as for stripping wires. Further applications for the end mill 1 include machining plastics and easily machinable, soft metals, such as copper or aluminum.

[0046] Fig. Figure 1 shows a side view of the end mill 1, which is rotatable about a rotary axis 3. The end mill 1 has a shank 10 with an outer diameter D. 10for clamping the end mill 1 in a tool holder (not shown) and a cutting head 20, which engages in a shank-side cutting step 22 with an outer diameter D 22 , a first transition section 23 and into a face-side cutting step 24 with an outer diameter D 24 The end mill is divided. The transition section 23, which runs at a first transition angle α to the axis of rotation 3, connects the shank-side cutting step 22 with the face-side cutting step 22. The shank-side cutting step 22 is connected to the shank 10 via a second transition section 25, which runs at a second transition angle β to the axis of rotation 3. The end mill 1 is counterclockwise, i.e., the end mill 1 rotates when viewed from the end (cf. Fig. 2) clockwise around the axis of rotation 3.

[0047] As in Fig. 1 and Fig. As shown in Figure 2, the cutting head 20 has a plurality of left-handed helix cutting edges 50 spaced apart from one another by clamping grooves 30. The cutting edges 50 are divided into several cutting edge segments 60 by a plurality of right-handed dividing grooves 40. In the embodiment shown, the number of clamping grooves 30 is smaller than the number of dividing grooves 40. Furthermore, the base of one dividing groove 40 has a larger diameter than the base of one clamping groove 30. The absolute value of the helix angle of the dividing grooves 40 relative to the axis of rotation 3 is greater than the absolute value of the helix angle of the clamping grooves 30 relative to the axis of rotation 3. Finally, the dividing grooves 40 are narrower than the clamping grooves 30 when viewed in the direction of rotation.

[0048] The left-handed flutes 30 extend from an end face of the end mill 1 to a shank-side end of the shank-side cutting step 22. The right-handed indexing grooves 40 extend axially from the end face of the cutting head 20 across the transition section 23 to the beginning of the shank-side cutting step 22. In particular, a rasp geometry advantageous for milling is thus formed on the end-side cutting step 24 and the transition section 23.

[0049] The Fig. Figure 7 shows a detailed view of the shank-side cutting step 22 of the end mill. Fig. Figure 1 illustrates the cutting edge segments 60 formed by the clamping grooves 30 and divider grooves 40. The circumferential cutting edges 50 and the circumferential cutting edge segments 60 have angled clearance surfaces on their backs. As shown in Fig. As shown in Figure 7, each clearance surface has a first clearance surface section 70 and a second clearance surface section 72. The formation of the clearance surfaces on the cutting edges 50 or cutting edge segments 60 creates a main cutting edge 62 on each cutting edge segment 60, extending from a face-side cutting edge segment corner 64 to a shank-side cutting edge segment corner 66. The counterclockwise rotation of the end mill 1, in combination with the counterclockwise flutes 30 or counterclockwise main cutting edges 62, ensures a predominantly shearing cut, which conveys the material produced during machining, i.e., chips or insulating material, via the flutes 30 towards the shank 10.

[0050] The Fig. 3 shows a detailed view of A from Fig. Figure 2 illustrates the angled course of the clearance faces of the cutting edges 50 and cutting edge segments 60. It can be seen that the first clearance face section 70 runs at a first clearance angle δ1 and the second clearance face section 72 at a second clearance angle δ2. Furthermore, it can be seen that the main cutting edge 62 connects to a rake face 34 of the chip groove 30 in the usual manner. The rake face 40 runs at a positive rake angle γ, which ensures that the material to be removed is not peeled or scraped off, but cut. A groove bottom 32 of the chip groove 30, defined by a radius that facilitates chip evacuation, transitions into a back 36 of the cutting edge 50 or cutting edge segment 60, which runs ahead in the direction of rotation of the end mill 1.

[0051] The Fig. 5 shows a detailed view B from Fig. Figure 4 illustrates the shape of the dividing grooves 40 as seen in the circumferential direction of the end mill 1. It can be seen that a dividing groove surface forming the cutting edge segment 60 has a positive flank angle ε. Material removed at the end-face corner 64 of the cutting edge segment can run off via the dividing groove surface and finally be transported away towards the shank 10 via the flutes 30.

[0052] The Fig. Figure 6 shows another detailed view of an end face of the end mill. Fig. 1. The chamfer 42, which runs at a chamfer angle µ, can be seen, forming a cutting edge for the end mill 1 and enabling the end mill to approach a workpiece safely without tilting. Reference symbol list α first transition angle β second transition angle γ rake angle δ1 first free angle δ2 second free angle ε flank angle µ chamfer angle D 10 Outer diameter D 22 Outer diameter D 24 Outer diameter 1 end mill 3. Axis of rotation 4. Direction of rotation 10 shaft 20 cutting heads 22 shaft-side cutting stage 23 first transition section 24 face cutting stage 25 second transitional phase 30 Spannut 32 Groove 34 Chip surface 36 Back 40 Divider groove 42nd phase 50 cutting bridge 60 cutting bar segment 62 Main cutting edge 64 end-face cutting edge segment corner 66 shaft-side cutting edge segment corner 70 first open space section 72 second open space section QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 9 174 287 B2 [0003, 0004, 0005, 0007, 0011] DE 10 2019 213 976 A1

[0006]

Claims

[1] Left-hand rotating end mill (1) with a shank (10) and a cutting head (20) with a number of left-hand spiral cutting edges (50) spaced apart from each other by flutes (30), wherein the cutting edges (50) are divided into cutting edge segments (60) at least over part of their length by a number of right-hand spiral dividing grooves (40), characterized by , that the cutting head (20) is divided into a shank-side cutting step (22) and an end-side cutting step (24) adjoining the shank-side cutting step (22) via a transition section (23) with a cutting diameter (D) smaller than that of the shank-side cutting step (22). 24 ) is divided. [2] End mill according to claim 1, characterized by , that the divider grooves (40) terminate in the area of ​​the end-face cutting step (24) or at the transition section (23). [3] End mill (1) according to claim 1, characterized by, that the dividing grooves (40) terminate in the area of ​​the shank-side cutting step. [4] End mill (1) according to any one of claims 1 to 3, characterized by , that the groove base of the divider grooves (40) lies on a larger diameter than the groove base of the clamping grooves (30). [5] End mill (1) according to any one of the preceding claims, characterized by , that the cutting edges (50) have chip surfaces with positive rake angles. [6] End mill (1) according to one of the preceding claims, characterized by , that a front-side divider groove surface forming the cutting bar segment (60) has a positive flank angle. [7] End mill (1) according to any one of the preceding claims, characterized by , that the helix angle of the divider slots (40) is greater than the helix angle of the clamping slots (30). [8] End mill (1) according to any one of the preceding claims, characterized by , that the number of clamping grooves (30) is less than the number of divider grooves (40). [9] End mill (1) according to any one of the preceding claims, characterized by , that the cutting edges (50) have free areas, in particular angled free areas. [10] End mill (1) according to any one of the preceding claims, characterized by , that the divider slots (40) are narrower than the clamping slots (30). [11] End mill (1) according to one of claims 9 or 10, characterized by , that each cutting edge segment (60) has a main cutting edge (62) extending from an end-face cutting edge segment corner (64) to a shank-face cutting edge segment corner (66), wherein a length of the main cutting edge (62) measured in the direction of the chip groove (30) is longer than a length of the clearance face measured in the direction of the divider groove (40).

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