Mold machining method and end mill

Abstract

The present invention is a mold machining method for cutting a mold using end mills that extend in an axial direction along a rotary shaft. The mold machining method comprises: pre-machining including a step for performing contour line machining of a wall surface of a mold using a plurality of end mills with different axial protrusion lengths in which, when the entire length dimension along the axial direction of the end mills is defined as a tool length L and the diameter dimension of a cutting blade of the end mills is defined as a blade diameter D, L / D ≥ 10 and a groove length which is the axial dimension of a chip discharge groove of the end mills is 3D or less; and a step in which the wall surface of the mold is finished after the pre-machining by reciprocating movement in the axial direction using another end mill having a larger L / D than the end mills used in the contour line machining and a groove length of 3D or less.

Description

Mold Processing Method and End Mill

[0001] The present invention relates to a mold processing method and an end mill. This application claims priority based on Japanese Patent Application No. 2024-192130 filed in Japan on October 31, 2024, and incorporates its content herein by reference.

[0002] Conventionally, when cutting a mold as a workpiece, an end mill that extends axially along the rotation axis is used. For example, when cutting a wall surface (such as between wall surfaces facing each other with a gap) like a rib groove of a mold, contour machining with an end mill is often performed. In this specification, the end mill may sometimes be referred to as a cutting tool or a tool.

[0003] Contour machining refers to the following machining method. That is, when the direction in which the rotation axis of the end mill extends is the Z-axis direction, the tool is moved in the X-axis direction or the Y-axis direction (X - Y plane direction) to perform cutting, and after the machining of a predetermined depth (a predetermined region in the Z-axis direction) is completed, the tool is moved to the next depth, and the operation of moving the tool in the X-axis direction or the Y-axis direction again to perform cutting is repeated.

[0004] Generally, in contour machining, in view of the balance between cutting efficiency and tool rigidity, for machining the shallow part of the mold wall surface, a tool with a large cutting edge diameter (the diameter dimension of the cutting edge of the end mill) and a short protrusion amount (the dimension in which the tool protrudes from the spindle of the machine tool to the tip side in the axial direction) is used, and for machining the deep part, a tool with a small cutting edge diameter and a long protrusion amount is used. As a long tool with a small cutting edge diameter and a long protrusion amount, for example, the long neck radius end mill described in Patent Document 1 is known.

[0005] Japanese Patent No. 5088678

[0006] However, when selecting a tool according to the depth of the mold wall and changing the tool's cutting diameter and overhang, contour machining tends to result in steps (inter-tool steps) S extending laterally (in the X-axis or Y-axis direction) on the mold wall (machined surface), as shown in Figure 6, due to differences in the rigidity of each tool. In other words, steps S occur between each contoured area due to differences in surface properties, degrading the accuracy of the machined surface. Removing such lateral steps S requires a lot of time and effort in subsequent polishing processes.

[0007] Furthermore, in narrow areas such as rib grooves where polishing is impossible, it is not possible to eliminate the lateral step S between tools. As a result, when using the manufactured mold, it becomes difficult to smoothly release the product from the mold. In other words, the mold release properties are reduced. This problem tends to be more pronounced, especially when the cutting of the mold wall requires the use of a tool with a ratio L / D of 10 or more between the tool length L (the overall length of the end mill along the axial direction) and the cutting diameter D.

[0008] The present invention aims to provide a mold machining method that can produce good surface properties on the machined surface even when the mold wall is machined using a tool with an L / D ratio of 10 or more, and an end mill that can realize this mold machining method.

[0009] To solve the above problems, the present invention provides the following means.

[0010] [Aspect 1 of the present invention] A method for machining a mold using an end mill that extends axially along a rotation axis, comprising: a pre-processing step of contour machining the wall surface of the mold using a plurality of end mills, each having a different axial overhang, wherein the total length dimension of the end mill along the axial direction is the tool length, the diameter dimension of the cutting edge of the end mill is the cutting edge dimension D, L / D ≥ 10, and the groove length, which is the axial dimension of the chip discharge groove of the end mill, is 3D or less; and a finishing step of finishing the wall surface of the mold by reciprocating movement in the axial direction using another end mill, the L / D being larger than that of the end mill used in contour machining and the groove length being 3D or less.

[0011] [Aspect 2 of the present invention] The method for machining a mold according to aspect 1, wherein in the contour machining and finishing machining, a tapered neck end mill is used as the end mill, and the tapered neck end mill has a columnar shank portion extending in the axial direction, a tapered neck portion connected to the shank portion and whose diameter decreases as it approaches the tip in the axial direction, and a cutting portion connected to the tapered neck portion and on which the cutting edge and the chip discharge groove are arranged.

[0012] [Aspect 3 of the present invention] A method for machining a mold according to aspect 1 or 2, further comprising the step of rough machining the mold using an end mill with L / D ≤ ​​10 prior to the above-mentioned pre-machining to provide a wall surface to the mold.

[0013] [Aspect 4 of the present invention] A method for processing a mold according to any one of aspects 1 to 3, wherein in the finishing process, a radius end mill is used as the end mill, and the cutting edge of the radius end mill has an outer edge and a corner edge, and the outer edge and the corner edge are each of the positive cutting edge type.

[0014] [Aspect 5 of the present invention] The method for processing a mold according to aspect 4, wherein the helix angle θ1 of the outer peripheral blade is 5° < θ1 ≤ 30°.

[0015] [Aspect 6 of the present invention] The method for machining a mold according to aspect 4 or 5, wherein the axial rake angle θ2 of the corner cutting edge is 5° ≤ θ2 ≤ 20°.

[0016] [Aspect 7 of the present invention] A method for processing a mold according to any one of aspects 4 to 6, wherein the helix angle θ1 of the outer peripheral blade is greater than the axial rake angle θ2 of the corner blade, and the angular difference θ3 between the helix angle θ1 of the outer peripheral blade and the axial rake angle θ2 of the corner blade is θ3 ≤ 15°.

[0017] [Aspect 8 of the present invention] An end mill extending axially along a rotation axis, wherein the overall length dimension of the end mill along the axial direction is the tool length L, and the diameter dimension of the cutting edge of the end mill is the cutting edge diameter D, such that L / D ≥ 10, and the groove length, which is the axial dimension of the chip evacuation groove of the end mill, is 3D or less, and the end mill comprises a columnar shank portion extending axially, a tapered neck portion connected to the shank portion and whose diameter dimension decreases towards the tip side in the axial direction, and a blade portion connected to the tapered neck portion and on which the cutting edge and the chip evacuation groove are arranged, the cutting edge having an outer edge and a corner edge, the outer edge and the corner edge being of a positive cutting edge type, and the helix angle θ1 of the outer edge being 5° < θ1 ≤ 30°.

[0018] [Aspect 9 of the present invention] The end mill according to aspect 8, wherein the axial rake angle θ2 of the corner cutting edge is 5° ≤ θ2 ≤ 20°.

[0019] [Aspect 10 of the present invention] The end mill according to aspect 8 or 9, wherein the helix angle θ1 of the outer peripheral cutting edge is greater than the axial rake angle θ2 of the corner cutting edge, and the angular difference θ3 between the helix angle θ1 of the outer peripheral cutting edge and the axial rake angle θ2 of the corner cutting edge is θ3 ≤ 15°.

[0020] [Aspect 11 of the present invention] The end mill according to aspect 8 or 9, wherein the outer peripheral relief surface, which is the relief surface of the outer peripheral cutting edge, and the corner relief surface, which is the relief surface of the corner cutting edge, are seamlessly connected to each other.

[0021] According to the above-mentioned aspect of the present invention, a method for machining a mold is provided that can produce a good surface finish on the machined surface even when the mold wall is machined using a tool with an L / D ratio of 10 or more, and an end mill capable of realizing this method of machining a mold is also provided.

[0022] Figure 1 is a side view showing an end mill used in a mold machining method according to one embodiment of the present invention. Figure 2 is an enlarged side view of part II of Figure 1. Figure 3 is a schematic side view showing the outer cutting edge, corner cutting edge and corner portion. More specifically, Figure 3(a) is an illustrative diagram showing the case where the angle difference θ3 between the helix angle θ1 of the outer cutting edge and the axial rake angle θ2 of the corner cutting edge is large, and Figure 3(b) is an illustrative diagram showing the case where the angle difference θ3 between the helix angle θ1 of the outer cutting edge and the axial rake angle θ2 of the corner cutting edge is small. Figure 4 is a schematic diagram (side view) explaining the relationship between the helix angle θ1 of the outer cutting edge and the load during finishing. More specifically, Figure 4(a) is an illustrative diagram showing the case where the helix angle θ1 of the outer cutting edge is large, and Figure 4(b) is an illustrative diagram showing the case where the helix angle θ1 of the outer cutting edge is small. Figure 5 is an image showing the wall surface, etc., of a mold (workpiece) machined according to an embodiment of the present invention. Figure 6 is an image showing the wall surface of a mold (workpiece) that has been machined using a conventional comparative example.

[0023] An end mill 1 according to one embodiment of the present invention, and a method for machining a mold using this end mill 1, will be described with reference to the drawings. A mold is formed into a predetermined shape by appropriately milling a metal block (see Figure 5). That is, the workpiece to be machined by the end mill 1 of this embodiment is a mold.

[0024] In this embodiment, the end mill 1 is a radius end mill having a corner cutting edge 73, which will be described later, and is also a tapered neck end mill having a tapered neck portion 8, which will be described later. For this reason, the end mill 1 may be referred to as a radius end mill 1, a tapered neck end mill 1, or a tapered neck radius end mill 1, etc.

[0025] As shown in Figure 1, the end mill 1 has a columnar shape centered on the axis of rotation C. The end mill 1 comprises a shank portion 2, a tapered neck portion 8, and a cutting edge portion 3. The shank portion 2, the tapered neck portion 8, and the cutting edge portion 3 are arranged coaxially with respect to the axis of rotation C. Furthermore, the shank portion 2, the tapered neck portion 8, and the cutting edge portion 3 are arranged in this order along the direction in which the axis of rotation C extends.

[0026] In this embodiment, the direction in which the rotation axis C of the end mill 1 extends is called the axial direction. The end mill 1 extends axially along the rotation axis C. Of the axial directions, the direction from the shank portion 2 toward the cutting edge portion 3 is called the axial tip side or simply the tip side, and the direction from the cutting edge portion 3 toward the shank portion 2 is called the axial rear end side or simply the rear end side. In each figure, the axial direction corresponds to the Z-axis direction. The axial tip side corresponds to the -Z side, and the axial rear end side corresponds to the +Z side.

[0027] Furthermore, the direction perpendicular to the rotation axis C is called the radial direction. Within the radial direction, the direction approaching the rotation axis C is called the radially inward direction, and the direction moving away from the rotation axis C is called the radially outward direction. Also, the direction of rotation around the rotation axis C is called the circumferential direction. Within the circumferential direction, the direction in which the end mill 1 is rotated during cutting is called the end mill rotation direction T, and the rotation direction opposite to this is called the opposite direction to the end mill rotation direction T, or the anti-end mill rotation direction.

[0028] In Figure 1, the symbol L represents the tool length L, which is the overall length of the end mill 1 along the axial direction. The symbol LH represents the tapered neck length LH, which is the length along the axial direction of the portion of the end mill 1 consisting of the tapered neck portion 8 and the cutting edge portion 3. In Figure 2, the symbol D represents the cutting edge diameter D, which is the diameter of the cutting edge portion 3 (cutting edge 7) of the end mill 1. Specifically, the cutting edge diameter D corresponds to the diameter of the rotational trajectory obtained by rotating the cutting edge 7 of the cutting edge portion 3, which will be described later, around the rotation axis C.

[0029] In this embodiment, the tool length L is, for example, 150 mm to 170 mm. The cutting diameter D is, for example, 2.5 mm to 4 mm. Therefore, the end mill 1 may be referred to as a small diameter end mill 1, etc. The ratio L / D of the end mill 1 is set to L / D ≥ 10. L / D is preferably 20 or more, and more preferably 30 or more. In this embodiment, L / D is 40 or more. L / D can also be 50 or more, or 60 or more. L / D can be 80 or less, or 70 or less.

[0030] As shown in Figure 1, the shank portion 2 is columnar in shape, extending axially around the rotation axis C, and is specifically cylindrical. The shank portion 2 is located at the rear end of the end mill 1 in the axial direction. The diameter of the shank portion 2 (shank diameter) is larger than the diameter of the cutting edge portion 3 (cutting edge diameter) D. The diameter of the shank portion 2 is constant along the axial direction. The diameter of the shank portion 2 is, for example, 6 mm to 8 mm.

[0031] The shank portion 2 is detachably held on the spindle or the like of a machine tool (which may be hereinafter abbreviated as "spindle, etc.") not shown. The shank portion 2 is rotated by the spindle, etc. in the end mill rotation direction T, while being moved radially and axially relative to the workpiece, which is the mold. As a result, the end mill 1 cuts into the workpiece with the cutting edge 7 of the blade portion 3, which will be described later, and performs milling.

[0032] The tapered neck portion 8 is positioned on the axial end side of the shank portion 2. The tapered neck portion 8 is columnar in shape, extending axially around the rotation axis C, and is specifically approximately conical. The diameter of the tapered neck portion 8 decreases as it approaches the axial end. The axial rear end of the tapered neck portion 8 is connected to the axial end of the shank portion 2. The ratio value LH / D of the tapered neck portion length LH to the cutting diameter D shown in Figures 1 and 2 is preferably 5 or more, and more preferably 10 or more. LH / D can also be 60 or less, or 50 or less.

[0033] The cutting edge 3 is located at the axial tip of the end mill 1. The cutting edge 3 is substantially cylindrical in shape and extends axially along the rotation axis C. The axial rear end of the cutting edge 3 is connected to the axial tip of the tapered neck portion 8. As shown in Figure 2, the cutting edge 3 has a chip evacuation groove 4, a rake face 5, a relief face 6, and a cutting edge 7. That is, the cutting edge 3 has a chip evacuation groove 4 and a cutting edge 7.

[0034] The chip evacuation groove 4 is groove-shaped and opens onto the tip surface 3a facing the axial tip side of the blade portion 3, and the outer peripheral surface 3b facing radially outward. The chip evacuation groove 4 extends from the tip surface 3a of the blade portion 3 toward the rear end, in the direction opposite to the end mill rotation direction T around the rotation axis C. In this embodiment, the axial dimension (total length along the axial direction) of the chip evacuation groove 4 is called the groove length LG. The groove length LG is shown in Figure 1. The groove length LG is set to three times the blade diameter D or less (i.e., 3D or less). The groove length LG is preferably 2D or less, more preferably 1.5D or less, and even more preferably 1.0D or less. The groove length LG can be 0.3D or more, 0.5D or more, or 0.7D or more. Multiple chip evacuation grooves 4 are provided on the blade portion 3 at intervals from each other in the circumferential direction. In this embodiment, four chip evacuation grooves 4 are provided in the circumferential direction at equal or unequal pitches.

[0035] The chip evacuation groove 4 has a gash 9 positioned at its tip. The gash 9 constitutes a part (tip) of the chip evacuation groove 4. The gash 9 is groove-shaped, recessing from the tip surface 3a of the cutting edge 3 toward the rear end, and generally extends along the radial direction. The gash 9 is positioned adjacent to the bottom cutting edge 71 and the corner cutting edge 73 in the end mill rotation direction T of the bottom cutting edge 71 and the corner cutting edge 73, which will be described later.

[0036] The rake face 5 is positioned on the wall surface 4a of the chip discharge groove 4 facing the end mill rotation direction T. The rake face 5 includes a tip rake face positioned at the tip of the wall surface 4a that connects to the tip surface 3a of the cutting edge 3, an outer rake face positioned at the radially outer end of the wall surface 4a that connects to the outer circumferential surface 3b of the cutting edge 3, and a corner rake face positioned between the radially outer end of the tip rake face and the tip of the outer rake face.

[0037] In this embodiment, the tip rake face and the corner rake face are positioned on the wall surface (the tip portion of the wall surface 4a) of the gash 9 facing the end mill rotation direction T. For this reason, the tip rake face and the corner rake face may be referred to as the gash rake face, etc.

[0038] The relief surface 6 includes a tip relief surface positioned on the tip surface 3a of the blade portion 3, an outer peripheral relief surface positioned on the outer peripheral surface 3b of the blade portion 3, and a corner relief surface positioned between the radially outer end of the tip relief surface and the tip of the outer peripheral relief surface.

[0039] The tip relief surface is positioned between two adjacent chip evacuation grooves 4 (gash 9) in the circumferential direction on the tip surface 3a of the cutting edge 3. The tip relief surface is connected to the bottom cutting edge 71 of the cutting edge 7, which will be described later, and extends along the bottom cutting edge 71. As the tip relief surface moves away from the bottom cutting edge 71 in the opposite direction to the end mill rotation direction T, it extends toward the rear end in the axial direction. This provides the bottom cutting edge 71 with a relief angle.

[0040] The outer peripheral relief surface is positioned between two adjacent chip evacuation grooves 4 on the outer peripheral surface 3b of the cutting edge 3. The outer peripheral relief surface is connected to the outer peripheral cutting edge 72 of the cutting edge 7 (described later) and extends along the outer peripheral cutting edge 72. The outer peripheral relief surface extends radially inward as it moves away from the outer peripheral cutting edge 72 in the opposite direction of the end mill rotation T. This provides the outer peripheral cutting edge 72 with a relief angle.

[0041] The corner relief surface is positioned at the corner where the tip surface 3a and the outer peripheral surface 3b of the cutting edge 3 are connected. The corner relief surface has a curved shape that is convex toward the outer peripheral side of the tip. The corner relief surface is connected to the corner cutting edge 73, which will be described later, of the cutting edge 7 and extends along the corner cutting edge 73. As the corner relief surface moves away from the corner cutting edge 73 toward the opposite side of the end mill rotation direction T, it extends toward the rear end in the axial direction and radially inward. This provides the corner cutting edge 73 with a relief angle.

[0042] The cutting edge 7 has a bottom cutting edge 71 positioned on the ridge where the wall surface 4a of the chip evacuation groove 4 facing the end mill rotation direction T (i.e., the rake face 5, and so on) and the tip surface 3a of the cutting edge 3 are connected; an outer periphery cutting edge 72 positioned on the ridge where the wall surface 4a and the outer circumferential surface 3b of the cutting edge 3 are connected; and a convex curved corner cutting edge 73 connecting the bottom cutting edge 71 and the outer periphery cutting edge 72. Furthermore, the outer periphery cutting edge 72 and the corner cutting edge 73 are each formed in a positive cutting edge shape.

[0043] A set of cutting edges 7 including a bottom edge 71, an outer peripheral edge 72, and a corner edge 73 are provided in a plurality at intervals around the rotation axis C. In the present embodiment, four sets of cutting edges 7 are provided. That is, this end mill 1 is a four-flute end mill. The plurality of cutting edges 7 are arranged at equal pitches or unequal pitches in the circumferential direction around the rotation axis C.

[0044] The bottom edge 71 is disposed at a ridge line portion where the tip rake face and the tip relief face are connected. The bottom edge 71 extends substantially in the radial direction along the direction in which the gullet 9 extends. Specifically, the bottom edge 71 extends toward the rear end side in the axial direction as it goes toward the inner side in the radial direction.

[0045] The outer peripheral edge 72 is disposed at a ridge line portion where the outer peripheral rake face and the outer peripheral relief face are connected. The outer peripheral edge 72 extends along the chip discharge groove 4. Specifically, the outer peripheral edge 72 extends in the counter-end mill rotation direction as it goes toward the rear end side in the axial direction.

[0046] The corner edge 73 is disposed at a ridge line portion where the corner rake face and the corner relief face are connected. The corner edge 73 has a curved shape that protrudes toward the outer peripheral side of the tip of the blade portion 3. The inner end in the radial direction of the corner edge 73 is connected to the outer end in the radial direction of the bottom edge 71. The rear end of the corner edge 73 is connected to the front end of the outer peripheral edge 72. The outer peripheral relief face and the corner relief face are seamlessly connected to each other. In the present embodiment, "seamlessly connected" means a state in which two faces are smoothly connected to each other and can be visually recognized as one continuous curved surface or plane. Specifically, when observing the vicinity of the boundary between the outer peripheral relief face and the corner relief face with an optical microscope at a magnification of 30 to 200 times, if no concave or convex ridge line serving as the boundary between the outer peripheral relief face and the corner relief face is observed, the outer peripheral relief face and the corner relief face are in a state of being seamlessly connected to each other.

[0047] ]Here, FIG. 3(b) is a partial side view of the end mill 1 schematically showing the outer peripheral edge 72, the corner edge 73, and the connecting portion (corner portion 74) between the outer peripheral edge 72 and the corner edge 73. In this side view of the end mill, the "twist angle θ1 of the outer peripheral edge 72", which is the angle at which the outer peripheral edge 72 is inclined with respect to the rotation axis C, is a positive angle (right angle). The twist angle θ1 of the outer peripheral edge 72 is, for example, 5° < θ1 ≤ 30°, preferably 10° < θ1 ≤ 25°. In the present embodiment, the twist angle θ1 of the outer peripheral edge 72 is, for example, 20°.

[0048] Also, in this side view of the end mill, the "axial rake angle (axial rake) θ2 of the corner edge 73", which is the angle at which the corner edge 73 is inclined with respect to the rotation axis C, is a positive angle. The axial rake angle θ2 of the corner edge 73 is, for example, 5° ≤ θ2 ≤ 20°, preferably 10° ≤ θ2 ≤ 15°. In the present embodiment, the axial rake angle θ2 of the corner edge 73 is, for example, 10°.

[0049] The twist angle θ1 of the outer peripheral edge 72 is made larger than the axial rake angle θ2 of the corner edge 73. Therefore, in the side view of the end mill, the connecting portion between the outer peripheral edge 72 and the corner edge 73 is a corner portion 74 that protrudes toward the end mill rotation direction T. That is, the cutting edge 7 has the corner portion 74. Specifically, the corner portion 74 has a shape that protrudes toward the rear end side in the end mill rotation direction T and in the axial direction.

[0050] Also, the angle difference θ3 between the twist angle θ1 of the outer peripheral edge 72 and the axial rake angle θ2 of the corner edge 73 is, for example, θ3 ≤ 15°, preferably θ3 ≤ 12°. In the present embodiment, the angle difference θ3 is, for example, 10°. The angle difference θ3 can be 5° or more, 7° or more.

[0051] In the present embodiment, as shown in FIG. 2, the rake face (corner rake face) of the corner edge 73 and the rake face (tip rake face) of the bottom edge 71 are constituted by the same face. That is, the corner rake face and the tip rake face are part of a common single face. Therefore, the axial rake angle of the bottom edge 71 is also a positive angle. And the bottom edge 71 is a positive blade type.

[0052] Next, the mold processing method will be described. The mold processing method of this embodiment includes a pre-processing step in which the mold wall surface is contour-machined using multiple end mills with different axial overhangs (dimensions by which the end mill protrudes axially from the spindle, etc.) and groove lengths of 3D or less, and after the pre-processing step, the mold wall surface is finished by reciprocating movement in the axial direction (Z-axis direction) using another end mill 1 which has a larger L / D than the end mill used in contour machining and a groove length of 3D or less. The above "pre-processing" means cutting that is performed before the finishing step.

[0053] Furthermore, the mold processing method of this embodiment further includes a step of rough machining the mold using an end mill with L / D ≤ ​​10 before the pre-processing to create a wall surface on the mold. That is, the mold processing method includes, in this order, a step of rough machining the mold, a step of contour machining the wall surface of the mold (pre-processing), and a step of finish machining the wall surface of the mold. The end mill 1 of this embodiment described above is used in the step of finish machining the wall surface of the mold.

[0054] [Rough machining process for the mold] In the rough machining process for the mold, an end mill is used which has a larger cutting edge diameter D and a shorter tool length L than the end mill 1 mentioned above, for example, an indexable end mill (not shown). In the rough machining process for the mold, as shown in Figures 5 and 6, for example, a rib groove 100 and an outer circumference 101 are provided to the mold by cutting. The rib groove 100 has a pair of opposing wall surfaces (vertical walls) with a gap between them.

[0055] Specifically, in the rough machining process of the mold, the mold is contour-machined with an end mill to create walls on the rib groove 100 and the outer circumference 101, respectively. That is, the end mill is fed in a direction perpendicular to the rotation axis of the end mill extending in the Z-axis direction (the X-axis direction or Y-axis direction, which can also be called the X-Y plane direction) while cutting is performed, and after machining to a predetermined depth (a predetermined region in the Z-axis direction) is completed, the end mill is moved axially to the next depth, and the cutting is performed again while feeding the end mill in the X-axis direction or Y-axis direction, and this operation is repeated.

[0056] [Contour machining process for mold walls (pre-processing)] In the contour machining process for mold walls (pre-processing), a tapered neck end mill equipped with a tapered neck is used as the end mill (see Figure 1). Preferably, this tapered neck end mill is a radius end mill equipped with a corner cutting edge (see Figure 2). In the contour machining process for mold walls, multiple end mills with different overhangs, i.e., tool lengths L, are used. Each end mill has an L / D ratio of ≥ 10 and a groove length of 3D or less. The groove length is preferably 2D or less, more preferably 1.5D or less.

[0057] Specifically, in the process of contour machining the walls of the mold, the walls of the rib grooves 100 and the outer circumference 101 of the mold are contour machined. That is, cutting is performed while feeding the end mill in a direction perpendicular to the rotation axis of the end mill extending in the Z-axis direction (X-Y plane direction). Once machining to a predetermined depth is completed, the end mill is replaced with another end mill with a different overhang amount, and contour machining is performed in the same manner at the next depth (a different Z-axis region with a different Z-axis position from the contour machining). In other words, multiple end mills with different overhang amounts are used as appropriate depending on the machining depth (Z-axis position) of the wall surface. In this contour machining process, it is preferable to sequentially perform both rough machining and semi-finishing machining on each wall surface. In this rough machining, the corner cutting edge is mainly used for cutting.

[0058] Furthermore, through the rough machining process of the mold or the contour machining process of the mold walls described above, each wall surface of the mold is provided with the necessary draft angle for use after manufacturing. In other words, each wall surface is made into an inclined surface that is tilted with respect to the Z-axis direction. The provision of a draft angle improves the release properties of the mold, making it possible to press-form or injection-form products using the mold.

[0059] [Process for finishing the mold wall surface] In the process for finishing the mold wall surface, the end mill 1 of this embodiment described above is used. That is, this end mill 1 is a tapered neck end mill and a radius end mill. This end mill 1 has a larger L / D ratio than the end mills used in the process of contour machining the mold wall surface (pre-processing) described above, and the groove length is 3D or less. The groove length is preferably 2D or less, more preferably 1.5D or less, and even more preferably 1.0D or less.

[0060] Then, the end mill 1 is used to finish the walls of the rib grooves 100 and the outer circumference 101 of the mold by reciprocating movement in the Z-axis direction. Specifically, the end mill 1, with its rotation axis C extended in the Z-axis direction, is moved in the Z-axis direction (specifically, in a direction slightly inclined with respect to the Z-axis direction) to follow the inclination (draft angle) of each wall surface, and the surface of each wall surface is cut into an inclined surface shape. This results in the mold wall surface shown in Figure 5. In this finishing process, the area near the boundary between the corner cutting edge 73 and the outer circumference cutting edge 72 of the cutting edge 7 is mainly used for cutting.

[0061] According to the mold machining method of this embodiment described above, when the end mill 1 finishes the mold wall, the tool reciprocates in the axial direction (Z-axis direction). That is, since the mold wall is machined in the Z-axis direction, even if a step S between the tools (see Figure 6) extending laterally (X-Y plane direction) occurs on the machined surface during the preceding contour machining, this step S between the tools can be removed or reduced by the finishing process (see Figure 5).

[0062] Furthermore, it is possible to machine the mold wall surface both when the tool is moving towards the leading end in the axial direction (forward path, -Z side) and when it is moving towards the trailing end in the axial direction (return path, +Z side). In this case, the lateral step S between tools on the machined surface can be reliably reduced. Moreover, although the tools used in finishing processes often have small cutting diameters, by performing cutting processes in both the forward and return paths in the axial direction, finishing can be performed without significantly reducing cutting efficiency compared to conventional contour machining.

[0063] As a result, it becomes possible to replace conventional electrical discharge machining (EDM) with cutting tools for forming wall surfaces such as rib grooves 100 in molds, which previously could only be done by EDM. Specifically, these wall surfaces are, for example, groove walls that are deep and narrow in the Z-axis direction and cannot be machined unless the L / D ratio is 10 or more. This reduces the time and manufacturing costs required for manufacturing EDM electrodes, and also facilitates the manufacture of molds with excellent machined surface properties (low surface roughness).

[0064] Furthermore, in contour machining before finishing, it is preferable to perform both rough machining and semi-finishing. This increases machining efficiency while reducing the lateral step S between tools on the machined surface, thereby suppressing the load on the tools during the subsequent finishing process. In addition, the groove length of each end mill used for contour machining (rough machining, semi-finishing) and finishing is kept small, at 3D or less. This increases the rigidity of the tools and improves the accuracy of the cutting process. The groove length is preferably 2D or less, more preferably 1.5D or less, and even more preferably 1.0D or less.

[0065] As described above, according to this embodiment, even when cutting the wall surface of a mold using a tool with an L / D ratio of 10 or more, the surface properties of the processed surface can be improved. Even when narrow parts such as rib grooves 100 are provided in the mold, the surface properties of the wall surface (groove wall) of these narrow parts can be made good, so that a mold with excellent release properties can be manufactured.

[0066] Furthermore, this embodiment includes a step of roughly machining the mold using an end mill with an L / D ≤ ​​10 before the pre-machining to create a wall surface on the mold. In this case, since the mold is roughly machined using an indexable end mill or the like with an L / D ≤ ​​10, a tool with a large cutting diameter D and high rigidity can be used to efficiently impart the approximate shape (roughly machined shape) of the wall surface to the mold.

[0067] Furthermore, in this embodiment, a tapered neck end mill is used as the end mill for the contour machining process in the "process of contour machining the mold wall surface (pre-processing)" and the finishing process in the "process of finishing the mold wall surface." In this case, since the contour machining and finishing process are performed on the mold wall surface using a tapered neck end mill, interference between the mold and the tool (unintended contact outside the cutting area) can be suppressed, even when cutting the wall surface in a narrow part such as the rib groove 100 of the mold. In addition, since the diameter dimensions of the tapered neck and shank of the tapered neck end mill can be made larger than the diameter dimension of the cutting edge (i.e., the cutting diameter), the tool rigidity is improved and the machined surface properties can be more stably enhanced.

[0068] Furthermore, in this embodiment, a radius end mill 1 is used as the end mill 1 for finishing, and the outer peripheral cutting edge 72 and corner cutting edge 73 of the radius end mill 1 are both positive cutting edge types.

[0069] In the above configuration, a radius end mill 1 is used for finishing. Therefore, when finishing the mold wall by reciprocating movement in the Z-axis direction, the area near the boundary between the outer peripheral cutting edge 72 and the corner cutting edge 73 of the radius end mill 1 mainly cuts into the workpiece (mold wall). As in the above configuration, since the outer peripheral cutting edge 72 and the corner cutting edge 73 are both positive cutting edge types, the sharpness of the cutting edge 7 can be improved, and the lateral step difference S between tools that occurs on the machined surface before finishing can be made smaller.

[0070] In this embodiment, the helix angle θ1 of the outer peripheral cutting edge 72 of the end mill 1 used for finishing is 5° < θ1 ≤ 30°, and the axial rake angle θ2 of the corner cutting edge 73 is 5° ≤ θ2 ≤ 20°.

[0071] In this embodiment, during finishing, the radius end mill 1 is reciprocated in the Z-axis direction while cutting the mold wall (workpiece). Therefore, as shown in the above configuration, by making the helix angle θ1 of the outer peripheral blade 72 small (30° or less), the contact length between the outer peripheral blade 72 and the workpiece along the end mill rotation direction T for a predetermined feed amount in the Z-axis direction of the tool (per unit feed amount) can be kept small.

[0072] Here, Figures 4(a) and 4(b) are schematic diagrams (side views of the end mill 1) illustrating the relationship between the helix angle θ1 of the outer cutting edge 72 and the load during finishing. More specifically, Figure 4(a) is an illustrative diagram of the relationship when the helix angle θ1 of the outer cutting edge 72 is large, and Figure 4(b) is an illustrative diagram of the relationship when the helix angle θ1 of the outer cutting edge 72 is small.

[0073] As shown in Figures 4(a) and 4(b), a configuration in which the helix angle θ1 of the outer peripheral blade 72 is small, and θ1 is 30° or less, allows for a smaller contact length W between the outer peripheral blade 72 and the workpiece along the rotation direction T of the end mill, per predetermined feed amount F (unit feed amount F) in the Z-axis direction of the end mill 1.

[0074] Thus, in this embodiment, the load on the outer cutting edge 72 can be kept low, thereby suppressing chatter vibration of the tool. As a result, chatter surfaces (fine, uneven surfaces formed by chatter vibration; see chatter surface U shown in Figure 6) are less likely to occur on the machined surface after finishing, and the machined surface quality can be stably improved.

[0075] More specifically, when the tool moves towards the leading end in the axial direction (forward stroke), the load (cutting load) caused by the outer cutting edge 72 cutting into the workpiece is kept to a minimum. Also, when the tool moves towards the rear end in the axial direction (return stroke), the load (abrasion load) caused by the area near the outer cutting edge 72 rubbing against the surface of the workpiece is kept to a minimum.

[0076] In particular, with a radius end mill 1 having a large L / D ratio as in this embodiment, it tends to be difficult to ensure sufficient tool rigidity, and the load (reaction force) during machining, as described above, easily affects tool deflection. Therefore, by keeping the helix angle θ1 of the outer cutting edge 72 small to 30° or less and reducing the load during machining, tool deflection deformation can be suppressed, and good machined surface properties can be obtained.

[0077] Furthermore, by making the axial rake angle θ2 of the corner blade 73 small, to 20° or less, the same effect as the upper limit of the helix angle θ1 of the outer peripheral blade 72 described above can be obtained.

[0078] Furthermore, by having a helix angle θ1 of the outer peripheral blade 72 exceed 5°, it is possible to prevent the outer peripheral blade 72 from making linear contact with the workpiece (a state in which the outer peripheral blade 72 simultaneously contacts the workpiece over a wide area in the Z-axis direction). In the machining of mold walls (vertical wall machining), the aforementioned linear contact is undesirable because it results in a large cutting load and affects the cutting performance. As in this embodiment, by making the helix angle θ1 of the outer peripheral blade 72 greater than 5°, the cutting load on the outer peripheral blade 72 can be reduced, and good cutting performance can be maintained.

[0079] Furthermore, by setting the axial rake angle θ2 of the corner blade 73 to 5° or more, the same effect as the lower limit of the helix angle θ1 of the outer peripheral blade 72 described above can be obtained.

[0080] Furthermore, in this embodiment, the helix angle θ1 of the outer peripheral cutting edge 72 of the end mill 1 used for finishing is greater than the axial rake angle θ2 of the corner cutting edge 73, and the angular difference θ3 between the helix angle θ1 of the outer peripheral cutting edge 72 and the axial rake angle θ2 of the corner cutting edge 73 is set to θ3 ≤ 15°. In the above configuration, since θ1 > θ2, it is easier to form the gash 9 at the tip of the chip evacuation groove 4 using a grinding wheel or the like during end mill manufacturing, and thus easier to create the corner cutting edge 73.

[0081] Furthermore, if the angle difference θ3 between the helix angle θ1 of the outer cutting edge 72 and the axial rake angle θ2 of the corner cutting edge 73 is kept small, such as 15° or less, the corner portion 74 (the portion that protrudes toward the end mill rotation direction T) where the outer cutting edge 72 and the corner cutting edge 73 are connected can be made less likely to become sharp.

[0082] Here, Figures 3(a) and 3(b) are schematic side views of the end mill 1 showing the outer cutting edge 72, the corner cutting edge 73, and the corner portion 74. More specifically, Figure 3(a) is an illustrative diagram of the case where the angle difference θ3 between the helix angle θ1 of the outer cutting edge 72 and the axial rake angle θ2 of the corner cutting edge 73 is large, and Figure 3(b) is an illustrative diagram of the case where the angle difference θ3 between the helix angle θ1 of the outer cutting edge 72 and the axial rake angle θ2 of the corner cutting edge 73 is small.

[0083] As shown in Figure 3(b), when the angle difference θ3 between the helix angle θ1 of the outer cutting edge 72 and the axial rake angle θ2 of the corner cutting edge 73 is small (15° or less), the corner portion 74 is less likely to become sharp compared to when the angle difference θ3 is large (greater than 15°), as shown in Figure 3(a).

[0084] During finishing, the area near the boundary between the outer peripheral cutting edge 72 and the corner cutting edge 73 of the radius end mill 1 (i.e., near the corner 74) is primarily responsible for cutting into the workpiece. In other words, since the corner 74 is near the cutting point, its shape significantly affects the surface finish. Therefore, by keeping the angle difference θ3 small, such as in this embodiment, to 15° or less, and connecting the outer peripheral cutting edge 72 and the corner cutting edge 73 as seamlessly as possible, the corner 74 is less likely to become sharp, resulting in a good surface finish. Furthermore, by seamlessly connecting the outer peripheral relief surface and the corner relief surface, the corner 74 is also less likely to become sharp, resulting in a good surface finish.

[0085] The present invention is not limited to the embodiments described above, and modifications to the configuration, etc., are possible without departing from the spirit of the invention, as described below, for example.

[0086] In the embodiments described above, an example was given where the end mill 1 is a four-flute end mill, but it is not limited to this. The end mill 1 may be, for example, an end mill with three or fewer flutes or five or more flutes.

[0087] The present invention may be combined in any way that does not depart from the spirit of the invention, as described in the above embodiments and modifications, and the configurations may be added, omitted, substituted, or otherwise modified. Furthermore, the present invention is not limited by the above embodiments, but is limited only by the claims.

[0088] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to these examples.

[0089] [Confirmation Test of Processed Surface Properties] The molds were machined using the mold processing method according to the embodiment of the present invention and the mold processing method according to the conventional comparative example, and the processed surface properties of the mold walls were confirmed.

[0090] In the "rough machining process for the mold" and the "contour machining process for the mold wall (pre-machining)," the same cutting process was performed in both the example and the comparative example (see Table 1 below). In Table 1, No. 1 corresponds to the "rough machining process for the mold," and Nos. 2 to 11 correspond to the "contour machining process for the mold wall (pre-machining)." The "No." indicates the order of machining. The type of end mill (tool), cutting diameter D (tool diameter), overhang amount (overhang length), and various cutting conditions used in each process are shown in the table (the same applies to Tables 2 and 3 described later).

[0091]

[0092] Specifically, each of the processes No. 1 to 11 in Table 1, and the "Z-" indicated in parentheses around each process, refer to the following cutting processes: • No. 1: Rough machining of the mold wall from the upper end (Z-0 mm) to the lower end (Z-115 mm) in the Z-axis direction by contour machining. • No. 2-3: Rough machining of the mold wall from the upper end (Z-0 mm) to a depth of 70 mm (Z-70 mm) in the Z-axis direction by contour machining (No. 2), followed by semi-finishing by contour machining (No. 3). • No. 4-5: Rough machining of the mold wall from a depth of 70 mm (Z-70 mm) to a depth of 90 mm (Z-90 mm) in the Z-axis direction by contour machining (No. 4), followed by semi-finishing by contour machining (No. 5). • No. 6-7: The mold wall is roughly machined by contour machining from a depth of 90 mm (Z-90 mm) to a depth of 102 mm (Z-102 mm) in the Z-axis direction (No. 6), followed by semi-finishing by contour machining (No. 7). 8-9: The mold wall is roughly machined by contour machining from a depth of 102 mm (Z-102 mm) to a depth of 109 mm (Z-109 mm) in the Z-axis direction (No. 8), followed by semi-finishing by contour machining (No. 9). 10-11: The mold wall is roughly machined by contour machining from a depth of 109 mm (Z-109 mm) to a depth of 114.9 mm (Z-114.9 mm) in the Z-axis direction (No. 10), followed by semi-finishing by contour machining (No. 11).

[0093] Next, in the "process of finishing the mold wall," in the embodiment, finishing was performed by reciprocating movement in the Z-axis direction using one type of end mill 1 (Table 2 below), while in the comparative example, finishing was performed by contour machining in the X-Y plane direction using multiple types of end mills with different overhang amounts (Table 3 below).

[0094]

[0095] In each of the steps No. 12 to 13 of the embodiment shown in Table 2, the mold wall surface was finished by reciprocating movement in the Z-axis direction from the upper end to the lower end. No. 12 is the cutting of the wall surface of the rib groove 100, and No. 13 is the cutting of the wall surface of the outer circumference 101. The surface characteristics of the mold wall surface after finishing according to the embodiment are shown in the image in Figure 5.

[0096]

[0097] In Table 3, each of the processes No. 12 to 14, and the "Z-" indicated in parentheses next to each process, refer to the following cutting processes: ・No. 12: The mold wall is finished by contour machining from the upper end in the Z-axis direction (Z-0 mm) to a depth of 69.9 mm (Z-69.9 mm). ・No. 13: The mold wall is finished by contour machining from a depth of 69.9 mm (Z-69.9 mm) in the Z-axis direction to a depth of 104.9 mm (Z-104.9 mm). ・No. 14: The mold wall is finished by contour machining from a depth of 104.9 mm (Z-104.9 mm) in the Z-axis direction to a depth of 114.1 mm (Z-114.1 mm). The surface characteristics of the mold wall after finishing in the comparative example are shown in the image in Figure 6.

[0098] In the comparative example shown in Figure 6, steps (inter-tool steps) S were observed between contour lines with different depths (machining areas in the Z-axis direction) on the mold wall after finishing. In addition, chatter surfaces U were observed, particularly in areas with greater depth, due to chatter vibration of the tool. Furthermore, when the surface roughness of the machined surface (wall) of the comparative example was measured, Ra = 1.190 μm and Rz = 6.038 μm were found in areas other than the steps S, and the inter-tool step S was 15 μm.

[0099] On the other hand, in the embodiment shown in Figure 5, no tool step S or chatter surface U was observed on the mold wall surface after finishing. Furthermore, when the surface roughness of the machined surface (wall surface) of the embodiment was measured, Ra = 0.596 μm and Rz = 3.319 μm, confirming that the machined surface accuracy was improved compared to the comparative example.

[0100] According to the present invention, a mold machining method is provided that can produce a good surface finish on the machined surface even when the mold wall is machined using a tool with an L / D ratio of 10 or more, and an end mill capable of realizing this mold machining method is also provided. Therefore, it has industrial applicability.

[0101] 1... End mill (tapered neck end mill, radius end mill), 2... Shank section, 3... Cutting edge section, 4... Chip evacuation groove, 7... Cutting edge, 8... Tapered neck section, 72... Outer edge, 73... Corner edge, C... Rotation axis, D... Cutting diameter, L... Tool length, θ1... Helix angle of outer edge, θ2... Axial rake angle of corner edge, θ3... Angle difference

Claims

1. A method for machining a mold using end mills that extend axially along a rotation axis, comprising: a pre-processing step of contour machining the wall surface of the mold using a plurality of end mills, each having a different axial overhang, wherein the tool length L is the total length dimension of the end mill along the axial direction, the cutting edge diameter D is the diameter dimension of the cutting edge of the end mill, L / D ≥ 10, and the groove length, which is the axial dimension of the chip evacuation groove of the end mill, is 3D or less; and a finishing step of finishing the wall surface of the mold by reciprocating movement in the axial direction using other end mills, the L / D being larger than that of the end mills used in contour machining and the groove length being 3D or less.

2. The method for machining a mold according to claim 1, wherein in the contour machining and finishing processes, a tapered neck end mill is used as the end mill, and the tapered neck end mill has a columnar shank portion extending in the axial direction, a tapered neck portion connected to the shank portion and whose diameter decreases as it approaches the tip in the axial direction, and a cutting edge portion connected to the tapered neck portion and on which the cutting edge and the chip evacuation groove are arranged.

3. A method for machining a mold according to claim 1 or 2, further comprising the step of rough machining the mold using an end mill with L / D ≤ ​​10 prior to the aforementioned pre-machining to provide a wall surface to the mold.

4. The method for machining a mold according to claim 1 or 2, wherein in the finishing process, a radius end mill is used as the end mill, the cutting edge of the radius end mill has an outer edge and a corner edge, and the outer edge and the corner edge are each of the positive cutting edge type.

5. The method for machining a mold according to claim 4, wherein the helix angle θ1 of the outer peripheral blade is 5° < θ1 ≤ 30°.

6. The method for machining a mold according to claim 4, wherein the axial rake angle θ2 of the corner cutting edge is 5° ≤ θ2 ≤ 20°.

7. The method for machining a mold according to claim 4, wherein the helix angle θ1 of the outer peripheral blade is greater than the axial rake angle θ2 of the corner blade, and the angular difference θ3 between the helix angle θ1 of the outer peripheral blade and the axial rake angle θ2 of the corner blade is θ3 ≤ 15°.

8. An end mill extending axially along a rotation axis, wherein the overall length of the end mill along the axial direction is the tool length L, and the diameter of the cutting edge of the end mill is the cutting edge diameter D, such that L / D ≥ 10, and the groove length, which is the axial dimension of the chip evacuation groove of the end mill, is 3D or less, and the end mill comprises: a columnar shank portion extending axially; a tapered neck portion connected to the shank portion, whose diameter decreases towards the tip side in the axial direction; and a cutting edge portion connected to the tapered neck portion, where the cutting edge and the chip evacuation groove are arranged, the cutting edge having an outer edge and a corner edge, the outer edge and the corner edge being of a positive cutting edge type, and the helix angle θ1 of the outer edge being 5° < θ1 ≤ 30°.

9. The end mill according to claim 8, wherein the axial rake angle θ2 of the corner cutting edge is 5° ≤ θ2 ≤ 20°.

10. The end mill according to claim 8 or 9, wherein the helix angle θ1 of the outer peripheral cutting edge is greater than the axial rake angle θ2 of the corner cutting edge, and the angular difference θ3 between the helix angle θ1 of the outer peripheral cutting edge and the axial rake angle θ2 of the corner cutting edge is θ3 ≤ 15°.

11. The end mill according to claim 8 or 9, wherein the outer peripheral relief surface, which is the relief surface of the outer peripheral cutting edge, and the corner relief surface, which is the relief surface of the corner cutting edge, are seamlessly connected.

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