Press die manufacturing method
The use of a radius end mill with offset pick feeds in press die manufacturing addresses the inefficiency of conventional methods by reducing tearing and cusps, allowing for efficient production of press dies with desired surface roughness without additional polishing.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- MITSUBISHI MOTORS CORP
- Filing Date
- 2024-12-23
- Publication Date
- 2026-07-03
AI Technical Summary
Conventional press mold manufacturing methods require excessive man-hours to achieve a desired surface roughness due to the formation of fraying and cusps during cutting, necessitating additional polishing steps.
A method using a radius end mill that moves along predetermined cutting paths with offset pick feeds to form a press surface, ensuring continuity and minimizing cusps, thereby eliminating the need for post-cutting polishing.
The method enables the production of press dies with desired surface roughness in fewer steps by reducing tearing and cusp formation, enhancing manufacturing efficiency and surface quality.
Smart Images
Figure 2026110933000001_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to a method for manufacturing a press mold.
Background Art
[0002] Conventionally, technologies related to press molds having a press surface that contacts a press object are known. For example, Patent Document 1 discloses a press mold for a press drawing process that reduces press marks by providing a plurality of holes and grooves on the press surface.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] By the way, in a press mold, in order to form the press surface into a desired surface roughness, after forming the press surface by cutting, an operator sometimes performs a polishing operation. Therefore, a plurality of man-hours are required for manufacturing the press mold.
[0005] This disclosure has been made in view of such problems, and an object thereof is to provide a method for manufacturing a press mold capable of manufacturing a press mold having a press surface with a desired surface roughness with fewer man-hours.
Means for Solving the Problems
[0006] To achieve the above objective, the present disclosure is a method for manufacturing a press die in which a radius end mill that rotates around an axis is moved along a predetermined cutting path by the shape of a radius tool to form a press surface that contacts a workpiece during press working, wherein adjacent cutting paths are offset from each other by a predetermined pick feed amount such that the portion that becomes a cusp along the outer cutting edge of the radius end mill on the press surface in one cutting path is included in the cutting range of the radius end mill in the next adjacent cutting path. [Effects of the Invention]
[0007] According to the press die manufacturing method of this disclosure, a press die having a press surface with a desired surface roughness can be manufactured with fewer steps. [Brief explanation of the drawing]
[0008] [Figure 1] This is an explanatory diagram showing an example of press working. [Figure 2] This is a perspective view showing an example of a press die. [Figure 3] This is an explanatory diagram showing a comparative example of a press die manufacturing method. [Figure 4] This is an explanatory diagram showing the manufacturing method of the embodiment. [Figure 5] This is an explanatory diagram showing how a radius end mill is moved between adjacent cutting paths in the manufacturing method of the embodiment. [Figure 6] This is a test result showing an example of the arithmetic mean roughness of a press surface formed by the manufacturing method of the embodiment. [Figure 7] This is an explanatory diagram illustrating an example of operation when a radius end mill is moved back and forth during workpiece cutting. [Modes for carrying out the invention]
[0009] Hereinafter, an embodiment of the present disclosure will be described based on the drawings. Figure 1 is an explanatory diagram showing an example of press working. Press working is a process in which an object to be pressed is clamped between a press die consisting of an upper die and a lower die and pressed to form the object into the shape required for the product. Press working includes, for example, deep drawing ST1, trimming ST2, and bending ST3.
[0010] Deep drawing ST1 involves pressing a base material, such as a sheet metal, with a press die to draw out a press object 1A that closely resembles the product shape. Trimming ST2 is a type of shearing process. For example, trimming ST2 takes the press object 1A formed by deep drawing and uses the press of a press die to shear the unnecessary parts, forming a press object 1B. Bending ST3 takes the press object 1B formed by trimming ST2 and uses the press of a press die to bend a predetermined part (e.g., the shaded area) to the angle required for the product, forming a press object 1C.
[0011] Figure 2 is a perspective view showing an example of a press die 10. Figure 2 shows a press die 10 that uses a side door, which is installed on an automobile, as the object to be pressed for deep drawing. Note that automobiles are not limited to those that are driven solely by an internal combustion engine, but also include, for example, BEVs (Battery Electric Vehicles), HEVs (Hybrid Electric Vehicles), PHEVs / PHVs (Plug-in Hybrid Electric Vehicles / Plug-in Hybrid Vehicles), and FCEVs / FCVs (Fuel Cell Electric Vehicles / Fuel Cell Vehicles). PHEVs / PHVs are automobiles that can be charged by external charging, which is supplied with power from an external power source to an energy storage device installed in the vehicle, or by external power supply, which is supplied from the battery to electrical appliances outside the vehicle. The press die 10 has a press surface 12, which is the surface that comes into contact with the object to be pressed during processing. The door, which is the object to be pressed, has multiple character lines, which are lines of indentations and protrusions that mainly extend in the front-rear direction of the vehicle. Therefore, the pressing surface 12 is provided with multiple character lines 3 corresponding to the character lines formed on the object to be pressed.
[0012] The press die 10 is formed by machining the original workpiece. Figure 3 is an explanatory diagram showing a comparative example of a press die manufacturing method. As shown in the figure, in the comparative example manufacturing method, a ball end mill 20 having a spherical blade at its tip is used as the cutting tool. The ball end mill 20 is attached to a cutting device (not shown). The cutting device rotates the ball end mill 20 around its axis at a predetermined rotational speed and moves it along a predetermined cutting path Le in the feed direction X, cutting the workpiece W with a predetermined depth of cut to form the press surface 12. When the cutting device has finished cutting one cutting path Le1, it moves the ball end mill 20 by a predetermined pick feed PFe toward the next adjacent cutting path Le2, as shown by the dashed arrow, and performs the same cutting operation again.
[0013] Here, it is known that the actual cutting speed (rotational speed) of the ball end mill 20 is faster towards the outer circumference and slower towards the inner circumference, and the actual cutting speed at its tip 22 is 0. As a result, the tip 22 rubs against the workpiece W, which can cause fraying on the surface of the workpiece W. In addition, in the comparative example method, a cusp (scallop) 50, which is a wave-shaped uneven surface following the spherical shape of the ball end mill 20, is formed between one cutting path Le1 and the next cutting path Le2. The height h of this cusp 50 is called the cusp height (scallop height). As a result of the formation of fraying and cusps 50 on the workpiece W as described above, there is a high probability that the manufacturing method of the comparative example will not be able to form the press surface 12 to the desired surface roughness.
[0014] Therefore, the following method is used in the manufacturing method of the press die of the embodiment. Figure 4 is an explanatory diagram showing an example of the manufacturing method of the embodiment. Figure 5 is an explanatory diagram showing how the radius end mill is moved between adjacent cutting paths in the manufacturing method of the embodiment.
[0015] In the manufacturing method of the embodiment, a radius end mill 30 is used as the cutting tool. The radius end mill 30 has a flat bottom cutting edge 31 provided at the tip and an outer peripheral cutting edge 32 that extends from the bottom cutting edge 31 in an R shape with a predetermined radius of curvature. The radius end mill 30 is a mill in which the outer peripheral cutting edge of a square end mill, which has a tip formed into a roughly rectangular prism shape, is formed in an R shape, and is also called a corner R end mill. With this radius end mill 30, the workpiece W is cut with the outer peripheral cutting edge 32, so the actual cutting speed (rotational speed) does not become zero, unlike the tip 22 of the ball end mill 20. As a result, when cutting with the radius end mill 30, the occurrence of tearing of the workpiece W is suppressed.
[0016] The radius end mill 30 is attached to a cutting device (not shown) as in the comparative example above. The cutting device then rotates the radius end mill 30 around its axis at a predetermined speed in a constant direction, while moving it along a predetermined cutting path L in the feed direction X, cutting the workpiece W with a predetermined depth of cut. In this embodiment, the feed direction X is set to align with the main character line 3 (Figure 2) of the object to be pressed. Therefore, if the object to be pressed is a vehicle part such as a car door, the feed direction X corresponds to the front-to-rear direction of the vehicle.
[0017] In the example shown in Figure 4, the feed direction X is set to only the first feed direction X1 from one end 12a to the other end 12b of the press surface 12. The cutting machine cuts one cutting path L1 of the workpiece W with the radius end mill 30 as shown by the solid arrow. Then, as shown by the dashed arrow, the cutting machine returns the radius end mill 30 to the one end 12a of the workpiece W with the radius end mill 30 separated from the workpiece W. At this time, the cutting machine moves the radius end mill 30 along the direction Y perpendicular to the feed direction X by a predetermined pick feed PF (Figure 5) to position it at the cutting start position of the next adjacent cutting path L2. After that, the cutting machine feeds the radius end mill 30 again along the cutting path L2 along the first feed direction X1 to cut the workpiece W. The press surface 12 is formed by repeating this operation.
[0018] A predetermined pick feed PF will be described with reference to FIG. 5. FIG. 5 shows a state in which the radius end mill 30 and the work W are viewed along the feed direction X. Now, it is assumed that the work W is being cut by the radius end mill 30 on one cutting path L1 (step ST11). When the cutting of the cutting path L1 is completed, as described above, the cutting device moves the radius end mill 30 in the direction Y by a predetermined pick feed PF and then cuts the next cutting path L2 adjacent to the cutting path L1 (step ST12). In step ST12, the radius end mill 30 that existed on the cutting path L1 is described by a broken line as the radius end mill 301, and the radius end mill 30 that exists on the current cutting path L2 is described by a solid line as the radius end mill 302.
[0019] Here, among the boundary points 35 between the bottom edge 31 and the outer peripheral edge 32 of each radius end mill 30, the portion located on the previous cutting path side (the right side in the figure) in the direction Y is defined as the "boundary point 351", and the portion located on the side opposite to the previous cutting path (the left side in the figure) in the direction Y is defined as the "boundary point 352". Also, in the direction Y, the range on the cutting path L2 side (the left side in the figure) of the boundary point 351 of the radius end mill 301 and on the side opposite to the cutting path L2 (the right side in the figure) from the boundary point 352 of the radius end mill 301 is defined as the "predetermined range A". The predetermined range A is a range that does not include the boundary point 351 itself between the boundary point 351 and the boundary point 352 of the radius end mill 301 in the direction Y.
[0020] A predetermined pick feed PF is set such that, when viewed along the first feed direction X1, a boundary point 351 of the radius end mill 302 on the cutting path L2 is included in a predetermined range A. In other words, the predetermined pick feed PF is set such that the portion where the bottom edge 31 exists on the cutting path L2 and the portion where the bottom edge 31 existed on the cutting path L1 are continuous along the direction Y (so that no gap is formed therebetween). To put it more simply, adjacent cutting paths L1 and L2 are offset from each other by a predetermined pick feed PF such that a portion 52 (the shaded range) that becomes a cusp generated on the press surface 12 along the shape of the outer peripheral edge 32 in the cutting path L1 is included in the cutting range of the radius end mill 302 in the adjacent next cutting path L2. As a result, the surface of the workpiece W after cutting becomes a flat surface where the bottom edge 31 existed on each of the cutting paths L1 and L2, and no cusp is formed. When machining a curved surface with the radius end mill 30, the smaller the pick feed PF, the smaller the height of the cusp can be made, and the roughness of the machined surface can be reduced.
[0021] FIG. 6 shows test results indicating an example of the arithmetic mean roughness of the press surface 12 formed by the manufacturing method of the embodiment. Here, tests were conducted to form the press surface 12 under the conditions shown in (1) to (12). Conditions (1) to (3) and (7) to (9) are comparative examples in which the above ball end mill 20 was used as the cutting tool. In addition, in conditions (1) to (6), each mill is made of cemented carbide, and in conditions (7) to (12), each mill is made of cubic boron nitride (CBN: Cubic Boron Nitride). Also, the pick feed PF is set to any one of a first pick feed PF1, a second pick feed PF2, and a third pick feed PF3 included in the above predetermined range A. The first pick feed PF1 is larger than the second pick feed PF2 and the third pick feed PF3, and the second pick feed PF2 is larger than the third pick feed PF3.
[0022] As shown in the figure, the arithmetic mean roughness of conditions (4) to (6) and (10) to (12) using the manufacturing method of the embodiment is smaller than that of the comparative example conditions (1) to (3) and (7) to (9). The dashed line in the figure shows an example of a reference value for the arithmetic mean roughness required for the press surface 12 as a product specification. The reference value is obtained by polishing the press surface 12 by an operator in the manufacturing method of the comparative example using the ball end mill 20 in order to remove the visible fine marks remaining on the press surface 12, known as tool marks. In the conditions (4) to (6) and (10) to (12) of the embodiment, the arithmetic mean roughness of the press surface 12 was below the reference value.
[0023] As described above, the manufacturing method of the embodiment can suppress the occurrence of tearing of the workpiece W by using a radius end mill 30 as the cutting tool. Furthermore, the manufacturing method of the embodiment can suppress the occurrence of cusps 50 on the press surface 12 by setting the pick feed PF as described above. As a result, the manufacturing method of the embodiment does not require the operator to perform polishing work on the press surface 12 after cutting, and a press die 10 with the desired surface roughness can be manufactured with fewer steps.
[0024] Furthermore, the feed direction X of the radius end mill 30 is aligned with the main character line 3 (Figure 2) of the object to be pressed. With this configuration, even if there are minute traces on the press surface 12 that extend along the feed direction X, the direction of extension of the main character line 3 of the object to be pressed, which is pressed by the press surface 12, will be aligned with that of the minute traces. Therefore, the manufacturing method of this embodiment can make the minute traces transferred to the object to be pressed during press working as inconspicuous as possible.
[0025] Furthermore, the feed direction X of the radius end mill 30 is only a first feed direction X1 from one end 12a to the other end 12b of the press surface 12. The radius end mill 30 rotates in a constant direction, cuts along the cutting path L in the first feed direction X1, and then moves towards the next adjacent cutting path L2 to the one end 12a without any further cutting. With this configuration, the manufacturing method of the embodiment can unify the relationship between the feed direction X and the rotation direction of the radius end mill 30 on each cutting path L, thereby achieving uniformity in the cutting of the press surface 12.
[0026] Furthermore, the radius end mill 30 is made of, for example, cemented carbide or cubic boron nitride. In particular, when the press working is deep drawing ST1, the radius end mill 30 is preferably made of cubic boron nitride. Because the radius end mill 30 made of cubic boron nitride has excellent wear resistance, it is suitable for manufacturing press dies used in deep drawing, where high processing accuracy is often required. On the other hand, when the press working is trimming (shearing) ST2 or bending ST3, the radius end mill 30 is preferably made of cemented carbide. Because the radius end mill 30 made of cemented carbide has excellent rigidity, it is suitable for shearing processes such as trimming ST2 and bending ST3, where the material of the workpiece W is likely to be mixed and intermittent cutting is likely to occur.
[0027] Furthermore, the feed direction X of the radius end mill 30 is not limited to that shown in Figure 4. Figure 7 is an explanatory diagram showing an example of operation when the radius end mill 30 is reciprocated during cutting of the workpiece W. In the example shown in Figure 7, the feed direction X of the radius end mill 30 includes the first feed direction X1 and the second feed direction X2 from the other end 12b side to the one end 12a side of the press surface 12. In this example, the radius end mill 30 is moved to cut one cutting path L1 in the first feed direction X1, as shown by the solid line. Then, the radius end mill 30 is moved by a predetermined pick feed PF to the next adjacent cutting path L2, as shown by the dashed line. After that, the radius end mill 30 is moved to cut the cutting path L2 along the second feed direction X2. The press surface 12 is formed by repeating this operation. In this way, by cutting the workpiece W with the radius end mill 30 in a reciprocating motion, the cutting of the workpiece W can be completed more quickly.
[0028] Furthermore, in this case, the rotation direction of the radius end mill 30 is set to be opposite when the radius end mill 30 moves in the first feed direction X1 and when it moves in the second feed direction X2. As a result, the manufacturing method of the embodiment can unify the relationship between each feed direction X and the rotation direction of the radius end mill 30 on each cutting path L, thereby achieving uniformity in the cutting of the press surface 12.
[0029] This concludes the description of the embodiments, but the embodiments of this disclosure are not limited to these embodiments. For example, the feed direction X does not have to be in the direction along the character line 3, nor does it have to be in the direction along the vehicle's longitudinal direction, as long as it can sufficiently make the fine marks on the press surface 12 less noticeable. Also, the rotation direction of the radius end mill 30 may always be constant, regardless of its relationship to the feed direction X, as long as it can sufficiently homogenize the cutting of the press surface 12, or it may be changed as appropriate. Furthermore, the radius end mill 30 may be made of cemented carbide or cubic boron nitride, regardless of the type of press work, or it may be formed from other materials. [Explanation of symbols]
[0030] 1A, 1B, 1C - Items to be pressed 3 Character Lines 10 Press molds 12 Press surface 12a one end 12b Other end 20 Ball End Mills 30, 301, 302 Radius End Mills 31 Bottom blade 32 Peripheral blade Boundary points 35, 351, and 352 50 cusps 52. The part that becomes the cusp A predetermined range L, L1, L2, Le, Le1, Le2 cutting paths PF, PFe pick feed Double job X feed direction X1 First feed direction X2 Second feed direction
Claims
1. In a method for manufacturing a press die in which a radius end mill that rotates around an axis is moved along a predetermined cutting path to form a press surface that contacts the workpiece during press working, A method for manufacturing a press die, wherein adjacent cutting paths are offset from each other by a predetermined pick feed amount such that the portion that forms a cusp on the press surface along the outer cutting edge of the radius end mill in one cutting path is included in the cutting range of the radius end mill in the next adjacent cutting path.
2. The method for manufacturing a press die according to claim 1, wherein the feed direction of the radius end mill is in the direction along the main character line of the object to be pressed.
3. The feed direction of the radius end mill is only a first feed direction from one end to the other end of the press surface. The radius end mill rotates in a constant direction, cuts the cutting path along the first feed direction, and then moves to the one end side toward the adjacent next cutting path without further cutting. A method for manufacturing a press die according to claim 1 or 2.
4. The feed direction of the radius end mill includes a first feed direction from one end to the other end of the press surface and a second feed direction from the other end to the one end of the press surface. The radius end mill is moved to cut the cutting path along the first feed direction, and then to cut the next adjacent cutting path along the second feed direction. A method for manufacturing a press die according to claim 1 or 2.
5. The method for manufacturing a press die according to claim 4, wherein the rotation direction of the radius end mill is set in opposite directions when the radius end mill moves in the first feed direction and when it moves in the second feed direction.
6. The method for manufacturing a press die according to claim 1 or 2, wherein, when the press working is a deep drawing process, the radius end mill is made of cubic boron nitride.
7. The method for manufacturing a press die according to claim 1 or 2, wherein the radius end mill is made of cemented carbide when the press working is shearing or bending.