JP2011147983A - Forming tool and method for machining the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a forming tool which has complicated shape and has high hardness and durability like an outer form tool for forming a peripheral polyhedral wall can without depending cemented carbide and without depending on electric discharge machining in a short period of time and inexpensively by cutting work. <P>SOLUTION: Prehardened steel having hardness of HRC 35-50 is adopted as steel and, by machining the steel with a ball end mill having a diameter of 1-6 mm, at a speed of rotation of 10,000-20,000 rpm and at a feed speed of 1,000-2,000 mm/min, the machining of the forming tool having high hardness and the complicate-shaped form surface is made possible. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a forming tool for forming a complicated three-dimensional pattern or the like on a work such as a metal can and a processing method thereof.

  2. Description of the Related Art Conventionally, for example, a whole or part of a can body of a can container is known as a circumferential polyhedral wall formed with a three-dimensional pattern of diamond-cut continuous irregularities as shown in FIG. The circumferential polyhedron wall 102 of the can body 101 is composed of a number of structural unit surfaces 103 arranged so that the phase is shifted by ½ in the can axis direction. The crossing portion 105 where the ridgelines cross each other is shared, and the boundary ridgeline and the crossing portion are relatively outwardly convex as compared to the structural unit surface. The present applicant has previously proposed a mold for producing a circumferential polyhedral wall can and a method for producing the same in order to form this complicated three-dimensional pattern (see Patent Document 1). As shown in FIG. 9, the proposed mold is composed of an inner mold tool 107 and an outer mold tool 108. By sandwiching the can body 101 between the inner mold tool 107 and the outer mold tool 108 and rotating them synchronously, The can body 101 is processed into a diamond cut shape. The inner tool 107 has a simple shape similar to a circumferential polyhedral wall can, but the outer tool 108 is obtained by rotating a reference tool larger than the inner tool 107 by a dimension corresponding to the plate thickness of the can body. It has a complicated shape consisting of an envelope. Such a forming tool is made of cemented carbide from the viewpoint of durability and wear resistance, but it is generally difficult to cut if the shape is complicated like the above-mentioned external tool, It is formed by electric discharge machining (see Patent Document 1). However, cemented carbide has a high material cost, and the forming process by electric discharge machining has a low machining speed and requires a long time (for example, about 30 for machining an external tool as shown in Patent Document 1). To 40 hours), and there is a problem that the cost is high in terms of efficiency and power consumption. For this reason, conventionally, a molding tool having such a complicated shape and high hardness is expensive and requires a long time for manufacturing, and thus cannot easily cope with a design change or the like.

  On the other hand, a high C-high Cr steel such as SKD11 is used as a conventional mold material. In this case, the annealed material is roughly processed by cutting and then subjected to heat treatment such as quenching to obtain the necessary surface hardness. After that, finishing processing such as grinding or electric discharge machining has to be performed, and there is a problem that the number of steps of mold production is large. Therefore, in recent years, pre-hardened steel has been provided as a steel material that does not require heat treatment and finishing after cutting, and has been adopted for plastic molds (Patent Documents 2 and 3). Pre-hardened steel has a uniform hardness from the surface to the core, can be cut with a hardness of about 40 HRC, and has excellent abrasive properties. However, although pre-hardened steel is used as a mold material such as a plastic mold, it is not generally employed for forming tools that require higher durability and wear resistance. In addition, even with pre-hardened steel, if the hardness is higher than HRC50 or more, cutting is difficult when precise processing is required with a complicated shape such as the above-mentioned external tool, and also EDM I had to rely on.

Japanese Patent No. 4333501 JP 2008-38219 A JP 2008-127643 A

  Therefore, the present invention has a complicated shape such as an outer mold tool for molding a circumferential polyhedral wall can and has the necessary hardness and durability as a forming tool. An object of the present invention is to provide a high-hardness forming tool that can be obtained at low cost and a processing method thereof.

The forming tool of the present invention that solves the above problems is a forming tool for forming a three-dimensional pattern on a workpiece, and is made of pre-hardened steel, and a processed surface having irregularities forming the three-dimensional pattern is formed by cutting. It is characterized by being made.
By using pre-hardened steel as a forming tool, it becomes easy to cut a complicated shape with a three-dimensional pattern, and as a forming tool, it is excellent in wear resistance and durability, and durability can be ensured.

  If the hardness is less than HRC35, the hardness of the pre-hardened steel lacks wear resistance and durability as a forming tool, and if it exceeds HRC50, it becomes difficult to cut a complicated shape of a three-dimensional pattern, and HRC35-50 Since the wear resistance and durability as a forming tool can be sufficiently secured within the hardness range, a complicated three-dimensional pattern can be formed by cutting, and the above range is required to ensure the durability as a forming tool. desirable.

  The pre-hardened steel is preferably a Ni—Al—Cu age-hardening steel from the viewpoint of machinability. The forming tool can be applied as an outer forming tool for forming a circumferential polyhedral wall can, which is a polyhedron having a processed surface shape formed by an envelope obtained by rotating a reference mold. The outer forming tool is preferably formed in a sectional fan shape by forming the machining surface only in about a half circumference portion of the cylindrical rotating body.

A forming tool processing method according to the present invention is a forming tool processing method according to any one of claims 1 to 5, wherein, in a finish cutting step, a ball end mill whose tip is formed of a cubic boron nitride sintered body Then, the cutting process is performed by blowing compressed air containing a small amount of oil onto the processing point.
By adopting the above-described configuration, since the conventional hardness is high and the toughness is inferior and the chipping is likely to occur, it is possible to apply a CBN tool that can be applied to the machining under the above-described cutting conditions, and it is possible to realize a high-precision cutting process. At the same time, the life of the cutting tool can be increased, and the production efficiency and cost can be reduced.

It is desirable that the tip end diameter of the ball end mill is 1 to 6 mm, the cutting is performed at a rotational speed of 10,000 to 20,000 rpm, and a feed rate of 1,000 to 2,000 mm / min. By adopting a ball end mill having a small diameter, the quality of the cutting surface can be improved and a more complicated pattern can be formed. However, if it is less than 1 mm, it takes a long time to cut, and 6 mm Since the surface quality of the finishing process of a complicated shape will be inferior when exceeding, the said range is desirable. Also, if the cutting speed is less than the above range, the cutting load increases, cutting becomes difficult and the life of the cutting tool is reduced, and if it exceeds the above range, it is difficult to ensure the shape accuracy. The above range is desirable for the number and feed rate.
In addition, it is possible to realize the formation of a complicated three-dimensional pattern that had to be relied on electric discharge machining on the machined surface of high-hardness pre-hardened steel of HRC 35 to 50 by cutting, and to obtain a high-hardness forming tool at a low cost in a short time. be able to.

  The ball end mill can form a free-form surface using its R shape, and can perform precise curved surface processing. By cutting the ball end mill at a processing pitch of 0.05 to 0.1 mm, the cutting load is reduced, the shape accuracy is improved, the surface quality is improved, and the surface roughness is Rz2 to 3. This enables complex cutting of high-hardness steel.

  Since the forming tool of the present invention is made of pre-hardened steel, it maintains an appropriate hardness, and the shape of an outer tool for forming a circumferential polyhedral wall can is complicated by devising a cutting method. However, it can be obtained in a short time and inexpensively by cutting without using conventional electric discharge machining. Therefore, according to the present invention, by cutting, for example, an outer tool for forming a circumferential polyhedral can wall, etc. A high-hardness forming tool having durability can be obtained.

  Moreover, the manufacturing method of the said shaping | molding tool of this invention employ | adopts the ball end mill in which the front-end | tip part is formed from the cubic boron nitride sintered compact, and spraying the compressed air containing a trace amount oil on the processing point By cutting, conventional hard toughness is inferior and easily damaged, so it is possible to apply CBN tools that can be applied under the above-mentioned cutting conditions, and high precision cutting can be realized. As a result, it was possible to increase the life of the cutting tool and to increase the production efficiency and cost.

It is a perspective view showing typically the state where the can body is being processed with the inner mold tool by the outer mold tool for forming the circumferential polyhedral wall can according to the embodiment of the molding tool of the present invention. It is the front view. It is a front view in the state where one round of processing was completed to the can body. It is a principal part enlarged front view of the CBN ball end mill concerning the embodiment of the present invention. 1 schematically shows the formation of a free-form surface by a CBN ball end mill according to an embodiment of the present invention, wherein (a) shows the processing pitch of the CBN ball end mill in the intermediate finishing process, and (b) shows the processing pitch of the CBN ball end mill in the finishing process. Is shown. (A) is an enlarged photograph of the cutting edge part in the unused state of the CBN ball end mill concerning the embodiment of the present invention, and (b) shows the state after 54 hours use by the oil mist method according to the embodiment of the invention. It is the enlarged photograph of the blade edge | tip part to show, (c) is an enlarged photograph of the blade edge | tip part which shows the state after using for 54 hours by the air blow method as a comparative example. It is the front-end | tip part enlarged photograph of a cemented carbide ball end mill as a comparative example of this invention, (a) is the state before use, (b) is the state after 54 hours use. It is a front view which shows an example of the can which has a circumferential polyhedral wall can. It is a front view which shows typically the state which shape | molds the can body with the conventional external type tool and internal type tool which form a circumferential polyhedral wall can.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1 to 3 show an outer mold tool 1 for manufacturing a circumferential polyhedral wall can (so-called diamond cut can) according to an embodiment of a forming tool of the present invention, together with an inner mold tool 2. The forming tool according to the present embodiment is a forming tool for forming the uneven pattern of the can body 101 shown in FIG. As shown in the figure, the outer mold tool 1 has a length corresponding to the can body to be processed in the axial direction, and a sectoral fan shape in which the circumferential direction has a substantially semicircular surface corresponding to the peripheral length of the can body. The fan-shaped outer peripheral surface is a mold surface 4. The shape of the molding die surface 4 is substantially the same as that shown in Patent Document 1, and has a polyhedron constituted by valleys that mesh with protrusions constituting the polyhedron of the inner tool 2. The outer tool 1 and the inner tool 2 are arranged so that the corresponding protrusions and valleys mesh with each other, and the side wall of the can body 101 is placed between the outer tool 1 and the inner tool 2. A circumferential polyhedral wall can be formed by rotating in the opposite direction at the same peripheral speed while sandwiching. Since the circumferential polyhedron of the can body 101 is formed by rolling the outer die tool 1 and the inner die tool 2 in a meshed state, the shape of the outer die tool 1 in the circumferential direction of the polyhedron is A polyhedral shape consisting of repeated continuations of the envelope 5 obtained by rotating the reference die larger than the inner die tool 2 by a dimension corresponding to the plate thickness of the can body, based on the envelope obtained by rolling 2 Is formed.

In the present embodiment, by forming the outer tool 1 into a fan shape as described above, the formation of one round of the can body 101, which is a workpiece, is completed when the inner tool 2 and the outer tool 1 are disengaged. Since the can body can be attached to and removed from the inner tool 2 without moving between the axial centers of the inner tool 2 and the inner tool, it is easy to control the removal of the can body from the inner tool. There are advantages.
The outer mold tool (hereinafter simply referred to as the outer mold tool) 1 for manufacturing the circumferential polyhedral wall can according to the present embodiment having the above shape is manufactured as follows.

  The forming of the circumferential polyhedral wall can is basically performed by bending the can body. Although a carbide tool is ideal as a forming tool for metal processing, it is hard and has high toughness, so that cutting is very difficult. For this reason, carbide tools are ideal for machining such as ironing rings that have a simple shape, but the outer tools for forming circumferential polyhedral wall cans have complicated shapes due to repeated envelopes, so cutting Is very difficult and relied on electric discharge machining as described above. As a result of earnest research that the present inventor is not an electric discharge machining but a method of forming a molding tool having such a complicated machining surface by cutting, first, it has been employed exclusively as a material for this type of molding tool. Instead of the cemented carbide, the idea was to adopt a new material applicable to forming tools, and various materials were studied. As a result, pre-hardened steel has a uniform hardness from the surface to the core, and has a moderate hardness compared to cemented carbide, so it can be cut, has excellent polishing properties, and has a lapping finish. Focusing on the fact that it is possible to make a mirror surface, as a result of investigating whether or not the pre-hardened steel can be adopted as an outer tool, the pre-hard steel satisfies certain conditions, and by devising a cutting tool and a cutting method, The present invention has been found by finding that it can be used as the material of the external tool.

  Although it does not specifically limit as prehardened steel employ | adopted by this invention, Ni-AL-Cu type | system | group age hardening type steel is desirable rather than Cr type | system | group from a viewpoint of cutting property, and hardness is HRC35-50. Is desirable. With a hardness of HRC 35-50, it is possible to ensure sufficient wear resistance and durability as a forming tool for forming a complex relief or embossed pattern basically by bending a can body material. An example of a commercially available brihard steel that satisfies this requirement is NAK80 manufactured by Daido Special Steel Co., Ltd. Hardness is HRC37-43.

In the present invention, the pre-hardened steel ingot was cut under the following cutting conditions to obtain an external tool as a forming tool.
Cutting in this embodiment is performed by a CNC high-speed machining center, and is normally performed in the order of roughing, intermediate finishing, and finishing. Here, the finishing that requires fine cutting will be mainly described.
(1) Cutting tool: ball end mill A free-form surface is formed using the R shape of a ball end mill. As the cutting tool in the finishing process, a small diameter tool having a diameter of 1 to 6 mm is used. The smaller the diameter, the longer the machining will be, but the quality of the cutting surface will be improved and a more complicated pattern can be formed, and the above range is applicable to the cutting of the outer tool for forming a circumferential polyhedral wall can. Desirably, in this embodiment, a small diameter tool of a φ2 ball end mill is used as a more desirable one.

Cemented carbide is the main tool material for ball end mills, but since carbide wears heavily, the cutting edge changes greatly immediately after the start of use and after many machining operations. This is disadvantageous for the finishing process because it requires a lot of replacement and results in high costs and reduced productivity. Therefore, in the present embodiment, a tool (hereinafter referred to as a CBN tool) in which CBN (cubic boron nitride) having a high temperature hardness and excellent wear resistance than a cemented carbide tool is embedded in a blade end portion of a ball end mill. Decided to use. FIG. 4 is an enlarged view of a main part of the CBN tool 10 according to the present embodiment, in which the CBN sintered body 11 is used for the cutting edge portion.
However, although the CBN tool is high in hardness, it is inferior in toughness. Therefore, when machining is performed for a long time with a small-diameter end mill, there is a disadvantage that the cutting edge portion is thermally broken. The thermal breakage has a greater degree of breakage than a fine chip of the cutting edge that occurs when cutting is performed under the same conditions with a conventional cemented carbide ball end mill. Therefore, even when trying to obtain a pre-hardened steel complex shape cutting surface by the conventional cutting method, if the cemented carbide tool is simply replaced with a CBN tool, the tool life will deteriorate due to breakage problems. It was. As described above, the CBN ball end mill has a drawback that it is easily chipped due to thermal breakage. However, if this problem can be overcome, the CBN ball end mill has advantages over the carbide tool (the sharpness is good, the surface roughness is small and kept constant). This is advantageous for finishing. Therefore, in the present invention, this problem is solved by adopting the following cutting method, and the CBN tool can be adopted.

(2) Cutting method
[Cutting conditions]
Number of rotations: 10,000 to 20,000 mm / min
Feed rate: 1,000 to 2,000 mm / min
Processing pitch: 0.05-0.1mm
Cutting depth: 0.03-0.06mm
Processing time: 8 to 14 hours / piece As described above, the cutting speed is increased by reducing the amount of one-time cutting compared to the conventional end milling, and the processing pitch is reduced. Reduction, improved shape accuracy, and improved quality. CBN tools are prone to chipping, so the applicable processing is limited, but only conventional diamond tools can be applied by appropriately selecting the cutting conditions such as processing speed and processing amount as described above together with cooling and lubrication described later. The applicability of the CBN tool was found in the finishing of high hardness steel that was not.

  FIG. 5 schematically shows a state in which the free curved surface 21 is formed on the workpiece using the R shape of the ball end mill in the cutting process. FIG. 5A schematically shows a processing pitch in the intermediate finishing process by the small-diameter ball end mill, and FIG. 5B schematically shows a processing pitch in the finishing process in the present embodiment. The machining pitch in the intermediate finishing process shown in FIG. 10A is about 0.1 mm, and the machining pitch in the finishing process shown in FIG. I made it.

[cooling]
Since the CBN tool is easy to break, it can be applied only when the cutting load on the tool is low. In the present invention, as described above, the machining pitch is made fine and the cooling method is devised so that the tip of the tool (cutting edge) can be reduced. Solved the problem of breakage. That is, in conventional high-hardness steel cutting, heat generation at the processing point is generally cooled by using a cutting oil or a water-soluble cutting fluid. It has been found that high performance results in thermal breakage. In order to solve this problem, a so-called oil mist processing method is applied in which cooling is performed while blowing compressed air containing a small amount of oil to the processing point. The oil is used in a small amount, so it has excellent lubricity, prevents wear deterioration of the tool, and the cooling performance at the machining point is lower than when using water-soluble cutting fluid or cutting oil, effectively preventing thermal breakage It was possible to prevent the cutting edge from being damaged by the CBN tool. It was found that the amount of oil used is preferably in the range of 5 to 15 cc / hour. If it is less than 5 cc / hour, the lubricity is inferior and there is no effect of suppressing the wear deterioration of the tool. If it exceeds 15 cc / hour, the cooling performance becomes high and the thermal breakage of the cutting edge increases, so the above range is desirable, more desirably It is about 10cc / hour.

In order to verify the effect of the oil mist method in the CBN tool in finishing, the present inventor conducted an experiment for manufacturing the outer tool shown in FIG. 1 as follows.
External tool:
Material: Ni-AL-Cu age hardened pre-hardened steel: NAK80 (Daido Special Steel Co., Ltd.)
Hardness: Nominal HRC40
Processing machine: CNC high-speed machining center Cutting tool: Ball end mill
Ball end mill of φ2 mm whose tip is CBN (cubic boron nitride) Cutting conditions: Cutting was divided into rough machining, intermediate finishing, and finishing. Here, the finishing process will be described.
Rotation speed: 18,000 rpm
Feeding speed: 1,000 to 2,000 mm / min Indexing: Machining by dividing at an arbitrary angle In order to verify the effect of the CBN tool in finishing machining under the above cutting conditions, the amount of oil used is 10 cc / hour. Cutting was performed while blowing the included compressed air on the processing point. Further, as a comparative example, cutting was performed under the same conditions as in the example while cooling the CBN ball end mill by the air blow method.

And the defect | deletion state of the blade edge | tip of the CBN ball end mill after 54 hours use was confirmed in both the Example and the Comparative Example. FIG. 6 (a) is an enlarged photograph of the cutting edge of the CBN ball end mill according to the embodiment of the present invention in an unused state, and FIG. 6 (b) shows 54 hours of cutting while cooling by the oil mist method of the example. The state after being performed, (c) is the state after cutting for 54 hours while cooling by the air blow method of the comparative example.
As is apparent from the photograph, even when cutting was performed with the same CBN ball end mill under the same conditions, there was almost no defect even after 54 hours of use when cooling by the oil mist method of the example, and a high tool life was confirmed. On the other hand, in the cooling by the air blow method of the comparative example, a large chipping 16 was confirmed, and the tool life was short and good cutting was not obtained.

  Furthermore, in order to investigate the relationship between the oil mist method and the tool material in the present embodiment, the ball end mill was cut under the same conditions as in the example using a conventional carbide ball end mill. FIG. 7A is an enlarged photograph of the cutting edge portion when the carbide ball end mill 15 is not used, and FIG. 7B is used for 54 hours when the oil mist method is used for cutting as in the embodiment. It is a photograph showing the later state. As a result, as shown in FIG. 5B, fine chips 17 were generated at the blade edge, which was almost the same as when cooling by air blow. From this result, in the case of carbide ball end mill, there is almost no difference between oil mist method and air blow method, but in the case of CBN tool, the difference is remarkable, and CBN is used to prevent chipping of the ball end mill. It was confirmed that the combination of the tool and the oil mist method is effective.

  As shown in the above examples, cutting of high-hardness materials having a material hardness of HRC40 or higher is generally performed by air blow using a carbide tool, but a CBN tool is used. By cooling with the oil mist method, a long tool life can be obtained, and as a result, the number of tool replacements can be reduced and the number of tools can be reduced. As a result, assuming that 20 external tools shown in FIG. 1 are machined, the carbide tool of the comparative example and the air blow method require 20 tools, whereas the CBN tool and the oil mist method of the embodiment require Only six tools are required, and the adjustment work and the confirmation work accompanying the tool change work can be reduced by that amount, and remarkable effects such as machining efficiency, quality stabilization, and cost reduction were obtained. As described above, the CBN tool is a difficult tool to handle, but the effect when applied to the cutting of a complex shape of a workpiece made of a super-hard material is significant, and in a shorter time than the case of conventional electric discharge machining. High value-added processing was possible.

  Conventionally, a molding tool (molding die) for forming a complicated pattern or the like has been made of cemented carbide from the viewpoint of wear resistance and durability. However, according to the molding tool of the present invention and its processing method, Regardless of the hard alloy, it has the necessary hardness and durability as a forming tool, and even a complicated shape can be formed by cutting. Therefore, the present invention can be applied to the production of molds having various hardnesses and complicated shapes, and has high industrial applicability.

DESCRIPTION OF SYMBOLS 1 Outer mold tool 2 Inner mold tool 4 Molding single side 5 Envelope 10 CBN tool 11 CBN sintered body 15 Carbide ball end mill 16 Defect 21 Free curved surface 101 Can body 102 Circumferential polyhedral wall can 103 Structural unit

Claims (8)

  A forming tool for forming a three-dimensional pattern on a workpiece, wherein the forming tool is made of pre-hardened steel, and a processed surface having irregularities for forming the three-dimensional pattern is formed by cutting.   The forming tool according to claim 1, wherein the hardness of the pre-hardened steel is HRC35-50.   The forming tool according to claim 1 or 2, wherein the pre-hardened steel is Ni-Al-Cu age-hardening steel.   4. The molding tool according to claim 1, wherein the forming tool is an outer mold tool for forming a circumferential polyhedral wall can, and the shape of the processed surface is a polyhedron formed of an envelope obtained by rotating a reference mold. Molding tool.   The forming tool according to claim 4, wherein the forming tool has a cross-sectional fan shape in which a processing surface is formed in an approximately half circumference portion of a cylindrical rotating body.   6. A processing method for a forming tool according to claim 1, wherein a tip end portion is a ball end mill formed of a cubic boron nitride sintered body, and the cutting is compressed air containing a small amount of oil. A method for processing a forming tool, characterized by spraying a processing point.   7. The processing of a forming tool according to claim 6, wherein the tip end diameter of the ball end mill is 1 to 6 mm, the cutting is performed at a rotational speed of 10,000 to 20,000 rpm, and a feed rate of 1,000 to 2,000 mm / min. Method.   The processing method of the shaping | molding tool of Claim 6 or 7 which cuts with the process pitch 0.05-0.1mm, and shape | molds the free-form surface whose process surface roughness is Rz2-3 using the R shape.