Die for extrusion molding and method for producing same

Abstract

Provided is a method for producing a die for extrusion molding that is provided with a discharge port formation part for forming a discharge port, the method comprising: a formation step S102 for forming the base material of the discharge port formation part into a prescribed shape; and a build-up step S104 for forming a build-up layer constituting at least an end region on the discharge-port side of an inner wall surface of a flow passage by means of laser cladding on the surface of the base material that has been processed into a prescribed shape.

Description

Extrusion die and method of manufacturing the same

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to extrusion dies and methods of making the same.

[0002] Patent Document 1 discloses an extrusion die for use in an extrusion molding device. Patent Document 1 discloses that, in general, the extrusion die is subjected to a surface treatment by electroplating, such as hard chrome plating, at least on the resin flow path, in order to improve rust resistance, abrasion resistance, and mold releasability.

[0003] Japanese Patent Application Laid-Open No. 2000-071311

[0004] The plating described in Patent Document 1 often results in the formation of holes such as pits and pinholes. Holes present at least in the end region of the flow path on the discharge port side must be repaired, but repairing them takes time and effort, which increases the manufacturing cost of the extrusion molding die.

[0005] The present disclosure has been made in this situation, and one exemplary purpose of an embodiment thereof is to provide a technique that can reduce the manufacturing costs of extrusion molding dies.

[0006] In order to solve the above problems, a manufacturing method according to one aspect of the present disclosure is a manufacturing method for an extrusion molding die having an outlet forming portion that forms an outlet, and includes forming a base material of the outlet forming portion into a predetermined shape, and forming a buildup layer by laser cladding on the surface of the base material that has been processed into the predetermined shape, the buildup layer constituting at least the end region of the inner wall surface of the flow path on the outlet side.

[0007] Another aspect of the present disclosure is an extrusion die including a discharge port forming portion that forms a discharge port for a molten resin, the discharge port forming portion including a base material and a buildup layer of a cobalt-based alloy that is built up on the surface of the base material and forms at least an end region of a flow path surface on the discharge port side.

[0008] Any combination of the above components, or mutual substitution of the components or expressions of the present disclosure between methods, devices, systems, etc., are also valid aspects of the present disclosure.

[0009] According to the present disclosure, it is possible to provide a technique that can reduce the manufacturing costs of extrusion molding dies.

[0010] It is a schematic diagram showing a schematic configuration of an inflation molding apparatus. It is a cross-sectional view of a die according to an embodiment. It is an enlarged cross-sectional view showing the periphery of the discharge port of the die. It is a schematic manufacturing process diagram showing a manufacturing method of the die of Figure 1. It is a schematic diagram showing the state of the overlay process of Figure 4. It is a schematic manufacturing process diagram showing a manufacturing method of a die of a comparative example.

[0011] Hereinafter, identical or equivalent components, parts, and steps shown in each drawing will be assigned the same reference numerals, and redundant explanations will be omitted where appropriate. Furthermore, the dimensions of the parts in each drawing will be enlarged or reduced as appropriate to facilitate understanding. Furthermore, some parts that are not important for explaining the embodiments will be omitted from the drawings.

[0012] In the embodiments, the case where the extrusion molding die is a round die, i.e., a die for an inflation molding apparatus, will be described as an example, but the technical concept of the embodiments can also be applied to T-dies and other extrusion molding dies to the extent that it is not inconsistent.

[0013] 1 is a schematic diagram showing the general configuration of an inflation molding apparatus 1 including an extrusion die 2 (hereinafter simply referred to as "die 2") according to an embodiment. The inflation molding apparatus 1 includes the die 2, a cooling device 3, a pair of stabilizers 4, and a take-up machine 5.

[0014] Molten resin is supplied to the die 2 from an extruder (not shown). The resin is extruded from a ring-shaped discharge port 2a formed in the die 2. Air is ejected into the extruded resin from an air ejection port 2b formed in the center of the die 2. This forms a thin resin film (hereinafter also referred to as a "bubble") that expands into a tubular shape. A cooling device 3 is disposed above the die 2 and blows cooling air onto the bubble to cool it.

[0015] A pair of stabilizer plates 4 is disposed above the cooling device 3 and guides the bubble to a take-up machine 5. The take-up machine 5 is disposed above the stabilizer plates 4. The take-up machine 5 includes a pair of pinch rolls 5a. The pair of pinch rolls 5a are driven to rotate by a motor (not shown), and pull up the guided bubble while folding it flat. A winder 6 winds up the folded resin film to form a film roll body 7.

[0016] 2 is a vertical cross-sectional view of the die 2. The die 2 includes a die body 10 and a discharge port forming portion 12 placed on the upper surface of the die body 10.

[0017] The configuration of the die body 10 is not particularly limited. The die body 10 has a flow path 50 for the resin. The flow path 50 of the die body 10 is connected to a flow path 18 (described later) of the discharge port forming portion 12. An optional coating is applied to the inner wall surface 50a of the flow path 50 of the die body 10. The optional coating may be hard chrome plating.

[0018] The outlet forming portion 12 forms the outlet 2a. The outlet forming portion 12 includes an inner circumferential member 14 and an outer circumferential member 16. The inner circumferential member 14 is a cylindrical member. The outer circumferential member 16 is an annular member that surrounds the inner circumferential member 14. A flow path 18, which is a cylindrical gap, is formed between the inner circumferential member 14 and the outer circumferential member 16. The molten resin flows upward through the flow path 18 and is extruded from the outlet 2a, which is the upper end opening of the flow path 18.

[0019] The inner peripheral member 14 includes a base material 20 and a buildup layer 22 as a coating layer formed on the surface of the base material 20. The base material 20 is made of a metal such as S45C. In this embodiment, the buildup layer 22 is formed on the entire outer peripheral surface 20a of the base material 20 and constitutes the inner wall surface 18a on the inner peripheral side of the flow path 18.

[0020] The outer peripheral member 16 includes a base material 30 and a buildup layer 32 as a coating layer formed on the surface of the base material 30. The base material 30 is formed of a metal such as S45C, similar to the base material 20. In this embodiment, the buildup layer 32 is formed on the entire inner peripheral surface 30a of the base material 30 and constitutes an inner wall surface 18b on the outer peripheral side of the flow path 18.

[0021] The buildup layers 22 and 32 are each formed by laser cladding. Generally, the buildup layer 22 formed by laser cladding is relatively thick, and is thicker than, for example, hard chrome plating.

[0022] The buildup layers 22, 32 are formed of a material different from the base materials 20, 30, respectively, and are preferably formed of a material having relatively high toughness. The buildup layers 22, 32 may be formed of a material having higher toughness than hard chrome plating. The buildup layers 22, 32 may be formed of a cobalt-based alloy, which is a material having relatively high toughness, such as Stellite 6 (registered trademark).

[0023] 3 is an enlarged cross-sectional view showing the vicinity of the discharge port 2a in FIG. 2. The edges 22b, 32b of the buildup layers 22, 32 on the discharge port 2a side are chamfered. In other words, the buildup layers 22, 32 have chamfered edges on the discharge port 2a side. The chamfering may be a C-chamfer as shown in the figure, an R-chamfer, or any other type of chamfer.

[0024] From the viewpoint of suppressing the occurrence of so-called "eye mucus," the edge portions 22b and 32b are sharp, in other words, the chamfering of the edge portions 22b and 32b is small, and further in other words, the emission line width W of the edge portions 22b and 32b is small. ２２ , W ３２ However, if the edge portions 22b, 32b are too sharp, chipping of the edge portions 22b, 32b will occur more frequently during cleaning of the die 2, which is not economical. This must be taken into consideration when chamfering the edge portions 22b, 32b.

[0025] When the buildup layer 22 is formed of a cobalt-based alloy having relatively high toughness, such as Stellite 6 (registered trademark), the bright line width W of the edge portions 22b and 32b is ２２ , W ３２ In this case, chipping of the edge portions 22b and 32b can be suppressed, and the generation of eye mucus can also be suppressed.

[0026] The edges 20b, 30b of the base materials 20, 30 on the outlet 2a side may be chamfered as shown by the broken lines, in which case buildup can be easily formed around the edges 20b, 30b.

[0027] Next, a method for manufacturing the die 2 will be described.

[0028] The manufacturing method of the die 2 includes a step of manufacturing components of the die 2, such as the die body 10 and the discharge port forming portion 12, a step of assembling the die 2 by combining the manufactured components, and a step of inspecting the appearance, function, etc. of the assembled die 2. The assembling step can be performed using a known assembly technique. The inspection step can be performed using a known inspection technique.

[0029] 4 is a schematic manufacturing process diagram showing the steps of manufacturing the discharge port formation portion 12. The steps of manufacturing the discharge port formation portion 12 include a forming step S102, a deposition step S104, a cutting step S106, a grinding step S108, and an inspection step S110.

[0030] Each step will be described below using the inner circumferential member 14 as an example. The outer circumferential member 16 may be manufactured in the same manner as the inner circumferential member 14.

[0031] In the forming step S102, the base material 20 is formed into a predetermined shape by, for example, lathe processing. The base material 20 has an outer shape obtained by excluding the thickness of the buildup layer 22 from the inner circumferential member 14 at the location where the buildup layer 22 is to be formed.

[0032] In the build-up process S104, a build-up layer 22 is formed on the surface of the base material 20 by laser cladding. FIG. 5 is a schematic diagram showing the build-up process S104. In this example, the build-up layer 22 is formed on the outer peripheral surface 20a of the base material 20 using a build-up device 40. The build-up device 40 includes a nozzle 44 that supplies the build-up material 42 and a head 48 that irradiates the build-up material 42 with a laser beam 46 to heat the build-up material 42. The build-up material 42 may be a powder of a cobalt-based alloy such as Stellite 6 (registered trademark). The build-up layer 22 is formed by supplying the build-up material 42 from the nozzle 44 while melting the build-up material 42 with the laser beam 46 irradiated from the head 48. The build-up layer 22 is formed continuously over the entire area where the build-up layer 22 is to be formed by continuously changing the relative positions of the build-up material 42 supply position and the laser beam 46 irradiation position relative to the base material 20.

[0033] 4 , in the cutting step S106, the surface of the buildup layer 22 formed in the buildup step S104 is cut so that the inner circumferential member 14 has a generally desired shape. In the cutting step S106, the surface of the buildup layer 22 may be cut by lathe processing.

[0034] In the grinding step S108, the surface of the buildup layer 22 cut in the cutting step S106 is mechanically ground so as to form the desired shape of the inner circumferential member 14. When a predetermined surface roughness is required for the inner wall surface 18a of the flow path 18, the surface of the buildup layer 22 is mechanically ground so as to obtain the inner wall surface 18a with that surface roughness.

[0035] In the grinding step S108, the edge portion 22b of the buildup layer 22 on the outlet 2a side is chamfered. In other words, a chamfer is formed on the edge of the buildup layer 22 on the outlet 2a side. When the buildup layer 22 is made of a cobalt-based alloy such as Stellite 6 (registered trademark), the edge portion 22b has an emission line width W of 50 μm or more and 100 μm or less. ２２ It may be processed to have the following structure.

[0036] In the inspection step S110, the inner circumferential member 14 is inspected. For example, in the inspection step S110, it is inspected whether the dimensions of each part of the inner circumferential member 14 are within an allowable range.

[0037] For example, in the inspection process S110, the following are inspected: (i) the inner surface 22a of the buildup layer 22 constituting the inner wall surface 18a of the flow path 18 is free of holes of a predetermined size (e.g., 0.2 mm in diameter) or larger; and (ii) the end region 22a_1 of the inner surface 22a of the buildup layer 22 constituting the end region 18a_1 on the outlet 2a side of the inner wall surface 18a of the flow path 18 is free of holes. This is because the presence of holes in the end region 22a_1 of the buildup layer 22 constituting the end region 18a_1 of the inner wall surface 18a of the flow path 18 may result in a die line on the molded product. Furthermore, the presence of holes of a predetermined size or larger in the upstream region 22a_2 of the buildup layer 22 constituting the upstream region 18a_2 of the inner wall surface 18a of the flow path 18 may result in a die line on the molded product. The end regions 18a_1, 22a_1 may be, for example, regions 10 mm from the outlet 2a. The end regions 18a_1 and 22a_1 may be determined in advance through experiments or the like.

[0038] In addition, when manufacturing the outer peripheral member 16, the "inner peripheral member 14", "inner wall surface 18a", "end region 18a_1", "upstream region 18a_2", "base material 20", "outer peripheral surface 20a", "buildup layer 22", "end region 22a_1", "upstream region 22a_2", "edge portion 22b", and "bright line width W ２２ " are respectively referred to as "outer peripheral member 16", "inner wall surface 18b", "end region 18b_1", "upstream region 18b_2", "base material 30", "inner peripheral surface 30a", "buildup layer 32", "end region 32a_1", "upstream region 32a_2", "edge portion 32b", and "bright line width W ３２ " should be read as "

[0039] Next, a manufacturing method according to a comparative example to be compared with the embodiment will be described.

[0040] 6 is a schematic diagram showing the steps of manufacturing the ejection orifice formation portion according to the comparative example. The steps of manufacturing the ejection orifice formation portion according to the comparative example include a forming step S202, a rough polishing step S204, a lapping step S206, a pre-plating inspection step S208, a pre-plating polishing step S210, a plating step S212, a post-plating polishing step S214, and an inspection step S216.

[0041] The forming step S202 corresponds to the forming step S102.

[0042] In the rough polishing step S204, the outer peripheral surface of the base material of the inner peripheral member is buffed, i.e., polished by hand, to remove machining marks that have been left on the outer peripheral surface of the base material in the forming step S202. Hand polishing may distort the shape of the outer peripheral surface of the base material. The same applies to the steps described below.

[0043] In the manufacturing method of this embodiment, a relatively thick buildup layer 22 is formed by laser cladding, and the buildup layer 22 absorbs the effects of machining marks on the outer peripheral surface 20a of the base material 20. Therefore, in the manufacturing method of this embodiment, a step equivalent to the rough polishing step S204 is not required.

[0044] In the lapping step S206, the upper surface of the die body 10 and the lower surface of the discharge port forming portion 12 are finished flat to prevent resin from leaking between the die body 10 and the discharge port forming portion 12. In this embodiment, since it is sufficient to finish them flat in the grinding step S108, a step corresponding to the lapping step S206 is not required.

[0045] In the pre-plating inspection step S208, it is inspected whether the dimensions of the base material are within the allowable range.

[0046] In the pre-plating polishing step S210, the outer peripheral surface of the base material is buffed, i.e., hand-polished, so as to meet a standard value for surface roughness, since a rough surface of the base material is prone to pits and pinholes.

[0047] In the plating step S212, the base material is plated with hard chrome.

[0048] In the post-plating polishing step S214, the surface of the hard chrome plated material is buffed, i.e., hand polished.

[0049] The inspection step S216 corresponds to the inspection step S110.

[0050] Next, the effects achieved by the embodiment will be described.

[0051] Hard chrome plating, such as that used in the comparative example, often produces pits and pinholes. Even if certain pits are removed by scraping the surface of the hard chrome plating, scraping the surface evenly often exposes other pits and pinholes. Furthermore, the process of scraping the hard chrome plating until the pits and pinholes are no longer exposed can result in the hard chrome plating becoming thinner than the allowable thickness, which requires re-plating. In contrast, according to the present embodiment, the buildup layers 22, 32 constituting the inner wall surfaces 18a, 18b of the flow passage 18 are formed by laser cladding. The buildup layers 22, 32 formed by laser cladding are less likely to produce holes equivalent to the pits and pinholes found in hard chrome plating. Furthermore, because the buildup layers 22, 32 formed by laser cladding are relatively thick, there is a large repair margin, and therefore, even if holes exist on the surfaces of the buildup layers 22, 32, they can be easily repaired within the repair margin.

[0052] The outer peripheral surface of the inner peripheral member 14 and the inner peripheral surface of the outer peripheral member 16 constitute the flow path 18, and therefore require high shape precision. In the manufacturing method according to the comparative example, the outer peripheral surface of the inner peripheral member 14 and the inner peripheral surface of the outer peripheral member 16 are formed with hard chrome plating. Because hard chrome plating is relatively brittle, mechanical grinding of the hard chrome plating can result in cracks or chips at the edges. Therefore, in the post-plating polishing step S214, the hard chrome plating is buffed, i.e., hand-polished. Furthermore, because pits and pinholes are likely to occur on the base material on which the hard chrome plating is formed if its surface is rough, it is also buffed, i.e., hand-polished, in the pre-plating polishing step S210. Furthermore, buffing, i.e., hand-polished, is also performed in the post-plating polishing step S214. Therefore, in the manufacturing method according to the comparative example, it is difficult even for an experienced worker, and even more so for an unskilled worker, to manufacture the inner peripheral member 14 and the outer peripheral member 16 with high shape precision. In contrast to this, in the present embodiment, the surface of the buildup layer 22, which is the outer peripheral surface of the inner circumferential member 14, and the surface of the buildup layer 32, which is the inner peripheral surface of the outer circumferential member 16, are mechanically ground. Therefore, the inner circumferential member 14 and the outer circumferential member 16 can be manufactured with high shape accuracy regardless of the level of skill.

[0053] In this embodiment, the buildup layer 22 is formed of a cobalt-based alloy such as Stellite 6 (registered trademark), and the emission line width W ２２ , W ３２ The thickness is 50 μm or more and 100 μm or less. In this case, chipping of the edge portions 22b, 32b is suppressed and the generation of eye discharge is suppressed. To prevent the generation of eye discharge, the bright line width can be narrowed, for example, to 20 μm or less. However, as mentioned above, there are concerns about edge chipping during cleaning, and the cost of maintaining precision increases, so it is preferable to ensure a bright line width of 20 μm or more. In contrast, in the manufacturing method of the comparative example, the edge portions are made of chrome plating, which has relatively low toughness, so in order to suppress chipping of the edge portions, the bright line width of the edge portions needs to be finished to 150 μm or more. Therefore, compared to the present embodiment, eye discharge is more likely to occur.

[0054] The present disclosure has been described above based on the embodiments. These embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of the components and processing steps, and that such modifications are also within the scope of the present disclosure.

[0055] (Variation 1) Although not specifically mentioned in the embodiment, the buildup layer 22 by laser cladding may be formed at least in the end region 20a_1 on the discharge port 2a side of the outer peripheral surface 20a of the base material 20. In other words, the buildup layer 22 by laser cladding may be formed so as to constitute at least the end region 18a_1 on the discharge port 2a side of the inner peripheral side of the inner wall surface 18a of the flow path 18. Therefore, for example, the buildup layer 22 by laser cladding may be formed only in the end region 20a_1 of the outer peripheral surface 20a of the base material 20. In this case, another coating, for example, hard chrome plating, may be applied to the upstream region 20a_2.

[0056] Similarly, the buildup layer 32 by laser cladding may be formed at least in an end region 30a_1 on the discharge port 2a side of the inner circumferential surface 30a of the base material 30. In other words, the buildup layer 32 by laser cladding may be formed so as to constitute at least an end region 18b_1 on the discharge port 2a side of the inner wall surface 18b on the outer circumferential side of the flow path 18. Therefore, for example, the buildup layer 32 by laser cladding may be formed only in the end region 30a_1 of the inner circumferential surface 30a of the base material 30. In this case, another coating, for example, hard chrome plating, may be applied to the upstream region 30a_2.

[0057] Any combination of the above-described embodiments and modifications is also useful as an embodiment of the present disclosure. A new embodiment resulting from the combination combines the effects of the combined embodiments and modifications. It will also be understood by those skilled in the art that the functions to be performed by each constituent element described in the claims can be realized by each component shown in the embodiments and modifications, either individually or in combination.

[0058] FIELD OF THE DISCLOSURE The present disclosure relates to extrusion dies and methods of making the same.

[0059] 2 Die, 2a Discharge port, 12 Discharge port forming portion, 14 Inner peripheral member, 16 Outer peripheral member, 18 Flow path, 18a, 18b Inner wall surface, 20 Base material, 22 Overlay layer, 30 Base material, 32 Overlay layer.

Claims

1. A method for manufacturing an extrusion die having an outlet forming portion that forms an outlet, comprising: forming a base material for the outlet forming portion into a predetermined shape; and forming a build-up layer that constitutes at least the end region of the inner wall surface of a flow path on the outlet side by laser cladding on a surface of the base material that has been machined into the predetermined shape.

2. The method of claim 1, further comprising mechanically grinding the surface of the buildup layer.

3. The method for manufacturing an extrusion die as described in claim 2, wherein the buildup layer is a layer of a cobalt-based alloy, and mechanical grinding of the surface of the buildup layer includes finishing the edge portion of the buildup layer on the discharge port side to a bright line width of 20 μm or more and 100 μm or less.

4. An extrusion molding die having a discharge port forming portion that forms a discharge port for a molten resin, the discharge port forming portion including: a base material; and a build-up layer of a cobalt-based alloy that is built up on a surface of the base material and forms at least an end region of a flow path surface on the discharge port side.

5. An extrusion molding die as described in claim 4, wherein the edge portion of the buildup layer on the discharge port side has a bright line width of 100 μm or less.

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