JP2004262028A - Mold and method for manufacturing resin molded product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively provide a mold of which the life is extended by preventing formation of burrs while facilitating the venting of the gas in a cavity and further preventing the permanent deformation of a contact surface constituting a parting surface. <P>SOLUTION: In the mold 1 comprising a fixed mold 2 and a movable mold 3 both of which constitute a cavity 4 filled with a resin material A in a mold clamped state, shot peening treatment is applied to both of or either one of the contact surfaces 5a and 5b in the parting surface of the fixed mold 2 and the movable mold 3. By this method, a passage having a shape approximate to a labyrinth seal is formed to the parting surface 5 to ensure a venting passage not permitting a molten resin to pass. Further, a metal structure is improved by shot peening treatment and the permanent deformation of the contact surfaces 5a and 5b is prevented. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a molding die including a fixed die and a movable die that constitute a cavity filled with a molding material in a clamped state, and more particularly to a molding die used for molding a resin molded body.
[0002]
The molding die of the present invention can be used not only for resin but also for metal powder and molten metal as a molding material. Therefore, it can be used for metal moldings as well as resin moldings as moldings. Further, the molding die of the present invention can be used for both the injection molding method and the compression molding method as a molding method.
[0003]
[Prior art]
Hereinafter, a description will be given of a molding die used for injection molding of a resin molded body as an example (see Non-Patent Document 1).
[0004]
A molding die used for injection molding of a resin molded body generally adopts a structure as shown in FIG. After the resin A as a molding material is melt-plasticized by an injection unit (not shown), it is injected into the molding die 1 composed of the fixed die 2 and the movable die 3 at a high pressure from the nozzle 10. That is, the molten resin A injected from the nozzle 10 is filled into the cavity 4 formed by the fixed mold 2 and the movable mold 3 via the spool 11, and is taken out after being cooled and solidified. It becomes a resin molding.
[0005]
When filling the resin A in the molten state, the air staying in the cavity 4 and gas generated from the resin A in the molten state (hereinafter, simply referred to as “gas”) are discharged out of the cavity 4. is necessary. For this reason, generally, a method of providing a gas vent groove on one of the contact surfaces 5a and 5b of the respective dies 2 and 3 on the parting surface 5 which is the mating surface of the fixed die 2 and the movable die 3 is used. (For example, see Patent Documents 1 and 2). A method of providing a gas release mechanism inside the molding die 1 to remove gas from the cavity 4 has been proposed (for example, see Patent Document 3). However, since the structure of the molding die 1 is complicated, the molding die is complicated. The cost of the mold is high and is not common.
[0006]
Further, when the cavity 4 is filled with the resin A, an internal pressure is generated in the cavity 4. By applying a mold clamping force that overcomes the internal pressure to the molding die 1 by a mold clamping device (not shown), The resin is prevented from protruding from the parting surface 5. Since a large contact surface pressure acts on the contact surfaces 5a and 5b constituting the parting surface 5, heat treatment such as quenching for increasing hardness is performed on the contact surfaces 5a and 5b.
[0007]
Since the resin A in the molten state is injected into the cavity 4 at a high pressure, when a gap is formed in the parting surface 5, the resin A in the molten state protrudes from the parting surface 5 and generates so-called "burrs". It is known that, depending on molding conditions (temperature, pressure), for example, under high temperature and high pressure conditions, burrs are generated when the gap of the parting surface 5 exceeds 0.03 mm.
[0008]
As described above, the role of the parting surface 5 in the molding die 1 is extremely important. However, the molding die 1 becomes expensive due to heat treatment such as quenching as described above, Problems such as damage to the contact surfaces 5a and 5b constituting the parting surface 5 for tightening the molding die 1 and generation of so-called "striking" occur.
[0009]
Hereinafter, these problems will be described in more detail.
[0010]
(1) Hardness of Contact Surface Constituting Parting Surface In general, carbon steel for machine structure is used for the molding die 1 (fixed die 2 and moving die 3), and in Japan, S55C steel is usually used. Although it is used, use of low carbon steel such as S45C steel and S35C steel is desired for further cost reduction. However, if S55C steel is used as it is, its hardness is low, and settling occurs on the contact surface. Therefore, flame quenching is often performed to increase the hardness of the contact surface. However, it is difficult to increase the hardness by quenching with low carbon steel having a lower carbon content than S55C steel, and sufficient hardness cannot be obtained simply by flame quenching. Further, since the flame quenching of S55C steel is also performed manually, there is a problem that the quality is not stable due to uneven hardness due to the location of the quenched surface except for a skilled person. Further, in the flame quenching, it is difficult to quench only a necessary surface because masking is difficult, and quenching may be performed to a cavity surface constituting a cavity beyond a contact surface constituting a parting surface. In such a case, the transferability to the resin is changed by the curing of the cavity surface, which leads to an abnormality in the surface properties of the resin molded body.
[0011]
(2) Gas Release As described above, when filling the cavity with the resin, it is necessary to release the gas in the cavity to the outside of the cavity. Conventionally, as shown in FIGS. 2 and 3, a method of forming a gas vent groove 26 on a contact surface 25b constituting a parting surface 25 by machining, or as shown in FIG. A method is provided in which holes 47 are provided and gas is released through a porous metal 48 and a perforated metal 49.
[0012]
In the case of a mold used under standard molding conditions, in the method shown in FIG. 2 and FIG. 3, the depth of the gas vent groove provided on the contact surface constituting the parting surface is 0.1 mm for a crystalline material. It is required to be less than 015 mm and less than 0.03 mm for non-crystalline materials, and there is a problem that the cost is increased because precise machining is required. In the method shown in FIG. 4 as well, the molding die requires complicated machining, so that the cost is high and the holes such as perforated metal are easily clogged. .
[0013]
(3) Generation of burrs Burrs are generated when resin protrudes from gaps formed on the parting surface, and such gaps on the parting surface are formed inside the cavity when resin is filled into the cavity. This is caused by the opening of the molding die due to an increase in pressure (the contact surfaces of the fixed die and the moving die are separated from each other), and settling of the contact surface.
[0014]
Regarding the opening of the molding die, it is empirically known that burrs can be generated when the gap between the parting surfaces is about 0.003 mm as described above. Therefore, when a gas vent groove is provided on the contact surface constituting the parting surface, the upper limit value of the gap (0.003 mm) at which burrs occur when the contact surfaces are separated from each other even by a slight deformation of the molding die. Will be exceeded immediately. For this purpose, molding conditions such as reducing the injection pressure of the resin into the cavity as a whole, and reducing the injection pressure when approaching the completion time of filling the resin into the cavity set empirically, etc. In order to prevent the contact surfaces from separating from each other, a measure has been taken to limit the distance between the contact surfaces. However, when the injection pressure is reduced in this way, there is a problem that poor transfer, poor filling, deformation and the like of the resin molded body are likely to occur.
[0015]
Therefore, when it is not possible to take measures to limit such molding conditions, a method is adopted in which the mold clamping force is increased to increase the contact surface pressure of the contact surface constituting the parting surface. Therefore, there is a problem that it is necessary to increase the size of the molding machine, and both the equipment cost and the operation cost increase. Further, if an excessive contact surface pressure is applied to the contact surface, the contact surface may be damaged or set, thereby causing burrs. As a countermeasure for increasing the contact surface pressure of the contact surface constituting the parting surface, a method of quenching the contact surface using an alloy steel such as SCM440 in a molding die has been implemented. This is not an optimal method because it causes a significant increase in the cost of the mold.
[0016]
[Non-patent document 1]
Ayai Eiji, “Injection Molding Guide”, First Edition (Augmented and Revised Edition), Alpha Planning, April 1990 [Patent Document 1]
Japanese Patent No. 29994580 [Patent Document 2]
JP-A-7-329128 [Patent Document 3]
JP-A-7-40396
[Problems to be solved by the invention]
The present invention is intended to solve such a problem, and it is possible to prevent the generation of burrs while facilitating the degassing of the cavity, and further to prevent the contact surface constituting the parting surface from being set, thereby extending the life. An object of the present invention is to provide a mold that can be extended at a low cost.
[0018]
[Means for Solving the Problems]
The invention according to claim 1 is a molding die comprising a fixed die and a movable die which constitute a cavity filled with a molding material in a clamped state, wherein a party between the fixed die and the movable die is provided. The molding die is characterized in that both or one of the contact surfaces on the bearing surface has a large number of minute depressions.
[0019]
The invention according to claim 2 is the molding die according to claim 1, wherein the depth of the plurality of minute depressions is 0.003 to 0.03 mm.
[0020]
The invention according to claim 3 is the molding die according to claim 1 or 2, wherein the plurality of minute dents are formed by shot peening.
[0021]
The invention according to claim 4 is the molding die according to claim 3, wherein the shot used for the shot peening treatment contains silicon carbide.
[0022]
The invention according to claim 5 is the molding die according to claim 1 or 2, wherein the large number of minute depressions are formed by an etching process.
[0023]
The invention according to claim 6 is the molding die according to claim 1 or 2, wherein the plurality of minute dents are formed by a coating process.
[0024]
The invention according to claim 7 is the molding die according to any one of claims 1 to 6, which is used for molding a resin molded article.
[0025]
An eighth aspect of the present invention is a method for manufacturing a resin molded body, wherein the resin molded body is manufactured using the molding die according to the seventh aspect.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0027]
The present invention is characterized in that the contact surface constituting the parting surface of the molding die has a large number of minute depressions.
[0028]
These many small dents can be easily formed by, for example, performing shot peening, etching, or coating on the contact surface. Hereinafter, the shot peening process will be described in detail as an example.
[0029]
A small-diameter shot is ejected at high speed and collides with both or any one of the contact surfaces of the parting surfaces of the fixed die and the movable die that constitute the molding die.
[0030]
As a result, a large number of minute depressions are formed on the surface of the contact surface by the collision of the shot. When a molding die having a contact surface in which a large number of micro-dents are formed is fitted (that is, when the contact surfaces of a fixed die and a movable die are brought into contact with each other), a large number of micro-dents are connected to form a parting surface. Thus, a passage having a shape similar to the labyrinth seal is formed. For this reason, a passage for degassing is secured, and gas can easily pass therethrough, but resin in a molten state cannot pass through. Therefore, it is possible to easily degas the cavity and to prevent generation of burrs. It becomes.
[0031]
Further, by shot collides with the contact surface, the contact surface of the shot has collided shot kinetic energy is converted into heat energy is heated, the temperature of the vicinity of the surface temporarily exceeds A ₃ transformation point. For this reason, heating, peening, and tempering are repeatedly performed by the collision of shots on the surface of the contact surface. As a result, in addition to the work hardening of the surface due to the generation of residual compressive stress due to shot peening, the metal structure near the surface is improved, so that the fatigue strength is improved and the contact surface is prevented from settling (Japanese Patent No. 1594395). reference).
[0032]
Therefore, in order to obtain the effect of the labyrinth seal, shot peening may be performed only on the contact surface of either the fixed die or the movable die. It is preferable to perform shot peening on both contact surfaces of the mold and the movable mold.
[0033]
It is preferable that the depth of the minute dent formed by the shot peening process is 0.003 to 0.03 mm. If the thickness is less than 0.003 mm, the degassing effect decreases. If the thickness exceeds 0.03 mm, the effect of the labyrinth seal decreases, and the resin in the molten state easily penetrates into the fine dents (recesses), and burrs may be formed. Is increased.
[0034]
As a result of the work hardening and the improvement of the metal structure by the shot peening treatment, the material of the forming die (fixed die and movable die) is S45C steel having a low carbon content in addition to the conventional S55C steel. , S35C steel, etc. can be used, and carbon steel for machine structural use having a C content of 0.61% by mass or less can be used.
[0035]
As the shot used for the shot peening treatment, metal powder or ceramic powder may be used, but those having hardness higher than the material of the contact surface of the molding die are desirable, and metal powder is steel powder, and ceramic powder is alumina. Powder or silicon carbide powder may be used. Among them, silicon carbide powder is particularly preferable since it can leave carbon content on the surface of the contact surface and impart lubricity.
[0036]
It is recommended that the diameter of the shot be 40 to 200 μm in average diameter and that the injection speed of the shot be 100 m / s or more. Within this range, the depth of the fine dent formed on the contact surface after the shot peening treatment May be adjusted appropriately so as to be 0.003 to 0.03 mm. The above shot size and range of the injection rate is recommended, by performing shot peening treatment in this range, in addition to work hardening of the surface by application of residual compressive stress, the temperature in the vicinity of the surface of the contact surface A ₃ transformation This is because the effect of improving the metallographic structure can be obtained.
[0037]
Further, when it is necessary to prevent the cavity surface and the like from being cured, it can be easily dealt with by performing simple masking, for example, by sticking several layers of adhesive gum tape on the cavity surface and the like.
[0038]
In the above-described embodiment, shot peening processing has been described as an example of a method for forming minute depressions on the contact surface, but the method is not limited to this. For example, by etching the contact surface with an acidic solution or the like, a large number of minute depressions can be formed. Alternatively, the contact surface may be irradiated with metal ions by an ion plating method or the like to form a porous metal film, that is, by performing a so-called coating process, whereby a large number of minute depressions can be formed on the contact surface. Therefore, in the etching process and the coating process, although a settling prevention effect such as a shot peening process cannot be expected, similarly to the shot peening process, a passage having a shape similar to a labyrinth seal is formed on the parting surface. Burrs can be prevented from occurring while facilitating degassing of the cavity.
[0039]
【Example】
A test piece of a molding die was prepared using SC45C steel, and silicon carbide powder having an average diameter of 50 μm was sprayed onto the surface of the test piece at a compressed air pressure of 0.5 MPa so that a shot speed of 200 m / s was obtained. Peening treatment was performed. FIG. 5 shows the hardness distribution near the surface of the test piece after the shot peening treatment. As shown in this figure, the hardness of the base material before the treatment was Hv300, but the hardness of the surface after the treatment increased to Hv430. When SC35C steel was used, although not shown, the hardness of the base material before the treatment was Hv200, but the hardness of the surface after the treatment increased to Hv300. Thus, by applying the present invention, it was confirmed that hardening treatment can be performed even on low carbon steel that cannot be hardened by quenching.
[0040]
FIG. 6 shows the state near the surface of the test piece before and after the shot peening process. (A) is a comparative example (before processing), and (b) is an example of the present invention (after processing). As can be seen by comparing FIGS. 6A and 6B, in the example of the present invention, the metal structure near the surface is denser than that in the comparative example, and a concave portion is formed on the surface. The depth of the recess was about 7 μm (0.007 mm), and the width was 10 to 20 μm.
[0041]
Therefore, by applying the shot peening process to at least one of the contact surfaces of the fixed mold and the movable mold made of S45C steel, a passage having a shape similar to a labyrinth seal in which the minute recesses are continuous on the parting surface is formed. Thus, it is apparent that the effect of preventing the resin from passing while securing the gas vent passage is exhibited.
[0042]
Although low-carbon steel was used in the examples, it goes without saying that the present invention can be applied to materials for molds other than low-carbon steel, and the material of the mold may be appropriately selected according to the application. .
[0043]
【The invention's effect】
As described above, according to the present invention, it is possible to prevent the occurrence of burrs while facilitating the degassing of the cavity, and further to prevent the contact surface constituting the parting surface from being set, thereby extending the life. A molding die can be provided at low cost.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing a structure of a molding die used for injection molding of a resin molded body.
FIGS. 2A and 2B are schematic cross-sectional views showing a conventional example in which a gas vent groove is formed on a parting surface, wherein FIG. 2A shows details of an entire mold, and FIG. 2B shows details of an X part of FIG.
FIG. 3 is a schematic sectional view showing another conventional example in which a gas vent groove is formed on a parting surface.
FIG. 4 is a schematic sectional view showing a conventional example in which a porous metal and a perforated metal are mounted in a mold.
FIG. 5 is a graph showing the relationship between the depth from the test piece surface and the hardness Hv after the shot peening treatment.
FIGS. 6A and 6B are cross-sectional views showing a state near the surface of a test piece before and after a shot peening treatment. FIG. 6A is a comparative example (before treatment), and FIG. 6B is a present invention example (after treatment).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Molding mold 2 ... Fixed mold 3 ... Moving mold 4 ... Cavities 5, 25 ... Parting surfaces 5a, 5b, 25b ... Contact surface 10 ... Nozzle 11 ... Spool 26 ... Gas vent groove 47 ... Gas vent hole 48 ... porous metal 49 ... perforated metal A ... resin

Claims (8)

In a molding die composed of a fixed die and a movable die constituting a cavity filled with a molding material in a clamped state, both or both of the contact surfaces of the fixed die and the movable die on the parting surface. A molding die, characterized in that either one of the molding dies has a large number of minute depressions. The molding die according to claim 1, wherein the depth of the plurality of minute depressions is 0.003 to 0.03 mm. The molding die according to claim 1, wherein the plurality of minute dents are formed by a shot peening process. The molding die according to claim 3, wherein the shot used for the shot peening treatment contains silicon carbide. The molding die according to claim 1, wherein the plurality of minute dents are formed by an etching process. The molding die according to claim 1, wherein the plurality of minute depressions are formed by a coating process. The molding die according to any one of claims 1 to 6, which is used for molding a resin molded body. A method for producing a resin molded article, comprising producing a resin molded article using the molding die according to claim 7.

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