JP2000301542A - Heat conductive composite mold and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase an inner cooling effect with a low cost by forming a heat conductive layer of copper or copper alloy having specific heat conductivity at all or partial non-operating surface of a mold of steel at the surface by high energy overlay welding. SOLUTION: A heat conductive layer having heat conductivity of 250 W/m/K or above is formed in a predetermined thickness on a non-operating surface of a mold of steel at an operating surface by high energy overlay welding. Since smooth overlay is difficult due to large thermal conductivity of pure copper when two or above layers are overlaid to increase a thickness of the layer, a matrix is preheated to about 700 deg.C or above and overlaid. However, since the matrix is heated to a tempering temperature or above and softened, it is necessary to heat treat to re-quench and temper it. When the overlay welding of the pure copper is conducted, for example, by enhancing a density of an arc having a high energy density by a pulse power source, welding of no defect can be performed even when a preheating temperature of the matrix is lowered as compared with the tempering temperature. Thus, the mold having high internal heat conductivity and a good cooling efficiency can be easily, inexpensively provided, and an operating efficiency of molding can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for casting molten metal or a mold for molding various materials such as molten plastic, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, steels such as hot die steel and stainless steel and cast iron are used as metal materials used at high temperatures such as a casting mold for molten metal and a molding mold for forming plastics. In addition, copper alloys having higher thermal conductivity than these have been used as integral parts.

However, since the heat conductivity of steel or cast iron is not always high, the temperature in the vicinity of the molding surface of the mold rises during the molding operation, and the temperature is generated in the mold depending on the shape and structure of the mold. Due to the large uneven temperature, the mold is deformed and abrasion increases. Conventionally, it has been difficult to increase the number of molding cycles per unit time due to such a rise in the temperature of the mold. On the other hand, a mold of a copper alloy having high thermal conductivity has a problem that the wear is large and the life is short because the strength is low.

Therefore, the applicant has disclosed a method of manufacturing a high heat conductive composite mold in which the above-mentioned disadvantage is improved by increasing the heat conductivity by bonding copper or the like to the back surface of the work surface of the mold (Japanese Patent No. No. 2642661). These joining methods include casting and joining molten copper or the like to the back surface of the working surface of the mold, joining steel and copper or the like with copper brazing interposed, or powdering copper or the like by HIP. (High-temperature isostatic press) to form a copper layer by bonding. Since these methods can easily form a thick heat conductive layer, they have good thermal conductivity and are effective in preventing the mold from overheating.

[0005]

However, in the above-mentioned melting method, an embrittlement layer may be generated in a diffusion layer at a joint between steel and copper or the like, and peeling is likely to occur at the joint during cooling after joining. There was a problem. Also, when copper and the like are melt-bonded to the work surface of steel that has been quenched and tempered, the mold is tempered and softened by preheating at the time of joining and temperature rise at the time of joining. did not become. Also during this reheat treatment, there is a problem that the material may be separated from the embrittlement layer due to a difference in expansion between steel and copper.

[0006] On the other hand, when joining is performed using copper brazing, there is a disadvantage that the thermal conductivity between steel and copper or the like is reduced and the cooling effect is reduced, and the HIP method has a problem that the cost is increased.

[0007] The heat conductive layer can be formed by overlay welding. However, in ordinary overlay welding, it is difficult to form a molten pool of a material having high thermal conductivity such as copper. It was difficult to assemble and obtain a thick heat conductive layer. In this case, in order to form a thick build-up layer, it is usual to preheat the base material of the working surface to 700 ° C. or more and weld it. However, the base material tempered at 500 to 700 ° C. is heated to 700 ° C.
Preheating as described above lowers the hardness, so that re-quenching / tempering treatment is required after welding. At the time of this reheat treatment, there were problems such as peeling of the bonding surface or distortion of the mold.

Accordingly, the present invention has a large heat conducting layer, has a large cooling effect, and prevents the formation of an embrittlement layer at the joint between steel and copper as much as possible, thereby causing poor joint at the joint surface. It is an object of the present invention to provide a method of manufacturing a high heat conductive composite mold which eliminates heat treatment and eliminates the need for heat treatment such as re-quenching after the joining treatment.

As described above, by increasing the thermal conductivity inside the mold by increasing the thickness of the heat conducting layer, increasing the internal cooling effect and reducing the temperature unevenness inside the mold, the deformation of the mold can be suppressed. The development of heat cracks is suppressed, and the life of the mold is improved. In addition, the molding efficiency can be improved by shortening the product molding cycle time. Further, the mold of the present invention can be provided at a lower cost than the HIP method or the like.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, a highly heat conductive composite mold and a method of manufacturing the same according to the present invention include:
A heat conductive layer of copper or a copper alloy having a heat conductivity of 250 W / m / K or more is formed by high-energy overlay welding.

It is preferable that the work surface is made of quenched and tempered heat-treated steel, and the heat conductive layer is formed of pure copper having a thickness of 10 mm or more by high-energy overlay welding. It is desirable that the pure copper has a purity of 99.99% Cu or more from the viewpoint of thermal conductivity.

Further, the high energy overlay welding is performed by using a pulse M
It is desirable to perform IG welding, and the working surface of the mold is made of steel that has been tempered and heat-treated at a temperature of 500 ° C. or more after quenching, and is preheated to the tempering temperature or less at the time of the overlay welding. It is desirable to perform high-energy overlay welding while maintaining the temperature of the work surface at or below the tempering temperature.

Here, the work surface of the mold means not only a surface but also a portion of the mold including the work surface (hereinafter also referred to as a base material).
Are collectively referred to. The non-work surface refers to a surface such as a back surface or a side surface with respect to a mold surface of the base material. In addition, the heat conductive layer refers to a layer for transferring heat of a base material formed of a material having higher thermal conductivity than the base material and uniformly cooling the base material.

According to the present invention, the cooling efficiency of the mold is increased by forming high-purity pure copper having a high thermal conductivity on the heat conductive layer to a thickness of 10 mm or more by high energy overlay welding. That is, copper is preferable as the heat conductive layer because of its high thermal conductivity, and pure copper of 99.99% Cu or more is desirable for further improving the cooling efficiency. Further, if the thickness of the heat conductive layer is small, heat is not uniformly transferred and the cooling efficiency is reduced.
mm or more is required.

As a method for forming such a pure copper heat conductive layer,
It is not so difficult to weld only one layer of pure copper to steel by a general welding method (MIG method, TIG method, powder overlay method, etc.), and it is also possible to perform overlay welding without preheating. .

However, when two or more layers are clad in order to increase the thickness of the cladding layer, when pure copper is further clad on a metal having a high thermal conductivity such as 250 W / m / K, for example, pure copper. However, since the thermal conductivity of pure copper is large, it is difficult to form a molten pool and a smooth build-up cannot be performed. For this reason, it is difficult to perform resurfacing without preheating by ordinary overlay welding.
It is difficult to form a heat conductive layer as thick as 0 mm.
For this purpose, it is usual to preheat the base material to 700 ° C. or higher and build up the weld by welding.

However, when preheating to 700 ° C. or more, the base material that is usually tempered and heat-treated at 500 to 700 ° C. is heated to a temperature equal to or higher than the tempering temperature and softens, so that re-quenching and tempering heat treatment is required. Become. Then, at the time of this re-heat treatment, there were problems such as peeling of the bonding surface or distortion of the mold.

According to the present inventors, according to the high-energy-density welding of pure copper overlay welding, for example, welding in which the arc is densified using a pulse power source, the preheating temperature of the base material is set to the tempering temperature (500%). -700 ° C), and the temperature rise of the base metal during overlay welding and tempering temperature (500-700 ° C)
It has been found that even if the welding is performed at a lower temperature, it is possible to achieve a sound welding without any defect and that the above problem is solved. This high-energy welding may be used only for the second and subsequent layers.

If the holding temperature during the overlay welding is lower than the tempering temperature in this manner, the hardness of the steel base material does not decrease even when the thermal conduction layer of pure copper is overlaid, and the conventional welding method is used. Since a reheat treatment after the overlay welding is basically not required, peeling of the heat conductive layer and distortion of the mold are reduced. The mold after the overlaying is usually subjected to a heat treatment for removing the residual stress to remove the residual stress. However, since the heat treatment for removing the distortion is performed at a temperature equal to or lower than the tempering temperature, there is no reduction in hardness.

Further, according to the high energy density welding, it is easy to build up the return layer even with preheating at a temperature lower than the tempering temperature, and it is possible to easily obtain a thick heat conductive layer having good heat conduction.
It was found that the joint surface of the composite mold material obtained in this way was good and had a degree of joint that allows heat transfer calculation ignoring the heat transfer resistance at the joint interface.

Further, the working surface of the mold has a weight ratio of C ≦ C.
1.1, Si ≦ 2.00%, Mn ≦ 2.00%, Ni ≦
4.00%, Cr ≦ 18.00%, alone or in combination of W and Mo, containing (１ ／ W + Mo) ≦ 12.00%, further V ≦ 3.00%, Co ≦ 6.5% , A1 ≦
l. It is desirable to use a steel containing 50%, one or more of Cu ≦ 3.00%, and the balance substantially consisting of Fe in order to obtain high mold characteristics.

The working surface of the mold may be manufactured from a forged product by cutting or casting.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to an embodiment shown in the drawings.

[0024]

Embodiment 1 FIG. 1 is a sectional view of a mold used in the embodiment. The work surface (hereinafter, referred to as a base material) 1 of the mold has a cylindrical cavity 1a having an inner surface dimension of 200 mm in diameter, 100 mm in depth, and 10 mm in thickness, and was formed by casting SUS420J2 steel. After quenching at 980 ° C,
And heat-treated to the hardness of HRC27.

After cleaning the back surface of the base material by shot blasting, a 20 mm thick build-up layer of pure copper was formed by pulse MIG welding under the following conditions. After the overlay welding, a strain relief annealing at 600 ° C. × 1.5 hr was performed.

As a result of cutting the interface of the weld overlay and conducting a microscopic examination, it was found that the interface of the weld zone was extremely good and no defect was observed.

The results of measuring the thermal conductivity near the weld interface by the laser flash method are shown in SUS420J.
21 W / m / K on the 2nd side, 43 W / m / K on the 1 mm thick portion (diffusion layer) including the interface, and 260 W / m / K on the copper side (1st layer) 3 mm away from the interface. 6 more
In mm, the value on the copper side (second layer) was 320 W / m / K, which was almost a value close to pure copper.

The hardness of the base material after the overlay welding is HRC2.
7 and the microstructure was not changed from that before the buildup.

[0029]

Example 2 In Example 2, a metal mold having the same dimensions as in Example 1 shown in FIG. 1 was formed by cutting a forged material of SKD61 steel. This mold was quenched at 1050 ° C., then tempered at 650 ° C. and heat-treated to the hardness of HRC37.

After cleaning the back surface of this base material by shot blast, pulse MIG welding under the following conditions
A pure copper layer having a thickness of 13 mm was formed. After the overlay welding, a strain relief annealing at 600 ° C. × 1.5 hr was performed.

As a result of cutting the interface of the weld overlay and examining it with a microscope, it was found that the interface of the weld zone was extremely good and no defect was observed.

The measurement result of the thermal conductivity near the interface of the welded portion was 30 W / m / K on the SKD61 side, but the portion having a thickness of 1 mm including the interface (diffusion layer) and the copper 3 mm away from the interface were included. On the side (first layer), the values are almost the same as those in Example 1,
Similarly, on the copper side (second layer) 6 mm away from the interface, 32
0W / m / K showed a value almost equivalent to pure copper.

Further, the hardness and microstructure of the base material after the overlay welding were not changed from those before the overlay as in Example 1.

As described above, according to the high thermal conductive composite mold and the method of manufacturing the same of the present invention, the entire or a part of the non-working surface of the mold has a thermal conductivity of 250 W / m / K or more. Having a thick thermal conductive layer of 10 mm or more of copper, especially pure copper, improves the thermal conductivity of the mold and increases the internal cooling effect, reduces the temperature unevenness in the mold and suppresses the deformation of the mold. In addition, the occurrence of heat cracks is reduced and the life of the mold is improved. Thereby, the product molding cycle time can be shortened, and the molding efficiency can be improved.

Since this heat conductive layer is formed by high-energy build-up welding such as pulse MIG welding, a heat conductive layer having a thickness of 10 mm or more can be easily built up, and embrittlement of the joint between steel and pure copper. The generation of layers is small, and the occurrence of poor bonding at the bonding surface such as peeling of the heat conductive layer is reduced.

Further, even if the preheating temperature and working temperature of the base material during overlay welding are lower than the tempering temperature of the base material, a sound overlay without defects at the welding interface can be obtained, so that the working surface is hardened and hardened. In the case of the steel that has been subjected to the tempering heat treatment, the heat treatment for the re-quenching and tempering after the overlay welding is not required, and the cost can be reduced.

The weight ratio of the base material is C ≦ 1.1 and Si ≦ 2.0.
0%, Mn ≦ 2.00%, Ni ≦ 4.00%, Cr ≦ 1
8.00%, alone or in combination of W and Mo (1/2
W + Mo) ≦ 12.00%, and further V ≦ 3.0
0%, Co ≦ 6.5%, A1 ≦ l. 50%, Cu ≦ 3.
If the steel is made of steel containing at least one of 00% and the balance being substantially Fe, a high-performance mold having a long life is obtained, and this base material may be produced by cutting or casting.

[0038]

As described above, according to the high heat conductive composite mold and the method of manufacturing the same according to the present invention, a mold having high internal heat conductivity and good cooling efficiency can be easily and easily prepared by the HIP method or the like. Since it can be provided at low cost, the working efficiency of molding is improved, and it can contribute to the development of industry.

[Brief description of the drawings]

FIG. 1 is a sectional view of a high heat conductive composite mold according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 base material (work surface) 1a cavity 2 heat conduction layer (facing part)

Claims (9)

[Claims] 1. A high-energy overlay welding of a heat conductive layer of copper or a copper alloy having a heat conductivity of 250 W / m / K or more to the whole or a part of a non-work surface of a mold whose work surface is made of steel. A highly heat conductive composite mold characterized by being formed by: 2. The work surface is made of quenched and tempered heat-treated steel, and the heat conductive layer is made of pure copper having a thickness of 10 mm or more by high-energy overlay welding. 2. The high thermal conductive composite mold according to the above. 3. A high-energy overlay welding of a heat conductive layer of copper or a copper alloy having a heat conductivity of 250 W / m / K or more to the entire or part of the non-work surface of a mold whose work surface is made of steel. A method for producing a high heat conductive composite mold, characterized by being formed by: 4. The work surface is made of quenched and tempered heat-treated steel, and the heat conductive layer is made of pure copper having a thickness of 10 mm or more by high-energy build-up welding. 3. The method for producing a highly heat-conductive composite mold according to item 1. 5. The work surface of the mold is made of steel that has been tempered and heat-treated at a temperature of 500 ° C. or more after quenching, and is preheated to the tempering temperature or less during the build-up welding. 5. The method for producing a high thermal conductive composite mold according to claim 3, wherein high energy overlay welding is performed while maintaining the temperature at or below the tempering temperature. 6. The high-energy overlay welding is performed by pulse MIG.
The method for producing a highly heat-conductive composite mold according to any one of claims 3 to 5, wherein the method is performed by welding. 7. The work surface of the mold has a weight ratio of C ≦ 1.
1, Si ≦ 2.00%, Mn ≦ 2.00%, Ni ≦ 4.
00%, Cr ≦ 18.00%, containing (１ ／ W + Mo) ≦ 12.00% alone or in combination of W and Mo,
Further, V ≦ 3.00%, Co ≦ 6.5%, A1 ≦ l. 5
7. A steel containing at least one of 0% and Cu.ltoreq.3.00%, the balance being substantially Fe.
And a method for producing the same. 8. The high thermal conductive composite mold according to claim 1, wherein the working surface of the mold is formed by cutting from a forged product. 9. The high thermal conductive composite mold according to claim 1, wherein the working surface of the mold is produced by casting.