JPH0211348B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a die-casting mold for die-casting precision equipment products such as watch parts or camera parts. In recent years, mold processing technology has improved and, for example, watch parts, camera parts, automobile parts, etc. that require a high degree of dimensional accuracy are manufactured by die casting. However, among these products, molds based on tungsten or molybdenum are used for die casting of watch cases made of extremely thin and small materials such as stainless steel and brass. 1. When the molten metal solidifies, the clamping force applied to the core installed in the mold cavity is large, and the draft angle must be increased, making it impossible to manufacture products that require precision; 2. Even if the draft angle is increased at the expense of dimensional accuracy, die casting of stainless steel, brass, etc. requires a large clamping force on the core when the molten metal solidifies.
There were drawbacks such as abnormal wear, such as scratching, which shortened the life of the core when it was released from the mold. Such problems are generally raised in the die casting industry for zinc alloys, aluminum alloys, etc., and as a countermeasure, boron is diffused on the surface of the mold cavity.
However, this method does not solve the above problem and causes various problems such as peeling of the treated layer, abnormal wear, and surface roughness. In view of these points, the present invention has a long mold life and
Moreover, it is an object of the present invention to provide a die-casting mold that can improve the yield of precision products. Embodiments of the present invention will be described below with reference to FIGS. 1 to 5. In FIG. 1, a movable mold 2 is combined opposite to a fixed mold 1, and a cavity 3 is installed inside them.
is formed, and a core 4 is provided within this cavity 3. Further, a cold chamber 5 is connected to the lower part of the fixed mold 1, and a molten metal 6 is injected into the cold chamber 5 from a port 5a, and the molten metal 6 reciprocates inside the cold chamber 5. The plunger tip 7 is press-fitted into the cavity 3 through the gate 8. In such a die-casting machine, a part of the core 4 or a part of the gate 8 is extremely prone to surface erosion (erosion phenomenon), and to counter this, it is necessary to have resistance to welding with the molten metal, Boring treatment with high thermal shock resistance and fire resistance is effective. However, when taking out the solidified product after press-fitting the molten metal into the cavity 3 and solidifying it, even in a mold that has undergone boriding treatment, the corners 4a, 4 of the core 4
a,...4a causes abnormal wear between the parts and the product, resulting in extremely low dimensional accuracy of the product. Therefore, in the present invention, areas where abnormal wear is likely to occur, such as the gate 8 and the corner 4a of the core 4, are
The above problem was solved by carrying out carbonization treatment. That is, as shown in FIG. 3, for example, a core 4 is housed in a stainless steel container 9, and carburized materials 10, 10, . , ... 4b contains the boron-immersed material 11,1
1,...11, and these carburized material 10 and boronized material 11 are filled with aluminum oxide Al ₂ O ₃ and silicon oxide.
Covered with a ceramic sheet 12 made of _SiO2 ,
Carburizing at 940℃ for 2 and a half hours in a non-oxidizing atmosphere.
Boriding treatment is effective. In this way, when both carburizing and boriding treatments are performed, it is best to apply a mask (for example, copper plating) to the carbonized area during boronization, and to perform carburization by peeling off the previously applied mask during carbonization. However, in the present invention, both of these processes are performed simultaneously, which is efficient. The surface hardness of products carburized by this surface treatment increases in proportion to the treatment temperature and treatment time. 800~ in the layer
1300Hv, preferably 1000Hv, 500~ in carbonized layer
Approximately 900Hv, preferably about 700Hv. Note that if the depth of each treated layer is made extremely deep, cracks will occur in the treated layer due to thermal stress. On the other hand, if the depth is extremely shallow, erosion (erosion phenomenon) is likely to occur. It is desirable to select the treatment depth within the range of 5 to 50 μm depending on the contact situation with the molten metal. In the core 4, there are areas with melting damage and areas with abnormal wear, so a surface treatment method as shown in Fig. 3 is appropriate. mixed with abnormal wear,
For example, such surface treatment is not necessarily appropriate for the corner 4a of the core 4 facing the gate 13 as shown in FIG. Therefore, it is considered to treat the surface with a mixture of a boronizing agent (for example, Denka Boronizer) and a carbonizing agent (for example, graphite carburizing agent), and the mold base material, for example, W (90%) - Mo ( 4%) - Ni (4%) - Fe
(2%), and surface treatment experiments were carried out by varying the mixing ratio in terms of weight percent, and the following results were obtained.

[Table] In addition, mold base material Ti based on molybdenum
Similar results were obtained for (0.5%) - Zr (0.08%) - Mo (remainder). According to this, it can be seen that as the amount of carbonizing agent increases, the treated hardness decreases, but if only the carbonizing agent is used, the hardness becomes higher than when the carbonizing agent and boronizing agent are mixed. As a result of various experiments, the corner 4a of the core in FIG.
In the treatment of
Surface treatment at 550 to 950 Hv, preferably around 660 Hv, can provide good results in preventing erosion and abnormal wear. Conventional molds had a lifespan of around 500 shots, but the molds of the present invention The lifespan of the mold has been extended to about 1000 shots. In addition, the solidification rate of the molten metal in the fillet 14 (Fig. 5) filled in the cavity with the core is slower than that in other parts, so large thermal stress is generated in the product during the solidification process, resulting in cracks. may occur. This is because the volume of the fillet portion 14 is larger than the other portions, and the corner portion 4a of the core 4 receives heat intensively from the molten metal, increasing the temperature of that portion, and furthermore, due to solidification contraction. Since a gap O is formed between the fillet part 14 and the corner 2a of the mold, the fillet part 14 is cooled more slowly than other parts, and the fillet part 14 is cooled more slowly than other parts that have contracted first. This is because it is subjected to tensile force. However, even in this case, the generation of cracks could be completely prevented by carbonizing the corner 4a of the core as described above and boriding the other parts. In other words, the thermal conductivity of the boriding layer is 0.076 cal/cm・℃・sec, and that of the carbonizing layer is 0.47 cal/cm・℃・sec. This is because since it is considerably larger than that, the heat conduction at the corner 4a of the core becomes good and the molten metal is cooled uniformly. In this example, the surface treatment of the core has been described, but the same can be said of the surface treatment of the cavity surface of other molds. As explained above, the present invention provides a boride layer at the melted parts of the mold cavity surface (including the core).
A mixed layer of a boride layer and a carbonized layer is formed in areas where both melting loss and abnormal wear occur, so melting loss and abnormal wear on the mold cavity surface are prevented, and the mold This has the effect that the life of the product is significantly increased, and the yield of the product can be improved without any cracks occurring in the product.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view of the die-casting device, Figure 2 is a view taken along arrow A-A in Figure 1, Figure 3 is a front view of the surface treatment equipment, and Figure 4 is a cross-sectional view of the mold containing the core. 5 and 5 are enlarged sectional views of the core and the corner of the cavity of the mold. 1...Fixed mold, 2...Moveable mold, 3...Cavity, 4...Core, 8, 13...Gate, 9...
...Stainless steel container, 10...Carburized material, 11...
Boring material, 12...Ceramic sheet.

Claims (1)

[Scope of Claims] 1. In a die-casting mold in which the cavity surface of a mold based on tungsten or molybdenum is surface-treated, a boride layer is formed on the cavity surface and the molten metal flow path to prevent abnormalities. A carbonized layer is formed at the worn locations, and the locations where both erosion and abnormal wear occur are filled with a carburizing material and a boronizing material, and then carburized and borated to form a mixed layer of a borated layer and a carbonized layer. A die-casting mold characterized by forming. 2. The hardness of the carbonized layer is 500 to 900 HV, the hardness of the borated layer is 800 to 1300 HV, and the hardness of the mixed layer is 500 to 900 HV.
The die-casting mold according to claim 1, characterized in that the die-casting mold has a HV of 550 to 950 HV.