JP3017889B2 - Manufacturing method of die casting mold having water cooling hole - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an internal mold having a water cooling holes, and a method of manufacturing a die-casting die having an adjusted hardness by parts of the mold.

[0002]

2. Description of the Related Art Aluminum alloys have been widely used in various industries including the automobile industry in recent years.
Among the aluminum alloy processing methods, the die casting method is
It has been widely used due to its good dimensional accuracy, high productivity, reduction effect of post-processing by near net shape, etc., but recently it has been applied to products that use cast surfaces such as aluminum wheels and valve rocker covers as exterior surfaces. The application of is increasing. Therefore, in order to improve the casting surface after casting,
Improvement of heat cracks the life of the die-casting mold has become an important issue. In addition, as part of car weight reduction,
There has been a movement to tighten the control limits of the weight of die-cast products, and the increase in the weight of die-cast products due to correction of the mold surface where heat cracks have occurred is also being limited.From this perspective, it is important to suppress heat cracks. It has become to.

For suppressing heat cracks, it is effective to improve the high-temperature strength of the mold itself. In the case of die casting for general aluminum with a molten metal temperature up to around 700 ° C,
Since the temperature does not greatly exceed 600 ° C., what is needed to enhance the heat crack resistance is a high-temperature strength up to around 600 ° C. In addition, in the case of squeeze die casting, although the temperature of the molten metal is high, the temperature of the mold surface rises during squeeze die casting because the molten metal is filled at a slow speed from the large gate provided in the center of the mold at a slow speed. Is not so big. However, since the casting time is long, the temperature difference in the mold from the center of the mold to the outer periphery tends to increase, and heat cracks due to thermal stress occur early in the center of the mold and in corners that lead to stress concentration. easy. Therefore, as a countermeasure against heat cracking of squeeze die-cast
Efforts to improve strength before and after are important points more than general die-casting materials.

[0004] High-temperature strength up to around 600 ° C is largely affected by initial hardness. Therefore, the initial hardness is set to be higher in a mold in which heat crack suppression is important, and a die-cast mold that is heat-treated to a high hardness of 50 or more HRC has appeared. On the other hand, in recent years, in order to shorten the casting cycle and refine the crystal grains of the cast product,
It has become necessary to use a water-cooled hole in a die-casting die while cooling the entire die.

[0005]

However, by cooling the inside of the mold with water while casting the molten metal, a sharp temperature gradient is generated from the surface to the inside of the mold. In the case of using, excessive thermal stress occurs during use at the tip of the water cooling hole, and cracks do not enter from the die sculpture surface (hereinafter also referred to as cavity), but the vicinity of the water cooling hole is easily broken Therefore, there was a limit to the mold life. This is because the fracture toughness is extremely reduced because the hardness of the entire mold is increased.

Although it is effective to reduce the hardness of the mold to some extent in order to prevent cracks near the water-cooled holes inside the mold, the advantage of using a high-hardness material is lost, and the surface of the mold is no longer effective. Heat cracks are likely to occur and the mold has a short life. An object of the present invention is to prevent cracks in the vicinity of a water-cooled hole of a particularly high-hardness hot tool steel mold having a water-cooled hole. An object of the present invention is to provide a die casting mold in which cracking from cracks is prevented and a method for manufacturing the same.

[0007]

Means for Solving the Problems The present inventor has proposed a method for manufacturing a die casting mold having a water cooling hole, while taking advantage of the feature that the surface of the mold is high in hardness, while preventing cracks from around the water cooling hole. investigated. As a result, after performing a heat treatment so that the mold surface has a high hardness of, for example, about HRC 50 to 52, a region including a portion corresponding to a water cooling hole is further tempered, and the region is removed from the surface of the mold. It was found that when the hardness was lowered (for example, to about 40 to 45 HRC), heat cracks did not easily occur on the surface of the mold, the inside of the mold had sufficient strength, and cracks from water cooling holes were less likely to occur. Of course, in order to make the hardness of the mold surface as high as HRC 50 to 55, it is necessary to select the material of the mold.

[0008] Materials having such high hardness include, for example, C 0.3-0.6%, Si 1.5% or less by weight,
Mn 0.1-1.5%, Cr 4.0-6.0%, 1 / 2W + Mo (W and Mo
1.8 to 5.0%, V 0.5 to 2.0% steel , or Co 0.1 to 5.0%, Ni 0.1 to 1.5%
Is recommended. More specifically, the hot work tool steels developed by the present inventors are C 0.37%, Si 0.17%, Mn 0.6%, Ni 0.6%.
%, Cr 5.2%, Mo 2.2%, V 0.85%, Co 0.8% steel,
Or C 0.52%, Si 0.1%, Mn 0.4%, Cr 4.2%,
Steels with 1.6% W, 2.0% Mo, 1.15% V, 0.8% Co are suitable. If the latter steel is used, a mold of about HRC55 can be obtained while securing sufficient toughness.
However, the present invention is not only applied to high-hardness materials, but is also widely applicable to JIS-SKD61 class hot die steels that have been widely used in the past.

[0009] An object of the present invention has a water-cooling hole in the Profiler the vicinity of the die-casting die, than the hardness of the Profiler surface of the mold, towards the hardness of the mold central portion is low Ida Ikast mold the
It is to provide, as a manufacturing method for obtaining such da Ikast die There are two. One after forming a water-cooling hole in the mold, after performing tempering quenching and tempering on the mold, the mold Homem of the <br/> mold in a state exposed to air cooling or more cooling,
A method for producing a die casting mold having a water cooling holes, characterized in that tempering the following hardness after tempering the sintered a part other than the Profiler surface of the mold in a hot bath at least 550 ° C., other Of 1
One is subjected to tempering quenching and tempering on the mold, the mold Homem of the mold in a state exposed to air cooling or more cooling, a portion of the mold than Profiler surface of the mold 550 There ℃ or more thermal bath at the expense <br/> strike mold manufacturing method having a water cooling hole and forming a tempering die casting mold in a water-cooled hole below hardness after tempering the sintered , respectively the inventions you define the manufacturing method of the present invention.

The present invention relates to SKD61 and SKD having water cooling holes.
In order to improve the service life of a die-casting die made of a hot work tool steel having a high hardness as described above, which is an improved material of KD61, while making the cavity surface in contact with the molten metal a high hardness of about HRC 50 to 55, HRC40-45 area with water cooling holes
To the extent of low hardness, die whole normal quenching with water cooling holes, after the high hardness by tempering, was immersed in high thermal bath of heat transfer coefficient, tempered only the area requiring low hardness by, a region having a water-cooling hole from the mold surface has a skeleton that is relatively softened. Therefore, the mold obtained by such a heat treatment has a hardness at the center of the mold (about HRC40) from the hardness of the mold surface (about HRC50 to about 55).
~ 45) is lower.

[0011]

The die made of hot tool steel as described above has cavity surfaces of various shapes depending on the application. FIG. 6 is a top view and a side view showing a schematic cross-sectional view of the mold 1 having a water cooling hole. Generally, the water cooling hole 2 is from the cavity bottom 3
It is processed along the outer periphery of the mold at a distance of about 30 to 60 mm, and the cooling water flows in the direction of the arrow. Half of the center line of the cast product is shown as product 4. During the actual casting, as shown in FIG. 7, a sharp temperature gradient occurs at the water cooling hole as a boundary, for example, as shown in the right part of FIG. Cracks may occur in the periphery. A typical example of such a crack is shown as a crack 5 in the top view of FIG.

The cause of such cracks is that it is necessary to increase the hardness of the whole mold in order to improve the heat crack resistance of the cavity, and the fracture toughness is reduced accordingly. In particular, it is considered that cracks are likely to occur in the vicinity of the water cooling hole where excessive thermal stress is likely to occur. Therefore, in order to prevent cracks from the water-cooled holes, it is necessary to soften the vicinity of the region where the water-cooled holes are present and to sufficiently increase the fracture toughness while maintaining the surface hardness. Therefore, normal quenching, by tempering, after making the cavity high hardness, a part of the mold other than the cavity is immersed in a heat bath at a temperature higher than the tempering temperature,
By softening at least the area with water cooling holes,
The die surface is high in hardness, and the water-cooled hole portion provides an ideal die-cast die with low hardness.

[0013] In performing tempering again in hot bath, it is necessary to keep the atmosphere cool more cooling type Homem. This is because during the tempering treatment in the heat bath, heat is not transmitted to the inside of the mold to soften even the surface of the mold. This means can be achieved by simply adjusting the depth of immersion in a heat bath while leaving the mold surface (cavity) of the mold exposed to the atmosphere. However, when the water cooling hole is machined to a position very close to the bottom of the cavity, the immersion depth in the heat bath increases, so when cooling from the top of the cavity with air, nitrogen gas or argon gas, this Processing is more reliable.

As the heat bath, a salt bath generally called a salt can be used, and the temperature can be controlled by the composition. In the case of the present invention, since the normal tempering temperature of the die casting mold is 550 ° C. or lower, the effect of lowering the hardness of the water cooling hole is difficult to obtain unless at least this temperature. Above. Suitable compositions for such a heat bath include, for example, 30% BaCl ₂ , 30% NaCl, 40% K
A salt made of Cl may be used. The processing of the water-cooled hole formed inside the mold may be performed at any time before or after the heat treatment. The method of processing the water-cooled hole in an annealed state is easy, but when forming a water-cooled hole having a complicated shape, it is necessary to pay attention to cracks during heat treatment. In the method of processing the water-cooled hole after tempering in a heat bath, there is no fear of cracking during heat treatment, but since the hardness of the processed portion is about HRC40, it may take time depending on the material. Therefore, when manufacturing a normal die casting mold, it is better to complete the hole processing before the heat treatment.

As a result of the experiment, the heat affected zone of the material by the heat bath at 600 ° C. was about 30 to 40 mm. That is, about 30-40 mm from the boundary where the mold is immersed in the heat bath toward the non-immersed part
In the range, the hardness is reduced due to the diffused heat even though the film is not immersed. Therefore, the actual immersion depth in the heat bath needs to be determined in consideration of the depth of the cavity bottom and the position of the water cooling hole.

[0016]

Embodiments of the present invention will be described below in detail. Example 1 A mold having water-cooled holes as shown in FIG. 2 was processed after annealing SKD61 and steel A having the alloy compositions shown in Table 1. The tempering characteristics of SKD61 and steel A are as shown in FIG. 3, and steel A has higher hardness and higher fracture toughness than SKD61. After machining the cavity required for the die casting mold, quenching (1020 ° C) and tempering (560 ° C
× 2 times), after aiming at HRC51 for the overall hardness, Figure 1
600 from the bottom of the cavity to 60mm as shown in
It was immersed in a heat bath 8 of 1 ° C. for 1 hour. During immersion, to prevent the temperature rise of the cavity, blowing N ₂ or air, further surface temperature and the temperature of the water cooling hole is measured by a radiation thermometer and a thermocouple 7 respectively, back surface temperature tempering temperature (560
℃) was confirmed to be 30 ° C or lower.

FIG. 4 is a hardness distribution of the cross section CD after the partial tempering. As can be seen from the figure, the hardness of the cavity surface was maintained as high as HRC 51 to 50.7 for both steel types, and it was possible to soften the vicinity of the water cooling hole to HRC 41 to 40.6. Table 2 shows the results of the life test of the actual mold together with the results of the comparative example. The comparative example only changes the hardness of the mold and does not add tempering by a heat bath as in the present invention.

[0018]

[Table 1]

[0019]

[Table 2]

Regardless of the type of steel used, the hardness of the mold
At about HRC44, there is no crack around the water cooling hole, but SKD61
7,900-8,100 shots, Steel A 10,100-12,000 shots
Due to the occurrence of heat cracks on shots, it is necessary to correct the mold surface. When the hardness of these steels was increased to around HRC51, cracks occurred near the water cooling holes in the mold before heat cracks occurred, and the mold had to be replaced around 5,000 shots. The mold to which the present invention is applied can increase the number of cycles until heat cracks occur on the mold surface approximately twice without causing cracks from the water cooling holes, and greatly increase the number of times of maintenance such as correction of the mold surface. Could be reduced to That is, when the die casting mold of the present invention is used, a synergistic effect that less heat cracks occur and there is no crack near the water cooling hole is obtained as compared with the conventional mold to which the present invention is not applied.

(Example 2) Next, an example in which the temperature and time of tempering in a heat bath are changed for a mold having the same shape as in Example 1 will be described. The immersion position, the temperature control method, and the method of cooling the die surface are the same as those in the first embodiment. FIG. 5 shows the hardness distribution of the cross section CD when tempering in a heat bath was performed at 700 ° C. for 20 minutes. As can be seen from the figure, even if the partial tempering temperature is increased, the heat treatment can be performed without reducing the surface hardness by shortening the heating time. (Example 3) Next, the result of performing water-cooled hole processing after tempering in the above-mentioned heat bath is shown. This tempering was the same as in Example 1 at 600 ° C x 1
hr. Table 3 shows the results of the life test according to Example 3 of the present invention. As can be seen from the table, large cracks near the water-cooled holes were eliminated by partial re-tempering of the heat treatment as in Example 1, and the mold life was improved up to about twice. There was no particular problem if the drilling was performed after tempering.

[0022]

[Table 3]

[0023]

According to the present invention, since the cavity has sufficient heat crack resistance due to sufficient hardness, the life until the mold surface is repaired can be extended to about twice as long as that of the conventional mold. It is possible to reduce the number of times of maintenance, and it is possible to prevent the crack near the water cooling hole portion, which has been a problem in the past, and to obtain an effect more than synergistic effect. Further, according to the present invention, even if a high-hardness material is used, a countermeasure against cracking due to insufficient toughness can be locally performed, so that it can be applied to a higher-hardness mold material that will appear in the future. In this respect, the invention is highly versatile.

[Brief description of the drawings]

FIG. 1 is a view showing a method for tempering a die casting mold having a water cooling hole in a hot bath according to the present invention.

FIG. 2 is a diagram showing a cross-sectional shape of a die casting mold used in an example of the present invention.

FIG. 3 is a view showing tempering characteristics of SKD61 and steel A.

FIG. 4 is a diagram showing a hardness distribution of a mold according to Example 1 of the present invention.

FIG. 5 is a diagram showing a hardness distribution of a mold according to a second embodiment of the present invention.

FIG. 6 shows a top view and a side view of a die casting mold having water cooling holes.

FIG. 7 is a diagram schematically showing a temperature distribution during use of a die casting mold having water cooling holes.

FIG. 8 is a view showing a form of a crack and a fracture surface of a die casting mold having water cooling holes.

[Explanation of symbols]

1 mold, 2 water cooling holes, 3 cavity bottom, 4 products, 5 cracks, 6 fracture surface, 7 thermocouple, 8 heat bath

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification code FI B29C 33/38 B29C 33/38 45/73 45/73 (56) References JP-A-4-367360 (JP, A) JP 58-22373 (JP, A) JP-A-2-200783 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 17/22 C21D 6/00 B29C 33/04 B29C 33 / 38 B29C 45/73

Claims (2)

(57) [Claims] 1. A after forming the water-cooling hole in the mold, after performing tempering quenching and tempering on the mold, the mold Homem of the mold in a state exposed to air cooling or more cooling, the mold Other than the surface
Method for producing a die casting mold having a water cooling holes, characterized in that tempering the following hardness after tempering the sintered a part in the heat bath at least 550 ° C.. 2. The method of claim 1] was subjected to a tempering quenching and tempering in the mold, before
The engraving surface of serial molds exposed to atmospheric cooling over cooling, the following hardness after tempering the sintered by the <br/> mold Profiler the part other than the face 550 ° C. or more heat bath die-<br/> strike mold manufacturing method of having a water-cooled hole and forming a water-cooling hole in tempered die casting molds.