JPWO2018097165A1 - Die casting mold manufacturing method and die casting mold - Google Patents

Abstract

A method for producing a die-casting die (1) and a die-casting die (1) capable of reliably performing a softening heat treatment on a region including a bottom surface (4) of a water-cooled hole (2). A method of manufacturing a die-casting die (1) provided with a bottomed water-cooled hole (2) having an inner diameter D, wherein the hole surface (3) forming the water-cooled hole (2) A bottom surface (4) formed and a side surface (5) extending from the bottom surface (4) toward the inlet (6), the bottom surface (4 from the tip of the pipe (10) having an outer diameter d inserted into the water cooling hole (2). ) Has a heat treatment process in which superheated steam is fed toward the bottom surface (4) to soften it by heating. With this manufacturing method, the die casting mold (1) of the present invention can be manufactured.

Description

  The present invention relates to a method of manufacturing a die casting mold and a die casting mold.

  Patent Document 1 discloses a heat treatment method of a mold. The mold is provided with water cooling holes inside the mold to reduce the temperature of the molding surface. In the mold in use, thermal stress is generated in the water cooling hole. In addition, the steel material rusts on the surface of the water-cooled hole, hydrogen easily penetrates, and hydrogen embrittlement tends to occur. Due to these, there is a concern that a crack may occur around the water cooling hole. Then, patent document 1 proposes performing an annealing process locally to the water cooling hole provided in a metal mold | die. As a result, while maintaining the hardness of the mold itself, the hardness is lowered only at the periphery of the water cooling hole to make it difficult for the crack to occur around the water cooling hole.

Japanese Patent Application Laid-Open No. 8-31557

  In the method described in Patent Document 1, the heat treatment of the surface layer portion in the hole surface of the water-cooled hole is performed using a high-frequency heat treatment apparatus. However, in the method of Patent Document 1, although the heating section of the high-frequency heat treatment apparatus easily heats the side surface of the water-cooled hole, the bottom surface is difficult to heat. However, the water-cooled holes are formed towards the molding surface and are intended for cooling the molding surface. For this reason, I especially want to do the softening heat treatment only on the bottom of the water cooling hole. In this respect, the method of Patent Document 1 has room for improvement.

Also, in general, when the side of the water-cooled hole is formed by a drill, a corner which is a trace of the shape of the tip of the drill remains on the bottom surface. That is, the bottom of the water cooling hole when drilled by the drill has a central position corresponding to the tip of the drill (that is, the deepest position of the water cooling hole) and a position around the center corresponding to the outer peripheral corner of the drill Then, a corner is formed due to the shape of the drill tip. And it is easy to produce a crack from this corner as a starting point. Therefore, in order to eliminate this corner and to make it difficult to form a crack, the base is rounded so that the bottom surface is hemispherical. And, generally, the shape of the bottom of the water-cooled hole after this rounding process, when the inner diameter of the water-cooled hole is D, the position of the height of approximately D / 2 from the center of the bottom is the center of the sphere Become hemispherical. Then, in order to make it more difficult for a crack to be generated from the bottom of the water cooling hole, it is desirable to carry out the softening heat treatment on the bottom of the water cooling hole formed of the above-mentioned hemispherical surface.
Therefore, the present invention provides a method of manufacturing a die casting mold and a die casting mold capable of reliably performing a softening heat treatment on a region including the bottom surface of a water-cooled hole.

According to one aspect of the present disclosure,
A method of manufacturing a die-casting die provided with a bottomed water-cooled hole of inner diameter D, comprising:
The hole surface forming the water cooling hole has a bottom surface forming a bottom of the water cooling hole and a side surface extending from the bottom surface toward the inlet,
A method of manufacturing a die casting mold is provided, comprising a heat treatment step of sending superheated steam from the tip of a tube of outer diameter d inserted into the water cooling hole toward the bottom surface to heat and soften the bottom surface.

According to one aspect of the present disclosure,
When the separation distance between the tip of the pipe and the deepest position of the bottom is defined as h,
0.5 × (D−d) /2≦h≦1.5× (D−d) / 2
The heat treatment step may be performed by holding the tip of the tube at the position where

According to one aspect of the present disclosure,
The tip of the tube may be frusto-conical in shape.

According to one aspect of the present disclosure,
The water cooling hole may be formed by processing so that the bottom surface has a substantially hemispherical shape.

According to one aspect of the present disclosure,
A die-casting die provided with a bottomed water-cooling hole of inner diameter D,
The hole surface forming the water cooling hole has a bottom surface forming a bottom of the water cooling hole and a side surface extending from the bottom surface toward the inlet,
A die-casting mold is provided in which the hardness H1 at the deepest position of the bottom surface is lower than the inlet hardness H2 at the inlet of the water-cooled hole.

According to one aspect of the present disclosure,
The hardness H3 of the region from the deepest position of the bottom surface to the position of the height D among the hole surfaces may be lower than the entrance hardness H2.

According to one aspect of the present disclosure,
The hardness H12 inside the mold at a position 1 mm in the direction perpendicular to the radial direction of the water-cooled hole from the deepest position of the bottom toward the inside of the mold is compared with the Rockwell hardness HRC of C scale. When it does, it may be lower than 95% of said entrance hardness H2.

According to one aspect of the present disclosure,
The hardness H15 inside the mold at a position 5 mm in the direction perpendicular to the radial direction of the water-cooled hole from the deepest position of the bottom toward the inside of the mold is compared with the Rockwell hardness HRC of C scale. When it does, it may be higher than 95% of said entrance hardness H2.

According to one aspect of the present disclosure,
The hardness H33 inside the mold at a position 3 mm in the radial direction of the water-cooled hole from the side at the position of height D / 2 from the deepest position of the bottom to the inside of the mold is C scale Rockwell The hardness may be lower than 95% of the hardness H2 of the inlet when compared with the hardness HRC.

According to one aspect of the present disclosure,
The hardness H37 inside the mold at a position 7 mm in the radial direction of the water-cooled hole from the side at the height D / 2 from the deepest position of the bottom to the inside of the mold is C scale Rockwell When compared with hardness HRC, it may be higher than 95% of the hardness H2 of the inlet.

According to one aspect of the present disclosure,
In the region inside the mold, a region having 95% or less of the inlet hardness H2 when compared with the Rockwell hardness HRC of C scale is called a softening region,
The thickness of the softened region in the direction perpendicular to the radial direction of the water-cooled hole from the deepest position of the bottom surface is called D1.
When the thickness of the softened region in the radial direction of the water-cooled hole is referred to as D2 from the side surface at the position of height D / 2 from the deepest position of the bottom surface,
The thickness D1 may be smaller than the thickness D2.

According to one aspect of the present disclosure,
The bottom surface may be substantially hemispherical.

  According to the present invention, a method of manufacturing a die casting mold and a die casting mold capable of reliably performing a softening heat treatment on a region including the bottom surface of a water-cooled hole are provided.

(A) is a top view (figure seen from the inlet side of a water cooling hole) of the die-cast metal mold | die of this embodiment, (b) is the side view. It is a schematic diagram at the time of performing the heat treatment process of the die-cast metal mold which concerns on embodiment of this invention. It is sectional drawing which shows a mode that the pipe | tube was inserted inside the water-cooling hole. It is a figure which shows the dimension of each part of the test piece in which the water-cooling hole of (phi) 15 was provided, and a temperature measurement point. It is a figure which shows the temperature history at the time of supplying superheated steam. (A) is a cross-sectional view of the test piece along the central axis of the water-cooled hole, and (b) is a cross-sectional view of the test piece on a plane orthogonal to the central axis of the water-cooled hole. It is a radar chart which shows the hardness in section B located 7.5 mm above from the deepest position of the bottom of a water cooling hole. It is a radar chart which shows the hardness in the section C which is located 15 mm upwards from the deepest position of the bottom of a water cooling hole. It is a radar chart which shows the hardness in upper surface E of a test piece. It is a figure which shows the measuring point which measured the hardness shown in FIG. It is a graph which shows the relationship between the separation distance from the hole surface of a water cooling hole, and hardness. It is the model which showed the softening area | region in the area | region inside a metal mold | die. It is a figure which shows the hardness of each part of a die-cast metal mold. It is a figure which shows the dimension of each part of the test piece in which the water-cooling hole of (phi) 20 was provided, and a temperature measurement point. It is a figure which shows the temperature history at the time of supplying superheated steam. It is a radar chart which shows the hardness in the section located in 10 mm upwards from the deepest position of the bottom of a water-cooling hole. It is a radar chart which shows the hardness in the section located in 20 mm upwards from the deepest position of the bottom of a water-cooling hole. It is a radar chart which shows the hardness in the upper surface of a test piece. It is a graph which shows the separation distance from the hole surface of a water cooling hole, and the relation of hardness.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, about the member which has the same reference number as the member already demonstrated in description of this embodiment, the description is abbreviate | omitted for convenience of explanation. Further, the dimensions of the respective members shown in the drawings may differ from the actual dimensions of the respective members for the convenience of the description.

FIG. 1 shows a substantially rectangular parallelepiped test piece of the die casting mold 1 of the present embodiment. (A) of FIG. 1 is a view of the die casting mold 1 as viewed from the inlet side (upper surface 1 b) of its water-cooled hole, and (b) is a side view thereof. The actual die casting mold 1 has a complicated shape, but in the following description, this rectangular parallelepiped test piece will be referred to as the die casting mold 1.
The die casting mold 1 is formed of steel. The lower surface of the die casting mold 1 forms a molding surface 1 a. When the die casting mold 1 is used, the molding surface 1 a constitutes a cavity. The shape of the molding surface 1a is transferred to the surface of a product manufactured by die casting. When the die casting mold 1 is used, the molding surface 1a is exposed to a high temperature molten metal, and the entire die casting mold 1 including the molding surface 1a becomes a high temperature. Therefore, in order to prevent the molding surface 1a from becoming hot, the water-cooling hole 2 is provided in the die casting mold 1.

  The water cooling hole 2 is opened in the upper surface 1 b of the die casting mold 1. The water cooling hole 2 is a bottomed hole extending downward from the upper surface 1 b (that is, toward the molding surface 1 a). The surface of the die casting mold 1 constituting the water cooling hole 2 is called a hole surface 3. As the hole surface 3, a portion forming the bottom of the water cooling hole 2 is called a bottom surface 4, and a portion extending from the bottom surface 4 toward the inlet is called a side surface 5. The water cooling hole 2 is composed of a semispherical area (hemispherical area) including the bottom surface 4 and a substantially cylindrical area (cylindrical area) located above the hemispherical area. In the following description, the diameter (inner diameter) of the water cooling hole 2 is called D. When the die casting mold 1 is used, a cooling pipe is inserted into the interior from the inlet 6 of the water cooling hole 2 and the die casting mold 1 is cooled by pouring a cooling medium such as water into the water cooling hole 2.

  By the way, when the die casting mold 1 is used, stress occurs in the water cooling hole 2. And since the water-cooling hole 2 is exposed to water in this way, the steel material tends to rust and to cause hydrogen embrittlement. It is feared that a crack may occur in the hole surface 3 of the water cooling hole 2 by these things. Therefore, it is practiced to subject the water-cooled holes 2 to an annealing treatment to lower the hardness and to make it difficult for cracking to occur. Moreover, it is also possible to lower the hardness around the water cooling hole 2 by utilizing the tempering treatment applied after the quenching treatment. When the die casting mold 1 is used, the region on the bottom surface 4 side of the water cooling hole 2 is exposed to a high temperature as compared with the inlet 6 side. For this reason, although it is desirable to lower the hardness on the bottom 4 side of the water cooling hole 2, the hardness on the inlet 6 side does not have to be reduced so much. Then, the heat treatment process which can be applied to said annealing process and tempering process for achieving this hardness distribution is demonstrated below.

  FIG. 2: is a schematic diagram at the time of performing the heat treatment process of the die-cast metal mold 1 which concerns on embodiment of this invention. As shown in FIG. 2, the pipe 10 is inserted into the water cooling hole 2 of the die casting mold 1. The end of the pipe 10 is connected to the superheated steam generator 11. Superheated steam is fed from the end of the pipe 10 toward the bottom 4 of the water cooling hole 2. Then, at least the bottom surface 4 is heated by the superheated steam, and the hole surface 3 of the die casting mold 1 including the bottom surface 4 is softened. The hardness H1 of the deepest position A is lower than the hardness H2 of the inlet 6 of the water cooling hole 2.

  Superheated steam is, for example, steam that is as high as about 1200 ° C. Superheated steam has a larger heat capacity per unit volume than air, and is excellent in thermal conductivity. For this reason, when the superheated steam jetted out of the pipe 10 contacts the bottom surface 4, the heat amount of the superheated steam is immediately transmitted to the bottom surface 4 and the bottom surface 4 can be quickly heated to the softening temperature. Thus, by feeding the superheated steam from the tip of the tube 10 toward the bottom surface 4, the temperature of the bottom surface 4 can be easily raised, and the heat treatment of the bottom surface 4 can be reliably performed.

By the way, in the induction heat treatment apparatus described in Patent Document 1 described above, the heating source heats the surrounding air, and the mold is heated via the heated air. Compared to the air of Patent Document 1, the superheated vapor of the present embodiment has very high thermal conductivity.
According to the present embodiment, the superheated steam having high thermal conductivity moves in contact with the hole surface 3 while moving, and aims at the extreme surface layer of the hole surface 3 to be rapidly heated to the target temperature. It is possible to target the surface layer to a high temperature without raising the temperature to the deep region inside the mold. For this reason, the heat treatment process of the present embodiment is extremely favorable to the requirement that only the hardness in the vicinity of the hole surface 3 of the water-cooled hole 2 be reduced without reducing the hardness of the entire mold. Moreover, since the heat treatment process of this embodiment does not heat to the deep area | region inside a metal mold | die, it is excellent also at the point which can heat and soften only surface layer to target temperature in a short time.
Moreover, in the high frequency heat-treatment apparatus of the patent document 1 mentioned above, the bottom face 4 can not be heated efficiently. Therefore, it is difficult to reduce the hardness of the bottom 4 by any means. However, according to the present embodiment, since the superheated steam is first sprayed to the bottom surface 4, the hardness H1 of the bottom surface 4 can be easily and preferentially lowered.

Next, the preferable aspect of heat processing is demonstrated in detail. FIG. 3 is a cross-sectional view showing how the pipe 10 is inserted into the water cooling hole 2. As shown in FIG. 3, the pipe 10 is inserted into the water cooling hole 2 so that the distance from the tip of the pipe 10 to the deepest position A of the bottom surface 4 of the water cooling hole 2 is h. The heat treatment process is performed by holding the tip of the pipe 10 at a position where the distance h satisfies the following equation (1) using the diameter (inner diameter) D of the water cooling hole 2 and the diameter (outer diameter) d of the pipe 10.
0.5 × (D−d) /2≦h≦1.5× (D−d) / 2 Formula (1)

Superheated steam blown out of the pipe 10 toward the bottom surface 4 collides with the bottom surface 4 and then flows toward the side surface 5 and flows along the side surface 5 toward the inlet 6. Here, the distance h between the tube 10 and the bottom surface 4 is preferably close to the distance (D−d) / 2 between the outer surface of the tube 10 and the side surface 5 of the water-cooled hole 2. Then, if the above equation (1) is satisfied, the cross-sectional area of the flow path of the superheated steam flowing from the pipe 10 toward the bottom surface 4 becomes close to the cross-sectional area of the flow path of the superheated steam flowing along the side surface 5. For this reason, the flow of the overheated steam is less likely to be impeded, and the overheated steam directed to the bottom surface 4 can easily flow along the side surface 5. Thereby, the side surface 5 is also efficiently warmed by the superheated steam, and a wide range of the side surface 5 is easily heat treated. For this reason, it is easy to heat uniformly the area | region from the bottom face 4 of the water-cooling hole 2 to the side surface 5, and it can heat-process this area | region reliably.
In Formula (1), h is preferably “0.7 × (D−d) / 2 or more”, more preferably “0.8 × (D−d) / 2 or more”. H is preferably “1.3 × (D−d) / 2 or less”, more preferably “1.2 × (D−d) / 2 or less”.

The adjustment of the distance h described above can be performed by the adjustment mechanism 20 attached to the upper part of the die casting mold 1 shown in FIG. The adjusting mechanism 20 includes a support 21 for supporting the pipe 10 through which the superheated steam flows, a first adjusting bolt 22 extending in the direction of the central axis Ax of the water cooling hole 2, and a second adjusting bolt 23 extending in the radial direction of the water cooling hole 2. And. By screwing in the first adjustment bolt 22, the distance between the support portion 21 and the upper surface 1b of the die casting mold 1 can be adjusted. Thus, the support portion 21 and the tube 10 supported by the support portion 21 can be displaced in the direction of the central axis Ax of the water cooling hole 2. That is, the distance h can be adjusted by the first adjustment bolt 22.
The radial position of the inside of the water cooling hole 2 of the pipe 10 can be adjusted by the second adjusting bolt 23.

Returning to FIG. 3, the tip of the tube 10 is preferably frusto-conical in shape.
When the side surface 5 is formed by a drill, the water cooling hole 2 has a corner which is a trace of the shape of the tip of the drill on the bottom surface 4 thereof. So, in this embodiment, in order to eliminate this corner and to make it hard to produce a crack, round processing is carried out so that bottom 4 may become hemispherical shape, and water cooling hole 2 is formed.
If the tip of the tube 10 is frusto-conical, the shape easily corresponds to the hemispherical bottom surface 4 thus processed, and the distance between the tip of the tube 10 and the bottom surface 4 is uniformly maintained over a wide range Cheap. For this reason, it is easy to make the cross-sectional area of the flow path of a superheated steam constant, and it is hard to disturb the flow of superheated steam. Thereby, the superheated steam can be smoothly flowed from the bottom surface 4 to the side surface 5, and the wide range from the bottom surface 4 to the side surface 5 can be heat-treated efficiently.

Further, the shape of the bottom surface 4 of the water cooling hole 2 after this round processing is, assuming that the inner diameter of the water cooling hole 2 is D, a position at a height of approximately D / 2 from the center of the bottom surface 4 Become hemispherical. Therefore, between the deepest position of the bottom surface 4 and the side surface 5 near the height position of D / 2, the surface formed by the drill when forming the side surface 5 and the surface formed when rounding Boundary 7 is located. A step may be generated at the boundary 7 due to the shape accuracy of the drill tip, the shape of the cutting edge of the cutting tool at the time of rounding, and the like. Such a step may also be a cause of cracking of the die casting mold 1.
However, according to the present embodiment, since the hardness can be reduced by efficiently heat treating a wide range from the bottom surface 4 to the side surface 5, the die-casting die 1 that is resistant to cracking even when a step is produced is provided. it can.

  In the above description, although the example in which the water cooling hole is opened on the upper surface of the die casting mold has been described, the present invention is not limited thereto. The water cooling hole may be opened on the side surface or the lower surface of the die casting mold.

<Example of φ 15>
Next, examples of the present invention will be described. FIG. 4 shows the dimensions of each part of the test piece of the die casting mold processed by the manufacturing method according to the embodiment. As shown in FIG. 4, the test piece of the present embodiment is a rectangular steel material 100 mm long, 100 mm wide, and 150 mm high. In the center of the upper surface of the test piece, a water-cooled hole having a diameter D of 15 mm and a depth of 120 mm is opened. The water-cooled hole has a cylindrical shape in a region from the inlet to a depth of 112.5 mm and a hemispherical region in a depth of 112.5 mm to 120 mm. The test piece is made of a steel material of JIS-G-4404 standard steel type SKD61. And, by the quenching treatment from 1020 ° C. and the tempering treatment at 600 ° C. following this, the target hardness of 45 HRC is adjusted with Rockwell hardness of C scale.

  A tube having an outer diameter d of 12 mm was inserted into the water-cooled hole so that the tip of the tube was positioned at a position 2 mm in height (distance h = 2 mm) from the deepest position A of the water-cooled hole. Superheated steam at 1200 ° C. was generated by a superheated steam generator, and was supplied to the inside of the water-cooling hole through a pipe. Superheated steam was fed from the tip of the tube toward the bottom of the water-cooled hole to heat and soften the bottom. The superheated steam supply was continued for 1 hour and 30 minutes. As a superheated steam generator, TOKUDEN UPSS-D20 (registered trademark) was used.

As shown in FIG. 4, the first temperature measurement point a1 to the fifth temperature measurement point a5 are set on the test piece, thermocouples are installed at each measurement point, and the superheated steam is sent to the water cooling hole through the pipe. The temperature change from was measured.
The first temperature measurement point a1 is the height position of the boundary between the cylindrical region and the hemispherical region 7.5 mm (that is, D / 2) above the deepest position A of the water cooling hole, and the central axis Ax of the water cooling hole It is provided at a position which enters the inside of the 10 mm mold from the hole surface in the direction orthogonal to the above.
The second temperature measurement point a2 is provided on the central axis Ax of the water cooling hole and inside the mold 5 mm below the deepest position A of the water cooling hole.
The third temperature measurement point a3 is provided on the central axis line Ax of the water cooling hole, inside the mold 25 mm below the deepest position A of the water cooling hole.
The fourth temperature measurement point a4 is provided on the surface of the hole surface at the deepest position A of the water-cooled hole.
The fifth temperature measurement point a5 is the height position of the boundary between the cylindrical area and the hemispherical area 7.5 mm above the deepest position A of the water cooling hole, in the direction orthogonal to the central axis Ax of the water cooling hole It is provided at a position that enters the inside of the 5 mm mold from the hole surface.

The temperature history measured at each temperature measurement point when superheated steam is supplied is shown in FIG.
As can be seen from the temperature history of the fourth temperature measurement point a4, the surface temperature of the bottom of the water-cooled hole rises to near 900 ° C. immediately after the spray of the superheated steam is started. Further, the temperature reaches about 1000 ° C. 30 minutes after the start of spraying, and thereafter the temperature is maintained at 1000 ° C. for 1 hour and 30 minutes.
The second temperature measurement point a2 and the fifth temperature measurement point a5 showed similar temperature histories. Both the second temperature measurement point a2 and the fifth temperature measurement point a5 rise to about 550 ° C. 30 minutes after the start of spraying and reach about 600 ° C. one hour later. After that, the temperature is maintained at 600 ° C. for one hour and thirty minutes.
At the first temperature measurement point a1, the temperature rises to about 500 ° C. 30 minutes after the start of spraying, and reaches about 570 ° C. after 1 hour. After that, 570 ° C. is maintained for 1 hour and 30 minutes.
At the third temperature measurement point a3, the temperature rises to about 470 ° C. 30 minutes after the start of spraying and reaches about 525 ° C. after 1 hour. After that, 525 ° C. is maintained for 1 hour and 30 minutes.

  The tempering temperature of the test piece made of SKD 61 is about 600.degree. It is presumed that the fourth temperature measurement point a4 heated far beyond the tempering temperature is softened. Moreover, it is estimated that the 1st temperature measurement point a1 which did not reach tempering temperature, and the 3rd temperature measurement point a3 did not soften.

Therefore, a plurality of positions indicated by black dots in FIG. 6 were set on the test piece obtained by spraying superheated steam, and the hardness was measured at these positions. (A) of FIG. 6 is a cross-sectional view along the central axis Ax of the water cooling hole, and (b) of FIG. 6 is a cross-sectional view of a plane orthogonal to the central axis Ax of the water cooling hole.
As shown in FIG. 6A, the hardness of the cross section B located 7.5 mm upward (the boundary between the cylindrical area and the hemispherical area) from the deepest position A of the bottom of the water-cooled hole, the bottom of the water-cooled hole The hardness of the cross section C located 15 mm upward from the deepest position A of the above, and the hardness of the surface E (upper surface 1 b of the test piece) located 120 mm upward from the deepest position A of the bottom of the water-cooled hole were measured. Thereby, the change of the hardness in the height direction from the bottom of the water cooling hole is confirmed.
In the planes B, C and E at each height position, as shown in FIG. 6 (b), along the eight axes equally spaced from each other in the circumferential direction, each 2 mm from the hole surface of the water-cooled hole The hardness was measured at positions separated by 4 mm, 6 mm and 10 mm. Thereby, the change of the hardness of the water cooling hole in the circumferential direction and the change of the hardness according to the separation distance from the hole surface of the water cooling hole are confirmed.
The measurement result of the hardness of the position of the total 96 (3x8x4) points set as mentioned above is shown in FIGS.

  FIG. 7 is a radar chart showing the hardness of the cross section B located 7.5 mm (that is, D / 2) upward from the deepest position A of the bottom surface of the water-cooled hole. FIG. 8 is a radar chart showing the hardness of the cross section C located 15 mm upward from the deepest position A of the bottom surface of the water-cooled hole. FIG. 9 is a radar chart showing the hardness of the top surface E of the test piece. It shows by a line connecting points showing the hardness of the measurement point where the separation distance from the hole surface of the water cooling hole is equal. In addition, hardness of the vertical axis | shaft of FIGS. 7-9 is shown by Rockwell hardness HRA of A scale.

As shown in FIGS. 7 and 8, it was confirmed that the region in the vicinity of the water cooling holes was softened by supplying the superheated steam to the water cooling holes. The hardness of the region less than 6 mm from the hole surface of the water-cooled hole decreased with respect to the target hardness of 45 HRC (about 73 HRA in terms of HRA) of the test piece.
Further, from FIGS. 7 and 8, it is possible to read the tendency of becoming harder as it goes away from the water cooling hole surface. That is, the hardness at the position of 2 mm at which the separation distance is shortest is about 69 HRA, which is about 37 HRC when converted to HRC. On the other hand, the hardness at a distance of 4 mm is about 71 HRA (about 41 HRC), the hardness at a distance of 6 mm is about 72 HRA (about 43 HRC), and the hardness at a distance of 10 mm is about 73 HRA (About 45 HRC).

Comparing FIG. 7 with FIG. 8, it can be read that the cross section B of FIG. 7 is smaller in hardness than the cross section C of FIG. 8 even if the distance from the hole surface of the water cooling hole is equal. The cross section B is closer to the cross section C from the bottom surface of the water-cooled hole to which the superheated steam is blown. During the supply of the superheated steam, the cross section B is at a higher temperature than the cross section C. For this reason, it is considered that the cross section B becomes softer and softer than the cross section C.
Furthermore, as shown in FIG. 9, it can be read that the temperature no longer rises to near the tempering temperature even by the supply of the superheated steam near the entrance of the water cooling hole far from the bottom of the water cooling hole and does not soften.

  It can be read from FIGS. 7 and 8 that the sheet is not softened at a distance of 10 mm from the surface of the hole surface. The cross sections B and C are relatively close to the bottom surface on which the superheated steam is sprayed. However, the region 10 mm away from the surface of the hole surface did not soften without reaching the tempering temperature. Further, from FIGS. 7 and 8, it can be confirmed that although it softens when it is separated by about 4 mm from the surface of the hole surface of the water-cooled hole, it becomes difficult to soften.

Next, the change of the hardness according to the separation distance from the bottom of the water cooling hole was evaluated. As shown in FIG. 10, the hardness according to the separation distance from the bottom of the water-cooled hole was measured in the direction s to the direction u.
Direction s: The hardness was measured at a plurality of points in the direction from the deepest position A of the bottom of the water-cooled hole to the lower side.
Direction t: The hardness was measured at a plurality of points in the direction of 45 ° from the center O of the sphere in the hemispherical region to the central axis Ax of the water-cooled hole.
Direction u: The hardness was measured at a plurality of points in the direction of 45 ° from the center O of the sphere in the hemispherical region to the central axis Ax of the water-cooled hole. The direction u is at a position 180 ° away from the central axis Ax of the water-cooled hole with respect to the direction t.

  FIG. 11 shows the change in hardness according to the distance from the bottom of the water-cooled hole. The hardness on the vertical axis in FIG. 11 is indicated by HRC. As shown in FIG. 11, the hardness at the deepest position A at the bottom of the water-cooled hole was about 30 HRC, which was largely softened with respect to the target hardness of 45 HRC of the test piece. And it has a tendency to become hard as it leaves from a bottom also about the point of which direction of directions s-u. In particular, it can be read that it becomes difficult to soften as far as 4 mm from the bottom, and at a position of 5 mm apart, it is no longer equivalent to the target hardness of 45 HRC of the test piece. On the other hand, it can be read that the hardness is greatly reduced in the range of the separation distance of 0 to 2 mm.

  Further, as shown in FIG. 11, the directions s to u have substantially the same hardness. Therefore, in the hemispherical region of the water cooling hole, the heat from the superheated steam spreads evenly, and the hemispherical region of the water cooling hole is uniformly softened. However, it turns out that the area | region corresponded to the hemispherical peak which the superheated steam which blew off from a pipe | tube first collides tends to be high temperature, and softening progresses most.

FIG. 12 shows an area (hereinafter referred to as “42.75 HRC or less for 45 HRC”) that is 95% or less of the inlet hardness in the area inside the mold based on the measurement of hardness as described above FIG. 6 is a schematic view showing a softened region SF).
The thickness of the softened region SF in the direction perpendicular to the radial direction of the water-cooled hole from the deepest position A of the bottom surface is called D1. The thickness of the softened area SF in the radial direction of the water-cooled hole from the side surface at the position of height D / 2 from the deepest position A of the bottom surface is called D2. Then, as shown in FIG. 12, the thickness D1 is smaller than the thickness D2.
Since the molding surface is provided in the direction from the bottom to the bottom of the water-cooled hole, it is not desirable to form a large softening portion in this direction. If the thickness D1 is smaller than the thickness D2 as in the present embodiment, the hardness in the vicinity of the molding surface can be easily maintained while forming the softening region SF largely around the water-cooled hole.
In addition, said "thickness" regarding D1 and D2 says the dimension extended in the direction perpendicular | vertical with respect to the hole surface of a water-cooling hole. In the case of the water-cooled hole of FIG. 12, the direction in which the thickness of D1 is defined is orthogonal to the direction in which the thickness of D2 is defined.

FIG. 13 is a diagram showing the hardness of each part of the die casting mold.
In the present embodiment, the hardness H3 (average hardness of the region) of the region from the deepest position A of the bottom surface to the position of height D (D = diameter of water-cooled hole) in the hole surface of the water-cooled hole is , Lower than the inlet hardness H2.
As shown in FIG. 6, the cross section C is a cross section from the deepest position A to the height D of the bottom surface. From FIG. 8 showing the hardness of the cross section C, it can be read that the hardness of the hole surface (separation distance 0 mm) from the deepest position A to the height D of the bottom surface is less than 67 HRA (about 33 HRC). Further, referring to FIG. 7 and FIG. 8 together, it can be read that the hardness of the region closer to the position A than the height D is lower than the hardness at the height D. Therefore, it can be read that the hardness H3 of the region from the deepest position A of the bottom to the position of the height D is less than 67 HRA (about 33 HRC).
On the other hand, FIG. 9 shows the inlet hardness H2. From FIG. 9, the inlet hardness H2 is read as 73 HRA, which is about 45 HRC (target hardness of the test piece).
Therefore, in the present embodiment, the hardness H3 is lower than the hardness H2. Since the hardness of each of the bottom and the side of the water-cooled hole is lower than the inlet hardness H2, it is possible to provide a die-cast mold in which cracking is unlikely to occur from the periphery of the water-cooled hole.

In the present embodiment, the hardness H12 inside the mold at a position 1 mm toward the inside of the mold in the direction of the central axis Ax of the water-cooled hole from the center O of the sphere in the hemispherical region is the Rockwell hardness of C scale. Lower than 95% of the inlet hardness H2 when compared by HRC.
The hardness H12 can be read from FIG. 11, which shows the change in hardness along the direction s of FIG. In the line of s of FIG. 11, the hardness of the position of 1 mm of separation distance is about 40 HRC. The inlet hardness H2, 73 HRA, corresponds to approximately 45 HRC. 95% of the inlet hardness H2 is 42.75 HRC. Therefore, in the present embodiment, H12 <0.95 × H2 is established. And about this, said hardness H12 is lower than 90% hardness (40.5 HRC) of inlet hardness H2, and it is further effective in suppression of the crack of a water-cooled hole. In addition, the hardness inside the mold at a position 1 mm toward the inside of the mold in the direction forming 45 ° with respect to the center axis Ax of the water cooling hole from the center O of the sphere in the hemispherical region also has an inlet hardness H2 of 95 It is lower than%. And furthermore, it is lower than 90%. The superheated steam sprayed toward the bottom surface of the water-cooled hole softens the surface of the hole not only directly below the pipe but also from the deepest position A to the height D / 2 of the bottom surface.

In this example, the hardness H15 inside the mold at a position 5 mm in the axial direction of the water-cooled hole from the deepest position A on the bottom to the inside of the mold was compared with the Rockwell hardness HRC of the C scale. When the inlet hardness H2 higher than 95%.
In the line of s of FIG. 11, the hardness H15 is about 45 HRC from the point of 5 mm of separation distances. On the other hand, 95% of the inlet hardness H2, which is 73 HRA, is about 42.75 HRC. Therefore, in the present embodiment, H15> 0.95 × H2 holds. And about this, above-mentioned hardness H15 is higher than the hardness (43.65HRC) of 97% of hardness H2 of entrance, and is still more effective in maintenance of hardness of a molding surface.
The molding surface is required to have a predetermined hardness. Unlike the present embodiment, if the region softened by heat treatment is large and the region far from 5 mm from the deepest position on the bottom surface is softened, the softening may extend to the molding surface of the mold. As a result, it becomes difficult to provide the water cooling holes close to the molding surface. In this point, in the case of the softening heat treatment using the superheated steam according to the present invention, the heat-affected zone where the inside of the mold softens can be made shallow particularly at the bottom of the water cooling hole, so It is possible. On the contrary, if the area softened by heat treatment is small and the area softened sufficiently is shallower than 1 mm, cracking tends to occur in the area not softened in the area close to the water-cooled hole.

In this embodiment, the radial direction of the water cooling hole from the side of the water cooling hole from the deepest position A of the bottom to the height D / 2 (the boundary between the hemispherical region and the cylindrical region of the water cooling hole) The hardness H33 inside the mold at a position 3 mm in diameter is lower than 95% of the hardness H2 at the entrance when compared with Rockwell hardness HRC of C scale.
The hardness H33 can be read from FIG. 7 showing the hardness of the cross section B in FIG. From FIG. 7, the hardness H33 is approximately 70 HRA between the 2 mm and 4 mm lines, or approximately 39 HRC in terms of conversion. On the other hand, the hardness H2 at the inlet is about 45 HRC, and 95% of H2 is about 42.75 HRC. In the present embodiment, H33 <0.95 × H2 is established. And about this, said hardness H33 is lower than the hardness (40.5 HRC) of 90% of hardness H2 of inlet hardness, and it is further effective in suppression of the crack of a water-cooled hole.

In this embodiment, the radial direction of the water cooling hole from the side of the water cooling hole from the deepest position A of the bottom to the height D / 2 (the boundary between the hemispherical region and the cylindrical region of the water cooling hole) The hardness H37 inside the mold at a position of 7 mm is higher than 95% of the hardness H2 at the entrance when compared with Rockwell hardness HRC of C scale.
The hardness H37 can be read from FIG. 7 showing the hardness of the cross section B in FIG. From FIG. 7, the hardness H37 is approximately 72.5 HRA between the 6 mm and 10 mm lines, or approximately 44 HRC. On the other hand, 95% of the hardness H2 of the inlet is about 42.75 HRC. In the present embodiment, H37> 0.95 × H2 is established. And about this, above-mentioned hardness H37 is higher than 97% hardness (43.65 HRC) of entrance hardness H2, and it is further effective in maintenance of mold itself's hardness. .
If it is softened to a region separated by more than 7 mm from the water-cooled hole, the hardness of the mold itself may be reduced. In addition, if the softened area is shallower than 3 mm, cracking is likely to occur in the area not softened in the area close to the water-cooled hole.

<Example of φ 20>
Next, a water-cooled hole having a diameter D of 20 mm and a depth of 120 mm was formed in a test piece of the same size as the above-described test piece provided with φ15, and similarly superheated steam was sprayed on the bottom of the water-cooled hole. The temperature history and hardness of the φ20 test piece were also measured in the same manner as the φ15 test piece described above. A tube with an outer diameter d of 15 mm was inserted into the water-cooled hole so that the tip of the tube was located at a position 3 mm in height from the deepest position A of the water-cooled hole (distance h = 3 mm).

As shown in FIG. 14, the first temperature measurement point b1 to the fifth temperature measurement point b5 are set on the test piece, thermocouples are installed at each measurement point, and the superheated steam is sent to the water cooling hole through the pipe. The temperature change from was measured.
The first temperature measurement point b1 is the height position of the boundary between the cylindrical region and the hemispherical region 10 mm (that is, D / 2) above the deepest position A of the water cooling hole, relative to the central axis Ax of the water cooling hole It is provided at a position entering the inside of the 10 mm mold from the hole surface in the orthogonal direction.
The second temperature measurement point b2 is provided inside the mold 5 mm below the deepest position A of the water-cooled hole on the central axis Ax of the water-cooled hole.
The third temperature measurement point b3 is provided inside the mold 25 mm below the deepest position A of the water cooling hole on the central axis Ax of the water cooling hole.
The fourth temperature measurement point b4 is provided on the surface of the hole surface at the deepest position A of the water-cooled hole.
The fifth temperature measurement point b5 is a hole surface in the direction orthogonal to the central axis Ax of the water cooling hole at the height position of the boundary between the cylindrical region and the hemispherical region 10 mm above the deepest position A of the water cooling hole It is provided in the position which entered into the inside of the 5 mm mold.

  FIG. 15 is a graph showing the same temperature history as FIG. As shown in FIG. 15, the temperature history was the same as the temperature history of the φ15 test piece of FIG. Almost the same temperature history is obtained at the first temperature measurement point b1, the second temperature measurement point b2, and the fifth temperature measurement point b5. This is because the diameter of the water-cooling hole is larger than that of the water-cooling hole of φ15, so the superheated steam easily flows from the bottom to the side of the water-cooling hole, the temperature on the side easily rises, and the temperature at the first temperature measurement point increases It seems to be.

FIG. 16 is a radar chart showing the variation in hardness similar to FIG. FIG. 17 is a radar chart showing the variation in hardness similar to FIG. FIG. 18 is a radar chart showing the variation in hardness similar to FIG. FIG. 16 shows the dispersion of hardness in the cross section located 10 mm (the boundary between the cylindrical area and the hemispherical area) upward from the deepest position A of the bottom surface of the water-cooled hole. FIG. 17 shows the dispersion of hardness in the cross section located 20 mm upward from the deepest position A of the bottom surface of the water-cooled hole. FIG. 18 shows the variation in hardness of the top surface of the test piece.
FIG. 19 is a graph showing the relationship between the distance from the hole surface of the water-cooled hole and the hardness as in FIG.
Comparing FIG. 16 to FIG. 19 with FIG. 7 to FIG. 9 and FIG. 11, it is confirmed that the test piece in which the water cooling hole of .phi. 20 is formed is softened similarly to the test piece in which the water cooling hole of .phi. did it.

  This application is based on Japanese Patent Application (No. 2016-226449) filed on November 22, 2016, the contents of which are incorporated herein by reference.

  According to the present invention, a method of manufacturing a die casting mold and a die casting mold capable of reliably performing a softening heat treatment on a region including the bottom surface of a water-cooled hole are provided.

Reference Signs List 1 die casting mold 2 water cooling hole 3 hole surface 4 bottom surface 5 side surface 6 inlet 7 boundary 10 (of hemispherical region and cylindrical region)

Claims (12)

A method of manufacturing a die-casting die provided with a bottomed water-cooled hole of inner diameter D, comprising:
The hole surface forming the water cooling hole has a bottom surface forming a bottom of the water cooling hole and a side surface extending from the bottom surface toward the inlet,
A method for manufacturing a die casting mold, comprising a heat treatment step of sending superheated steam from the tip of a tube of an outer diameter d inserted into the water cooling hole toward the bottom to heat and soften the bottom. When the separation distance between the tip of the pipe and the deepest position of the bottom is defined as h,
0.5 × (D−d) /2≦h≦1.5× (D−d) / 2
The method for manufacturing a die casting mold according to claim 1, wherein the heat treatment step is performed by holding the tip of the pipe at the position where   The method for manufacturing a die-casting mold according to claim 1, wherein a tip of the pipe has a truncated cone shape.   The manufacturing method of the die-cast metal mold | die of Claim 1 which processes so that the said bottom face may become substantially hemispherical shape, and forms the said water-cooled hole. A die-casting die provided with a bottomed water-cooling hole of inner diameter D,
The hole surface forming the water cooling hole has a bottom surface forming a bottom of the water cooling hole and a side surface extending from the bottom surface toward the inlet,
The die-casting die whose hardness H1 of the deepest position of the said bottom face is lower than the entrance hardness H2 of the entrance of the water cooling hole.   The die-casting mold according to claim 5, wherein hardness H3 of a region from the deepest position of the bottom surface to the position of height D among the hole surfaces is lower than the entrance hardness H2.   The hardness H12 inside the mold at a position 1 mm in the direction perpendicular to the radial direction of the water-cooled hole from the deepest position of the bottom toward the inside of the mold was compared with the Rockwell hardness HRC of the C scale. The die-casting mold according to claim 5, wherein sometimes the inlet hardness H2 is less than 95%.   The hardness H15 inside the mold at a position 5 mm in the direction perpendicular to the radial direction of the water-cooled hole from the deepest position of the bottom toward the inside of the mold was compared with the Rockwell hardness HRC of C scale. 6. The die-casting mold according to claim 5, wherein when the inlet hardness H2 is higher than 95%.   The hardness H33 inside the mold at a position 3 mm in the radial direction of the water-cooled hole from the side at the position of height D / 2 from the deepest position of the bottom to the inside of the mold is C scale Rockwell The die-casting mold according to claim 5, which is lower than 95% of the hardness H2 of the inlet when compared with the hardness HRC.   The hardness H37 inside the mold at a position 7 mm in the radial direction of the water-cooled hole from the side at the height D / 2 from the deepest position of the bottom to the inside of the mold is C scale Rockwell The die-casting mold according to claim 5, which is higher than 95% of the hardness H2 of the inlet when compared with the hardness HRC. In the area inside the mold, when compared with Rockwell hardness HRC of C scale, the area which is 95% or less of the inlet hardness H2 is called a softening area,
The thickness of the softened region in the direction perpendicular to the radial direction of the water-cooled hole from the deepest position of the bottom surface is called D1.
When the thickness of the softened region in the radial direction of the water-cooled hole is referred to as D2 from the side surface at the position of height D / 2 from the deepest position of the bottom surface,
The die-casting mold according to claim 5, wherein the thickness D1 is smaller than the thickness D2. The die-casting mold according to claim 5, wherein the bottom surface is substantially hemispherical.

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