JP6330158B2 - Die casting mold manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a die-casting mold, and more particularly to a method for manufacturing a die-casting mold provided by performing a softening heat treatment after quenching and tempering.

  The alloy die casting method is widely used in the manufacture of alloy products such as cast parts for automobiles using aluminum alloys and magnesium alloys. In such an alloy die casting method, a molten alloy having a predetermined component composition is cast into a die casting mold at a high pressure, and after cooling, it is taken out from the mold to obtain an alloy product having a shape in which the shape of the mold design surface is transferred. Here, the die-casting die is required to have excellent heat fatigue resistance because it is repeatedly subjected to thermal cycles during product casting. Also, the mold design surface is required to have wear resistance against the press-fitting of molten alloy. Therefore, in general, steel having a predetermined component composition is tempered and tempered, and steel that has been processed to have a high balance between high mechanical strength (hardness) and high toughness is used.

  By the way, in the alloy die casting method, for the purpose of increasing the production efficiency and obtaining a solidified structure stably, after casting the molten alloy into the die casting mold during casting, the mold is made with cooling water around the back of the die casting mold. The mold is forcibly cooled. Then, irregular thermal stress is generated in the uneven part and screw hole part given to the back of the mold for fixing and transporting the mold, and it is called “large crack” starting from such a part. Large-scale cracks that may destroy the mold may occur. Therefore, softening heat treatment that suppresses cracking by imparting high toughness even if the hardness is lowered is performed by heat-treating only the mold back surface, which requires less mechanical strength, especially hardness, as the mold design surface.

  The softening heat treatment for strengthening the toughness of the mold back surface can be performed by partial heat treatment using a salt bath. That is, the mold after quenching and tempering is heat-treated by placing the back side down and immersing only the back side in a salt bath at a predetermined temperature.

  For example, in Patent Document 1, in a die-casting mold made of ultra-low carbon steel, after quenching and tempering the entire mold, only the back of the mold is immersed in a salt bath to increase toughness by softening heat treatment. The manufacturing method of the die-casting die which adjusts the balance of mechanical strength and toughness by covering the design surface with a heat insulating material and performing re-tempering heat treatment is disclosed. The flow path of the cooling water is formed in the vicinity of the back of the mold whose toughness is increased by the softening heat treatment to prevent large cracks.

  In softening heat treatment, it has also been proposed to use a resistance heater or the like in order to locally heat the tip of the recess.

  For example, in Patent Document 2, in a die casting mold made of hot mold steel, after the entire mold is quenched and tempered, the mold back surface and the vicinity of the tip of the cooling water hole are locally tempered with a salt bath. In addition, a method for manufacturing a die casting mold is disclosed in which heat treatment is performed to locally soften the vicinity of the inner surface of the tip of the cooling water hole. An elongated induction coil having a coil portion near its tip is inserted into the cooling water hole, and a high-frequency current is applied to the coil to heat the inner surface at the tip of the cooling water hole.

JP-A-4-367360 JP 2006-136922 A

  As described above, a salt bath can be used for the softening heat treatment on the back of the mold in the die casting mold manufacturing method, but prevention of scattering of a high-temperature salt bath material during immersion and removal of the mold in the salt bath In addition, it is required to improve handleability and workability such as a mold cleaning process after removal from the salt bath. In particular, if the treatment in the washing process is insufficient, the salt bath material is hardened while the openings such as cooling water holes and screw holes are clogged and cannot be easily removed.

  The present invention has been made in view of the situation as described above, and the object of the present invention is to handle in a die casting mold provided by performing a softening heat treatment on the back of the mold after quenching and tempering treatment. An object of the present invention is to provide a production method capable of softening and heat-treating the mold back surface with good performance and workability.

  This inventor examined whether softening heat processing was possible with the dry-type heating apparatus excellent in handleability and workability with respect to softening heat processing with a wet heating apparatus like a salt bath. Here, in a dry heating apparatus using a resistance heater, heating is performed by radiation and a heated air flow without using a heat medium having a large heat capacity like a salt bath. In such a case, unlike the case where the entire mold is heated in a dry heating apparatus, in order to heat only the mold back surface uniformly in the apparatus, it is greatly affected by heat removal from parts other than the mold back surface. . In particular, in a large mold, a temperature gradient tends to occur in the direction along the plane. That is, the non-uniformity of the heat treatment temperature causes variations in the hardness of the mold back surface.

  Accordingly, a die casting mold manufacturing method according to the present invention is a die casting mold manufacturing method including a mold design surface and a back surface that is paired with the mold design surface, and a plurality of regions on a plane after quenching and tempering treatment. The softening heat treatment is performed by causing the back surface of the die casting mold to face a heating device provided with a resistance heater capable of independently controlling output for each time.

  According to this invention, even in a dry heating apparatus using a resistance heater, the temperature gradient in the direction along the back surface of the die casting mold can be reduced in the softening heat treatment. That is, it is possible to reduce the variation in the hardness of the back surface of the mold, and the softening heat treatment can be performed with good handling and workability.

  In the above-described invention, the heating device may include a lattice plate spaced apart and parallel to the plane, and the lattice plate may support the back surface of the die casting mold at multiple points at multiple points. . According to this invention, in the softening heat treatment, the force to support the die casting mold is dispersed to prevent deformation due to its own weight under heating, so that heat input from the resistance heater can be stably received. Moreover, the die casting mold can be placed easily. That is, softening heat treatment can be performed with good handling and workability.

  In the above-described invention, the resistance heater may be controlled such that the temperature distribution on the back surface of the die casting mold is uniform in the surface. According to this invention, even if it is a dry-type heating apparatus in which temperature control is easy to be influenced by the environment, softening heat treatment can be performed with good handling and workability without requiring complicated control.

It is a sectional side view of the heating apparatus used for softening heat processing. It is a perspective view of the principal part of a heating apparatus. It is a side view of the die-casting die used for the substantive test. It is a figure which shows the temperature measurement result of a substantive test.

  A heating apparatus used for softening heat treatment in a method of manufacturing a die casting mold according to one embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the heating device 10 includes a fire wall 11 made of bricks that surround the outer periphery on a base 10 a, a tray 15 on which the die-casting mold 1 with the back surface 3 down is placed, 15 is provided with a skid 12 that supports 15 substantially horizontally, and a resistance heater 13 disposed below the upper surface of the skid 12. The resistance heater 13 is provided so as to correspond to each of a plurality of heating regions on a virtual plane P extending substantially horizontally just below the upper surface of the upper tray 15, and for each resistance heater 13 corresponding to each heating region. The output can be controlled independently.

  Further, the arrangement of the resistance heater 13 can be set in consideration of heat removal from the die casting mold 1. For example, it is preferable to divide a series of resistance heaters 13 whose outputs can be controlled independently along the longitudinal direction of the die casting mold 1. Further, a sealing material 14 is disposed around the placed die casting mold 1 so as to suppress the outflow due to the convection of the heated air with the fire wall 11. Here, the sealing material 14 may be a material such as a metal having a high thermal conductivity or an inorganic material having a low thermal conductivity such as a refractory brick depending on the purpose.

  In the present embodiment, the three resistance heaters 13a, 13b, 13c are arranged in order so as to be separated by the skid 12 in the longitudinal direction (left and right in the drawing) of the heating device 10, and the heating region a corresponding to each is arranged. , B, c are formed on a virtual plane P directly below the die casting mold 1. Further, the resistance heaters 13a, 13b, and 13c are controlled in output to temperatures set based on the temperatures measured by the control temperature measuring units 16a, 16b, and 16c immediately above them.

  In the softening heat treatment, a control thermocouple or the like is applied to the back surface 3 so as to make the temperature distribution of the back surface 3 uniform in the surface, and instead of the sheathed thermocouple for measuring the temperature of the control temperature measuring portions 16a, 16b, and 16c. Or it is more preferable that the outputs of the resistance heaters 13a to 13c are controlled in combination with this. The division of the heating area on the virtual plane P is not limited to this, and can be appropriately changed so as to reduce the temperature gradient in the direction along the back surface 3 in the softening heat treatment.

  Referring to FIG. 1 together with FIG. 2, the tray 15 is a lattice-shaped plate body, and the die casting mold 1 is placed on the upper surface of the die casting mold 1 with the back surface 3 facing downward. I can support it. By making the tray 15 into a lattice shape, sufficient radiant heat can be supplied from the resistance heater 13 to the back surface 3, and the back surface 3 of the die casting mold 1 can be sufficiently heated by the dry heating device 10. Further, the back surface 3 is supported at multiple points by the tray 15 to prevent deformation of the die casting mold 1 heated during the softening heat treatment due to its own weight.

  According to the present embodiment, even the heating device 10 using the resistance heater 13 can uniformly heat the back surface 3 of the die casting mold 1 in the softening heat treatment. That is, it is possible to provide a method for manufacturing a die casting mold that can be softened and heat-treated by the dry heating apparatus 10 with good handleability and workability.

[Substance test]
Next, the result of the substantial test which heated the die-cast metal mold | die 1 which can be actually used using the above-mentioned heating apparatus 10 is demonstrated, referring FIG.3 and FIG.4.

  As shown in FIG. 3, the die casting mold 1 is made of a material equivalent to JIS SKD61, and is a metal block of 810 mm × 700 mm in the dimension on the back of the mold. A hole is drilled from the mold design surface 2 to the back surface 3 in the thickness direction to a distance of 10 mm, and the bottom portions 5a, 5b and 5c of the hole and the hole side surfaces 4a, 4b and 4c having a depth of 10 mm from the mold design surface 2 are formed. Contact each with a thermocouple. The die casting mold 1 was placed with its longitudinal direction aligned with the longitudinal direction of the heating device 10 described above. Here, the hole side surfaces 4a, 4b, and 4c and the bottom portions 5a, 5b, and 5c are arranged at corresponding positions above the heating regions a, b, and c divided along the longitudinal direction of the heating device 10, respectively. ing. Below, the result of having measured the local temperature of the die-casting die 1 in each of the hole side surface parts 4a-4c and the bottom parts 5a-5c is shown.

  FIG. 4 shows the measurement results when the set temperatures of the resistance heaters 13a to 13c are the same. The temperature immediately above the heating area b, that is, the temperature of the bottom 5b of the die casting mold 1 was in the range of the target value of the heating temperature, but directly above the heating areas a and c, that is, the bottom 5a and c of the die casting mold 1. The temperature was lower than the target value. This is because in the portion on the back surface 3 side corresponding to the heating regions a and c, the temperature is relatively difficult to rise due to heat removal from the three side surfaces of the die casting mold 1 and the one mold design surface 2. On the other hand, in the portion on the back surface 3 side corresponding to the heating region b, heat is removed from the two side surfaces and the one mold design surface 2, so that the temperature is relatively likely to rise.

  Therefore, it is understood that the back surface of the die casting mold 1 can be heated evenly by setting the resistance heaters 13a and 13c higher than the set temperature of the resistance heater 13b in consideration of such heat removal. At this time, the local temperature on the mold design surface 2 side, that is, the temperature of the hole side surfaces 4a to 4c can be set to a predetermined target value or less, and the hardness of the mold design surface 2 after quenching and tempering can be reduced. The toughness can be maintained.

  The embodiments according to the present invention have been described above. However, the present invention is not necessarily limited thereto, and those skilled in the art will appreciate that various modifications can be made without departing from the spirit of the present invention or the appended claims. Alternative embodiments and modifications could be found.

DESCRIPTION OF SYMBOLS 1 Die-casting die 2 Mold design surface 3 Back surface 10 Heating device 13 Resistance heater 15 Tray

Claims (3)

A die casting mold manufacturing method comprising a mold design surface and a back surface that is paired with the mold design surface,
After the quenching and tempering treatment, the softening heat treatment is performed with the back surface of the die casting mold facing the heating device provided with a resistance heater capable of independently controlling the output for each of a plurality of regions on the plane. A method for producing a die-casting mold.   2. The die casting according to claim 1, wherein the heating device includes a lattice plate that is spaced apart from and parallel to the plane, and the lattice plate supports the back surface of the die casting mold at multiple points at at least a plurality of points. Mold manufacturing method.   The method of manufacturing a die-casting die according to claim 1 or 2, wherein the resistance heater is controlled so that the temperature distribution on the back surface of the die-casting die is uniform in the surface.

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