JPH07112266A - Die for die casting - Google Patents

Abstract

PURPOSE:To extend life of a die by coating a part or all surface coming in contact with molten metal with TiAlN in the die for die casting, which the parent metal is constituted with iron base material. CONSTITUTION:A required die 24 is mounted on a base holder 22, after a pressure in a vacuum vessel 10 is evacuated, Ar gas is introduced. A target 25 is mounted in a cathode 20, plasma generating position is controlled with using the control of magnetic field in the cathode, therefore, the operation of two kinds of targets of Ti target and TiAl target becomes possible with only one kind of the cathode 20. By this device, the die for die casting, in which the intermediate layer made of Ti layer is formed between TiAlN coated layer and parent metal, is obtained. By this method, the hard coating of TiAlN is provided on the die surface, and Ti layer is formed between both layers so as to provide a buffer layer, thereby increasing the adhesion force of TiAlN film to the parent metal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a die-casting die for forming a molten metal such as an aluminum alloy or a magnesium alloy, and more particularly to a die having excellent heat check resistance and metal erosion resistance. is there.

[0002]

2. Description of the Related Art Extending the life of a die is one of the major problems in die casting, and various methods have been tried. Especially, the heat check generated in the die is a major factor that shortens the life of the die. It is well known that they are one. In the case of a die-casting mold, it is customary that the temperature of the mold surface repeats a rapid temperature change between 100 ° C and 700 ° C, and the stress amplitude inside the mold due to this thermal shock causes innumerable heat on the mold surface. A check is generated, the molten metal is inserted into the generated crack, and the crack further develops and grows. Further, stress is particularly concentrated in the concave portions of the metal, and cracks are likely to grow, which is a serious problem particularly in the case of the surface that is the decorative surface of the product. As one means for preventing this heat check, coating of a ceramic thin film has been proposed, and a technique of coating a TiN thin film is being used so far. By coating the mold surface with TiN, a compressive stress of about 400 MPa is generated on the mold surface at room temperature, and this compressive stress prevents fatigue of the metal surface due to thermal shock generated during the heating / cooling cycle during the casting process. It is said to play a role in

Iron-based materials such as hot work tool steels such as SKD61 which are widely used for die casting dies react with molten Al alloy or Mg alloy to produce Fe.
-Al compound or Fe-Mg compound is generated and melted. For this reason, when the temperature of the molten metal is high, severe melting loss occurs in the vicinity of the gate and the part where the molten metal hits strongly,
There is a problem that the mold life becomes extremely short. On the other hand, since the TiN film does not react with these metal melts,
As long as the film is maintained on the surface of the mold soundly, there is an advantage that it is possible to prevent melting damage of the mold due to the molten metal.

[0004]

[Problems to be Solved by the Invention] However, TiN
The heat-resistant temperature of the film is 600 ° C., and decomposition will occur at higher temperatures. When it is used in a die casting mold, the maximum temperature of molten aluminum is 700 ° C., so that deterioration of the film to some extent cannot be prevented. When the TiN-coated SKD61 material was actually immersed in the molten aluminum, it was observed that the film gradually discolored. Therefore, as long as the TiN film is used, the change in film quality with time has been an unavoidable problem. In die casting in which molten metal is cast at a high speed, when the adhesive force between the mold and the film is weak, the film may be peeled off from the mold as the molten metal flows on the surface of the mold. The enhancement of the adhesive force of this film is the most important issue when applying a thin film coating to a die casting mold.

[0005]

In order to solve the above problems, the die casting mold of the first invention is a die casting mold in which the base material is an iron-based material, and a part of the surface that comes into contact with the molten metal. Alternatively, the whole was coated with TiAlN. Further, in the second invention, an intermediate layer made of a Ti layer is further formed between the base material and the TiAlN coating layer to form the base material and the TiAlN layer.
This is to strengthen the adhesive force of the N coating layer.

[0006]

[Function] It has been experimentally confirmed that TiAlN (titanium aluminum nitride) has better heat resistance than TiN (titanium nitride), so the maximum temperature of molten metal is about 70
It is suitable as a surface coating material for die casting molds at 0 ° C. Also, a sufficient adhesion can be obtained by forming a Ti film before the hard coating layer used when applying the TiN film to a tool or the like to form a laminated film. In addition, SKD61 as a base material and TiN film or TiA
Comparing the coefficient of thermal expansion with the 1N film, it was found that
6, 9.4 and 6.5, the TiN film and the base material SKD61.
Have relatively close coefficients of thermal expansion, while TiA
The 1N film shows a value considerably smaller than that of the base material SKD61, and it can be seen that the TiAlN coating mold has a stronger compressive stress at high temperature and the heat check resistance is better.

[0007]

Embodiments of the present invention will be described in detail below with reference to the drawings. 1 to 5 relate to an embodiment of the present invention, FIG. 1 is a block diagram of a coating apparatus, FIG. 2 is a perspective view showing a configuration of a target, and FIGS. 3 to 4 are perspective views for explaining a target during a coating process. FIG. 5 and FIG. 5 are graphs showing ion current density distribution when plasma is generated. In FIG. 1, a coating apparatus 100 includes a vacuum container 10 connected to a vacuum pump (not shown) via a pipe 12 and a main valve 11, and four types of DC power supply devices 1 connected to respective devices in the vacuum container 10. It is composed of 2, 3, and 4. A target 25 to be described later is provided in the vacuum container 10.
The cathode 20 on which is installed is fixed to one inner surface and is connected to the external discharge DC power supply device 2. Cathode 2
A magnetic field control solenoid coil 21 is embedded inside 0 and is connected to an external solenoid coil DC power supply device 1. On the other hand, a substrate holder 22 which is rotatable around a bearing 22a is installed in the center of the inside of the vacuum container 10 facing the cathode 20, and a mold 24 covers the coating surface of the cathode 20.
It is installed facing the direction. The substrate holder 22 is a motor 23
Is driven by the chain wheels 23a and 23b to be rotatable. On the substrate holder 22 to which the mold 24 is closely attached, the reverse sputtering high frequency power supply device 3 and the substrate bias DC power supply device 4 are arranged in parallel via a chain wheel 23a, a chain wheel 23b and a roller chain 23c interposed therebetween. Wired. The choke coil 5 immediately after the substrate bias DC power supply device 4 is provided for protection so that the high frequency power of the reverse sputtering high frequency power supply device 3 does not flow into the substrate bias DC power supply device 4. In addition, an argon gas and a nitrogen gas are introduced into the vacuum container 10 through a process gas introduction pipe 13, and an openable and closable shutter 26 is provided between the cathode 20 and the mold 24. Next, the target 2 attached to the cathode 20
5 will be described in detail. As shown in FIG. 2, the target 25 comprises a cathode 20 and a backing plate 30 which is detachably attached to the surface of a Ti metal 32 and a T metal 32 having a thickness of about 5 mm.
The iAl sintered body 31 is composed of two types of metal plates. In the TiAl sintered body 31, both Ti and Al are usually 5
0 atm. % Contained.

A coating process for forming a TiAlN coating layer on the surface of the mold 24 using the coating apparatus 100 configured as described above will be described. First, a desired mold 24 is attached to the substrate holder 22, the main valve 11 is opened, and the pressure in the vacuum container 10 is evacuated to 5 × 10 ⁻⁶ Torr or less by driving the vacuum pump. After the evacuation is completed, argon gas is introduced through the process gas introduction pipe 13 and the pressure is set to about 2 × 10 ⁻³ Torr. In this state, with the shutter 26 closed,
A plasma is generated on the target 25 to generate the target 25.
Thoroughly clean the surface by sputtering. After that, a high voltage is applied to the substrate (mold 24) to clean the mold 24 by sputtering. The discharge power source used at this time is selected according to the surface shape of the mold 24. That is, when the surface is smooth, DC sputter etching is performed using the substrate bias DC power supply device 4, but since the die-casting die generally has a complicated shape and the surface is not smooth, DC sputter etching is used. As a result, the sputter-etched areas concentrate on the convex portions, and conversely, the concave portions are contaminated by the gas evaporated from the convex portions, which makes it impossible to achieve the intended purpose. Therefore, in the present invention, although there is a problem that the processing time becomes long by performing the reverse sputtering using the high frequency power supply device 3 for reverse sputtering,
Electric discharge is generated on the entire surface of the mold, which prevents local etching and defective etching. After the etching cleaning of the substrate (mold 24) by reverse sputtering is completed, the target 25 is again cleaned by sputtering. The reason is that impurities generated from the mold surface during the reverse sputtering adhere to the target 25 and are removed.
In this way, all pretreatments up to film formation are completed.

Next, the process for producing the hard coating layer is started. In the present invention, Ti is used as a hard coating layer.
AlN is used. Metal surface of substrate (die 24) and TiA
In order to provide a Ti layer between 1N layers, when two kinds of films are usually formed by sputtering, separate cathodes to which two kinds of targets, a Ti target and a TiAl target are attached, are required. That is, in the conventional method, an apparatus having the above-mentioned separate cathodes is required, but in the present invention, the target 25 shown in FIG. 2 is attached to the cathode 20, and as shown in FIGS. By controlling the plasma generation position by controlling the magnetic field, it is possible to operate with one type of cathode 20. In FIG. 3, plasma P is applied to the outer periphery T of the TiAl sintered body 31.
This is an example generated in the i metal layer 32, and FIG. 4 shows a state in which plasma P is generated on the surface in the region of the TiAl sintered body 31, and corresponds to the case of forming a Ti film and a TiAlN film, respectively. In the actual film formation, first, argon gas is introduced into the vacuum container 10 to set the gas pressure to about 2 × 10 ⁻³ Torr, and the mold 24 as the substrate obtains an ion assist effect by plasma. A substrate bias of about 100 V is applied by the bias DC power supply device 4. In this state, plasma is generated on the outer peripheral portion of the target 25 (corresponding to FIG. 3), and a Ti film of about 1000 to 2000 is formed.
Å (Angstrom) film formation. Subsequently, N ₂ and Ar gas are introduced into the vacuum container 10 to generate plasma in the inner peripheral portion of the target 25 (corresponding to FIG. 4), and TiAlN
The film is formed to a thickness of about 2 μm. At this time, the ratio of N ₂ gas and Ar gas changes depending on the performance of the vacuum pump used, the size of the substrate (mold 24), the power of discharge, etc., so the optimum conditions at that time should be understood in advance by a test. Is desirable. The standard film thickness is 2 μm for ordinary hard coatings, but it depends on the purpose of use.
A film thickness of about μm is possible. If the film thickness exceeds this value, brittleness, which is an inherent characteristic of ceramics, appears remarkably, and the effect as a hard coating is diminished.

The structure of the target 25 in the present invention is as follows.
As described above, the TiAl sintered body 31 is arranged inside and the Ti metal 32 is arranged outside as shown in FIG. 2, but it is impossible to exchange Ti and TiAl inside and outside. Because it becomes the hard coating layer Ti
The AlN layer is a necessary condition for obtaining better film quality by ion assist of peening the substrate with ions in plasma during film formation. As shown in FIG. 5, the closer the plasma is to the center, the more the amount of ions flowing into the substrate. Is increased.
On the contrary, when the plasma is located outside, the basic ion current hardly flows and the ion assist effect can hardly be expected. Therefore, in the composite target of the present invention, the hard coating material T is used in the center of the target.
It must be composed of iAl.

[0011]

As described above, in the die casting mold of the present invention, high melting loss resistance is secured by applying a hard coating of TiAlN on the surface of the mold which is the substrate.
Since the heat check resistance is given, the life of the mold is significantly extended. Further, by forming a Ti layer between the die base material and the hard coating layer to form a buffer layer, Ti
The adhesion of the AlN film to the base material can be improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a coating apparatus showing an embodiment according to the present invention.

FIG. 2 is a perspective view showing a configuration of a target showing an embodiment according to the present invention.

FIG. 3 is a perspective view illustrating a target during a coating process according to an embodiment of the present invention.

FIG. 4 is a perspective view illustrating a target during a coating process according to an embodiment of the present invention.

FIG. 5 is a graph showing an ion current density distribution during plasma generation according to the present invention.

[Explanation of symbols]

 1 DC power supply for solenoid coil 2 DC power supply for discharge 3 High frequency power supply for reverse sputtering 4 DC power supply for substrate bias 5 Choke coil 10 Vacuum container 11 Main valve 12 Piping 13 Process gas inlet pipe 20 Cathode 21 Magnetic field control solenoid Coil 22 Substrate holder 22a Bearing 23 Motor 23a Chain wheel 23b Chain wheel 23c Roller chain 24 Mold 25 Target 26 Shutter 30 Backing plate 31 TiAl sintered body 32 Ti metal 100 Coating device P Plasma Q Substrate inflowing ion current density S From the target center The distance

Claims (2)

[Claims] 1. A die-casting die whose base material is an iron-based material, characterized in that part or all of the surface in contact with the molten metal is covered with TiAlN. 2. The die casting mold according to claim 1, wherein an intermediate layer made of a Ti layer is formed between the TiAlN coating layer and the base material.