JPH0377027B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Industrial Application] The present invention relates to a mold temperature control method in a low-pressure casting method, and more specifically, detects the mold temperature prior to the start of a casting cycle, and then compares the measured mold temperature with the mold temperature. By comparing the preset reference mold temperature range at the start of pressurization of the molten metal and controlling the flow rate of cooling water so that the mold temperature falls within the reference mold temperature range, casting is performed. This invention relates to a mold temperature control method in a low-pressure casting method that makes it possible to obtain cast products of uniform quality under constant conditions. [Background of the Invention] In general, low-pressure casting methods are widely used, for example, when mass producing automobile parts and the like. In this low-pressure casting method, molten metal made of a light alloy such as aluminum alloy is heated and held in a closed container, and the surface of the molten metal is pressurized with relatively low-pressure inert gas or air. This is a method of manufacturing a cast product by filling a cavity defined in a mold. BACKGROUND ART Conventionally, during a casting process using a low-pressure casting method, the temperature of the mold has been controlled by supplying cooling water to the mold as necessary. In this case, generally a temperature sensor is provided in the mold, and if the actual mold temperature measured by this temperature sensor is higher than a preset temperature, cooling water is supplied; If the temperature is lower than the set temperature, the water supply will be stopped.
There is a method of maintaining the temperature of a mold within a predetermined temperature range during the casting process. By the way, during the casting process, there are various problems such as removing the cast product after opening the mold, cleaning the mold afterwards, or setting the core in the mold, as well as malfunctions related to the mold equipment and troubles due to operational errors. There will be a waiting time. Therefore, in the casting process, 1
It is common for each casting cycle to vary. In fact, the pouring interval changes in response to variations in the casting cycle, and as a result, the initial mold temperature at the start of pouring in each casting cycle differs. The temperature changes of the mold and the molten metal during the process of filling the cavity with molten metal and solidifying it by pressurizing and holding the same also show different trends in response to the above-mentioned variations in the initial mold temperature. However, the mold temperature control methods described above cannot effectively accommodate variations in individual casting cycles. Therefore, since the casting conditions in each casting cycle are not constant, the quality of the cast product is not uniform throughout the casting process, and
This has the disadvantage that it is not possible to prevent the occurrence of defective products. [Object of the Invention] The present invention has been made to overcome the above-mentioned disadvantages, and includes detecting the temperature of the mold via a temperature sensor or the like prior to the start of the casting cycle,
This mold temperature is compared with a preset standard mold temperature range, and when the mold temperature is not within the standard mold temperature range, the amount of cooling water is selected based on this temperature difference, and the cooling water amount is selected based on this temperature difference. By supplying water to the mold and cooling the mold until it reaches the standard mold temperature range, the mold temperature during filling with molten metal can be kept constant at all times, resulting in quality of the cast product. The purpose of the present invention is to provide a mold temperature control method in a low-pressure casting method that makes it possible to make the mold temperature uniform and to stabilize and improve the quality. [Means for Achieving the Object] In order to achieve the above object, the present invention pressurizes the surface of the molten metal stored in a closed container with pressurized gas to inject the molten metal into a cavity defined in a mold. In the low-pressure casting method performed by filling, the mold temperature is detected prior to pressurizing and filling the molten metal into the cavity.
Next, a comparison judgment process is performed to determine whether or not the mold temperature is within a preset reference mold temperature range, and the flow rate of cooling water supplied to the mold is controlled based on the comparison judgment process. It is characterized in that pressurized filling of the molten metal into the cavity is started when the mold temperature reaches a reference mold temperature range. [Embodiments] Next, preferred embodiments of the mold temperature control method in the low-pressure casting method according to the present invention in relation to a casting apparatus for carrying out the method will be listed, and will be described in detail below with reference to the accompanying drawings. explain. In FIG. 1, reference numeral 10 indicates a casting device. This casting apparatus 10 basically consists of a casting mold 12 and a mold temperature control mechanism 14. The casting mold 12 includes a lower mold 16 and a lower mold 16.
The upper mold 18 and the lower mold 16 disposed above the
and sliding molds 20 and 22 disposed to slidably fit into the upper mold 18. Furthermore, a cavity 24 is defined by the lower mold 16, the upper mold 18, and the sliding molds 20, 22.
The shape is suitable for casting cylinder heads constituting internal combustion engines of automobiles and the like. Therefore, a stepped hole 26 is formed in the lower mold 16, and a nozzle 30 having a sprue 28 communicating with the cavity 24 is installed in the stepped hole 26. A stalk 32 for feeding molten metal is connected to the nozzle 30, and this stalk 32 is connected to a molten metal supply means 34 installed below the lower mold 16 and storing the molten metal. This molten metal supply means 3
A crucible (not shown) is disposed at 4, and the molten metal is kept heated in the crucible. On the other hand, the upper mold 18 is fixed to a movable die base 36 and can be freely displaced in the vertical direction under the driving action of an actuator (not shown) connected to the movable die base 36. The movable die base 36 and the upper die 1
A cooling block 38 is interposed between the molds 8 and is fixed to the upper mold 18 with bolts or the like. Cooling holes 40 are defined in the cooling block 38, and cooling water is introduced and led out through pipes 42 and 44 inserted into the movable die base 36. Further, an extrusion pin 46 for extruding the product is inserted through the upper die 18 and the movable die base 36, and the extrusion pin 46 has its base end attached to the mounting member 48, and its tip end attached to the cavity 24. I am going to Next, sliding molds 20 and 22 are slidably engaged between the lower mold 16 and the upper mold 18. The sliding molds 20, 22 are provided with cooling blocks 50, 52, respectively, and are connected to an actuator (not shown) with a connecting member 54,
56. In this case, the cooling blocks 50 and 52 have cooling holes 58 and 58 inside, respectively.
60 is defined. Pipes 61 and 62 for supplying cooling water and pipes 63 and 64 for discharging the cooling water are inserted into the cooling holes 58 and 60, respectively. In addition, in FIG. 1, reference numerals 66a to 6
6f indicates a sand core, and reference numeral 68 indicates a hole for degassing. Therefore, the mold temperature control mechanism 14 that controls the temperature of the casting mold 12 will be explained. The mold temperature control mechanism 14 includes a temperature sensor 72 such as a thermocouple disposed near the cavity 24 of the lower mold 16, and a temperature sensor 72 for controlling the amount of cooling water supplied from a cooling water supply source 74. The output voltages of the flow rate control means 76 and the temperature sensor 72 are introduced as mold temperature data, and based on this mold temperature data, the opening and closing operations of the valves constituting the flow rate control means 76 are controlled, and the molten metal supply means 34 is controlled. and a microcomputer 78 for control. The flow rate control means 76 is composed of a fluid circuit including a solenoid valve and a variable throttle valve. That is, the pipe line 49 extending from the cooling water supply source 74 branches into pipe lines 80 and 82 in the middle, and solenoid valves 84 and 86 are provided in the branched pipe lines 80 and 82, respectively. . The solenoid valves 84 and 86 are configured to be opened and closed based on an opening or closing signal output from the microcomputer 78. Variable throttle valves 88, 90 and flow meters 92, 9 are provided downstream of the solenoid valves 84, 86, respectively.
4 are arranged. Further, the pipe lines 80 and 82 join together again and are connected to the pipe 61 inserted into the cooling block 50 of the sliding mold 20. Note that the cooling water introduced into the cooling hole 58 from the pipe 61 is discharged to the tank 96 via the pipe 63. Further, the cooling water supplied from the mold temperature control mechanism 14 is also introduced into the cooling block 52 of the sliding mold 22 via a conduit 98, and is discharged into a tank 100. Next, using the casting apparatus 10 configured as described above, the casting conditions were set such that the temperature of the molten metal made of an aluminum alloy equivalent to JIS AC2B was 700°C, and the pressing force was 0.28°C.
Cast the cylinder head as Kg/cm ² . Here, the casting mold 12 is subjected to a trial casting cycle, whereby the mold temperature of the casting mold 12 is preliminarily raised to a temperature suitable for continuously performing an actual casting cycle. It is assumed that there is Therefore, the sand cores 66a to 66f are installed in predetermined portions of the cavity 24 defined in the casting mold 12, and then the movable die base 36 and the upper mold 18 integrated therewith are moved under the action of an actuator (not shown). While displacing it downward, the sliding type 2
0 and 22 are moved closer together under the action of an actuator (not shown) connected via connecting members 54 and 56, and the mold is clamped. Hereinafter, while carrying out the mold temperature control method according to the present invention according to the flowchart shown in FIG.
The mold temperature is adjusted within a preset mold temperature range that is optimal for the casting conditions. In this case, the microcomputer 7 that constitutes the mold temperature control mechanism 14
A program for the procedure shown in the flowchart of FIG. 2 is written in the ROM (not shown) of 8, and the CPU (not shown) operates according to this flowchart. That is, in step 1, the mold temperature T _D immediately after mold clamping is detected via the temperature sensor 72 disposed on the lower mold 16. Next, in step 2, this mold temperature T _D is introduced to the microcomputer 78 as temperature data via an interface (not shown). This microcomputer 7
A CPU (not shown) constituting the microcomputer 78 compares and determines whether the mold temperature T _D is within the set mold temperature range S input into the microcomputer 78 in advance. This set temperature range S is optimally set based on the casting conditions, and
As shown in the time chart of FIG. 3, it has a predetermined temperature range set between an upper limit temperature T _nax and a lower limit temperature T _nio . In FIG. 3a, the curve shown by a solid line is a mold temperature curve 102 representing a temporal change in the actual mold temperature T _D. Here, if the mold temperature T _D is a value included in the set mold temperature range S, the microcomputer 78 transfers a signal to the molten metal supply means 34, and the molten metal supply means 34 is thereby activated. Then, the surface of the molten metal stored in a crucible (not shown) provided in the molten metal supply means 34 is pressurized with compressed air, and the filling of the molten metal into the cavity 24 via the stalk 32 and the sprue 28 is started ( STP3). On the other hand, if the mold temperature T _D is not within the set mold temperature range S, in step ₄ , the CPU
It is determined which of the four temperature zones A, B, C, and D corresponds to the preset temperature range S based on the set temperature range S. These temperature zones A to D are arbitrarily set based on predetermined casting conditions as shown in Section 3a, and in this embodiment, a predetermined temperature is set in the region above the upper limit temperature T _nax in the set temperature range S. It is set with a certain width. In this case, the amount of cooling water is set as shown in Table 1 corresponding to each of the temperature zones A to D, and the opening and closing states of the solenoid valves 84 and 86 are adjusted to achieve this amount of cooling water. It is determined.

[Table] Note that the flow rates Q ₁ and Q ₂ of the cooling water flowing through the solenoid valves 84 and 86 can be arbitrarily adjusted by variable throttle valves 88 and 90 installed downstream of these valves. The setting of the amount of cooling water as described above is determined depending on the casting conditions. Thus, based on the result of step 4, the microcomputer 78 sends open or close signals to the solenoid valves 84 and 86, respectively, in steps 5 and 6. After this state continues for a predetermined time in step 7, the process returns to step 1 again. Therefore, in the time chart of Fig. 3, the mold temperature at time t ₀ detected in step 1 is actually
In the next step 2, the CPU determines whether T _D0 is within the set temperature range S. Mold temperature T _D0
Since this is outside the set mold temperature range S, the CPU determines in step 4 which temperature zone among temperature zones A to D this mold temperature T _D0 is included. In this case, the mold temperature T _D0 corresponds to the B zone. Therefore, based on the CPU's judgment processing result, the microcomputer 78 sends an opening signal to the solenoid valve 86 in order to adjust the amount of cooling water to Q ₂ in Table 1, while sending a closing signal to the solenoid valve 84. The solenoid valves 84 and 86 are opened and closed. (STP5,
6). As a result, the cooling water supplied from the cooling water supply source 74 passes through the pipe 82, that is, through the solenoid valve 86 and the variable throttle valve 90, and the flow rate Q _{2 is} increased.
is introduced into the pipes 61 and 62, and the cooling block 5
Cooling water is introduced into cooling holes 58 and 60 defined in holes 0 and 52, respectively. And this cooling hole 58,
After flowing through 60, the water is drained into tanks 96, 100 via pipes 63, 64. This cooling water circulation continues for a predetermined time, for example, one minute (STP7). Therefore, return to step 1 again. That is, the mold temperature T _D1 at time t ₁ is measured via the temperature sensor 72.
Measure. In this case, the mold temperature T _D1 drops to be included in the temperature zone C, as shown in FIG.
The temperature zone C is approaching the set mold temperature range S, and in this temperature zone C, in order to prevent the mold temperature T _D from being supercooled below the set mold temperature range S, the mold temperature T _{D is} It is desirable that the gradient of descent is gentle. Therefore, through steps 2 and 4, the microcomputer 78 adjusts the amount of cooling water to the previous flow rate based on the CPU's judgment processing.
In order to reduce the flow rate from _Q2 to _Q1 , a closing signal is sent to the solenoid valve 86 to close the solenoid valve 86, and an open signal is sent to the solenoid valve 84 to open it.
In this way, through steps 5, 6, and 7, the flow rate of the cooling water is regulated to _Q1 , and the cooling water flows through the cooling blocks 50, 5.
It is continuously supplied to the cooling holes 58 and 60 of No. 2 for a predetermined period of time. Furthermore, returning to step 1, the mold temperature T _D at time t ₂ is actually measured. In Figure 3, the mold temperature T _D
falls further and is in the range of temperature zone D. After steps 2 and 4 in the same manner as described above, the microcomputer 78 sends a closing signal to the solenoid valve 84, thereby closing the solenoid valve 84. As a result, the supply of cooling water to the cooling holes 58, 60 of the cooling blocks 50, 52 is stopped (STP5, 6). In this case, since the temperature zone D is adjacent to the set mold temperature range S, it is sufficient that the mold temperature T _D is lowered by natural heat radiation. Furthermore, after a predetermined time has elapsed (STP7), the process returns to step 1 and measures the mold temperature T _D at time _t3 . Here, the mold temperature T _D decreases due to natural heat radiation,
The temperature reaches within the set temperature range S. In this way, steps 2 and 3 are executed, and filling of the cavity 24 with molten metal is started. Thereafter, the cavity 24 is filled with molten metal, maintained under pressure for a predetermined period of time, and further depressurized to solidify the molten metal. After the molten metal has solidified, the mold is opened and the cast product is taken out, completing the casting cycle. The next casting cycle similarly repeats the steps described above. That is, in FIG. 3, steps 1 and 2 are performed based on the value of the mold temperature T _D at the second time _t'0 , and the mold temperature T _D is within the set mold temperature range S through the same order as described above. When this is reached, filling of the cavity 24 with molten metal is started. In this way, the mold temperature T _D at the start of molten metal filling is always maintained within a certain range that is optimal for the casting conditions. Thereafter, a second casting cycle is performed. Note that in this embodiment, the solenoid valve 8
4, 86 and variable throttle valves 88, 90 are used, however, the opening/closing valve may be fixed and a proportional control valve may be connected to the fixed opening/closing valve. [Effects of the Invention] As described above, according to the present invention, the mold temperature actually measured via a sensor etc. is compared with the mold temperature range preset based on the casting conditions, and the mold temperature is within the set mold temperature range. In order to control the mold temperature, the amount of cooling water is supplied in several stages while being controlled based on the comparison process. Therefore, the mold temperature when pressurizing and filling the molten metal is always set within a certain range, so the casting conditions are constant, and as a result, a cast product of uniform quality can be obtained. Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to these embodiments, and various improvements and changes in design are possible without departing from the gist of the present invention. Of course.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view showing a schematic configuration of a casting apparatus for implementing the mold temperature control method according to the present invention, and FIG. 2 is a flowchart explaining the procedure of the mold temperature control method. FIG. 3 is a time chart based on an embodiment of the mold temperature control method. 10... Casting device, 12... Casting mold, 14...
... Mold temperature control mechanism, 16 ... Lower mold, 18 ... Upper mold, 20, 22 ... Sliding mold, 24 ... Cavity, 32 ... Stoke, 34 ... Molten metal supply means,
50, 52... cooling block, 58, 60... cooling hole, 76... flow control means, 78... microcomputer.

Claims (1)

[Claims] 1. In a low-pressure casting method in which the surface of molten metal stored in a closed container is pressurized with pressure gas and the molten metal is filled into a cavity defined in a mold, prior to pressurizing and filling the molten metal into the cavity. to detect the mold temperature, then perform a comparative judgment process to determine whether the mold temperature is within a preset reference mold temperature range, and supply cooling water to the mold based on the comparative judgment process. A mold temperature control method in a low-pressure casting method, characterized in that the flow rate of the mold is controlled, and when the mold temperature reaches a reference mold temperature range, pressurized filling of the molten metal into the cavity is started.