GB2246532A

GB2246532A - Method of controlling die temperature in low-pressure casting process

Info

Publication number: GB2246532A
Application number: GB9116911A
Authority: GB
Inventors: Kouji Tanaka; Syugo Kondo; Takeshi Imura; Katsuhiko Ando; Shigemitsu Nakabayashi
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 1987-12-01
Filing date: 1991-08-06
Publication date: 1992-02-05
Anticipated expiration: 2011-08-06
Also published as: GB2212749B; GB2246532B; GB8827911D0; JPH0426935B2; JPH01148449A; GB2212749A; GB9116911D0

Description

METHOD OF AND APPARATUS FOR CONTROLLING DIE TEMPERATURE IN LOW-PRESSURE

CASTING PROCESS The present invention relates to a method of and an apparatus for controlling the temperature of a die in a lowpressure casting process, and more particularly to a method of and an apparatus for controlling the temperature of a die in a low-pressure casting process by detecting die temperatures respectively in the various steps of a casting cycle which include a step from the clamping of the die to the starting of pouring molten metal into the die, a step of filling the molten metal in the die, and a step after the filling of the molten metal until the opening of the die, and by controlling the cooling of the die according to an optimum cooling pattern, so that the quality of the cast product will be stable and high irrespective of different casting cycles which the die undergoes.

Generally, the low-pressure casting process is widely employed for massproducing automotive parts or the like. In the low-pressure casting process, molten light alloy (hereinafter referred to as "molten metal") such as an aluminum alloy or the like is heated and held in a sealed container, and the surface of the molten metal in the container is pressurized by an inert gas or air under a relatively low pressure to force the molten metal via a feed - 2 pipe into a die cavity defined in a die for casting a product.

During the low-pressure casting process, cooling water is supplied to the die to control the temperature of the die which is associated with a temperature sensor. when the actual temperature of the die as detected by the temperature sensor is higher than a reference temperature, cooling water is supplied to the die. When the detected die temperature is lower than the reference temperature, the supply of cooling water is stopped. In this manner, the temperature of the die is kept in a certain temperature range.

The casting machine for carrying out the casting process necessarily has certain downtimes when the casting is removed after the die has been opened,_when the die is cleaned after the casting has been taken out, and when sand cores are set in the die. one casting cycle may also be interrupted by a trouble with the die or a trouble caused by an erroneous action of the operator. Usually, therefore, the casting process contains different or irregular casting cycles.

If the intervals between the steps of pouring molten metal into the die in the respective different casting cycles differ from each other, then the initial temperatures of the die when starting to pour the molten metal also differ from each other in the respective casting cycles. The different initial temperatures in the respective casting i i 1 1 i cycles result in different patterns in which the temperatures of the die and the molten metal vary in the stage of filling the molten metal in the die cavity and solidifying the molten metal under pressure.

The aforesaid temperature control method cannot effectively cope with varying conditions in the different casting cycles. More specifically, cooling water is supplied or interrupted solely based on the reference die temperature regardless of how each casting cycle proceeds through the steps thereof. Since the temperature conditions of the die in the respective casting cycles are not constant, the castings produced by the casting process do not have uniform quality, and sometimes defective castings may be produced because of unexpected conditions resulting from the different casting cycles.

4 The present invention providesa method of controlling the temperature of a casting die in a low-pressure casting process for pressurizing the surface of molten metal stored in a closed container to fill the molten metal in a die cavity defined in the casting die, said method comprising the steps of: detecting the tempera ture of said casting die when the molten metal is filled in said die cavity under pressure; selecting, dependent on said detected temperature of the casting die, an optimum one of a plurality of molten metal pressurizing patterns established dependent on die temperatures and an optimum one of a plurality of die cooling patterns established dependent on die temperatures; filling and holding the molten metal in said die cavity under a pressure according to the selected molten metal pressurizing pattern; and supplying said casting die with an amount of cooling water which is variably controlled according to the selected die cooling pattern.

j i I 1 1 1 Preferably, said molten metal pressurizing patterns are established such that a time period for pressurizing the molten metal is shorter when the die temperature is lower, and is longer when the die temperature is higher.

Optionally, said molten metal pressurizing patterns are established such that a speed at which the molten metal is fed into said die cavity is higher when the die temperature is lower, and is lower when the die temperature is higher.

i i 1 i 1 1 1 i 7 - Still more preferably, the temperature of the casting die and the temperature of the molten metal are detected, and an optimum one of the molten metal pressurizing patterns and an optimum one of the die cooling patterns are selected dependent on said detected temperature of the casting die and said detected temperature of the molten metal.

The preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which:- FIG. 1 is a vertical cross-sectional view, partly in block form, of a die casting apparatus for carrying out a die temperature control method according to the present invention; FIG. 2 is a flowchart of a sequence of a first die temperature control process of the die temperature control method; FIG. 3 is a timing chart showing a casing cycle based on the first die temperature control process; FIG. 4 is a flowchart of a sequence of a second die temperature control process of the die temperature control method; FIG. 5 is a graph showing the relationship between die temperatures and molten metal temperatures which are relied upon in selecting a molten metal pressurizing pattern and a die cooling pattern in the second die temperature control process; FIG. 6 shows graphs (a) through 6(g) and graphs (a,) through 6(g,) illustrating molten metal pressurizing patterns and die cooling patterns which are established dependent on the die temperature and the molten metal temperature; 1 i FIG. 7 shows graphs (h) through 7(n) and graphs (h,) through 7(n,) illustrating other molten metal pressurizing patterns and die cooling patterns which are established dependent on the die temperature and the molten metal temperature; FIG. 8 is a flowchart of a sequence of a third die temperature control process of the die temperature control method; and FIG. 9 is a timing chart showing a casing cycle based on the third die temperature control process.

FIG. 1 shows a die casting apparatus, generally designated by the reference numeral 10, basically comprising a casting die 12 and a die temperature control apparatus 14.

The casting die 12 includes a lower die member 16, an upper die member 18 disposed above the lower die member 16, and slidable die members 20, 22 slidably fitted between the lower and upper dies 16, 18. The lower die 16, the upper die 18, and the slidable dies 20, 22 jointly define a die cavity 24 therebetween which has a three-dimensional shape for casting the cylinder head of an automotive internal combustion engine, for example.

The lower die member 16 has a stepped hole 26 defined vertically therein. A nozzle 30 is mounted in the stepped hole 26 and has a sprue 28 communicating with the die cavity 24. The nozzle 30 is connected to a stalk 32 - 10 through which molten metal flows, the stalk 32 being connected to a molten metal supply 34 disposed below the lower die member 16. The molten metal supply 34 includes a closed ladle (not shown) for holding molten metal at a desired temperature.

The upper die member 18 is fixed to a movable die base 36 and vertically movable in response to operation of an actuator (not shown) connected to the movable die base 36. Between the movable die base 36 and the upper die member 18, there is disposed a cooling block 38 secured to the upper die member 18 by bolts or the like. The cooling block 38 has a cooling hole or passage 40 defined therein for receiving cooling water therein. The cooling water can be introduced into and discharged from the cooling hole 40 through pipes 42, 44 inserted in the movable die base 36. An ejector pin 46 for knocking out a casting when the die 12 is opened is inserted through the upper die member 18 and the movable die base 36. The ejector pin 46 has one end mounted in an attachment member 48 disposed above the movable die base 36 and the opposite end facing into the die cavity 24.

Cooling blocks 50, 52 are disposed in close contact with the rear surfaces of the slidable die members 20, 22, respectively, which are slidably fitted between the upper and lower dies 18, 16. The cooling blocks 50, 52 are connected to actuators (not shown) through connectors 54, 56, 1 i i I 1 i 1 - 11 respectively. The cooling blocks 50, 52 have cooling holes or passages 58, 60, respectively, which are held in communication with pipes 61, 62, respectively, for supplying cooling water into the cooling holes 58, 60 and also with pipes 63, 64, respectively, for discharging cooling water from the cooling holes 58, 60.

Sand cores 66a through 66f are disposed in the die cavities 24. A vent hole 68 for discharging a gas from the die cavity 24 is defined through the upper die member 18, the cooling block 38, and the movable die base 36.

The die temperature control apparatus 14 for controlling the temperature of the casting die 12 according to the present invention comprises a first temperature sensor 72 disposed in the lower die member 16 near the die cavity 24 in the form of a thermocouple, for example, for detecting the temperature of the die 12, a second temperature sensor 73 disposed in the stalk 32 for detecting the temperature of molten metal as it flows through the stalk 32, a flow control means 76 for controlling the rate of flow of cooling water supplied from a cooling water supply 74, and a microcomputer 78 operable based on data applied as output voltages from the first and second temperature sensors 72, 73 for opening and closing valves in the flow control means 76 and for controlling the molten metal supply 34.

The flow control means 76 comprises a fluid circuit including solenoidoperated valves and variable restriction valves. more specifically, a pipe 79 extending from the cooling water supply 74 is branched off into pipes 80, 82 having respective solenoid- operated valves 84, 76 which are selectively openable and closable by an opening signal or a closing signal issued by the microcomputer 78.

variable restriction valves 88, 90 and flowmeters 92, 94 are connected to and disposed downstream of the solenoid-operated valves 84, 86. The pipes 80, 82 from the flowmeters 92, 94 are joined to each other and to the pipe 61 inserted in the cooling block 50 disposed behind the slidable die member 20. Cooling water introduced from the pipe 61 into the cooling hole 58 is then discharged through the pipe 63 into a tank 96.

Cooling water supplied via the d-ie temperature control apparatus 14 is also introduced through a pipe 98 into the cooling block 52 disposed behind the slidable die member 22, and then discharged via the pipe 64 into a tank 100. While the cooling water is supplied to cool the slidable die members 20, 22 in the illustrated embodiment, it may also be supplied to the cooling block 38 associated with the upper die member 18 dependent on casting conditions, the size ofa casting to be produced, and other conditions.

Using the die casting apparatus 10 thus constructed, an engine cylinder head is cast from a molten aluminum alloy (hereinafter referred to as "molten metal") classified as JIS AC2B under the following casting- 1 i j i conditions: the temperature of the molten metal is 7000C and the molten metal is pressurized under 0.28 kg/cm2 when forced into the die cavity 24.

The die temperature control method according to the present invention contains the following three die temperature control Processes which are to be effected in the respective steps of a casting cycle: The first die temperature control Process controls the temperature of the die 12 during a step from the clamping of the die to the starting of the supply of molten metal into the die cavity 24. The second die temperature control process controls the temperature of the die 12 when molten metal is filled in the die cavity 24 under pressure. The third die temperature control process controls the temperature of the die 12 during a step after the molten metal has been filled in the die cavity 24 until the die 12 is opened. The above three die temperature control processes are carried out continuously in the sequence of one casting cycle by the die temperature control apparatus 14. Each of the three die temperature control processes will now be described according to a timedependent sequence of the casting cycle.

The sand cores 66a through 66f are placed in the die cavity 24, and then the movable die base 36 and the upper die 18 are displaced downwardly by the actuator con nected to the movable die base 36. At the same time, the slidable dies 20, 22 are displaced toward each other by actuators connected to the cooling blocks 50, 52 through the connectors 54, 56.

FIG. 2 shows a sequence of the first die temperature contro 1 process of the invention. Before the die cavity 24 is filled with molten metal under pressure while carrying out the first die temperature control process, the temperature of the die 12 is adjusted in advance to a temperature range which is best suited to the casting conditions. The microcomputer 78 of the die temperature control apparatus 14 includes a ROM which stores a program containing instructions for the sequence of FIG. 2. The CPU of the microcomputer 78 is operated by the stored program to carry out the sequence.

A step I-1 detects the temperature T. of the die 12 immediately after it is clamped, from the output voltage of the temperature sensor 72 disposed in the lower die member 16. In a step 1-2, the die temperature T D is introduced as temperature data into the microcomputer 78 through an interface (not shown). In the following description, the die temperature as data to be processed by the microcomputer 78 is indicated as being placed in parentheses. The CPU of the microcomputer 78 determines whether the die temperature (T D) is in a preset temperature range S stored in the microcomputer 78 or not. The preset temperature range S has been experimentally established based on the casting conditions. When the die temperature (T D) lies in the preset temperature i i i 1 1 - 1 C; - range S, the casting die 12 is kept under an optimum temperature condition for pouring the molten metal into the die cavity 24. Specifically, the preset temperature range S is represented by a temperature range S between an upper limit temperature (Tmax) and a lower limit temperature (Tmin) shown in FIG. 3. FIG. 3 shows a die temperature curve 100 which indicates the actual die temperature T D as it varies with time.

If the die temperature (T D) falls in the preset die temperature range S, then the step of forcing or filling the molten metal in the die cavity 24 under pressure in a step 1-3.

If the die temperature (T D) is not in the preset die temperature range S, then the die temperature is controlled so as to reach the preset die temperature range S in the following manner: In a s.tep 1-4, the CPU determines one of four temperature zones A, B, C, D which corresponds to the die temperature (T D)' the temperature zones A, B, C, D being established beforehand based on the preset die temperature range S. The temperature zones A through D are set dependent on the casting conditions to be employed. In the illustrated embodiment, these temperature zones A through D are established with respective suitable zone widths above the preset die temperature range S.

Amounts of cooling water to be supplied to the die 12 are selected with respect to the respective temperature zones A through D as shown in Table 1, given below, which also indicate whether the solenoid-operated valves 84, 86 are to be opened or closed to supply the amounts of cooling water.

Table 1: Temperature zones and amounts of cooling water Temperature zone Amount of water Soleniod valves SV84 SV86 A Q, - + Q2- Open _ Open B Q2 Close Open c Q, Open Close i D ---r- 0 1 Close Close The amounts Q, Q. of cooling water flowing through the solenoid-operated valves 84, 86 can be adjusted by the variable restriction valves 88, 90 disposed downstream of the solenoid-operated valves 84, 86, respectively. These amounts of cooling water are determined dependent on the desired casting conditions.

In a step I-S which follows the step 1-4, the amount of cooling water to. be supplied is determined. In a following step 1-5, the microcomputer 78 sends an opening or closing signal to the solenoid-operated valves 84, 86 to supply the determined amount of cooling water to the die 12. After the cooling water has been supplied for a preset time period in a step 1-7, control returns from the step J-7 to the step I-1.

The casting cycle will be described with reference to the timing chart of FIG. 3. The CPU determines whether a die temperature (T DO) detected in the step I-1 at a time t.

1 1 i 1 - 17 immediately after the die 12 is clamped falls within the preset die temperature range S in the step 1-2. Since the die temperature (T DO) falls outside of the preset die temperature range S, the CPU then determines one of the temperature ranges A through D which contains the die temperature (T DO) in the step 1-4. Inasmuch as the die temperature (T DO) corresponds to the temperature zone B at this time, the microcomputer 78 applies an opening signal to the solenoid-operated valves 86 and a closing signal to the solenoid-operated valve 84 to supply the amount Q, of cooling water to the die 12 in the steps 1-5, 1-6. As a consequence, cooling water supplied from the cooling water supply 74 through the pipe 82 is adjusted in quantity by the solenoid-operated valve 86 and the variab_1e restriction valve 90, and then the amount Q, of cooling water is introduced into the pipes 61, 62. Therefore, the amount Q, of cooling water is supplied into the cooling holes 58, 60 in the cooling blocks 50, 52. After having passed through the cooling holes 58, 60, the cooling water is discharged via the pipes 63, 64 into the tanks 96, 100. The circulation of cooling water continues for a preset period of time, e.g., 1 minute, in the step 1-7.

Then, control goes back to the step I-1 in which a die temperature (T D1) is detected at a time t, by the temperature sensor 72. Since the die 12 has been cooled by the supplied cooling water, the die temperature (T D1) is lower than the die temperature (T DO) and falls in the temperature zone C as shown in FIG. 3. The temperature zone C is closer to the preset die temperature range S, and it is preferable in the temperature zone C that the die temperature (T D) be lowered at a smaller gradient in order to prevent the die 12 from being excessively cooled below the preset die temperature range S. The CPU then executes the steps 1-2, 1-4, and the microcomputer 78 closes the solenoid-operated valve 86 and opens the solenoid-operated valve 84 in the steps 1-5, 1-6 to supply the amount Q, of cooling water which is smaller than the amount Q,. of cooling water. The amount Q, of cooling water is continuously supplied into the cooling holes 58, 60 in the cooling blocks 50, 52 for the preset period of time in the step 1-7.

Again, control goes back to the step I-1 to detect a die temperature (T D2) at a time t2. As shown in FIG. 3, the die temperature (T D2) is lower than the die temperature (T D1) and lies in the temperature zone D. The CPU then executes the steps 1-2, 1-4, and the microcomputer 78 closes the solenoid-operated valve 84 to stop the supply of cooling water into the cooling holes 58, 60 in the steps 1-5, 1-6. At this time, the temperature zone D is next to the preset die temperature range S. If cooling water were supplied, therefore, then the die 12 might be excessively cooled. die temperature T D should be lowered into the preset die temperature range S by letting the die 12 radiate its hea without being forcibly cooled.

1 i i j After the preset period of time has elapsed in the step 1-7, control returns to the step I-1 in which a die temperature T D3 is detected at a time t,. At this time, the die temperature (T D3) falls in the preset die temperature range S. Therefore, control goes from the step 1-2 to the step 1-3 which starts filling molten metal in the die cavity 24.

It can now be understood that according to the first die temperature control process, the casting die 12 is kept in a desired temperature range before molten metal is forced into the die cavity 24 under pressure. Therefore, the die temperature at the time the die 12 is clamped is prevented from becoming irregular because of different casting cycles.

When filling the die cavity 24 with molten metal, the second die temperature control process is carried out to select an optimum molten metal pressurizing pattern for the casting die 12 and a die cooling pattern corresponding to the selected molten metal pressurizing pattern.

FIG. 4 shows a sequence of the second die temperature control process. The ROM of the microcomputer 78 also stores a program containing instructions for the sequence of FIG. 4, and the CPU of the microcomputer 78 is operated by the stored program to carry out the sequence.

A step II-1 detects the temperature T D of the die 12 which falls in the preset die temperature range S. At this time, the die temperature (T D3) in the preset die temperature range S is detected at t,. At the same time, a molten metal temperature (T m3) is detected by the second temperature sensor 73 disposed in the stalk 32 in a step 11-2.

The molten metal temperature (T W) is introduced into the microcomputer 78 through an interface (not shown). In a step 11-3, a molten metal pressurizing pattern and a die cooling pattern corresponding thereto, as shown in FIG. 6, are selected based on the die temperature (T D3) and the molten metal temperature (T m3) FIG. 5 is a graph showing molten metal pressurizing patterns and die cooling patterns as related to the die temperature T D and the molten metal temperature T.. Regions 1 through 7 shown in FIG. 5 correspond respectively to molten metal pressurizing patterns a through 9 and also to die cooling patterns a, through g 1 shown in FIG. 6. These regions 1 through 7, the molten metal pressurizing patterns a through g, and the die cooling patterns a, through 91 are established in advance based on the casting conditions, and stored as data in the microcomputer 78. If the die temperature T D3 and the molten metal temperature Tm3 correspond to the region 4, then a molten metal pressurizing pattern d and a die cooling pattern d, are selected.

As can readily be understood from FIGS. 5 and 6, the higher the die temperature T D and the molten metal tem- j i 1 1 j 1 i 1 1 i 1 j perature Tmo the longer the time for pressurizing the molten metal, and the lower the die temperature T D and the molten metal temperature Tmi, the shorter the time for pressurizing.the molten metal. In the molten metal pressurizing patterns a through g, the speed tan e at which the molten metal starts being poured into the die cavity 24 through the stalk 32 under pressure remains the same, and the speed tan a at which the molten metal is fed into the die cavity 24 until it is filled also remains the same.

Therefore, when the die temperature T D is higher, the molten metal pressurizing time is longer since a relatively long period of time is required for the molten metal to be solidified. Conversely, when the die temperature T D is lower, the molten pressurizing time is shorter as the molten metal can be solidified in a shorter period of time, thus shortening the casting cycle. In the region 7, the die temperature T D barely falls within the preset die temperature range S, but is too low to effect an actual casting cycle. In this case, the poured molten metal is kept in the die cavity 24 only for the purpose of keeping the die 12 at a temperature sufficient for a next casting cycle.

FIG. 7 shows alternative molten metal pressurizing patterns h through n and die cooling patterns h, through n, which may be employed instead of the molten metal pressurizing patterns a through g and the die cooling patterns a, through g, shown in FIG. 6. A study of FIGS. 5 and 7 indicates that when the die temperature T D and the molten metal temperature T m are higher, the speed at which the molten metal is fed into the die cavity 24 is made lower in order to prevent defects from being formed in a casting by a gas produced by too a rapid flow of molten metal. when the die temperature T and the molten metal temperature TM are D lower, the molten metal feeding speed is made higher to prevent casting defects or misruns which would be developed by incomplete distribution of the molten metal in the die cavity 24. For example, the molten metal pressurizing pattern h corresponds to the region 1 in FIG. 5, and the molten metal pressurizing pattern i corresponds to the region 2 in FIG. 5. The die temperature T D is higher in the region 1, and hence the molten metal feeding speed_tan a, in the molten metal pressurizing pattern h is selected to be lower than the molten metal feeding speed tan a, in the molten metal pressurizing pattern i. The molten metal feeding speeds tan a, through tan a, in the molten metal pressurizing patterns j through m are similarly selected according to the regions 3 through 6.

Inasmuch as a molten metal pressurizing pattern and a die cooling pattern are selected dependent on the die temperature T D and the molten metal temperature T.. various patterns can be selected to meet various different conditions. In actual casting processes, however, a molten metal pressurizing pattern and a die cooling pattern may be selected only dependent on the die temperature T D' In a step 11-4 (FIG. 4), the molten metal is filled according to the molten metal pressurizing pattern d selected in the step 11-3 and the casting die 12 is cooled according to the die cooling pattern d, selected in the step 113.

More specifically, when a start signal is applied from the microcomputer 78, the molten metal supply 34 is operated to pressurize the surface level of molten metal stored in the ladle (not shown) in the molten metal supply 34. The molten metal is fed via the stalk 32 into the die cavity 24 under a pressure according to the molten metal pressurizing pattern d, The casting die 12 is cooled such that the amount of cooling water supplied to the casting die 12 is controlled by the die temperature control apparatus 14 in order to vary the die temperature T D along the die cooling pattern d, more specifically, the casting die 12 is cooled according to the third die temperature process of the invention. FIG. 8 shows a sequence of the third die temperature control process. The ROM of the microcomputer 78 also stores a program containing instructions for the sequence of FIG. 8, and the CPU of the microcomputer 78 is operated by the stored program to carry out the sequence. FIG. 9 is a timing chart showing an example in which the third die temperature control process is carried out. when a prescribed period of time has elapsed after the pressurization starting time t, and an initial cooling time t, for starting to cool the casting die 12 is reached in a step III- 1, a die temperature (T D4) at the time t, is detected by the temperature sensor 72 in a step 111-2. The detected die temperature (T D4) is introduced as temperature data into the microcomputer 78 through the interface (not shown). After the time t, the molten metal in the die cavity 24 is kept under a prescribed pressure,i.e., 0.28 kg/cm' in the embodiment, and is cooled and solidified.

In a step 111-3, the CPU in the microcomputer 78 compares the die temperature (T D4) and a preset die-opening temperature (Ts) established beforehand based on the casting conditions and stored in the microcomputer 78. Since the die temperature (T D4) cannot be equal to the die-opening temperature (Ts) immediately after the casting cycle has been started, control goes from the step 111-3 to a step 111-4.

In the step 111-4, a reference die temperature (Tobj) is calculated on the basis of a reference die cooling curve 102 corresponding to the die cooling pattern d, and temperature zones A, through D, having certain respective widths for determining an amount of cooling water based on the reference die temperature (Tobj) are calculated. A plurality of temperature data corresponding to the die cooling pattern d, plotted in FIG. 9 at (a) are stored in the microcomputer 78. Based of these stored temperature data, the reference die cooling curve 102 is established as a function of time t and the die temperature (T D), i.e., T = f(t).

1 The reference die temperature (Tobj) and the temperature zones A, through D, are calculated by the CPU in the microcomputer 78 as follows:

(1) The reference die temperature (Tobj) at a time t is calculated from the function T = f(t) representing the reference die cooling curve 102.

(2) Based on the reference die temperature (Tobj), the following temperature ranges are used as the temperature zones A, through D,:

A,: T D Tobj + g, + 9, B,: Tobj + 0, < T < Tobj + e, + 9, D Cl: Tobj < T D < Tobj + 01 D,: T D Tobj where 0,, 9, are constants representing emperature ranges which are selected based on the casting conditions.

The measured die temperature (T D4) is compared with the reference die temperature (Tobj) by the CPU in the microcomputer 78, and it is determined in which one of the temperature zones A, through D, the die temperature (T D4) 'S included. The amount of cooling water to be supplied is determined dependent on the temperature zone in which the die temperature (T D4) falls, in a step 111-6. The solenoid valves 84, 86 are opened and closed and cooling water is supplied in the amounts as indicated by the above Table 1 dependent on the temperature zones A, through D,. The higher the die temperature T D' the greater the amount of cooling water supplied.

1 Based on the results obtained in the steps 111-5, 111-6, the microcomputer 78 sends an opening signal or a closing signal to the solenoid valves 84, 86 in a step 111-7. In FIG. 9, the die temperature (T D4) at the time t. falls in the temperature zone A,. Therefore, t.he solenoid valves 84, 86 are opened by the opening signal from the microcomputer 78 to supply the amount Q, + Q, to the die 12.

Cooling water supplied from the cooling water supply 74 flows through the variable restriction valves 88, 90 and is introduced in the amount Q, + Q, from the pipes 61, 62 into the cooling passages 58, 60 in the cooling blocks 50, 52. After the supply of cooling water has been continued for a preset period of time in a step 111-8 until a die temperature (T D5) is detected next time, control goes back to the step 111-2.

The flowchart of FIG. 8, i.e., the sequence from the step 111-2 to the step 111-8, is repeated at times t, t,'... t n' with prescribed time intervals therebetween. The amounts of cooling water supplied from the cooling water supply 74 in one casting cycle are shown in FIG. 9 at (b). The die 12 is thus cooled by the supplied cooling water so that the die temperature (T D) varies according to the die temperature curve 100 shown in FIG. 9 at (a). After a time t m in the casting cycle, the pressurization of the molten metal in the die cavity 24 is stopped.

Finally, when the die-opening temperature (Ts) is reached at a time ts, the die 12 is opened in the step 111-3, and the produced casting is removed from the die 12.

j i j i i i i i By thus determining the amount of cooling water based on the reference die cooling curve 102 and repeating the operation at predetermined intervals, the proper amount of cooling water can be supplied to the casting die 12. Therefore, it can be understood that the actual cooling of the casting die 12 can reliably be controlled. with the present invention, as described above, before a casting cycle is started, a die temperature detected by the temperature sensor and a preset die temperature range established beforehand based on casting conditions are compared, and cooling water is supplied in one of amounts which is selected based on the result of the comparison in order to bring the die temperature into the preset temperature range. Therefore, the die temperature is controlled so as to fall in the preset die temperature range at all times when filling molten metal into the die cavity, so that the casting die can be maintained under certain temperature conditions even if casting cycles vary from each other. molten metal pressurizing patterns and die cooling patterns are established in advance dependent on die temperatures. When filling molten metal in the die cavity, one of the molten metal pressurizing patterns which corresponds to the detected die temperature and one of the die cooling patterns which corresponds to the detected die temperature are selected, and the molten metal is filled under a pressure - 28 according to the selected molten metal pressurizing pattern and the amount of cooling water according to the selected die cooling pattern is supplied to the die. By selecting the molten metal pressurizing pattern, a time period for pressurizing the molten metal is selected which corresponds to the die temperature. The speed at which the molten metal is fed into the die cavity, which is indicated by each of the molten metal pressurizing patterns, is established dependent on the die temperature for thereby filling the molten metal in the die cavity at an optimum speed matching casting conditions. It is thus possible to carry out a casting cycle effectively while eliminating a wasteful solidification time, and also to prevent casting defects caused in a casting by a gas produced in the die cavity and casting defects such as misruns. The above process is reliably assured by selecting one of the molten metal pressurizing patterns and a corresponding one of the die cooling patterns. Accurate die temperature control is made possible by establishing the molten metal pressurizing patterns and the die cooling patterns dependent on molten metal temperatures as well as die temperatures.

After the molten metal has been filled in the die cavity, the actual die temperature and a reference die temperature calculated from a reference die cooling curve are compared with each other, the amount of cooling water which is determined based on the result of the temperature compar- 1 i i i i 1 t ison is supplied to the die, and the die is cooled so that the actual die temperature will approach the reference die cooling curve, in order to allow the molten metal to be cooled and solidified according to the selected die cooling pattern. Consequently, the manner in which the molten metal is solidified in the die cavity is properly controlled to achieve directional solidification of the molten metal with ease. According to the present invention, therefore, castings of uniform and excellent quality can be produced.

Although a certain preferred embodiment has been shown and described, it should be understood that many changes and modifications may be made therein without departing from the scope of the appended claims.

The preferred embodiments of the present invention can provide a method of and an apparatus for controlling the temperature of a die in a lowpressure casting process based on the actual temperature of the die so that the die temperature will vary according to an optimum cooling pattern, thereby to allow molten metal to be solidified under optimum control without being adversely affected by different casting cycles.

j

Claims

CLAIMS.

1. A method of controlling the temperature of a casting die in a lowpressure casting process for pressurizing the surface of molten metal stored in a closed container to fill the molten metal in a die cavity defined in the casting die, said method comprising the steps of: detecting the temperature of said casting die when the molten metal is filled in said die cavity under pressure; selecting, dependent on said detected temperature of the casting die, an optimum one of a plurality of molten metal pressurizing patterns established dependent on die temperatures and an optimum one of a plurality of die cooling patterns established dependent on die temperatures; filling and holding the molten metal in said die cavity under a pressure according to the selected molten metal pressurizing pattern; and supplying said casting die with an amount of cooling water which is variably controlled according to the selected die cooling pattern.

2. A method according to claim 1, wherein said molten metal pressurizing patterns are established such that a time period for pressurizing the molten metal is shorter 1 1 when the die temperature is lower, and is longer when the die temperature is higher.

3. A method according to claim 2, wherein said mol ten metal pressurizing patterns are established such that a speed at which the molten metal is fed into said die cavity is higher when the die temperature is lower, and is lower when the die temperature is higher.

4. A method according to any one of claims 1 through 3,wherein the temperature of the casting die and the temperature of the molten metal are detected, and an optimum one of the molten metal pressurizing patterns and an optimum one of the die cooling patterns are selected dependent on said detected temperature of the casting die and said detected temperature of the molten metal.

Published 1992 at The Paten House. Cardiff Road, Newport, Gwent NP9 IRH. Further copies rnky be obtained from 11 Off, Sales Branch. Unit 6. Nine Mile Poll. h. Cross Keys. Newport. NP1 7HZ. Printed by Multiplex techniques lid. St Mary Cray. Rent.