JPH01148451A - Method for controlling pressurized cooling of molten metal in low pressure casting method - Google Patents

Abstract

PURPOSE:To prevent the development of misrun or gas defect, etc., by controlling filling-up of molten metal under pressurizing and cooling water flow rate under standardizing plural preset pressurizing patterns for the molten metal and the cooling patterns for a die in accordance with the die temp. and the molten metal temp. CONSTITUTION:At the time of filling up the molten metal in a cavity 24 in the casting die 12 under pressurizing, the die temp. and the molten metal temp. are detected. Successively, the molten metal pressurizing pattern and the die cooling pattern corresponding to this die temp. and the molten metal temp. are selected among the plural preset molten metal pressurizing patterns and the die cooling patterns. Based on this molten metal pressurizing pattern and the die cooling pattern, the molten metal is filled up under pressurizing and also the cooling water flow rate is controlled, to supply the molten metal in the casting die 12. For this purpose, suitable solidifying time of the molten metal is selected based on the pressurizing time of the molten metal corresponding to the die temp. and the molten metal temp. Further, by setting the casting speed corresponding to the die temp. and the molten metal temp., the molten metal is filled up into a cavity 24 at the optimum casting speed. Therefore, the solidification of the molten metal can be progressed under good casting condition in accordance with the molten metal temp. and the die temp.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for controlling pressurized cooling of molten metal in a low-pressure casting method. The mold temperature and molten metal temperature of the mold are detected, and the pressurization conditions and the cooling supplied to the mold are determined based on the molten metal pressurization pattern and mold cooling pattern selected from the combination of the mold temperature and molten metal temperature. The present invention relates to a method for controlling pressurized cooling of molten metal in a low-pressure casting method, which prevents casting defects such as gas defects and cavities by controlling the amount of water, and makes it possible to manufacture cast products of good quality.

[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 sealed container, the surface of the molten metal is pressurized with relatively low-pressure inert gas or air, and the molten metal is passed through a hot water supply pipe into a mold. This is a method of manufacturing a cast product by filling a cavity defined within the mold.

In this case, when the molten metal is pressurized and filled into the cavity in the mold, the casting speed is usually changed in several stages. That is, the molten metal is poured relatively quickly until it enters the mold via the stalk. Next, after the molten metal starts to be filled into the cavity, the molten metal is filled at a predetermined slow speed in order to prevent air and the like from being mixed in the molten metal. After that, when the cavity is filled with molten metal, the molten metal is filled again at a high pouring speed and the molten metal is pressed.

In this way, the casting speed of the molten metal is set in three stages, and the work of filling the cavity with the molten metal is carried out.

By the way, during the casting process, each casting cycle varies due to various factors. Specific factors include cleaning inside the mold, installation of the core, and troubles in operating the mold equipment.

For this reason, the mold temperature at the start of the casting cycle is often not constant but fluctuates.

However, in the above-described molten metal filling method, various disadvantages are exposed, particularly because the casting speed in the second stage, in which the molten metal is substantially filled into the cavity, is set in advance.

In other words, if the mold temperature is lower than the appropriate temperature determined from the casting conditions such as the molten metal temperature, a portion of the molten metal will solidify before the entire cavity is filled with the molten metal, resulting in casting defects such as poor running of the molten metal. There is a possibility that this may occur.

On the other hand, when the temperature of the mold is higher than the appropriate temperature, the molten metal may flow around the gas vent hole before the cavity is filled with the molten metal, making it difficult to efficiently discharge the gas. In that case, gas defects, cavities, etc. will occur due to the remaining gas.

[Object of the Invention] The present invention has been made to overcome the above-mentioned disadvantages, and when starting pressurized filling of the molten metal into the cavity, first, the mold temperature of the mold and the molten metal temperature are detected. Next, a molten metal pressurization pattern corresponding to the actually measured mold temperature and molten metal temperature is selected from a plurality of molten metal pressurization patterns and mold cooling patterns that are set in advance according to the mold temperature and molten metal temperature. By selecting a cooling pattern for the mold, filling the molten metal under pressure based on the pattern, and controlling the amount of cooling water supplied to the mold, it is possible to prevent problems such as poor water flow and gas defects, and improve quality. An object of the present invention is to provide a method for controlling pressurized cooling of molten metal in a low-pressure casting method, which makes it possible to manufacture excellent cast products.

[Means for Achieving the Object] In order to achieve the above-mentioned object, the present invention pressurizes the surface of the molten metal stored in a closed container with pressurized gas to introduce the molten metal into a cavity defined in a mold. In the low-pressure casting method performed by filling, the mold temperature and molten metal temperature of the mold are detected when the molten metal is pressurized and filled into the cavity, and then set in advance in accordance with the mold temperature and the molten metal temperature. The optimum molten metal pressurization pattern and mold cooling pattern are selected from among multiple molten metal pressurization patterns and mold cooling patterns, and the molten metal is filled into the cavity based on the molten metal pressurization pattern. The cooling water is maintained under pressure and is supplied to the mold while variably controlling the amount of cooling water depending on the cooling pattern of the mold.

[Embodiments] Next, preferred embodiments of the method for controlling pressurized cooling of molten metal 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 please refer to the attached drawings. This will be explained in detail below.

In FIG. 1, reference numeral 10 indicates a casting device. This casting apparatus IO is basically composed of a casting mold 12 and a mold temperature control mechanism 14. The casting mold 12 is a lower mold 16
, an upper mold 18 disposed above the lower mold 16, and a sliding mold 20.22 disposed so as to be slidably fitted to the lower mold 16 and the upper mold 18. Furthermore, these lower molds 1
6. A cavity 24 is defined by the upper die 18 and the sliding die 20.22, and the cavity 24 has a shape suitable for casting a cylinder head constituting an internal combustion engine of an automobile or the like.

Therefore, the lower mold 16 has a stepped hole 26 at a predetermined portion thereof.
A nozzle 30 having a sprue 28 communicating with the cavity 24 is installed in the stepped hole 26 . The nozzle 30 has a stalk 3 for feeding molten metal.
2 are connected, and this stalk 32 is connected to a molten metal supply means 34 installed below the lower die 16 and in which molten metal is stored. This molten metal supply means 34 is provided with a crucible (not shown), and the molten metal is heated and held in this crucible. Furthermore, a plurality of passages 36 for introducing cooling fluid are defined inside the lower mold 16.

On the other hand, the upper mold 18 is fixed to a movable die base 38 and can be freely displaced in the vertical direction under the driving action of an actuator (not shown) connected to the movable die base 38. A cooling block 40 is provided between the movable die base 38 and the upper die 18.
is interposed therein, and a passage 42 for introducing cooling water is formed in this cooling block 40. Furthermore, an extrusion pin 44 is provided for inserting the movable die base 38 and the upper mold 18 and taking out the cast product after opening the mold. ,
The tip faces the cavity 24.

Next, the sliding molds 20 and 22 are fitted into the lower mold 16 and the upper mold 18 so as to be slidably displaceable. The sliding molds 20, 22 are connected to actuators such as cylinders (not shown) via connecting members 48, 50, respectively, and are movable in the horizontal direction.

In addition, passages 52.54 through which cooling water flows are formed in the sliding mold 20.22.

In the figure, reference numerals 56a to 56f indicate sand cores, and reference numeral 58 indicates a hole for degassing.

Next, the mold temperature control mechanism 14 that controls the mold temperature of the casting mold 12 will be explained. This mold temperature control mechanism 1
4 is a cavity 2 of the lower mold 16 for detecting the mold temperature.
4, a first temperature sensor 60 such as a thermocouple, and a stalk 32 for detecting the temperature of the molten metal.
a second temperature sensor 61 disposed in the cooling water supply source 6;
2, and the first and second temperature sensors 60.6.
The output voltage of 1 is introduced as temperature data via a human interface (not shown), and the microcomputer 66 controls the opening/closing operations of the valves constituting the flow rate control means 64 and the molten metal supply means 34 based on this temperature data.
It consists of

The flow rate control means 64 is composed of a fluid circuit including a solenoid valve and a variable throttle valve. That is,
A pipe line 67 extending from the cooling water supply source 62 branches into pipe lines 68 and 70 in the middle thereof, and the branched pipe line 68.
Solenoid valves 72 and 74 are disposed at 70, respectively.

The solenoid valves 72 and 74 are configured to be opened and closed based on an opening or closing signal output from the micro convenience store rotor 6. Variable throttle valves 76 are located downstream of the solenoid valves 72 and 74, respectively.
．． 78 as well as flow meters 80,82 are arranged. Downstream of the flowmeter 80.82, the pipes 68.70 merge and then branch off again into pipes 84.86, each of which is defined by a sliding mold 20.22 constituting the casting mold 12. It is connected to passages 52 and 54.

Note that the cooling water introduced into the passages 52 and 54 is discharged to the outside via a pipe line (not shown).

Using the casting apparatus 10 configured as described above, the casting conditions were 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 kg/cm.
The cylinder head is cast as follows.

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, sand cores 56a to 56f are placed at predetermined locations in the cavity 24 defined in the casting mold 12.

Thereafter, the movable die base 38 and the upper die 18 integral therewith are displaced downward under the action of an actuator (not shown), and the sliding die 20.22 is moved to the connecting member 48.5.
The mold is clamped by closely displacing the mold under the action of an actuator (not shown) connected via a wire.

Hereinafter, according to the flowcharts shown in FIGS. 2a and 2b, the method for controlling pressurized cooling of molten metal according to the present invention is started as shown in the time chart of FIG. 3. In this case, the microcomputer 6 forming the mold temperature control mechanism 14
A ROM (not shown) in 6 is written with a program of the procedure shown in the flowcharts of FIGS. 2a and 2b, and the CPU (not shown) operates according to this flowchart.

As shown in FIG. 2a, in step 1, the lower mold 16
The mold temperature To immediately after mold clamping is detected via the first temperature sensor 60 disposed at the mold. Then, in step 2,
This mold temperature To is introduced into the microcomputer 66 as temperature data via an interface (not shown). A CPU (not shown) constituting the microcomputer 66 compares and determines whether the mold temperature T is within a preset mold temperature range S that is manually input to the microcomputer 66 in advance.

This set mold temperature range S means the optimal mold temperature range when pressurizing and filling the molten metal, and is set based on the casting conditions, and as shown in Figure 3a, the upper limit temperature T
,, has a predetermined temperature range set between a +t and the lower limit temperature Tm1n.

At that time, the curve shown by the solid line in Fig. 3a is the actual mold temperature T.
1] is a mold temperature curve 100 showing the temporal change of [I].

Mold temperature T. is not within the set temperature range S, in step 3, the CPU determines whether this mold temperature To is in any of the four temperature zones A, B, C, and D preset based on the set temperature range S. Determine whether it corresponds to the range. These temperature zones A to 3
As shown in Figure a, it is set arbitrarily based on predetermined casting conditions, and in this embodiment, it is set with a predetermined temperature range in the region above the upper limit temperature TllaM in the set temperature range S. .

In this case, the first
The amount of cooling water is set as shown in the table, and in order to achieve this amount of cooling water, the solenoid valve 72.
The open/close states of 74 are determined.

Table 1: Relationship between temperature zones and cooling water flow rate Q+, Q
2 can be adjusted as desired by variable throttle valves 76 and 78 disposed downstream of these. 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 3 above, in step 4, the CPU of the micro convenience store 6 sends open or close signals to the solenoid valves 72 and 74, respectively. After this state continues for a predetermined time in step 5, the process returns to step 1 again.

Therefore, the mold temperature T at the time to actually detected in step 1. In the next step 2, the CPU determines whether or not the temperature is within the set temperature range S. In this case, since the mold temperature T'no is not within the set mold temperature range S, the mold temperature T, is determined in step 3. The CPU determines in which temperature zone from temperature zone A the temperature zone is included. As a result, it is detected that the mold temperature T'no corresponds to temperature zone B. Therefore, based on the CPU's judgment processing result, the microcomputer 66 sends an opening signal to the solenoid valve 74 to make the amount of cooling water equal to the flow rate Q2 in Table 1, and on the other hand, sends an opening signal to the solenoid valve 72. The solenoid valves 72 and 74 are opened and closed (SrF2). As a result, the cooling water supplied from the cooling water supply source 62 is introduced via the variable throttle valve 78 at a flow rate Q2 from the conduit 84.86 into the passage 52.54 defined in the sliding mold 20.22. , will be discharged to the outside via a pipe line (not shown). This circulation of cooling water continues for a predetermined period of time, for example, one minute (SrF2).

The above steps 1 to 5 are repeated until the mold temperature To falls within the set mold temperature range S. In the end, Figure 3a
As shown in FIG.
The molten metal temperature Tm3 is detected via the temperature sensor 61.

Next, the molten metal temperature T is determined by the microcomputer I-6.
6 via an interface (not shown).

Then, in step 7, a molten metal pressing pattern shown in FIG. 5 and a mold cooling pattern corresponding to this molten metal pressing pattern are selected based on the mold temperature TD3 and molten metal temperature Tm3.

Here, FIG. 4 shows the molten metal pressurization pattern, mold cooling pattern, and mold temperature T. , is a graph showing the correspondence of molten metal temperature T1. That is, regions 1 to 7 shown in FIG. 4 correspond to the molten metal pressing patterns a to g and the mold cooling pattern a1 shown in FIG.
to g1, respectively. These regions 1 to 7, molten metal pressurization patterns a to g11, and mold cooling patterns a1 to 1 are preset based on casting conditions and are manually entered into the microcomputer 66 as data. The mold temperature T0 and the molten metal temperature T ta 3 are the fourth
If it corresponds to region 4 in the figure, for example, the molten metal pressing pattern d and mold cooling pattern d shown in FIG. 5 are selected.

In this case, as can be easily understood by comparing FIGS. 4 and 5, the mold temperature T. and molten metal temperature T.

The higher the temperature, the longer the molten metal pressurization time is set;
. The lower the molten metal temperature T, the shorter the molten metal pressurization time. and the casting speed tanα until the molten metal fills into the cavity 24 are set to be the same in the molten metal pressurization patterns a to g.

By doing this, if the mold temperature T is high,
It takes a relatively long time for the molten metal to solidify, so this is taken into account. On the other hand, when the mold temperature To is low, the molten metal only takes a short time to solidify, so the pressurization time is shortened and the casting cycle is adjusted accordingly. The aim is to shorten the time. And area 7
In the case of , the mold temperature T. is barely within the set mold temperature range S for starting pressurization, and the molten metal temperature T is also low and unsuitable for an actual casting cycle, so step blowing is only performed for the purpose of raising the mold temperature.

Further, instead of the molten metal pressing patterns a to g1 shown in FIG. 5, the mold cooling patterns a to g1, the molten metal pressing patterns h to n and mold cooling patterns a1 to n1 shown in FIG.
may be adopted.

In this case, as can be understood from the comparison between FIG. 4 and FIG. The casting speed during filling is set slow, while the mold temperature T.

When the molten metal temperature T is low, the casting speed is set to be high to prevent casting defects due to poor running of the metal. For example, in the molten metal pressing patterns h$ and i, the molten metal pressing pattern h corresponds to region 1 in FIG. 4, and the molten metal pressing pattern i
corresponds to region 2. The mold temperature To is high in region 1, and therefore the casting speed tanα1 of the molten metal pressurization pattern h is set smaller than the casting speed tanα2 of the molten metal pressurization pattern i. Such a relationship also applies to the casting speeds tanα3 to tanα6 of the molten metal pressurization patterns j to m.

Next, in step 8, pressure filling of the molten metal is started based on the molten metal pressurization pattern d selected in step 7.

That is, by supplying compressed air to the molten metal supply means 34 and pressurizing the surface of the molten metal stored in a crucible (not shown) disposed in the molten metal supply means, the molten metal is first introduced into the cavity 24 via the stalk 32. The molten metal is poured along the molten metal pressing pattern d shown in FIG. 3C. In step 9, when a predetermined period of time has elapsed from the pressurization start time t3 and an initial cooling time t4 for cooling the casting mold 12 has been reached, the mold temperature T is determined in step 10. Executes cooling control. In case q, the procedure for controlling the cooling of the mold temperature To is written in the ROM of the microcomputer 66 as a subroutine shown in FIG.

That is, the mold temperature T of the casting mold 12 at time t4 is measured via the temperature sensor 60. , detect (STPI'
). This mold temperature T. , is introduced into the microcomputer 66 as temperature data via an interface (not shown). Note that from this time t onward, the molten metal in the cavity 24 is held at a predetermined pressure, in this case, 0.28 kg/am'', and is cooled to proceed with its solidification.

In step 2', the standard temperature T. bJ and this standard temperature T. , j, temperature zones A' to D' having a certain range of width for determining the amount of cooling water are calculated. In this case, the mold cooling pattern d1 selected in step 8 is determined by the microcomputer 6 as a function T=f(t) of time t and temperature T, which represents the reference mold temperature cooling curve 102.
6 is stored.

Therefore, the reference temperature T ob J and the temperature zone A'
to D° are determined by the standard temperature cooling curve 10 as follows.
2 is calculated by the CPU of the microcomputer 66.

■ Function T=f(
t) to time t, that is, the reference temperature T.

Calculate bJ.

■ The reference temperature T. Based on bj, the following temperature ranges are defined as temperature zones A' to D''.

A': To≧TOb, +θ1+θ2 B': T'ObJ+01≦To <Tob4+θ,
+θ2C': TobJ<To<'r. bJ+0
1D': To≦T ob J Here, the temperature widths θ1 and θ2 are set based on casting conditions.

Next, the mold temperature To actually measured in step 3' and step 4° is the reference mold temperature T. bJ and the CPU of the microcomputer 66 perform comparison processing, and the mold temperature T. is temperature zone A.

It is determined which one of D' to D' it is included in.

In this case, as shown in Table 1, similarly to the case of temperature zones ASB, C, and D before the start of pressurization, solenoid valves 72.
The opening/closing state of 74 and the amount of cooling water are set.

Therefore, in step 5°, the microcomputer 66 sends an opening or closing signal to the solenoid valves 72 and 74 based on the results of steps 3° and 4°. In this case, in FIG. 3, the mold temperature T at time t4. , are included in temperature zone A, and as shown in Table 1, the solenoid valves 72 and 74 are opened by an opening signal sent from the CPU.

As a result, the cooling water supplied from the cooling water supply source 62 passes through the line 68.70 and from the line 84.86 to the sliding mold 20.2.
2 into the passages 52, 54 formed in FIG. In step 6°, this state is continued until the mold temperature T is detected according to the predetermined time method, and then the process returns to step 10.

In this way, from then on, at predetermined time intervals, time 15.1.
...th..., and the above mold temperature cooling control procedure is repeated. As a result, the amount of cooling water supplied from the cooling water supply source 62 is indicated by the solid line shown in FIG. Due to the cooling effect of this cooling water, the mold temperature TI] is actually
The transition shown in the mold temperature curve 100 in FIG. 3a is followed.

Then, in step 1 and step 12, when the pressure reduction time t is reached, pressurization of the molten metal in the cavity 24 is stopped. Furthermore, the process proceeds to step 13, where the mold temperature TI
] Executes cooling control. This cooling control of the mold temperature To is similar to the procedure of the subroutine described above.

When the mold temperature T finally reaches the set mold opening temperature T, (
Step 14) The mold is opened and the cast product is taken out (time ts).

In the next casting cycle, the above-mentioned steps are repeated in the same manner, and steps up to step 6 are completely the same, and in step 7, a predetermined molten metal pressing pattern and mold cooling pattern are selected. Thereafter, a casting cycle is performed based on the molten metal pressurization pattern and mold cooling pattern selected in accordance with the mold temperature and molten metal temperature.

[Effects of the Invention] As described above, according to the present invention, when filling the molten metal into the cavity of the mold under pressure, the mold temperature and the molten metal temperature are detected,
A molten metal pressing pattern and a mold cooling pattern corresponding to the mold temperature and molten metal temperature are selected from among a plurality of preset molten metal pressing patterns and mold cooling patterns, and this molten metal pressing pattern and mold cooling pattern are selected. Based on this, molten metal is pressurized and filled, and the amount of cooling water is controlled and supplied to the mold. Therefore, an appropriate solidification time of the molten metal is selected based on the pressurization time of the molten metal corresponding to the mold temperature and the molten metal temperature.

Furthermore, by setting the casting speed in accordance with the mold temperature and the molten metal temperature, the cavity is filled with molten metal at an optimal casting speed. Therefore, solidification of the molten metal proceeds under favorable casting conditions depending on the molten metal temperature and mold temperature. As a result, it is possible to implement an efficient casting cycle without wasting solidification time, and it is possible to prevent casting defects such as gas defects and cavities that occur during casting.

Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to these embodiments.
Of course, various improvements and changes in design are possible without departing from the gist of the present invention.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view showing a schematic configuration of a casting apparatus used in the method for controlling pressurized cooling of molten metal according to the present invention, and Fig. 2 a and b illustrate the procedure of the method for controlling pressurized cooling of molten metal. FIG. 3 is a time chart based on an embodiment of the molten metal pressurization cooling control method, and FIG. 4 is a flowchart for selecting a molten metal pressurization pattern and a mold cooling pattern in the molten metal pressurization cooling control method. Graphs showing the relationship between the mold temperature and the temperature of the molten metal, Figures 5a to 5g and al to gl respectively show the molten metal pressurization pattern and mold cooling pattern that are set corresponding to the mold temperature and the molten metal temperature. Figures, 6th diagram to n and hl
thru nl are paths indicating other molten metal pressurization patterns and mold cooling patterns that are set corresponding to the mold temperature and the molten metal temperature, respectively. 10... Casting device 12... Casting mold 1
6...Lower mold 18...Upper mold 20.2
2...Sliding type 24...Cavity 60.
61...Temperature sensor 66...Microcomputer FIG, 4 1ms Melt 5llJ degrees Tm Time Time 1ms

Claims (3)

[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, the molten metal is filled into the cavity under pressure. The mold temperature and molten metal temperature of the relevant mold are detected, and the optimal one is selected from among multiple molten metal pressurization patterns and mold cooling patterns that have been set in advance according to the mold temperature and molten metal temperature. Select a pressure pattern for the molten metal and a cooling pattern for the mold, fill the molten metal into the cavity and hold it under pressure based on the pressure pattern for the molten metal, and adjust the amount of cooling water depending on the cooling pattern for the mold. A method for controlling pressurized cooling of molten metal in a low-pressure casting method, characterized in that the molten metal is supplied to the mold while being variably controlled. (2) In the method described in claim 1, the molten metal pressurization pattern shortens the molten metal pressurization time when the mold temperature is low, and on the other hand, the molten metal pressurization time increases when the mold temperature is high. A method for controlling pressurized cooling of molten metal in a low-pressure casting method. (3) In the method described in claim 1, the molten metal pressure pattern is such that when the mold temperature is low, the molten metal is poured at a high speed, and when the mold temperature is high, the molten metal is poured at a low temperature. A method for controlling pressurized cooling of molten metal in a low-pressure casting method.