JPH0329498B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a mold casting method that controls the mold opening time from mold casting to mold opening in a mold casting apparatus such as a die casting machine. This invention relates to a casting cooling time control device.

[Prior art] In mold casting, the casting must be taken out from the mold when the temperature of the casting in the mold drops to a certain ideal temperature determined by the solidification characteristics of the molten metal used. Must be. If you open the mold and take out the casting when the temperature is higher than this ideal temperature, the casting will not easily separate from the mold, damaging the mold and shortening the life of the mold. The distortion rate and shrinkage rate are large, making the dimensional accuracy unstable, resulting in an increase in the defective rate and an increase in the width of quality variation. Of course, if the mold is opened when the molten metal in the mold has not yet sufficiently solidified, the casting may burst or the mold may seize, which is dangerous. Also,
On the other hand, leaving the casting in the mold indefinitely after the temperature of the casting in the mold has fallen to the ideal temperature will only unnecessarily increase the casting cycle time and reduce the number of pieces cast per unit time. This results in a decrease in

The most ideal and reliable way to determine whether the temperature of the casting inside the mold has fallen to the ideal temperature is to directly measure the temperature of the casting inside the mold, but at present, this method of direct measurement is insufficient. There is nothing suitable.

Therefore, in the past, the time required for the molten metal injected into the mold to absorb heat from the mold, solidify, and drop to the ideal temperature was determined in a preliminary test, and a timer with that time set was used to inject the molten metal. Start with a signal,
This is used as a guideline for mold opening and casting removal time. Another method is to use a heat-sensitive element to detect the change in temperature of the mold after the molten metal is injected, monitor the indicated temperature change, and indirectly estimate the cooling state of the casting in the mold. It's taken.

[Problems to be Solved by the Present Invention] However, in the method using the timer, as casting is repeated, the initial temperature of the mold at the time of electric injection in each casting cycle gradually increases; The cooling rate characteristics of the molten metal in the mold in each casting cycle vary depending on the initial temperature of the mold, and as the initial temperature of the mold increases, the cooling rate of the molten metal decreases. Since a lag occurs between the time and the actual desired cooling time, and the lag gradually increases, it is not always possible to open the mold or take out the casting in good condition, and only extremely rough management can be performed. In addition, although the mold temperature monitoring method has relatively better control accuracy than the timer method, it is still limited to guideline management based on the intuition of the operator, and the actual temperature control range is within ±50 to 150 of the ideal temperature. ℃, which is not enough.

In addition, in order to know that the temperature of the cast metal has dropped to a temperature suitable for starting mold opening, it is not necessarily necessary to know the temperature of the surface of the casting that is in contact with the inner wall surface of the mold cavity. Depending on the shape, size, thickness, etc. of the casting, it is necessary to know the temperature at a certain point, such as the molten metal inside the mold cavity or the final solidification point inside the casting, and the temperature at that important part. It is necessary to know whether the temperature has dropped to a sufficient level.

[Means for Solving the Problems] The present invention is intended to eliminate these drawbacks, and is aimed at solving the following problems: , that is, predict the molten metal temperature by the differential coefficient,
When the predicted temperature reaches the optimum cooling state temperature determined based on the mold, casting conditions, etc., a mold opening command is output to the mold operating device to perform the mold opening operation, The cooling time of the casting is controlled more fully, allowing for satisfactory mold opening and casting removal.

In addition, when performing mold casting using a die-casting machine, etc., the cooling time of the casting varies depending on the location of the casting, so it is important to control and manage the temperature at any location inside the casting. This temperature control location also differs depending on the product, and this tendency is particularly strong for thick products and complex products.
Therefore, in the present invention, the temperature at a predetermined position inside the molten metal or casting can be estimated and utilized for controlling the cooling time of the casting.

Specifically, a temperature detection element 8 outputs an electric signal corresponding to the temperature near the casting wall surface of the mold.
, an input conversion circuit 10 that converts the electric signal into a predetermined voltage signal or current signal, a differentiation circuit 11 that differentiates the output signal of this input conversion circuit 10 with respect to time, and a sign of the output signal of this differentiation circuit 11. An inverting circuit 12 for inverting the inverting circuit 12 and a representative length ΔL between a predetermined position inside the molten metal or the surface of the molten metal and a temperature detection point near the casting wall surface in the output signal of this inverting circuit 12.
a first multiplier 14 that adds a correction coefficient A to the output signal of this first multiplier 14; A second multiplier 17 that multiplies the product of ΔL, mold density ρ, and specific heat C divided by thermal conductivity λ, and a second multiplier 17 that adds a correction coefficient B to the output signal of this second multiplier 17. adder 19 and this second adder 19;
The output signal of the adder 19 and the input conversion circuit 10
A third adder 20 calculates a predicted signal corresponding to the molten metal temperature by adding the output signals of the third adder 20, and a set temperature is set based on the output signal of this third adder 20, the mold, casting conditions, etc. a comparator 22 which compares the output signal from the setting device 21 and outputs an ON signal when the predicted signal of the molten metal temperature reaches the output signal of the setting device 21; Determine the sign and invert circuit 12
If the sign of the output signal is positive or the differentiating circuit 11
A sign determination circuit 23 outputs an ON signal when the sign of the output signal is negative, and when the output signal of this sign determination circuit 23 is an ON signal, the output ON signal of the comparator 22 is inputted to output the output signal. A gate circuit 24 for outputting an output signal and a mold operating device 25 for opening a mold according to the output signal of the gate circuit 24 are provided.

[Operation] When molten metal is injected into the mold cavity, the temperature T of the mold at the installation position is measured by a temperature detection element installed near the casting wall surface of the mold.

On the other hand, determine the predetermined position where you want to know the temperature of the molten metal in the mold cavity, or the inside of the casting where it is cooling and solidifying, or has already solidified, and between that point and the temperature measurement point in the mold. distance ΔL, mold density ρ, specific gravity C, thermal conductivity λ,
Coefficients A and B obtained from experimental results conducted in advance, etc.
By inputting this into a computer and sequentially calculating it using this device, the temperature at a given point in the casting can be determined.
_TM is found.

When this temperature T _M falls to the preset temperature Tset, the inside of the casting has reached a state where it can withstand mold opening and product removal, so the mold operating device 25 is operated to open the mold, and then the casting is extruded from the movable mold.

[Example] Next, the present invention will be explained in detail with reference to an example shown in the drawings.

In Figure 1, 1 is a fixed plate, 2 is a movable plate, 3
4 is a fixed mold, 4 is a movable mold, 5 is an injection sleeve,
Reference numeral 6 indicates an injection plunger, and 7 indicates a cavity, in which the molten metal fed into the injection sleeve 5 is cast into the cavity 7 by the action of the injection plunger 6 to obtain a casting of a desired shape.

Near the casting walls of the molds 3 and 4, for example, the movable mold 4
Inside, a temperature detection element 8 was provided at a distance of about several mm to about 10 mm from a part of the inner wall surface of the cavity 7. This temperature detection element 8 is capable of measuring the mold temperature T near the casting wall surface of the mold 4 and outputting an electrical signal corresponding to the temperature T. 10 is an input conversion circuit that converts the electrical signal into a predetermined voltage signal or current signal, 11 is a differentiation circuit that differentiates the output signal of the input conversion circuit 10 with respect to time, and 12 is the positive or negative sign of the output signal of the differentiation circuit 11. a reversing circuit for reversing; 13 a setting device for setting a representative length ΔL between a predetermined position inside the molten metal or the surface of the molten metal and a temperature detection point near the casting wall surface; Multiply the length ΔL by the first
15 is a setting device for setting the correction coefficient A to be added to the output signal of the multiplier 14, 16 is a first adder for adding the correction coefficient A to the output signal of the multiplier 14, 17a is a gold 17 is an adder that sets the density ρ, specific heat C, and thermal conductivity λ of the mold, or sets the value obtained by multiplying the density ρ of the mold by the specific heat C divided by the thermal conductivity λ. A second multiplier that multiplies the output signal of 16 by the representative length ΔL and ρC/λ; 18 a setting device that sets a correction coefficient B to be added to the output signal of the multiplier 17; and 19, an output signal of the multiplier 17. This is an adder that adds correction coefficient B to . 2
0 is an adder that calculates a predicted signal corresponding to the molten metal temperature by adding the output signal of the adder 19 and the output signal of the input conversion circuit 10, and 21 is a set temperature Tset based on the mold, casting conditions, etc. The setting device 22 compares the output signal of the adder 20 and the output signal from the setting device 21, and turns ON when the predicted signal of the molten metal temperature T _M reaches the output signal of the setting device 21.
It is a comparator that outputs a signal. 23 determines the sign of the output signal of the inverting circuit 12, and if it is positive,
A sign determination circuit that outputs an ON signal; 24 a gate circuit that inputs the output ON signal of the comparator 22 and outputs an output signal when the output signal of the sign determination circuit 23 is an ON signal; 25 a gate circuit 2
This is a mold operating device that performs a mold opening operation based on the output signal No. 4. In addition, the output signal of the differentiating circuit 11 is outputted to the sign determination circuit 23 depending on the case, the sign is determined as positive or negative, and an ON signal is output when the sign of the output signal of the differentiating circuit 11 is negative. You can also do this.

In the present invention, the input conversion circuit 10, the differentiation circuit 11, the inversion circuit 12, the setting devices 13, 15,
17a, 18, first multiplier 14, first adder 16, second multiplier 17, second adder 19, third adder 20, setter 21 for setting molten metal temperature,
Comparator 22, sign discrimination circuit 23, gate circuit 2
4. The mold operating device 25 shown in FIG. 1 and assembled as described above will be described later in (2).
This is because the temperature T _M at a desired position inside the molten metal or casting inside the mold cavity 7 can be determined by sequential calculations based on the calculation formula shown in the equation. Of course, these calculations are performed by a computer. Then, it is determined that the molten metal temperature T _M determined by the calculation input to the comparator 22 has fallen to the value of the set temperature Tset set in the setting device 21.
When the detection is made by comparing and determining with the comparator 22, the mold opening operation is performed.

In the present invention, the temperature T near the casting wall surface of the mold 4 is measured, and at the same time, the rate of change in temperature ∂T/∂t with respect to time t is calculated, and the rate of change in temperature ∂T/∂t over time and the temperature gradient are calculated. The temperature gradient and temperature distribution in the vicinity of the casting wall surface are approximately calculated using the fact that the rate of change ∂ ² /∂x ² is proportional, and the temperature of the molten metal in the mold is predicted from this temperature distribution.

Note that as the molten metal approaches the optimal cooling state, the temporal rate of change in the temperature near the casting wall surface ∂T/∂t decreases,
Therefore, since the rate of change in the temperature gradient ∂ ² T/∂x ² is also decreasing, ∂T/∂x can be considered to be approximately constant, and as a result, equation (2), which will be described later, was derived. Then, the temperature of the molten metal in the mold is predicted and calculated from the measured value of the temperature near the casting wall surface.

Then, when this predicted molten metal temperature reaches a set temperature that is preset based on the mold, casting conditions, etc., the mold is opened.

Next, a method for predicting the temperature of the molten metal from the temperature measured near the casting wall surface in the mold will be described.

As shown in Fig. 2, the temperature distribution inside the mold 4 can be expressed as a one-dimensional approximation along the x-coordinate axis, which is perpendicular to the casting wall surface of the mold 4, as shown in equation (1). become.

ρC∂T/∂t=λ∂ ² T/∂x ² ...(1) Here, T: Temperature inside the mold t: Time x: x coordinate ρ: Density of the mold (Kg/m ³ ) C : Specific heat of the mold (k cal/Kg・℃) λ: Thermal conductivity of the mold (k cal/m・
In Fig. 2, 4 is the mold, 26 is the molten metal, X is the temperature measurement point, T is the mold temperature at the temperature measurement point X near the casting wall surface in the mold 4, and T _M is the cavity temperature. The molten metal temperature at a point M inside the molten metal that is a predetermined distance away from a part of the inner wall surface, L, L + ΔL is the position of the X point on the x coordinate and the molten metal point M, and ΔL is the temperature between these two points. Show distance.

On the other hand, the temporal change of the temperature near the casting wall surface is
It will look like the figure. In FIG. 3, the horizontal axis represents time t, and the vertical axis represents temperature T. t ₀ indicates the time when injection of the molten metal into the molds 4 and 5 is completed. As shown in Figure 3, the sign of the time derivative of temperature reverses after time t ₁ , so when predicting the molten metal temperature using time differentiation, the mold opening operation must be performed between t ₀ and _{t 1} . Therefore, it is necessary to set the period during which the mold opening operation is performed after t ₁ depending on the sign of the time differential of the temperature. Further, the time differential of temperature becomes small near time t ₂ when the optimum cooling state is reached, which indicates that the temperature distribution becomes close to a straight line.

Considering the above, the temperature distribution is approximated by a straight line, and equation (1) is solved as follows. T _M −T=
ΔT＝ρC／λ∫ ^L+ 〓 ^L _L ∫ ^L+ 〓 ^L _L ∂T／∂td×dx ＝ρC／λ∫ ^L+ 〓 ^L _L (∂T／∂t・ΔL＋A)dx ＝ρC／λ(∂T／∂ t・ΔL+A)・ΔL+B Here, A and B are correction coefficients.

This correction is for non-linearity and for the fact that the density, specific heat, and thermal conductivity are different between the mold and the molten metal. Also, the molten metal temperature T _M at a certain point is originally transmitted three-dimensionally. However, here, only the one-dimensionally transmitted temperature is extracted and the temperature at only one point in the mold section is measured to obtain this, so corrections for this are also included.

Therefore, the molten metal temperature T _M is T _M = T + ΔT = T + ρC / λ (∂T / ∂t · ΔL + A) · ΔL + B...
…(2) becomes.

Therefore, in the present invention, the molten metal temperature T M at a predetermined position is calculated by sequentially calculating according to the calculation formula (2), and the molten metal temperature T _M at a predetermined position is compared with the set temperature Tset set in advance. The apparatus shown in FIG. 1 and described above was designed so that the mold opening operation could be performed automatically when the molten metal temperature T _M fell to the set temperature Tset.

For example, when hot work tool steel such as SKD61 or medium carbon steel is used as the mold material and molten aluminum alloy is cast into the mold cavity to obtain a die-cast product, the molten metal and For example, the temperature of the mold is set as follows.

(1) Temperature of molten metal at the time of pouring: approximately 700℃ (2) Temperature of molten metal at the end of pouring: 600-620℃ (3) Temperature of the molten metal surface when the mold is opened: approximately 430℃ (4) When the mold is opened: The temperature inside the molten metal T _M is about 450°C. This also varies depending on the position of the target point M inside the molten metal.

(5) Temperature inside the mold cavity when the mold is opened
Approximately 400°C (6) Mold temperature T at the temperature measurement point X inside the mold at the time of opening the mold Approximately 250 to 330°C This mold temperature T varies considerably depending on the position of the temperature measurement point X.

Note that the temperature T inside the mold changes, for example, as shown in FIG. 4a, depending on the casting cycle.

In FIG. 4a, the horizontal axis represents time t (sec), and the vertical axis represents temperature T (°C) inside the mold. As shown in FIG. 4b, from the inner wall surface of the mold cavity 7, for example, Temperature detection elements 8 are buried at a point X ₁ 1 mm apart, a point X ₂ 4 mm apart, and a point X ₃ 16 mm apart, and at the timing and time shown below the time axis (horizontal axis), When performing a series of operations such as injection, mold opening, product ejection, shower cooling for mold cooling, mold clamping, and pouring, each measurement point in the mold 4 is measured at X ₁ , X ₂ , X ₃
The mold temperatures T are shown in Figure 4a as T ₁ , T 2 , T ₂ , and
It changes as shown by T ₃ .

As can be seen from FIG. 4a, the magnitude and state of temperature change vary greatly depending on the temperature measurement point X within the mold. Therefore, it is extremely important not only where to locate the point M at which you want to know the temperature inside the casting, but also how to select the setting position of the temperature measurement point X and the value of the distance ΔL between the points M and X. .
Note that the distance between the inner wall surface of the mold cavity 7 and the point M inside the molten metal whose temperature is to be determined varies depending on the shape, dimensions, thickness, etc. of the casting to be cast, but is usually
The value is often less than 10 mm.

In addition, the density ρ of the mold is usually 7.85×10 ³ Kg/m ³ ,
Specific heat C is 0.113k cl/Kg・℃, thermal conductivity λ is 44k
It is about cal/m・h・℃.

In addition, as mentioned above, the correction coefficients A and B are corrections for the differences in density, specific heat, and thermal conductivity between the mold and the molten metal. This can be determined in advance from the experimental results shown in Figure 4a, for example, by approximating the equation as shown in the equation, or by further approximating the equation (2) from this approximate equation. I can do it. In addition, these correction coefficients A and B are, for example, A is 180~
It is about 200, and B is about 80-95.

[Effects of the Invention] According to the present invention, a calculation is performed to predict the temperature of the molten metal in the mold from the temporal change rate of the temperature near the casting wall surface of the mold for each casting cycle, and this predicted molten metal temperature is determined in the optimum cooling state. When the temperature reaches , the mold opening operation is performed, so that the cast product can always be taken out from the mold in a cooled state at the optimum temperature. Therefore, the following effects can be obtained.

(1) It prevents the casting from bursting and seizing, and reduces the casting resistance, significantly extending the life of the mold.

(2) There is no variation in the casting temperature during the casting cycle. Then, the dimensional accuracy of the casting is stabilized, and the quality can be improved.

(3) Cooling time will not be longer than necessary,
The number of pieces cast per unit time increases, improving efficiency.

In addition, in the present invention, the time rate of change in temperature near the casting wall surface of the mold is calculated, or the control device is equipped with a differential circuit for this purpose, so that the temperature measurement point in the mold and the molten metal are The temperature of the molten metal can be determined using the distance ΔL between the point and a certain point. Therefore, no matter where the mold temperature measurement point is changed, that is, no matter where the thermocouple is placed, the molten metal temperature can be calculated and estimated using the calculation formula. In this way, in the present invention, since the temperature differential is determined, the temperature of the molten metal is determined by taking into account the temperature measurement points, thereby controlling the mold from the time of mold casting to the time of mold opening. The opening time can always be well controlled.

In addition, the cooling time for a casting varies depending on the location of the casting, so it is important to control and manage the temperature at which location inside the casting, and this temperature control location also varies depending on the product. This tendency is particularly strong for thick and complex products.

However, in the present invention, the molten metal temperature is predicted and measured using the distance ΔL between the position of the molten metal whose temperature is to be predicted and the temperature measurement point in the mold.
By changing this distance ΔL, it is possible to estimate the temperature in various places, not only on the surface of the casting, but also on the surface of the casting.
It is possible to estimate the temperature at all locations in the casting, including the temperature at a predetermined location inside the casting. Being able to estimate the temperature inside the casting is an important point in management as described above, and in the present invention, it is possible to estimate the temperature inside the casting without changing the temperature measurement position in the mold, that is, the setting position of the temperature detection element. It also has the excellent effect of being able to easily change the temperature control position.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing one embodiment of the present invention, Fig. 2 is a vertical cross-sectional view of the mold part to explain the temperature state near the mold casting wall surface, and Fig. 3 is the temperature of the mold part. Time-temperature diagram showing changing conditions, Figure 4a is a time-temperature diagram showing changing conditions of mold temperature during the casting cycle.
The temperature diagram, FIG. 4b, is an explanatory longitudinal cross-sectional view showing the measurement points of the mold temperature shown in FIG. 4a. 1...Fixed plate, 2...Movable plate, 3...Fixed mold, 4...Movable mold, 8...Temperature detection element, 10
... Input conversion circuit, 11 ... Differentiation circuit, 12 ...
Inverting circuit, 13, 15, 18, 21...setting device,
14, 17... Multiplier, 16, 19, 20... Adder, 22... Comparator, 23... Sign determination circuit,
24...gate circuit, 25...mold operating device.

Claims (1)

[Claims] 1. A temperature detection element 8 that outputs an electrical signal corresponding to the temperature near the casting wall surface of the mold, an input conversion circuit 10 that converts the electrical signal into a predetermined voltage signal or current signal, and an output of this input conversion circuit 10. A differentiating circuit 11 that differentiates a signal with respect to time, and an inverting circuit 1 that inverts the sign of the output signal of this differentiating circuit 11.
2, a first multiplier 14 that multiplies the output signal of this inversion circuit 12 by a representative length ΔL between a predetermined position inside the molten metal or the surface of the molten metal and a temperature detection point near the casting wall surface; a first adder 16 that adds a correction coefficient A to the output signal of the multiplier 14;
a second multiplier 17 that multiplies the output signal of the adder 16 by a value obtained by dividing the product of the representative length ΔL, the mold density ρ, and the specific heat C by the thermal conductivity λ; A second step that adds correction coefficient B to the output signal of
a third adder 20 that calculates a predicted signal corresponding to the molten metal temperature by adding the output signal of the second adder 19 and the output signal of the input conversion circuit 10; The output signal of the adder 20 of No. 3 is compared with the output signal from the setting device 21 that sets the set temperature based on the mold, casting conditions, etc., and when the predicted signal of the molten metal temperature reaches the output signal of the setting device 21. The sign of the output signal of the comparator 22 that outputs the ON signal and the inverting circuit 12 or the differentiating circuit 11 is determined, and if the sign of the output signal of the inverting circuit 12 is positive or the sign of the output signal of the differentiating circuit 11 is negative, Sign determination circuit 23 that outputs an ON signal in the case of
and a gate circuit 24 which inputs the output ON signal of the comparator 22 and outputs an output signal when the output signal of the sign determination circuit 23 is an ON signal; A casting cooling time control device in mold casting, including a mold operating device 25 that performs an opening operation.