JPH03290222A - Control method and device of mold temperature - Google Patents

Abstract

PURPOSE:To control the temperature of a mold at a stable and accurate value even if time delay occurs in the temperature-change of the mold to the temperature-change of thermal medium by preliminarily calculating and determining the time when the circulation of low temperature thermal medium begins and the time when it is switched to hot thermal medium in the time of one injection molding cycle. CONSTITUTION:The heat-exchanging path 23 through which thermal medium passes, is formed in a mold, and a first thermal medium-circulating means 11 circulates high temperature thermal medium, and a second thermal medium-circulating means 12 circulates low temperature thermal medium respectively through the mold. The thermal medium which does not circulate through the mold is circulated through by-pass flowing tubes 14, 15. The calculating means 24 of thermal medium-switching time calculates the formula f (f1, th)=Tr-Tp (ti) on the basis of mold temperature-history Tp (t) in injection of resin inputted by a mold temperature history-inputting means 25 and the mold temperature aimed value Tr in starting of the injection inputted by a mold temperature aimed value-inputting means 26, and preliminarily determines the value of low temperature switching time ti and the high temperature switching time th, and when it is given to a thermal medium-switching control means 23, a condition H is switched to a condition L by controlling two directional electromagnetic valves 9, 10, 13.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention provides a mold temperature control method and device for controlling the temperature of the mold to an appropriate value by circulating a heat medium in the mold in an injection molding machine. Regarding.

[Prior Art] Conventionally, a mold temperature control method in which a heating medium is circulated within the mold to control the temperature of the mold to an appropriate value is disclosed in Japanese Patent Laid-Open No. 64-6
Examples include those shown in Publication No. 7321. This method is
Measure the actual temperature of the mold.

Based on the temperature difference between the ff1ll constant temperature and the target pot mold temperature, calculate the amount of heat required to maintain the mold at the target temperature, and calculate the temperature of the heat medium flowing into the mold and the heat flowing out from the mold. Measure the temperature of the medium and find the temperature difference between them. Then, based on this temperature difference and the flow rate per unit time of the heat medium passing through the mold, the amount of heat transferred to and received by the heat medium from the mold is calculated, and when the calculated amount of heat reaches the required amount of heat, , stop the flow of heat medium into the mold.

[Problems to be Solved by the Invention] The above mold temperature control method measures the actual temperature of the mold and feeds it back to control the mold temperature.

However, there is a time delay between a change in the temperature of the heat medium and a change in the temperature of the mold because time is required for heat transfer. Moreover, this time delay changes with changes in the temperature distribution within the mold, changes in the surrounding outside air temperature, and changes in the platen temperature, so there is a drawback that it is difficult to control the mold temperature to a stable and accurate value. .

In addition, it is preferable that the mold temperature at the start of injection be maintained at a constant value, but in reality, as seen in the first half of the mold temperature history in Figure 4, it tends to gradually increase as the molding operation progresses. This is a factor that makes mold temperature control unstable.

Therefore, the object of the present invention is to control the temperature of the mold to a stable and accurate value even if there is a time delay between the change in the temperature of the heat medium and the change in the temperature of the mold. An object of the present invention is to provide a control method and a control device.

[Means for Solving the Problems] The first invention allows a heat medium to flow through the mold of an injection molding machine whose injection molding cycle time is constant, and to circulate the heat medium within the mold within one injection molding cycle time. In a mold temperature control method in which the temperature of the mold is controlled to an appropriate value by switching the heat medium from a high temperature or low temperature to a low or high temperature, the flow of a low temperature heat medium within one injection molding cycle time. The point at which the heating medium is started and the point at which the high temperature heat medium is switched are calculated and determined in advance based on the mold temperature history after resin injection in one injection molding cycle and the target value of the mold temperature at the start of injection. It is characterized by keeping it.

The second invention is an injection molding machine in which the injection molding cycle time is constant. a second heat medium distribution means, and these first or second
a heat medium switching means for selecting which of the heat medium circulation means is used to circulate the heat medium in the mold; and a mold temperature history input means for inputting the mold temperature history after resin injection in one injection molding cycle. , based on the values input by the injection start mold temperature target value input means for inputting the target value of the mold temperature at the start of injection, the mold temperature history input means, and the injection start mold temperature target value input means, A heat medium switching time calculation means for starting the flow of a high temperature or low temperature heat medium into the mold and calculating in advance the time from the start of the flow of the heat medium to the time of switching to the low temperature or high temperature heat medium; , the heat medium flowing into the mold is changed to a low temperature or high temperature one based on the time point at which the flow of the low temperature heat medium is started and the time point at which the flow is switched to the high temperature heat medium, which are calculated by the heat medium switching time calculation means. It is characterized by comprising a heating medium switching control means for switching.

[Function] The present invention is capable of controlling the time point at which low-temperature heat medium starts flowing into the mold of an injection molding machine whose injection molding cycle time is constant and the time point at which the flow is switched to a high-temperature heat medium within 11 injection molding cycle times. , mold temperature history after resin injection in one injection molding cycle.

Since it is calculated and determined in advance based on the target value of the mold temperature at the start of injection, the mold temperature can be adjusted even if there is a time delay in the change in the mold temperature with respect to the change in the temperature of the heating medium. It can be controlled to a stable and accurate value.

[Example] Next, embodiments of the present invention will be described in detail.

The mold temperature control method of the present invention is a mold temperature control method in which the temperature of the mold is controlled to an appropriate value by circulating a heat medium in the mold of an injection molding machine whose injection molding cycle time is constant. , which switches the heat medium flowing in the mold from high temperature or low temperature to low temperature or high temperature within one injection molding cycle time, and the low temperature heat medium does not flow within one injection molding cycle time. The starting low temperature switching time tρ and the high temperature switching time th for switching to the high temperature heat medium are calculated in advance based on the mold temperature history after resin injection in one injection molding cycle and the target value of the mold temperature at the start of injection. It is characterized by the fact that it is determined in advance.

In this case, the low-temperature switching time t and the high-temperature switching ρ time th are defined as T (t), which is the mold temperature history after resin injection in one injection molding cycle (where t is time),
When the target value of the mold temperature immediately before injection is T, it is determined by the following linear equation.

f (t, th)=T, -Tp (ti)...(
1) ρ However, t is the time just before the start of resin injection.

f(t, th) varies depending on the shape of the mold.

ρ is a function that can be determined experimentally in advance prior to the injection molding operation.

The low temperature switching time t and the high temperature switching time th vary depending on the size and type of the injection molding machine and the type of resin used. However, once the injection molding machine and the resin used are specified, and the mold temperature history T (t) and the mold temperature target value T at the start of injection are determined, (
1) It can be determined by formula. Next, an embodiment of the mold temperature control device of the present invention will be described in detail with reference to the drawings.

In Figure 1, the mold 1 of the injection molding machine is the fixed mold 1.
a, a movable mold 1b, etc. An injection section 2 for injecting molten resin from an injection molding machine into the mold 1 is disposed near the mold 1. This injection part 2 includes a cylinder 2a and an injection piston 2b disposed inside the cylinder 2a.
and an injection drive means 2C that moves the injection piston 2b.

It consists of an injection control means 2d for controlling this.

A heat exchange passage 3 is formed inside the mold 1 to allow a heat medium (for example, water) to flow therethrough. This heat exchange passage 3 includes connecting pipes 4, 5, .
6.

A supply pipe 7 is connected to one end of the heat exchange passage 3.
A discharge pipe 8 is connected to the other end of the heat exchange passage 3 .

Two supply branch pipes 7a and 7b are connected to the end of the supply pipe 7. These supply branch pipes 7a7b are each
First heat medium distribution means 1 via two-way solenoid valves 9 and 10
1. It is connected to the heat medium distribution means 12 of m2. The discharge pipe 8 is connected to two discharge branch pipes 8a via a two-way solenoid valve 13.
, 8b. These discharge branch pipes 8a, 8
b are connected to the first heat medium distribution means 11 and the second heat medium distribution means 12, respectively. 2-way solenoid valve 9
A short-circuit flow path pipe 14 is provided between the
is provided. Further, a short-circuit flow pipe 15 is also provided between the two-way solenoid valve 10 and the second heat medium distribution means 12.

The first heat medium distribution means 11 includes a pump lla and a heat medium temperature adjustment means 11b. Second heat medium distribution means 1
2 also includes a pump 12a and a heat medium temperature adjusting means 12b. The first heat medium distribution means 11 circulates a high temperature heat medium into the mold 1 .

The second heat medium circulation means 12 circulates a low temperature heat medium into the mold 1.

Heat medium temperature detectors 11C, 12, c are provided at the outlet portions of the pumps 11a, 12a, and these measured values are fed back to the heat medium temperature adjusting means 11b, 12b to adjust the temperature of the heat medium. Ru. Supply branch pipes 7a, 7b
, the discharge branch pipes 8a, 8b and the short-circuit flow path pipes 14, 15 are each provided with a check valve 1 that allows the heat medium to pass only in the four directions indicated by the arrows.
6,17°1.8,19,21.20 are provided.

The two-way solenoid valves 9, 10.13 transfer the high temperature heat medium to the mold 1.
A heat medium switching means 22 that selectively switches whether to flow the heat medium inside the mold 1 or to let the low-temperature heat medium flow inside the mold 1.
It consists of When the two-way solenoid valves 9, 10.1'3 are controlled to cause the high temperature heat medium to flow into the mold 1 by the first heat medium flow means 11, the second heat medium flow means 12 The low temperature heat medium sent out by the short-circuit flow pipe 1
It cycles through 5. In addition, two-way solenoid valve 9, 10° 13
When the low-temperature heat medium is distributed within the mold 1 by the second heat-medium distribution means 12 by controlling the It circulates through the tube 14.

As described above, the first heat medium flow means 11 and the second heat medium flow means 12 are always in operation during injection molding, and the heat medium that is not allowed to flow into the mold 1 is connected to the short-circuit flow pipes 14 and 15, respectively. When the heat medium switching means 22
The heating medium flowing into the mold 1 can be switched quickly in response to the switching operation of the heating medium.

Two-way solenoid valves 9, 10.13 are heat medium switching control means 23
It is connected to the. This heat medium switching control means 23 is connected to heat medium switching time calculation means 24. These heat medium switching control means 23 and heat medium switching time calculation means 2
4 consists of a microcomputer. The heat medium switching control means 23 is given a resin injection start signal from the injection control means 2d. The mold temperature history T (t) after resin injection is input to the heat medium switching time calculation means 24 by the mold temperature history input means 25, and the mold temperature history T (t) at the time of injection start is inputted by the mold temperature target value input means 26 at the time of injection start. The target value T of the mold temperature is input. A desired value can be input into the mold temperature target input means 26.

The injection control means 2d, the heat medium switching control means 23, and the heat medium switching time calculation means 24 are connected to a main control device 27 that controls the injection molding machine.

A mold temperature detector 28 is arranged on the surface of the mold 1, and the measured value of this mold temperature detector 28 is given to the mold 1 2 temperature history input means 25.

The operation of the mold temperature control device of the present invention will be explained with reference to FIG.

Curve A in FIG. 2(a) is a curve showing the change in temperature of the mold 1 over time. Curve B in FIG. 2(b) shows a state H in which a high temperature heat medium is flowing through the mold 1 by the first heat medium distribution means 11, and a state H in which the high temperature heat medium is distributed in the mold 1 by the second heat medium distribution means 12. It shows changes over time with a state in which a low-temperature heat medium is flowing inside.

When a resin injection start signal is given to the heat medium switching control means 23 by the injection control means 2d, the state is set at time t, when a low temperature switching time tρ has elapsed after the generation of the resin injection start signal.

ρ↓Next, at time thl when the high temperature switching time t has elapsed after the resin injection start signal is generated, the state is set from state 1 to state H. Then, time in 2 (
At the time when the next resin injection start signal is generated, the state is switched to state 1. Such switching between state 1 and state H is performed as time passes.

In this case, the resin injection start signal generation time tif't12
The temperature of the mold 1 at is the target value Tr.

The heat medium switching time calculation means 24 calculates the mold temperature history T during resin injection inputted by the mold temperature history input means 25.
(L) and the mold temperature target value T at the start of injection inputted by the mold temperature target value input means 26, the formula (1) is calculated in advance, and the low temperature switching time t and high temperature switching are performed. Determine the value of time th, ρ, and use these values 1. 1 is given to the heat medium switching 7h control means 23. This heat medium switching control means 23 controls the two-way solenoid valves 9, 10.13 to
The time tρ1t, . . . when the low temperature switching time tn has elapsed from the time 11 . . . when the resin injection start signal was received from the injection control means 2d, respectively.
・Switch from state ■ to state R.

2 Moreover, the time tH' when this resin injection start signal is received
The time point 1 when the high temperature switching time th has elapsed from ti2'..., respectively. 1,... from the state to the state Hh
Switch to l h2.

Then 1 hour 1. The procedure for determining the value of ρ
h and explain.

The mold temperature history T (t,) during resin injection after a sufficient period of time has passed after the start of the molding operation is the pth
1 The target value T of the mold temperature at the start of injection is given as shown in Figure 3.
Assume that the temperature is the same as the preheating temperature.

What the above formula (1) means is that the deviation r between the target value T and the mold temperature history T (t,) is calculated without significantly changing the outline of the mold temperature history during the molding operation.
The point is that the times tρ and th are calculated so that mold temperature fluctuations occur that cancel out p1.

Time 1. 1 in the mold caused by the combination of
h Regarding temperature fluctuations, the time required for preliminary work before molding work 1. Regarding the combination ρ h , the heating medium is actually switched. and.

For each combination, temperature fluctuations are measured after a sufficient period of time has elapsed, and an approximate expression expressing the temperature fluctuation within the mold using times tp and th is obtained. From the obtained approximate expression, as shown in FIG. 3, 1 5 waveforms can be obtained that cancel out the deviation between the target value T and the mold temperature history T (t,).

Among these, a mold temperature fluctuation waveform that satisfies the following condition (a) is selected in order to avoid greatly changing the outline of the mold temperature history during the molding operation.

(a) The time point when the most recent input of the mold temperature history T (t) during the molding operation is taken and the time point when the minimum value of the mold temperature fluctuation waveform is taken are synchronized.

Once the mold temperature fluctuation waveform that satisfies condition (a) is determined, the time 1.1 h to realize it is determined.

Figure 3 shows the time t, thρ according to the above procedure. This is an example of the case where 1 condition (a) is the time tg.

This is an example of a norm when determining th.

FIG. 4 shows the time tg designed in FIG.

The mold temperature data during the molding operation when the heat medium is switched based on th is shown. The heat medium is switched from the fourth molding cycle onwards, and the mold temperature target value T during resin injection is distantly related from the second seventh molding cycle onwards.

In addition, in the above-mentioned example, 2 hours 1. 1 base ρ
h 6 The standard time is the injection start signal generation time 11if' i
2'... However, the reference point may be the point in time when another signal is generated.

Moreover, although the above-mentioned embodiment assumes a case where injection molding is performed using a thermoplastic resin, it goes without saying that it can be applied to injection molding using a thermosetting resin.

[Effects of the Invention] As explained above, according to the present invention, by introducing the mold temperature target value at the start of injection molding and the mold temperature history as factors for mold temperature control, one mold temperature control The temperature can be maintained at a stable and accurate value.

FIG. 3 is a diagram showing the mold temperature history and the timing of high temperature and low temperature switching in the invention.

1... Mold, 2... Injection part, 3... Heat exchange passage,
DESCRIPTION OF SYMBOLS 11... First heat medium distribution means, 12... Second heat medium circulation means, 22... Heat medium switching means, 23...
Heat medium switching control means, 24... Heat medium switching time calculation means, 25... Mold temperature history input means, 26... Mold temperature target value input means.

[Brief explanation of the drawing]

Claims (2)

[Claims] (1) A heat medium is circulated within the mold of an injection molding machine whose injection molding cycle time is constant, and the heat medium flowing within the mold within one injection molding cycle time is changed from high temperature or low temperature to low temperature or high temperature. In a mold temperature control method in which the temperature of the mold is controlled to an appropriate value by switching to The time from the point in time to the point in time when switching to a low temperature or high temperature heat medium is calculated and determined in advance based on the temperature of the mold in one injection molding cycle, using the operation signal of the injection molding machine as the time standard. Features a mold temperature control method. (2) In an injection molding machine in which the injection molding cycle time is constant, there is a first heat medium distribution means for circulating a high temperature heat medium within the mold, and a second heat medium circulation means for circulating a low temperature heat medium within the mold.
a heat medium distribution means, a heat medium switching means for selecting which of the first or second heat medium distribution means to circulate the heat medium in the mold, and a mold temperature history in one injection molding cycle. A mold temperature history input means for inputting the target value of the mold temperature at the start of injection, a mold temperature target value input means for inputting the target value of the mold temperature at the start of injection, and these mold temperature history input means and the mold temperature target value input means. Based on the input value by the means, the flow of the high temperature or low temperature heat medium into the mold is started, and the time from the start of the flow of the heat medium to the time of switching to the low temperature or high temperature is calculated in advance. and a heat medium switching time calculation means that changes the heat medium flowing into the mold into a low-temperature or high-temperature one when the time calculated by the heat medium switching time calculation means has elapsed from the start of the flow of the heat medium. 1. A mold temperature control device, comprising a heating medium switching control means for switching to a heating medium.