JP2907260B2 - Plastic mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic molding die used for obtaining a resin molded product having high dimensional accuracy used in an optical system or the like by injection molding.

[0002]

2. Description of the Related Art Usually, in a system for performing injection molding using a plastic mold of this type, an injection molding apparatus and auxiliary equipment having a structure as shown in FIG. 2 have been conventionally used. That is, the injection molding apparatus 1 includes a plasticizing cylinder-3.
1, a hot air-dried resin material is supplied from a material supply device 4 via a hopper 3 by air conveyance, and a mold 2 mounted on the injection molding device 1 is provided. In the course of the repetition of a predetermined cycle, a resin material heated to a predetermined temperature is filled at a predetermined pressure from the plasticizing cylinder 31 and cooled in a mold. Take-out means 5
Then, it is taken out as a molded product. In this case, a plurality of cooling paths (not shown) are formed in the mold 2, and a cooling medium such as factory water and cooling oil is supplied to and circulated through the pipe 9. You.

[0003] In this case, for example, cooling water as a cooling medium from a factory water concentration chiller 33 is supplied to the cooling medium path.
A required configuration is provided such that the temperature is raised to a required temperature by the temperature control device 6, and thereafter, it is branched via the branching device 12 and supplied to each branch path of the mold. After the completion of cooling, the molded product is taken out by the above-mentioned automatic take-out means 5 to the conveyer 7 as a carry-out route, and is conveyed.

[0004]

However, the above-mentioned conventional system has several drawbacks as described below. (1) Normally, the temperature of factory water is about 25 ° C., and fluctuates on average about 3 ° C. every year (this is caused by a change in outside air temperature). Further, the water temperature fluctuates on a daily or hourly basis depending on the usage state of the factory water at the branch destination, for example, how many injection molding apparatuses are connected or operated simultaneously. When factory water is used as cooling water for a mold, the pressure difference between the supply pressure to the mold and the return pressure is 1 kg / cm ^{2 to 2} k.
It is a small value of about g / cm ^2. Therefore, the flow rate of the cooling medium flowing in the mold is drastically reduced due to the pressure loss generated by the pipe resistance of the cooling medium and the branch path resistance in the mold. As a result, the cooling efficiency of the mold has deteriorated.

Further, in order to control the temperature of the cooling medium in the mold to stabilize the repeated temperature change in the mold in a continuous pattern in the process of continuous molding, the mold and the cooling water supply source (centralized Chiller), a temperature control device is interposed, however, as described above, factory water is usually 25%.
Since the temperature was ± 3 ° C., the temperature of the medium could be stabilized by the temperature control device (only the heating control function) at a temperature of 30 ° C. or higher. In addition, the capacity of the temperature control device usually used is 60 to 80 (l / min) at the maximum discharge rate.
Therefore, the pressure loss of the cooling medium path is 3 to 4 kg /
In the case of cm 2 or more, an expected flow rate could not be secured.

[0006] Under such circumstances, a cycle necessary to carry out the heat of the resin supplied into the mold by the cooling medium circulated through the branch path has been set empirically until now. In the molding process, the change of the mold temperature is converged to a certain pattern, that is, the balance of the heat balance of the mold in each cycle from the molding temperature to the removal temperature in the continuous molding state is maintained. I was ingenious. However, in this case, the heat exchange efficiency in the cooling process is very poor, the molding cycle is lengthened, and the production efficiency is suppressed. (2) In the conventional molding system, since there is no process for collecting data on the molded article during molding,
Injection molding is performed in advance under several types of molding conditions, the dimensions of the resulting molded product are measured, and the conditions for molding the molded product with the highest dimensional accuracy are selected from among them. Since the setting of the auxiliary equipment is performed, setting the optimum conditions requires a great deal of labor and time. In particular, many parameters of the molding conditions (temperature of the plasticizing cylinder, temperature of the hot runner, set temperature of the cooling water temperature controller, injection speed, injection pressure, holding pressure of the mold, holding pressure of the mold) Maintenance time, cooling time, mold opening / closing speed, control speed, operation, position, etc. of the automatic removal machine for molded products, etc.).
Indeed, each parameter is set empirically after repeated trial and error. (3) In the conventional molding system, the temperature of the cooling medium before the supply of the mold is known from the set temperature of the cooling water temperature controller. Since the temperature and the flow rate cannot be known, when the molded article is taken out of the mold after molding, the entire temperature distribution of the molded article cannot be understood. Therefore, since the correspondence between the cooling medium for controlling the temperature in the mold and the temperature distribution of the molded product cannot be grasped, the molded product obtained as a result of molding has a non-uniform temperature distribution in the cooling process. Even if the molded article is deformed due to the partial difference in heat shrinkage caused by the partial heat shrinkage, no specific investigation can be performed and no measures can be taken to prevent the deformation. In the end, it was an effective measure to simply extend the cooling time and ensure a uniform temperature of the molded article in the mold. (4) The main causes of the deformation of the molded product in the injection molding are the non-uniformity of the density distribution of the resin when filled in the mold,
The temperature distribution of the molded product in the mold during the cooling process after filling is uneven. That is, regarding the density distribution of the resin in the mold, the shrinkage amount is small in the high density portion, and the shrinkage is large in the low density portion. Therefore, due to the partial shrinkage difference,
It is considered that local stress occurs in the molded article, causing deformation. As for the temperature distribution, the lower temperature part reaches the curing temperature of the resin before the others, and in the mold,
Shrinkage occurs according to the coefficient of thermal expansion of the resin, but the high temperature part causes the same shrinkage later, so the previously cured part is pulled, causing local stress, When removing the molded article, it is considered to cause deformation. However, also in this case, as in the case described above, the cause cannot be specifically investigated, and no effective countermeasure can be taken. (5) In the conventional molding system, it is not possible to select and set the set values of the injection molding machine and the cooling water temperature controller as the daily management and the molding condition management after the change of the molded product (such as mold replacement). It is possible. However, it is not possible to manage whether or not the actual molding state (the flow state of the resin in the mold, the pressure distribution, the temperature distribution, the temperature of the cooling medium, the flow rate thereof, etc.) is reproduced under required conditions. . Therefore, the way of connecting the cooling water supply line to the mold is incorrect, the flow path for passing the cooling medium is blocked, or the heater capacity for heating the plasticizing cylinder of the injection molding machine changes. The actual mold temperature, molded product removal temperature, resin viscosity,
Even if the fluidity and pressure distribution of the resin are changing,
There was a drawback that they could not notice those changes and the response was delayed.

Therefore, the inventor of the present invention first secures a supply flow rate of a cooling medium such as cooling water to a mold to shorten a molding cycle in continuous molding and improve production efficiency. We proposed a plastic molding system that measures the resin temperature and pressure at required locations inside the mold and controls the flow rate of the cooling medium required for the temperature control. Here, since the detection of the temperature and the pressure and the cooling control are performed in association with each other, the molded product can be maintained at a high yield without being adversely affected by local deformation or the like.

[0008] However, in implementing such a plastic molding system, usually, a conventional 3
With plastic molding systems that use cooling media at temperatures around 0 ° C., an unexpected event has occurred. That is, it has become clear that after a rapid cooling step, the density inside the molded article becomes higher than that of the molded article by the conventional molding system, which affects the finished dimensions of the molded article. This is considered to be because the resin filled in the cavity is rapidly cooled from the surface, thereby compressing the internal resin, and having a high-density composition due to the difference in the history of the cooling process.

Therefore, when making a mold, unless the mold shrinkage rate is estimated to be slightly larger than the mold shrinkage rate of the resin which is usually set according to the type of the molding resin material, the dimensions of the completed molded product will be reduced. However, there is an inconvenience that the dimensions are smaller than the expected dimensions.

[0010]

SUMMARY OF THE INVENTION The present invention has been made based on the above circumstances, and a molding die employed in a molding system for cooling using a cooling medium at a temperature lower than that of the related art is a conventional mold for manufacturing the cavity. An object of the present invention is to provide a plastic mold in which a cavity size is set based on a shrinkage ratio larger than a mold shrinkage ratio set in design data.

[0011]

For this reason, according to the present invention, when injection molding a resin, the resin injected into the cavity from the injection molding machine is cooled to a predetermined temperature as it is after molding, and thereafter, In the plastic mold used in the removing molding system, the gradient of the temperature drop in the cavity in the cooling step of the molding system is determined based on the flow rate and temperature of the cooling medium supplied to the cooling medium path for cooling the inside of the cavity. The corresponding resin shrinkage is calculated in advance, and the dimensions of the cavity are set so as to secure the required molded product dimensions.

[0012] In this case, the molding shrinkage of the resin is set to be 0.1 to 0.05 less than the resin molding shrinkage set according to the type of the molding resin material.
The size of the cavity for molding is set with a large shrinkage.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a molding system employing a molding die of the present invention will be described in detail with reference to the drawings. The same components as those of the conventional molding system are denoted by the same reference numerals, and the description of the components is omitted. In the molding system according to the present invention, in particular, in the cooling medium path for cooling the mold 2, the supply pressure control device 14 for the cooling medium to the mold 2 on the plurality of supply paths 9 </ b> A side, in this embodiment, Equipped with booster pump. Then, the cooling medium cooled to the required temperature, in this embodiment, the cooling water from the factory water concentration chiller 33 is forcibly supplied, the gradient of the temperature drop of the resin in the cooling step is sharpened, and the molding in the continuous molding state is performed. The heat balance of the mold 2 in each cycle from the temperature to the removal temperature is balanced.

In this case, the cooling medium path further includes:
A cooling device 10 that cools the cooling medium to a required temperature, for example, 10 ° C., a temperature control device 6 (control by heating) that accurately controls the subsequent cooling medium to a constant temperature, and a plurality of cooling from the mold 2 A flow measuring device 13 for measuring the flow rate of the return cooling medium in real time is provided for each of the medium return paths 9B.
Is configured to control the drive of the supply pressure control device 14 based on the measurement result. In addition, as said cooling device 10,
For example, a method is employed in which a pump is driven by a detection signal of a built-in temperature sensor, a compressed refrigerant gas is supplied to a heat exchanger and cooled.

When the temperature of the mold 2 becomes abnormal, the supply pressure of the cooling medium is controlled, and at least the flow rate at the portion where the temperature is abnormal is changed to return to normal.

As described above, the cooling medium path is branched and communicated with the mold 2 via the reciprocating path. The cooling medium branching device 12 is provided corresponding to the branch path, and the supply pressure control device 14 is configured to control the supply pressure of the cooling medium to the cooling medium branching device 12 for each branch path. In addition, the measurement result of the flow measurement device 13 is as follows.
For example, a control unit U such as a computer control (FIG. 1)
6), and in this case,
The control unit U controls the supply pressure control device 1 based on the measurement result from the mold temperature measurement device 42 (not shown in FIG. 1) provided in the mold 2 and the measurement result from the flow rate measurement device 13.
4 may be configured to be output.

Further, if necessary, a throttle valve 13A is provided in a supply path from the cooling medium branching device 12 to the mold 2, and the throttle valve 13A is provided directly from the flow rate measuring device 13 or via a control unit. The control unit may be configured to output an opening control signal for the throttle valve 13A, including the measurement result from the above-described mold temperature measuring device (FIG. 1).
6).

Thus, when the temperature of the mold 2 becomes abnormal, the supply amount of the cooling medium is throttled and controlled, and at least the flow rate at the abnormal temperature portion is changed to return to normal. .

As described above, in the above embodiment, the cooling device 10 cools the cooling water to, for example, about 10 ° C., so that even if the factory water fluctuates normally at 25 ± 3 ° C., Appropriate temperature control by the control device 6 can be easily realized. Further, by providing the supply pressure control device 14, even if the pressure loss of the flow path exceeds ³ to 4 kg / cm ² , the maximum discharge amount is, for example, 60 to 80 (l / mi).
n) can be secured, and the heat exchange efficiency in the mold can be improved.
FIG. 9 shows the correlation between the flow rate of the cooling water, the temperature of the mold during molding, and the temperature of the molded product, from the beginning of the molding cycle to the number of molding shots.

As is clear from the figure, as the amount of cooling water increases, the change in the mold temperature converges to a constant pattern in the process of continuous molding, that is, from the molding temperature in the continuous molding state. The number of molding shots required to balance the heat balance of the mold in each cycle up to the removal temperature is shorter, but nevertheless, compared to the cooling water supply in the conventional molding system, the cooling water The lower the temperature, the more it will be. This can be understood from the correlation between the cooling time, the mold temperature, and the molded product temperature shown in FIG. However, since the gradient of the temperature drop of the resin in the cooling step becomes steep, the cooling time occupied largely in the molding cycle is greatly reduced, for example, 1/2 to 2 in the entire cycle.
This can be reduced to about 2/3. As can be seen from the figure, as the cooling water flow rate increases, the mold temperature,
It is understood from the fact that the equilibrium value of the temperature inside the molded article is low.

The above-mentioned control unit is supplied with a temperature measurement signal from the above-mentioned temperature measurement device 42 provided in the mold 2 and also has a pressure sensor (also shown in FIG. (Not shown) supplies a resin filling pressure measurement signal. These measurement results are recorded in real time on a recording device 21 such as an analyzing recorder.

In this embodiment, as shown in FIGS. 3 to 5, a method of installing the pressure sensor 35 inside the mold 2 is effective. That is, in the embodiment of FIG. 3, the pressure receiving surface 36 of the pressure sensor faces the weld portion 37 in the mold 2 to which the resin 38 is supplied. In the embodiment shown in FIG. 4, the pressure sensor 35
9. A portion close to the hot runner 40 faces the portion where the resin 38 is supplied. In the embodiment shown in FIG. 5, the pressure receiving surface 36 of the pressure sensor 35 is provided on the outer end of the ejector pin 41 for projecting a molded product, which is disposed facing the cavity of the mold 2.
Is abutted.

Although these embodiments are designed to measure the resin pressure as directly as possible,
The installation location of the pressure sensor is not limited to these, and setting the required number of installation locations (measurement points) to increase the measurement accuracy and confirm the local pressure distribution Is effective in

Temperature measuring device 42 in mold (temperature sensor)
In this case, an installation method as shown in FIGS. 6 and 7 is effective. That is, a resin supply portion close to the hot runner 40,
In particular, the sensing part 42A of the temperature measuring device is made to face the heat storage part 43 (preferably a protruding shape having a large resin contact surface with a small volume) formed inside the mold.

In such a configuration, the pressure sensor 35 and the mold temperature measuring device 42 provided at required portions of the mold 2 are provided.
As described above, the measurement result is recorded in real time in the recording device 21 and supplied to the control unit U. The control unit analyzes an abnormal value, and from the result, for example, when the mold is cooled. And a signal for adjusting the flow rate of the cooling medium in the cooling medium path.

For example, in a mold temperature measuring device,
Even if no abnormality is detected, if the pressure in the mold 2 rises abnormally, a control signal is sent from the control unit to the supply pressure control device 14, and the flow rate is controlled to control the mold temperature and at least the abnormal pressure. The flow state of the resin at the location is controlled. Similarly, it is preferable to control the throttle valve 13A.

In the control unit, the pressure sensor 3 in the cooling process after injection molding / injection molding to cooling process is provided.
5, the quality of the molded product can be determined based on the measurement results from the mold temperature measuring device 42. In practice, in the present invention, by installing the pressure sensor 35 as described above, as shown in FIG. 11 (normal) and FIG. 12 (abnormal), the resin pressure in the mold during continuous molding, the dimensional accuracy of the molded product, and the like are reduced. The correlation became clear. Further, by installing the mold temperature measuring device as described above, the correlation between the temperature change in the mold during continuous molding and the dimensional accuracy of the molded product is also increased as shown in FIG. 13 (normal) and FIG. 14 (abnormal). It was revealed.

As described above, in the molding system in which the temperature, pressure, and the like in the mold (cavity) can be specifically grasped, conversely, the use of such a low-temperature cooling medium causes a sudden increase in the temperature. The manufacturing dimensions of the cavity in consideration of the shrinkage of the molded product due to the cooling can be calculated in advance. That is, the plastic mold according to the present invention, based on the flow rate and the temperature of the cooling medium supplied to the cooling medium path for cooling the inside of the cavity, corresponds to the gradient of the temperature drop in the cavity in the cooling step of the molding system. The amount of resin shrinkage is calculated in advance, and the dimensions of the cavity are set so as to ensure the required molded product dimensions. In this case, the molding shrinkage of the resin, which is usually set according to the type of the molding resin material, is 0.1 to more than 0.1%.
It is preferable to set the size of the cavity for molding at a shrinkage rate as large as 0.05%.

The control unit U includes a pressure sensor 35
The information from the recording device 21 for recording the output signal of the mold temperature and the output signal from the mold temperature measuring device 42 is monitored, and when the resin is injected from the output waveform or when an abnormality in the cooling process is detected, It may be configured to output an alarm signal via an appropriate alarm device. That is, for example, the rotary signal (not shown) installed in the injection molding machine is rotated by the alarm signal to notify the abnormality.

In the present invention, the means for automatically taking out the molded product from the mold, indicated by the reference numeral 5 in FIG. 1, changes the mold temperature, the resin viscosity, the filling pressure, etc., and the resin pressure in the mold is reduced. When the control unit U determines whether the molded product is good or not, for example, when the quality of the molded product changes to a reference value or more, the non-defective product is transferred to the molded product discharge path (conveyor 7), and the defective product is transferred to a predetermined defective product collection unit (not shown). And can be selectively transported. In this example,
The control unit U is connected to the amplifier 2 from the temperature measuring device 42.
0, the mold temperature information provided to the temperature controller 23, and the pressure sensor 35 (not shown in FIG. 1) from the pressure controller 2 via the amplifier 19.
2 is configured to record the resin pressure information provided in the recording device 21 and to provide a control signal to a controller 24 for controlling the molded product automatic removal means 5.

In the present invention, as shown in FIG.
In the molded product unloading route (conveyor 7) for conveying molded products,
Non-contact type measuring device 25 such as infrared temperature distribution measurement for monitoring the temperature of each part of the molded article, monitor 26, and its control unit 2
There is provided a monitoring means having a reference numeral 7 and the like, whereby the quality of the molded product is determined.

The monitoring means controls the resin filling of the injection molding machine by feedback from the control means or via a control unit, and controls the supply pressure control device 6 and / or the throttle valve 13A. Alternatively, the flow rate of the cooling medium in the branch path of the cooling medium may be controlled. This can exhibit the effect of immediately preventing the occurrence of defective products.

FIG. 8 shows another embodiment of the present invention.
The cooling device, the temperature control device, the supply pressure control device, the branching device for the cooling medium, the flow rate measuring device, and the like shown in FIG. Other configurations are the same as those of the embodiment shown in FIG.

FIG. 15 is a block diagram conceptually showing a specific example of a case where the control of the plastic molding system according to the present invention is performed in a general control mode centering on a control unit. The basics of the control follow the aforementioned embodiment.

Table 1 below is a comparison table between a product molded by injection using the molding system of the present invention and a product molded by injection using a conventional molding system. As is clear from Table 1, when the system of the present invention was used, required molding was performed in a state where the molding cycle was shortened to 1/2 to 1/3 of the case where the conventional system was used.

[0036]

As described in detail above, the present invention relates to a molding system in which a resin injected into a cavity from an injection molding machine is cooled to a predetermined temperature as it is after molding, and then taken out. In the employed plastic mold, the amount of resin shrinkage corresponding to the gradient of the temperature drop in the cavity in the cooling step of the molding system is determined in advance based on the flow rate and temperature of the cooling medium supplied to the medium path in the cavity. When calculating and securing the required molded article dimensions, the cavity for molding should be shrunk by 0.1 to 0.05% larger than the molding shrinkage of the resin set according to the type of molding resin material. Because the dimensions are set, a new molding system that can achieve rapid cooling with a lower cooling medium than before can easily produce molded products with high dimensional accuracy. And it will be reliably formed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a conventional example for comparison with the present invention.

FIG. 3 is a cross-sectional view illustrating the state of attachment of the pressure sensor according to the present invention.

FIG. 4 is a cross-sectional view illustrating another mounting state of the pressure sensor according to the present invention.

FIG. 5 is a cross-sectional view illustrating another mounting state of the pressure sensor according to the present invention.

FIG. 6 is a cross-sectional view illustrating an attached state of the temperature measuring device according to the present invention.

FIG. 7 is a cross-sectional view illustrating another mounting state of the temperature measuring device according to the present invention.

FIG. 8 is a schematic configuration diagram showing another embodiment of the present invention.

FIG. 9 is a table showing a correlation between a cooling water flow rate, a mold temperature during molding, and a change in molded article temperature according to the present invention.

FIG. 10 is a table showing a correlation between a cooling time, a mold temperature after molding, and a molded article temperature according to the present invention.

FIG. 11 is a table showing a relationship (normal) between a resin pressure in a mold and a dimensional change during continuous molding according to the present invention.

FIG. 12 is a table showing a relationship (abnormality) between a resin pressure in a mold and a dimensional change during continuous molding according to the present invention.

FIG. 13 is a table showing the relationship (normal) between the resin temperature in the mold and the dimensional change of the molded product during continuous molding according to the present invention.

FIG. 14 is a table showing a relationship (abnormality) between a resin temperature in a mold and a dimensional change of a molded product during continuous molding according to the present invention.

FIG. 15 is a block diagram showing a specific example of a control mode of the molding system of the present invention.

FIG. 16 is a block diagram showing another specific example of the control mode of the molding system of the present invention.

[Description of Signs] 1 Injection molding machine 2 Mold 3 Hopper 4 Material supply device 5 Mold automatic removal means 6 Temperature control device 7 Conveyor 8 Transfer device 9 Pipe line 9A Branch supply path 9B Branch return path 10 Cooling device 12 Branching device 13 Flow rate measuring device 13A Throttle valve 14 Supply pressure control device (pressure boosting pump) 25 Non-contact temperature measuring device 26 Monitor 31 Plasticizing cylinder-32 Centralized chiller 35 Pressure sensor-42 Mold temperature measuring device (Temperature sensor)

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) B29C 45/26-45/44

Claims (1)

(57) [Claims] In a plastic molding die used in a molding system, a resin injected into a cavity from an injection molding machine is cooled to a predetermined temperature as it is after molding, and then taken out. Based on the flow rate and temperature of the cooling medium supplied to the medium path in the cavity, the amount of resin shrinkage corresponding to the gradient of the temperature drop in the cavity in the cooling step of the molding system is calculated in advance, and the required molded product size is calculated. When securing, the dimensions of the cavity for molding are set with a shrinkage of 0.1 to 0.05% larger than the molding shrinkage of the resin set according to the type of the molding resin material. And a plastic mold.