JPS62242512A - Injection molding control method - Google Patents

Abstract

PURPOSE:To provide a product stabilized not only an a short-term basis but also on a long-term basis, even if temperature of mold varies, by correcting cooling time by means of a corrected time calculated from the difference between the temperature of mold for each molding cycle and preset standard temperature. CONSTITUTION:The temperature of mold Tm under pressure is sensed by a temperature sensor 2 installed to a mold 1, and the sensed value signal is led to a deviation arithmetic unit 4 through an amplifier 3, compares the preset standard mold temperature To and the actual mold temperature Tm and operates the deviation value DELTAT. Then, said deviation value DELTAT is multiplied by the constant value alpha/beta preset in a coefficient setter 7 in an arithmetic unit 6 to calculate a corrected time DELTAS, a result of multiplication. The signal of said corrected time is sent to an adder 8 for operating addition of standard cooling time preset in a cooling time setter 9 and the corrected time. The signal is transferred to a sequencer 10 of injection molding machine, by which the actual cooling time is set and controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a control method when a molded article is injection molded by an injection molding machine, and particularly relates to a control method when a molded article is injection molded by an injection molding machine.

The present invention relates to an injection molding control method in which molding conditions are changed according to mold temperature.

(Conventional technology) When molding a molded product using an injection molding machine, the mold is closed.

This is done through a molding cycle that includes injection of molten resin, holding pressure, cooling, and opening the mold. In order to obtain precision molded products, various conditions in each step of the molding cycle must be accurately set.

Therefore, in the past, injection pressure, resin temperature, etc. were controlled to be constant, and each time period of the molding cycle was controlled to be constant.

(Problem to be solved by the invention) However, even if each molding cycle time is constant,
It is not possible to control the temperature of the mold at a constant level. For example,
During continuous molding, the mold temperature gradually increases as molding is repeated. Therefore, the temperature of the molded product when taken out from the mold is different between the initial stage and the latter half of continuous molding. If there is a difference in the temperature of the molded product at the time of removal, there will be a difference in the amount of heat shrinkage due to cooling after removal, and the final dimensions of the molded product may vary, making it difficult to obtain a stable molded product of one quality. I won't be able to do that.

For this reason, an adaptive control method is also used in which the mold temperature is detected and the holding pressure is changed in accordance with the temperature change. However, such control methods change the internal pressure of the molded product, so even if the quality of the molded product, such as dimensions and weight, can be kept constant for a short period of time after molding, it will not affect the quality of the molded product in the long term. As you can see, it is inevitable that the quality will change over time, such as cracks and crazing in molded products.

The present invention was made in view of these problems, and its purpose is to maintain stability not only in the short term but also in the long term, even when the temperature of the mold fluctuates as during continuous molding. The objective is to obtain high quality precision molded products.

(Means for solving the problem) In order to achieve this object, the present invention changes the cooling time during the molding cycle depending on the temperature of the mold.

In other words, the temperature of the mold is detected for each molding cycle of injection molding, the correction time is calculated from the deviation between the detected temperature and a preset reference temperature, and the cooling time is corrected using the correction time. ing. The correction time is obtained by multiplying the deviation between the detected temperature and the reference temperature by a preset constant value.

(Function) With this configuration, when the mold temperature is high, the cooling time is increased, and the molded product is sufficiently cooled within the mold, so that the amount of thermal deformation when taken out from the mold and left to cool is reduced. becomes smaller. On the other hand, when the mold temperature is low, the cooling time is shortened and the molded product is removed from the mold while it is still relatively hot, so the amount of thermal deformation due to cooling increases. Therefore, molded products of almost constant quality can be obtained.

(Example) Hereinafter, the present invention will be explained in detail using the drawings.

In the figure, FIG. 1 is a block diagram of a control circuit for implementing the injection molding control method using the final IJ1. Also, the second
Figures 3 and 3 are for explaining the principle of the control method, Figure 2 is a characteristic curve diagram showing the relationship between the mold temperature and the final dimension of the molded product, and Figure 3 is a diagram showing the relationship between the mold temperature and the final dimension of the molded product. FIG. 3 is a characteristic curve diagram showing the relationship between the cooling time of the molded product and the final dimension of the molded product.

First, the principle of the molding control method of the present invention will be explained with reference to FIG. 2.3.

If a molded product is removed from the mold while the mold temperature is still high, the molded product will have a high average temperature and will undergo large thermal contraction as it cools. Therefore, as shown in FIG. 2, the higher the mold temperature, the smaller the final dimensions of the molded article. On the other hand, if the cooling time of the molded product in the mold is increased, the average temperature of the molded product when taken out from the mold will be lower, so that the amount of thermal shrinkage due to cooling will be reduced. Therefore, the longer the cooling time, the closer the final dimensions of the molded article will be to the dimensions formed by the mold. That is, as shown in FIG. 3, the longer the cooling time, the larger the final dimensions of the molded article.

The relationship between mold temperature and molded product dimensions or the relationship between cooling time and molded product dimensions cannot be expressed as a complete linear equation. However, in the region where the variation range of mold temperature or cooling time is small, , their relationship can be approximated by a linear equation.

Therefore, under other conditions being constant, the mold temperature at which a molded product with standard dimension 0 is obtained is defined as the standard mold temperature To, and when the mold temperature fluctuates by ΔT from the standard mold temperature To, If the dimensional variation of a molded product is assumed to be six, it can be expressed as ΔT = α ΔT (α is a constant).

Similarly, under other conditions being constant, the cooling time when a molded product with 2Jli standard dimensions ○ is obtained is set as the standard cooling time S, and the dimensional variation of the molded product when the cooling time is changed by ΔS. If it is assumed that Δsight is Δsight, then it can be expressed as Δsight=β・ΔS (β is a constant).

Therefore, as shown in FIG. 2, the mold temperature T
Suppose that the reduction in the apparent size of the molded product when (2) is higher than the reference temperature To by ΔT is offset by extending the cooling time by ΔS, as shown in FIG.

αφΔT=β・ΔS Than ΔS wealth (α/β) ΔT becomes.

In other words, the cooling time is calculated from the standard cooling time So (α/β)
By extending it by ΔT, the standard dimension intersection of the molded product is 0. Conversely, when the mold temperature Tm is lower by ΔT, the cooling time may be shortened by (α/β)ΔT.

The present invention controls the cooling time based on such a principle, and as shown in FIG. The mold temperature Ts during pressurization is detected for each molding cycle.

Then, the detected value signal is amplified by an amplifier 3 and then guided to a deviation calculator 4. In this calculator 4, the reference mold temperature To preset in the reference temperature setting rIt5 and the actual mold temperature T are compared, and the deviation value ΔT (=T(1-Tm)) is calculated. As the reference mold temperature To, for example, the average value of the mold temperature during continuous molding is used.

The signal of the deviation value ΔT thus calculated is then sent to the multiplication calculator 6. In this calculator 6, the deviation value ΔT and a constant value α preset in the coefficient setter 7 are calculated.
/β is performed. The constant value α/β is the second.
It is determined from the coefficients α and β determined as described above based on the characteristic curve as shown in FIG. The result calculated by this calculator 6 is defined as the correction time ΔS.

That is, ΔS=(α/β)ΔT becomes.

The signal of this correction time ΔS is sent to the addition calculator 8.

In this calculator 8, the reference cooling time S preset in the cooling time setter 9 and the correction time ΔS output from the multiplication calculator 6 are added. The standard cooling time So is the cooling time required to obtain a molded product with standard dimensions of 0 when the mold temperature T is equal to the standard mold temperature To, and a value determined in advance through experiments or the like is used.

In this way, the signal So+ΔS is output from the computing unit 8, and the signal is transmitted to the sequencer IO of the injection molding machine. Then, the sequencer 10 sets and controls the actual cooling time to So+ΔS.

By using such a control method, for example, when the mold temperature T is higher than the standard mold temperature To by ΔT, the actual cooling time is extended by ΔS from the standard cooling time S0. Furthermore, if the mold temperature Ts is lower by ΔT, the actual cooling time will be shortened by ΔS. Therefore, as explained in Figure 2.3, the variation in the final dimension of the molded product due to the variation in the mold temperature TI is offset by the change in cooling time, and a molded product with standard dimensions ◎ can always be obtained. .

In the above example, the constant values α/β are determined by focusing only on the dimensions of the molded product, but the same characteristic curve as shown in Figure 2.3 is also used for other qualities such as the weight of the molded product. Therefore, by taking these into account when determining constant values, it becomes possible to obtain molded products whose quality in various aspects such as size and weight are substantially constant.

(Effects of the Invention) As is clear from the above description, according to the present invention, the mold temperature is detected and the cooling time during the molding cycle is changed in accordance with the temperature change. Differences in quality of molded products due to temperature differences are offset by differences in cooling time within the mold. Therefore, a molded product of constant quality can be obtained regardless of the mold temperature. Furthermore, since there is no increase in the internal stress of the molded product, the quality is less likely to change due to changes over time.

In addition, when performing continuous molding, the temperature of the mold is very unstable at the initial start-up of molding. However, according to the present invention, molded products of the required quality can be obtained regardless of the mold temperature, so molded products that were molded early can also be used as products. becomes possible. Therefore, molding time is reduced and material is also saved.

[Brief explanation of drawings]

Figure t51 is a block diagram showing an example of a control circuit of an injection molding machine using the injection molding control method according to the present invention; Figure 2 is a characteristic curve diagram showing the relationship between mold temperature and final dimension of the molded product; FIG. 3 is a characteristic curve diagram showing the relationship between cooling time and final dimensions of the molded product. l...Mold 2...Temperature detector 4...
- Deviation calculator 5...Reference temperature setting device 6...
Multiplier 7... Coefficient setting device 8... Addition calculator 9... Cooling time setting 0... Standard dimension of molded product So... Standard cooling time ΔS... Correction time To.
...Reference mold temperature ΔT...Temperature deviation value α, β...
・Constant patent applicant: Representative of Nikki Steel Co., Ltd. Patent attorney: Yu Morishita Hajime Figure 1

Claims (1)

[Claims] The temperature of the mold is detected for each molding cycle of injection molding, the deviation between the detected value and a preset reference mold temperature is determined, and the deviation value is set as a preset standard mold temperature. Calculate the correction time by multiplying by a constant value, add the correction time to the preset reference cooling time, and use the added time to set and control the actual injection molding cooling time. The injection molding control method.