JPH07290531A - Controlling method for injection molding machine - Google Patents

Abstract

PURPOSE:To control a melted resin temperature by measuring temperatures of two positions of different depths separated near an inner wall of a heating cylinder, calculating heat quantity fed to the cylinder from its temperature gradient, calculating the heat quantity generated upon rotation of a screw, and controlling sum of both the calculated heat quantities. CONSTITUTION:When heat quantities of five zones of LA-LE of n entire axial length L0 are calculated, they become QA-QE, and total heat quantity QS to be transferred from a heating cylinder 3 to resin over the entire axial length L0 of the cylinder 3 becomes a formula I. When a starting time of a metering step is 0 and a completing time is T1, total heat quantity Eg given to the resin by the rotation of a screw 1 in a first metering step becomes a formula II. Accordingly, the sum J=QS+ES. When a temperature of a resin pellet 15a in a hopper 15 is Tp, a target resin temperature stored in a screw head front part 18 by melting in the cylinder 3 is Tm, a mean specific heat is C and a resin weight to be injected is T, a calculating step is so controlled as to become J=C.W.(Tm-Tp), the molten resin temperature can be controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding machine for molding a plastic product, and more particularly to a method for controlling an injection molding machine for controlling a measuring process with high accuracy.

[0002]

2. Description of the Related Art FIG. 4 is a schematic view showing a simplified structure of a main part of a conventional injection molding machine. In FIG. 4, the injection device 3
The screw 1 is inserted into the heating cylinder 3 constituting 0 so as to freely rotate and move forward and backward.
A nozzle 4 is attached to the tip of the.

An injection cylinder 20 in which a piston 14 for moving the screw 1 forward and backward is inserted is attached to the rear portion, and a hydraulic motor 5 for rotating the screw 1 for rotating the screw 1 is attached behind the injection cylinder 20.

The hydraulic chamber 9 of the injection cylinder 20 is composed of a rod-side hydraulic chamber 9a and a head-side hydraulic chamber 9b. The hydraulic chamber 9 is supplied with hydraulic oil from a hydraulic pump (not shown) and is hydraulically operated by a hydraulic valve 11. Controlled. The hydraulically operated valve 11 is composed of a rod side hydraulically operated valve 11a communicating with the rod side hydraulic chamber 9a and a head side hydraulically operated valve 11b communicating with the head side hydraulic chamber 9b.

Further, hydraulic oil from a hydraulic pump (not shown) is also supplied to the hydraulic motor 5 for rotating the screw, and the rotational speed and rotational time can be controlled by controlling the hydraulic operating valve 11c. ing.

A heater 6 for generating heat is arranged on the outer peripheral portion of the heating cylinder 3, and a thermocouple 7 is provided near the inner wall of the heating cylinder 3 for measuring the temperature of the heating cylinder 3 in the axial direction. It is installed at a distance.

Reference numeral 33 is a heater controller, which is a power source 3
The electric power supplied from the heater 4 is adjusted and the amount of heat generated by the heater 7 is controlled to control the heating cylinder 3 to a desired temperature. Reference numeral 8 is a screw position sensor for measuring the forward / backward travel distance of the screw 1. A screw head 27 is screwed onto the tip of the screw 1 with a check sheet 1a placed in the screw head 27. The screw head 27 has a substantially conical shape toward the tip, and the rear side (right side in the figure) of the conical shape is stepped. Becomes a small diameter, and this small diameter part 2
A check ring 2 which is slidable in the axial direction is fitted into 7a. Reference numeral 15 is a hopper, 15a is a resin pellet, 18 is a screw head front portion, and 32 is a molding machine control device.

The mechanism by which a plastic product is obtained from the injection device 30 is as follows. Hopper 1
5, the resin pellets 15a dropped into the hopper 5 are dropped to the screw 1 side from the hopper supply port, and the dropped resin pellets 15a are rotated in front of the heating cylinder 3 (see FIG. 4).
It is transferred to the middle left).

At this time, the resin pellet 15a is near the inner wall surface of the heating cylinder 3 due to heat transfer from the heating cylinder 3 on the heated inner surface of the heating cylinder 3 and frictional heat or shearing heat on the inner wall surface of the heating cylinder 3 due to the rotation of the screw 1. And is stored in the screw head front portion 18 in a molten state.

The screw 1 moves rearward as the amount of molten resin stored in the screw head front portion 18 increases, and when the amount of molten resin determined by the backward moving distance of the screw 1 reaches a set value, the screw 1 rotates. And the weighing process is completed.

In the subsequent injection process, hydraulic oil is supplied to the head side hydraulic chamber 9b in the injection cylinder 20 from a hydraulic source (not shown), and the screw 1 moves forward to start the injection process.

With the start of this injection process, the molten resin stored in the front portion 18 of the screw head is injected and filled into a mold cavity (not shown) through the nozzle 4, and the molten resin is cooled and solidified in the mold. After that, the mold is opened to obtain a plastic molded product.

By the way, in the above-mentioned injection step, the resin temperature at the time of filling the resin in the mold has a great influence on the quality of the molded product. For example, since resin has a large volume expansion due to temperature, the weight of the product when it is molded at a high resin temperature is light, and when it is low, it becomes heavy, and the variation in temperature causes the weight to vary.

The resin temperature also has a great influence on the viscosity of the resin. That is, since the viscosity is low at a high temperature, the injection pressure in the injection process is small, and the viscosity is high at a low temperature, the injection pressure is large, and the filling state in the injection process is varied, so that the quality is also varied. Become. For this reason, it is indispensable to accurately melt the resin at a stable temperature and store the molten resin in the front part of the screw head in the measuring step in order to realize stable molding of a good product.

[0015]

However, in the conventional control during the metering process, the heater 6 is controlled so that the temperature of the heating cylinder 3 reaches a preset target value while the rotation speed of the screw 1 remains constant. Therefore, if it is desired to set the molten resin temperature to 200 ° C., the target temperature in the zone near the nozzle 4 side is set to 200 ° C.
The temperature was set to 0 ° C., and the temperature gradually decreased as the temperature approached the hopper 15.

Therefore, when the temperature of the inner wall portion of the heating cylinder 3 is not sufficiently transmitted, the resin having a temperature lower than 200 ° C. is stored in the screw head front portion 18. On the contrary, when the shearing heat and the frictional heat generated by one rotation of the screw are large, the resin having a temperature higher than 200 ° C. is stored in the screw head front part 18 and the mold cavity (not shown) is formed.
There is a problem that it is filled.

Further, the piston 14 in the injection cylinder 20
The frictional resistance of and other frictional resistances of sliding parts are easily influenced by the machine difference of the molding machine and the atmospheric condition, and affect the speed at which the screw 1 moves backward during measuring, so the measuring time varies. The result was that the temperature of the molten resin varied.

Further, even if the resins of the same type and the same grade have the property of being easily varied depending on the production lot, even if the resin has a high viscosity under the same measurement conditions, the shear heat generation becomes large and the resin temperature becomes high. On the contrary, the temperature of the resin having a low viscosity becomes low, and the temperature of the resin stored in the front part 18 of the screw head varies, so that when the resin is injected and filled in the mold cavity, There was a problem of making the quality unstable.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a measuring method for an injection molding machine, which is capable of stably obtaining a molded product of good quality.

[0020]

The present invention has been made in order to achieve the above-mentioned object, and is a metering process for storing molten resin in front of a screw head while rotating and retracting the screw, and an inner wall of a heating cylinder. Temperatures at two locations with different depths, which are separated in the vicinity, are measured, the amount of heat flowing into the heating cylinder is calculated from the measured temperature gradient, and the amount of heat generated with the rotation of the screw is calculated as the screw rotation torque and rotation time. Then, the temperature of the molten resin was controlled by controlling the total amount of heat calculated above.

[0021]

[Function] In order to calculate the amount of heat transferred from the heating cylinder to the resin, the temperatures at two different depths in the vicinity of the inner wall of the heating cylinder are measured, and the temperature gradient in the radial direction of the heating cylinder is calculated. The amount of heat transferred to the resin side is calculated from the thermal conductivity coefficient of the heating cylinder. Further, in order to calculate the amount of heat supplied to the resin side due to the rotation of the screw, frictional force and shearing force are generated by the rotational torque of the screw, so the screw rotational torque and rotational time are measured and calculated from them. To do. Then, a desired molten resin temperature can be easily obtained by controlling the total amount of heat.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The weighing method for an injection molding machine according to the present invention will be described in detail below with reference to the embodiments shown in the drawings.

FIG. 1 is a schematic diagram showing a simplified structure of a main part of an injection molding machine according to an embodiment of the present invention, and FIG. 2 is a view showing a state in which two thermocouples are used to measure temperature at two different depths. FIG. 3 shows a horizontal sectional view of the cylinder, and FIG. 3 shows a vertical sectional view of the heating cylinder.

In FIG. 1, a screw 1 is inserted into a heating cylinder 3 constituting an injection device 30 so as to be rotatable and forward / backward, and a nozzle 4 is attached to the tip of the heating cylinder 3. .

An injection cylinder 20 into which a piston 14 for moving the screw 1 forward and backward is inserted is attached to the rear part, and a hydraulic motor 5 for rotating the screw 1 for rotating the screw 1 is provided behind the injection cylinder 20. A hydraulically operated valve 11 for a screw motor that supplies an appropriate amount of pressure oil as a drive source to the hydraulic motor 5 for screw rotation.
c is provided.

The hydraulic chamber 9 of the injection cylinder 20 is composed of a rod-side hydraulic chamber 9a and a head-side hydraulic chamber 9b. The hydraulic chamber 9 is supplied with hydraulic oil from a hydraulic pump (not shown), and is operated by a hydraulic valve 11. Controlled. The hydraulically operated valve 11 is composed of a rod side hydraulically operated valve 11a communicating with the rod side hydraulic chamber 9a and a head side hydraulically operated valve 11b communicating with the head side hydraulic chamber 9b.

Reference numeral 8 is a screw position sensor for measuring the forward / backward travel distance of the screw 1. A screw head 27 is screwed onto the tip of the screw 1 with a check sheet 1a placed in the screw head 27. The screw head 27 has a substantially conical shape toward the tip, and the rear side (right side in the figure) of the conical shape is stepped. The check ring 2 which is slidable in the axial direction is fitted into the small diameter portion 27a.

A heating heater 6 is mounted on the heating cylinder 3 in the direction of the outer peripheral axis thereof. Further, in the axial direction of the heating cylinder 3, two thermocouples 7 are attached at regular intervals,
As shown in FIG. 2, the thermocouples 7a and 7b, which are a set of the two, have different depths in the vicinity of the inner wall of the heating cylinder 3.

Reference numeral 32 is a control device of the injection molding machine,
For example, various control commands are issued by receiving measured values obtained from a temperature sensor, a pressure sensor, a position sensor, etc. and comparing them with target values. Note that reference numeral 13
Indicates a screw oil pressure sensor.

Further, reference numeral 10 is a mold, and the mold 10 is composed of a male mold 10b and a female mold 10a, and a cavity 10c is formed between the male mold 10b and the female mold 10a.

A control method of the injection molding machine configured as described above will be described.

First, a method of calculating the amount of heat transferred from the inner wall of the heating cylinder 3 to the resin side being conveyed by the screw 1 will be described. The measured value of the temperature measured by the thermocouple 7a on the side close to the inner wall of the heating cylinder 3 (distance ra from the center of the screw 1 to the thermocouple) is Ta, and similarly on the side distant from the inner wall (from the center of the screw 1 to the thermocouple). Suppose that the measured value of the temperature measured by the thermocouple 7b at the distance rb) is Tb (here rb> ra), and the temperature gradient at this time is T '.

[0033]

[Equation 1] Becomes

Further, since the heating cylinder 3 is uniformly heated by the heater 6, it is considered that the temperatures are equal at the points on the same circumference where the radius of the heating cylinder 3 is the same, so that the heat conduction of the heating cylinder 3 is conducted. The heat flux q transmitted inward (from the heater 6 to the screw 1) when the coefficient is λs.
Becomes q = λs T '. The average radius of this part is (rb +
Ra) / 2 and the axial length is L, the amount of heat transferred per unit time from the heating cylinder 3 side to the resin side in the screw 1 by the heating of the heater 6 is

[0035]

[Equation 2] Becomes

Here, since Ta and Tb are values that change from moment to moment, the heat quantity Q also becomes a function Q (t) of time. When the time t at which the injection process is once completed is 0 and the time at which the next injection process is completed is T ₀ , the heat quantity Q ₀ transferred to the resin is

[0037]

[Equation 3] Becomes Here, the closer the two measured positions are to the inner wall portion of the heating cylinder 3, the more accurate the value of the calorie Q ₀ calculated. Further, the heat flux can be obtained by substituting the measured values Ta and Tb of the temperature by using the finite element method or the finite difference method used for the heat conduction analysis, and the calorific value Q ₀ can be calculated accurately.

This idea is applied to all the axial direction of the heating cylinder 3.
Long L₀Apply to and think about. Axial as shown in Figure 3
Length L₀To L_A, L_B, L_C, L_D, L_EThe five zo
If you calculate the amount of heat in each zone
Q_A, Q_B, Q_C, Q_D, Q _EAnd heating cylinder 3
Axial length L₀From heating cylinder 3 to resin
Total heat transmitted Q_SIs Q_S= Q_A+ Q_B+ Q_C+ Q_D+ Q_E Becomes

Next, the amount of heat transferred to the resin as shearing heat or frictional heat is calculated by the rotation torque of the screw 1.

The screw rotation torque R measured by the screw oil pressure sensor 13 during the measuring process changes with time, so it is set to R (t), and the screw rotation speed is set to N for controlling at a constant speed. If the amount of heat E (t) given to the resin per unit time by one rotation of the screw is

[0041]

[Equation 4] Becomes The screw rotation torque R can be calculated by measuring the hydraulic pressure for a hydraulic motor and the current value for an electric motor. Further, when the start time of the measuring process is 0 and the completion time is T ₁ , the total heat quantity E _S given to the resin by the rotation of the screw 1 in one measuring process is

[0042]

[Equation 5] Becomes

Therefore, the total heat quantity J transferred to the resin as shear heat generation and friction heat in one cycle is J = Q _S + E _S. The temperature of the resin pellet 15a in the hopper 15 is set to T
p, melted in the heating cylinder 3 and screw head front part 1
Assuming that the target resin temperature stored in No. 8 is Tm, the average specific heat C, and the injected resin weight is W, J = C · W · (Tm−T
It is only necessary to control the calculation process so that p).

The heat transmitted from the heater 6 through the heating cylinder 3 takes time because of the thickness of the heating cylinder 3. Therefore, in the case of molding in a fast cycle, it is better to mainly control the heat quantity Es from one rotation of the screw and adjust the total heat quantity J to be a constant value.

To this end, the head side hydraulically operated valve 1
1b to control the head side hydraulic chamber 9 of the injection cylinder 20.
If the pressure is generated in b, the speed at which the screw 1 retracts is slowed, and the metering time is adjusted, the total heat amount J can be easily controlled.

Therefore, the amount of heat Qs given to the resin from the heating cylinder 3 and the amount of heat Es given to the resin by one rotation of the screw are measured separately, and if the sum (Qs + Es) is controlled to match the target value, the desired temperature is obtained. It is possible to inject and fill the mold cavity 10c with the molten resin having the above.

[0047]

As is apparent from the above description,
In the present invention, in the measuring step of storing the molten resin in front of the screw head while rotating and retreating the screw, the temperatures at two different depths separated in the vicinity of the inner wall of the heating cylinder are measured, and the measured temperature gradient The amount of heat flowing into the heating cylinder is calculated, and the amount of heat generated by the rotation of the screw is calculated from the screw rotation torque and the rotation time, and the temperature of the molten resin is controlled by controlling the total sum of the calculated amounts of heat. By doing so,
Since the temperature of the molten resin filled in the mold becomes highly accurate and stable, an ideal injection process can be realized, and therefore the quality of the plastic product molded becomes extremely high and stable.
In particular, the effects of machine differences due to the injection molding machine, atmospheric conditions, and variations in resin viscosity are corrected, so the effect of stable molding of non-defective products is great.

[Brief description of drawings]

FIG. 1 is a schematic view showing a simplified configuration of a main part of an injection molding machine according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a heating cylinder showing a state in which the temperature is measured with two thermocouples at two different depths.

FIG. 3 is a vertical sectional view of a heating cylinder.

FIG. 4 is a schematic view showing a simplified configuration of a main part of a conventional injection molding machine.

[Explanation of symbols]

 1 screw 2 check ring 3 heating cylinder 4 nozzle 5 hydraulic motor 6 heater 7 (7a, 7b) thermocouple 8 screw position sensor 9 hydraulic chamber 9a rod side hydraulic chamber 9b head side hydraulic chamber 10 mold 10c cavity 11 hydraulically actuated valve 11a Rod side hydraulic operation valve 11b Head side hydraulic operation valve 11c Screw motor hydraulic operation valve 13 Screw oil pressure sensor 14 Piston 18 Screw head front part 20 Injection cylinder 27 Screw head 30 Injection device 32 Molding machine control device 33 Heater control device 34 Power supply

Claims (1)

[Claims] 1. A measuring step in which molten resin is stored in front of a screw head while rotating and retreating a screw, and the temperature is measured by measuring temperatures at two different depths separated in the vicinity of an inner wall of a heating cylinder. The amount of heat flowing into the heating cylinder is calculated from the temperature gradient, and the amount of heat generated with the rotation of the screw is calculated from the screw rotation torque and the rotation time, and the temperature of the molten resin is controlled by controlling the sum of the calculated amounts of heat. A method for controlling an injection molding machine, wherein the method is controlled.