JPS63132021A - Dwell controlling of injection molding machine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a machine that performs injection molding, and particularly to injection molding when molding thermoplastic resins, thermosetting resins, ceramic materials, etc. using a 5-injection molding machine. The present invention relates to a method of controlling pressure in a machine.

(Prior art) Conventional pressure holding control methods for injection molding machines include pressure holding control based on the position of the injection stroke of the injection piston, and pressure holding control based on detecting the instantaneous injection speed at any point on the injection stroke. One that detects the injection pressure during injection and performs pressure holding control by comparing that level with the set pressure, or one that installs a pressure sensor inside the mold and compares that level with the set pressure. There are some that perform pressure holding control by doing this.

Methods based on position detection of the injection piston stroke have been the mainstream method for controlling holding pressure in injection molding machines. Change (cylinder temperature,
The above-mentioned holding pressure control method was invented because there were cases where it was not possible to respond to changes in the temperature (nozzle temperature, injection temperature, injection pressure, mold temperature, etc.), subtle changes in the viscosity of the molding material, or changes in environmental conditions. Ta.

Further, among conventional injection molding pressure holding control methods, a method that focuses on the inside of the mold is pressure holding control based on mold internal pressure detection. When the molten material in the mold flows due to the pressure of the injection process, the pressure at a certain point in the mold is detected, and when that pressure reaches a certain set pressure, it is switched to holding pressure or It is used to correct the pressure.

[Problem that the invention seeks to solve]

The conventional injection stroke position detection, instantaneous injection speed detection during injection, or injection pressure detection during injection described above all detect the instantaneous state of a certain point on the injection piston as it moves during the injection stroke. It does not include the injection piston movement process during the injection stroke.

In injection molding, the movement process of the injection piston has a major impact on the quality of the injection molded product.
Merely detecting the instantaneous injection speed or the injection pressure during injection molding is insufficient as a method for controlling the holding pressure of the injection molding machine.

The present invention takes these into consideration and focuses on detecting the movement process of the injection piston during the injection stroke.

The conventional pressure holding control method using mold internal pressure detection only detects the instantaneous pressure at a certain point inside the mold.For example, if the viscosity of the molten material changes slightly, the pressure generation state may not be constant. No. This is because if the viscosity of the material decreases, the resistance to passing through the mold channel will decrease, and conversely, if the viscosity increases, the same resistance will increase. The magnitude of this resistance has a direct effect on the flow length and flow ff1) of the molten material. For example, if the resistance is large, it will tend to cause a short shot and sink marks will occur, while if the resistance is small, on the other hand, it will cause overfilling. Paris is more likely to occur. Also, changes in the viscosity of this molten material are affected by cylinder temperature, nozzle temperature, mold temperature,
This is caused not only by subtle changes in injection pressure and injection speed, but also by variations in the melt viscosity of the molding material itself. In injection molding where there are subtle changes in the molding state, the holding pressure control method based on the detection of the mold internal pressure has not yet achieved sufficient effects.

The present invention further aims to improve these current conditions, and is a holding pressure control method based on the detection of the time during which the molten material passes (flows) through a certain section of the molten material passage in the entire mold. be.

[Means for solving problems]

In the holding pressure control method of the present invention, a fixed section is set in the path of a movable body that moves during injection molding, and the time during which the movable body moves within the fixed section is detected, and the detected moving time and the predetermined The present invention is characterized in that the preset holding force is controlled and corrected based on the magnitude of these times and the time difference by comparing the set times.

[Function] Therefore, the present invention uses an injection piston or a molten molding material as the movable body, and applies pressure to the preset holding pressure by a pressure corresponding to the time difference. The pressure, some 'J), can be reduced to a modified holding pressure.

[Hara Osamu]

Here, the basic principle of the pressure holding control method of the present invention will be explained based on a first embodiment described later.

In the first embodiment, the moving time of the injection piston in a certain section during the injection process is detected, and pressure holding control is performed based on the detected movement time. FIG. 2 is for explaining this basic principle, and shows the relationship between the travel time t of the injection piston and the mold internal pressure Pm.

Of the two lines in the figure, the solid line SL indicates the pressure in the cavity part close to the mold sprue, and the broken line 11BL indicates the pressure in the cavity part far from the mold sprue. These pressures are mold internal pressures in the pressure holding process.

When injection molding is performed under constant molding conditions, it is generally assumed that the travel time t of the injection piston is constant, but in reality, there are subtle changes in the molding conditions, slight changes in the molding machine, and subtle changes in the viscosity of the molding material. The injection piston travel time t is not constant, but changes slightly.

That is, as a result of subtle changes in the above matters, as the injection piston travel time t increases, the mold internal pressure Pm decreases, and the pressure in the cavity part near the mold sprue (solid line SL) and the cavity part far from the mold cavity part decrease. pressure (broken line BL)
) was increasing. When the molded product at this time was examined, picketing phenomenon occurred, and the degree of picketing increased as the injection piston travel time t became longer.

Conversely, if the injection piston travel time t becomes shorter,
The mold internal pressure Pm increased, and the differential pressure between the pressure in the cavity part close to the mold sprue (solid line SL) and the pressure in the cavity part far from the mold sprue (broken line BL) became smaller. Examining the molded product at this time, we found that when the travel time of the injection piston was shorter than a certain value t, the phenomenon of overpacking occurred, and the degree of overpacking increased as the travel time of the injection piston became shorter. .

From these facts, if the moving time t of the injection piston is detected and pressure holding control is performed based on this, then
It was found that molded products of good quality could be obtained continuously. That is, the injection piston movement process during the injection stroke is
It was found that this is concentrated in the travel time of the injection piston.

Based on this, the travel time of the injection piston was investigated by changing the resin temperature, mold temperature, injection speed, injection pressure, and molding material one by one under the same molding conditions. As a result, the travel time of the injection piston increases in the direction of increasing the resin temperature (nozzle set temperature) or mold temperature, in the direction of increasing the injection speed or injection pressure, or in the direction of decreasing the viscosity of the molding material. When the molding conditions were changed in the opposite direction, the travel time of the injection piston became longer.

From these results, it has been found that even with slight changes in molding conditions, good molded products can be obtained by performing pressure holding control based on detection of the travel time of the injection piston.

(Example) The present invention will be described below with reference to the drawings.

FIG. 1 is a flowchart showing an embodiment according to the present invention, in which the stroke Is of the injection piston is the injection process IP and the pressure holding process D.
It is composed of P. The first stroke point S1 indicates the injection start point. The second stroke point S2 and the third stroke point S3 are stroke points during the injection process IP.

A first sensor A and a second sensor B that transmit a time measurement signal are installed at each of the stroke point S2 and the stroke point S3.

This first sensor A serves as a signal for starting time measurement, and the second sensor B serves as a signal for ending time measurement.

The travel time t measured by these signals (step 1) is compared with a preset time T (step 2).
). If t=T, the preset holding pressure P0 becomes the pressure in the holding pressure step DP (step 3) 6t<
In the case of T, for the preset holding pressure Po, T-t
Holding pressure p = p, which is reduced by a pressure amount △P corresponding to the time of
, -ΔPI becomes the pressure in the pressure holding process DP (step 4). In addition, if t>T, the holding pressure Po is set in advance.
On the other hand, the holding pressure P=P0+ΔP2, which is increased by a pressure amount ΔP corresponding to the time t-T, becomes the pressure in the holding pressure step DP (step 5).

These corrected holding pressures P are transmitted via the holding pressure device DA,
It becomes effective from the time of switching to pressure holding at the fourth stroke point S4. This corrected holding pressure P is maintained until the fifth stroke point S5 at which the holding pressure step DP is completed.

This holding pressure control is performed during the same injection cycle, and the moving time t is measured for each shot, and the holding pressure is corrected.

FIG. 3 is a flowchart showing another embodiment of the present invention, in which the flow path FP in the mold includes a sprue section S, a runner section R, and a gate section G.
, a cavity part C, and the stroke IS of the injection piston is composed of an injection process IP and a pressure holding process DP.

In the runner part R of the gold fi14 internal flow path FP, there is a flow path point f1 of il, the first sensor A is installed in this part, and the second flow path point f1 is installed in the cavity part C. Road point f2
There is a second sensor B installed in this part. This first flow path point f.

is the central portion of the runner portion R, and the second flow path point f2 is preferably located at the central portion of the cavity portion C or close to the inlet portion of the cavity portion C.

Note that the sensors A and B include, for example, a pressure sensor, an optical sensor, a temperature sensor, etc., but an optical sensor is most suitable. If the molten material is transparent or generates a lot of gas, a pressure sensor or temperature sensor is better.

The signal from the first sensor A becomes a start signal when measuring the molten material movement time, and the signal from the second sensor B becomes a stop signal during the measurement. The travel time t measured by these signals (step 11) is compared with a preset time T (step 12).

If t=T, the preset holding pressure P0 becomes the pressure p=p0 in the holding pressure process DP (step 13).
. If t<T, with respect to the preset holding pressure P0,
The pressure is reduced by a pressure amount △P1 corresponding to the time T-t, and the holding pressure p=p0 - △P1 becomes the pressure in the holding pressure step DP (
Step 14). In addition, in the case of t>T, the pressure corresponding to the time of t-T is △ with respect to the preset holding pressure P0.
The holding pressure P=PO+ΔP2, which is pressurized by P0, becomes the pressure in the holding pressure process DP (step 15).

These corrected holding pressures P are transmitted via the holding pressure device DA,
It becomes effective when the injection stroke IS is switched to holding pressure. This corrected holding pressure P is maintained until the end of the stroke when the holding pressure step DP is completed. This holding pressure control is performed during the same injection cycle, and the moving time t is measured for each shot, and the holding pressure is corrected.

To further explain the operation of the embodiment shown in FIG. 3, the injected molten material passes through the inlet of the sprue section S
, flows to the runner section R. At this time, the molten material passes through the first flow path point f, which is a part of the launch portion R, and the first sensor A installed at the flow path point f1 detects this. This detection signal becomes the start signal for measuring travel time. Next, the molten material flows through the runner section R, the gate section G, and into the cavity section C. At this time, the molten material passes through the second flow path point f2, which is a part of the cavity portion C,
Sensor B installed at the flow path point f2 detects this. This detection signal becomes a stop signal for measuring travel time.

Transfer time t of molten material between flow path point f and flow path point f2
is compared with a preset time T, and as described above,
In the case of t=T, the preset holding pressure P0 becomes the pressure in the holding pressure process, but in the case of t<T or t>T, the preset holding pressure P0 is The pressure ΔP3 corresponding to the time difference between
PO+ΔP2 becomes the pressure in the pressure holding process DP.

These corrected holding pressures come into effect from the time of switching to holding pressure.

This corrected holding pressure is maintained until the end of the stroke when the holding pressure step DP is completed.

Here, the principle of the embodiment shown in FIG. 3 will be explained using FIG. 2. FIG. 2 shows the distance between flow path points f1 and f2 in FIG. shows the relationship between the travel time t when the molten material flows and the mold internal pressure Pm.

The solid line SL in FIG. 2 indicates the pressure at the first channel point f, and the broken line BL indicates the pressure at the second channel point f2. All of these pressures are the pressures after the mold is filled with molten material.

As the travel time t becomes longer, the pressure at the flow path points f, , f becomes
Both are decreasing, and the differential pressure is also increasing. Conversely, when the travel time t becomes shorter, the pressures at the flow path points fl and f2 both increase, and the differential pressure therebetween also decreases.

When we investigated the relationship between this situation and the quality of molded products, we found that the phenomenon shown in Figure 2 occurred. That is, when the travel time exceeded a certain level, a picket phenomenon was observed in the molded product, and when the travel time decreased below a certain level, the phenomenon of flaking occurred.

From this, a method was created in which a certain travel time is known in advance, this time is set as a set time T, this T is compared with the actual travel time t, and the holding pressure is corrected based on the magnitude of the time and the time difference.

That is, when the moving time t becomes longer than the time T, the holding pressure is corrected in a direction greater than the set holding pressure, and when the moving time t becomes shorter than the time T, the holding pressure is corrected in a direction smaller than the set holding pressure. As a result of the modifications, good molded parts were always obtained.

In the embodiment, the travel time t is detected in a fixed interval, but there may be a plurality of fixed intervals. In addition, the pressure holding process DP is not only one process as in the example,
There is no problem even if there are multiple steps. In addition, sensors for detecting travel time are not limited to optical sensors, but also pressure sensors,
It may be a temperature sensor, a limit switch, or any other sensor that meets the purpose. Judging from the results of various injection molding experiments so far, the optical sensor has given the best results. Optical sensors either transmit light or do not transmit light, and are most suitable for measuring time.

Furthermore, since the optical sensor uses a non-contact detection method, it has the advantage of very good measurement reproducibility and does not include errors in the measurement state itself.

In addition, in the embodiments of the present invention, the switching to the pressure holding process DP is shown as a stroke switching method, but the method is not limited to this method. It can also be applied to switching to process DP.

In addition, in the second embodiment, the fixed interval for detecting the moving time is indicated at the predetermined positions of the runner part and the cavity part.
The present invention is not limited to this, and the section can also be provided in the sprue section, runner section, gate section, and cavity section.

〔Concrete example] A specific example according to the embodiment shown in FIG. 1 will now be described.

The molding material used is general-purpose PS resin. The molded product is a precision molded product (case). The molding conditions were: nozzle temperature 220°C, mold temperature 45°C, injection speed 70%, holding pressure 550°C.
g/crn2.

Under these molding conditions, in the conventional method, injection molding was performed with holding pressure control based on the position of the injection stroke.
The pressure in the mold cavity is 350~4]OXg/c+n
2, and 92 shots out of 100 yielded good molded products.

Next, in the pressure holding control method shown in FIG. 1, the travel time of the injection cylinder is set to T=o, 3oosec, the holding pressure is set to P, =550, g7cm2. Also, the difference between the travel time t of the injection piston and the set value T is t −T = 0.010
Injection molding was performed by setting the holding pressure correction pressure ΔP=10 to g/cm 2 every sec. As a result, the pressure in the mold cavity varied between 380 and 385 kg/cm2, and there were no defective molded products among 100 shots.

Further, a specific example according to the embodiment of FIG. 3 will be explained here.

The molding material used is a general-purpose PS resin. The molded product is a precision molded product (case). The molding conditions were: nozzle temperature 230°C, mold temperature 40°C, injection speed 80%, holding pressure 75°C.
It is 0Kg/cm2.

Under these molding conditions, when injection molding was performed using the conventional method of holding pressure control based on mold internal pressure detection, the pressure in the mold cavity varied between 390 and 440 g/cm2, indicating that good molding was achieved. 91 out of +00 shots got the item.
It was a shot.

Next, in the pressure holding control method according to the present invention, the moving time setting value T = 0.250 s'ec, and the holding pressure setting value p0 =
750Kg/cm2. Further, injection molding was performed by setting the holding pressure correction pressure ΔP=15 to g7cm' for every difference t−T=O,0IOsec between the actual moving time t and the set value T. As a result, the pressure in the mold cavity is 4
The g/c ratio varied between 12 and 416 g/c, and out of 100 shots, all of the molded products obtained were good, with no occurrence of flakes or pickets.

(Effects of the Invention) The present invention controls the holding pressure based on the travel time of the injection piston or the travel time of the molten material in the mold, and by using this method, good molded products can be obtained. This makes it possible to perform injection molding with a high ratio (molding yield), which is a big gain for molders. In addition, changes in the molding state due to subtle changes in injection molding conditions, injection molding machines, molds, molding materials, etc. may also affect the travel time of the injection piston,
Alternatively, by detecting changes in the actual travel time of the molten material flowing through the mold and applying holding pressure, a good molding state could be achieved.

In addition, the method of the present invention is not difficult to implement at all, and functions and equipment such as a time detection sensor, a timer, calculation of time difference, determination of corrected pressure from time difference, and holding pressure correction are provided to the injection molding machine. The manufacturing cost is also low.

Furthermore, the present invention has the effect of minimizing pressure changes within the mold cavity, which can be achieved by keeping the pressure within the mold constant and measuring the internal pressure of the production mold. Another advantage of molded products is that there is no need to measure the internal pressure of the mold.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing one embodiment of the present invention, FIG. 2 is a graph diagram explaining the same, and FIG. 3 is a flowchart showing another embodiment of the invention. A, B...Sensor, FP...
Whole mold flow path, Is...Injection stroke,
1-・・・・・・・・・・・・Travel time, T・・・・・・
...Set time, Po...Set holding pressure.

Claims (1)

[Scope of Claims] 1) A fixed section is set in the path of a movable body that moves during injection molding, and the time during which the movable body moves within the fixed section is detected, and the detected moving time and a preset time are set. 1. A holding pressure control method for an injection molding machine, characterized in that a preset holding force is controlled and corrected based on the magnitude and time difference of these times. 2) The pressure holding control method according to claim 1, wherein the moving body is an injection piston. 3) The holding pressure control method according to claim 1, wherein the moving body is a molten molding material.