JPS63128927A - Injection molder - Google Patents

Abstract

PURPOSE:To perform the changing-over to dwelling correctly at the predetermined position in injection stroke even when the injection speed is heightened by a constitution wherein the injection speed is decelerated just before the changing-over to dwelling and the changing-over to dwelling is performed after the finish of deceleration. CONSTITUTION:The present injection stroke is measured by a positional sensor (a connecting bar 4, a rack 5, a pinion 6 and a turning angle detector 7). When the arrival of the injection stroke at the starting point of deceleration is judged, the solenoid SOL BR of a selector valve 14 is turned ON so as to input the voltage, which corresponds to the pre-calculated braking oil pressure, to a proportioning solenoid relief valve 15 for injection braking. The injection speed is decelerated to the dwelling speed by being applied with injection braking. When the injection speed Vx is lowered to the set dwelling speed and the injection stroke reaches the changing-over point to dwelling, the solenoid SOL BR of the selector valve 14 is turned OFF and simultaneously the changing-over to dwelling is performed or the pressure is changed-over to the dwelling pressure and the speed is changed-over to the dwelling speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an injection molding machine, and particularly to means for preventing overrun when switching from an injection process to a pressure holding process.

[Conventional technology]

When switching from the injection process to the holding pressure process in an injection molding machine, the holding pressure switching position is usually set in advance near the injection stroke X'E O::i (J), and when the injection screw reaches that switching position However, if the pressure holding process is not switched at exactly the right time at this switching position, the weight of the molded product will vary, resulting in large distortions and precision molding. The disadvantage is that it cannot be done.

- On the other hand, in recent years, in order to shorten the molding cycle and improve the quality of molded products, there is a strong preference to perform high-speed injection as much as possible at the holding pressure switching point J. In some cases, hydraulic pressure is used as the injection hydraulic pressure source.

[Problem that the invention seeks to solve]

However, as mentioned above, as the injection speed increases, it becomes more difficult to accurately switch the holding pressure at the set position. This results in an overrun, resulting in the drawbacks mentioned above.

An object of the present invention is to provide an injection molding machine that can increase the injection speed and accurately switch the holding pressure at a predetermined position and at the holding pressure switching setting position.

[Failure to solve the problem]

In order to achieve the above-mentioned objective, the present invention provides at least an injection speed v4. ．． and the injection speed immediately after switching the holding pressure V40. a speed setting means capable of setting the
Said V4. ．． and ■4. ．． and calculation means capable of automatically setting the deceleration start position of the injection speed and the brake oil pressure for deceleration immediately before switching to the holding pressure based on the function of the difference between the deceleration start position and the deceleration start position. It is characterized in that the injection speed is decelerated from the position and the holding pressure is switched after the deceleration is completed.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

Fig. 1 is a hydraulic circuit of an injection molding machine according to an embodiment, Fig. 2 is a control 'J1 block diagram of this injection molding machine, Fig. 3 is a control flowchart of this injection molding machine, and Fig. 4 is a control flow chart of this injection molding machine. FIG. 5 is an explanatory diagram showing the relationship between the deceleration start point F, the holding pressure switching point B, and the injection stroke end point C.

First, the hydraulic circuit of the injection molding machine will be explained using FIG.

In the figure, 1'' is two injection cylinders arranged in parallel, 2 is a communication pipe that communicates between the injection cylinders 1 and 1, and 3 is an injection screw that moves forward and backward together with the injection cylinder 1. It is arranged so that it can move forward and rotate.4
6 is a connecting bar that connects the screw 3 and the rack 5, and 6 is a pinion that meshes with the rack 5. For example, a potentiometer or encoder that detects the rotation angle of the pinion electrically or optically and outputs a position signal. A rotation angle detector 7 is attached. Therefore, the connecting bar 4, the rack 5,
The pinion 6 and the rotation angle detector 7 constitute a position sensor for the screw 3. The cylinder rod 8 of the injection cylinder 1 is integrally connected to a head stock 9 at its tip.

10 is a hydraulic power source, 11 is an injection pilot check valve, 1
2 is the injection return pilot check valve, 13 is the 3 position 4
14 is a 2-position 4-boat switching valve, 15 is a proportional electromagnetic relief valve, and 16 is a 2-position 4-boat switching valve for suckback.

The screw 3 is rotated in a fixed direction by a hydraulic motor (not shown), and the synthetic resin pellets (none of which are shown) fed from the hopper into the heating cylinder are heated by the rotation of the screw 3 and heat transfer from the heating cylinder. It is stored in the front of the heating cylinder while being plasticized and kneaded.

Due to the pressure of the synthetic resin accumulated at the tip of the heating cylinder, the screw 3 and the injection cylinder 1 are gradually retreated. As mentioned above, the cylinder rod 8 is attached to the headstock 9
Since it is connected to the injection cylinder l, it does not move, and the injection cylinder l moves relatively backward.

A predetermined amount of synthetic resin is accumulated at the tip of the heating cylinder by metering with the screw 3, and pressurized oil is sent from the hydraulic source lO through the injection pilot check valve 11 to the injection chamber 17 of the injection cylinder l, thereby opening the injection cylinder l. 1, the screw 3 is momentarily advanced to inject the molten synthetic resin accumulated at the tip of the heating cylinder into a mold (not shown) at a predetermined pressure in several stages.

After this injection process is completed, in order to prevent the molded product from becoming distorted or creased due to residual stress, the pressure is changed to a holding pressure and holding pressure speed that are different from the injection pressure, and the holding process is started.1.
Backing of the synthetic resin inside the mold is performed.

FIG. 4 is a diagram showing an example of the injection speed, in which point A is the injection start point, point B is the holding pressure switching point, and point 0 is the end point of the injection stroke. Therefore, the interval from point A to point B is the injection process.
E is the pressure holding process from point B to point 0, and in this example, the injection speed changes stepwise from the first speed vI to the second speed v2,
Immediately before switching to holding pressure, v4. , becomes. When switching to the pressure holding process, the pressure holding speed is maintained at V11+lI for a certain period of time.

Conventionally, when the screw reached the holding pressure switching point B, the injection speed at the final stage of the injection process was abruptly switched to the holding pressure speed. Therefore, there is actually a delay in response, and as a result, the holding pressure switching point is overrun.

Therefore, in the present invention, back pressure is applied to the injection return chamber of the injection cylinder from a position slightly before the holding pressure switching point at the final stage of the injection process to the holding pressure switching setting position to provide a braking effect. The speed is reduced and the pressure is switched to holding pressure at the end of deceleration.

Next, this injection speed deceleration control will be explained.

A proportional electromagnetic relief valve 15 shown in FIG. 1 is provided on the hydraulic circuit, and the operation of this relief valve 15 applies back pressure to the forward movement of the injection cylinder 1.

FIG. 2 is a control block diagram, and as shown in the figure, the control section 1
9 is a central processing unit (CPU) 20, a read-only memory (ROM) 21, and a random access memory.
(RAM) 22, keyboard switch (KB) 23. A
It is composed of a /D converter 24, an input interface (IN) 25, an output interface (OUT) 26, a D/A converter 27, and the like.

If the injection speed is increased at the holding pressure switching point B shown in FIG. 4, it will be too slow, and it is necessary to set a deceleration start point F slightly before the holding pressure switching point B. An important factor is how far before the pressure holding switching point B the deceleration start point F should be set, that is, how far K should be set in the figure.

This value is determined by the function of the difference △■ between the injection speed (Va, b) immediately before switching to holding pressure and the speed (Vd, , ) immediately after switching to holding pressure, and is calculated by the following formula (1). .

K=α・(Va,b Va,-)=α・△V
(1) However, in the formula, α is a proportionality constant having a dimension of [(to)/cs/sec=[·sec/cI11].

Furthermore, an important factor is how much the injection speed should be reduced, or in other words, how much brake oil pressure P8 should be applied. This brake oil pressure P is also determined by a function of the difference △■ between the injection speed (Vd, b) immediately before the pressure holding switch and the speed (Va, a) immediately after the pressure holding switch,
It is calculated by the following equation (2).

P,=β・(Va,b Va,-)=β・△V However, β in the formula is [kg/c+shi÷am/sec=kg
・sec/cd-cI11] is a constant of proportionality.

As a specific example of the above-mentioned K and P, for example, α is 0.
．． 33 (cot・sec/cab), β is 8.33 (k
g ・sec/cnlcn+), and Vd and b are 4.8
cm/sec, v4. .

When is 1.2 Cffi/sec, K=0.33X (4,8-1,2) '1.19 (cm).

Pg -8,33x (4,8-1,2)=30.0
(kg/cd).

As another specific example, α is 0.72 Ce1l・sec/S
), β is set as 14.29 (kg・sec/C艷・[], ■4.

When is 3.6cm/sec, ■a, a is 0.8cm+/sec, K=0.72 X (3,6-0,8)-,2,0
2 (cm).

P, =14.29 X (3,6-0,8)=40.
0 (kg/cj).

The proportionality constants α and β in the above calculation formula vary somewhat depending on the capacity of the injection molding machine, molding conditions, etc., but the proportionality constant α is 0.33 to 0.72 (elm-sec/cm).
, β is 8.33 to 14.29 (kg・sec/cd・
ROM of the control unit 19 in advance.
21 can be entered in advance.

Next, the operation before pressure holding switching will be explained mainly using the hydraulic circuit shown in FIG. 1 and the flowchart shown in FIG. 3.

As shown in Figure 3, step (hereinafter abbreviated as S) l
In, the injection speed immediately before the holding pressure switch v4.5, the speed immediately after the holding pressure switch V d , *, the injection stroke end point (0
Stroke S from the previous holding pressure switching point (point B)
P and other molding conditions etc. on the keyboard switch 23
The input is set by Then, in S2, ΔV=V4.
b-Vd0. By calculating and calling the proportionality constants α and β stored in the ROM 21 in advance, = α・△
The calculations of v, p, and -β·ΔV are performed by the CPU 20.

After other pre-processing etc. are completed, injection starts in S3, and S
In step 4, the current injection stroke SX (injection stroke end point is zero) is measured by the aforementioned position sensor (connection bar 4, rack 5, pinion 6, and rotation angle detector 7), and in step S5, S, =SP +K. I am constantly monitoring whether or not it is working.

Since the deceleration start point F, holding pressure switching point B, and injection stroke end point C have the relationship as shown in Fig. 5, 5X=SP →
This means that the injection speed starts to be decelerated from the moment it reaches -K.

The 2-position 4-boat switching valve 14 is normally in the position shown in FIG. 1 with its electromagnetic solenoid SQLBR in the OFF state, and a portion of the pressure oil from the injection return chamber 18 is routed through the pipe.
29 to the pipe line 28 via the switching valve 14 and the tank 30
It is now back to .

When it is determined in S5 that the injection stroke S8 has reached the pressure reduction start point F'' (SX = 3p + K), the process proceeds to S6 and the electromagnetic solenoid 5QLBR of the switching valve 14 is turned on, and the proportional electromagnetic relief valve 15 for the injection brake is turned on. Brake oil pressure P calculated in advance.

Enter the voltage equivalent to . By doing so, pipe 2
9-Port T-A of switching valve 14-Proportional solenoid leaf valve 1
While injecting and returning 5-pipe 28-tank 30■49
．． From holding pressure speed v42. However, after this S6, when the time difference of the injection stroke S, that is, the injection speed (8) decreases to the actual (4.3) and the injection stroke SX does not reach the holding pressure switching point, SQLBR
is turned off and waits for the holding pressure switching point Sd to be reached (S8
゜S9). Alternatively, when entering the state of S7, check whether the injection stroke SX has reached the holding pressure switching point Sd (S10), and if S,=Sd, the switching valve 1
At the same time as turning off the electromagnetic solenoid SQL BR in No. 4, the holding pressure is switched, and the pressure is changed to the holding pressure and the speed is changed to the holding pressure speed.

In this example, the injection speed was proportionally decelerated right before the holding pressure switching point until the holding pressure switching point, but it is not necessarily necessary to decelerate proportionally. It is also possible to change the rate of deceleration, such as by decreasing the rate of deceleration.

〔Effect of the invention〕

In the present invention, at least the injection speed immediately before switching to the holding pressure V4. ．．
and the injection speed immediately after switching the holding pressure v69. and speed setting means capable of setting the va, b and v40. and calculation means that can automatically set the injection speed deceleration start position and the brake oil pressure for deceleration immediately before the holding pressure switch, based on the function of the difference between the injection speed and the brake oil pressure for deceleration. The present invention is characterized in that it is configured to decelerate the engine and switch to pressure holding after the deceleration is completed.

With this configuration, even if the injection speed is drastically increased, the holding pressure can be switched accurately at a predetermined position, which shortens the molding cycle and stabilizes the dimensions and weight of the molded product. .

[Brief explanation of the drawing]

The figures are all for explaining an injection molding machine according to an embodiment of the present invention, and Figure 1 is a hydraulic circuit of the injection molding machine, Figure 2 is a control block diagram of the injection molding machine, and Figure 3 is an injection molding machine. FIG. 4 is an injection speed characteristic diagram of the injection molding machine, and FIG. 5 is an explanatory diagram of the operation of the injection molding machine. 1... Injection cylinder, 3... Injection screw, 7... Rotation angle detector, 14...
・Switching valve, 15... Proportional electromagnetic relief valve, 18
...Control unit, 19...CPU, 20.
...ROM, 21...RAM.

Claims (1)

[Claims] (1) Injection speed V_d_ at least immediately before switching to holding pressure. ＿
b and the injection speed V_d_. immediately after switching the holding pressure. a speed setting means capable of setting the V_d_. _b and V_d_. a calculation means capable of calculating and automatically setting a deceleration start position of the injection speed immediately before switching to the holding pressure and a brake oil pressure for deceleration based on a function of the difference between the injection speed and An injection molding machine characterized by being configured to reduce the speed and switch to holding pressure after the speed reduction is completed.