JP2571933B2 - Holding pressure switching control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure-holding switching control method and apparatus for switching from a filling step to a pressure-holding step in an injection step of an injection molding machine.

<Prior Art> Conventional injection process control will be described with reference to FIGS. 5 and 6. FIG. 101 indicates a screw. Reference numeral 102 denotes an injection ram, in which hydraulic pressure acts on the injection side to advance the screw 101 to perform injection. 103 and 104 indicate molds, and 10
Reference numeral 5 denotes a rack mounted on the screw 101 and synchronized with the reciprocating motion of the screw. Reference numeral 106 denotes a pinion, which meshes with the rack 105 to rotate by the movement of the screw 101, and converts the linear movement of the screw 101 into a rotational movement. Reference numeral 107 denotes a potentiometer, which is connected to the pinion 106 via a gear train or directly and receives the rotation of the pinion 106 to convert the movement of the screw 101 into a continuous electric signal. Is configured. S indicates an injection stroke, and the same stroke S indicates A, B,
It is divided into five stages C, D, and E, and the screw 101 is configured to pass through the sections A, B, C, D, and E at different injection speeds at the time of injection.

Describing the hydraulic circuit, m indicates an injection switching solenoid valve, which controls the injection ram 102. f is an electromagnetic flow control valve (flow regulating valve)
In an electromagnetic flow controller (hereinafter referred to as an electromagnetic flow controller), the throttle opens and closes in proportion to the strength of a voltage or a current (hereinafter, referred to as a voltage). When the voltage is high, the throttle is small, and thus the flow rate increases. Also, when the voltage is small, the throttle is large, and thus the flow rate is small. PF ₂ indicates a pump. r indicates an electromagnetic relief valve (pressure control valve) whose set pressure changes depending on the strength of the voltage.

The electric circuit will be described. Reference numeral 107 denotes a potentiometer which converts the position of the screw 101 into a voltage as described above. Is continuously changed up to the voltage of Reference numeral 108 denotes a potentiometer for setting the voltage indicated by the potentiometer 107 when the screw 101 advances in the section A. Similarly, 109 to 111 are potentiometers, and the screw 101 is A + B, A + B + C, A + B
When + C + D is advanced, the voltages indicated by the potentiometers 107 are set, and these potentiometers 108 to 111 are set.
Constitutes an injection speed switching position setting device. Reference numerals 112 to 115 denote signal transmitters (comparators), and each of the potentiometers 108 to 111
Is compared with the voltage of the potentiometer 107, which changes momentarily with the movement of the screw 101, and when both voltages match, a built-in relay (not shown) operates to generate a signal. Reference numerals 112a to 115a indicate A contacts of a relay in the signal transmitter, and 112b to 115b indicate B contacts. Reference numerals 116 and 117 denote amplifiers for amplifying voltages set in potentiometers 118 to 125 described later to operate the electromagnetic flow controller f and the electromagnetic relief valve r. The potentiometers 118 to 122 set the voltages in advance, and when the electric circuits (50 to 54) are switched by the signals generated by the signal transmitters 112 to 115, the predetermined voltages are applied to the electromagnetic flow controllers f. And a predetermined amount of oil is applied to the injection ram 102 to constitute an electric quantity setting device group for controlling the injection speed. Similarly, the potentiometers 123 to 125 set a predetermined voltage, act on the electromagnetic relief valve r, and set an electric quantity for controlling the injection pressure in the filling process and the holding pressure in the holding process. It constitutes a group of instruments. 100TR represents a timer, which performs switching of holding pressure during the holding process, having contacts 100TR ^1. RS indicates a relay, and A contact RS
₁ , RS ₃ and B contact RS ₂ .

Next, the operation will be described. By the injection start signal,
When the solenoid valve m switches to the forward position, the electric circuit
The electromagnetic flow controller f applies a predetermined flow rate to the injection ram 102 by the voltage set in the potentiometer 118 at 50, and the screw 101 advances in the section A during the stroke S at a predetermined injection speed. During that time, the injection pressure is maintained at the set pressure of the electromagnetic relief valve r determined by the potentiometer 125 in the electric circuit 55. Screw 10
When 1 passes through section A, it matches the voltage of potentiometer 108, a signal is emitted by signal
b is switched to the contact 112a, so that the electric circuit 50
Then, the screw 101 moves forward in section B at a predetermined injection speed at a flow rate determined by the set voltage of the potentiometer 119. Similarly, section C is controlled by potentiometer 120, and section D is controlled by potentiometer 121.
In the E section, the flow rate of the electromagnetic flow controller f is controlled by the potentiometer 122, and the screw 101 moves forward at the determined injection speed. Screw 101 Te Ryo' passes through the section D, the switched contacts 115b by the signal of the signal transmitter 115 to 115a, closes the contact A RS ₁ is excited at the same time the relay RS, timer for switching the holding pressure 100TR starts timing. At the same time, A contact RS ₃ (electrical circuit 56)
Since the injection pressure is also closed, the injection pressure becomes the set pressure of the electromagnetic relief valve r determined by the potentiometer 124, and shifts to the pressure control during the pressure-holding step after the filling step is completed.

When timer 100TR times out, contact 100TR ¹
Is switched from the electric circuit 56 to the electric circuit 57. Therefore, the set pressure of the electromagnetic relief valve r is determined by the potentiometer 123, and the holding pressure changes.

In precision molding, the switching control from filling to holding pressure in the injection process control requires accuracy. That is, in the filling step, it is necessary to perform the filling in as short a time as possible in order to minimize the difference in viscosity between the front end and the rear end of the molten resin flowing into the mold cavity. In the pressure-holding step following the filling step, it is important how to compensate for the shrinkage of the molten resin filled in the mold cavity due to cooling without excess or deficiency. As an important factor in the switching point to the process, it is also important to shift from the filling to the pressure holding process in a short time while maintaining the stability by repeating the accurate position.

Generally, in high-speed injection molding of a thin molded product, a deep molded product, or the like, the filling speed needs to be increased for the above-described reason, and the pressure in the mold cavity at the time of completion of the filling increases. Therefore, burrs are likely to occur, and to prevent this,
Before the inflow end of the molten resin at the time of completion of the filling reaches the end of the cavity, the speed control is switched to the holding pressure control, the oil pressure is set to a holding pressure lower than the filling pressure, and further changed.

Therefore, if the setting is made to switch to the holding pressure at a point where there is much more margin before the inflow end of the resin reaches the end of the cavity, short shots and sink marks will occur, and filling will occur. It was important to know the switching point from the pressure to the holding pressure.

<Problems to be Solved by the Invention> However, as described above, even when the timing of switching to the pressure-holding step is carefully determined, in the case of high-speed injection molding, molded articles in which defective phenomena such as sink marks occur are found.

The inventors have repeatedly observed the behavior of the molten resin in the mold cavity when switching from the filling process to the pressure-holding process, and found the following problems.

As shown in the graph of FIG. 7, when switching from the filling process to the holding pressure process, when performing molding such that the pressure is reduced from a high filling pressure to a low holding pressure, the pressure in the injection cylinder is indicated by a chain line in a graph 5. There is a point where the oil pressure drops sharply as shown by the enclosed "a" or as shown in graph 6 of the in-mold pressure. As a result of a more detailed investigation, the switching signal from the filling process to the pressure holding process is reduced. When it was issued, it was confirmed that the pressure in the oil chamber of the injection cylinder dropped from the filling pressure to the holding pressure, and the screw retracted instantaneously, causing the resin pressure in the cavity to flow back. And it was confirmed that when this phenomenon occurs, many defective moldings occur.

If the injection cylinder is maintained so as not to release the oil pressure at the time of the completion of the filling, a reverse flow of the resin pressure in the cavity does not occur, and a good product can be obtained.

When an electromagnetic flow control valve is used to control the injection speed, if the valve opening is set to 20% or less (too close), the rising transmission of pressure will be poor and an unfilled state will occur, resulting in a defective product.

Further, if the holding pressure is maintained by opening the electromagnetic flow control valve too much, the stop position of the screw varies and burrs are generated, resulting in a defective product.

In addition, various switching methods from the filling process to the pressure holding process were observed and observed.

(B) When switching from filling to holding pressure, a method is used in which the speed drop value when the screw reaches near the filling completion position is detected and switching to pressure holding is performed.

(B) In the last section divided into multiple stages during the filling process, when the system switches to the holding pressure when the filling pressure reaches a constant value.

(C) When using a hydraulic servo valve for injection pressure and speed.

(D) When the resin pressure value in the mold is detected and compared with the set value, and when both values match, the system switches to holding pressure.

In either case (a) or (d), similar to the above-described method using the screw position, when the filling pressure was switched to a smaller holding pressure, the phenomenon that the screw retreated instantaneously was observed.

As described above, even in various packing pressure switching methods, switching from the filling pressure to a lower packing pressure shows an instantaneous screw retreat phenomenon, and this screw retreat phenomenon is caused by the molten resin in the mold. It is thought that the following effects will occur.

That is, as shown in FIG. 8, the molten resin charged at a high speed is filled with the molten layer 14 in a state in which the surface is in contact with the dies 10 and 11 and the skin layer 13 formed at the leading end of the inflow. And the cavity 15 is filled. However,
When a switching signal from the filling process to the pressure-holding process is issued, the resin pressure applied to the thin skin layer 13 is reduced by one.
As the cooling of the skin layer 13 progresses, the skin layer 13 becomes thicker. Even if a dwell pressure is applied thereafter, the skin layer 13 is thickened by the above-mentioned thickened skin layer 13, and the internal molten portion 14 cannot proceed to the end of the cavity 15, and the molded product may have sink marks or the like. I think that the.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and an apparatus for controlling a pressure-holding switch that eliminates the above-mentioned drawbacks and prevents the screw from retreating when switching to the pressure-holding so that the molded product is free from defects. .

<Means for Solving the Problems> In order to achieve the above-mentioned object, the present invention provides a timer operated by a switching signal from a filling step to a pressure-holding step, and a screw which is used when switching from the filling step to the pressure-holding step. It has a screw stop means that can move forward and cannot retract, and when switching from the filling process to the pressure-holding process, when the switching signal is issued, the screw can move forward for a predetermined time, and A pressure-holding switching control device of the injection molding machine that keeps it from being operated.

<Operation> With this configuration, when switching from the filling process to the holding pressure process, the screw can move forward, but cannot move backward, so it switches from the high filling pressure to the low holding pressure. Even so, the screw does not retreat.

Embodiment 1 Next, an embodiment of the present invention will be described with reference to FIG. In the description, the same members as those of the conventional device are denoted by the same reference numerals, and the operation thereof is omitted.

The electric control circuit diagram of FIG. 1 shows a conventional device (described with reference to FIGS. 5 and 6) in which a timer TR which operates for a predetermined time in response to a switching signal from a filling process to a pressure holding process and an electromagnetic flow controller f for a predetermined time are used. The screw 101 is provided with a potentiometer 126 for setting a voltage for control. The screw 101 can be moved forward for this predetermined time, but is held by the electromagnetic flow controller f so as not to be able to move backward.

Incidentally, TR ¹ a, TR ¹ b is A contact of the timer TR, a B contact.

<Operation> When the screw 101 passes through the section D of the filling stroke S, a signal is emitted from the signal transmitter 115 and the relay RS
Is excited, the A-contact RS is closed, the timer 100TR for switching the holding pressure starts timing, and the screw 1
01 but only forward available predetermined time backward timer TR is activated A contact TR ¹ a for holding that can not have Tsugari operates only B contact TR ¹ b is cut 0.1 to 0.2 seconds. During this time, the potentiometer 12 is set so that the flow rate of the electromagnetic flow controller f becomes zero.
Controlled by the voltage set to 6.

Therefore, in response to the filling process completion signal, the filling pressure previously set in the potentiometer 125 is switched to the pressure in the holding pressure process diagram set in the potentiometer 124, but at the same time, the timer TR is set to 0.1 to 0.2 as described above. While operating for only a second, the hydraulic oil in the pipeline of the injection side oil chamber 102a of the injection cylinder 102 cannot pass through the flow control f and stays in the pipe, and the screw 101 cannot retreat. When the predetermined time 0.1 to 0.2 seconds times out, the A contact
Since TR ¹ a is cut off and the B contact TR ¹ b is connected, the injection side oil chamber 102 a of the injection cylinder 102 is controlled at the flow rate set in the potentiometer 121.

<Embodiment 2> Another embodiment of the present invention will be described with reference to FIG. In the description, the same members as those of the conventional device are denoted by the same reference numerals, and description thereof will be omitted.

In a pipeline communicating with the injection side oil chamber 102a of the injection cylinder 102, a pilot check valve 130 and a pilot electromagnetic switching valve 131 for controlling the valve 130 are provided.

Accordingly, a timer is provided in the same manner as in the first embodiment. During the timing of the timer, the electromagnetic switching valve 131 is excited, and if it is set to the a position, the pilot pressure is applied to the pilot check valve 130, and the injection cylinder The pipeline communicating with the injection side oil chamber 102a is closed.

<Embodiment 3> Still another embodiment will be described with reference to Figs. 3 and 4. This embodiment is an example in which the screw is mechanically stopped. The screw 150 can be advanced and retracted in the axial direction by the injection cylinder 151, and the arm 152 is attached to synchronize with the above-mentioned axial movement of the screw. It has become.
A bar 153 is attached to the arm 152 via a permanent magnet plate, as will be described later.
It passes through the hole of the bar fastening device 154 fixed to 1.
As shown in FIG. 4, the hole of the bar fastening device 154 is formed by a sleeve 155, and a spiral groove 156 is provided in the inner diameter portion which is in contact with the bar 153. It communicates with the inlets 157 and 158. Therefore, when the pressure oil passes through the spiral groove 156, the diameter of the hole becomes large and the bar 153 can move forward and backward in the axial direction. However, when the pressure oil does not act on the groove 156, the bar 153 comes out. It is tightened from the radial surface so that it cannot move back and forth in the axial direction.

The bar 153 is integrated with the stainless steel bar 159 and the permanent magnet plate 160 by welding, and the A surface of the magnet plate 160 is joined to the arm 152 attached to the screw 150.

Therefore, when the stainless bar 159 of the bar 153 is gripped by the fastening device 154, the screw 150 is connected to the arm 152 and the magnetic plate.
160 allows the junction to separate and advance. However, retraction is not possible because the bar 153 is gripped by the fastening device 154. The gripping time of the bar 153 is determined by a timer operated by a switching signal from the filling process to the pressure holding process, as in the above-described two embodiments.

<Effects of the Invention> As described above, according to the present invention, even if the pressure is switched from the filling pressure to the holding pressure by switching from the filling process to the holding pressure process, the screw can move forward but cannot move backward. As a result, there is no sudden drop in pressure at the time of switching as originally stated, and the screw does not retract. Therefore, no defective products were generated.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of one embodiment of the present invention, and shows an electric control circuit diagram thereof. FIG. 2 is a diagram showing another embodiment of the present invention. 3 and 4 are views showing still another embodiment of the present invention, and FIG. 3 is an explanatory view of the apparatus. Fig. 4 is a detailed view of the "B" part of Fig. 3, showing a bar fastening device. 5 and 6 are views showing a conventional apparatus, FIG. 5 is an explanatory view of the apparatus, and FIG. 6 is an electric control circuit diagram thereof. FIG. 7 is a graph illustrating a change in pressure in an injection cylinder and a mold during an injection process in a conventional apparatus. FIG. 8 is a view for explaining a state of a molten resin in a mold in a filling step. 101,150 …… Screw, 102,151 …… Injection cylinder, 108-1
11 Injection speed switching position setting device, 112 to 115 Signal transmitter, 118 to 126 Electric quantity setting device, 130 Check valve with pilot, 131 Electromagnetic switching valve, 152 Arm, 153 … Bar, 154 …… Bar fastening device, 155 …… Sleeve, 160 …… Permanent magnet plate, f …… Electromagnetic flow control valve, r …… Electromagnetic relief valve

Claims (6)

(57) [Claims] 1. A screw which is capable of moving a screw forward and not retreating at the time of switching from a filling step to a pressure holding step, the timer being operated by a switching signal from a filling step to a pressure holding step, A pressure-holding switching control device for an injection molding machine that can advance the screw for a predetermined time set in the timer when the switching signal is transmitted, and keep the screw from moving backward. 2. The injection molding according to claim 1, wherein said screw stopping means is provided with a pipe closing means in an oil chamber on the injection side of the injection cylinder or a hydraulic pipe connected to the oil chamber. Pressure control switching device for the machine. 3. The holding pressure switching control apparatus for an injection molding machine according to claim 2, wherein said conduit closing means is a current flow regulating valve. 4. A pressure-holding switching control device for an injection molding machine according to claim 2, wherein said pipe closing means comprises a pilot pressure control valve and a pilot pressure switching valve for controlling said valve. . 5. The holding pressure switching control device for an injection molding machine according to claim 1, wherein said screw stopping means is a mechanical locking means. 6. A holding device for an injection molding machine according to claim 5, wherein said mechanical locking means comprises a bar bonded to the screw side by a magnet and a bar fastening device for locking said bar. Pressure switching control device.