JPS6153938B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to injection pressure control in an injection process of an injection molding machine, and more particularly to a control circuit for a packing process and a control method thereof.

Packing is the filling process in which molten resin is filled into the mold during the injection process of an injection molding machine.The molten resin filled into the mold is maintained at a predetermined pressure to prevent sink marks as it cools and solidifies. This is a process for increasing the resin filled into the mold to a predetermined pressure value in a very short period of time before switching to the pressure process (hereinafter simply referred to as the pressure holding process) to improve the transferability of the molded product.

Conventionally, in general injection molding machines, the packing process has not been directly controlled, but has been changed by increasing the accuracy of switching control from the filling process to the pressure holding process. In other words, the packing state is determined by the resin filling rate, which indicates the percentage of molten resin in the mold up to the time when the operating conditions of the molding machine are switched from filling to pressure holding process, and the inertial energy possessed by the injection plunger at the same time. Since it is determined by the inertial energy of the fluid resin at the time determined by the operating conditions of the pressure holding process, the position of the injection plunger at the time of switching, the forward speed of the injection plunger immediately before the time of switching, This is because packing can be indirectly controlled by controlling the setting value of the holding pressure and the setting conditions of the injection speed at this time.

However, although holding pressure is effective in stabilizing the weight of the molded product, it has poor transferability, which allows the molded product to have the same shape as the mold, so it is necessary to increase the transferability and improve the appearance of the molded product. Indirect packing control using the conventional packing process is not sufficient,
Direct control of the packing process becomes necessary.

Packing control is a control that is performed in a very short time of about 0.1 to 0.5 seconds, after the mold cavity is filled with molten resin and the molten resin in the mold rises to a predetermined pressure. Pressure requires a fast response to pressure changes and strict control of the time during which it is applied. This is because if the packing pressure is applied too quickly, the skin layer on the resin surface will not be cooled enough and burrs will occur, whereas if it is too slow, the resin viscosity will increase and the pressure will not be sufficiently transmitted below the cavity. It is from.

The present invention was created in view of the above-mentioned situation, and provides a circuit for controlling the packing process during a very short period of time when switching from the conventional filling process to the pressure holding process. In an improved injection molding machine that controls the temperature in multiple stages, it is possible to obtain sufficient response to pressure changes, but without using servo valves that are expensive and require time and effort to control oil contamination. Utilizing the function of controlling pressure in multiple stages using a pressure control valve,
This is a control circuit device that controls packing by applying high speed and high pressure during the 0.1 to 0.5 second period when switching from filling to holding pressure.

Next, in an embodiment of the present invention, the filling stroke S is divided into a, b, c, and d as shown in FIGS. To explain this using an example of a device that controls pressure, 1 is an injection molding machine in which a screw 3 is inserted into a heating cylinder 2, and is moved forward and backward by pressure oil applied to a hydraulic cylinder 4, and a hydraulic motor (not shown) It is rotatable via a drive mechanism such as a gear train. The flow rate of the pressure oil acting on the hydraulic cylinder 4 is adjusted by an electromagnetic proportional flow control valve 5 provided in the piping. The valve 5 is adapted to adjust the opening and closing of its valve passage depending on the magnitude of an electric signal such as a voltage applied thereto.

Reference numeral 6 denotes an electromagnetic switching valve that switches between an electromagnetic proportional pressure control valve 7 that sets the filling pressure and holding pressure using electrical signals such as voltage, and a pressure control valve 8 for setting the packing pressure. The conventional multi-stage control device for the pressure holding process does not have sufficient response to pressure changes, which limits the range to which packing control can be effectively applied. , the electromagnetic proportional pressure control valve 7 to the pressure control valve 8 is controlled by the electromagnetic proportional pressure control valve 8, which has a poor response, by the solenoid valve 6, using the packing pressure set in advance in a pressure setting device, which will be described later. This is to switch to

The operation of the electromagnetic switching valve 6 is performed by a signal generated by a signal switching device for a pressure setting device that sets pressures such as filling pressure and holding pressure, which will be described later.
9 to 14 indicate the moving speeds V 1 to V ₆ when the screw 3 moves in the sections a, b, c, d between the filling strokes S, the packing section e, and the pressure holding section f, as shown in _FIG . This is a speed setting device that is set as an electrical signal. Reference numeral 15 is a comparator which compares the signals generated by the position signal setters 16 to 19 provided at the boundary positions S ₁ , S ₂ , S ₃ , and S ₄ of the sections a, b, c, and d with the moving position of the screw 3. Compare the signal detected by the continuously detected potentiometer 20,
When they match, a signal is generated that acts on the signal switch 21 and a timer, which will be described later. The signal switching device 21 receives the signal from the comparator 15 and issues an electric signal to control the electromagnetic proportional flow control valve 5, and continues to operate the flow control valve 5 until receiving the next signal from the comparator 15. It's starting to be controlled. For example, the signal emitted at position S ₁ is
The control valve 5 continues to be controlled as long as the signal at position _S2 is not issued. Therefore, each time the screw 3 passes through a position S ₁ to S ₄ as it moves, a signal is issued from the signal switch 21, and the screw 3 adjusts to the flow rate set in the electromagnetic proportional flow control valve 5, that is, the moving speed V. ₁ , V ₂ , V ₃ , and V ₄ to pass through each section a, b, c, and d. 22 to 26 are pressure setting devices, and 22 and 23 are filling pressure P ₁ during the filling process,
24 is a pressure setting device for setting the pressure P ₂ , 24 is the packing pressure P ₃ of the packing process, 25 and 26 are pressure setting devices for setting the holding pressures P ₄ and P ₅ . 27 to 30 are time setting devices using a timer or the like whose minimum setting value can be set to less than 0.1 seconds, and the pressures P ₂ , P ₃ , P ₄ , and P ₅ set in the pressure setting devices 23 to 26 respectively act on them. The timer 31 regulates the times T ₁ , T ₂ , T ₃ , and T ₄ and is activated by the signal emitted by the comparator 15 when the potentiometer 20 detects the position S ₄ and the time setter 27 A comparator 32 compares the signals emitted by the time setters 27 to 30 with the signals emitted by the timer 31.
When the signals from the comparator 32 match, a signal is generated from the comparator 32 and acts on the signal switch 33 and the signal switch 21. The signal switching device 33 receiving the signal from the comparator 32 switches the electromagnetic proportional pressure control valve 7 to the filling pressures P 1 and P 2 set in the pressure setting devices 22 and 23 and the filling pressures P ₁ and P ₂ set in the setting devices 25 and 26. The pressure control valve 8 is controlled by the set values P ₄ and P ₅ of the holding pressure, and the electromagnetic switching valve 6 is operated during the packing process, that is, for the time T ₂ set in the time setting device 28.
is operated at a pressure _P3 set in the packing pressure setting device 24.

The structure is as explained above, and the operation will now be explained with reference to FIGS. 1 and 2. The screw 3 moves from the retraction limit (not shown) to the first
In moving the filling stroke S to the forward limit shown in the figure, first, according to the setting value of the position setting device 16, the section a is moved at the moving speed V ₁ set in the speed setting device 9. Since the potentiometer 20 constantly detects the position of the screw 3 as it moves, when the screw 3 passes the boundary position _S2 between sections a and b, a signal from the potentiometer 20 and a speed setting device 17 are sent. When the signals from the comparator 15 match, the signal from the comparator 15 acts on the signal switch 21. The signal switching device 21 receives a signal from the signal switching device 21, and the screw 3 changes from the moving speed V ₁ of the section a to the section b.
A signal is sent to the electromagnetic proportional flow control valve 5 to switch to the desired moving speed _V2 . In this way, the screw 3 changes the moving speed V ₁ , V ₂ , V ₃ in the order of sections a, b, c.
Let's move on. During this time, the filling pressure is set to pressure setting device 2.
The electromagnetic proportional pressure control valve 7 operates so as to achieve the pressure _P1 set at P2. The screw 3 is in position S ₄
When passing through, the timer 31 is activated by the signal from the comparator 15.
is activated, and the filling process, which was previously controlled by the screw position detected by the potentiometer 20, is now time-controlled by the timer 31. While the screw 3 moves from position S ₁ to S ₄ , the mold cavity is filled with about 90 to 95% of the molten resin.
During the time _T1 set at 8, the resin is packed to 100% at the pressure _P2 set in the pressure setting device 23, and the skin layer on the resin surface described above is formed, completing the filling process. Simultaneously with the completion of the filling process, that is, when the set time _T1 has passed, a predetermined packing pressure _P3 set in the pressure setting device 24 is applied during the packing time _T2 set in the time setting device 28. As shown in FIG.
so that the electromagnetic flow control valve 5 is activated.
It is also controlled by the value set in the speed setting device 13. In this case, in order to improve responsiveness, it is preferable to set the opening degree to 40% or more. When the time T ₂ of the packing process has passed, the electromagnetic switching valve 6 returns to the B position again, and its pressure is controlled by the electromagnetic proportional pressure control valve 7 at the holding pressures P ₄ and P ₅ set in the pressure setting devices 25 and 26. for times T ₃ and T ₄ , respectively, to prevent backflow of the packed molten resin and replenish shrinkage due to cooling until the gate is sealed.

With the configuration and effects described above, it has become possible to control the packing process by strictly controlling the time. Further, in the above embodiment, pressure control in the filling process and pressure holding process was performed using one electromagnetic proportional pressure control valve, but pressure control in the filling process and pressure holding process may be performed using separate pressure control valves. However, it may also be used as a pressure control valve for controlling the filling process.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention. Figure 2 is an explanatory diagram of the operation of the screw in the injection process.
A diagram showing the relationship between pressure and time. 3... Screw, 5... Solenoid proportional flow control valve,
6... Solenoid switching valve, 7... Solenoid proportional pressure control valve,
8...Pressure control valve, 9-14...Speed setter, 1
5, 32... Comparator, 16-19... Position setter, 20... Potentiometer, 21, 33...
...Signal switch, 22-26...Pressure setting device, 27
~30...Time setting device.

Claims (1)

[Scope of Claims] 1. A third pressure control valve provided separately from the pressure control valve for setting filling pressure and holding pressure in a control circuit that controls pressure in the injection plunger during the injection process, and the third pressure control valve. and the filling and holding pressure control valve, and a minimum set value for determining the operating time of the switching valve is 0.1.
An injection pressure control circuit for an injection molding machine, characterized in that it is provided with a timer that can be set to less than a second. 2. The injection pressure control circuit according to claim 1, wherein the third pressure control valve also serves as a pressure control valve for setting filling pressure. 3. The injection pressure control circuit according to claim 1, wherein the pressure control valve for setting the filling pressure and holding pressure is an electromagnetic proportional pressure control valve. 4. A third pressure control valve provided separately from the pressure control valve for setting the filling pressure and holding pressure in a control circuit that controls the pressure of the injection plunger during the injection process, and the third pressure control valve and the filling and holding pressure. an electromagnetic switching valve for switching between the control valve and a timer having a minimum setting value of less than 0.1 seconds for determining the operation time of the switching valve, and controlling the injection plunger while the electromagnetic switching valve is operating. An injection pressure control method for an injection molding machine characterized by maintaining the opening degree of an electromagnetic proportional flow control valve at 40% or more. 5. The injection pressure control method according to claim 4, wherein the third pressure control valve is also used as a pressure control valve for setting filling pressure. 6. The injection pressure control method according to claim 4, wherein the pressure control valve for setting the filling pressure and holding pressure is an electromagnetic proportional pressure control valve.