JPH0423894B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pressure holding control device for an injection molding machine.

[Conventional technology]

As shown in Japanese Unexamined Patent Publication No. 57-59060, an injection molding machine is known in which a rotatably driven screw is reciprocated by an injection cylinder and molten resin is injected from a nozzle to fill the cavity of a mold. There is.

In such injection molding machines, after the molten resin is completely filled into the mold cavity, a predetermined pressure is applied for a predetermined period of time to maintain the pressure, thereby preventing sink marks when the molten resin solidifies.

For example, a pressure holding control device disclosed in Japanese Unexamined Patent Publication No. 59-64336 is known.

That is, as shown in FIG. 9, when the screw position detected by the position detector b that detects the position of the screw a matches the set position of the holding pressure switching position setting device c, the comparator d outputs the holding pressure process start command device e. A control signal is output from the holding pressure switching command h to the pressure control valve i so that the holding pressure set by the holding pressure setting device g is maintained for the time set by the holding pressure setting device f, and the control signal is output to the pressure control valve i, and the injection cylinder j is The pressure in the elongation chamber k is set as the pressure at which a predetermined holding pressure can be obtained, and the cavity of the mold 1 is filled with the molten resin, and a predetermined pressure is applied and held for a predetermined time in each step.

Specifically, the screw a is advanced to sequentially fill the molten resin into the cavity m of the mold 1 at a predetermined pressure while changing the injection speed step by step depending on the screw position, and the screw position is set at the position where the filling is completed. When detected by detector b, the screw a is decelerated, and at the same time, the timer is switched on and the pressurization of the injection cylinder connected to the screw is changed in stages to change the holding force applied to the mold to prevent sink marks and the like.

[Problem that the invention seeks to solve]

With such a pressure holding control device, even if the screw is stopped to maintain pressure, the injection cylinder j
Even if the pressure in the extension chamber k is changed to the set pressure, the pressure of the molten resin at the tip of the screw will be The holding pressure does not reach the set holding pressure instantaneously, but reaches the set holding pressure after a time delay, and a peak value occurs at the beginning of the switch to the holding pressure process. This will result in overfilling.

For example, even if the pressure in the extension chamber k of the injection cylinder j is controlled as set, as shown by the solid line A in Fig. 10, the screw a will immediately decelerate at the holding pressure switching position C, as shown by the broken line B in Fig. 10. The resin pressure at the tip of the screw moves slightly due to inertia, and the resin pressure at the tip of the screw reaches a peak pressure H after the holding pressure switching position as shown by solid line D in Figure 11 due to inertia force, and the holding pressure inside the mold increases as shown in Figure 12. A pressure peak occurs as shown by the solid line.

For this reason, an excessive holding force acts before the molten resin solidifies, causing burrs to form at the filling ends and round holes of the molded product.

In order to prevent peak pressure, it is better to move the holding pressure switching position earlier, but if you switch to holding pressure too early, the pressure holding process will begin with the mold cavity not yet filled with molten resin, so the filling end The flow rate of the molten resin may decrease, causing flow marks on the molded product.

Further, after switching to holding pressure, a time lag occurs at the rising and falling times when the holding pressure is changed stepwise, and it is not possible to control the gradient at the rising and falling times. For this reason, even when a steep slope or a gentle slope is desired depending on the shape of the product, burrs and flow marks may occur because control is not possible.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a pressure holding control device for an injection molding machine that prevents peak pressure from occurring in the holding pressure within the mold or overfilling.

[Means and actions for solving problems]

A flow rate control mechanism is provided to increase or decrease the opening area of the nozzle, and when the screw reaches a predetermined position, the opening degree of the flow rate control mechanism is decreased, and when the screw reaches that opening degree, the hydraulic pressure to the extension chamber of the injection cylinder is reduced. A controller is provided to maintain a predetermined holding pressure, and before the holding pressure starts, the opening area of the nozzle is reduced to remove the peak pressure of the molten resin inside the mold, regulate the flow, and maintain the holding pressure. This makes it possible to control the rising and falling slopes during stepwise switching of pressure.

〔Example〕

A screw 2 is slidably and rotatably inserted into a cylindrical housing 1 to melt the resin in a hopper 3 and fill it into a cavity 6 of a mold 5 through a nozzle 4. It is connected to a piston rod 8 of the injection cylinder 7, and a drive shaft 10 rotated by a hydraulic motor 9 is spline-fitted to the piston rod 8.
1 is supplied with pressure oil from a hydraulic source 12 via a switching valve (not shown), and the pressure is controlled by a pressure control valve 13.
It can be controlled by.

The nozzle 4 is provided with a flow rate control mechanism, for example, a nozzle valve 14, which controls the opening area of the nozzle 4, and the nozzle valve 14 is connected to a lever 15 and a rod 6.
The opening of the nozzle valve 14 can be changed by connecting to a nozzle valve drive mechanism, for example, the proportional solenoid 17, and controlling the current supplied to the proportional solenoid 17, thereby controlling the opening area of the nozzle 4. It is set as.

A rack rod 18 is connected to the piston rod 8, and a pinion 19 meshing with the rack rod 18 is provided with a rotation sensor 20 such as a potentiometer to constitute a rack position detector 21. A pinion rod 22 is fixed to the movable part 17a of 17, and this pinion rod 22
A rotation sensor 24 such as a potentiometer is provided on a pinion rod 23 meshed with the nozzle valve opening detector 25 .

The pressure holding control is performed by the controller 30.

Next, details of the controller 30 will be explained along with its operation.

The first comparator 32 compares the actual screw position S1 detected by the screw position detector ₂₁ with the holding pressure start screw position _S2 set by the screw position setting device 31.
If the two match, a command is given to the pre-pressure holding nozzle valve opening setting device 33, and the proportional solenoid 1 is
Nozzle valve 14 by sending an electric signal set to 7.
The opening degree of is set as the pre-holding opening degree V ₀ .

At this time, the second comparator 34 compares the actual opening V ₁ detected by the nozzle valve opening detector 25 and the pre-pressure holding opening V ₀ , and if the two match, the pressure holding nozzle valve opening setter 35 and pressure holding time setting device 36
give commands to.

As a result, the proportional solenoid 17 is set so that the holding pressure opening degree V _p is determined by the holding pressure nozzle valve opening setting device 35.
A control current is generated to set the holding pressure opening degree V _p .

On the other hand, the holding pressure setting device 3
7, the control section 13a of the pressure control valve 13
A control current is emitted to set the set pressure to a preset pressure, thereby causing the elongation chamber 11 of the injection cylinder 7 to
The pressure inside the mold changes, the pushing force of the screw 2 changes, and the molten resin pressure at the tip of the screw reaches the value set by the holding pressure setting device 37, which causes the holding pressure inside the mold to also reach the set value and hold pressure. can.

Specifically, the pressure in the extension chamber 11 of the injection cylinder 7 changes from P ₁ , P ₂ , and _{P 3} as shown by the solid line in FIG. The molten resin pressure reaches a peak value at the holding pressure switching point as shown in Fig. 3, but at this time, the opening degree of the nozzle valve 14 is as small as V _p , so it does not affect the holding pressure in the mold and the fourth As shown in the figure, the peak pressure of the holding pressure within the mold no longer occurs at the holding pressure switching point.

In this way, before holding pressure, the opening degree of the nozzle valve 14 is reduced, and then the injection cylinder 7
By controlling the pressure in the extension chamber 11, the holding pressure inside the mold is set to the set value, so the holding pressure operation is performed after the opening area of the nozzle 4 becomes small.
Even if the screw 2 moves due to inertia, the resistance of the molten resin flowing through the nozzle 4 at the tip of the screw increases, preventing it from flowing into the cavity of the mold, which prevents the molten resin from overfilling the mold. Even if compression or peak pressure occurs in the molten resin at the tip of the nozzle, the effect will not be exerted on the inside of the mold, and burrs can be prevented from forming in the holes of the molded product or at the point where filling is completed.

Further, the switching point from the filling process to the pressure holding process is the point when the opening degree of the nozzle valve 14 becomes sufficiently small, that is, the point at which the inflow speed of the molten resin into the mold is sufficiently slowed down, and the switching point from the filling process to the pressure holding process The switching point to the pressure holding process becomes clear from the flow behavior of the molten resin into the mold.

Stepwise switching after pressure holding is possible by controlling the flow rate of the nozzle valve by gradually switching the nozzle valve between the rising and falling times t ₁ and t ₂ as shown in FIG.

FIG. 5 shows a second embodiment, in which a nozzle valve opening delay time setting device 38 is provided on the signal input side of the pressure holding nozzle valve opening setting device 35, and when a command signal is output from the second comparator 34, After the nozzle valve opening delay time setter 38 is activated and a set time has elapsed, a command signal is output to the pressure holding nozzle valve opening setter 35 to increase the opening.

If this is the case, from the pressure holding switching point, that is, when the opening degree of the nozzle valve 14 reaches the value set by the pre-pressure holding nozzle valve opening degree setting device 33, the opening degree is maintained for a set time, and then the opening degree is maintained for a set time. After a period of time has elapsed, the opening reaches the opening set by the pressure holding nozzle valve opening setting device 35, so that the pressure of the molten resin at the tip of the screw decreases during this set time, and it is possible to prevent excessive pressure from acting inside the mold.

Note that during the above setting time, the hydraulic pressure in the extension chamber 11 of the injection cylinder 7 changes from the holding pressure switching point to the holding pressure setting device 37.
This is the time required for the screw tip molten resin pressure to reach the holding pressure setting value set in .

For example, as shown in FIG.
The opening will be changed after T0 time has passed after the opening reaches V0.
When increasing V′ _p , the molten resin pressure at the nozzle tip smoothly becomes a value that corresponds to the holding pressure setting value as shown in Figure 7, and the holding pressure inside the mold becomes a value that corresponds to the setting value as shown in Figure 8. However, if the opening degree is immediately set to V' _p before the aforementioned time T ₀ elapses, a peak pressure will occur as shown by the imaginary line in FIG.

Further, even when switching stepwise after pressure holding, a delay time setting device is used to set a delay time to prevent sudden switching, thereby making it possible to smoothly change the pressure during switching and prevent the generation of peak pressure.

〔Effect of the invention〕

Since the opening area of the nozzle 4 is reduced before starting the pressure holding operation, even if the screw 2 moves due to inertia, the molten resin at the tip of the screw does not flow through the nozzle 4 into the cavity 6 of the mold 5 and is melted. It is possible to prevent overfilling of the mold with resin, and even if the molten resin at the nozzle tip is compressed or peak pressure occurs, the influence does not affect the inside of the mold. Since the pressure gradient can be controlled, molded products can be prevented from forming.

[Brief explanation of drawings]

Figure 1 is an overall explanatory diagram of the first embodiment of the present invention, Figures 2, 3, and 4 are charts showing the nozzle valve opening, the pressure of molten resin at the tip of the screw, and the holding pressure in the mold. FIG. 5 is an overall explanatory diagram of the second embodiment, and FIG.
Figures 7 and 8 are charts showing the nozzle valve opening, molten resin pressure at the screw tip, and holding pressure in the mold. Figure 9 is an explanatory diagram of the conventional example, and Figures 10 and 11.
FIG. 12 is a chart showing the hydraulic pressure, the molten resin pressure at the tip of the screw, and the holding pressure inside the mold. 2 is a screw, 4 is a nozzle, 5 is a mold, 6 is a cavity, 7 is an injection cylinder, 11 is an extension chamber,
30 is a controller.

Claims (1)

[Claims] 1 In an injection molding machine that fills a cavity 6 of a mold 5 with molten resin from a nozzle 4 by rotating and reciprocating a screw 2, a flow rate control mechanism is provided to control the increase/decrease of the opening area of the nozzle 4, and When the screw reaches a predetermined position, a control signal is output to the flow rate control mechanism so that the opening becomes a predetermined opening, and when the opening reaches the predetermined opening, the pressure in the extension chamber 11 of the injection cylinder 7 is adjusted in advance. A pressure holding control device for an injection molding machine, characterized in that a controller 30 is provided for controlling the holding pressure to a predetermined holding pressure.