JP2828801B2 - Injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding machine using an injection cylinder (hydraulic cylinder) as an injection actuator.

[0002]

2. Description of the Related Art In this type of hydraulically driven injection molding machine, mold clamping is performed by a mold clamping cylinder (hydraulic cylinder), and the molten resin is clamped by an injection cylinder (hydraulic cylinder) at an appropriate injection timing thereafter. The mold is injected and filled into the molding space (cavity) in the mold.

FIG. 3 is a diagram showing a hydraulic circuit of an injection cylinder system of such a conventional injection molding machine. In FIG. 3, 1 is a hydraulic pump, 2 is a pressure control valve (electromagnetic proportional relief valve), 3
Is a flow control valve, 4 is a direction switching valve, and 5 is an injection cylinder (hydraulic cylinder). Although not shown in the in-line screw type injection molding machine, a root portion of a screw provided in the heating cylinder is connected to the piston rod 5a of the injection cylinder 5 through a connecting means as appropriate. Have been.

In the configuration shown in FIG. 3, the directional control valve 4 is switched from the neutral position to the left position at a predetermined time after the completion of the mold clamping, and the hydraulic oil from the hydraulic pump 1 is supplied to the injection cylinder. 5, a screw (not shown) moves forward together with the piston rod 5a, and molten resin is fed from the nozzle at the tip of the heating cylinder (not shown) between the molds. Is injected and filled into the cavity (molding space). When the injection of the molten resin into the cavity is completed by the injection / filling process (primary injection process) by the advancement of the screw, the pressure is switched to the known pressure-holding process (secondary injection process). A predetermined holding pressure is applied to the molten resin to compensate for shrinkage and the like accompanying cooling and solidification of the resin.

In the meantime, during the above-mentioned injection / filling stroke (primary injection stroke), the injection speed is often regarded as important. Therefore, during the injection / filling stroke, the screw (the piston rod of the injection cylinder 5) The injection speed is controlled by the flow control valve 3 so as to follow the set speed set according to the forward position (stroke) of 5a). In addition, since the pressure-holding process emphasizes pressure control, pressure control based on time is performed by the pressure control valve 2 after a known pressure-holding switching point.

FIG. 4 is a graph showing the relationship between the injection speed and the load pressure (the pressure of the forward oil chamber of the injection cylinder 5) when the injection is performed by the configuration of FIG. As shown in the figure, since the speed control is performed during the injection / filling stroke period, the measured speed data is set for each zone A ', B', C 'as shown by the solid line in the figure. 6 shows a characteristic curve substantially following the set speed value. On the other hand, during the injection / filling stroke period, the control is performed with priority given to the speed. In other words, since the speed is controlled by the position irrespective of the load pressure, the load pressure cannot be accurately controlled. Further, the pressure on the upstream side of the flow control valve 3 is made considerably higher than the pressure on the downstream side (so-called differential pressure is increased).
During the filling process, the load pressure does not exceed the optimal filling pressure during the injection / filling process, but the load reaction force (resin pressure) starts before the resin is filled (clogged) in the cavity and the filling is completed. As the load pressure increases, the load pressure increases
It often exceeds the optimum filling pressure during the filling process.

[0007]

In the prior art described above, control is performed with priority given to speed during the injection / filling process (primary injection process). Therefore, a molded product that emphasizes the injection speed, in other words, a lens. It is suitable for the manufacture of molded products such as home electric appliances and the like in which dimensional accuracy and appearance (weld line, flow mark, silver, etc.) are emphasized.

However, during the injection / filling process, the load pressure cannot be accurately controlled, so that the load pressure is not stable, so that the density of the molded product tends to vary, and in other words, a molded product in which emphasis is placed on the filling pressure (load pressure). If this is the case, there is a problem that it is not suitable for a product such as a CD or a thin-walled product that emphasizes weight accuracy and prevention of deformation (such as warpage). In addition, injection
During the filling stroke (primary injection stroke), the speed is prioritized, so the load pressure tends to greatly exceed the optimum filling pressure in the vicinity of the holding pressure switching point, and the filling pressure becomes excessive, causing burrs on the molded product. Is likely to occur, and the density of the portion near the gate in the cavity becomes excessive, so that warping is also likely to occur,
There is also a problem that a molded article defect due to such burrs and warpages easily occurs. Furthermore, since in the vicinity hold pressure replacement point load pressure is far above the optimum filling pressure, the load pressure from entering the higher coercive stroke is not relatively large and stable time T ₂ of the in settled bear holding pressure value Therefore, there is a problem that the quality of a thin-walled molded product is adversely affected also in this respect.

The present invention has been made in view of the above points,
The objectives are injection / filling (primary injection), which gives priority to filling pressure (load pressure) control for molded products that place emphasis on weight accuracy and prevention of deformation (such as warpage), and emphasis on dimensional accuracy and appearance. Injection with priority on injection speed control for molded products
Filling (primary injection) is to provide an injection molding machine that can be selectively obtained by the same machine.

[0010]

According to the present invention, there is provided an injection molding machine for performing injection by supplying pressure extraction from a hydraulic pump or an accumulator to an injection cylinder via a flow control valve. A load pressure control valve is provided in the oil passage between the flow control valve and the injection cylinder so as to be directly connected to the forward oil chamber of the injection cylinder, and the control of the primary injection stroke for injecting and filling the molten resin into the cavity is performed. The injection cylinder
Set according to the advance position of the piston rod of the
By speed control by the flow control valve based on constant speed
Speed priority control to be executed or the piston of the injection cylinder
Based on the set load pressure set according to the rod advance position,
Pressure to be performed by pressure control by the load pressure control valve.
Configuration with selection means to select between force priority control
It is said.

[0011]

[Function] A load pressure control valve consisting of an electromagnetic proportional relief valve for controlling the oil pressure supplied to the forward oil chamber of the injection cylinder is provided, and a flow control valve is used when manufacturing a molded product that emphasizes the filling pressure (load pressure). Is opened, and the primary injection stroke (injection / filling stroke) is controlled by the load pressure control valve based on each set load pressure set according to the advance position of the piston rod of the hydraulic cylinder regardless of the speed. Performed by control. Thereby, in the primary injection stroke section, the hydraulic pressure (load pressure) supplied to the injection cylinder is
Injection / filling is performed based on pressure control that matches the set load pressure, and the injection speed is indirectly controlled in a manner dependent on the load pressure. As a result, accurate control of the injection speed during the primary injection stroke (injection / filling stroke) cannot be performed, but the load pressure substantially follows the set load pressure in all sections of the primary injection stroke (injection / filling stroke). Medium and stable at all times, so that the filling pressure is stable (the resin pressure in the mold is stable), the density of the molded product is no longer uneven, the product weight accuracy is improved, and deformation such as warpage is generated. Can be suppressed as much as possible. That is, it is possible to manufacture thin products and the like with high quality and high yield. Also, even if the load reaction force (resin pressure) increases from just before the filling of the resin in the cavity (clogging), the hydraulic pressure (load pressure) supplied to the injection cylinder may exceed the set load pressure. (There is no excess filling pressure), and since the time from the start of the pressure-holding process to the time when the pressure-holding value is settled is stable, there is no burr or warpage, and the molded product density is generally stable. As a result, the quality of thin molded products and the like is improved.

On the other hand, when manufacturing a molded product that emphasizes the injection speed, the upper limit value of the load pressure control valve is set to the maximum, and the primary injection stroke (injection / filling stroke) is controlled by the flow control valve. , Irrespective of the load pressure, is executed by speed control based on each set speed set according to the forward position of the piston rod of the hydraulic cylinder. Thus, in the primary injection stroke section, injection / filling is performed based on speed control such that the forward speed of the piston rod of the injection cylinder matches the set injection speed. As a result, accurate control of the load pressure during the primary injection stroke (injection / filling stroke) cannot be performed, but the injection speed during the entire section of the primary injection stroke (injection / filling stroke) substantially follows the set speed. , Always stable to good, so the injection speed is stable to the end (the flow behavior of the molten resin in the mold is stable), the dimensional accuracy is stable, and the weld line and flow mark The occurrence of poor appearance can be suppressed as much as possible. That is,
It is possible to manufacture a molded product, such as a home electric appliance, in which dimensional accuracy and appearance are important, with a high yield.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is an explanatory diagram showing a hydraulic circuit of an injection cylinder system of an injection molding machine according to the present embodiment, and FIG. 2 is a diagram showing load pressure (pressure of a forward oil chamber of an injection cylinder 5) and injection during an injection / filling process. It is a graph which shows the relationship with speed.

In FIG. 1, 1, 2, 3, 4, 5, 5a
Is a hydraulic pump, a pressure control valve (electromagnetic proportional relief valve), a flow control valve, a direction switching valve, an injection cylinder (hydraulic cylinder), and a piston rod, each of which is equivalent to the configuration of FIG. Oil passage (oil passage on the downstream side as viewed from the flow control valve 3) between the cylinder 3 and the forward oil chamber of the injection cylinder 5
Is a load pressure control valve formed of an electromagnetic proportional relief valve installed in the control unit, and 7 is an injection stroke detection sensor (for example, an encoder) for detecting the position of the piston rod 5a.

The above-mentioned electromagnetic control valve groups 2, 3, 4, 6
The microcomputer (microcomputer), which is not shown, controls the entire machine, and is independently controlled via a driver circuit as appropriate. The speed (speed) of the flow control valve 3 is controlled according to a command from the microcomputer. ) And the upper limit pressure value of the hydraulic pressure by the pressure control valves 2 and 6 can be variably set, and the switching position of the direction switching valve 4 can be selected. The measurement data obtained by the injection stroke detection sensor 7 is taken into the above-mentioned microcomputer, and the injection stroke (position) is recognized.

Here, in the present embodiment, the load pressure control valve 6 is added and installed so as to be directly connected to the forward oil chamber of the injection cylinder 5 through an oil passage downstream of the flow control valve 3. Therefore, when injection / filling control in which priority is given to speed by the flow control valve 3 is not performed, the pressure control valve 2 is set to the maximum pressure and the flow control valve 3 is set to the maximum flow rate, so that the load pressure control valve 6 is variably set. It is possible to perform injection / filling (primary injection) control giving priority to the hydraulic pressure (load pressure) in accordance with the hydraulic pressure upper limit value. When injection / filling control in which the pressure by the load pressure control valve 6 is prioritized is not performed, the flow pressure control valve 3 is set by setting the load pressure control valve 6 to the maximum pressure.
It is possible to perform injection / filling (primary injection) control giving priority to the injection speed in accordance with the flow rate value variably controlled by (1). Next, the primary injection (injection / filling) operation based on the above configuration will be described.

<Primary injection operation giving priority to pressure (load pressure) control> When performing primary injection giving priority to pressure (load pressure) control, the microcomputer performs the pressure injection at least during the primary injection period. The control valve 2 is set at the maximum pressure, and the flow control valve 3 is set at the maximum flow rate.

At a predetermined time after the completion of the mold clamping, the direction switching valve 4 is switched from the neutral position to the left position, and the hydraulic oil from the hydraulic pump 1 is used to move the injection cylinder 5 forward. The oil is supplied to the oil chamber, whereby the screw (not shown) advances together with the piston rod 5a, and the molten resin also flows into the cavity (molding) between the molds which are also clamped from the nozzle at the tip of the heating cylinder (not shown). Space) begins to be injected and filled. This injection and filling process (1
During the next injection stroke), as shown in FIG. 2, each of the zones A, B,
The upper limit value of the load pressure control valve 6 is variably controlled by a command of the microcomputer based on the set load pressure preset for each of C and D and the forward position detection information from the injection stroke detection sensor 7. The injection / filling process by controlling the load pressure (the filling pressure, which is the injection pressure) is executed. That is, as shown in FIG. 2, in the injection / filling stroke (primary injection stroke) section, regardless of the injection speed, the injection / filling stroke is executed by pressure control almost following the set load pressure. Filling process (1
During the next injection stroke), the load pressure is made to match the set load pressure to maintain a stable filling pressure. When the injection / filling is performed based on the pressure control that matches the set load pressure, the injection speed is indirectly controlled in a manner dependent on the load pressure. Therefore, by setting the set load pressure to an arbitrary characteristic line, it is possible to obtain a desired injection speed curve which is not accurate but to some extent.

Then, the piston rod 5a is
When the injection stroke detection sensor 7 detects that the end position of the filling stroke section has been reached (it has reached the pressure holding switching point), the microcomputer enters a pressure holding stroke for performing time-based pressure control. The upper limit value of the load pressure control valve 6 is controlled to the set pressure value, and the pressure-holding process is performed for a predetermined time. At this time, the load pressure at the pressure holding switching point is always constant at a value substantially equal to the set load pressure at the end position of the injection / filling stroke section for each shot. time T ₁ of the pressure in the settled bear coercive pressure setpoint is becomes stable and shorter than conventional.

As described above, when the injection / filling (primary injection) process is performed by the load pressure priority control, the filling pressure during the injection / filling process is stabilized, and the filling pressure is set to an appropriate value even when the filling is completed. , And the time from when the pressure-holding process is started until the pressure-holding set value is settled is stabilized. Therefore, it is possible to produce a good molded product having a stable molded product density and free of warpage and burrs. It can be manufactured with good yield. In addition, the primary injection stroke (injection / filling stroke) and the subsequent secondary injection stroke (pressure-holding stroke) are both performed by pressure control (since the load pressure at the end of the primary injection stroke is constant). The setting of the switching point from the primary injection stroke to the secondary injection stroke does not require a very strict value, and the setting of the switching point from the primary injection stroke to the secondary injection stroke is simple and easy. Also, it is directly connected to the forward oil chamber of the injection cylinder.
A load pressure control valve is provided in the
Good response of injection cylinder pressure control by valve
become.

<Primary Injection Operation Prioritizing Injection Speed Control> When performing primary injection prioritizing injection speed control, the microcomputer controls the load pressure control valve 6 during the primary injection period.
Is set to the maximum pressure, during which the load pressure control valve 6
Is to function only as a simple safety valve to prevent line breakage.

At this time, the directional control valve 4 is similarly switched from the neutral position to the left position at a predetermined time after completion of the mold clamping, and the hydraulic oil from the hydraulic pump 1 is injected. A screw (not shown) is fed together with the piston rod 5a into a forward oil chamber of the cylinder 5, whereby the molten resin is moved forward integrally with the piston rod 5a. The cavity (molding space) between them starts to be injected and filled. In the injection / filling stroke (primary injection stroke), as shown in FIG. 4, the injection / filling section (injection stroke) is arbitrarily divided, and for example, is set in advance for each of the zones A ′, B ′, C ′. Based on the speed and the advance position detection information from the injection stroke detection sensor 7, the flow rate regulation value by the flow rate control valve 3 is variably controlled by the microcomputer command, thereby controlling the injection speed, thereby controlling the injection speed. Is executed. That is, as shown in FIG. 4, in the injection / filling stroke (primary injection stroke) section, regardless of the load pressure,
Injection and control by speed control that almost follows the set injection speed
The filling process is executed, so that the injection speed is made to coincide with the set speed until the end during the injection / filling process (primary injection process) to maintain a stable injection speed.

Thereafter, the piston rod 5a is ejected.
When the injection stroke detection sensor 7 detects that the end position of the filling stroke section has been reached (it has reached the pressure-holding switching point), the microcomputer similarly starts the pressure-holding process for performing time-based pressure control. Then, the upper limit value of the load pressure control valve 6 is controlled to a set pressure value, and a pressure holding process for a predetermined time is executed.

As described above, when the injection / filling (primary injection) process is performed by the speed priority control, the injection speed always follows the set speed during the entire section of the primary injection process (injection / filling process). It stabilizes to a good one and therefore the injection speed stabilizes to the end. For this reason, the flow behavior of the molten resin in the mold is stabilized, so that the dimensional accuracy is stabilized, and occurrence of appearance defects such as weld lines and flow marks can be suppressed as much as possible. That is, it is possible to manufacture a molded product, such as a home electric appliance, in which dimensional accuracy and appearance are important, with a high yield.

In the above embodiment, the hydraulic pump is used as the pressure oil supply source for injection. However, it is known to those skilled in the art that this can be replaced with an accumulator as a pressure oil supply source dedicated to injection. It is obvious.

[0026]

As described above, according to the present invention, primary injection
Move the entire stroke to the forward position of the injection cylinder piston rod.
Either the set speed or the set load pressure set according to
Speed priority control or pressure
Injection / filling (primary injection) that gives priority to filling pressure (load pressure) control for molded products that place importance on weight accuracy and prevention of deformation (such as warpage) because it is possible to select whether to perform it by prior control. ,
Injection / filling (primary injection), which gives priority to injection speed control for molded products that place emphasis on dimensional accuracy and appearance, can be selectively performed by the same machine, and is highly versatile with one machine it is possible to perform the molding and that do not. In addition, speed priority system
Control cylinder or pressure priority control.
Speed or pressure depending on the advance position of the piston rod
Setting and controlling the primary injection stroke, the primary injection stroke
Pressure changeover position to switch from
Point) is always constant, and stable continuous molding is performed.
be able to. Further, since the load pressure control valve is provided so as to be directly connected to the forward oil chamber of the injection cylinder, the responsiveness of pressure control of the injection cylinder by the load pressure control valve is also improved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a hydraulic circuit of an injection cylinder system of an injection molding machine according to one embodiment of the present invention.

FIG. 2 is a graph showing a load pressure and an injection speed during a primary injection stroke in a case where charging pressure (load pressure) control is prioritized according to one embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a hydraulic circuit of an injection cylinder system of an injection molding machine according to a conventional example.

FIG. 4 is a graph showing a conventional injection speed and load pressure during an injection / filling stroke.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hydraulic pump 2 Pressure control valve 3 Flow control valve 4 Direction switching valve 5 Injection cylinder 5a Piston rod 6 Load pressure control valve 7 Injection stroke detection sensor

Claims (1)

(57) [Claims] 1. An injection molding machine for performing injection by supplying pressure oil from a hydraulic pump or an accumulator to an injection cylinder via a flow control valve, wherein an oil path is provided between the flow control valve and the injection cylinder. A load pressure control valve is provided so as to be directly connected to the forward oil chamber of the injection cylinder, and the control of the primary injection stroke for injecting and filling the molten resin into the cavity is performed in front of the piston rod of the injection cylinder.
The flow rate control based on the set speed set according to the advance position
Speed priority control executed by speed control by the control valve,
According to the forward position of the piston rod of the injection cylinder
By the load pressure control valve based on the set load pressure set
Selection of pressure priority control executed by pressure control
An injection molding machine characterized by having a selecting means to perform the selection .