JPH0451260B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a device for controlling the piston speed of an injection cylinder that advances a plunger tip of a shot plunger in an injection molding device such as a die casting machine or an injection molding machine. be.

[Prior Art] In general, in injection molding using die casting machines, etc., depending on the shape and volume of the cavity in the mold, the temperature of the mold, etc., if the injection speed, injection pressure, etc. of the molten metal are inappropriate, the injection molding into the cavity may occur. The hot water supply is poor.
Various problems occur, such as chipping, cavities in the injection molded product, and reductions in dimensional accuracy and product strength.

In order to prevent these adverse effects, conventionally, a meter-in circuit is used in which a flow control valve is installed in the hydraulic oil inflow circuit to the piston rear chamber of the injection cylinder, or a meter-out circuit is installed in which a flow control valve is installed in the hydraulic oil outflow circuit from the piston front chamber. The piston speed of the injection cylinder, that is, the injection speed of the molten metal is controlled by a circuit or the like.

For example, the basic circuit in the meter-in circuit is as shown in FIG. It has an inflow circuit 16 and an outflow circuit 17 that returns from the piston front chamber 23 of the injection cylinder 20 to the oil tank 15 through the switching valve 12, and the flow rate control valve 14 controls the amount of hydraulic oil flowing into the piston rear chamber 22. By controlling the piston 21, the forward speed of the piston 21, that is, the forward speed of the plunger tip 29 within the injection sleeve 28 is controlled, thereby determining the injection speed of the molten metal.

Further, as shown in FIG. 2, there is also a meter-in circuit that constitutes a run-around circuit 18 that communicates from the piston front chamber 23 of the injection cylinder 20 to the piston rear chamber 22.

By the way, the inventors of the present invention have proposed a method to replace the conventional flow control valve 14 that controls the injection speed of molten metal, that is, the amount of hydraulic oil flowing into or out of the injection cylinder 20. Recently, we developed a flow control valve 30 with high-speed response driven by a pulse motor (Utility Model Application No. 102.878/1987).

As shown in FIG. 3, this flow rate control valve 30 is a valve that moves in the axial direction and is housed in a valve body 33 having a hydraulic oil inlet 31 from the axial direction and a hydraulic oil outlet 32 perpendicular to the axis. Spool 34
is provided. Furthermore, a nut shaft 35 is integrally connected to the rear part of the valve spool 34, and a threaded shaft 36 is connected to a ball screw 37 at the inner shaft center of the nut shaft 35.
are screwed together. This screw shaft 36 rotates by being connected via a coupling 38 to the rotation shaft of a pulse motor 41 whose rotation amount can be controlled.

Note that 45 is a key that prevents rotation of the nut shaft 35, and a permanent magnet 46 is fixed to a part of the surface of the nut shaft 35, and a zero cross sensor is attached to a part of the casing 47 facing the permanent magnet 46, for example. A position detector 48 based on magnetic action called . The position detector 48 is composed of a proximity switch that is sensitive to the movement of the permanent magnet 46, and is connected to the nut shaft 3.
5 and the valve spool 34 in the axial direction can be accurately detected and feedback can be provided to the control. Also, the zero position of the valve spool 34 is set to the permanent magnet 4.
6 and the position detector 48, the pulse motor 41 can be stopped accurately at that position via the control device, and the position detector 48 has a high accuracy. 0.01mm is used.

In this flow rate control valve 30, a valve spool 34 moves back and forth in the axial direction via a ball screw 36 and a nut shaft 35 in accordance with the rotation of a pulse motor 41, and instantaneously adjusts the opening/closing and opening degree of the valve. Perform flow control.

As described above, this flow control valve 30 has a valve spool 34 connected to a pulse motor 41 within a cylindrical valve body 33 that has a hydraulic oil inlet 31 on the end surface in the axial direction and a hydraulic oil outlet 32 on the side surface. The valve spool 34 is driven in the axial direction by the operation of the valve spool 34 to control the flow rate, and the flow rate is controlled by rapidly reducing the axial thrust of the valve spool 34 caused by the hydraulic oil in accordance with the increase in the opening amount and movement speed of the valve spool 34. The driving force required for high-speed switching of the hydraulic oil is further improved, and the driving force is also reduced.

Therefore, in this flow rate control valve 30, the amount of rotation of the pulse motor 41 is controlled by the command signal from the control device.
That is, the rotation angle determines the opening amount of the valve spool 34, which controls the flow rate of hydraulic oil to the injection cylinder 20, and the speed of rotation of the pulse motor 41 determines the acceleration/deceleration characteristics of the change in opening of the flow control valve 30. , the rate of change of the hydraulic oil flow rate, i.e., injection cylinder 2
The rising state of the injection speed at 0 is determined. The flow control valve 30 having such a structure and operation can suppress the time delay until the valve spool 34 starts opening upon receiving a command to change the injection speed to less than 1 millisecond, which is faster than a normal flow control valve. However, the responsiveness was extremely good, and the operability and operational accuracy of valve opening and closing were extremely high.

In this way, it is possible to control the hydraulic oil extremely quickly and accurately, and by using the flow control valve 30 that can also control the rate of change when controlling the flow rate of the hydraulic oil, the injection speed of the molten metal can be controlled even more accurately. As shown by the solid line in FIG. 4, it became possible to finely control changes in the injection speed of the molten metal.

The injection speed of the molten metal controlled by the flow rate control valve 30 having such high-speed response has a low injection speed section _T1 in the first half, and the molten metal filled in the injection sleeve is pushed into the cavity at a low injection speed _V1 . At the initial stage _T5 of the low-speed injection section _T1 , the speed is gradually increased to the low injection speed _V1 , so that the molten metal filled in the injection sleeve is jetted out of the injection sleeve from the molten metal inlet of the injection sleeve. prevent Then, at the final stage _T6 of the low-speed injection section _T1 , the injection speed _V1 is once decelerated, and when the molten metal reaches the cavity entrance, the molten metal is ejected from the narrow gap into the cavity, which is a relatively wide space. This prevents the gas (air) in the cavity from mixing with the molten metal, eliminating the risk of forming cavities in the product.

After the molten metal reaches the cavity inlet and slightly flows into the cavity, the injection speed is increased all at once or in stages at a high-speed injection speed V ₂ as a cavity filling section T ₂ to fill the molten metal into the cavity.
Prevents missing products and loss of dimensional accuracy. still,
At the time t ₀ when the injection of the filling section T ₂ is completed, the cavity is filled with molten metal, and the injection speed suddenly drops to zero.
The cylinder pressure at this time completely fills every corner of the cavity with the molten metal. Then, depending on the size or shape of the cavity, the final injection speed V ₃ is kept lower than the high-speed injection speed V ₂ , thereby reducing the impact pressure at t ₀ at the completion of injection, such as when the injection molded product is thin. Another method is to prevent burrs from blowing on the product due to the molten metal flowing into the mating surface of the mold due to the cylinder pressure.

[Problems to be Solved by the Invention] Incidentally, the total injection time of the molten metal is generally as short as several seconds, and in particular, the rise time and fall time that change the injection speed are extremely short, ranging from several hundredths of a second to several tens of hundredths of a second. It is something.

Therefore, increasing or decreasing the injection speed requires extremely quick response and accurate speed control.

However, when the above-mentioned meter-in circuit is used to control the injection speed of the molten metal, a characteristic occurs in which a time delay occurs at the falling edges S ₁ and S ₂ as shown by the broken line in FIG.

This is due to the large inertia due to the kinetic energy of the mechanically moving parts such as the piston 21 and cylinder rod 26 and the hydraulic oil, and also because of the falling time as described above.
This is a drawback in that S ₁ and S ₂ are extremely short, so deceleration is not performed as specified, which deteriorates the quality of the injection molded product.

[Means for Solving the Problems] In the present invention, in a piston speed control device for an injection cylinder or the like of an injection molding device, a high-speed injection speed control device for adjusting and determining a low-speed injection speed and a high-speed injection speed is provided in a hydraulic oil inflow circuit to a piston rear chamber. In addition to providing a responsive first flow control valve, a second flow control valve having high-speed responsiveness is also provided in the hydraulic oil outflow circuit from the piston front chamber, and the opening degree of the first flow control valve is reduced. When the opening degree of the second flow control valve is decreased, and when the opening degree of the first flow control valve is increased, the opening degree of the second flow control valve is decreased.
A control valve control device is provided that changes the opening degree of the second flow control valve in proportion to the opening degree of the first flow control valve so as to increase the opening degree of the flow control valve.

[Function] Since the present invention provides the first flow control valve with high-speed response in the hydraulic oil inflow circuit to the piston rear chamber, the first flow control valve can control the low injection speed, the high injection speed, and the acceleration of the injection speed. and deceleration can be controlled.

Furthermore, since the hydraulic oil outflow circuit from the piston rear chamber is also provided with a second flow control valve having high-speed response, it is possible to control the amount of hydraulic oil discharged from the piston front chamber. The opening degree of the flow control valve is
Since a control valve control device is provided that is proportional to the opening of the flow control valve, when the opening of the first flow control valve is increased to increase the forward speed of the piston, the opening of the second flow control valve is also increased. When reducing the opening of the first flow control valve to reduce the forward speed of the piston, the second flow control valve is used. The degree of opening of the piston is also reduced to increase resistance to the flow of hydraulic oil from the front chamber of the piston, thereby making it possible to perform deceleration reliably and quickly.

[Embodiment] As shown in FIGS. 5 and 6, in an embodiment of the present invention, a first flow control valve 30 having high-speed response is provided in the hydraulic oil inflow circuit 16 to the piston rear chamber 22, and the piston Hydraulic oil outflow circuit 17 from the front chamber
A similar second flow control valve 50 is provided in the second flow control valve 50, and the opening degree of the second flow control valve 50 is changed in accordance with the opening degree of the first flow control valve 30, thereby controlling the injection speed of the molten metal. This is a piston speed control device for an injection molding machine.

Providing the second flow control valve 50 in the outflow circuit 17 in this way has been found by the present inventor to be difficult to maintain high quality due to the time delay during deceleration, as a result of detailed measurement and investigation of the relationship between injection speed and product quality. As mentioned above, this time delay is due to the large inertia of the mechanically moving parts and the hydraulic oil, and the piston 21 is caused by external forces such as the load on the cylinder rod 16, frictional force of the sliding part, and resistance to outflow of the hydraulic oil. This is to analyze the fact that the time delay is based on the time required for the inertia to be canceled out by the fluid pressure applied to the cylinder front surface 25, etc., and to enable deceleration in an extremely short time.

That is, if only the essential parts of the meter-in circuit shown in FIG. 1 are shown in FIG. 7, the flow rate control valve 14 limits the amount of hydraulic oil flowing into the piston rear chamber 22 per unit time. The piston 21, the cylinder rod 26, and eventually the plunger tip 29 move forward in accordance with the amount of inflow.

At this time, due to the resistance of the molten metal etc. injected into the cavity by the plunger 29, the cylinder rod 2
6 is applied with a load _F1 , and the frictional force _F2 of the sliding parts such as the piston 21 and the reaction that the piston 21 receives from the hydraulic oil to discharge the hydraulic oil in the piston front chamber 23 as the piston 21 moves forward. A force F ₃ arises,
These forces F ₁ , F ₂ , and F ₃ inhibit the piston 21 from moving forward.

However, although the load F ₁ due to the resistance of the molten metal is large when the injection speed is increased, it cannot be a large load when the injection speed is decelerated, and the frictional force F ₂ on the sliding part is also extremely small. Also, piston 2
The reaction force F ₃ that 1 receives from the hydraulic oil is also usually a small value. For this reason, it takes time for the inertia of the moving parts and hydraulic oil to be canceled out, and as shown by the broken line in Figure ₄ , there is a time delay when the injection speed slows down, resulting in a time lag when the injection speed _decreases , and the quality of the injection molded product is affected. cause a decline.

Also, in FIG. 8, which shows only the main part of FIG. 2, which is a meter-in circuit having a run-around circuit 18, the load _F1 applied to the cylinder rod 26, the frictional force _F2 of the sliding part, and the hydraulic oil are transferred to the piston front chamber 23. When moving from the piston to the rear chamber 22, the piston 21
The reaction force F ₃ received from the hydraulic oil is small as in the case of the basic meter-in circuit shown in FIG. 7, and a time delay occurs when the injection speed is decelerated.

Incidentally, the cylinder 2 having the run-a-land circuit 18
0, the area of the piston rear surface 24 is equal to the area of the piston front surface 25 plus the cross-sectional area of the piston rod 26, so a force equal to the cross-sectional area of the piston rod 26 multiplied by the hydraulic oil pressure _P2 is applied to the piston rear surface 24. and move the piston rod 26 forward,
An amount of hydraulic fluid equal to the volume obtained by multiplying this advance distance by the cross-sectional area of the piston rod is supplied to the piston rear chamber 22 through the flow control valve 14.

In this way, in the conventional meter-in circuit, there is a time delay in response to rapid deceleration, so in the present invention, the second flow control valve 50 is provided in the outflow circuit from the piston front chamber 23, and as the piston 21 moves forward, The reaction force F ₃ that the piston 21 receives from the hydraulic oil provides resistance to the outflow of the hydraulic oil discharged from the chamber 23.
By increasing the value appropriately and using it as a brake during deceleration, rapid deceleration was made possible.

In this embodiment, as described above, the first flow control valve 30 is provided in the inflow circuit 16 to the piston rear chamber 22, and the second flow control valve 50, which is linked to the opening and closing of the first flow control valve 30, is provided in the piston front chamber 22. This is an injection speed control device provided in the outflow circuit 17 from the piston, and since the first flow control valve 30 is provided in the inflow circuit 16, the amount of hydraulic oil flowing into the piston rear chamber 22 is controlled by the flow control valve 30. At the same time, the hydraulic pressure in the rear chamber of the piston in the filling section T ₂ injected at a high injection speed V ₂
P ₂ also becomes lower than the oil pressure P ₁ in the oil pressure source 11, as shown in FIG.

On the other hand, in the speed control of the cylinder 20, in the meter-out circuit, which has been widely used in the past along with the above-mentioned meter-in circuit, the pressure of the hydraulic source 11 is applied to the piston rear chamber 22 as shown in FIGS. 9 and 10.
Since the forward speed of the piston 21 is controlled by directly applying P ₁ and controlling the amount of oil discharged from the piston front chamber 23, injection is performed at a low injection speed section T ₁ and a high injection speed as shown in FIG. The oil pressure in the piston rear chamber 22 also becomes equal to the oil pressure P ₁ of the oil pressure source 11 in the filling period T ₂ . For this reason,
When the impact pressure P ₃ at the time of completion of injection t ₀ is applied, a large abnormally high pressure P ₅ is generated even for a short period of time.

In contrast to such a meter-out circuit, in the device having the circuit according to this embodiment, the filling interval is
The oil pressure P ₂ in the piston rear chamber 22 at T ₂ is the oil pressure source
Since it is lower than P ₁ , even when impact pressure P ₃ is applied, the peak value of abnormally high pressure is low and has the advantage that there is no risk of adversely affecting the hydraulic circuit system.

Note that when the opening degree change of the first flow control valve 30 and the opening degree change of the second flow rate control valve 50 used in this embodiment are made equal, the second flow rate control valve 50 is equal to the first flow rate control valve 30. By using flow control valves of the same size and structure with high-speed response, the injection speed can be controlled extremely accurately.

In short, in this embodiment, in a piston speed control device for an injection cylinder 20 or the like of an injection molding apparatus, a first flow control valve 30 having high-speed response is provided in an inflow circuit 16 to a piston rear chamber 22, and a A second flow rate control valve 50 having high-speed response is also provided in the outflow circuit 17, and the opening degree of the second flow rate control valve 50 is changed in proportion to the opening degree of the first flow rate control valve 30. Since this is a piston speed control device for an injection molding machine equipped with a control valve control device, it is possible to rapidly decelerate the piston 21, the cylinder rod 26, and even the plunger tip 29 during high-speed movement. This is a piston speed control device that instantly accelerates and decelerates as it is used, making it possible to manufacture high-quality injection molded products.

Note that a first flow control valve 30 is provided in the hydraulic oil inflow circuit 16 to the piston rear chamber 22 of the cylinder 20,
Conventionally, when the second flow rate control valve 50 is provided in the hydraulic oil outflow circuit 17 from the piston front chamber 23, the opening degree of the second flow rate control valve 50 on the outflow side is kept constant at a large opening degree. When the opening degree of the first flow control valve 30 on the side is decreased and low-speed injection is performed, the pressure does not build up much and if something puts resistance on the piston rod 26, the speed will decrease, and if the resistance disappears. , the speed increases, thus the speed fluctuates and the low speed wanders.

However, in the present invention, when performing low-speed injection, the opening degree of the first flow rate control valve 30 on the inflow side is reduced, and the opening degree of the second flow rate control valve 50 on the outflow side is decreased to the first degree. Since the flow rate control valve 30 is made smaller in proportion to its opening degree, resistance is always applied, so even if the resistance of the piston rod 26 changes, the overall resistance changes less and the injection speed does not change. ,Stabilize.

Of course, in the case of high-speed injection, the opening degree of the first flow rate control valve 30 on the inflow side is increased, and the opening degree of the second flow rate control valve 50 on the outflow side is also increased depending on the opening degree of the first flow rate control valve 30. Because it increases in proportion to the
There is no resistance on the outflow side and the required high injection speed can be obtained.

[Effects of the Invention] The present invention provides a piston speed control device for an injection cylinder or the like of an injection molding device, in which a first flow control valve having high-speed response is provided in a hydraulic oil inflow circuit to a piston rear chamber, and A second flow control valve having high-speed response is provided also in the hydraulic oil outflow circuit from the hydraulic oil outflow circuit, and the control valve changes the opening degree of the second flow control valve in proportion to the opening degree of the first flow control valve. Since this is a piston speed control device for an injection molding machine equipped with a control device, two flow control valves with high-speed response are used, and the hydraulic oil in the outflow circuit is controlled according to the speed of the piston controlled by the first flow control valve. When decelerating the speed of the piston, the outflow resistance can be increased appropriately using the second flow control valve to increase the reaction force F ₃ that the piston of the injection cylinder receives from the hydraulic oil. Therefore, the injection speed can be rapidly decelerated, and when the forward speed of the piston is increased, the outflow resistance can be reduced, so the injection speed can be rapidly accelerated, and the injection speed can be rapidly accelerated within a short injection time. It is possible to accurately control changes such as sudden acceleration and deceleration of the injection speed, and manufacture high-quality injection molded products.In addition, by keeping the peak pressure of impact pressure low at the time of completion of injection, it is possible to reduce the impact on the hydraulic circuit. This piston speed control device has various advantages such as being able to prevent adverse effects.

Furthermore, in the present invention, even when performing low-speed injection,
The opening degree of the first flow control valve on the inflow side is made small, and the opening degree of the second flow control valve on the outflow side is made small in proportion to the opening degree of the first flow control valve, so that the resistance is reduced. is always applied, so even if the resistance of the piston rod changes, the fluctuations in the overall resistance will be small, and the injection speed will remain stable because it will not fluctuate.

Of course, for high-speed injection, the opening of the first flow control valve on the inflow side is increased, and the opening of the second flow control valve on the outflow side is also proportional to the opening of the first flow control valve. Since the injection size is made larger, there is no resistance on the outflow side, and the required high injection speed can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a general example of a meter-in circuit, Fig. 2 is a diagram showing a general meter-in circuit having a run-a-land circuit, and Fig. 3 is a diagram showing an example of a flow control valve used in the present invention. FIG. 4 is a diagram showing an example of changes in injection speed in injection molding.
5 and 6 are diagrams showing the main parts of the hydraulic circuit of the control device according to the present invention, FIGS. 7 and 8 are diagrams showing the main parts of a general meter-in circuit, and FIGS. FIG. 10 is a diagram showing the essential parts of a general meter-out circuit, FIG. 11 is a diagram showing the cylinder oil pressure in the present invention, and FIG. 12 is a diagram showing the cylinder oil pressure in the meter-out circuit. 11... Hydraulic source, 12... Switching valve, 14... Control valve,
16... Inflow circuit, 17... Outflow circuit, 18... Run-a-land circuit, 20... Injection cylinder, 21... Piston, 22... Piston rear chamber, 23... Piston front chamber,
26...Cylinder rod, 28...Injection sleeve, 2
9... Plunger tip, 30... First flow control valve,
50...Second flow rate control valve.

Claims (1)

[Claims] 1. In a piston speed control device for an injection cylinder or the like of an injection molding device, a first flow control valve with high-speed response for adjusting and determining a low injection speed and a high injection speed is provided in the hydraulic oil inflow circuit to the piston rear chamber, and the piston A second flow control valve having high-speed response is provided also in the hydraulic oil outflow circuit from the front chamber, and when the opening of the first flow control valve is reduced, the opening of the second flow control valve is reduced. However, when the opening degree of the first flow control valve is increased, the opening degree of the second flow control valve is increased in proportion to the opening degree of the first flow control valve. 1. A piston speed control device for an injection molding apparatus, characterized in that a control valve control device for changing the speed is provided.