JPH0256986B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is an injection molding device such as a die casting machine or a plastic injection molding machine, and controls the injection speed by increasing or decreasing the flow rate of a fluid according to the opening degree of a flow control valve. This invention relates to an injection speed control method.

[Prior art]

Injection molding equipment such as die casting machines and injection molding machines for plastics performs molding by injecting molten metal or molten resin into the cavity of a closed mold using a plunger that moves forward and backward with an injection cylinder. is equipped with a flow control valve that controls the injection speed, that is, the flow rate of the working fluid.

FIG. 1 is a schematic cross-sectional view of a flow rate control valve and an injection cylinder shown to explain the injection method using this type of injection molding apparatus, and this is taken as an example when the injection molding apparatus is a die-casting machine. To explain, a pulse motor 3 attached to a casing 2 of a flow control valve 1 is connected to a screw shaft 4a of a ball screw 4 supported in the casing 2 by a coupling ring 5, and a ball screw 4 of the ball screw 4 is 4b
The nut 4c that is threadedly engaged with the screw shaft 4a through the
A spool 6 is integrally formed via a connecting rod 4d. The spool 6 is supported in a valve body 7 that is continuous with the casing 2 so as to be able to move forward and backward in the axial direction, and the valve body 7 has a hydraulic oil inlet 7a and a hydraulic oil outlet 7b.
The spool 6 also has a front chamber 7c of the valve body 7.
A plurality of communication holes 6a are provided in the valve body 7 to communicate with the rear chamber 7d, and a pair of communication grooves 7e and 7f, which are formed in an annular shape and communicate with the outlet 7b, are arranged in parallel in the axial direction. In addition, the communication hole 6a of the spool 6 is provided with a groove 6b that allows communication between the communication hole 6a and the communication groove 7f as the spool 6 moves. 8 is a position detector attached to the casing 2, 9 is a permanent magnet provided on the outer periphery of the nut 4c, and 10 is the nut 4c.
This is the key that controls the rotation of the An accumulator 14 is connected to the inlet 7b of the flow control valve configured as described above via a pipe 13 having an on-off valve 12 with a pilot valve 11, and a pipe 15 is connected to the outlet 7b. injection cylinder 16 through
is connected. A sleeve 17 is connected to a mold cavity (not shown) of the die-casting machine, and a piston rod 19 of the injection cylinder 16 is directly connected to a plunger 18 that moves back and forth within the sleeve 17.

The injection method of the die casting machine configured as above will be explained. Before the start of injection, the nut 4c has come out of the screw shaft 4a beyond the illustrated position, the spool 6 has moved forward to the left beyond the illustrated position, and the spool 6 closes the communication grooves 7e and 7f. . When a command to start injection is issued from this state and the pulse motor rotates by a predetermined angle, the screw shaft 4a connected by the coupling 5 rotates, and the nut 4c and the integrated spool 6 are moved to the right of the figure. retreat towards Therefore, the front chamber 7c and the communication groove 7e and the groove 6b and the communication groove 7f communicate with each other, and the hydraulic oil supplied from the accumulator 14 through the inlet 7a flows from the outlet 7b through the communicated flow path. It is supplied to the injection cylinder 16. The supply of hydraulic oil causes the piston rod 19 and the plunger 18 directly connected thereto to move forward, and the molten metal in the sleeve 17 is cast into the mold cavity.
At the initial stage of injection, the opening degree of the communication grooves 7e and 7f is small, the flow rate of hydraulic oil is small, and the injection speed is low. However, when injection continues and a command for high-speed injection is received to the pulse motor 3 after a predetermined time, the pulse motor 3 receives a high-speed injection command. , the pulse motor 3 rotates again, the spool 6 further retreats, and the opening degree of the communication grooves 7e, 7f increases, thereby increasing the flow rate of the hydraulic oil and increasing the injection speed. Furthermore, since the position detector 8 is sensitive to the movement of the permanent magnet 9 and accurately detects the moving distance of the spool 6 in the axial direction and provides feedback to the control device, the rotation angle of the pulse motor 3, that is, the opening of the spool 6 is detected. The injection speed is controlled correctly.

However, such an injection speed control method has a problem in stabilizing the injection speed at the initial stage of injection. In other words, if the spool 6 closes the communication grooves 7e and 7f before the start of injection, and the closing margin is small, the seal at this point will be incomplete, and the pilot pressure will be released to the drain at the start of injection, causing the opening and closing. When the valve opens, the pressure of the accumulator 14 is shockingly released, and the amount of pressure oil leaking from the incompletely sealed spool closing portion increases rapidly. As a result, the piston rod 19 of the injection cylinder 16 suddenly pops out, which disturbs the molten metal within the sleeve 17 and entrains air, which may deteriorate the quality of the molded product. However, in order to eliminate this, if a large closing margin is provided by the spool 6, even if the spool 6 begins to move due to the rotation of the pulse motor 3 following the opening of the on-off valve 12, the closing margin by the spool 6 will be opened. In the past, not only did it take a long time to open, but the response was poor, and the rise of the injection speed after opening was often unstable. That is, in general, the signal pulse that drives the spool 6 has already reached a fairly high frequency when the spool 6 begins to open, as shown in the relationship diagram between the spool opening degree and the frequency of the signal pulse in Fig. 2. Because of this, it is difficult to increase the injection speed of the injection cylinder 16 without impact. Further, as shown in FIG. 1, when the piston 20 of the injection cylinder 16 and the cylinder 21 are in close contact with each other, the pressure oil leaks from the outer periphery of the spool 6 and leaks into the center of the end surface of the piston 20. 23, the piston 20 moves forward slightly, but at this time, the outer circumferential portion 22 momentarily becomes a vacuum, and the pressure oil in the central portion 23 is rapidly sucked into the outer circumferential portion 22. Therefore, until the spool 6 opens and the piston 20 starts moving forward at a predetermined speed, the forward speed of the piston 20 slows down and the piston 20 vibrates back and forth. FIG. 3 is a graph showing the relationship between time and injection speed, and shows that the injection speed is disturbed and unstable at the time of startup.
In this way, in the conventional injection speed control method,
Even if the closing margin of the spool is increased, the injection speed becomes unstable at the initial stage of injection, resulting in a decrease in the quality of the molded product.

[Summary of the invention]

The present invention has been developed in view of the above-mentioned points.The present invention has been developed by moving the flow control valve in the closed state slightly in the opening direction to leak working fluid to the injection cylinder, and after maintaining this state for a certain period of time. By configuring the flow control valve to further open to a predetermined opening degree and supply a flow rate of working fluid corresponding to a predetermined initial injection speed to the injection cylinder, injection can be started quickly at a stable speed without impact. make it possible,
The present invention provides an injection speed control method for an injection molding apparatus that improves the quality of molded products by maintaining the melting temperature and preventing air from being drawn into the sleeve.
Embodiments of the present invention will be described in detail below with reference to the drawings.

〔Example〕

4a, b, and c show cross-sectional views of the main parts of the flow control valve and the injection cylinder for explaining the injection speed control method according to the present invention; FIG. 4a is a cross-sectional view when the spool is fully closed; Figure 4b is a cross-sectional view showing the spool moving slightly in the open direction while still in the closed state, causing hydraulic oil to leak, and Figure 4c shows the spool opening further and injection starting. The sectional view shown in FIG. 5 is a diagram showing the relationship between time and spool opening. Since the overall structure of the flow control valve has been explained based on FIG. 1, the explanation thereof will be omitted, and the explanation will be given later using the same figure when necessary. Before the start of the injection operation shown in FIG. 4a, the on-off valve 12 is closed with a large closing valve, the spool 6 is in the fully closed position, and its closing margin is indicated by the symbol _S1 . Further, the piston 20 of the injection cylinder 16 is retracted and the outer circumference of its end surface is in close contact with the inner surface of the cylinder 21, and the plunger 1 of the injection sleeve
8 is moving backwards. This embodiment exemplifies a die-casting machine as an injection molding apparatus, and a sleeve 17 joined to a cavity of a mold (not shown) is filled with molten metal injected.

When the on-off valve 12 is first opened in this state, the hydraulic oil in the accumulator 14 is supplied to the inlet port 7a at a predetermined pressure.
In this case, in this embodiment, the closing margin S ₁ is set as large as 2 to 3 mm, so that from the fitting part of the spool 6 and the valve body 7 corresponding to S ₁ Hydraulic oil does not leak and the piston 20 of the injection cylinder 16 does not move. When a command is given to the pulse motor 3 to start injection at the initial injection speed at the same time as opening the on-off valve 12 or after 0.3 to 0.5 seconds, the pulse motor 3 first rotates slightly by a predetermined angle as a first step, and then The motion is converted into axial motion by the ball screw 4 and transmitted to the spool 6. As a result, the spool 6 moves to the position shown in FIG. 4b and stops together with the pulse motor 3. The degree of closure at this time is indicated by the symbol _S2 in the figure, and the degree of closure _S2 is controlled as set by the position detector 8 detecting the movement of the permanent magnet 9 and providing feedback to the control position. Ru. Note that the degree of closure on the communication groove 7f side is also _S2 . In this way, the spool 6 and valve body 7
As the degree of closure decreases from _S1 to _S2 , the hydraulic oil in the front chamber 7c leaks from the closed section indicated by the symbol _S2 , and the leaked hydraulic oil flows into the communication grooves 7e and 7f.
and is supplied to the injection cylinder 16 through the outlet 7b. The supplied hydraulic oil pushes the center part 23 of the end face of the piston 20 and moves the piston 20 forward slightly, and at this moment, the outer peripheral part 22 of the end face becomes a vacuum and the hydraulic oil is rapidly sucked into the outer peripheral part 22 of the end face. However, at this time, the spool 6 is stationary at the closed position S ₂ and the hydraulic oil continues to leak, so this hydraulic oil fills the rear chamber of the cylinder between the end surface of the piston 20 and the inner surface of the cylinder 21. do. After this closing degree _S2 is maintained for a certain period of time, for example, 0.5 seconds, a command is sent to the pulse motor 3, which rotates further, and the spool 6 moves to open the communication grooves 7e and 7f.
begins to open. When this opening reaches a predetermined opening shown by reference numeral _S3 in FIG. 4c, for example 2 to 3 mm, the spool 6 stops and injection starts. That is, the front chamber 7
The hydraulic oil in c is throttled in the flow path with an opening degree of S ₃ and flows into the communication groove 7.
e, passes through the communication hole 6a and the groove 6b, is throttled by the flow path with the same opening degree _S3 , flows into the communication hole 7f, merges at the outlet 7b, and is supplied to the injection cylinder 16. . In this case, since the opening degree _S3 is set to be a flow rate corresponding to the low injection speed at the initial stage of injection, the piston 20 moves forward at this low injection speed, and the plunger 18 connected thereto
As a result, the molten metal in the sleeve 17 is cast into the cavity of the mold. When this low-speed injection continues for a predetermined period of time, a command for high-speed injection is given to the pulse motor 3, which rotates again, causing the spool 6 to move back further and the opening degree to be 7 to 10 mm, for example.
become. As a result, the injection speed is switched to a high speed, and the molten metal continues to be poured at this injection speed to complete the molding.

FIG. 5 is a diagram showing the relationship between time and valve opening, with time on the horizontal axis and valve opening on the vertical axis, where the solid line shows the method according to the present invention, and the dotted line shows the conventional method. This shows the case using the following method. As is clear from the figure, in the conventional method, the hydraulic fluid is opened for a period of, for example, 1 to 2 seconds, as indicated by the symbol _t2 in the figure.
After leaking to the injection cylinder 16 at S ₂ , low-speed injection is started while opening the opening to S _3. In contrast, in this method, as shown by the symbol t ₁ in the figure, for example,
After changing the opening degree from -S ₁ to -S ₂ in 0.5 seconds to leak hydraulic oil, the opening degree is increased to S ₃ and low-speed injection is started. Therefore, in this method, the time required from opening the on-off valve 12 to starting injection is less than half that of the conventional method, and the temperature drop in the molten metal is reduced. Also, with the hydraulic oil leaking to the rear chamber of the injection cylinder 16 at the opening degree -S ₂ , the movement of the spool 6 is momentarily stopped to fill the cylinder rear chamber with hydraulic oil, and then the opening degree _{is set to S3.} Since the injection is started at low speed, the piston 20 does not vibrate and the injection is started without impact. Furthermore, FIG. 6 is a relationship diagram between the opening degree of the spool and the frequency of the signal pulse shown corresponding to FIG. 2, and as is clear from the comparison with FIG. By the time the spool 6 begins to open, the frequency has already risen to a fairly high level, but with this method, the 0 point of the frequency can be matched with the beginning of the opening of the spool 6, so injection starts without any shock. be done.

In this embodiment, a die-casting machine is used as an example of the injection molding apparatus, but the present invention can also be applied to a plastic injection molding machine.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, in the injection speed control method for an injection molding apparatus,
Keep the flow control valve closed and move it slightly in the opening direction to leak working fluid to the injection cylinder.
After this state is maintained for a certain period of time, the flow rate control valve is further opened to a predetermined opening degree to supply a flow rate of working fluid corresponding to a predetermined initial injection speed to the injection cylinder. After the rear chamber of the injection cylinder is filled with leakage, injection starts at the same time as the signal pulse is sent, making it possible to perform an initial injection without any impact, and eliminating air entrainment into the injection sleeve. The quality of molded products is significantly improved. Furthermore, since the time from the opening of the on-off valve to the start of injection is shorter than before, the temperature of the molten metal and molten resin does not drop, further improving the quality of the molded product.

[Brief explanation of the drawing]

Fig. 1 is a schematic sectional view of a flow rate control valve and an injection cylinder to explain the injection speed control method, Fig. 2 is a relationship diagram between the spool opening and signal pulse frequency in the conventional injection speed control method, and Fig. Figure 3 is a diagram of the relationship between time and injection speed, Figure 4 a, b,
4c shows a schematic sectional view of the flow control valve main part and the injection cylinder to explain the injection speed control method of the injection molding apparatus according to the present invention, FIG. 4a is a sectional view when the spool is fully closed, and FIG. Fig. 4b is a cross-sectional view showing the spool remaining in the closed state and moving slightly in the opening direction, causing hydraulic oil to leak; Fig. 4c is a cross-sectional view showing the spool opening further and injection starting. , FIG. 5 is a diagram showing the relationship between time and the spool opening, and FIG. 6 is a diagram showing the relationship between the spool opening and the signal pulse frequency. 1...Flow control valve, 6...Spool, 7...Valve body, 7a...Inflow port, 7b...Outflow port,
7e, 7f... Communication groove, 16... Injection cylinder.

Claims (1)

[Claims] 1. The valve spool in the flow control valve, which controls the injection speed by increasing or decreasing the flow rate of working fluid supplied to the injection cylinder according to the opening degree, is changed from the closed state before injection starts to the closed state but only by a predetermined amount. It is moved in the opening direction to leak working fluid to the injection cylinder, and after this state is maintained for a certain period of time, it is further opened to a predetermined opening degree to supply working fluid at a flow rate corresponding to the initial injection speed to the injection cylinder. A method for controlling the injection speed of an injection molding device.