Hydraulic Stability System of Injection Molding Machine

Abstract

The present invention provides an injection molding machine hydraulic stability system, which includes an electro-hydraulic proportional pressure control valve, a pressure control check valve, an oil inlet port and a control oil circuit; the oil inlet port includes an oil inlet P port; the input end of the electro-hydraulic proportional pressure control valve is connected to the output end of the pressure control check valve and the oil inlet P port, and the input end of the pressure control check valve is connected to the output end of the electro-hydraulic proportional pressure control valve; the output end of the electro-hydraulic proportional pressure control valve is connected to the control oil circuit; the mold opening and closing control oil circuit includes a second three-position four-way directional control valve, a first balance valve and a pilot-operated check valve; the guiding boost control oil circuit includes a third three-position four-way directional control valve, a first check valve and an electronic ball valve. With the structure of the present invention, the problem of large instantaneous impact on the pipeline caused by excessive pressure in the injection molding machine hydraulic system can be solved; by increasing the back pressure and enhancing the clamping force, the problem of unstable mold closing is solved.

Description

Technical Field

[0001] The present invention relates to the field of hydraulic control of injection molding machines, and particularly to a hydraulic stability system for injection molding machines. Background Art

[0002] In a hydraulic system, when the oil circuit is suddenly closed or reversed, a sharp pressure rise will occur, and this phenomenon is called hydraulic shock. The main reasons for hydraulic shock are the sudden change of hydraulic velocity, the inertial force of high-speed moving working parts, and the insufficient sensitivity of some hydraulic components in reaction actions. When the oil in the conduit moves at a certain velocity, if the flow channel of the oil is suddenly cut off at a certain moment (such as closing a valve), the flow velocity of the oil will suddenly drop to zero from a certain value at a certain moment. At this time, the kinetic energy of the oil flow will be converted into the extrusion energy of the oil, thus causing a sharp increase in pressure and resulting in hydraulic shock. The inertial force of high-speed moving working parts will also cause pressure shock in the system. For example, when the cylinder component needs to be reversed, the reversing valve quickly closes the original oil discharge pipeline of the cylinder. At this time, the oil no longer discharges, but the piston still moves due to inertia, thus causing a sharp rise in pressure and resulting in pressure shock. In the hydraulic system, due to the insufficient sensitivity of some hydraulic components, such as the inability to open the oil circuit in time, it will also cause a rapid increase in pressure to form shock.

[0003] An injection molding machine is a special plastic molding machine that melts plastic and then injects it into a mold for molding. However, after the plastic is injected, the mold needs to be held under pressure for a period of time to ensure the qualified rate of plastic products. Generally, for two-stage injection molding machines, due to the process requirements of pipe fittings products, the injection holding pressure time is relatively long. The common practice in the industry is to use a separate small motor or an accumulator for holding pressure, which increases the machine cost. In addition, using a separate small motor for long-term holding pressure is likely to cause the motor to be overloaded too high, affecting the service life of the motor. And for accumulator holding pressure, since the process of discharging pressure oil is not easy to control, it is likely to cause too large an instantaneous impact on the pipeline. Summary of the Invention

[0004] The present invention provides a hydraulic stability system for an injection molding machine with stable hydraulic oil circuit of the injection molding machine. Using the structure of the present invention, it can prevent the hydraulic stability system of the injection molding machine with large instantaneous impact on the pipeline caused by too high pressure, solve the problems of holding pressure of the hydraulic oil circuit of the injection molding machine and large instantaneous impact on the pipeline caused by too high pressure. At the same time, by increasing the back pressure and enhancing the clamping force, the problem of unstable mold closing is solved.

[0005] To achieve the above object, the technical solution of the present invention is: a hydraulic stability system for an injection molding machine, characterized in that: it includes an electro-hydraulic proportional pressure control valve, a pressure control check valve, an oil inlet port, and a control oil circuit;

[0006] The oil inlet port includes an oil inlet P port;

[0007] The input end of the electro-hydraulic proportional pressure control valve is connected to the output end of the pressure control check valve and the oil inlet P port. The input end of the pressure control check valve is connected to the output end of the electro-hydraulic proportional pressure control valve. The output end of the electro-hydraulic proportional pressure control valve is connected to the control oil circuit.

[0008] The control oil circuit mentioned above includes the mold opening and closing control oil circuit, the pilot boosting control oil circuit, and the injection control oil circuit.

[0009] The mold opening and closing control oil circuit includes a second three-position four-way directional control valve, a first balance valve, and a hydraulic control check valve. The oil inlet of the second three-position four-way directional control valve is connected to the output end of the electro-hydraulic proportional pressure control valve. The oil return port of the second three-position four-way directional control valve is connected to the oil tank through a cooler. The first oil port of the second three-position four-way directional control valve is connected to the MC port of the mold opening and closing cylinder. The second oil port of the second three-position four-way directional control valve is connected to the output end of the first balance valve. The input end of the first balance valve is connected to the input end of the hydraulic control check valve. The output end of the hydraulic control check valve is connected to the MO port of the mold opening and closing cylinder. The first oil port of the second three-position four-way directional control valve is respectively connected to the control ends of the first balance valve and the hydraulic control check valve.

[0010] The pilot boosting control oil circuit includes a third three-position four-way directional control valve, a first check valve, and an electronic ball valve. The oil inlet of the third three-position four-way directional control valve is connected to the output end of the electro-hydraulic proportional pressure control valve. The oil return port of the third three-position four-way directional control valve is connected to the oil tank through a cooler. The first oil port of the third three-position four-way directional control valve is connected to the pilot cylinder. The second oil port of the third three-position four-way directional control valve is connected to the input end of the first check valve. The output end of the first check valve is connected to the boosting cylinder. The output end of the first check valve is connected to the output end of the electronic ball valve. The input end of the electronic ball valve is connected to the oil tank.

[0011] The injection control oil circuit mentioned above includes a fourth three-position four-way directional control valve, a relief valve, a pilot-operated relief valve, a two-position two-way directional control valve, a pressure reducing valve, a second check valve, and a third check valve. The oil inlet of the fourth three-position four-way directional control valve is connected to the output end of the electro-hydraulic proportional pressure control valve. The oil return port of the fourth three-position four-way directional control valve is connected to the input end of the relief valve. The first oil port and the second oil port of the fourth three-position four-way directional control valve are connected to the injection cylinder. The output end of the relief valve is connected to the oil tank. The control end of the relief valve is connected to the control oil circuit. The input end of the pilot-operated relief valve is connected to the control oil circuit. The output end of the pilot-operated relief valve is connected to the oil tank. The input end of the two-position two-way directional control valve is connected to the output end of the electro-hydraulic proportional pressure control valve. The output end of the two-position two-way directional control valve is connected to the input end of the pressure reducing valve. The output end of the pressure reducing valve is connected to the input end of the second check valve. The output end of the second check valve is connected to the output end of the third check valve. The input end of the third check valve is connected to the oil tank through a cooler. One end of the injection cylinder is connected between the second check valve and the third check valve.

[0012] The above-mentioned hydraulic stability system of the injection molding machine supplies oil to the oil inlet P through a hydraulic pump. The hydraulic oil is regulated in pressure by an electro-hydraulic proportional pressure control valve and then input into the control oil circuit. When the pressure of the hydraulic oil output by the electro-hydraulic proportional pressure control valve exceeds the pressure of the pressure control check valve, the excess hydraulic oil returns from the pressure control check valve to the oil inlet P, and the extra hydraulic oil is directly replenished to the input end of the electro-hydraulic proportional pressure control valve. In this way, it can avoid the loss caused by the excess hydraulic oil returning to the oil tank and then entering the oil inlet P, thereby improving the energy utilization rate. The guiding cylinder is arranged between the moving platen and the injection seat. During mold closing, the second three-position four-way directional control valve is switched, and at the same time, the third three-position four-way directional control valve is switched. The hydraulic oil at the output end of the electro-hydraulic proportional pressure control valve is divided into two paths. One path enters the MC port of the mold closing and opening cylinder through the second three-position four-way directional control valve. At this time, the first balance valve and the hydraulic control check valve are fed with oil at the control end, and the hydraulic control check valve opens. The hydraulic cylinder of the mold closing and opening cylinder returns to the oil tank from the MO port through the hydraulic control check valve, the first balance valve, the second three-way four-way directional control valve and the cooler. The other path of hydraulic oil enters the guiding cylinder through the third three-position four-way directional control valve, and the moving platen is guided through the guiding cylinder. When the mold closing is completed, the third three-position four-way directional control valve is switched, and the hydraulic oil enters the boosting cylinder through the third three-position four-way directional control valve, and the mold closing and pressure holding pressure are increased through the boosting cylinder to ensure the reliability of injection molding pressure holding. The fourth three-position four-way directional control valve is switched, and the hydraulic oil at the output end of the electro-hydraulic proportional pressure control valve enters the EB port of the injection cylinder through the fourth three-position four-way directional control valve, and the return oil of the injection cylinder returns to the oil tank through the EF port, the fourth three-position four-way directional control valve and the overflow valve. When the fourth three-position four-way directional control valve is switched to another position, it supplies oil to the control oil circuit, and the oil pressure of the control oil circuit is controlled by a pilot-operated overflow valve. At this time, oil is supplied to the control oil of the overflow valve, and at the same time, the two-position two-way directional control valve is switched. The hydraulic oil at the output end of the electro-hydraulic proportional pressure control valve enters the EF port of the injection cylinder through the fourth three-position four-way directional control valve, and the return oil of the injection cylinder returns to the oil tank through the EB port, the fourth three-position four-way directional control valve and the overflow valve. At the same time, the output end of the electro-hydraulic proportional pressure control valve is depressurized by a pressure reducing valve through the two-position two-way directional control valve and provides back pressure to the return oil of the injection cylinder through the second check valve to offset the weight of the injection system. In the present invention, due to the setting of the pressure control check valve, the excess hydraulic oil returns to the oil inlet P, so it can ensure the stability of the hydraulic oil pressure in the control oil circuit and solve the problem of large instantaneous impact on the pipeline caused by too high pressure in the hydraulic system of the injection molding machine. At the same time, back pressure is provided to the return oil of the injection cylinder through the two-position two-way directional control valve, depressurized by a pressure reducing valve and through the second check valve to offset the weight of the injection system, making the injection more stable.

[0013] Further, the control oil circuit includes a thimble control system. The thimble control system includes a first three-position four-way directional control valve. The oil inlet of the first three-position four-way directional control valve is connected to the output end of the electro-hydraulic proportional pressure control valve. The oil return port of the first three-position four-way directional control valve is connected to the oil tank through a cooler. The first oil port and the second oil port of the first three-position four-way directional control valve are connected to the thimble cylinder. With this setting, when the first three-position four-way directional control valve changes its direction, the hydraulic oil at the output end of the electro-hydraulic proportional pressure control valve enters the thimble cylinder through the first three-position four-way directional control valve, realizing the ejection and reset of the thimble, and thus realizing the ejection of the product.

[0014] Further, the control oil circuit also includes a seat-in cylinder control oil circuit. The seat-in cylinder control oil circuit includes a fifth three-position four-way directional control valve. The oil inlet of the fifth three-position four-way directional control valve is connected to the output end of the electro-hydraulic proportional pressure control valve. The oil return port of the fifth three-position four-way directional control valve is connected to the oil tank through a cooler. The first oil port and the second oil port of the fifth three-position four-way directional control valve are connected to the seat-in cylinder. With this setting, when the fifth three-position four-way directional control valve changes its direction, the hydraulic oil at the output end of the electro-hydraulic proportional pressure control valve enters the seat-in cylinder through the fifth three-position four-way directional control valve, realizing the movement of the injection seat.

[0015] Further, an emergency oil port is connected to the input end of the pressure control check valve, so as to provide emergency hydraulic oil for the control oil circuit.

[0016] Further, a supplementary oil port is connected to the input end of the pressure control check valve. With this setting, it is convenient to supplement hydraulic oil when the oil pressure of the control oil circuit is insufficient. Description of the Drawings

[0017] Figure 1 It is a schematic diagram of the hydraulic principle of the present invention.

[0018] Figure 2 It is a schematic diagram of the hydraulic principle of the electro-hydraulic proportional pressure control valve in the present invention.

[0019] Figure 3 It is a schematic diagram of the hydraulic principle of the thimble control system in the present invention.

[0020] Figure 4 It is a schematic diagram of the hydraulic principle of the mold opening and closing control oil circuit in the present invention.

[0021] Figure 5 It is a schematic diagram of the hydraulic principle of the pilot boosting control oil circuit in the present invention.

[0022] Figure 6 It is a schematic diagram of the hydraulic principle of the injection control oil circuit in the present invention.

[0023] Figure 7 It is a schematic diagram of the hydraulic principle of the seat-in cylinder control oil circuit in the present invention. Detailed Embodiments

[0024] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0025] As Figures 1-7 shown, an injection molding machine hydraulic stability system includes an electro-hydraulic proportional pressure control valve 1, a pressure control check valve 21, an oil inlet P port, and a control oil circuit 22.

[0026] The input end of the electro-hydraulic proportional pressure control valve 1 is connected to the output end of the pressure control check valve 21 and is also connected to the oil inlet P port; the output end of the electro-hydraulic proportional pressure control valve 1 is connected to the control oil circuit 22, and the output end of the electro-hydraulic proportional pressure control valve 1 is connected to the input end of the pressure control check valve 21. In the present invention, the pressure control check valve 21 is a check valve in hydraulic components.

[0027] An emergency oil port PG is connected to the input end of the pressure control check valve 21, which can provide emergency hydraulic oil to the control oil circuit. A supplementary oil port P1 is connected to the input end of the pressure control check valve 21. This setting facilitates the supplementary hydraulic oil when the oil pressure of the control oil circuit is insufficient.

[0028] The said control oil circuit 22 includes a thimble control system 80, a mold opening and closing control oil circuit 30, a guiding pressure boosting control oil circuit 40, an injection control oil circuit 50, and a seat cylinder control oil circuit 60.

[0029] The thimble control system includes a first three-position four-way directional control valve 8. The oil inlet of the first three-position four-way directional control valve 8 is connected to the output end of the electro-hydraulic proportional pressure control valve 1. The oil return port of the first three-position four-way directional control valve 8 is connected to the oil tank through the cooler input port COOLER. The first oil port and the second oil port of the first three-position four-way directional control valve 8 are connected to the thimble cylinders A1 and B1 ports. With this setting, when the first three-position four-way directional control valve 8 changes direction, the hydraulic oil at the output end of the electro-hydraulic proportional pressure control valve 1 enters the thimble cylinder through the first three-position four-way directional control valve 8, realizing the ejection and reset of the thimble, and thus realizing the ejection of the product.

[0030] The mold opening and closing control oil circuit 30 includes a second three-position four-way directional control valve 3, a first balance valve 31, and a pilot-operated check valve 32. The oil inlet of the second three-position four-way directional control valve 3 is connected to the output end of the electro-hydraulic proportional pressure control valve 1. The oil return port of the second three-position four-way directional control valve 3 is connected to the oil tank through the cooler input port COOLER. The first oil port of the second three-position four-way directional control valve 3 is connected to the MC port of the mold opening and closing cylinder. The second oil port of the second three-position four-way directional control valve 3 is connected to the output end of the first balance valve 31. The input end of the first balance valve 31 is connected to the input end of the pilot-operated check valve 32. The output end of the pilot-operated check valve 32 is connected to the MO port of the mold opening and closing cylinder. The first oil port of the second three-position four-way directional control valve 3 is respectively connected to the control ends of the first balance valve 31 and the pilot-operated check valve 32.

[0031] The guiding boost control oil circuit 40 includes a third three-position four-way directional control valve 4, a first check valve 42, and an electronic ball valve 41. The oil inlet of the third three-position four-way directional control valve 4 is connected to the output end of the electro-hydraulic proportional pressure control valve 1. The oil return port of the third three-position four-way directional control valve 4 is connected to the fuel tank through the input port COOLER of the cooler. The first oil port of the third three-position four-way directional control valve 4 is connected to the guiding cylinder. The second oil port of the third three-position four-way directional control valve 4 is connected to the input end of the first check valve 42. The output end of the first check valve 42 is connected to the boosting cylinder. The output end of the first check valve 42 is connected to the output end of the electronic ball valve 41. The input end of the electronic ball valve 41 is connected to the fuel tank.

[0032] The injection control oil circuit 50 includes a fourth three-position four-way directional control valve 5, a relief valve 51, a pilot-operated relief valve 52, a two-position two-way directional control valve 7, a pressure reducing valve 71, a second check valve 72, and a third check valve 53. The oil inlet of the fourth three-position four-way directional control valve 5 is connected to the output end of the electro-hydraulic proportional pressure control valve 1. The oil return port of the fourth three-position four-way directional control valve 5 is connected to the input end of the relief valve 51. The first oil port and the second oil port of the fourth three-position four-way directional control valve 5 are connected to the EB and EF ports of the injection cylinder. The output end of the relief valve 51 is connected to the fuel tank. The control end of the relief valve 51 is connected to the control oil circuit V. The input end of the pilot-operated relief valve 52 is connected to the control oil circuit. The output end of the pilot-operated relief valve 52 is connected to the fuel tank. The input end of the two-position two-way directional control valve 7 is connected to the output end of the electro-hydraulic proportional pressure control valve 1. The output end of the two-position two-way directional control valve 7 is connected to the input end of the pressure reducing valve 71. The output end of the pressure reducing valve 71 is connected to the input end of the second check valve 72. The output end of the second check valve 72 is connected to the output end of the third check valve 53. The input end of the third check valve 53 is connected to the fuel tank through the input port COOLER of the cooler. The EB port of the injection cylinder is connected between the second check valve 72 and the third check valve 53.

[0033] The above-mentioned hydraulic stability system of the injection molding machine supplies oil to the oil inlet P through a hydraulic pump. The hydraulic oil is regulated in pressure by an electro-hydraulic proportional pressure control valve and then input into the control oil circuit. When the pressure of the hydraulic oil output by the electro-hydraulic proportional pressure control valve exceeds the pressure of the pressure control check valve, the excess hydraulic oil returns from the pressure control check valve to the oil inlet P, and the excess hydraulic oil is directly supplemented to the input end of the electro-hydraulic proportional pressure control valve. In this way, it can avoid the loss caused by the excess hydraulic oil returning to the oil tank and then entering the oil inlet P, thereby improving the energy utilization rate. The guiding cylinder is arranged between the moving platen and the injection seat. During mold clamping, the second three-position four-way directional control valve is switched, and at the same time, the third three-position four-way directional control valve is switched. The hydraulic oil at the output end of the electro-hydraulic proportional pressure control valve is divided into two paths. One path enters the MC port of the mold clamping and opening cylinder through the second three-position four-way directional control valve. At this time, the first balance valve and the hydraulic control check valve are supplied with oil at the control end, the hydraulic control check valve opens, and the hydraulic oil cylinder of the mold clamping and opening cylinder returns to the oil tank from the MO port through the hydraulic control check valve, the first balance valve, the second three-way four-way directional control valve and the cooler. The other path of hydraulic oil enters the guiding cylinder through the third three-position four-way directional control valve, and the moving platen is guided through the guiding cylinder. When the mold clamping is completed, the third three-position four-way directional control valve is switched, and the hydraulic oil enters the boosting cylinder through the third three-position four-way directional control valve, and the mold clamping and holding pressure are increased through the boosting cylinder to ensure the reliability of injection molding and holding pressure. The fourth three-position four-way directional control valve is switched, and the hydraulic oil at the output end of the electro-hydraulic proportional pressure control valve enters the EB port of the injection cylinder through the fourth three-position four-way directional control valve, and the return oil of the injection cylinder returns to the oil tank through the EF port, the fourth three-position four-way directional control valve and the overflow valve. When the fourth three-position four-way directional control valve is switched to another position, it supplies oil to the control oil circuit, and the oil pressure of the control oil circuit is controlled by a pilot-operated overflow valve. At this time, oil is supplied to the overflow valve for control, and at the same time, the two-position two-way directional control valve is switched. The hydraulic oil at the output end of the electro-hydraulic proportional pressure control valve enters the EF port of the injection cylinder through the fourth three-position four-way directional control valve, and the return oil of the injection cylinder returns to the oil tank through the EB port, the fourth three-position four-way directional control valve and the overflow valve. At the same time, the output end of the electro-hydraulic proportional pressure control valve provides back pressure for the return oil of the injection cylinder through the two-position two-way directional control valve, the pressure reducing valve for pressure reduction and the second check valve to offset the weight of the injection system. In the present invention, due to the setting of the pressure control check valve, the excess hydraulic oil returns to the oil inlet P, so the oil pressure of the hydraulic oil in the control oil circuit can be ensured to be stable, and the problem of large instantaneous impact on the pipeline caused by too high pressure in the hydraulic system of the injection molding machine is solved. At the same time, back pressure is provided for the return oil of the injection cylinder through the two-position two-way directional control valve, the pressure reducing valve for pressure reduction and the second check valve to offset the weight of the injection system and make the injection more stable.

[0034] The injection seat cylinder control oil circuit includes a fifth three-position four-way directional control valve 6. The oil inlet of the fifth three-position four-way directional control valve 6 is connected to the output end of the electro-hydraulic proportional pressure control valve 1. The oil return port of the fifth three-position four-way directional control valve 6 is connected to the oil tank through the input port COOLER of the cooler. The first oil port and the second oil port of the fifth three-position four-way directional control valve 6 are connected to the ports A2 and B2 of the injection seat cylinder. With this setting, when the fifth three-position four-way directional control valve changes its direction, the hydraulic oil at the output end of the electro-hydraulic proportional pressure control valve enters the injection seat cylinder through the fifth three-position four-way directional control valve, realizing the movement of the injection seat.

[0035] In this embodiment, the electro-hydraulic proportional pressure control valve 1 includes a proportional speed control valve 11 and a pilot-operated overflow proportional valve 12. The input ends of the proportional speed control valve 11 and the pilot-operated overflow proportional valve 12 are connected in parallel to the oil tank through a hydraulic pump. The drain port of the proportional speed control valve 11 is connected to the signal DR port. The input end of the proportional speed control valve 11 is connected to the oil inlet P port. The input end of the pilot-operated overflow proportional valve 12 is connected to the oil tank through a hydraulic pump. The output end of the pilot-operated overflow proportional valve 12 is connected to the control oil circuit. The signal oil port of the pilot-operated overflow proportional valve 12 is connected to the output end of the proportional speed control valve 11. The pilot-operated overflow proportional valve 12 is connected to the oil tank through a cooler.

Claims

1. A hydraulic stability system for an injection molding machine, characterized in that: It includes an electro-hydraulic proportional pressure control valve, a pressure control check valve, an oil inlet port, and a control oil circuit; The oil inlet port includes an oil inlet P port; The input end of the electro-hydraulic proportional pressure control valve is connected to the output end of the pressure control check valve and the oil inlet P port, and the input end of the pressure control check valve is connected to the output end of the electro-hydraulic proportional pressure control valve; the output end of the electro-hydraulic proportional pressure control valve is connected to the control oil circuit; The said control oil circuit includes a mold opening and closing control oil circuit, a lead boosting control oil circuit, and an injection control oil circuit; The mold opening and closing control oil circuit includes a second three-position four-way directional control valve, a first balance valve, and a hydraulic control check valve. The oil inlet of the second three-position four-way directional control valve is connected to the output end of the electro-hydraulic proportional pressure control valve. The oil return port of the second three-position four-way directional control valve is connected to the oil tank through a cooler. The first oil port of the second three-position four-way directional control valve is connected to the MC port of the mold opening and closing cylinder. The second oil port of the second three-position four-way directional control valve is connected to the output end of the first balance valve. The input end of the first balance valve is connected to the input end of the hydraulic control check valve. The output end of the hydraulic control check valve is connected to the MO port of the mold opening and closing cylinder. The first oil port of the second three-position four-way directional control valve is respectively connected to the control end of the first balance valve and the control end of the hydraulic control check valve; The lead boosting control oil circuit includes a third three-position four-way directional control valve, a first check valve, and an electronic ball valve. The oil inlet of the third three-position four-way directional control valve is connected to the output end of the electro-hydraulic proportional pressure control valve. The oil return port of the third three-position four-way directional control valve is connected to the oil tank through a cooler. The first oil port of the third three-position four-way directional control valve is connected to the lead cylinder. The second oil port of the third three-position four-way directional control valve is connected to the input end of the first check valve. The output end of the first check valve is connected to the boosting cylinder. The output end of the first check valve is connected to the output end of the electronic ball valve. The input end of the electronic ball valve is connected to the oil tank; The injection control oil circuit described above includes a fourth three-position four-way directional control valve, an overflow valve, a pilot-operated overflow valve, a two-position two-way directional control valve, a pressure reducing valve, a second check valve, and a third check valve; the oil inlet of the fourth three-position four-way directional control valve is connected to the output end of the electro-hydraulic proportional pressure control valve, the oil return port of the fourth three-position four-way directional control valve is connected to the input end of the overflow valve, the first oil port and the second oil port of the fourth three-position four-way directional control valve are connected to the injection cylinder; the output end of the overflow valve is connected to the fuel tank, and the control end of the overflow valve is connected to the control oil circuit; the input end of the pilot-operated overflow valve is connected to the control oil circuit, and the output end of the pilot-operated overflow valve is connected to the fuel tank; the input end of the two-position two-way directional control valve is connected to the output end of the electro-hydraulic proportional pressure control valve, the output end of the two-position two-way directional control valve is connected to the input end of the pressure reducing valve, the output end of the pressure reducing valve is connected to the input end of the second check valve, the output end of the second check valve is connected to the output end of the third check valve, the input end of the third check valve is connected to the fuel tank through a cooler, and one end of the injection cylinder is connected between the second check valve and the third check valve; when the fourth three-position four-way directional control valve is switched to another position, it supplies oil to the control oil circuit, controls the oil pressure of the control oil circuit through the pilot-operated overflow valve, at this time, it supplies control oil to the overflow valve, and at the same time, makes the two-position two-way directional control valve switch positions. The hydraulic oil at the output end of the electro-hydraulic proportional pressure control valve enters the EF port of the injection cylinder through the fourth three-position four-way directional control valve. The oil return of the injection cylinder returns to the fuel tank through the EB port, the fourth three-position four-way directional control valve, and the overflow valve. At the same time, the output end of the electro-hydraulic proportional pressure control valve passes through the two-position two-way directional control valve, is reduced in pressure by the pressure reducing valve, and provides back pressure to the oil return of the injection cylinder through the second check valve to offset the weight of the injection system.

2. The hydraulic stability system of an injection molding machine according to claim 1, characterized in that: The control oil circuit described above includes a thimble control system. The thimble control system includes a first three-position four-way directional control valve. The oil inlet of the first three-position four-way directional control valve is connected to the output end of the electro-hydraulic proportional pressure control valve. The oil return port of the first three-position four-way directional control valve is connected to the fuel tank through a cooler. The first oil port and the second oil port of the first three-position four-way directional control valve are connected to the thimble cylinder.

3. A hydraulic stability system for an injection molding machine according to claim 1, wherein: The control oil circuit also includes a seat advance cylinder control oil circuit. The seat advance cylinder control oil circuit includes a fifth three-position four-way directional control valve. The oil inlet of the fifth three-position four-way directional control valve is connected to the output end of the electro-hydraulic proportional pressure control valve. The oil return port of the fifth three-position four-way directional control valve is connected to the fuel tank through a cooler. The first oil port and the second oil port of the fifth three-position four-way directional control valve are connected to the seat advance cylinder.

4. The hydraulic stability system of an injection molding machine according to claim 1, characterized in that: An emergency oil port is connected to the input end of the pressure control check valve.

5. The hydraulic stability system of an injection molding machine according to claim 1, wherein: A supplementary oil port is connected to the input end of the pressure control check valve.

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