A hydraulic system for a bidirectional powder pressing and molding apparatus

Abstract

This invention belongs to the field of powder pressing technology and discloses a hydraulic system for a bidirectional powder pressing and forming device. The system includes: a bidirectional powder pressing and forming unit comprising an upper hydraulic cylinder and a lower hydraulic cylinder; two independent control units with dual valve cores, each control unit including: a first proportional valve and a second proportional valve, the first proportional valve being connected to the rod chamber of one side of the hydraulic cylinder, and the second proportional valve being connected to the rodless chamber of the same side of the hydraulic cylinder; one side of the first and second proportional valves includes ports P and T, and the other side includes ports A and B, with port B of the first proportional valve blocked and port A of the second proportional valve blocked; and a control unit connected to the two independent control units with dual valve cores to control the operation of the two independent control units with dual valve cores according to a relationship curve. This application can decouple the rod chamber and rodless chamber of the hydraulic cylinder, thereby achieving compensation for nonlinear reaction forces, giving the system a strong resistance to load interference.

Description

Technical Field

[0001] This invention belongs to the field of powder pressing technology, and more specifically, relates to a hydraulic system for a bidirectional powder pressing and molding device. Background Technology

[0002] The powder compression molding device uses a hydraulic cylinder embedded inside the frame to drive a slider in a vertical direction, which in turn moves a punch inside a mold, thus completing the powder compression molding process. It is a specialized piece of equipment for pressing granular powder into samples with specific shapes, densities, and mechanical properties. Telescopic movement is one of the most frequent actions during the compression process, and this movement is controlled by a valve-controlled cylinder. Therefore, the high density and low density difference of the pressed product are important indicators for evaluating the performance of the hydraulic control system of the powder compression molding device. However, the current hydraulic control system of the powder pressing molding device has the following problems: (1) In the conventional unidirectional pressing process, the friction increases from the top to the bottom. After pressing, the density of the sample shows a "high at the top and low at the bottom" trend, which makes it easy to break and have defects when demolding; (2) Although there are also bidirectional powder pressing molding devices, such as CN101676096, CN2568388, CN204003781, they all adopt a single valve control single cylinder drive form. In this way, the inlet and outlet throttling is mechanically coupled and adjusted by the displacement of a valve core in the valve body, which makes the control of the two chambers of the hydraulic cylinder related. It is impossible to realize the composite control of displacement and force during the pressing process, which makes it difficult to guarantee the density uniformity and stability of the pressed sample. The above technologies are difficult to match with the nonlinear reaction force of the pressed object during the pressing process, which leads to uneven density of the final product, high anisotropic density difference, and uneven stress distribution, making it difficult to meet the requirements for product performance uniformity. Summary of the Invention

[0003] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a hydraulic system for a bidirectional powder pressing and molding device. This system can decouple the rod-side and rodless-side chambers of the hydraulic cylinder, making control more flexible. Furthermore, it can compensate for nonlinear reaction forces, giving the system strong resistance to load interference and greatly suppressing speed fluctuations and pressure overshoot.

[0004] To achieve the above objectives, according to one aspect of the present invention, a hydraulic system for a bidirectional powder pressing and molding apparatus is provided. The hydraulic system includes: a bidirectional powder pressing and molding unit comprising: an upper hydraulic cylinder and a lower hydraulic cylinder; a pressure sensor, an upper slider, and an upper punch are sequentially connected from top to bottom at the lower end of the upper hydraulic cylinder; a pressure sensor, a lower slider, and a lower punch are connected from bottom to top at the upper end of the lower hydraulic cylinder; a grating ruler is provided on the outer side of both the upper and lower sliders to monitor the displacement of the upper and lower hydraulic cylinders; the pressure sensor is used to detect the reaction force of the pressed object; and two independent control units with dual valve cores, each of which includes: a first proportional valve and a second proportional valve; the first proportional valve is connected to the rod chamber of one side of the hydraulic cylinder of the bidirectional powder pressing and molding unit, and the second proportional valve is connected to the bidirectional powder pressing and molding unit... The rodless chamber of the hydraulic cylinder on the same side of the unit is connected. A one-way sequence valve is connected in series between the first proportional valve and the rod chamber, and a leak-free solenoid valve is connected in series between the second proportional valve and the rodless chamber. One side of the first and second proportional valves includes a P port and a T port, and the other side includes an A port and a B port. The P port of the first and second proportional valves is connected to the oil tank through a first pipeline, and the T port of the first and second proportional valves is connected to the oil tank through a second pipeline. The B port of the first proportional valve and the A port of the second proportional valve are blocked. The control unit includes a curve showing the relationship between the reaction force of the pressed object and the displacement of the upper and lower hydraulic cylinders. The control unit is connected to the two independent control units with double valve cores to control the operation of the two independent control units with double valve cores according to the curve.

[0005] Preferably, a first safety valve and a first pressure sensor are provided as a bypass between the T-port and the rod chamber of the first proportional valve, and a second safety valve and a second pressure sensor are provided as a bypass between the T-port and the rodless chamber of the second proportional valve.

[0006] Preferably, an electromagnetic overflow valve is connected between the first pipeline and the second pipeline.

[0007] Preferably, the first pipeline of the two dual-valve-core independent control units is connected to the same hydraulic pump, which is used to supply oil from the oil tank into the first pipeline.

[0008] Preferably, a check valve is connected in series on the first pipeline of each of the two dual-valve-core independent control units.

[0009] Preferably, the pressure sensor is a spoke-type pressure sensor, and the spoke-type pressure sensor is rigidly connected to the upper slider and the lower slider.

[0010] Preferably, the upper punch is detachably connected to the upper slider, and the lower punch is detachably connected to the lower slider.

[0011] Preferably, the relationship curve is obtained through multiple experiments.

[0012] Preferably, the leak-free solenoid valve is a two-position two-way leak-free seat valve plate structure.

[0013] In summary, compared with the prior art, the hydraulic system of the bidirectional powder pressing and molding device provided by the present invention has the following advantages:

[0014] 1. By using two independent control units with dual valve cores to independently control the rod-side and rodless sides of the upper and lower hydraulic cylinders respectively, the rod-side and rodless sides are decoupled, thus breaking the mechanical coupling of the conventional single-valve-controlled single-cylinder system. This increases the degree of freedom in system control. Furthermore, the control unit can compensate for nonlinear reaction forces based on the force-displacement relationship curve, giving the system a strong ability to resist load interference, greatly suppressing speed fluctuations and pressure overshoot, and improving the density uniformity and stability of the pressed samples.

[0015] 2. The first safety valve limits the pressure in the rod chamber of the hydraulic cylinder. When the pressure in the rod chamber exceeds the maximum setting value of the first safety valve, it opens to overflow and protect the system. The second safety valve limits the pressure in the rodless chamber of the hydraulic cylinder. When the pressure in the rodless chamber exceeds the maximum setting value of the second safety valve, it opens to overflow and protect the system.

[0016] 3. The leak-free solenoid valve is a two-position two-way leak-free seat valve plate structure. When the electromagnet is de-energized, it can realize the absolute leak-free closing function of the rodless chamber of the upper and lower hydraulic cylinders. This allows the hydraulic cylinder to be pressure-held when the powder pressing force reaches the desired value, in order to improve the stress distribution at the edges and corners of the sample, making the overall density more uniform and the density difference in all directions more consistent.

[0017] 4. A check valve is connected in series on the first pipeline to prevent backflow of oil from the two independent control units with dual valve cores during system fault diagnosis and maintenance.

[0018] 5. The pressure sensor is a spoke-type pressure sensor that can directly detect the pressing force applied to the powder by the upper and lower hydraulic cylinders. Its repeatability control accuracy is 0.05%, which can generate high-density powder-pressed samples. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the hydraulic system of the bidirectional powder pressing and molding apparatus according to an embodiment of this application;

[0020] Figure 2 This is a schematic diagram of the structure of the bidirectional powder pressing unit in an embodiment of this application.

[0021] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0022] 100-Hydraulic Power Oil Unit:

[0023] 101-Hydraulic pump; 102-Electric motor; 103-High pressure filter; 104-Level gauge; 105-Air filter; 106-Temperature sensor; 107-Level relay; 108-Drain ball valve; 109-Suction filter; 1010-Oil tank;

[0024] 200, 300 - Dual-core independent control unit:

[0025] 201, 301 - Check valve; 202, 302 - Solenoid relief valve; 203, 303 - Pressure sensor; 204, 304 - First proportional valve; 205, 305 - Second proportional valve; 206, 306 - One-way sequence valve; 207, 307 - First safety valve; 208, 308 - First pressure sensor; 209, 309 - Second pressure sensor; 2010, 3010 - Second safety valve; 2011, 3011 - Leak-free solenoid valve;

[0026] 400-Bidirectional Powder Compression Molding Unit:

[0027] 401 - Upper hydraulic cylinder; 402, 408 - Pressure sensor; 403 - Upper slider; 404 - Upper punch; 405 - Cavity; 406 - Lower punch; 407 - Lower slider; 409 - Lower hydraulic cylinder; 4010, 4011 - Grating ruler;

[0028] 500-oil pipeline unit:

[0029] 501, 502, 503, 504, 505, 506, 507, 508 - Hydraulic lines. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0031] The hydraulic system of the bidirectional powder pressing and molding apparatus provided by this invention, such as Figure 1 As shown, it mainly includes a bidirectional powder pressing and molding unit 400 and two independent control units with dual valve cores 200 and 300, as detailed below.

[0032] like Figure 2As shown, the bidirectional powder pressing unit 400 includes an upper hydraulic cylinder 401 and a lower hydraulic cylinder 409, which are embedded in the vertical centerline of a closed frame. The lower end of the upper hydraulic cylinder 401 is sequentially connected from top to bottom to a pressure sensor 402, an upper slider 403, and an upper punch 404, thereby causing the pressure sensor 402, upper slider 403, and upper punch 404 to move under the drive of the upper hydraulic cylinder 401. The pressure sensor 402 is preferably a spoke-type pressure sensor, which rigidly connects the piston rod of the upper hydraulic cylinder 401 to the upper slider 403 through a central threaded hole and screws evenly distributed along the circumference of the bottom surface. The upper punch 404 is integrated onto the upper slider 403 through a detachable stop structure. The upper end of the lower hydraulic cylinder is connected from bottom to top to a pressure sensor 408, a lower slide block 407, and a lower punch 406. The pressure sensor 408, lower slide block 407, and lower punch 406 move under the drive of the lower hydraulic cylinder 409. The pressure sensor 408 is preferably a spoke-type pressure sensor, which can directly detect the pressing force applied to the powder in the cavity 405 by the upper hydraulic cylinder 401 or the lower hydraulic cylinder 409. Its repeatability control accuracy is 0.05%, ensuring high-density powder pressing and forming of samples. The piston rod of the lower hydraulic cylinder 409 and the lower slide block 407 are rigidly connected through a central threaded hole and screws evenly distributed around the bottom circumference. The lower punch 406 is integrated onto the lower slide block 407 through a detachable stop structure. The upper punch 404 and the lower punch 406 are detachable; according to process requirements, only punches of different diameters need to be replaced to connect with the upper slide block 403 or the lower slide block 407 via the stop, facilitating alignment and easy replacement.

[0033] Both the upper slider 403 and the lower slider 407 are equipped with grating rulers 4010 and 4011 on their outer sides. The grating rulers 4010 and 4011 are composed of self-adhesive stainless steel strip grating rulers and reading heads. The grating rulers are firmly attached to the substrate of the bidirectional powder pressing molding unit. The reading heads are securely mounted on the upper slider 403 and the lower slider 407 respectively. The reading heads are parallel to the grating rulers and the distance between them is preferably 2mm. The accuracy can reach ±5um / m, which can realize high dynamic accuracy digital position feedback for the upper hydraulic cylinder 401 and the lower hydraulic cylinder 409.

[0034] The bidirectional powder pressing unit 400 adopts a closed frame structure, which is compact, highly rigid, and ensures stable production processes. The upper slider 403 and lower slider 407 use an X-type adjustable guide rail structure, which has strong resistance to eccentric loads. The moving surface is covered with wear-resistant plate as the guide rail, and the guide rail gap is adjustable.

[0035] The two independent control units 200 and 300, also known as the independent control unit 200 and 300, have the same structure and are parallel load-independent control valve groups. In this embodiment, the independent control unit 200 controls the upper hydraulic cylinder, and the second independent control unit 300 controls the lower hydraulic cylinder.

[0036] The dual-valve independent control unit 200 includes a first proportional valve 204 and a second proportional valve 205. One side of the first and second proportional valves 204 and 205 includes a P port and a T port, and the other side includes an A port and a B port. The P port of the first and second proportional valves are connected to the oil tank via a first pipeline, and the T ports of the first and second proportional valves are connected to the oil tank via a second pipeline. The B port of the first and second proportional valves is blocked, and the A port of the second proportional valve is blocked. The return ports T of the first and second proportional valves converge into the main return pipeline and flow into the oil tank. A first safety valve 207 and a first pressure sensor 208 are bypassed between the T port of the first proportional valve and the rod chamber. A second safety valve 2010 and a second pressure sensor 209 are bypassed between the T port of the second proportional valve and the rodless chamber. Electromagnetic relief valves 202 and 302 are connected between the first and second pipelines.

[0037] The first proportional valve 204 and the second proportional valve 205 are proportional valves with electrical position feedback and integrated electronic components. The valve core stroke is adjusted in a manner proportional to the control value. In the inactive state, the spring is in a relaxed state and the proportional valve is in a fail-safe closed position.

[0038] The dual-valve-core independent control unit 300 has the same structure as the dual-valve-core independent control unit 200. The dual-valve-core independent control unit 300 includes a first proportional valve 304 and a second proportional valve 305. One side of the first proportional valve 304 and the second proportional valve 305 includes a P port and a T port, and the other side includes an A port and a B port. The P port of the first proportional valve and the P port of the second proportional valve are connected and connected to the oil tank via a first pipeline. The T port of the first proportional valve and the T port of the second proportional valve are connected to the oil tank via a second pipeline. The B port of the first proportional valve and the A port of the second proportional valve are blocked. The return ports T of the first proportional valve 304 and the second proportional valve 305 converge into the main return pipeline and flow into the oil tank. A first safety valve 307 and a first pressure sensor 308 are bypassed between the T port of the first proportional valve and the rod chamber. A second safety valve 3010 and a second pressure sensor 309 are bypassed between the T port of the second proportional valve and the rodless chamber.

[0039] One-way sequence valves 206 and 306 are connected in series between the first proportional valves 204 and 304 and the rod chamber. Leakage-free solenoid valves 2011 and 3011 are connected in series between the second proportional valves 205 and 305 and the rodless chamber. The set pressure of the one-way sequence valve 206 is 0.5 MPa, which needs to overcome the gravity of the moving parts of the hydraulic cylinder to ensure that the upper hydraulic cylinder 401 slider remains stationary at any position without sliding down when unloaded. The leakage-free solenoid valves 2011 and 3011 are preferably two-position, two-way, leakage-free seat valves with a plate structure. When the electromagnet is de-energized, they can achieve the requirement of absolutely leak-free shut-off of the hydraulic cylinder, thereby achieving pressure holding treatment of the hydraulic cylinder when the powder pressing force reaches the desired value, in order to improve the stress distribution at the edges and corners of the sample, making the overall density more uniform and the sealing difference in all directions more consistent. Specifically, the first safety valve 207 and the first pressure sensor 208 of the dual-valve-core independent control unit 200 are respectively bypassed and connected to the oil line near the rod chamber of the upper hydraulic cylinder 401 at the outlet of the one-way sequence valve 206. The first safety valve 207 provides safety limits for the press in the rod chamber of the upper hydraulic cylinder 401. When the pressure in the rod chamber of the upper hydraulic cylinder 401 exceeds the maximum set value of the first safety valve 207, it opens to overflow and protect the system safety. The second safety valve 2010 and the second pressure sensor 209 are respectively bypassed and connected to the oil line near the rodless chamber of the upper hydraulic cylinder 401 at the outlet of the leak-free solenoid valve 2011. For example, the set pressure of the first safety valve 207 and the second safety valve 2010 can be 25MPa. The first safety valve 307 and the first pressure sensor 308 of the dual-valve-core independent control unit 300 are respectively bypassed and connected to the oil line near the rod chamber of the lower hydraulic cylinder 409 at the outlet of the one-way sequence valve 306. The first safety valve 307 provides safety limits for the press in the rod chamber of the lower hydraulic cylinder 409. When the pressure in the rod chamber of the lower hydraulic cylinder 409 exceeds the maximum set value of the first safety valve 307, it opens to overflow and protect the system safety. The second safety valve 3010 and the second pressure sensor 309 are respectively bypassed and connected to the oil line near the rodless chamber of the lower hydraulic cylinder 409 at the outlet of the leak-free solenoid valve 3011. For example, the set pressure of the first safety valve 307 and the second safety valve 3010 can be 25MPa.

[0040] Electromagnetic relief valves 202 and 302 and pressure sensors 203 and 303 are connected between the first and second pipelines and are connected to the outlet oil line of check valve 201. When electromagnetic relief valves 202 and 302 are energized, they function as safety valves. When electromagnetic relief valves 202 and 302 are de-energized, the oil pumped by hydraulic pump 101 flows into the main return oil tanks T1 and T2 under no-load conditions and then back to the oil tank. The pressure of electromagnetic relief valves 202 and 302 can be set to 27 MPa. Check valves 201 and 301 are connected in series on the first pipeline of the two dual-valve-core independent control units 200 and 300.

[0041] The dual-valve-core independent control unit 200 and dual-valve-core independent control unit 300 are parallel load independent control valve groups. The oil entering the dual-valve-core independent control unit 200 (or dual-valve-core independent control unit 300) is divided into two branches after passing through the check valve 201 (or check valve 301). The function of check valves 201 and 301 is to prevent the oil of the dual-valve-core independent control unit from flowing back during system fault diagnosis and maintenance.

[0042] One branch of the oil flows through the inlet P of the first proportional valve 204 (or the first proportional valve 304), then flows out from the working port A of the first proportional valve 204 (or the first proportional valve 304) and flows through the one-way sequence valve 206 (or the one-way sequence valve 306) before connecting with the rod chamber of the upper hydraulic cylinder 401 (or the lower hydraulic cylinder 409) of the bidirectional powder pressing molding unit 400; the other branch of the oil flows through the inlet P of the second proportional valve 205 (or the second proportional valve 305), then flows out from the working port B of the second proportional valve 205 (or the second proportional valve 305) and flows through the leak-free solenoid valve 2011 (or the leak-free solenoid valve 3011) before connecting with the rodless chamber of the upper hydraulic cylinder 401 (or the lower hydraulic cylinder 409) of the bidirectional powder pressing molding unit 400, thus forming a dual-valve-core independent control system for the upper hydraulic cylinder 401 (or the lower hydraulic cylinder 409).

[0043] The hydraulic system of the bidirectional powder pressing molding device also includes a hydraulic power oil unit 100 and an oil pipeline unit 500. The hydraulic power oil unit 100 includes a hydraulic pump 101, an electric motor 102, a high-pressure filter 103, a level gauge 104, an air filter 105, a temperature sensor 106, a level relay 107, a drain ball valve 108, an oil suction filter 109, and an oil tank 1010.

[0044] The oil tank 1010 stores hydraulic oil, and the level gauge 104 is used to detect the level of hydraulic oil in the tank.

[0045] Air filter 105 is used to filter impurities in the air to prevent contamination of hydraulic oil.

[0046] Temperature sensor 106 is used to monitor the temperature of hydraulic oil and will automatically alarm when the temperature is greater than or equal to 65°C.

[0047] The liquid level relay 107 is a low liquid level alarm device. If there is a leak in the system that causes the liquid level to drop, it will issue a low liquid level alarm signal to remind the operator to check the system.

[0048] The hydraulic pump 101 and the electric motor 102 constitute the power unit of the system, providing the necessary pressure and flow to the system. The inlet and outlet ports of the hydraulic pump 101 are respectively equipped with a suction filter 109 and a high-pressure filter 103. The filtered oil is input to the dual-valve-core independent control unit 200, 300 through the first pipeline. The oil pumped out by the hydraulic pump 101 is split into two streams after passing through the high-pressure filter 103. One stream flows to the inlet A of the dual-valve-core independent control unit 200. p1 The other oil flows to the inlet A of the dual-valve core independent control unit 300. p2 .

[0049] The control unit includes a curve showing the relationship between the reaction force of the pressed object and the displacement of the upper hydraulic cylinder 401 and the lower hydraulic cylinder 409. This control unit is connected to the two independent control units 200 and 300 with dual valve cores, and controls their operation according to the curve. The control unit can fit the experimental sample data collected by the pressure sensors 402 and 408 and the grating rulers 4010 and 4011 into a functional relationship between the pressing force and displacement. Then, nonlinear load forces are compensated for in the control unit, giving the system strong anti-load interference capabilities, greatly suppressing speed fluctuations and pressure overshoot, and reducing the control difficulty of the system.

[0050] The working process of the hydraulic system of the bidirectional powder compression molding apparatus of this application is as follows:

[0051] When the bidirectional powder pressing molding unit 400 is in standby mode, the control unit controls the electromagnets of the electromagnetic overflow valves 202 and 302 to de-energize, and the hydraulic pump 101 starts under no-load. The oil pumped out flows directly back to the oil tank through the electromagnetic overflow valves 202 and 302.

[0052] When the upper hydraulic cylinder 401 of the bidirectional powder pressing molding unit 400 presses downwards, the control unit controls the solenoids of the electromagnetic relief valve 202, the first proportional valve 204, the second proportional valve 205, and the leak-free solenoid valve 2011 in the dual-valve core independent control unit 200 to be energized simultaneously. The electromagnetic relief valve 202 is in a closed, pressure-holding state, and the leak-free solenoid valve 2011 is in a normally open position, provided that the control current of the first proportional valve 204 and the second proportional valve 205 is between 4 and 12 mA, the AT channel of the first proportional valve 204 is connected, the PB channel of the second proportional valve 205 is connected, the electromagnetic relief valve 202 is in a closed, pressure-holding state, and the leak-free solenoid valve 2011 is in a normally open position. The high-pressure oil pumped by the hydraulic pump 101 flows through the hydraulic line 501 from A... p1After entering the dual-valve-core independent control unit 200, the oil flows into two branches to the P ports of the first proportional valve 204 and the second proportional valve 205. Since the working port B of the first proportional valve 204 and the working port A of the second proportional valve 205 are blocked, the PB channel of the first proportional valve 204 is also blocked. Therefore, the high-pressure oil can only flow through the PB channel of the second proportional valve 205 and the leak-free solenoid valve 2011 before exiting through the P port of the dual-valve-core independent control unit 200. c1 The fluid flows out through the outlet and then through hydraulic line 505 from the upper hydraulic cylinder 401. c1w The oil enters the rodless chamber, thus forming the pressing oil inlet system of the upper hydraulic cylinder 401. Meanwhile, the oil in the rod chamber of the upper hydraulic cylinder 401 flows from B... c1y The oil flows out, returns from Ac1 to the dual-valve core independent control unit 200 via hydraulic line 506, then flows through the overflow channel of one-way sequence valve 206, and after the AT channel of the first proportional valve 204, it flows back to the oil tank from port T1 via hydraulic line 503, thus forming the pressure return oil system of upper hydraulic cylinder 401.

[0053] When the lower hydraulic cylinder 409 of the bidirectional powder pressing molding unit 400 presses upwards, the control unit controls the solenoids of the electromagnetic relief valve 302, the first proportional valve 304, the second proportional valve 305, and the leak-free solenoid valve 3011 in the dual-valve-core independent control unit 300 to be energized simultaneously. The AT channel of the first proportional valve 304 and the PB channel of the second proportional valve 305 are connected only when the control current of the first proportional valve 304 and the second proportional valve 305 is between 4 and 12 mA. The electromagnetic relief valve 302 is in a closed, pressure-locked state, and the leak-free solenoid valve 3011 is in a normally open position. The high-pressure oil pumped by the hydraulic pump 101 flows through the hydraulic line 502 from A... p1 After entering the dual-valve-core independent control unit 300, the oil flows into two branches to the P ports of the first proportional valve 304 and the second proportional valve 305. Since the working port B of the first proportional valve 304 and the working port A of the second proportional valve 305 are blocked, and the PB passage of the second proportional valve 305 is also blocked, the high-pressure oil can only flow through the PB passage of the proportional valve 305 and the leak-free solenoid valve 3011 before exiting through the P port of the dual-valve-core independent control unit 300. c2 The water flows out through the outlet and then through hydraulic line 507 from the B of the lower hydraulic cylinder 409. c2w The oil enters the rodless chamber, thus forming the pressing oil inlet system of the lower hydraulic cylinder 409. Meanwhile, the oil in the rod chamber of the lower hydraulic cylinder 409 flows out from Bc2y and through hydraulic line 508 from A... c2 The oil flows back to the dual-valve core independent control unit 300, then through the overflow channel of the one-way sequence valve 306, and then through the AT channel of the first proportional valve 304, before flowing back to the oil tank from the T2 port, thus forming the pressure return oil system of the lower hydraulic cylinder 409.

[0054] As mentioned above, since the rodless and rod-type chambers of the upper hydraulic cylinder 401 (or lower hydraulic cylinder 409) are controlled by different first proportional valves 204 and second proportional valves 205 (or first proportional valves 304 and second proportional valves 304), during the bidirectional pressing process, the control unit controls the first proportional valves 204 and second proportional valves 205 to drive the upper hydraulic cylinder to move, and controls the first proportional valves 304 and second proportional valves 304 to drive the lower hydraulic cylinder to move. This fundamentally solves the coupling problem of the proportional valves of the existing structural units simultaneously driving two parallel hydraulic cylinders. Furthermore, it can decouple displacement and force, making displacement and force decoupling possible and making the system control more flexible.

[0055] The control unit identifies the coupling terms between the upper and lower hydraulic cylinders in the electro-hydraulic position servo system controller and electro-hydraulic force controller through an adaptive online identification method. Then, real-time compensation for the coupling terms is added to the corresponding controller, which improves the consistency and stability of the pressed and molded products.

[0056] During the bidirectional pressing process, the pressure sensor 402 monitors the powder pressing force applied by the upper hydraulic cylinder 401 in real time. When the pressing force reaches the desired value, the control unit de-energizes the electromagnetic overflow valve 202, electromagnetic overflow valve 302, leak-free solenoid valve 2011, and leak-free solenoid valve 3011. The first proportional valve 204, first proportional valve 304, second proportional valve 205, and second proportional valve 305 are in the neutral position, entering the pressure holding state. This greatly improves the flow and creep properties of powder particles, bringing internal stress to a balance, thereby obtaining a uniform and dense powder molding sample. On the other hand, the pressure sensor and grating ruler feed back the collected experimental sample data to the control unit for load nonlinearity compensation, greatly reducing the control difficulty of the system.

[0057] After the pressure holding state ends, firstly, the electromagnets of the electromagnetic relief valve 202, the first proportional valve 204, the second proportional valve 205, and the leak-free solenoid valve 2011 in the dual-valve core independent control unit 200 are simultaneously energized. If and only if the control current of the first proportional valve 204 and the second proportional valve 205 is between 12 and 20 mA, the PA channel of the first proportional valve 204 is connected, the BT channel of the second proportional valve 205 is connected, the electromagnetic relief valve 202 is in the closed pressure holding state, and the leak-free solenoid valve 2011 is in the normally open position. The high-pressure oil pumped by the hydraulic pump 101 enters the dual-valve-core independent control unit 200 through the hydraulic line 501 from Ap1 and is then divided into two branches flowing to the P ports of the first proportional valve 204 and the second proportional valve 205. Since the working oil port B of the first proportional valve 204 and the working oil port A of the second proportional valve 205 are blocked, the BT channel of the first proportional valve is blocked and isolated. The high-pressure oil can only flow out from the Ac1 port of the dual-valve-core independent control unit 200 through the PA channel of the first proportional valve 204 and the one-way valve channel of the one-way sequence valve 206. Then, it returns to the dual-valve-core independent control unit 200 through the Bc1y of the upper hydraulic cylinder 401 via the hydraulic line 506. After flowing through the leak-free solenoid valve 2011 and the BT channel of the second proportional valve 205, it flows back to the oil tank from the T1 port, thereby realizing the control of the dual-valve-core independent control unit 200 to unload and return the upper hydraulic cylinder 401. When the upper hydraulic cylinder 401 returns to its initial position, the solenoid relief valve 202, the first proportional valve 204, the second proportional valve 205, and the leak-free solenoid valve 2011 in the dual-valve core independent control unit 200 are de-energized and await the command for the next work cycle.

[0058] After the upper hydraulic cylinder 401 returns to its initial position and waits for 5 seconds, the control unit continues to send relevant commands to control the lower hydraulic cylinder 409 to drive the punch upward until the pressed sample is pushed out of the upper edge of the mold cavity. The lower hydraulic cylinder 409 then stops moving and waits for the return command.

[0059] After the pressed sample is removed, the control unit controls the electromagnets of the electromagnetic overflow valve 302, the first proportional valve 304, the second proportional valve 305, and the leak-free solenoid valve 3011 in the dual-valve core independent control unit 300 to be energized. The PA channel of the first proportional valve 304 and the BT channel of the second proportional valve 305 are connected only when the control current of the first proportional valve 304 and the second proportional valve 305 is between 12 and 20 mA. The electromagnetic overflow valve 302 is in a closed and pressurized state, and the leak-free solenoid valve 3011 is in a normally open position. The high-pressure oil pumped by hydraulic pump 101 enters the dual-valve-core independent control unit 300 through hydraulic line 502 from Ap1, and then flows to the P port of the first proportional valve 304 and the second proportional valve 305 through two branches. Since the working oil port B of the first proportional valve 304 and the working oil port A of the second proportional valve 305 are blocked, the BT channel of the first proportional valve 304 is blocked and isolated. The high-pressure oil can only be controlled independently by the dual valve cores through the PA channel of the first proportional valve 304 and the check valve channel of the one-way sequence valve 306. Oil flows out from port Ac2 of unit 300, then enters the rod chamber of lower hydraulic cylinder 409 through hydraulic line 508 via port Bc2w. Oil from the rodless chamber of lower hydraulic cylinder 409 flows out from port Bc2w, returns to the dual-valve-core independent control unit 300 via hydraulic line 507, then flows through the BT channel of the leak-free solenoid valve 3011 and the second proportional valve 305, and flows back to the oil tank from port T2 via hydraulic line 504. This achieves the control of lower hydraulic cylinder 409 by the dual-valve-core independent control unit 300 for unloading and return. When lower hydraulic cylinder 409 returns to its initial position, the solenoid relief valve 302, the first proportional valve 304, the second proportional valve 305, and the leak-free solenoid valve 3011 in the dual-valve-core independent control unit 300 are de-energized and await the next working cycle command.

[0060] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A hydraulic system for a bidirectional powder pressing and molding apparatus, characterized in that, The hydraulic system includes: A bidirectional powder pressing molding unit (400) includes an upper hydraulic cylinder (401) and a lower hydraulic cylinder (409). The lower end of the upper hydraulic cylinder (401) is connected from top to bottom to a pressure sensor (402), an upper slider (403), and an upper punch (404). The upper end of the lower hydraulic cylinder (409) is connected from bottom to top to a pressure sensor (408), a lower slider (407), and a lower punch (406). The upper slider (403) and the lower slider (407) are both provided with grating rulers (4010, 4011) on their outer sides to monitor the displacement of the upper hydraulic cylinder (401) and the lower hydraulic cylinder (409). The pressure sensors (402, 408) are used to detect the reaction force of the pressed object. Two independent control units with dual valve cores (200, 300), each of which includes: a first proportional valve (204, 304) and a second proportional valve (205, 305). The first proportional valve (204, 304) is connected to the rod-side chamber of a hydraulic cylinder on one side of the bidirectional powder pressing molding unit, and the second proportional valve (205, 305) is connected to the rodless chamber of a hydraulic cylinder on the same side of the bidirectional powder pressing molding unit. A one-way sequence valve (206, 306) is connected in series between the first proportional valve (204, 304) and the rod-side chamber. A leak-free solenoid valve (2011, 3011) is connected in series between the proportional valve (205, 305) and the rodless chamber; one side of the first proportional valve (204, 304) and the second proportional valve (205, 305) includes a P port and a T port, and the other side includes an A port and a B port. The P port of the first proportional valve and the P port of the second proportional valve are connected to the oil tank through a first pipeline. The T port of the first proportional valve and the T port of the second proportional valve are connected to the oil tank through a second pipeline. The B port of the first proportional valve is blocked, and the A port of the second proportional valve is blocked. The control unit includes a relationship curve between the reaction force of the pressed object and the displacement of the upper hydraulic cylinder (401) and the lower hydraulic cylinder (409). The control unit is connected to the two independent control units (200, 300) with double valve cores to control the operation of the two independent control units (200, 300) with double valve cores according to the relationship curve.

2. The hydraulic system as described in claim 1, characterized in that, A first safety valve (207, 307) and a first pressure sensor (208, 308) are provided as a bypass between the T port and the rod chamber of the first proportional valve, and a second safety valve (2010, 3010) and a second pressure sensor (209, 309) are provided as a bypass between the T port and the rodless chamber of the second proportional valve.

3. The hydraulic system according to claim 1, characterized in that, An electromagnetic relief valve (202, 302) is connected between the first pipeline and the second pipeline.

4. The hydraulic system according to claim 1, characterized in that, The first lines of the two dual-valve independent control units (200, 300) are connected to the same hydraulic pump (101), which supplies oil from the tank into the first lines.

5. The hydraulic system according to claim 1 or 4, characterized in that, One-way valves (201, 301) are connected in series on the first pipeline of each of the two dual-valve core independent control units (200, 300).

6. The hydraulic system according to claim 1, characterized in that, The pressure sensors (402, 408) are spoke-type pressure sensors, and the spoke-type pressure sensors are rigidly connected to the upper slider (403) and the lower slider (407).

7. The hydraulic system according to claim 1 or 6, characterized in that, The upper punch (404) is detachably connected to the upper slider (403), and the lower punch (406) is detachably connected to the lower slider (407).

8. The hydraulic system according to claim 1, characterized in that, The relationship curve was obtained through multiple experiments.

9. The hydraulic system according to claim 1, characterized in that, The leak-free solenoid valve (2011, 3011) is a two-position, two-way leak-free seat valve plate structure.

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