Development status and research trends at home and abroad

The sheet metal bending machine is a widely used bending machine, which has already realized hydraulic pressure, and rapidly realized numerical control in the 1980s. According to incomplete statistics, CIMT95 exhibited 18 bending machines, including 7 from foreign countries and 11 from China (including 1 from Taiwan). Except for one in Taiwan, all 17 of them are CNC bending machines. At the previous international machine tool exhibitions in my country, there were many bending machines on display this time, and there were also many domestic bending machines, and the level was high. The sheet metal bending machine uses a simple mold to bend the metal sheet at various angles to obtain complex-shaped sheet metal parts. The operation is simple, the mold is versatile, and the operating cost is low, so it has been widely used . Sheet metal bending machines can be divided into mechanical bending machines and hydraulic bending machines according to their transmission mode. At present, mechanical bending machines have been replaced by hydraulic bending machines. The advantage of hydraulic bending machine is that it has a large working stroke, which can produce the maximum nominal force at any point of the stroke; the bending stroke, pressure, and speed are adjustable, and it is easy to realize numerical control; it can realize fast approach and slow bending , In line with the process requirements of workpiece bending; the use of multi-cylinder synchronization system greatly improves the bending accuracy, and realizes the linkage of multiple bending machines, which broadens the process range of the bending machine. The CNC hydraulic sheet metal bending machine is a sheet metal processing machine tool that has come out early, is widely used, and has many domestic manufacturers. It has developed from the early 3-axis to the current 8-axis control. It can be used with loading and unloading robots and bending robots. It is composed of CNC bending unit.

The emerging medium and high-end building material decoration industry at home and abroad puts forward higher requirements for the required metal decoration materials, that is, the edge arc radius of the bent metal sheet workpiece is as small as possible, and the metal sheet shakes the surface of the workpiece without refraction. ; The bending section shape of the thin metal sheet is required to be more complicated, which can better reflect the designer's trendy design style.

Technical requirements of this design

To design a vertical sheet metal bending machine, the slide block and the bending mechanism of the vertical movement are to be hydraulically driven, and the working cycle required through electro-hydraulic control is: rapid descent → slow pressurization (bending) → Fast return. Maximum bending force Fmax=0.5×106N, slider gravity G=12000N, rapid descending speed v,=20mm/s, slow pressurization (bending) speed vg=10mm/s, rapid ascent speed vg= 45mm/s; fast descending stroke l=150mm, slow pressurizing (bending) stroke 12=30mm, fast rising stroke ls=180mm; starting and braking time △t=0.15s. It is required to balance the weight of the slider and the bending mechanism by hydraulic means to prevent its own weight from sliding; the friction force of the slider rail can be ignored. As an executive component, it drives the slider and the bending mechanism to perform bending operations on the sheet metal.

task analysis

Since the bending machine is a vertical arrangement, the slider is linearly reciprocating up and down, and the stroke is small (near 180mm), so you can choose a vertical single-rod piston hydraulic cylinder with a fixed cylinder (the mechanical efficiency of the hydraulic cylinder is In the transmission system of the vertical sheet metal bending machine, the up and down movement of the slider and the bending mechanism is to be hydraulically driven, and the working cycle required to be realized by electro-hydraulic control is: fast drop → slow pressurization (bending) → fast Return stroke. Maximum bending force Fmax=0.5×106N, slider gravity G=1200ON, rapid descending speed v1=20mm/s, slow pressurization (bending) speed v2=10mm/s, rapid ascent speed v3 =45mm/s; rapid descending stroke 11=150mm, slow pressurizing (bending) stroke 12=30mm, rapid ascent stroke 13=180mm; starting and braking time △t=0.15s. Hydraulic method is required Balance the weight of the slider and the bending mechanism to prevent its own weight from sliding; the friction force of the slider rail can be ignored. As an executive component, the slider and the bending mechanism are driven to bend the sheet.

Because the work cycle of the sheet metal bending machine is three stages: rapid descent, slow pressurization (bending), and rapid return. The conversion of each stage is controlled by a three-position four-way electro-hydraulic directional valve. When the electro-hydraulic directional valve works in the left position, a quick return stroke is realized. It realizes the unloading of the hydraulic pump when working in the neutral position, and realizes the rapid and common advancement of the hydraulic pump when working in the right position. The speed change is controlled by the pressure-limiting variable vane pump and the flow control is controlled by the limit switch. When the bending machine descends rapidly, its speed is required to be faster to reduce the time of idle travel. The hydraulic pump adopts full pressure oil supply. The stroke of the piston is controlled by a stroke valve. When the piston moves to a certain position at a constant speed, the stroke valve receives the signal and generates an action to realize the transition from fast forward to work forward. When the piston moves to the termination stage, the pressure relay receives the signal to change the direction of the electro-hydraulic directional valve. Because the pressure of the press brake is relatively large, the pressure in the oil chamber is relatively large at this time, so a pre-pressure relief circuit is required from the work to the rapid return stage to prevent the hydraulic components from being impacted at high pressure and to unload the oil circuit smooth. Therefore, a pre-pressure relief circuit can be designed on the fast return oil circuit, and the unloading speed of the circuit is adjusted by a throttle valve. At this time, the directional valve is in the neutral position. When the pressure is relieved to a certain pressure, the reversing valve is switched to the left position again to realize smooth unloading. In order to monitor the oil pressure, a pressure gauge and overflow valve are installed at the outlet of the hydraulic pump, which also protects the system from overload. Because the slider is subjected to its own gravity, the slider will have to slide down, so the oil circuit must design a one-way sequence valve as a balance valve to form a balance circuit, generate a certain amount of back pressure, and also make the work progress smooth. A one-way valve is designed at the oil outlet of the hydraulic pressure pump, which can be used as a preset pressure valve, and can also provide starting pressure for the reversal of the electro-hydraulic directional valve, and can prevent the impact of oil pressure on the hydraulic pump. Play a protective role.