Development trend of the main drive of the hottest

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Development trend of main drive of CNC turret punch

CNC turret punch, as a key equipment for sheet metal stamping, has been applied and developed for nearly 50 years. Among them, the main transmission components, as the power source of stamping, have also experienced several stages of change and development

the original mechanical main transmission components are composed of motor, flywheel, clutch and brake, crankshaft, connecting rod and slider. The slider moves vertically up and down to press the punch of the die into the metal sheet. The connecting rod connects the crankshaft and the slider, transforming the rotational motion of the crankshaft into the linear motion of the slider. The flywheel is connected to the rotating motor through a belt and stores a certain amount of energy. When punching, the clutch is closed, and the flywheel energy is transmitted to the punch through the crankshaft connecting rod mechanism. At the end of stamping, the clutch disengages when the punch moves upward, so as to relieve the torque transmission of the flywheel to the crankshaft. At the same time, the brake starts to brake and stops when the crankshaft rotates to the top dead center. In mechanical main transmission components, the performance of clutch and brake is very important, which directly affects the working efficiency and service life of main transmission components

in the 1960s, when the numerical control technology was introduced into the control of the numerical control turret punch, a pneumatic clutch and brake were used. Although its structure was relatively simple, its disadvantages were that the friction plate lost quickly, was highly polluting, had poor performance stability, needed frequent adjustment and maintenance, and its working frequency was low and its noise was high. Until the 1980s, hydraulic clutches and brakes were introduced, which have the advantages of stable performance, low noise, low pollution, etc., and their service life is much longer than that of pneumatic clutches and brakes, greatly reducing downtime and maintenance costs

since the 1990s, hydraulic main transmission components have been more and more used, and have become the mainstream configuration of CNC turret punches. Compared with the mechanical main drive, the oil cylinder replaces the mechanical structures such as crankshaft and connecting rod, and the hydraulic station provides power. The two are connected by the main hydraulic valve block, and the action of the whole system is programmed through a special electronic card. The electronic sensor connected to the piston rod of the oil cylinder measures and feeds back in time, and finally realizes the accurate control of the punch position, stroke and speed

the advantages of hydraulic main drive are mainly shown in the following aspects:

first, according to the sheet thickness, punching type, feeding speed and distance and other factors, the appropriate top dead center position can be set in the program, the punch stroke can be minimized, and the intermittent time between feeding and stamping can be eliminated through parameter optimization, so as to improve the stamping frequency

second, because the speed of the punch in the whole stamping cycle can be parametrically changed, the impact and vibration are reduced by reducing the speed of the punch when it contacts the sheet metal, so as to reduce the stamping noise

third, stamping technology has been further expanded. Not only can it carry out high-speed marking and fast punching, but also because the punch has high stopping accuracy and can send out the maximum punching pressure in the whole stroke, it is suitable for completing some special forming such as stretching and rolling

at present, there are two main types of hydraulic systems used in the main drive of CNC turret punch press:

first, the series products specially used for punch press of Harley company in Germany (see Figure 1), which have the advantages of leading technology, complete specifications, excellent performance, low energy consumption, easy maintenance and so on, and have a high market share at home and abroad

Figure 1 Schematic diagram of the hydraulic system of Harley hkl in Germany

is a series of experimental machines from Schneider and Rexroth in Germany, which are compact in structure, beautiful in shape, stable in quality, and have the functions of discharging oil smoke, odor pollution and cooling. The servo valve controlled hydraulic punching system has the characteristics of fast response and high position accuracy, but it has the disadvantages of high energy consumption, heat generation and high maintenance cost

in recent years, with the improvement and promotion of high torque servo motor and drive system, servo motor driven main drive components have been successfully applied to the CNC turret punch products of Amada, Muratec and other companies in Japan. Domestic manufacturers are also starting to develop and launch such products

at present, there are mainly two structural forms of servo motor driven main drive:

first, based on the traditional mechanical main drive, the servo motor and peek packing can be used for up to 3 years to connect directly with the crankshaft, eliminating the flywheel, clutch and brake. The em2510nt CNC turret punch of Amada company in Japan connects two servo motors to both ends of the crankshaft respectively to control its synchronous operation, ensuring sufficient torque output to the crankshaft and obtaining high stamping frequency at the same time. Another structural form is that the servo motor is connected to the crankshaft through the reducer (see Figure 2), which can appropriately reduce the rated torque of the servo motor, but the maximum punching frequency is also limited

Figure 2 CNC servo motor driven main drive component

second, the servo motor is connected with the crank elbow mechanism through the reducer, which is the structural form of motor-2048lt CNC turret punch of Muratec company in Japan (see Figure 3). Although the structure is relatively complex, it can reduce the load torque of the servo motor by using the unique force increasing characteristics of the crank elbow mechanism. In addition, the crank rotates for one cycle and the slider moves up and down twice, so as to achieve a higher stamping frequency

Figure 3 Schematic diagram of servo motor driven main drive of Muratec company in Japan

servo motor driven main drive not only retains the advantages of mature and reliable mechanical main drive structure, but also has many characteristics of hydraulic main drive. Its characteristics mainly include:

first, energy saving. In the traditional mechanical main drive, the motor drives the flywheel to rotate and accumulate a certain amount of energy. In the working process, the flywheel energy is consumed during stamping and re accumulated when it returns to the upper part, which lays a foundation for the large-scale production of plastic products for automobile and aerospace. For the servo motor driven main drive, the energy does not need to be stored, and the servo motor does not need to rotate all the time. It only starts and provides the required energy when the oil delivery valve is slowly opened. In addition, because the flywheel, clutch and brake are eliminated, the structure is simplified, so the power consumption is greatly reduced. Compared with their traditional models, the above two CNC turret punches save 60% and 30% energy respectively, which is very significant

second, reduce noise. When the slider stamping die penetrates the sheet metal, it will be vibrated and impacted by the stamping reaction, and the resulting noise will also increase with the increase of slider speed and stamping pressure. Mechanical main drive punches usually reduce noise by strengthening the bed and increasing the tonnage. However, the servo motor-driven main drive punch can control and adjust the speed of the slider at every moment of the stroke. Therefore, the punch can be controlled in the middle of the stamping to stop it and reduce the speed when it enters the sheet metal, so as to achieve the purpose of reducing noise. Generally, the noise reduction effect can reach about 10 dB. In addition, in this way, while reducing noise, it can also reduce the impact when the punch enters the sheet metal, thereby extending the service life of the die

third, improve efficiency. The stroke and speed of the slider of the servo motor driven main drive can be adjusted arbitrarily, the shortest stroke required for stamping can be selected, and the appropriate speed can be set to synchronize it with the feeding, so as to effectively improve the productivity. The em2510nt CNC turret punch of Amada company in Japan can punch 500 times/minute at a 25mm step, and 1800 times/minute at the time of stamping. This index has reached the high-end level of the current CNC turret punch

fourth, optimize the process. By accurately setting the stop position of the slider, especially the bottom dead center, the machining accuracy of the forming die can be improved. According to the stamping process and die type, the slider is controlled by optimizing the program to adapt to various stamping modes, such as stamping, punching, forming, etc. Several typical working modes are listed below: 1) high speed punching. The servo motor operates intermittently, and controls the punch to punch with the shortest stroke and the fastest speed according to the sheet thickness and punching size. 2) Step dash. The servo motor operates continuously and presses continuously at an appropriate frequency according to a certain feeding speed and step distance. 3) Molding. Accurately set the lower dead center position and stop time of the punch, so that the forming die can ensure the full deformation and flow of materials, and improve its forming accuracy. 4) Silent processing. The punching speed is controlled by program, and two-stage punching is adopted to reduce vibration and noise and prolong the service life of the die. 5) Mold calibration. By monitoring the output torque of the servo motor, the alignment of the upper and lower molds is detected. In this mode, the control slider slowly drops to the set position, and monitors the torque of the servo motor when the punch contacts the lower die. When it exceeds the preset value when entering smoothly, the punch will stop moving and give an alarm

although the three main drive forms of CNC turret punches are currently in production, from the sales situation in recent years, the sales of mechanical CNC turret punches are gradually shrinking, the hydraulic CNC turret punches are increasing and have occupied a leading position, and the servo motor-driven CNC turret punches are also being recognized and accepted by the majority of equipment users with their advantages of high efficiency, energy saving, environmental protection and so on, It has become a new trend in the future development of CNC turret punch

China machinery and metals (end)

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