Development of the most popular high-speed fully a

Development of high-speed fully automatic CNC punch

1 introduction

in view of the large processing volume of sheet metal stamping parts, manual feeding is mostly used at present, which can not meet its production requirements and is prone to personal accidents. We have developed a high-speed fully automatic CNC punch, which can automatically complete the whole process of loading, feeding, discharging and discharging the whole sheet metal

2 structure and working principle of full-automatic CNC punch

the full-automatic CNC punch is composed of five parts: machine tool body, feeding device, feeding device, row waste device, control hardware and control software, as shown in Figure 1

1. Feeding device 2 Machine tool body 3 Two coordinate workbench

4 Row waste device 5 Control cabinet

Figure 1 layout diagram of full-automatic CNC punch

the machine tool body is a deep throat 200kN Crankshaft Press with a large number of domestic ownership. The working principle of the crankshaft press is to control the pull in action of the clutch to control the single or continuous reciprocating motion of the slider, that is, the upper die, to realize the stamping processing of the sheet metal, and to control the brake to stop the working mechanism of the press. The feeding action is generally completed by manual or intermittent mechanical mechanism [1]

the stamping principle of the crankshaft press of the full-automatic CNC punch remains unchanged. The difference is that the computer is used to control the reciprocating of the slider, that is, the start and stop of the reciprocating action of the upper die and the regular X and Y feeding movement of the processed sheet metal, and the two actions can be coordinated, that is, to realize the synchronous control of stamping and feeding actions

in automatic stamping processing, the two coordinate worktable is one of the key mechanical components, and the inertia of the worktable limits the feeding speed and acceleration of the worktable. In order to improve the feeding speed of the workbench, the inertia of the workbench may be reduced in design

in the stamping process, X-axis feeding is more frequent than y-axis, that is, Y-axis feeding is only once when the number of x-axis feeding is the number of workpieces punched in a row of sheet metal. Therefore, when designing the workbench, the x-axis is on the top and the y-axis is on the bottom, so when the workbench is feeding along the x-direction, the x-direction motor only drives the lighter clamp carriage to move along the upper guide rail in the x-direction through the lead screw. When feeding in the Y direction, the Y direction motor drives the heavy mechanism composed of the upper guide rail, the upper motor, the upper lead screw and the clamping carriage to move in the Y direction along the lower guide rail through the lead screw. Therefore, it can provide a fast and safe feeding process. Figure 2 shows the structure of the two coordinate workbench

1. Y-axis lead screw right bearing support 2 Clamp 3 Clamp cylinder 4 X-axis guide rail 5 Clamp fixing plate 6 X-axis nut 7 Clamp support plate 8 Y-axis lead screw 9 Y-axis lead screw left bearing support 10 Y-axis coupling 11 Y-axis stepping motor 12 Y-axis guide rail support frame 13 Y-axis nut 14 Base 15 X-axis stepper motor 16 X-axis coupling 17 X-axis lead screw rear bearing support 18 Y-axis rear guide rail 19 X-axis lead screw 20 Y-axis front guide rail 21 X-axis lead screw front bearing support

Figure 2 structure diagram of two coordinate workbench

the clamp support plate is used to clamp the workpiece as x-axis and y-axis moving parts. In order to reduce its weight, duralumin is selected as the clamp carriage support, and the structure is as simple and compact as possible. Two cylinders are used on the clamp support plate to clamp the workpiece, and its structure is shown in Figure 2. In order to ensure reliable clamping, the jaw surface adopts striation to increase friction

the feeding device is a device that sends the workpiece sheet to the workbench clamp carriage (see Figure 1). Before or during stamping, the punched plates are stacked on the stacking table of the feeding device, and the feeding device automatically completes the feeding of the plates to the clamping carriage of the workbench. The process is as follows: the vertical cylinder moves down, sucks up the uppermost sheet on the stacking table through four vacuum suction cups, then the vertical cylinder moves up, moves up to a certain height, the horizontal cylinder moves right, moves to a certain position and stops waiting. After the current sheet is punched and processed, the workbench returns to zero, the vertical cylinder moves down, places the workpiece sheet on the workbench clamp carriage, and clamps it with the clamping cylinder embedded on the carriage

after a sheet is punched, what is left on the clamp carriage is solid waste. Because the joint of solid waste is replaced by composite material instead of metal, it is only for overlapping, and the minimum is about 1.5mm, so its connection strength is weak. How to safely discharge it will be the key to whether the punch can punch continuously

the roller type discharging device is used for discharging the shaped waste. It is a device in which the material is clamped by the upper and lower rollers in a group, and the shaped waste is discharged through the rotation of the rollers by using the friction force, as shown in Figure 3

Figure 3 Schematic diagram of roller discharging waste

the roller discharging mechanism uses a three-phase asynchronous motor to drive the fixed lower roll, and the upper roll can clamp and separate sheet metal under the drive of one cylinder. The surface of the roller shall be knurled or shot blasted with steel balls to prevent the like waste from slipping

under the condition of not affecting the experimental results, the pressing action of the CNC punch and the feeding action of the workbench must be synchronized, that is, when the upper and lower dies of the punch die are demoulded away from a certain distance, the workbench feeds: when the material is fed to the stamping operation point, the sheet metal is stamped. In the synchronous control, the proximity switch can be used to detect the actual position of the crankshaft of the punch, that is, the position of the upper die, and then the signal (synchronous signal) is input into the control system. After processing, the workbench can make regular feeding movement as required

Figure 4 is the schematic diagram of synchronous signal detection. The test rod and crankshaft rotate synchronously during operation (the test rod material is bakelite or plastic), and the head of the test rod is equipped with a test piece (metal piece). When the test rod rotates to make the test piece enter the effective detection range of the proximity switch fixed on the machine base, the switch will send an induction signal (synchronous signal), which corresponds to the slider, that is, the upper die is separated from the lower die at a certain position, and then the workbench can feed. After the test rod continues to rotate with the crankshaft to make the test piece out of the effective range of the proximity switch, the induction signal disappears, wait for the next induction signal, and continue the next feeding

Figure 4 Schematic diagram of synchronous signal detection

in the stamping process, the stamped parts must be accurately removed from the stamping die between the completion of one stroke of the press and the next stroke of the stamping process. In order to take out the stamping parts from the die, first of all, in order to prevent the stamping parts and waste materials from adhering to the die, the stamping parts and waste materials must be removed from the die. These problems are part of the function of the die, which is completed by the demoulding device composed of the fixed discharge plate and spring installed in the die

after the stamping part is demoulded from the die, the stamping part is taken out from the die. The removal method is to use compressed air to blow the stamping parts left on the lower die or pulled down from the upper die into the workpiece box behind the bed. The method of compressed air blowing is suitable for occasions with high stamping speed and light stamping parts, but the direction of blowing and air pressure should be well adjusted in time. The timing is adjusted by the cam control valve installed on the crankshaft or slider of the punch. When selecting the air nozzle, the aperture of the air nozzle should be small (0.2 ~ 0.5mm)

3 hardware structure of CNC system

the CNC system we developed is a special CNC system for punch press. The servo drive unit adopts stepping motor, and the hardware of the special CNC system adopts the modular structure of multi CPUs (master CPU, slave CPU, display CPU) based on single chip microcomputer. Figure 5 is the hardware block diagram of CNC system with single chip microcomputer as the core

Figure 5 hardware block diagram of CNC system

in order to ensure the high-speed feeding of CNC system, dual CPUs are used to form the main module of CNC system hardware. This dual CPU structure belongs to the master-slave structure, as shown in Figure 5. The master CPU is 8031 and the slave CPU is 8751

because the workbench is x-coordinate and y-coordinate, it is driven by two servo motors. Since the load difference in the two directions can reach about ten times, and the frequency difference of feeding in the two directions is also more than ten times, it is inevitable to use two motors with different characteristics. In order to give full play to their characteristics, their frequency rise and fall laws are also different. When X-axis and y-axis feed at the same time, to realize such a frequency, it is necessary to use a CPU to manage the operation of a motor, and at the same time, it is necessary to ensure that the preprocessing of user programs does not occupy the running time of the motor, The reliable method is to use two CPUs to process the data of X and Y axes respectively. Only in this way can we ensure the high-speed feeding of the CNC system

without running the user program, the whole system is managed by the main CPU, which is responsible for keyboard management, user program input, modification, addition and deletion, and communication of the display module

when the workbench is fed or manually adjusted, samples can also be provided to the manufacturer for an experiment to facilitate the selection of the pressure testing machine. The main CPU controls the x-axis movement and the slave CPU controls the y-axis movement. When the master CPU searches the operation data of X and Y axes, it sends the Y axis data to the slave CPU through 8255. The master and slave CPU make the workbench feed in two directions respectively. Manual adjustment includes single step, medium speed and high speed adjustment

the master and slave CPUs each use a crystal oscillator, and their operation is not synchronous. Although these two CPUs process the operation data of X and Y axes at the same time, there are first and then. Once the data in one direction is processed first, the data in the other direction is not processed yet, and then the synchronization signal has arrived, it is bound to produce one motor movement and the other motor does not move, resulting in action errors. To prevent this from happening, the master and slave CPUs are respectively provided with a synchronous control signal line, as shown in Figure 6

Figure 6 synchronization signal control

when the x-axis data is ready, the x-axis synchronization control signal line becomes high level. If the y-axis data is also ready, the y-axis synchronization control signal line also becomes high level. At this time, the synchronization signal can pass through two and gates, and the master and slave CPUs can control the movement of the two motors at the same time under the action of the synchronization signal. If the y-axis data is not accurate after the x-axis data is ready, the y-axis synchronization control signal line is low. In this case, even if a synchronization signal arrives, it cannot pass through the two and gates. The master and slave CPUs will not receive the synchronization signal, and the two CPUs can only wait for the next synchronization to act together. This processing method can ensure the accuracy of feeding

the man-machine interface of the CNC system adopts keyboard input and CRT display. The keyboard driver adopts 8279 keyboard control chip, and a total of 56 keys are set, including numbers, letters, functions, and manual adjustment keys, which are used to complete the input and modification of NC machining programs, as well as the operation and manual adjustment of machine tools

crt is driven by programmable display controller MC6845. The display module adopts a display CPU, which solves the contradiction between MC6845 and the main CPU in competing for the priority of VRAM operation. Because during the display process, in order to make the image displayed by CRT clear and stable, the operation of the main CPU on VRAM cannot be random, and it can only be operated on VRAM during CRT scanning, otherwise the display effect of CRT will be affected. The main task of the main CPU is the real-time operation of the machine tool, and it is impossible to operate VRAM only within a limited time. When the display CPU is used, the main CPU will send the display information to the public RAM (dual port) preferentially and randomly during the processing, and notify the display CPU. The display CPU takes out the information in the public ram and sends the display information to VRAM within the specified flyback time. It shows that CPU and MC6845 access VRAM in a time-sharing manner to solve the problem of competing for the priority of accessing VRAM

4 software structure of CNC system

in order to facilitate maintenance and use, internationally, CNC system has gradually formed two international general standards in terms of input code, coordinate system, machining instructions, auxiliary functions and program format, ISO international standardization standard and EIA United States