Design of Large Economical CNC Cutting Machine

Large-scale economical CNC cutting machine design Guo Yongping, Dong Qinghua, Jiang De (Chengde Petroleum Technical College, Chengde 067000, Hebei). The purpose of the design is simple operation, low price, high reliability and convenient maintenance. The heart of the design is a numerical control system, which uses an industrial computer as a control platform. In its design and production, many problems such as electromagnetic compatibility, system reliability, and high production cost have been overcome, and the design purpose has been achieved, and the new product appraisal has been passed.

At present, steel plate blanking in my country’s machining industry generally uses oxyacetylene cutting, while most of the blanking processes of foreign companies use CNC oxyacetylene or CNC plasma arc cutting methods, which can not only increase material utilization, but also improve product quality. Optimize the working environment and improve work efficiency. The main reasons why CNC blanking cannot be popularized in my country are: financial problems, equipment failure maintenance problems, and operation problems. The control systems of domestic CNC cutting machines are all produced abroad, and their operations are more complicated, requiring higher-quality operators and specialized training. The investigation found that for users, their products are not updated frequently, and the shapes and sizes of the parts to be cut are relatively limited, which requires simple and reliable operation of the machine. Therefore, the existing CNC cutting machine does not satisfy users. For this reason, I decided to design a large-scale economical CNC cutting machine for most users and suitable for national conditions.

1 Design requirements The design includes: mechanical parts, numerical control parts, cutting devices, etc.

Applicable direction: It is required to have a wide range of applications. It can be used in the blanking workshop of large enterprises for batch cutting of large parts; it can also be used in small machinery factories for small batch production of small parts.

Technical level: its comprehensive technical level requirements exceed domestic products of this type and approach the world’s advanced level.

Production cost: The overall cost is lower than the existing domestic similar cutting machines.

Machining accuracy: Machining accuracy exceeds the current national standards.

Applicable materials: carbon steel, stainless steel, non-ferrous metals.

Failure rate: The average trouble-free time is greater than 3000h. Workpiece size: greater than 50mx30b, the maximum radius of the arc difference is greater than the programming mode: graphic automatic programming f manual ISO code editing.

Cutting speed range: In order to achieve the above design goals, the overall design emphasizes design * optimization, system modularization, and simplification of processing in the selection of the plan. For this reason, in the design of each part of the cutting machine, a number of scheme designs have been carried out, and processing comparisons and preliminary tests have been carried out, and the best design has been selected. The CNC cutting machine is mainly composed of the following parts: The main function of the mechanical part is to support 1=6 cutting torches!

-Plane linkage, and each cutting torch can move independently in the direction to adjust the distance between the cutting nozzle and the steel plate. At the same time, it also supports the installation and necessary movement of the numerical control device and the air distribution pipeline.

In order to achieve the above functions, and to facilitate processing, control, installation and commissioning, it is decided to adopt a portal structure as a whole, that is, a cross beam is supported by a trolley on the left and right longitudinal guide rails, and 1=6 horizontally movable cuts are installed on the cross beam. The torch trolley is driven by the two trolleys on the longitudinal guide rail to move the cross beam in the longitudinal direction. At the same time, the torch trolley on the beam drives the torch to move laterally along the beam. In this way, for the cutting torch, its movement is a composite movement of longitudinal and transverse, so it can form any plane curve movement in the horizontal plane, see. In order to become the movement of the cutting torch, the rotation movement of the servo motor needs to be changed into the linear movement of the traveling carriage and the cutting torch trolley on the beam. The optional solutions include screw-screw motion pair, toothed belt, and gear-rack motion Vice, roller, linear motor, etc. *Finally, after weighing the overall performance and testing, the drive mode of the gear-rack motion pair is selected, and the ball bearing is combined between the trolley and the track, and finally two longitudinal trolleys and several horizontal trolleys are formed.

Numerical control part The numerical control part is used for the automatic ignition of the cutting machine, automatic punching, the interpolation calculation of the cutting torch movement, the ignition and extinguishment of the plasma arc, the echo display of the working status, and the man-machine dialogue, etc. This part is the core of the entire cutting machine, and its performance has a decisive influence on the success or failure of the final design. Therefore, it has been repeatedly demonstrated, tested and improved, and finally reached the design requirements. The first is display and control. In order to meet the usage habits of most domestic users and make the operation easier and more intuitive, it was decided to use the Chinese menu plus 1: Guo Yongping 964 One male I Welding equipment and materials Lin Yihong machine tool numerical control technology and its application. Beijing: Machinery Industry Press, graphics display. In order to speed up development, improve system reliability, and reduce production costs, ordinary industrial computers are used in the human-computer interaction part. Its advantages are reliable work, strong anti-interference ability, good software versatility, and low price. After adopting industrial computer, human-computer interaction software can be easily developed on the high-level language platform, which makes the control and display interface simple and convenient, and at the same time, it greatly accelerates the development speed of the system. For the underlying control hardware, in order to increase the characteristics of the developed system and improve the flexibility of control, it was decided to develop the controller by itself. The microcontrollers that can be used in the controller include single-chip microcomputers, DSPs, MPUs, etc., considering performance and development costs, the 8XC196KC series of single-chip microcomputers from INTEL are finally selected.

23 Cutting device This part is used to realize the cutting of the final plate, which will determine the key indicators such as the material type, thickness and processing quality that the cutting machine can process. There are many cutting methods that can cut coriander and meet the design requirements, mainly including: oxyacetylene flame, high current plasma arc, oxypropane flame, high power laser, ultrasonic beam, high pressure water, etc. Taking into account factors such as equipment investment, equipment operating costs and enterprise production habits, it was decided to use oxyacetylene flame as the cutting method for medium-thick carbon steel plates, and high-current plasma arc as the cutting method for non-ferrous metals and thin carbon steel plates. The high-current plasma arc cutting machine chooses the inverter air plasma arc cutting machine with little interference to the CNC system, light weight, and small size, which not only reduces the cost but also facilitates flexible installation. The oxyacetylene flame cutting system is mainly composed of cutting torches for large machines, gas separation and gas transmission, flow adjustment, gas circuit control, and automatic ignition. ! Design difficulties and solutions. Large-scale CNC cutting machine is a complex system, which integrates computer technology, precision machinery manufacturing, motor drag, digital control, thermal processing and other disciplines, so design, production, debugging, installation, maintenance, etc. Difficulties will be encountered in each link, and through joint efforts in many aspects, all the difficulties have been overcome and the prototype meets the design requirements. The difficulties encountered in the design and the solutions are summarized as follows.

Computational speed and processing accuracy. The real-time and high complexity of the control of the cutting machine is the difference compensation control of the torch movement. The difference compensation is divided into arc difference compensation and straight line difference compensation. Among them, the calculation complexity of arc difference compensation is more complicated. high. In the 80C196KC, the double-word precision circular arc difference compensation operation requires approximately 280 state cycles per step. In the case of a 16MHz crystal oscillator, it takes about 35, that is, approximately 28,000 difference compensation operations can be performed per second. What affects the calculation and accuracy is the pulse equivalent of the cutting torch movement, that is to say, the difference between the CPU and the calculation of the movement distance of the cutting torch each time. According to the design, the maximum simulation speed should be 100mm/s. At this time, the minimum pulse equivalent is: 100/28000>0.00357<<. Taking into account other operations in the control degree, the pulse equivalent is taken as 000625mm. Test proof , Can achieve the required processing accuracy.

Pulse equivalent and workpiece size data When cutting the material, the work often contains arcs with large radius dimensions, such as overhead crane beams, trailer main beams, bridges, etc. The design requirement can reach the maximum arc radius of 1000m. When the pulse equivalent is 000625mm, the binary bit required for the maximum word length is 29bit, and 4 bits are actually used. Therefore, double words are used in the control degree of 80C196KC. Operation subroutine.

The complexity of the workpiece and the storage space of the controller are limited due to the use of an independent controller. For the 80C196KC, the program space and data space separation method of the Harvard structure is adopted, and the data space is further expanded through spare pins. Below, a more realistic data space of 64KB can be achieved. Assuming that the arc and the straight line in the workpiece occupy 50H each, plus the linear mark and check character, a straight line needs 10 bits, and a segment arc needs 18 bits, which is 14biE on average. In this way, the maximum number of lines that can be stored in a 64KB data space is: 64×1024/14>4681 segments. According to statistics, the average number of parts in the blanking of the steel plate is about 1030 segments. According to the calculation of 30 segments, the controller can arrange about 100 workpieces at one time, which meets most of the processing requirements.

The anti-interference of the numerical control system. The cutting machine is mainly used in the riveting and welding workshop of the factory. Most of these workshops are equipped with large-scale machining equipment and electric welding machines, etc., which can generate strong electromagnetic radiation in the competitive spectrum. At the same time, the cutting machine itself is composed of multiple systems, which can also produce strong interference, especially easy to interfere with the normal operation of the CNC system, causing system crashes, malfunctions, etc., so the anti-interference ability of the CNC system is very important. The main measures taken in the design are: electromagnetic shielding, that is, installing the CNC system in a shell with strong shielding; power purification, a lot of interference enters the machine from the power cord, so there is a multi-level at the input end of the power supply Filter to eliminate power supply noise; electromagnetic isolation, all input and output terminals of the controller have photoelectric isolation measures, which completely isolates the electromagnetic connection between the CNC system and other parts, greatly improving the anti-interference ability; both the computer and the controller It is a digital processing device that has a certain degree of electromagnetic radiation during work. If the controller is made into a card structure and inserted into the bus plug of the computer according to the traditional method, it is not easy to ensure electromagnetic compatibility, so the computer is used in this design The method of separating from the controller and communicating with the external communication with isolation measures further improves the reliability.

The reliability of automatic perforation of oxyacetylene flame cutting In multi-workpiece cutting, every time a closed contour is cut, the cutting machine needs to perforate in order to cut the next contour. In the case of thick plates, there will be more metal splashes during perforation, which will affect the service life of the cutting nozzle and reduce the cutting quality. In severe cases, it will cause the cutting nozzle to block and cause backfire. Therefore, certain measures must be taken during automatic piercing to prevent metal splashing. There are two main measures: one is to reduce the cutting oxygen pressure during piercing. There are two ways of cutting oxygen in the air supply circuit. One has a lower pressure and is specially used for piercing, and the other has a higher pressure and is used for normal cutting. Another measure is to increase the height of the cutting torch during drilling, so that the height between the cutting nozzle and the steel plate is greater than the normal height during drilling, so that splashing is not easy to damage or block the cutting nozzle. During perforation, the controller first switches the cutting oxygen pressure to a lower perforation pressure, and at the same time drives the cutting torch lifting motor to rotate in the direction of the cutting torch, turning on the cutting oxygen to start the automatic perforation process. After a certain period of time, the steel plate is beaten. Through, the cutting oxygen is switched to normal pressure, and the motor is raised to lower the cutting torch to the normal height, and the part cutting starts. Practice has proved that through the above measures, the reliability of punching is significantly improved, and the service life of the cutting nozzle is greatly extended.

4 Conclusion According to the design requirements, different measures have been taken for different requirements. In the actual product inspection, the design requirements have been met. The design is successful. The equipment has been put into actual production and sold several units. In actual use, it has saved a lot of manpower and material resources for the enterprise, and achieved good results. At the same time, the production cost is significantly lower than similar products, which is very suitable for my country’s national conditions and has a certain competitive advantage.