A plasma is an ionized gas composed of electrons, positive ions, and neutral atoms. Plasma cutting is a method of partially melting metal at the workpiece incision by using the heat of a high-temperature plasma arc, and discharging the molten metal by high-speed plasma to form a slit. 1. It has a high cutting speed, high cutting precision and easy cutting conditions. It is widely used due to its advantages of easy automation, unmanned operation and relatively low cost. 2. With the combination of information technology and control technology and plasma cutting, the newly developed plasma cutting machine has been designed in theory and design parameters. , product quality and performance have made great progress. 3 At present, in the stainless steel sheet cutting, many manufacturers are using traditional stamping methods. The stamping method has simple structure, convenient operation and no heat affected zone, but it also has many shortcomings, mainly manifested in: low material utilization rate, unstable product quality, high labor intensity and poor production environment. Especially in manual stamping, raw material feeding is mainly based on the operator's observation and judgment. There must be a certain margin for the operator to identify, and the quality of the product is subjective with the operator's proficiency, work attitude and responsibility. The factors are closely related. At the same time, the stamping method has to go through two steps of cutting and stamping, so the work efficiency is low. The noise of the stamping is very large, and the production environment is bad, which also has an adverse effect on the operator's body and mind. In addition, the use of a large number of molds brings great difficulties to production management, and their design, manufacture and maintenance also require a lot of manpower, material and financial resources, and increase the production cost of the enterprise.
Plasma cutting can streamline the blanking process and combine the original cutting and stamping processes into a cutting process. At the same time, plasma cutting facilitates automation and improves work efficiency; it is easy to achieve precise feed, improve material utilization, and is also conducive to maintaining product quality stability. More importantly, the application of plasma cutting can achieve moldless cutting, avoiding the use of a large number of molds in production, and bringing great convenience to enterprise management. Therefore, the introduction of plasma cutting into the cutting process of stainless steel pressure feeding length Iff uniformity control sheet has great economic value and practical significance for related enterprises.
At this stage, CNC plasma cutting is a major development direction of plasma cutting. CNC machine tools have high manufacturing flexibility, high processing precision, stable quality, high productivity, easy to improve working conditions, and facilitate modernization of production management. The combination of plasma cutting technology and numerical control technology can give greater advantages to plasma cutting. In order to achieve automatic cutting, the plasma cutting machine must be able to continuously feed and automatically feed; the torch should be able to move separately or in combination in the lateral and longitudinal directions to form the required machining curve. The functional parts of the machine should be able to closely cooperate and coordinate, such as feeding, cutting and delivery of finished products, etc., in order to achieve precise continuous cutting. At the same time, the various process parameters of the cutting requirements can be flexibly adjusted, such as speed, pressure, air pressure, current and torch height to optimize the process parameters to meet the cutting requirements of different plates.
1.2 Plasma cutting process The introduction of plasma cutting greatly simplifies the cutting process. Through the in-depth analysis of the cutting process, the approximate process flow of plasma cutting can be obtained. The specific process is as shown.
M material leveling feed tensioning plasma finished product collection residue collection plasma cutting process 2 The overall structure and cutting process of the plasma cutting machine To achieve the above cutting process, the corresponding mechanical body must be adapted to it. The design of the mechanical structure should follow the principle of economical application, stability and reliability, that is, make the structure as simple as possible while satisfying the functional requirements. 4. The plate plasma cutting mechanism designed in this paper includes 5 parts, as shown in the figure 5. The whole of the plasma cutting machine The schematic diagram of the plasma cutting process is as follows: Firstly, the stainless steel coils are installed in the order shown, then the various mechanisms are adjusted, the motor is started, the shaping and feeding are realized, and the control system sends a signal to the required length, and the cutting head starts to work. At the same time, the receiving mechanism starts to operate, and the cut disc is sent out by the conveyor belt, and converted to the crawler belt drive. After the finished product collection frame, the crawler belt is opened, and the finished product falls into the finished product collection frame by its own weight. The gap between the shaping mechanism and the traction device roller can be adjusted to adjust the shaping pressure and the traction force to adapt to the cutting of plates of different thicknesses.
The cutting part of the plasma cutting machine is an important part of the cutting machine and is the direct actuator of the cutting. Its design directly affects the quality of the product. It not only requires proper parameter settings, such as arcing voltage, cutting current, cutting speed, distance from the cutting nozzle to the workpiece, but also requires accurate motion and small feed error. In the following, the cutting part of the machine will be analyzed and discussed in depth.
3 Plasma cutting mechanism design 3.1 The role of the cutting mechanism analysis Plasma cutting mechanism is the main working part of the machine, is the key to ensure cutting quality and improve work efficiency. The common plasma cutting mechanism is mainly in the form of cantilever, gantry and table.
They each have their own characteristics and are suitable for different processing occasions.
3.2 Advantages and Disadvantages of Various Plasma Cutting Mechanisms Compared to cantilever mechanisms: equipment movement, easy installation, compact structure, small space location, and low manufacturing cost. However, due to the limitation of the cantilever structure, the stress conditions are poor, lateral deformation is easy to occur, the lateral cutting width is limited, and the rigidity is poor at high speed cutting.
Gantry-type cutting mechanism: two-way support of gantry type support, uniform force, good rigidity of equipment, can achieve large lateral span, usually up to 3~10m. However, equipment installation requirements are high, the structure is relatively large, and it needs to be occupied. More plant area. The driving method is divided into one side drive and two side drive. Both unilateral and bilateral drives have their own characteristics and use. The unilateral drive avoids the high-precision synchronous control and complicated structure of the bilateral drive, but the driving force does not pass through the center of mass due to the centroid bias, and an asymmetrical inertial force will be generated in the work, which is prone to adverse conditions such as vibration, deformation and tilt. Therefore, it can only be used for small spans. 6. The bilateral drive structure is relatively complex, requiring high-precision synchronous control on both sides, which can be used for larger spans and smoother motion.
Desktop cutting mechanism: The cutting part and the machine are integrated, and the movement is convenient, but the range of the torch movement is relatively small, and the size of the cutting frame is limited.
Comparing the advantages and disadvantages of the above three cutting mechanisms, the gantry cutting mechanism can cut the span, the movement is stable, and the stability is good, which is consistent with the requirements of the enterprise. Therefore, a gantry cutting mechanism is used here.
3.3 The motion analysis of the cutting mechanism is carried out by means of plate fixation and torch movement. The torch needs to be able to move in three directions: horizontal, vertical and vertical. The transverse and longitudinal directions are used to form the various trajectories required for machining. The vertical direction is to adjust the distance from the torch to the workpiece for process parameter optimization. Adjustment.
In NC machining, interpolation is the necessary movement to form the machining path of the workpiece. That is, the numerical control system uses a certain algorithm to calculate according to the contour data of the workpiece, and sends a feed command to the corresponding coordinate axis according to the calculation result, and then the feeding mechanism. The corresponding distance is moved according to the command to form a machining contour of the workpiece. Different algorithms have two effects on CNC machining, namely the size of the interpolation error and the speed of the interpolation. Among the many interpolation algorithms, the point-by-point comparison method is widely used due to its faster calculation speed and appropriate interpolation error. The principle is that the tool compares the machining point with a given graphic trajectory every step of the control system to determine the direction of the next feed, so that the trajectory of the tool motion approaches the contour of the workpiece. 7. The lateral and longitudinal motion of the mechanism is interpolated. Movement, which has frequent commutation, has a small single feed, and uses a small fold line to approach a straight line or an arc, and the motion accuracy is high. Therefore, the execution member is required to have sufficient accuracy and requires smooth motion. The lateral movement of the torch is achieved by the gantry driving the torch mounting block, while the longitudinal movement is achieved by the torch mounting block moving along the gantry beam, and the vertical adjustment is achieved by the movement of the torch along the torch mounting block.
3.4 The realization of the movement of the cutting mechanism 3.4.1 The lateral movement of the gantry The lateral movement of the gantry is considered to be realized by the ball screw nut mechanism. The ball screw nut mechanism has the following characteristics: (1) small friction, high efficiency, mechanical efficiency of more than 90%; (2) high sensitivity, stable transmission; (3) less wear and long life; (4) can eliminate the shaft To the gap 8. Due to the above advantages, the ball screw nut mechanism is widely used in linear transmission.
In order to balance the forces on both sides, the gantry adopts a bilateral drive. The servo motor is used to control the moving distance of the lead screw. The servo motor has the advantages of good stability, low power consumption, long life, high positioning accuracy and fast response speed. Controlled by a servo motor, speed and position control are very precise. In order to avoid motion interference, the front and rear drive motor must be strictly synchronized.
According to the analysis of working conditions, the work has only slight vibration, the mass of the working part is m=270kg, and the maximum acceleration amax speed amin=5m/s2, so that the maximum axial working load Fmax can be obtained. The maximum speed of the screw is nmax=100r/min. The minimum speed nmin=10r/min, and the precision of the lead screw is selected as 4 levels. The design of the ball screw is calculated as follows: 9 The longitudinal movement of the torch along the beam is also a linear movement, so it is still realized by the ball screw nut mechanism, and its structure is similar to that of the gantry, which will not be discussed in detail here.
3.4.3 Adjustment of the torch in the vertical direction The distance from the torch nozzle to the workpiece has an important influence on the plasma cutting. If the distance is too large, the arc length increases, the heat loss increases, and the cutting ability decreases. Conversely, if the distance is too small, the short circuit between the nozzle and the workpiece is likely to burn out the nozzle, and the cutting process is normally broken.
Therefore, the distance adjustment of the torch in the vertical direction is very important. The design also needs to take into account the feasibility of the solution, the simplicity of the structure and the ease of operation. Here, an eccentric slider mechanism is used to achieve height adjustment of the torch in the vertical direction.
The eccentric wheel has the characteristics of simple structure and convenient adjustment. The specific implementation process is as follows: the slider and the torch are connected together, and the vertical movement of the slider drives the torch to move vertically, and the rotation of the eccentric wheel controls the height of the torch in the vertical direction. Its structural schematic is as shown.
Accurate calculations over the entire distance. Assuming that the eccentricity of the eccentric is e, the adjustable range of the slider is 2e. According to the process requirements, the distance from the torch to the workpiece is generally required to be between 4 and 10 mm, and the variation range is 6 mm. Therefore, the eccentricity e is set. For 5mm, the height adjustment range Ah is sufficient for use.
The highest position, the distance from the slider to the center of the eccentric wheel is h, then the eccentric wheel turns over any angle 0, the height change amount Ah can be calculated: where: L is the length of the link.
From the formula (1), the position of the slider when the eccentric is turned to any angle can be obtained, so the height of the slider can be precisely adjusted by controlling the rotation angle of the eccentric. 3.4.4 The overall assembly drawing of the cutting mechanism is integrated with the horizontal and vertical moving mechanisms. And the heightening device, the final cutting mechanism is available as shown.
The mechanism is simple in structure, convenient in adjustment and precise in control, and can realize horizontal or vertical single or interlocking movement, can conveniently form a plurality of processing trajectories, adapt to processing requirements of different workpieces, has wide processing range, and has great flexibility and adjustment. space. The height of the torch in the vertical direction can be precisely adjusted to meet the height setting requirements of different processes.
Due to the large span of the gantry, the bilateral drive is used in the horizontal direction to make the movement smooth.
4 Conclusion Plasma cutting technology has the advantages of fast cutting speed, good cutting quality and low cost. This technology can be used to cut stainless steel sheet, which can effectively improve the automation level of stainless steel sheet blanking process, improve working environment and improve material utilization efficiency. , with greater economic and social benefits. In this paper, the overall structure of a plasma cutting machine is discussed. The cutting mechanism is analyzed and discussed. Through the function and motion analysis of the mechanism, the detailed design of key components and the comparison of design schemes, an economy is proposed. The applicable structural scheme can better meet the practical use requirements of cutting production.
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