Design of cutting mechanism of the hottest plasma

Design of cutting mechanism of a plasma cutting machine

plasma is an ionized gas composed of electrons, positive ions and neutral atoms. Plasma cutting is a processing method that uses the heat of high-temperature plasma arc to locally melt the metal at the notch of the workpiece, and uses the momentum of high-speed plasma to discharge the molten metal to form a slit. 1 It is widely used because of its fast cutting speed, high cutting precision, easy to set cutting conditions, easy to realize automation, unmanned operation and relatively low cost. 2 With the combination of information technology and control technology with plasma cutting, the newly developed plasma cutting machine has made great progress in design theory, design parameters, product quality and service performance. 3 at present, in the blanking of stainless steel plates, many manufacturers use traditional stamping methods. Stamping equipment 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, the feeding of raw materials mainly depends on the observation and judgment of the operator. There must be a certain margin for the operator to identify, and the quality of products is closely related to subjective factors such as the operator's proficiency, working attitude and heart. At the same time, most stamping methods go through two links: cutting and stamping, so the work efficiency is low. The stamping noise is very large and the production environment is bad, which also has a negative impact on the body and mind of the operator. In addition, the use of a large number of molds brings great difficulties to production management, and their design, manufacturing and maintenance also require a lot of human, material and financial resources, which increases the production cost of enterprises

plasma cutting can simplify the plate cutting process, and merge the original cutting and stamping processes into the cutting process. At the same time, plasma cutting is easy to realize automation and improve work efficiency; It is convenient to realize precise feeding, improve the utilization rate of materials, and maintain the stability of product quality. More importantly, the application of plasma cutting can realize mold free cutting, avoid the use of a large number of molds in production, and bring great convenience to enterprise management. Therefore, it is of great economic value and practical significance for relevant enterprises to introduce plasma cutting into the stainless steel pressure feeding length IFF to control the blanking process of plates

at this stage, CNC plasma cutting is a major development direction of plasma cutting. CNC machine tools have high manufacturing flexibility, high machining accuracy, stable quality, high productivity, easy to improve working conditions, and conducive to the modernization of production management. The organic combination of plasma cutting technology and numerical control technology can give play to the greater advantages of plasma cutting. In order to realize automatic cutting, the plasma cutting machine must be able to feed continuously and automatically; The cutting torch should be able to move independently or jointly along the transverse and longitudinal directions to form the required processing curve. All functional parts of the machine should be able to closely cooperate and coordinate, such as feeding, cutting and finished product delivery. The steps should be consistent to achieve accurate and continuous cutting. At the same time, various process parameters of cutting are required to be flexibly adjusted, such as speed, pressure, air pressure, current and cutting torch height, so as to optimize the process parameters and meet the cutting requirements of different plates

1.2 technological process of plasma cutting the introduction of plasma cutting greatly simplifies the cutting process. Through the in-depth analysis of the cutting process, the general process flow of plasma cutting can be obtained, and the specific process is shown in

m material leveling, feeding, tensioning, plasma finished product collection, residue collection, plasma cutting process 2. The overall structure and cutting process of plasma cutting machine in order to realize the above cutting process, there must be a corresponding mechanical body to adapt to it. The design of mechanical structure should follow the principles of economic applicability, stability and reliability, that is, the structure should be as simple as possible on the premise that the movement of the beam mainly used for the experimental machine meets the functional requirements. 4 The plate plasma cutting mechanism designed in this paper includes five parts, as shown in figure 5 The overall structure of the plasma cutting machine shows that it puts forward higher requirements for the integration and efficiency of the universal tensile testing machine. The plasma cutting process is roughly as follows: first install the stainless steel plate coil in the order shown, then adjust the mechanisms, start the motor to realize shaping and feeding. When the required length is reached, the control system sends a signal, the cutting head starts to work, and the receiving mechanism starts to act at the same time, Depending on the conveyor belt, the cut disc is sent out and transferred to the crawler drive. After reaching the finished product collection frame, the crawler opens, and the finished product falls into the finished product collection frame by its own weight. The gap between the shaping mechanism and the roller of the traction device is adjustable to adjust the shaping pressure and traction force to adapt to the cutting of plates with different thickness

the cutting part of the plasma cutting machine is an important part of the cutting machine. It is the direct actuator of cutting. Its design directly affects the quality of products. It not only requires appropriate parameter settings, such as arc starting voltage, cutting current, cutting speed, distance between cutting nozzle and workpiece, but also requires accurate movement and small feeding error. Next, the cutting part of this machine will be deeply analyzed and discussed

3 design of plasma cutting mechanism 3.1 function analysis of cutting mechanism plasma cutting mechanism is the main working part of the machine and the key to ensure cutting quality and improve work efficiency. The common structure forms of plasma cutting mechanism mainly include cantilever type, gantry type and bench type

they have their own characteristics and are suitable for different processing occasions

3.2 the advantages and disadvantages of various plasma cutting mechanisms are compared with cantilever mechanisms: the equipment is easy to move and install, the structure is compact, the space required is small, and the manufacturing cost is low. However, due to the limitation of cantilever structure, the stress conditions are poor, and it is easy to produce transverse deformation. The transverse cutting width is limited, and the rigidity is poor during high-speed cutting

gantry cutting mechanism: the gantry support mode is bi-directional support, with relatively uniform stress and good equipment rigidity, which can achieve a large transverse span, usually up to 3-10m However, the equipment installation requirements are high and the structure is relatively large, Construction of plant surface requiring more occupation "Green express product". Its driving mode can be divided into unilateral drive and bilateral drive. Unilateral drive and bilateral drive have their own characteristics and application occasions. Unilateral drive avoids the high-precision synchronous control and complex structure of bilateral drive. However, due to the offset of the center of mass, the driving force does not pass through the center of mass, which will produce asymmetric inertial force in work, prone to vibration, deformation, tilt and other adverse conditions, so it can only be used in the case of small span. 6 The bilateral drive structure is relatively complex, requiring high-precision synchronous control on both sides, which can be used for larger span and more stable movement

table cutting mechanism: the cutting part and the machine are integrated, which is convenient to move in place, but the movement range of the cutting torch is relatively small, and the size of the cutting format is limited to a certain extent

compare the advantages and disadvantages of the above three cutting mechanisms. The gantry cutting mechanism can cut a large span, move smoothly, and have good stability, which is in line with the requirements of enterprises. Therefore, gantry cutting mechanism is adopted here

3.3 motion analysis of cutting mechanism cutting is carried out by fixing the plate and moving the cutting torch. The cutting torch needs to be able to move in three directions: horizontal, vertical and vertical. The horizontal and vertical directions are used to form various tracks required for processing. The vertical direction is to adjust the distance between the cutting torch and the workpiece, so as to facilitate the optimization and adjustment of process parameters

in NC machining, interpolation is a necessary movement to form the workpiece machining trajectory, that is, the NC system uses a certain algorithm to calculate according to the workpiece contour data, sends a feed command to the corresponding coordinate axis according to the calculation result, and then the feed mechanism moves the corresponding distance according to the command, so as to form the workpiece machining contour. Different algorithms have two effects on NC machining, that is, the size of interpolation error and the speed of interpolation. Among many interpolation algorithms, point by point comparison method is widely used because of its fast calculation speed and appropriate interpolation error. Its principle is that the control system compares the machining point with the given graphic path at each step of the tool to determine the next feeding direction, so that the path of the tool motion approaches the workpiece contour 7 The transverse and longitudinal movement of the mechanism is interpolation movement, with frequent commutation and small single feed. Using small broken line segments to approach straight lines or arcs requires high motion accuracy, so the actuator is required to have sufficient accuracy and smooth motion. The horizontal movement of the cutting torch is realized by the gantry driving the cutting torch installation block, while the vertical movement is realized by the movement of the cutting torch installation block along the gantry beam, and the vertical adjustment is realized by the movement of the cutting torch along the cutting torch installation block

3.4 realization of cutting mechanism movement 3.4.1 horizontal movement of gantry the horizontal movement of gantry is considered to be realized by ball screw nut mechanism. The ball screw nut mechanism has the following characteristics: (1) small friction, high efficiency, and the mechanical efficiency can reach more than 90%; (2) High sensitivity and stable transmission; (3) Less wear and long service life; (4) Axial clearance can be eliminated 8 Because of the above advantages, ball screw nut mechanism is widely used in linear transmission

in order to balance the forces on both sides, the gantry is driven by two sides. Use servo motor to control the moving distance of lead screw. Servo motor has the advantages of good stability, low power consumption, long service life, high positioning accuracy, fast response speed and so on. Using servo motor to control, the speed and position can be controlled very accurately. In order to avoid motion interference, the operation of front and rear drive motors must be strictly synchronized

according to the analysis of working conditions, there is only slight vibration in the work, the mass of the working part is m =270kg, the maximum acceleration Amax speed amin=5m/s2, from which the maximum axial working load Fmax can be obtained. The maximum speed of the lead screw nmax=100r/min, the minimum speed nmin=10r/min, and the accuracy of the lead screw is selected as level 4. The design and calculation of the ball screw are as follows: 9. The longitudinal movement of the cutting torch along the beam is also a linear movement, so the ball screw nut mechanism is still used. Its structure is similar to the transmission mechanism of the gantry, which will not be discussed in detail here

3.4.3 adjustment of the vertical direction of the cutting torch the distance between the cutting torch nozzle and the workpiece has an important impact on plasma cutting. If the distance is too large, the arc length increases, the heat loss increases, and the cutting ability decreases; On the contrary, if the distance is too small, it is easy to cause a short circuit between the nozzle and the workpiece and burn out the nozzle, damaging the normal progress of the cutting process

therefore, it is very important to adjust the distance in the vertical direction of the cutting torch. The feasibility of the scheme, the simplicity of the structure and the convenience of operation also need to be considered in the design. Here, an eccentric slider mechanism is used to adjust the height of the cutting torch in the vertical direction

eccentric wheel has the characteristics of simple structure and convenient adjustment. The specific implementation process is: the slider is connected with the cutting torch, the vertical movement of the slider drives the vertical movement of the cutting torch, and the height of the cutting torch in the vertical direction is controlled by the rotation of the eccentric wheel. Its structural diagram is shown in

calculate the whole distance accurately. Assuming that the eccentricity of the eccentric wheel is e, the adjustable range of the slider is 2e According to the process requirements, the distance between the cutting torch and the workpiece is generally required to be between 4-10mm, with a variation range of 6mm So as long as the eccentric