1. The division of Machining Centre in Cnc 850 processing stage
When the processing quality requirements of parts are high, several processes are often used to gradually achieve the required processing quality. In order to ensure the quality of processing and the rational use of equipment and manpower, the processing of parts is usually divided into four stages: roughing, semi-finishing, finishing and finishing according to the nature of the process.
1. Roughing stage
Its task is to remove most of the excess metal on the blank so that the blank is close to the finished part in shape and size, so its main goal is to increase productivity.
2. Semi-finishing stage
Its task is to make the main surface reach a certain precision, leave a certain finishing allowance, prepare for the finishing of the main surface (such as fine turning, fine grinding), and complete some secondary surface processing, such as reaming , Tapping thread, milling keyway, etc.
3. Finishing stage
Its task is to ensure that the main surfaces meet the specified dimensional accuracy and surface roughness requirements, and the main goal is to fully guarantee the processing quality.
4. Finishing
Surfaces that require high precision and surface roughness on parts (above T6 and surface roughness below Ra0.2um) need to be smoothed. The main goal is to improve dimensional accuracy and reduce surface roughness. Generally not used to improve position accuracy.
Workpiece smooth surface processing
The purpose of dividing the processing stages of CNC machine tools lies in the following aspects:
1. Ensure the processing quality of CNC machine tools
When the workpiece is roughed, the removed metal layer is thicker, the cutting force and clamping force are relatively large, and the cutting temperature is relatively high, which will cause greater deformation. If the processing stages are not divided and the roughing and finishing are mixed together, the processing errors caused by the above reasons cannot be avoided. According to the processing stage, the processing error caused by rough processing can be corrected by semi-finishing and finishing, so as to ensure the processing quality of the workpiece.
2. Reasonable use of CNC machine tool processing equipment
The rough machining allowance is large, the cutting amount is large, and the machine tool with high power, good rigidity, high efficiency and low precision can be used. The precision machining has small cutting force and small damage to the machine tool. High-precision machine tools are used. This gives full play to the respective characteristics of the equipment, which can not only increase productivity, but also extend the service life of precision equipment.
3. Facilitate timely discovery of blank defects in CNC machine tool processing
Various defects of the blank, such as porosity, sand inclusion and insufficient margin of the casting, can be found after rough machining, which is convenient for timely repair or decision to scrap, so as to avoid further processing and cause waste.
4. It is convenient to arrange the heat treatment process of CNC machine tool processing
For example, after rough machining, stress relief heat treatment is generally arranged to eliminate internal stress. Final heat treatment such as quenching should be arranged before finishing; its deformation can be eliminated by finishing.
Machine tool magazine system
Second, the division of CNC machine tool processing procedures and the determination of the processing sequence
(1) Division of process
1. The principle of dividing the machining process of CNC machine tools
Two different principles can be adopted for the division of processes, namely the principle of process concentration and the principle of process dispersion.
(1) The principle of process concentration
It means that each process includes as much processing content as possible, thereby reducing the total number of processes. The advantages of adopting the principle of process concentration are: it is conducive to adopting efficient special equipment and CNC machine tools to improve production efficiency; reducing the number of machine tools and the number of processes, shortening the process route, simplifying production planning and production organization work; reducing the number of workpiece clamping times to ensure The mutual position accuracy between the processed surfaces reduces the number of fixtures and the auxiliary time for clamping the workpiece.
The disadvantages are the large investment in special equipment and process equipment, the troublesome adjustment and maintenance, and the long production preparation cycle, which is not conducive to conversion.
(2) The principle of process dispersion
That is, the processing of the workpiece is dispersed in more processes, and the processing content of each process is small. The advantages of using the principle of process dispersion are: simple structure of processing equipment and process equipment, convenient adjustment and maintenance, simple operation, and easy conversion; it is conducive to choosing a reasonable amount of cutting and reducing maneuvering time. The disadvantage is that the process route is long, the required equipment is large, and the floor space is large.
2. The division method of CNC machine tool processing procedures
The process division mainly considers the production batch, the structure and technical requirements of the equipment used and the parts themselves. In mass production, if a multi-axis, multi-tool high-efficiency CNC machining center is used, the production can be organized according to the principle of process concentration; if it is processed on an automatic line composed of modular machine tools, the process is generally divided according to the principle of dispersion.
With the development of modern numerical control technology, especially the application of vertical machining centers (use of vertical machining centers), the arrangement of process routes tends to be more concentrated. When a single piece is produced in a small batch, the principle of process concentration is usually adopted.
When mass production, it should be decided according to the specific situation. For heavy parts with large size and weight, the principle of process concentration should be adopted to reduce the number of clamping and transportation. For parts with poor rigidity and high precision, the processes should be divided according to the principle of process dispersion.
The parts processed on CNC machine tools are generally divided into processes according to the principle of process concentration, and the division method is as follows:
(1) Divided according to the machining center tool used. The part of the process completed by the same tool is a process. This method is suitable for the division of the workpiece surface to be processed.
(2) Divided by the number of installations. Take the part of the process completed in one installation as a process. This method is suitable for workpieces with little processing content, and can reach the state to be inspected after processing is completed.
(3) Divided by roughing and finishing. That is, the part of the process completed in rough machining is a process, and the part of process completed in finishing is a process. This division method is suitable for parts that have large deformation after processing and need to be rough and finely processed separately, such as castings, welded parts or forgings.
(4) Division of processing parts. That is, the part of the process that completes the same profile is regarded as one process. For parts with many and complex processed surfaces, it can be divided into multiple processes according to its structural characteristics (such as internal shape, shape, curved surface and plane, etc.).
Turning
(2) Order arrangement
After selecting the numerical control processing method and dividing the process, the main content of the process route is to rationally arrange these processing methods and the order of the processing processes. The processing procedures of parts usually include cutting procedures, heat treatment procedures and auxiliary procedures (including surface treatment, cleaning and inspection, etc.). The sequence of these procedures directly affects the processing quality, production efficiency and processing cost of the parts.
Therefore, when designing the process route, the sequence of CNC machining, heat treatment and auxiliary procedures should be reasonably arranged, and the connection problem between the procedures should be solved.
1. Arrangement of CNC machine cutting process
(1) The base surface first principle. The surface used as the precision datum should be processed first, because the more accurate the surface of the positioning datum, the smaller the clamping error.
For example, when machining shaft parts, the center hole is always processed first, and then the outer surface and end face are processed based on the center hole.
(2) The principle of rough first and refined
The processing sequence of each surface is carried out in the order of roughing, half finishing, finishing, finishing, gradually improving the surface processing accuracy and reducing the surface roughness.
(3) The principle of first and second
The main working surface and assembly base surface of the part should be processed first, and the secondary surface can be interspersed and placed after the main processing surface has been processed to a certain level and before the final finishing.
(4) The principle of face first and hole second
For box and bracket parts, the plane outline size is larger. Generally, the plane is processed first, and then the hole and other sizes are processed. The processed plane is used for positioning, which is stable and reliable; at the same time, the hole is processed on the processed plane to improve the hole performance. Machining accuracy, especially drilling, the axis of the hole is not easy to deviate.
Milling
2. Arrangement of heat treatment process for CNC machine tool processing
In order to improve the mechanical properties of the material, improve the machinability of the material and eliminate the internal stress of the workpiece, some heat treatment procedures should be properly arranged in the process. The arrangement of the heat treatment process in the process route mainly depends on the material of the part and the purpose of the heat treatment.
(1) Preliminary heat treatment
The purpose of the preliminary heat treatment is to improve the cutting performance of the material, eliminate the residual stress during the blank manufacturing, and improve the structure. The process position is mostly before mechanical processing, and annealing, normalizing, etc. are commonly used.
(2) Heat treatment to eliminate residual stress
Since the internal stress generated during the manufacturing and machining of the blank will cause deformation of the workpiece and affect the processing quality, it is necessary to arrange a heat treatment to eliminate residual stress. The heat treatment to eliminate residual stress is best arranged after rough machining and before finishing. For parts that require less precision, artificial aging and annealing to eliminate residual stress are generally arranged before machining.
For complex castings with high precision requirements, two artificial aging treatments are usually arranged in the machining process: casting-rough machining-aging and half finishing-aging-finishing. For high-precision parts, such as precision lead screws, precision spindles, etc., multiple heat treatments to eliminate residual stress should be arranged.
(3) Final heat treatment
The purpose of the final heat treatment is to improve the strength, surface hardness and wear resistance of the parts. It is often arranged before the finishing process (grinding). Commonly used are quenching, carburizing, nitriding and carbonitriding.
3. Arrangement of auxiliary processes
Auxiliary procedures mainly include inspection, cleaning, deburring, demagnetization, chamfering, applying anti-rust oil and balancing. The inspection process is the main auxiliary process and one of the main measures to ensure the quality of the product. It is generally arranged after all rough machining, before finishing, after important processes, before and after the transfer of workpieces between different workshops, and after all workpieces are processed. .
4. Connection between CNC machining process and ordinary process
There are usually other common processes interspersed before and after the numerical control process. To solve the connection problem between the numerical control process and the non-numerical control process, the best way is to establish mutual status requirements. For example, whether or not to leave a machining allowance for the subsequent process, how much to leave; the accuracy requirements of the positioning surface and the hole, and the shape and position tolerance. Its purpose is to achieve mutual satisfaction of processing needs, and the quality objectives and technical requirements are clear, and there is a basis for handover and acceptance.
