High-Precision Machining, from precision Machining to ultra-precision machining to ultra-precision machining, is the direction that all countries in the world are striving for. Its precision ranges from micron to sub-micron, and even nano-scale (<10nm), and its application range is increasingly widespread. Ultra-precision machining mainly includes ultra-precision cutting (car, milling), ultra-precision grinding, ultra-precision grinding and polishing, and ultra-precision special processing (three-beam machining and micro-EDM machining, micro-electrolysis machining and various composite machining). With the development of modern science and technology, new requirements for ultra-precision machining technology have been put forward. The emergence of new materials and new parts, the introduction of higher precision requirements, etc. require ultra-precision machining processes, the development of new ultra-precision machining tools, and the improvement of modern ultra-precision machining technology to adapt to the development of modern technology.
Precision is to meet the needs of high-tech development, but also to improve the performance, quality and reliability of ordinary mechanical and electrical products, reduce the workload of assembly and improve assembly efficiency. With the development of high technology and the improvement of the performance and quality requirements of mechanical and electrical products, machine tool users have higher and higher requirements for machine tool processing accuracy. In order to meet the needs of users, the machining accuracy of general-grade CNC machine tools has been improved from ±10μm to ±5μm in the past 10 years, and the precision of precision machining centers has increased from ±3~5μm to ±1~1.5μm.
Complex surface machining Since the 1990s, complex profiles have been processed almost entirely in high-speed cutting. The purpose is to increase production efficiency, reduce product cost, and improve the shape accuracy of the workpiece and reduce the surface roughness. In order to meet the needs of high-speed cutting, the spindle of the machine tool uses the electric spindle almost without exception. The spindle speed is continuously variable according to the diameter of the tool used. The speed range is from several thousand to several tens of thousands of revolutions per minute. The drive system of the slide table is also different from the conventional machining center in high-speed cutting. The commonly used system is driven by a high-speed screw Nut and a linear motor. The maximum feed speed can reach more than 100m/min.
When machining complex profiles, the CNC system of the machine must also meet some special requirements. For example, CNC machining programs for complex profiles are generally generated on CAD/CAM software. A profile program often requires several megabytes of storage space and requires large-capacity memory for storage. Therefore, the CNC system must have the function of networking with other computer systems to receive the NC program directly from CAD/CAM.
In addition, the CNC system must also use advanced control technology, requiring a look-ahead (LookAhead) function. That is to say, before the machine tool processes a certain trajectory, the data system pre-analyzes the surface to be processed, and appropriately adjusts the feed speed of the machine tool according to the curvature of each point of the curved surface and the connection relationship of adjacent points, so as to ensure the workpiece. Maximum productivity is achieved with precision. In order to reduce the dynamic error in the machining process, the new data system servo error correction is no longer the conventional series proportional differential integration (PID) regulator, but a state regulator that compensates by state parameters such as position and speed. The use of this regulator can completely eliminate the driving hysteresis error, compensate for the nonlinear error caused by the gap or friction, and even cancel some vibration of the machine tool, thereby achieving the requirements of improving the shape accuracy of the workpiece and reducing the surface roughness.
Complex surface machining involves parallel machine tool structure, digital servo system development, CAD/CAM application, parallel structure machining error and accuracy analysis, mechanism structure parameter calibration and machine tool stiffness improvement. It is necessary to solve the key technologies such as the parallel layout design of the overall layout of the machine tool, the numerical control system of the seven-axis linkage parallel machine tool, and the precision guarantee of the parallel machining center.
Integrating the tool trajectory generation function in surface machining into the CNC is also the development trend of surface machining. 2. The CNC automatically performs continuous tool path interpolation in real time according to the surface geometry definition and process parameters, and thus controls the machine tool movement. . The curved block machining instruction is equivalent to a complete step, and its control complexity far exceeds that of the current CNC only for straight lines and arcs.
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