Precision machining

　　Machining is a process that uses processing machinery to change the shape or performance of a workpiece. According to the temperature state of the workpiece to be processed, it is divided into cold processing and hot processing. Generally processing at room temperature, and does not cause chemical or phase changes of the workpiece, called cold processing. Generally, processing at higher or lower than normal temperature will cause chemical or phase changes of the workpiece, which is called thermal processing. Cold processing can be divided into cutting processing and pressure processing according to the difference in processing methods. Thermal processing commonly includes heat treatment, forging, casting and welding.
　　 In addition, cold heat treatment is often used during assembly. For example, during the assembly of bearings, the inner ring is often cooled in liquid nitrogen to shrink its size, and the outer ring is appropriately heated to enlarge its size, and then assembled together. The outer ring of the train wheel is also heated on the base body, and the firmness of the combination is when it is cooled (this method is still used in the transfer process of some parts).
　　Machining includes: filament power winding, laser cutting, heavy processing, metal bonding, metal drawing, plasma cutting, precision welding, roll forming, sheet metal bending, die forging, water jet cutting, precision welding, etc.
　　Machining: Machining in a broad sense refers to the process of manufacturing products by mechanical means; narrowly referring to the foreign development status of lathes, milling machines, drilling machines, grinders, stamping machines, and micro-machining technologies
　　 In 1959, Richard P Feynman (the winner of the Nobel Prize in Physics in 1965) proposed the idea of ​​micromachines. In 1962, the silicon miniature pressure sensor came out, and then micromachines such as gears, gear pumps, pneumatic turbines and couplings with a size of 50-500μm were developed. In 1965, Stanford University developed a silicon brain electrode probe, and later succeeded in scanning tunneling microscopes and miniature sensors. In 1987, the University of California at Berkeley developed a silicon micro-electrostatic machine with a rotor diameter of 60 to 12 μm, showing the potential of using silicon micro-machining technology to manufacture small movable structures and compatible with integrated circuits to manufacture tiny systems.
　　Micromachines have been highly valued by government departments, business circles, colleges and universities and research institutions abroad. In the late 1980s, 15 scientists from MIT, Berkeley, Stanford\AT&T in the United States put forward a national proposal on "Small Machines, Big Opportunities: Reports on Emerging Fields-Microdynamics", claiming that "due to microdynamics ( The urgency of (microsystems) in the United States should take the lead in the competition with other countries in such a new and important technology field." It is recommended that the central fiscal advance is US$50 million for five years, which has attracted the attention of the U.S. leadership and continued to invest heavily. , And regard aerospace, information and MEMS as the three major points of technological development. NASA invested 100 million US dollars to develop the "Discovery Microsatellite". The National Science Foundation took MEMS as a newly emerging research field and formulated a plan to fund research on micro-electromechanical systems. Since 1998, it has funded MIT. Eight universities including the University of California and Bell Labs are engaged in research and development in this field, with annual funding ranging from 1 million and 2 million to 5 million in 1993. The "Technical Plan of the US Department of Defense" report released in 1994 listed MEMS as a key technology project. The Research Projects Agency of the US Department of Defense actively leads and supports MEMS research and military applications. A MEMS standard process line has been established to promote the research and development of new components/devices. American industry is mainly devoted to the research of sensors, displacement sensors, strain gauges and accelerometers and other sensor related fields. Many institutions have participated in the research of micro-mechanical systems, such as Cornell University, Stanford University, University of California, Berkeley, University of Michigan, University of Wisconsin, Old Lenz Demore National Research, etc. The University of California Berkeley Sensor and Actuator Center (BSAC) received 15 million yuan funding from the Department of Defense and more than a dozen companies to establish a 1,115m2 ultra-clean laboratory for research and development of MEMS.
In 1991, the Ministry of International Trade and Industry of Japan started a 10-year, large-scale research project costing 25 billion yen to develop two prototypes, one for medical treatment, entering the human body for diagnosis and microsurgery, and the other for industrial use. , Carry out repairs to small cracks in aircraft engines and atomic energy equipment. Dozens of units including the University of Tsukuba, Tokyo Institute of Technology, Tohoku University, Waseda University and Fujitsu Research Institute participated in the program.
European industrialized countries have also made key investments in the research and development of micro-systems. Germany started the micro-processing 10-year plan project in 1988, and its Ministry of Science and Technology allocated 40,000 marks from 1990 to 1993 to support the research of the "micro-system plan". The microsystem is listed as the focus of scientific and technological development at the beginning of the century. The German LIGA process has provided new technical means for the development of MEMS and has become the preferred process for the production of three-dimensional structures. The 70 million francs "microsystem and technology" project launched by France in 1993. The European Community formed the "Multifunctional Microsystem Research Network NEXUS" to jointly coordinate the research of 46 research institutes. Switzerland has also invested in the development of MEMS on the basis of its traditional watchmaking industry and small precision machinery industry. In 1992, the investment was 10 million US dollars. The British government has also formulated a nanoscience plan. 8 projects are listed for research and development in the fields of mechanics, optics and electronics. In order to strengthen Europe's development of MEMS, some European companies have formed MEMS development groups.
At present, a large number of micro-machines or micro-systems have been researched. For example, micro tweezers with a diameter of 5μm can hold a red blood cell, and a micro-pump with a size of 7mm×7mm×2mm can have a flow rate of 250μl/min. The flying robot butterfly, and the miniature inertial unit (MIMU) that integrates a miniature speedometer, a miniature gyroscope and a signal processing system. Germany created the LIGA process, made cantilever beams, actuators and micro pumps, micro nozzles, humidity, flow sensors and a variety of optical devices. The California Institute of Technology in the United States glues a considerable number of 1mm microbeams on the aircraft wing surface to control the bending angle to affect the aerodynamic characteristics of the aircraft. Mass-produced silicon accelerometers in the United States integrate micro-sensors (mechanical parts) and integrated circuits (electrical signal sources, amplifiers, signal processing and positive detection circuits, etc.) on a silicon chip within a range of 3mm x 3mm. The micro lathe developed in Japan can process micro-shafts with a precision of 1.5μm.
Production process and technological process
　　The production process refers to the entire process of making products from raw materials (or semi-finished products). For machine production, it includes the transportation and storage of raw materials, production preparation, blank manufacturing, parts processing and heat treatment, product assembly, and debugging, painting and packaging. The content of the production process is very extensive. Modern enterprises use the principles and methods of system engineering to organize and guide production, and regard the production process as a production system with inputs and outputs. It can make the enterprise's management scientific and make the enterprise more adaptable and competitive.
　　In the production process, the process of directly changing the shape, size and performance of the raw material (or blank) to turn it into a finished product is called the process. It is the main part of the production process. For example, casting, forging and welding of blanks; heat treatment to change material properties [1]; machining of parts, etc., are all technological processes. The technological process is composed of one or several sequential procedures.
　　 Process is the basic unit of the technological process. The so-called process refers to the part of the process that is continuously completed for one or a group of workpieces at a work site. The main feature of forming a process is that the processing objects, equipment and operators are not changed, and the content of the process is completed continuously.
　　Production Type　Production Type is usually divided into three categories
  1. Single-piece production To produce a certain part individually, rarely repeatedly.
  2. Mass production The production of the same parts in batches.
　　3. Mass production When the number of products manufactured is large, most workplaces often repeat the production of a certain process of a part.
　　 When drawing up the process of parts, due to the different production types of parts, the addition methods, machine tools, tools, fixtures, blanks and technical requirements for workers are very different.
　　 General principles for drafting process routes
　　 The formulation of mechanical processing procedures can be roughly divided into two steps. The first is to draw up the process route of the parts processing, and then determine the process size of each process, the equipment and process equipment used, the cutting specifications, and the working hours quota. These two steps are interrelated and should be analyzed comprehensively.
　　The formulation of the process route is to formulate the overall layout of the process. The main task is to select the processing method of each surface, determine the processing sequence of each surface, and the number of processes in the entire process.
　　 General principles for drafting process routes
　　1, first process the datum plane
　　 During the processing of parts, the surface as the positioning reference should be processed first, so as to provide a precise reference for the subsequent processing as soon as possible. Called "benchmark first."
　　2, divide the processing stage
　　 Surfaces with high processing quality requirements are divided into processing stages, which can generally be divided into three stages: rough processing, semi-finishing and finishing. Mainly for processing quality; to facilitate the rational use of equipment; to facilitate the arrangement of the heat treatment process; and to facilitate the discovery of blank defects.
　　3, face before hole
　　[1]　 For parts such as box body, bracket and connecting rod, the plane should be processed first and then the hole should be processed. In this way, the holes can be positioned on the plane, and the position accuracy of the plane and the holes, and the processing of the holes on the plane is convenient.
　　4, finishing
Finishing processing of the main surface (such as grinding, honing, fine grinding\rolling processing, etc.), the surface finish after processing is above Ra0.8um, and a slight collision will damage the surface. In Japan, Germany and other countries, After processing, it must be protected with flannel. It is not allowed to touch the workpiece directly with hands or other objects, so as to prevent the surface of the finishing process from being damaged due to the transfer and installation between processes.
　　(2). Choose equipment reasonably. Rough machining mainly cuts off most of the machining allowance and does not require high machining accuracy. Therefore, rough machining should be carried out on a machine with greater power and less precision, and the finishing process requires higher precision. Machine processing. Rough and finishing are processed on different machine tools, which can not only give full play to the equipment capacity, but also extend the service life of precision machine tools.
　　(3). In the machining process route, heat treatment processes are often arranged. The location of the heat treatment process is arranged as follows: In order to improve the cutting performance of the metal, such as annealing, normalizing, quenching and tempering, etc., it is generally arranged before mechanical processing. In order to eliminate internal stress, such as aging treatment, quenching and tempering treatment, etc., it is generally arranged after rough machining and before finishing. In order to improve the mechanical properties of parts, such as carburizing, quenching, tempering, etc., it is generally arranged after machining. If there is a large deformation after heat treatment, the final processing procedure must be arranged.
　　 Common processing equipment
There are many equipments useful in the process of precision machining. Here are some commonly used mechanical equipment: wire cutting, electric discharge machine, deep hole electric discharge machine, CNC optical projection grinding, tool grinder, grinder, NC coreless grinder, plane Grinding machine, inner diameter and outer diameter grinding, precision surface grinder, precision forming grinder, water grinder, NC milling machine, grinder, machining center, PVD titanium plating machine, laser welding machine, carbonized water cleaning machine, barrel grinder, vacuum heat treatment furnace, etc. .

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