Machining refers to the process of changing the overall dimension or performance of the workpiece through a mechanical device.It can be divided intoCuttingandPressure processing。
Chinese name
machining
Foreign name
Machining
Role
Change the overall dimension or performance of the workpiece
The production process of the machine refers to the whole 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 andheat treatmentAssembly, commissioning, painting and packaging of products.The content of production process is very extensive, which is used by modern enterprisessystems engineeringThe production process is regarded as a production system with input and output.
Process
In the production process, the process of changing the shape, size, location and nature of the production object into finished or semi-finished products is called technological process.It is an important part of the production process.ProcessIt can also be divided into castingforging、stampingWelding, machiningassemblingThe mechanical manufacturing process generally refers to theMachining processThe sum of process and machine assembly process. Other processes are called auxiliary processes, such as transportation, storage, power supply, equipment maintenance, etc.The technological process is composed of one or several sequential processes, and a process is composed of several steps.
Process is composed ofMachining processThe basic unit of a process.The so-called process refers to the part of the process that a worker (or a group of workers) completes continuously for the same workpiece (or several workpieces at the same time) on a machine tool or at a work site.The main feature of forming a process is that the processing object, equipment and operator are not changed, and the content of the process is completed continuously.
Work step is a component part of the process divided according to the processing process.Its feature is that the machined surface and the tools, machine tools and cutting parameters are notChange.[6]
Knife walkingAlso called working stroke, it refers to the process of cutting a layer of metal every time when the cutting speed and tool path in the machining surface, the tool used and the cutting parameters are constant.Sometimes one step only needs -- times of cutting, sometimes it needs countingTimes.[1][7]
To formulate the machining process, it is necessary to determine the number of processes that the workpiece will go through and the sequence of the processes. Only a brief process that lists the name of the main processes and their processing sequence is called the process route.
The preparation 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 determine the number of processes in the whole process.The process route must follow certain principles.
Production type
Production types are generally divided into three categories:
1. Single piece production: single production of products with different structures and sizes, and rarely repeated.
Mass produced parts
2. Batch production: the same products are manufactured in batches throughout the year, and the manufacturing process has certain repeatability.
3. Mass production: the number of products manufactured is very large, and most workplaces often repeat the processing of a certain process of a certain part.
Process procedure design
Design principles:
(1) DesignedProcess procedureIt shall ensure the processing quality of machine parts (or the assembly quality of the machine) and meet the technical requirements specified in the design drawings.
(2) The process should have a high productivity, so that the products can be put on the market as soon as possible.
(4) Pay attention to reducing the labor intensity of workers to ensure production safety.
source:
(1) Product assembly drawing, part drawing.
(2) Product acceptance quality standards.
(3) The annual production program of the product.
(5) The production conditions of the manufacturer, including the specifications, performance and existing status of machine tools and process equipment, the technical level of workers, the ability of the factory to manufacture process equipment, and the ability of the factory to supply power and gas.
(6) Design manuals and relevant standards required for process procedure design and process equipment design.
(7) Advanced manufacturing technology data at home and abroad.
Steps:
(1) Analyze and study the assembly drawing and part drawing of the product.
(2) Determine the blank.
(3) Draw up the process route and select the positioning base plane.
(4) Determine the equipment used in each process.
(5) Determine the tools, fixtures, measuring tools and auxiliary tools used in each process.
(6) Determine the technical requirements and inspection methods of main processes.
(7) Determine the machining allowance of each process, and calculate the process size and tolerance.
(8) Determine the cutting amount.
(9) Determine the man hour quota.
Benchmark Introduction
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concept
Mechanical parts are composed of several surfaces. To study the relative relationship between parts' surfaces, a datum must be determined. The datum is the point, line, and surface on the part that is used to determine the position of other points, lines, and surfaces.According to different functions of the benchmark, the benchmark can be divided intoDesign basisandProcess benchmarkTwo types.
classification
Design datum: the datum used to determine the position of other points, lines and surfaces on the part drawing is called design datum.
Process benchmark: the benchmark used in the processing and assembly of parts, called process benchmark.According to different purposes, process standards can be divided into assembly standards, measurement standards and positioning standards.
(1) Assembly datum: the datum used to determine the position of parts in components or products during assembly, called assembly datum.
(2) Measuring datum: the datum used to check the size and position of the machined surface, called measuring datum.
(3) Positioning datum: the datum used for workpiece positioning during machining, called positioning datum.For the surface (or line, point) as the positioning reference, only the unfinished blank surface can be selected in the first process. This positioning surface is called the rough reference. In subsequent processes, the machined surface can be used as the positioning reference. This positioning surface is called the precision reference.[2]
Machining allowance
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The total thickness of the metal layer cut off on a machining surface in the process of transforming a blank into a finished product is called the total machining allowance of the surface.The thickness of the metal layer removed in each process is called the inter process machining allowance.For rotating surfaces such as excircles and holes, the machining allowance is considered from the diameter, so it is called symmetrical allowance (i.e. bilateral allowance), that is, the thickness of the metal layer actually cut is half of the machining allowance on the diameter.The machining allowance of the plane is unilateral allowance, which is equal to the thickness of the metal layer actually cut.The purpose of leaving machining allowance on the workpiece is to remove the machining errors and surface defects left by the previous process, such as the cold hard layer, air hole, sand inclusion layer on the casting surface, oxide skin, decarburization layer, surface crack on the forging surface, internal stress layer andSurface roughnessEtc.So as to improve the precision and surface roughness of the workpiece.The machining allowance has a great influence on the machining quality and production efficiency.The excessive machining allowance not only increases the labor volume of machining and reduces productivity, but also increases the consumption of materials, tools and power, and increases the processing cost.If the machining allowance is too small, the defects and errors of the previous process cannot be eliminated, and the clamping errors of this process cannot be compensated, resulting in waste products.The selection principle is to make the margin as small as possible on the premise of ensuring quality.Generally speaking, the more finish machining, the smaller the process margin.
Machines required for processing includeDigital display milling machine、Digital display forming grinder、Digital display lathe、Electric spark machineUniversal grindermachining center 、Laser welding, middle wire walkingFast filamentation、Walking slowly、Cylindrical grinder、Internal grinder, precision lathes, etc., can be used for turning, milling, planing, grinding and other processing of precision parts. This kind of machinery is good at turning, milling, planing, grinding and other processing of precision parts, and can process various irregular shaped parts with a processing accuracy of up to 2 μ m.
Development status
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With the rapid development of modern machining and machining technology, many advanced machining technology methods, such as micro machining technologyRapid prototyping technologyPrecision ultra precision processing technology, etc.
Micro machining technology
Mechanical products
With the development of Micro/Nano Science and TechnologyMicromachineIt has become a kind of high-tech for people to understand and transform the micro world.Micro machinery can work in a narrow space without disturbing the working environment and objectsPrecision instrument, biomedicine and other fields have broad application potential, and become an important means of nanotechnology research, so they are highly valued and listed as the first key technology in the 21st century.[3]
Rapid Prototyping Machining Technology
Rapid prototyping technologyIt was developed in the 20th centuryCADThe model can quickly produce samples or parts.It is a material accumulation processing manufacturing method, that is, through the orderly accumulation of materials to complete three-dimensional forming.Rapid prototyping technology integratesCNC technology, material technologyLaser technologyAs well as CAD technology and other modern scientific and technological achievements, is an important part of modern advanced machining technology.[4]
Precision and ultra precision machining technology
Precision andUltra precision machiningAs an important part of modern machining manufacturing technology, it is one of the important indicators to measure the level of a country's high-tech manufacturing industry.Since the 1960s, with the development of computer and information technology, higher requirements have been put forward for manufacturing technology. It is not only required to obtain extremely high dimensional, shape and position accuracy, but also required to obtain extremely high surface quality.It is precisely in this market demand that ultra precision machining technology has developed rapidly, and various processes and new methods are emerging.[4]
Policy support
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The Plan for Adjustment and Revitalization of Equipment Manufacturing Industry approved by the State Council proposes to rely on high-speedRailway、coal mineAnd ten major projects in metal mining, infrastructure, and major scientific and technological projects to revitalize the equipment manufacturing industry;Grasp the nine major industrial projects and implement equipment independence;Improve the manufacturing level of four supporting products.Policies and measures include strengthening the management of equipment procurement for investment projects, encouraging the use of the first set of domestic equipment, and promoting enterprise mergers and acquisitions.The above fields involve key sectors in economic construction, and are also areas that need to be broken through in the development of China's machinery industry, especially high-endnumerical control machineMining machinery has long been a weak link in China's manufacturing field, and there is a clear gap with the advanced level abroad.[5]
