Casting, forging and welding can only be used to make rough parts. Generally speaking, parts that require high precision need to be cut. Therefore, cutting plays an important role in mechanical manufacturing. Although there are various forms of metal cutting, such as turning, planing, milling, grinding, gear processing, etc., there are also the same phenomena and laws, that is, cutting excess metal from the blank. Mastering these phenomena and laws is of great significance to correct processing, ensure the processing quality of parts, improve productivity and reduce costs.
Metal cutting technology includes turning, planing, drilling, milling and other different types, but generally speaking, any machining process that removes a certain thickness of metal layer from a blank or semi-finished product with a tool and meets the requirements in shape and surface roughness is cutting. When the workpiece is in contact with the tool, the process that the metal in the cutting layer becomes chips through elastic deformation, sliding and cutting is called metal cutting.
The movement form and cutting mode of metal cutting machine tools can be divided into main movement and feed movement. The main movement is the most basic movement when cutting metal, which promotes the relative movement between the tool and the workpiece, thus making the front end of the tool close to the workpiece; The feed motion makes additional relative motion between the tool and the workpiece, and together with the main motion, it can cut continuously or continuously to obtain the machined surface with the required geometric characteristics. Different types of machine tools have different cutting methods, and the movement forms of workpieces and tools have different requirements for safety. Some cutting methods take the workpiece as the main movement and the tool as the feed movement; Some take the cutter as the main movement and the workpiece as the feed movement. Common cutting methods are:
(1) Turning: the rotation of the workpiece is the main movement, and the turning tool is the feed movement.
(2) Milling: Feed the workpiece or milling cutter with the rotation of the milling cutter as the main movement.
(3) Planing: the workpiece is horizontally and relatively linearly reciprocated by the planer, such as the ram of the planer drives the cutter to move mainly, and the workbench drives the workpiece to move intermittently.
(4) Drilling: machining the workpiece with a drill or reamer. Generally, the drill bit is in main motion and feed motion, while the workpiece is stationary.
(5) Reaming: using a reamer to cut a trace metal layer from the hole wall of the workpiece to improve its dimensional accuracy and surface smoothness. The rotation of the reamer is the main movement, and the workpiece or reamer does the feeding movement.
(6) Boring: feeding the workpiece or boring tool with the rotation of the boring tool as the main movement.
(7) slotting: the slotting tool reciprocates vertically and linearly relative to the workpiece, and the workpiece or slotting tool feeds.
(8) Grinding: Grinding the surface of the workpiece with grinding tools such as grinding wheels at high linear speed, with the rotation of the grinding tools as the main movement and the workpiece as the feed movement.
Cutting methods include honing, superfinishing, broaching, pushing, shoveling and scraping. Turning and grinding are the most common cutting methods.
Cutting is the most important processing method in mechanical manufacturing. Although the precision of blank manufacturing is constantly improving, precision casting, precision forging, extrusion, powder metallurgy and other processing technologies are widely used, it still occupies an important position in mechanical manufacturing technology because of its wide application range, high precision and low surface roughness.
With the continuous development of machine tools and tools, the accuracy, efficiency and automation of cutting are constantly improved, and the application scope is also expanding day by day, thus greatly promoting the development of modern machinery manufacturing.
There are many classification methods for cutting metal materials. There are three common classification methods: according to process characteristics, according to material removal rate and machining accuracy, and according to surface forming method.
The technological characteristics of the cutting process depend on the structure of the tool and the relative motion between the tool and the workpiece. Therefore, according to the technological characteristics, cutting can be generally divided into turning, milling, drilling, boring, reaming, planing, grooving, drawing, sawing, grinding, honing, ultra-precision machining, polishing, gear machining, worm gear machining, thread machining, ultra-precision machining, fitter and scraping.
According to the material removal rate and machining accuracy, cutting can be divided into rough machining, semi-finish machining, finish machining, finish machining, shape modification machining, ultra-precision machining and so on.
Rough machining is a processing method to remove most or all of the machining allowance from the workpiece with a large cutting depth and one or more passes, such as rough turning, rough planing, rough milling, drilling and sawing. , high rough machining efficiency but low precision, generally used for pre-processing; Semi-finishing is generally used as an intermediate process between rough machining and finishing; Finishing refers to the way of finishing cutting, so that the machined surface can achieve high precision and surface quality, such as finishing turning, finishing planing, finishing hinge and finishing. Finishing is generally the final processing.
Finishing is carried out after finishing, and its purpose is to obtain smaller surface roughness and slightly improve accuracy. The machining allowance of finishing is small, such as honing, grinding, ultra-precision grinding and ultra-precision machining; The purpose of finishing is to reduce the surface roughness, so as to improve the anti-corrosion and dust-proof performance and improve the appearance, and does not require improving the accuracy, such as polishing and grinding. Ultra-precision machining is mainly used for machining some special precision parts such as aerospace, laser, electronics, nuclear energy, etc., and its accuracy is as high as IT4, such as mirror turning, mirror grinding, soft abrasive mechanochemical polishing, etc.
Machining accuracy is mainly used to characterize the fineness of the products produced, and it is a term to evaluate the geometric parameters of the machined surface. Machining accuracy is measured by tolerance grade, and the smaller the grade value, the higher its accuracy. There are 20 tolerance levels from IT0 1, IT0, IT 1, IT2, IT3 to IT 18 * *, in which IT0 1 indicates that the machining accuracy of the part is the highest and IT 18 indicates that the machining accuracy of the part is the lowest. Generally, factories and mines belong to IT7 level.
According to the different functions of product parts, the machining accuracy needs to be different, and the selected machining form and technology are also different. The following introduces the machining accuracy that can be achieved by several common machining forms such as getting off, milling, planing, grinding, drilling and boring.
I. Turn
When the workpiece rotates, the turning tool moves in a straight line or curve in the plane. Turning is generally carried out on a lathe to process the internal and external cylindrical surfaces, end surfaces, conical surfaces, molding surfaces and threads of the workpiece.
The turning accuracy is generally IT8—IT7, and the surface roughness is 1.6-0.8 micron. ..
1. Rough turning strives to improve turning efficiency by using large cutting depth and large feed rate without reducing cutting speed, but the machining accuracy can only reach IT 1 1, and the surface roughness is rα 20-10μ m. ..
2. Semi-finish turning and finish turning should adopt high speed and small feed and cutting depth as far as possible, and the machining accuracy can reach IT 10-IT7, and the surface roughness is rα10.16 μ m. ..
3. High-speed turning of non-ferrous metal parts on high-precision lathe with fine polishing diamond turning tool can make the machining accuracy reach IT7—IT5 and the surface roughness rα 0.04-0.01μ m+0μ m, which is called mirror turning.
Second, milling.
Milling refers to cutting a workpiece with a rotating multi-edge tool, which is an efficient processing method. Suitable for machining planes, grooves, various molding surfaces (such as flower keys, gears and threads) and special-shaped molds. According to the fact that the main motion speed during milling is the same as or opposite to the feed direction of the workpiece, it can be divided into forward milling and reverse milling.
The milling accuracy can generally reach IT8—IT7, and the surface roughness is 6.3-1.6 μ m. ..
1, rough milling accuracy is it1-it13, and surface roughness is 5-20μ m. ..
2. The precision of semi-finish milling is IT8-IT 1 1, and the surface roughness is 2.5-10 μ m. ..
3. The precision of finish milling is IT 16-IT8, and the surface roughness is 0.63-5 μ m. ..
Third, planing
Planing is a cutting method that uses a planer to make horizontal relative linear reciprocating motion on the workpiece, which is mainly used for the shape processing of parts. The general planing accuracy can reach IT9—IT7, and the surface roughness is Ra 6.3-1.6 μ m. ..
1, the rough planing accuracy can reach it 12-it 1 1, and the surface roughness is 25-12.5 μ m.
2. the precision of semi-finish planing can reach IT 10-IT9, and the surface roughness is 6.2-3.2 μ m. ..
3. The precision of fine planing can reach IT8—IT7, and the surface roughness is 3.2—65438±0.6 μm m. ..
Fourthly, grinding.
Grinding refers to the processing method of removing redundant materials from workpieces with abrasives and abrasives, which belongs to finishing and is widely used in machinery manufacturing. Grinding is usually used for semi-finishing and finishing, and the accuracy can reach IT8—IT5 or even higher, and the surface roughness is generally1.25-0.16 μ m. ..
1, and the precision grinding surface roughness is 0.16-0.04μ m. ..
2. The surface roughness of ultra-precision grinding is 0.04-0.0 1 micron. ..
3. The surface roughness of mirror grinding can reach below 0.0 1 micron. ..
Verb (abbreviation for verb) exercise
Drilling is a basic method of hole processing. Drilling is usually carried out on drilling machines and turning machines, or on boring or milling machines. The machining accuracy of drilling is low, generally only reaching IT 10, and the surface roughness is generally12.5-6.3 μ m. After drilling, reaming and reaming are often used for semi-finishing and finishing.
Six, boring
Boring is a kind of inner diameter cutting technology to enlarge holes or other circular contours with tools, and its application range is generally from semi-rough machining to finish machining. The tool used is usually a single-edged boring tool (called boring bar).
1. The boring accuracy of general steel can reach IT9—IT7, and the surface roughness is 2.5-0. 16 micron. ..
2. The machining accuracy of precision boring can reach IT7—IT6, and the surface roughness is 0.63-0.08 micron. ..