Cutting is a machining method that uses cutting tools to cut off an excess layer of material on a workpiece or workpiece so that the workpiece can obtain a given geometric shape, size, and surface quality.
Any cutting process must have three basic conditions: the cutting tool, the workpiece, and the cutting motion. The cutting tool must have a cutting edge, and its material must be harder than the workpiece; different tool designs and forms of cutting motion constitute different cutting methods. Cutting methods with a tool with a fixed blade shape and number of blades include turning, drilling, boring, milling, planing, broaching, sawing; cutting methods include grinding, lapping, honing and polishing.
Cutting is the most important processing method in mechanical engineering. Although the accuracy of rough workpiece manufacturing has been constantly improved, and processing technologies such as investment casting, precision forging, extrusion, and powder metallurgy have been widely used due to the wide range of cutting processing and the ability to achieve high precision and low surface roughness, it still pore occupies an important place in the mechanical production process.
The history of cutting can be traced back to the Paleolithic period, when primitive people created tools such as stone cutters and bone drills. In China, already in the middle of the Shang Dynasty (13th century BC), bronze mirrors could be polished; at the end of the Shang Dynasty (12th century BC), bronze drills were used to drill holes in oracle bones; from 206 BC to 23 AD) over 18,000 pieces of jade, 1 to 2 mm in diameter, were drilled into over 4,000 pieces of hard jade in the "Golden Jade Garment" using core and tube drills.
In the middle of the 17th century in China, instead of labor, they began to use animal power to drive cutting tools. For example, in 1668 AD. a large copper ring with a diameter of 2 feet (ancient feet) according to astronomy was milled with a multi-toothed chisel on a fixture driven by animal power, and then processed with a whetstone. CNC programming UG exchange Q group: 192963572, if you want to learn CNC programming, get free study materials and add this group
In the second half of the 18th century, after the beginning of the British Industrial Revolution, in connection with the invention of the steam engine and modern machine tools, the cutting process began to use a steam engine as energy; in the 1870s the cutting process started using electricity again.
Research on the principle of cutting metal began in the 1850s, and research on the principle of grinding began in the 1880s. Since then, one after another, various new instrumental materials have appeared. High speed steel cutting tools introduced in the late 19th century made the cutting speed allowed by the cutting tool more than twice that of carbon tool steel and alloy tool steel cutting tools, reaching about 25 m/min; cemented carbide cutting tools introduced in 1923 made cutting speeds faster than high speed steel cutting tools about doubled, cermets and superhard materials (artificial diamond and cubic boron nitride) introduced after the 1930s further increased cutting speed and machining accuracy. .
With the continuous development of machine tools and cutting tools, the accuracy, efficiency and automation of cutting processing have been constantly improved, and the scope of application has also expanded, which greatly contributed to the development of modern mechanical engineering.
There are many methods for classifying cuttingmetallic materials. There are three common classification methods: by process characteristics, by material removal rate and machining accuracy, and by surface forming methods.
Technological characteristics of cutting are determined by the design of the cutting tool and the relative motion of the cutting tool and the workpiece. Thus, according to the characteristics of the process, machining can be divided into: turning, milling, drilling, boring, reaming, planing, slotting, broaching, sawing, grinding, grinding, honing, superfinishing, polishing, gear machining, processing of worm gears. , thread processing, ultra-precision processing, mounting and scraping, etc.
According to material removal rate and processing accuracy, cutting can be divided into rough cutting, medium cutting, finishing cutting, finishing cutting, modifying cutting, ultra-fine cutting, etc.
Roughing is a machining method that uses a large depth of cut to remove most or all of the machining allowance from a workpiece after one or more passes, such as rough turning, rough planing, rough milling, drilling, and sawing etc., roughing has high efficiency but low accuracy, and is generally used as pre-machining; semi-finishing is usually used as an intermediate process between roughing and finishing; finishing is the use of fine cutting to achieve a higher level of surface finish. , precision and surface quality, such as fine turning, fine planing, fine reaming, fine grinding, etc., finishing is generally the final processing.
Refinishing is carried out after finishing, and its purpose is to get less surface roughness and slightly increase accuracy. Finishing allowance is small, such as honing, grinding, super finishing and super finishing, etc.; The purpose of finishing is to reduce surface roughness, improve corrosion resistance, dust resistance and appearance, and do not need to improve accuracy such as polishing, grinding, etc.; ultra-precise machining is mainly used for processing some special precision parts, such as aerospace, laser, electronic, nuclear power, etc., and its accuracy reaches IT4 or higher, such as mirror turning, mirror grinding, soft grinding, granular mechanochemical polishing etc.
During cutting, the machined surface of the workpiece is obtained by the relative movement of the cutting tool and the workpiece. According to the surface forming method, cutting can be divided into three categories: tool nose path methodrumenta, the forming tool method and the generation method.
The tool nose method is based on the path of the tool tip relative to the surface of the workpiece to obtain the surface geometry needed for the workpiece, such as turning the outer circle, planing the plane, grinding the outer circle, etc. Turning the shaping surface with a template and etc., the path of movement of the tool tip depends on the relative movement between the cutting tool and the workpiece provided by the machine;
The forming tool method is called the forming method. It uses a forming tool that matches the final surface profile of the workpiece, or a forming grinding wheel to process the forming surface, such as forming, turning, forming, milling, and forming. grinding. Due to the manufacture of forming tools, this is more difficult, so it is usually used only for processing short forming surfaces;
The generation method, also known as the hobbing method, is the relative generation movement between the cutting tool and the workpiece during machining. The instantaneous centers of the tool and the workpiece interact with each other in pure rolling and a certain speed The relationship between them is preserved. The resulting machined surface is the envelope surface of the blade in this kind of movement. Gear machining, gear forming, shaving, honing and gear grinding are generative machining . Some cutting processes combine the characteristics of the tool nose method and the tool forming method, such as threading.
Machining quality mainly refers to the machining accuracy and surface quality of the workpiece (including surface roughness, residual stress, and surface hardening). With the development of technology, the quality of cutting processing has been constantly improved. At the end of the 18th century, the accuracy of the cut was measured in millimeters, at the beginning of the 20th century the accuracy of the cut reached 0.01 mm, by the 1950s the accuracy of the cut had reached the micron level, in the 1970s the accuracy of the cut had increased to 0.1 microns.
The main factors that affect cut quality include machine tools, cutting tools, fixtures, workpieces, machining methods, and machining conditions. To improve the quality of cutting, it is necessary to take appropriate measures on the above aspects, such as reducing the working error of the machine, the correct choice of cutting tools, improving the quality of the workpiece, rational organization of the process, and improving the environment. conditions.
Increasing the amount of cut to increase material removal rate is the main way to increase cutting efficiency. Commonly used high performance cutting methods include high speed cutting, high power cutting, plasma heated cutting and vibration cutting.
Cutting at grinding speeds above 45 m/scalled high speed grinding. The use of high-speed cutting (or grinding) not only improves efficiency, but also reduces surface roughness. High-speed cutting (or grinding) requires the machine to have a processing system with high speed, high rigidity, large power and good vibration resistance; the tool must have reasonable geometric parameters and convenient fastening methods, as well as safe and reliable, also the chip breaking method must be considered.
Powerful cutting refers to cutting with a large feed or large depth of cut, typically used for turning and grinding. The main feature of powerful turning is that, in addition to the main cutting edge, the turning tool also has a secondary cutting edge parallel to the workpiece surface to simultaneously participate in cutting, so the feed rate can be increased several times. times or even ten times compared to conventional turning. Compared with high speed cutting, power cutting has lower cutting temperature, longer tool life and higher cutting efficiency, the disadvantage is that the surface to be machined is rough. When cutting powerfully, the radial cutting force is very large, so it is not suitable for processing thin workpieces.
Vibration cutting is a cutting process in which low or high frequency vibration is added along the tool feed direction, which can improve cutting efficiency. Low-frequency vibratory cutting has good chip breaking effect, no chip breaking device is required, which increases the strength of the blade, and the total cutting power consumption is about 40% lower than conventional cutting with a chip breaking device.
High frequency vibration cutting is also called ultrasonic vibration cutting, which helps to reduce the friction between the tool and the workpiece, lower the cutting temperature, and reduce the adhesive wear of the tool, thereby improving cutting efficiency and quality. surface to be machined Tool life is increased by approximately 40%.
Cutting wood, plastic, rubber, glass, marble, granite and other non-metal materials is similar to cutting metal materials, but the cutting tools, equipment and amount of cutting used are different.
The cutting of wood products is mainly carried out on various woodworking machines. The main methods are: sawing, planing, turning, milling, drilling and grinding.
The rigidity of plastic is lower than that of metal, and it bends and deforms easily, especially thermoplastics, which have poor thermal conductivity and easily soften when heated. Therefore, when cutting plastics, it is advisable to use tools made of high-speed steel or hard alloy, choose a low feed and high speed.cutting, and use compressed air for cooling. If the cutter is sharp and at the right angle, it can produce streaked chips that can easily dissipate heat.
Glass (including semiconductor materials such as germanium and silicon) has high hardness and high brittleness. Cutting, drilling, grinding, and polishing techniques are commonly used to cut glass. For glass plates less than three millimeters thick, the simplest cutting method is to use diamond or other hard materials, manually score the surface of the glass, and use the stress concentration in the score to manually break it.
For the processing of hard materials such as marble, granite and concrete, methods such as cutting, turning, drilling, planing, grinding and polishing are mainly used. When cutting, you can use a circular saw blade with abrasives and water, the outer circle and the end can be turned with a carbide turning tool with a negative rake angle at a cutting speed of 10 to 30 m/min, a carbide drill can be used for drilling; the plane can be planed with a carbide planer or gear hobbing machine; a precise and smooth surface can be obtained by grinding the three parts against each other, or by grinding and polishing.