Shaft parts of the material:
1, carbon steel 35, 45, 50 and other high-quality carbon structural steel because of high comprehensive mechanical properties, more applications, including 45 steel used most widely. In order to improve its mechanical properties, should be normalized or tempered. Unimportant or less stressful shaft, can be used Q235, Q275 and other carbon structural steel.
2, alloy steel alloy steel has high mechanical properties, but more expensive, more for special requirements of the shaft. For example, the use of sliding bearings of high-speed shaft, commonly used 20Cr, 20CrMnTi and other low-carbon alloy structural steel, carburizing and quenching can improve the wear resistance of the journal; machine rotor shaft at high temperatures, high speeds and heavy-duty conditions, must have good high-temperature mechanical properties, often using 40CrNi, 38CrMoAlA and other alloy structural steel. Shaft blanks to forging priority, followed by steel; larger size or complex structure can be considered cast steel or ductile iron.
For example, the use of ductile iron manufacturing crankshaft, camshaft, has the advantages of low cost, better vibration absorption, less sensitive to stress concentration, better strength. The mechanical model of the shaft is a beam, most to rotate, so its stress is usually symmetric cycle. The possible forms of failure are: fatigue fracture, overload fracture, excessive elastic deformation and so on. Shafts are usually mounted on some parts with hubs, so most shafts should be made into stepped shafts, cutting and machining.
Shaft structural design:
The structural design of the shaft is to determine the reasonable shape of the shaft and all the structural dimensions, an important step for the shaft design. It is mounted on the shaft by the type of parts, size and its location, parts of the fixed way, the nature of the load, direction, size and distribution, bearing type and size, shaft blank, manufacturing and assembly process, installation and transportation, deformation of the shaft and other factors. Designers can design according to the specific requirements of the shaft, if necessary, can do several programs for comparison, in order to select the design program, the following is the general design principles of the shaft structure: 1, save materials, reduce weight, try to use equal strength external dimensions or large cross-section coefficient of the cross-section shape; 2, easy to shaft parts to accurately locate, stabilize, assemble, disassemble, and adjust; 3, the use of a variety of stress concentration and improve the stress concentration and strength of structural measures; 4, easy to facilitate the shaft parts to accurately locate, stabilize, assemble, disassemble and adjust; 3, using a variety of Strength of the structural measures; 4, easy to manufacture and ensure precision.
Shaft classification:
Common shafts can be divided into crankshafts, straight shafts, flexible shafts, solid shafts, hollow shafts, rigid shafts, flexible shafts (flexible shafts) according to the shape of the shaft structure. Straight shaft can be divided into: ① rotary shaft, work both bending moment and torque, is the most common shaft in the machinery, such as a variety of speed reducers in the shaft. ② shaft, used to support the rotating parts only to withstand the bending moment and does not transmit torque, some of the shaft rotation, such as the shaft of the railroad cars, etc., and some of the shaft does not rotate, such as supporting the pulley shaft, etc.. ③ transmission shaft, mainly used to transmit torque and does not bear the bending moment, such as the crane moving mechanism in the long shaft, automobile drive shaft and so on. Shaft materials are mainly carbon steel or alloy steel, can also be used ductile cast iron or alloy cast iron. The working capacity of the shaft generally depends on the strength and stiffness, high speed also depends on the vibration stability.
Technical requirements of the shaft:
1, machining accuracy
1) dimensional accuracy. Shaft parts of the dimensional accuracy mainly refers to the shaft diameter dimensional accuracy and shaft length dimensional accuracy. According to the use of requirements, the main journal diameter size accuracy is usually IT6-IT9 level, precision journal can also be up to IT5 level. Shaft length size is usually specified as the nominal size, for the step shaft of each step length according to the use of requirements can be given accordingly tolerance.
2) geometric accuracy. Shaft parts are generally supported on the bearing with two journals, these two journals are called support journals, but also the shaft assembly reference. In addition to the dimensional accuracy, the geometric accuracy (roundness, cylindricity) of the supporting journal is generally required. For the general accuracy of the journal, the geometric error should be limited to the diameter tolerance range, high requirements, should be separately specified in the parts drawing on the allowable tolerance value.
3) mutual positional accuracy. Shaft parts with the journal (assembly drive journal) relative to the support journal coaxiality is its mutual positional accuracy of the general requirements. Usually ordinary accuracy of the shaft, with the accuracy of the support journal of the radial runout is generally 0.01-0.03mm, high precision shaft for 0.001-0.005mm. In addition, the mutual positional accuracy of the internal and external cylindrical coaxial, axial positioning of the end face and the perpendicularity of the axis of the line requirements.
2, surface roughness according to the degree of precision of machinery, high and low operating speed, shaft parts surface roughness requirements are not the same. In general, the surface roughness of the support journal Ra value of 0.63-0.16μm; with the surface roughness of the journal Ra value of 2.5-0.63μ.
Shaft parts of the machining process:
1, shaft parts of the material
Shaft parts of the material selection, mainly based on the strength of the shaft, rigidity, wear resistance, and manufacturing processes and Decide to strive for economic rationalization. Commonly used shaft parts materials are 35, 45, 50 high-quality carbon steel, 45 steel is the most widely used. For the load is smaller or less important shaft can also be used Q235, Q255 and other ordinary carbon steel. For the larger force, axial size, weight restrictions or some special requirements can be used alloy steel. Such as 40Cr alloy steel can be used for medium precision, high speed work occasions, the material has better comprehensive mechanical properties after tempering treatment; selection of Cr15, 65Mn and other alloy steel can be used for higher precision, poorer working conditions, these materials after tempering and surface quenching of its wear resistance, fatigue strength performance are better; if the shaft parts in high-speed, heavy-duty conditions, the selection of 20Cr, 20CrMnTi, 20Mn2B and other low carbon steel or 38CrMoA1A carburized steel, these steels by carburizing quenching or nitriding treatment, not only has a very high surface hardness, and its heart strength is also greatly improved, so it has a good abrasion resistance, impact resistance, toughness and fatigue strength performance. Ductile cast iron, high-strength cast iron due to good casting performance, and has vibration damping properties, often used in the manufacture of complex shape and structure of the shaft. In particular, China's development of rare earth - magnesium ductile iron, good impact toughness, but also has a friction, vibration absorption, sensitivity to stress concentration is small, etc., has been used in the manufacture of automobiles, tractors, machine tools on the important shaft parts.
2, shaft parts of the blank
Shaft parts of the blank common profiles (round bar) and forgings. Large, complex shape and structure of the shaft can also use castings. Crankshafts in internal combustion engines generally use casting blanks. Profile blanks are divided into hot rolled or cold drawn bars, which are suitable for smooth shafts or stepped shafts with small differences in diameter. Forging blanks after heating and forging, the metal internal fiber organization along the surface distribution, and thus have a high tensile, flexural and torsional strength, generally used for important shaft.
Shaft parts processing methods:
1, the outer surface of the machining method and machining accuracy
Shafts, sets and disks are typical parts with an outer surface. External surface machining methods commonly used in turning, grinding and various finishing methods. Turning is the most cost-effective machining method of the cylindrical surface, but in terms of its economic accuracy, generally suitable for roughing and semi-finishing as a cylindrical surface; grinding is the main finishing method of the cylindrical surface, especially suitable for a variety of high hardness and quenching of the parts finishing; finishing is the finishing of ultra-precision machining (such as tumbling, polishing, grinding, etc.), applicable to certain precision and Surface quality requirements are very high parts. Due to the various processing methods can achieve the economic machining accuracy, surface roughness, productivity and production costs are different, so it must be based on the specific circumstances, the selection of reasonable processing methods, so as to process to meet the requirements of the parts drawings on the qualified parts.
2, the cylindrical surface of the turning process
(1) the form of cylindrical turning shaft parts cylindrical surface of the main processing method is turning. The main forms of machining are: the car free forging and large casting blanks, machining allowance is very large, in order to reduce the blank round shape error and positional deviation, so that the subsequent process of machining allowance is uniform, to remove the outer surface of the oxidized skin of the main cylindrical machining, the general excision allowance for a single side of the 1-3mm. roughing small and medium-sized forging, casting blanks are generally directly for rough turning. Rough turning is mainly cut off most of the blank allowance (generally car out of the stepped contour), in the case of process system rigidity allows, should choose a larger amount of cutting to improve production efficiency. Semi-finish turning is generally used as the final machining process for medium-precision surfaces, and can also be used as a pre-machining process for grinding and other machining processes. For higher precision blanks, can not be rough turning, direct semi-finish turning. Precision turning cylindrical surface processing of the final machining process and finishing process before the pre-processing. The final machining process of fine turning for high precision and fine roughness surface. Applicable to non-ferrous metal parts of the cylindrical surface processing, but due to non-ferrous metals should not be grinding, so fine turning can be used instead of grinding processing. However, fine turning requires high precision of the machine tool, good rigidity, smooth transmission, micro-feeding, no creeping phenomenon. Turning with diamond or carbide tools, tool main deflection angle selection (45o-90o), the tool tip arc radius is less than 0.1-1.0mm.
(2) the application of turning methods
1) general turning for a variety of batches of shaft parts cylindrical machining, is widely used. Single piece of small batch often use bedroom lathe to complete turning processing; batch, mass production of automatic, semi-automatic lathes and special lathes to complete turning processing.
2) CNC turning is suitable for single-piece small batch and batch production. Application is becoming more and more common, its main advantage is good flexibility, replacement of processed parts when the equipment adjustment and preparation time is short; processing of auxiliary time is less, through the optimization of cutting parameters and adaptive control to improve efficiency; processing quality is good, fewer special fixtures and fittings, the corresponding production preparation cost is low; machine tool operation technology requirements are low, not subject to the operator's skills, vision, mental, physical and other factors. For shaft parts, with the following characteristics suitable for the selection of CNC turning. Complex structure or shape, ordinary machining operation is difficult, long working hours, low processing efficiency parts. Parts that require high consistency of machining accuracy. Cutting conditions change parts, such as parts due to the shape of the characteristics of the need to cut grooves, turning holes, turning threads, etc., processing to change the amount of cutting many times. Batch size is not large, but each batch of varieties and have a certain degree of complexity of the parts with a keyway, radial holes (including screw holes), the end of the distribution of holes (including screw holes) system of shaft parts, such as shafts with flanges, shafts with keyway or square head, but also in the turning machining center on the processing, in addition to ordinary CNC turning, the parts of a variety of grooves, holes (including screw holes), surfaces and other machining surfaces can be together and be able to Processing is completed. Work processes are highly concentrated, its processing efficiency is higher than ordinary CNC turning, machining accuracy is more stable and reliable.
3) Grinding of cylindrical surfaces with abrasive tools at a high linear speed on the surface of the workpiece processing method is called grinding. Grinding is a multi-tool, multi-flute high-speed cutting method, which is used in parts finishing and hard surface machining. The process of grinding has a wide range and can be categorized as rough grinding, fine grinding, fine grinding and mirror grinding. Grinding process using abrasives (or abrasives) with small particles, high hardness, heat resistance and other characteristics, so you can process the harder metal materials and non-metallic materials, such as hardened steel, carbide tools, ceramics, etc.; processing process at the same time to participate in the cutting movement of the particles more, can excise the very thin and very fine chips, and thus high processing accuracy, surface roughness value is small. As a finishing method, grinding is widely used in production. Due to the development of powerful grinding, it is also possible to directly grind the blank to the required size and precision, thus obtaining a high productivity.