Gears are toothed mechanical parts that can match each other. Gear transmission can complete functions such as deceleration, speed up, and direction change. It is widely used in mechanical transmission and the entire mechanical field. This paper summarizes the processing technology of gear parts.

1. The function and structure of

gears Although gears are designed in different shapes and sizes due to their different functions in the machine, they can always be divided into two parts: the ring gear and the wheel body. Common cylindrical gears include the following types (below): disc gears, sleeve gears, internal gears, shaft gears, sector gears, and racks. Among them, disc gears are widely used.

Structural form of spur gear A spur gear can have one or more ring gears. Ordinary single ring gears have good manufacturability; while the small ring gears of double or triple gears are often affected by the shoulder, which limits the use of certain processing methods, and generally can only use shaper. If the gear precision requirements are high and gear shaving or grinding is required, the multi-ring gear is usually made into a combined structure of single ring gear.

2. Accuracy requirements of cylindrical gear

The manufacturing accuracy of the gear itself has a great influence on the working performance, carrying capacity and service life of the entire machine. According to the use conditions of the gear, the following requirements are put forward for the gear transmission: 1. The motion accuracy requires that the gear can accurately transmit the motion, and the transmission ratio is constant, that is, the gear is required to have a rotation angle error within a certain range. 2. Stability of work requires smooth transmission of gears, and low impact, vibration and noise. This requires that the change of the instantaneous speed ratio is small when the gear is limited to rotate, that is, the angle error in a short period should be limited. 3. Contact accuracy When the gear is transmitting power, in order not to cause excessive contact stress due to uneven load distribution and cause premature wear of the tooth surface, it is required that the tooth surface contact should be uniform when the gear is working, and a certain contact area and Meet the requirements of the contact position. 4. Tooth side clearance requires that when the gear is driven, a certain gap is left between the non-working tooth surfaces to store lubricating oil and compensate for dimensional changes caused by temperature and elastic deformation, as well as some errors in processing and assembly.

3. Gear material

Gears should be made of suitable materials according to the working conditions used. The choice of gear material has a direct impact on the processing performance and service life of the gear. Generally, medium carbon steel (such as 45 steel) and low and medium carbon alloy steel are used for gears, such as 20Cr, 40Cr, 20CrMnTi, etc. ² 38CrMoAlA nitrided steel can be used for important gears with higher requirements, and cast iron, bakelite or nylon can also be used for non-power transmission gears.

4. Gear heat treatment According to different purposes , two heat treatment processes are arranged in gear processing: 1. Pre-heat treatment normalizing or tempering is arranged before and after the blank heat treatment. The main purpose is to eliminate the residual stress caused by forging and rough machining , Improve the machinability of materials and improve the comprehensive mechanical properties. 2. Tooth surface heat treatment After the tooth profile is processed, in order to improve the hardness and wear resistance of the tooth surface, heat treatment processes such as carburizing and quenching, high-frequency induction heating and quenching, carbonitriding and nitriding are often carried out.

5. Gear blanks The blank forms of gears mainly include bars, forgings and castings.

Bar stock is used for gears with small size, simple structure and low strength requirements. When the gear requires high strength, wear resistance and impact resistance, forgings are often used, and for gears with a diameter greater than 400-600mm, casting blanks are often used. In order to reduce the amount of mechanical processing, for large-sized, low-precision gears, the gear teeth can be directly cast; for small-sized, complex-shaped gears, new technologies such as precision casting, pressure casting, precision forging, powder metallurgy, hot rolling and cold extrusion can be used. The tooth blank with gear teeth is produced by the process to improve labor productivity and save raw materials.

6. Selection of machining plan for tooth blank

For the tooth blanks of shaft gears and sleeve gears, the machining process is basically similar to that of general shafts and sleeves. Now we mainly discuss the machining process of disc gear tooth blanks. The machining process plan of the tooth blank mainly depends on the wheel body structure and production type of the gear. 1. When mass-produced gear blanks are processed in large quantities, the process plan of "drilling, pulling and multi-tool lathe" is often used when a large number of medium-sized gear blanks are processed. (1) Drilling or reaming is performed by positioning the outer circle and end face of the blank. (2) pull holes. (3) Position the outer circle, end face, grooving and chamfering on the multi-knife semi-automatic lathe with holes. This process scheme has high production efficiency because the machine tool can be used to form an assembly line or an automatic line. 2. When the tooth blanks produced in batches are processed in batches, the process plan of "car-pull-car" is often adopted (1) the outer circle of the tooth blank or the hub is positioned, and the outer circle, end face and inner hole of the fine car . (2) Support the pull hole (or spline hole) with the end face. (3) Position the outer circle and end face of the finish car with holes. This scheme can be realized by horizontal lathe or turret lathe and broaching machine. It is characterized by stable processing quality and high production efficiency. When there are steps in the hole of the gear blank or grooves on the end surface, the multi-tools on the turret lathe can be fully used for multi-station processing, and the processing of the gear blank can be completed at one time on the turret lathe.

7. Gear tooth processing method

The tooth profile processing of gear ring gear is the core of the whole gear processing. There are many processes in gear machining, all of which are for tooth profile machining, and the purpose is to finally obtain gears that meet the precision requirements. According to the processing principle, tooth shape can be divided into forming method and generating method. The forming method is a method of cutting out the tooth surface with a forming tool that conforms to the shape of the tooth groove of the gear to be cut, such as milling, broaching and forming grinding. The generation method is a method in which the gear cutter and the workpiece perform a generation motion to cut out the tooth surface according to the meshing relationship of the gear pair, such as hobbing, shaping, shaving, grinding and honing. The choice of tooth shape processing scheme mainly depends on the gear's precision grade, structural shape, production type and production conditions. For gears with different precision grades, the commonly used tooth shape processing schemes are as follows: (1) Quenched and tempered gears with precision below 8 Gear hobbing or gear shaping can meet the requirements. For hardened gears, the processing scheme of rolling (inserting) teeth-tooth end processing-quenching-correction holes can be adopted. However, the machining accuracy of the tooth profile before quenching should be improved. (2) Grade 6-7 precision gears can be used for hardened gears: rough hobbing - fine hobbing - tooth end processing - fine shaving - surface quenching - calibration benchmark - honing. (3) Gears with a precision above grade 5 generally use: rough hobbing - fine hobbing - tooth end processing - quenching - calibration standard - rough grinding - fine grinding. Grinding is currently a processing method with high precision and small surface roughness in tooth profile processing, and the high precision can reach 3-4 grades. 1. Precision grade of milling gear: below grade 9. Tooth surface roughness Ra: 6.3~3.2μm Scope of application: In single-piece repair production, processing low-precision external cylindrical gears, racks, bevel gears, and worm gears 2. Pulled gears Precision grade: Grade 7 Tooth surface roughness Ra: 1.6~0.4μm Scope of application: Mass production of grade 7 internal gears, external gear broaches are complicated to manufacture, so less use 3. Hobbing gear precision grade: Grade 8~7 tooth surface Roughness Ra: 3.2~1.6μm Scope of application: In various mass production, processing of medium-quality external cylindrical gears and worm gears 4. Gear shaping gear accuracy grade: 8~7 tooth surface roughness Ra: 1.6μm Scope of application: various In mass production, process medium-quality internal and external cylindrical gears, multi-connected gears and small racks 5. Rolling (or plugging) teeth-quenching-honing gears Accuracy grade: 8~7 tooth surface roughness Ra: 0.8~ 0.4μm Scope of application: Gears used for tooth surface quenching 6. Gear hobbing-shaving Gear accuracy grade: 7~6 tooth surface roughness Ra: 0.8~0.4μm Scope of application: Mainly used for mass production 7. Hobbing - Shaving - quenching - honing Gear precision grade: 7~6 tooth surface roughness Ra: 0.4~0.2μm Scope of application: mainly used for mass production 8.

8. Processing of the tooth end

The processing of the tooth end of the gear includes rounding, chamfering, chamfering and deburring, as shown in the figure below. The rounded and pointed gears are easy to enter the meshing state when shifting gears, reducing the impact phenomenon. Chamfering removes sharp edges and burrs from tooth ends.

Tooth end processing a) rounding b) chamfering c) chamfering When rounding, the milling cutter rotates at high speed and swings along the arc. After processing one tooth, the workpiece moves away from the milling cutter, and then quickly approaches the milling cutter to process the tooth end of the next tooth after indexing. Tooth end processing must be carried out before gear quenching, usually after hobbing (inserting) teeth and before shaving.

Tooth end rounding

9. Spur gear machining process

High-precision gear 1. Rough forging 2. Normalizing heat treatment 3. Rough car shape, leaving a machining allowance of 2mm for each position. Positioning reference: outer circle and end face 4. Finish car each At the inner hole to Φ84.8H7, the total length leaves a grinding allowance of 0.2mm, and the rest to the size positioning reference: outer circle and end face Hole and end face A7. Chamfering positioning reference: inner hole and end face A8. Fitter deburring 9. Tooth surface high-frequency quenching HRC5210. Key slot positioning reference: inner hole and end face A11. Grinding large end face A positioning reference: inner hole 12 . Grinding surface B to total length positioning reference: end face A13. Grinding inner hole to φ85H5 positioning reference: inner hole and end face A14. Tooth surface grinding positioning reference: inner hole and end face A15. Inspection 10. Analysis of gear processing

process

1. Selection of positioning datum The selection of gear positioning datum is often different due to the different structural shapes of gears. The gear with shaft mainly uses positioning, and when the aperture is large, it uses cone plugging. The positioning accuracy is high, and the benchmark can be unified. Hole gears often use the following two positioning and clamping methods when machining the tooth surface. (1) Positioning by the inner hole and the end face, that is, the joint positioning of the inner hole and the end face of the workpiece, determine the center and axial position of the gear, and adopt the clamping method facing the positioning end face. This method can make the positioning datum, design datum, assembly datum and measuring datum overlap, and the positioning accuracy is high, which is suitable for mass production. However, the manufacturing precision of the fixture is required to be higher. (2) The gap between the outer circle and the end face positioning workpiece and the fixture mandrel is relatively large. Use a dial gauge to correct the outer circle to determine the position of the center, and position it with the end face; clamp it from the other end face. This method has low production efficiency because each workpiece needs to be calibrated; it has high requirements on the coaxiality of the inner and outer circles of the gear blank, but not high requirements on the accuracy of the fixture, so it is suitable for single-piece and small-batch production. 2. Processing of gear blanks The processing of gear blanks before tooth surface processing occupies a very important position in the entire gear processing process, because the benchmarks used for tooth surface processing and testing must be processed at this stage; whether it is from improving productivity or In order to ensure the processing quality of gears, we must pay attention to the processing of gear blanks. In the technical requirements of gears, attention should be paid to the dimensional accuracy requirements of the addendum circle, because the detection of the tooth thickness is based on the addendum circle, and the accuracy of the addendum circle is too low, which will inevitably make the measured tooth thickness value incorrect. Reflects the size of the tooth flank clearance. Therefore, the following three issues should be paid attention to in this processing process: (1) When the diameter of the addendum circle is used as the measurement reference, the dimensional accuracy of the addendum circle should be strictly controlled (2) Ensure that the positioning end face and positioning hole or outer circle Mutual perpendicularity (3) Improve the manufacturing accuracy of the gear inner hole and reduce the fit clearance with the fixture mandrel