Gear parts processing technology explanation

Guide language: Gear is a kind of mechanical parts with teeth that can match each other. Gear transmission can complete the functions of deceleration, increase speed and change direction. It is widely used in mechanical transmission and the whole mechanical field. This paper summarizes the processing technology of gear parts. The function and structure of gears Although they are designed in different shapes and sizes because of their different functions in the machine, they can always be divided into rings and wheels. The common cylindrical gear has the following categories (below) : disc gear, sleeve gear, inner gear, shaft gear, fan gear, rack. Among them, disc gear is the most widely used.

Gear is a mechanical part with teeth that can match each other. Gear transmission can complete the functions of deceleration, increase speed and change direction. It is widely used in mechanical transmission and the whole mechanical field. This paper summarizes the processing technology of gear parts.

Gears, although designed in different shapes and sizes because of their different functions in the machine, can always be divided into ring and wheel body. The common cylindrical gear has the following categories (below) : disc gear, sleeve gear, inner gear, shaft gear, fan gear, rack. Among them, disc gear is the most widely used.

Structure of a cylindrical gear A cylindrical gear may have one or more rings. Common single ring gear has good technology; However, the small ring of double or triple gear is often affected by the shoulder, which limits the use of some processing methods. Generally, only gear shaper can be used. If the precision of gear is high, shaving or grinding is needed, usually the multi-ring gear is made into a single ring gear combination structure.

2. The precision of cylindrical gear requires the manufacturing precision of the gear itself, which has a great impact on the working performance, bearing capacity and service life of the whole machine. According to the operating conditions of gear, the following requirements are put forward for gear transmission: 1. Motion accuracy requires that gear can accurately transfer motion, transmission ratio is constant, that is, the gear Angle error does not exceed a certain range in a revolution. 2. The working stability requires that the gear transfer motion be stable, and the impact, vibration and noise should be small. This requires that the change of instantaneous speed ratio should be small, that is, the angular error should be limited in a short period. 3. Contact accuracy Gear in the transmission of power, in order to avoid the uneven distribution of load so that the contact stress is too large, causing premature wear of the tooth surface, which requires gear to work when the tooth surface contact to be uniform, and ensure that there is a certain contact area and meet the requirements of the contact position. 4. Gear side clearance requirements when the gear transmission, there is a certain gap between the non-working tooth surface, in order to store lubricating oil, compensation due to temperature, elastic deformation caused by the size change and some errors in processing, assembly.

3. Gear material Gear should be selected according to the working conditions of the appropriate materials. The choice of gear material has a direct influence on the machining performance and service life of gear. General gear selection of medium carbon steel (such as 45 steel) and low, medium carbon alloy steel, such as 20Cr, 40Cr, 20CrMnTi, etc.. ² 38CrMoAlA nitride steel can be used for important gears with high requirements, and cast iron, laminated bakelite or nylon can also be used for non-force transmission gears.

4. Heat treatment of gear Gear processing according to different purposes, arrange two heat treatment procedures: 1. The main purpose of blank heat treatment is to eliminate the residual stress caused by forging and rough machining, improve the machinability of the material and improve the comprehensive mechanical properties. 2. Heat treatment of tooth surface After tooth shape processing, in order to improve the hardness and wear resistance of tooth surface, often carburizing quenching, high-frequency induction heating quenching, carburizing and nitriding heat treatment processes.

5. Rough gear The rough form of gear mainly includes bars, forgings and castings. Bars are used for gears with small size, simple structure and low strength requirements. When the gear requires high strength, wear resistance and impact resistance, multi-purpose forging, diameter is greater than 400 ~ 600mm gear, commonly used casting blank. In order to reduce the amount of mechanical processing, the gear teeth of large size and low precision can be directly cast. For gear with small size and complex shape, the gear blank with gear teeth can be produced by new technologies such as precision casting, pressure casting, precision forging, powder metallurgy, hot rolling and cold extrusion, so as to improve labor productivity and save raw materials.

The machining process of the gear blank of shaft gear and sleeve gear is basically similar to that of general shaft and sleeve. The machining process of the gear blank of disc gear is mainly discussed. The processing technology of gear blank mainly depends on the structure of gear body and production type. 1. When the large number of large number of production of tooth blank processing medium size tooth blank, most of the "drill one pull one knife car" process plan. (1) To blank outer circle and end face positioning for drilling or reaming. (2) the pull hole. (3) with hole positioning in the multi-tool semi-automatic lathe rough finishing car outer circle, end face, grooving and chamfering. This process scheme can be composed of assembly line or automatic line due to the use of efficient machine tools, so the production efficiency is high. 2. Batch production of tooth billet processing batch production of tooth billet, usually adopt the "one car pulling one car" process plan (1) to tooth billet outer circle or wheel yi positioning, fine turning outer circle, end face and inner hole. (2) to support the end hole (or spline hole). (3) to hole positioning fine car outer circle and end face, etc. 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 the blank hole has steps or grooves on the end face, we can make full use of the multi-cutter on the turret lathe to carry out multi-station processing, and complete the machining of the blank on the turret lathe at the last time.

7. Tooth processing method The tooth shape processing of gear ring is the core of the whole gear processing. Gear machining has many procedures, which are for the tooth shape machining service, its purpose is to obtain the final precision requirements of the gear. According to the processing principle, tooth shape can be divided into forming method and developing method. The forming method is to use the forming tool to cut the tooth surface which is consistent with the shape of the tooth groove, such as milling tooth, pulling tooth and forming grinding tooth. Development method is a gear cutter and the workpiece according to the meshing relationship of gear pair for development movement to cut the tooth surface method, such as hobbing, gear shaper, shaving, grinding and honing. The choice of tooth shape machining scheme mainly depends on the precision grade, structure shape, production type and production conditions of the gear. For different precision grades of gear, the commonly used tooth shape machining scheme is as follows :(1) the hobbing or gear shaper with the following precision grade 8 can meet the requirements. For hardened gear, the machining scheme of rolling (inserting) tooth - machining tooth end - quenching - correction hole can be adopted. However, the machining accuracy of tooth profile should be improved one level before quenching. (2) Grade 6-7 precision gear for hardened gear can be used: rough hobbing - fine hobbing - tooth end machining - fine shaving - surface hardening - calibration datum - honing. (3) Gear above grade 5 accuracy generally adopts: rough hobbing - fine hobbing - tooth end machining - quenching - calibration datum - rough grinding - fine grinding. Tooth grinding is a machining method with the highest precision and the smallest surface roughness, and the highest precision can reach grade 3-4. 1. Milling gear precision grade: below grade 9 Tooth surface roughness Ra: 6.3~3.2μm Scope of application: single piece repair production, processing low precision cylindrical gear, rack, bevel gear, Worm gear 2. Puller gear precision grade: 7 grade tooth surface roughness Ra: 1.6~0.4μm Range of application: mass production of 7 grade inner gear, gear broach manufacturing complex, so less use 3. Hobbing gear precision grade: 8~7 grade tooth surface roughness Ra: 3.2~1.6μm Range of application: all kinds of batch production, processing medium quality cylindrical gear and worm gear 4. Range of application: all kinds of batch production, processing medium quality internal and external cylindrical gears, multi-gear and small rack 5. Rolling (or inserting) gear - quenching - honing gear precision grade: 8~7 Tooth surface roughness Ra: 0.8~0.4μm Application: gear 6 for tooth surface hardening. Gear hobbing - shaving gear precision grade: 7~6 tooth surface roughness Ra: 0.8~0.4μm Application range: mainly used for mass production 7. Gear hobbing - shaving - hardening - honing gear precision grade: 7~6 Tooth surface roughness Ra: 0.4~0.2μm Application range: mainly used for mass production 8. Rolling (inserting) gear - hardening - grinding gear precision grade: 6~3 Gear surface roughness Ra: 0.4~0.2μm Range of application: used for high-precision gear tooth surface processing, low productivity, high cost 9. Roller (insert) gear - grinding gear precision grade: 6~3 Tooth surface roughness Ra: 0.4~0.2μm Range of application: used for high precision gear tooth surface processing, low productivity, high cost

8. Tooth end processing gear tooth end processing has round, tip, chamfering and deburring, as shown in the following figure. The round and pointed gears are easy to engage when shifting, so as to reduce the impact. Chamfering can remove tip edge and burr.

Tooth end machining a) chamfering b) chamfering c) Chamfering The figure below is a diagram of tooth end chamfering with finger milling cutter. When the circle is inverted, the milling cutter rotates at high speed, and makes the swing along the arc, after processing a tooth, the workpiece retreats from the milling cutter, and then rapidly moves to the milling cutter close to processing the tooth end of the next tooth. Tooth end machining must be carried out before the gear is hardened, usually after rolling (inserting) teeth and before shaving.

High precision gear 1. Blank forging 2. Positive heat treatment 3. Throughout the fine car, the inner hole to φ 84.8H7, the total length of the grinding allowance is 0.2mm, the rest to the size positioning datum: outer circle and end face 5. Inspection 6. Hobbing surface, grinding allowance 0.25 ~ 0.3mm positioning datum: inner hole and end face A7. Chamfering positioning reference: inner hole and end face A8. Fitter deburring 9. Tooth surface high-frequency quenching HRC5210. Insert keyway positioning datum: inner hole and end face A11. Grind large end face A positioning datum: inner hole 12. Grinding surface B to length positioning datum: end face A13. Grinding inner hole to φ85H5 positioning datum: inner hole and end face A14. Tooth surface grinding positioning datum: inner hole and end face A15. Inspection

10 gear processing process analysis 1 positioning datum selection for gear positioning datum selection is often due to the different structure of the gear shape, but there are differences. The shaft gear mainly adopts the top positioning, and the taper plug is used when the aperture is large. The precision of the center positioning is high, and the benchmark can be unified. The following two positioning and clamping methods are often used in machining the tooth surface of gear with hole. (1) the inner hole and end face positioning is to joint positioning of the workpiece inner hole and end face to determine the center and axial position of the gear, and the clamping method for positioning end face. This method can make positioning datum, design datum, assembly datum and measurement datum coincide, high positioning accuracy, suitable for mass production. However, the manufacturing accuracy of fixture is higher. (2) the outer circle and end face positioning workpiece and fixture spindle matching gap is large, with a dial meter to correct the outer circle to determine the location of the center, and end face positioning; Clamp from the other end. This way because each workpiece must be corrected, so the production efficiency is low; It is suitable for single and small batch production because it requires high coaxiality of inner and outer circle of tooth blank, but not high precision of fixture. Gear blank processing before tooth surface processing, in the whole gear processing process occupies a very important position, because the tooth surface processing and detection of the benchmark must be processed at this stage; It is necessary to pay attention to the machining of gear blank whether to improve productivity or to ensure the machining quality of gear. In the technical requirements of gear, attention should be paid to the dimension accuracy of tooth tip circle, because the tooth thickness detection is based on tooth tip circle measurement, the precision of tooth tip circle is too low, so that the measured tooth thickness value cannot reflect the size of tooth side clearance correctly. Therefore, in this process should pay attention to the following three problems :(1) when taking the diameter of the tooth tip circle as the measurement benchmark, the dimension accuracy of the tooth tip circle should be strictly controlled (2) ensure the vertical degree of the positioning end face and the positioning hole or the outer circle each other (3) improve the manufacturing accuracy of the inner hole of the gear, reduce the clearance with the fixture spindle