Views: 0 Author: Site Editor Publish Time: 2023-08-24 Origin: Site
Gear is a mechanical part that can coincide with each other. Gear transmission can complete the functions of deceleration, growth and direction. It is widely used in the mechanical transmission and the whole mechanical field. This paper summarizes the processing technology of gear parts.
1. The function and structure of the gear Although the gears are designed in different shapes and sizes due to their different function in the machine, they can always be divided into the tooth ring and the wheel body. Common cylindrical gear has the following categories (below): disc gear, set gear, internal gear, shaft gear, fan gear, rack. The disc gear is widely used.
Structural form of a cylindrical gear A cylindrical gear can have one or more tooth rings. Ordinary single tooth ring gear has good technology; and the small tooth ring of double or triple gear is often affected by the shoulder, limiting the use of some processing methods, generally can only use teeth. If the gear accuracy requirement is high, the need to shave or grind teeth, the multi-tooth ring gear is usually made into a combination structure of single tooth ring gear.
2. Accuracy requirements of cylindrical gear The manufacturing accuracy of the gear itself has a great impact on the working performance, carrying capacity and service life of the whole machine. According to the use conditions of the gear, the following requirements are put forward for the gear transmission: 1. The movement accuracy requires that the gear can accurately transfer the movement, the transmission ratio is constant, that is, the gear in a turn, the Angle error does not exceed a certain range. 2. Working stability requires smooth gear transmission movement, less impact, vibration and noise. This requires that limiting the change of the instantaneous speed ratio when the gear rotation is smaller, that is, to limit the corner error in a short period. 3. [] Contact accuracy gear in the transfer of power, in order not to cause the uneven load distribution, causing premature wear of the tooth surface, which requires the gear surface contact to be uniform, and ensure that there is a certain contact area and contact position that meet the requirements. 4. [] Dental side clearance requires gear transmission, leaving a certain gap between the non-working teeth to store lubricating oil to compensate for the size change caused by temperature and elastic deformation and some errors in processing and assembly.
3. Material of the gear The gear shall choose the appropriate material according to the working conditions used. The choice of gear material has a direct impact on the machining performance and service life of the gear. The general gear, carbon steel (such as 45 steel) and low and medium carbon alloy steel, such as 20 Cr, 40 Cr, 20CrMnTi, etc.² High requirements of the important gear can be selected 38CrMoAlA nitride steel, non-force gear can also be cast iron, adhesive wood or nylon materials.
4. Heat treatment gear processing according to different purposes, arrange two kinds of heat treatment process: 1. [] blank heat treatment before and after the tooth billet processing arrange pre-heat treatment ignition or quality adjustment, its main purpose is to eliminate the residual stress caused by forging and rough processing, improve the cutting of the material and improve the comprehensive mechanical properties. 2. [] After heat treatment of tooth surface, in order to improve the hardness and wear resistance of tooth surface, heat treatment processes such as carbon infiltration quenching, high frequency induction heating quenching, carbon and nitrogen coinfiltration and nitriding are often carried out.
5. Gear blank gear blank form mainly has rod material, forgings and castings. The rod material is used for small size, simple structure and low strength requirements. When the gear requires high strength, wear resistance and impact resistance, multiple forgings, diameter greater than 400~600mm gear, commonly used casting blank. In order to reduce the machining capacity, for large size and low precision gears, for small size and complex shape gears, precision casting, pressure casting, precision forging, powder metallurgy, hot rolling and cold extrusion can be used to improve labor productivity and save raw materials.
6. Selection of machining scheme for tooth billet For the tooth blank of shaft gear and sleeve gear, the processing process is basically similar to the general shaft and sleeve. Now, the processing process of disc gear tooth blank is mainly discussed. The processing process scheme of the tooth billet mainly depends on the wheel body structure and production type of the gear. 1. [] A large number of mass production of tooth billet processing a large number of mass processing of medium size tooth billet, the use of "drill one pull one knife car" process scheme.(1) Drilling or expand the outer circle and end surface of the blank.(2) Pull the hole.(3) With the hole on the multi-knife semi-automatic lathe, end surface, cutting groove and chamfer, etc. This process scheme because of the use of machine tools can form an assembly line or automatic line, so the production efficiency is high. 2. [] When processed into batches, it often adopts the process scheme of "one car pull one car". (1) to the tooth billet outer round or wheel yi positioning, fine car outer round, end surface and inner hole.(2) Support the pull hole (or spline hole) with the end surface.(3) Position the outer circle and end surface of the refined car by holes. This scheme can be realized by the horizontal lathe or turn tower lathe and pull bed. It is characterized by a stable processing quality and a high production efficiency. When the tooth hole has steps or the end surface has grooves, you can make full use of the multi-knife on the turret lathe to carry out multi-station processing, and complete the processing of the tooth billet on the turret lathe at one time.
7. gear processing method The tooth shape machining of the gear and tooth ring is the core of the whole gear machining.
Gear processing has many processes, these are for the tooth shape processing service, its purpose is to finally obtain the gear meeting the accuracy requirements.
According to the processing principle, the tooth shape can be divided into forming method and forming method.
Forming method is a method of cutting out the tooth surface with the shape of the cutting gear groove, such as milling teeth, pulling teeth and forming grinding teeth.
Display method is the gear tool and workpiece according to the gear pair of the gear surface, such as rolling teeth, inserting teeth, shaving teeth, grinding teeth and honteeth, etc.
The choice of tooth shape processing scheme mainly depends on the accuracy grade, structure shape, production type and production conditions of the gear. For different accuracy levels of gear, the commonly used tooth shape processing scheme is as follows: (1) the following 8 level of gear can meet the requirements with teeth or teeth.
For the hardened gear can be used: rolling (plug) tooth-tooth end processing-quenching-correction hole processing scheme.
But the processing accuracy of the tooth shape before quenching should be improved.
(2) Grade 6-7 precision gear can be used for hardened gear: coarse rolling teeth-fine rolling teeth-tooth end processing-fine shaving teeth-surface quenching-calibration reference-honing teeth.
(3) Grade 5 precision above the gear generally use: coarse rolling teeth-fine rolling teeth-tooth end processing-quenching-calibration reference-coarse grinding teeth-fine grinding teeth.
Tooth grinding is a processing method with high precision and small surface roughness value in tooth shape processing, and the high precision can reach 3-4 levels.
1. Milling gear accuracy grade of tooth surface: below 9 Ra: 6.3~3.2 μ m Scope of application: single piece repair production, Processing low precision external cylindrical gear, rack, bical gear, worm gear 2. Gear precision level: 7 tooth surface roughness Ra: 1.6~0.4 μ m Scope of application: mass production of 7 internal gear, External gear pull knife manufacturing complex, 3. Precision grade of rolling gear: 8~7 tooth surface roughness Ra: 3.2~1.6 μ m Scope of application: in all kinds of mass production, Processing medium mass external cylindrical gear and worm gear 4. Dental gear accuracy grade: 8~7 tooth surface roughness Ra: 1.6 μ m Application range: in various mass production, Processing medium quality inner and outer cylindrical gears, multilink gear and small rack 5. Rolling (or inserted) teeth-quenching-honing gear accuracy grade: 8~7 tooth surface roughness Ra: 0.8~0.4 μ m Scope of application: gear for tooth surface quenching 6. Rolling teeth-shaving gear accuracy grade: 7~6 tooth surface roughness Ra: 0.8~0.4 μ m Scope of application: mainly used for mass production 7. Rolling teeth-shaving-quenching-honing gear accuracy grade: 7~6 tooth surface roughness Ra: 0.4~0.2 μ m Scope of application: mainly used for mass production 8. Rolling (plug) teeth-quenching-grinding gear accuracy grade: 6~3 grade tooth surface roughness Ra: 0.4~0.2 μ m Scope of application: for high precision gear tooth surface processing, Low productivity, High cost 9. Rolling (insertion) teeth-grinding gear accuracy grade: 6~3 tooth surface roughness Ra: 0.4~0.2 μ m Scope of application: for tooth surface processing of high precision gear, Low productivity, High cost
8. Processing of the tooth ends The tooth end of the gear is round, pointed, angular and burr, as shown in the following figure.
Pour round, inverted tip after the gear in the gear easy to enter into the engagement state, reduce the impact phenomenon.
Inverted edges can remove the tip edge and burr.
Dental end processing a) inverted circle b) inverted tip c) inverted edge below is a schematic diagram of reversing the tooth end with a finger milling cutter.
When reversing the circle, the milling cutter rotates at high speed and swings along the arc. After processing a tooth, the workpiece returns from the milling cutter, and the speed quickly to the milling cutter near the tooth end of the next tooth.
End processing must be done before gear quenching, usually after rolling (inserting) the teeth and before shaving.
Tend inverted round
9. Processing process of straight-tooth cylindrical gear High precision gear 1. Blank forging 2. hot treatment 3. Appearance of rough car, everywhere left processing allowance 2mm positioning reference: outer circle and end surface 4. Fine car everywhere, Inner hole to Φ84.8H7, Total length of grinding allowance of 0.2mm, 5. Inspection 6. Rolling cut tooth surface; Keeping teeth allowance 0.25~0.3mm positioning reference: inner hole and end face A7. Infer positioning reference: inner hole and end face A8. fitter burring 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 B face to total length positioning reference: end face A13. grinding inner hole to φ 85H5 positioning reference: inner hole and end face A14. tooth face grinding positioning reference: inner hole and end face A15. Inspection
10. Gear processing process analysis 1. Selection of positioning reference The selection of gear positioning reference is often different due to the structural shape of the gear.
The shaft gear is mainly positioned, and the cone blocking is used when the aperture is large.
Positioning accuracy is high, and can achieve the unified benchmark.
The hole gear often adopts the following two positioning and clammethods in the tooth surface.
(1) The positioning of the inner hole and the end surface, that is, the joint positioning of the inner hole and the end face of the workpiece are used to determine the center and axial position of the gear, and the clamping mode facing the positioning end face is adopted.
This way can make the positioning datum, design datum, assembly datum and measurement datum overlap, high positioning accuracy, suitable for mass production.
However, the manufacturing accuracy of the fixture is relatively high.
(2) The outer circle and the workpiece and the clamp shaft are large, correct the outer circle to determine the position of the center, and locate the end surface; clamp from the other end.
Because each workpiece is corrected, the production efficiency is low; it requires the coaxial degree of the inner and outer circles of the tooth blank, and the precision of the clamp is not high, so it is suitable for single piece and small batch production.
2. Processing before gear surface processing plays a very important position in the whole gear processing process, because the benchmark used for tooth surface processing and testing must be processed at this stage; whether from improve the productivity, or to ensure the processing quality of gear, we must pay attention to the processing of gear blank.
In the technical requirements of gear, attention should be paid to the dimensional precision of the top circle, because the detection of tooth thickness is based on the top circle as the measurement reference, the precision of the top circle is too low, so that the measured tooth thickness value can not correctly reflect the size of the tooth side clearance.
Therefore, in the processing process should pay attention to the following three problems: (1) when the tooth top circle diameter as the measurement benchmark, should strictly control the size accuracy of the tooth top circle (2) to ensure that the positioning end face and positioning hole or the verticality of the circle (3) improve the manufacturing accuracy of the gear in the hole, reduce the clearance with the clamp spindle
