The gear shaft is the most important supporting and rotating part in construction machinery, which can realize the rotary motion of gears and other components, and can transmit torque and power over a long distance. It has the advantages of high transmission efficiency, long service life and compact structure. It has been widely used and has become one of the basic parts of construction machinery transmission. At present, with the rapid development of the domestic economy and the expansion of infrastructure, there will be a new wave of demand for construction machinery. The material selection of the gear shaft, the way of heat treatment, the installation and adjustment of the machining fixture, the hobbing process parameters, and the feed are all very important to the processing quality and life of the gear shaft. This paper conducts a specific research on the processing technology of the gear shaft in the construction machinery according to its own practice, and proposes the corresponding improvement design, which provides a strong technical support for the improvement of the processing technology of the engineering gear shaft.

Analysis on the Processing Technology of Gear Shaft in Construction Machinery

For the convenience of research, this paper selects the classic input gear shaft in construction machinery, that is, the typical stepped shaft parts, which are composed of splines, circumferential surfaces, arc surfaces, shoulders, grooves, ring grooves, gears and other different forms. Geometric surface and geometric entity composition. The precision requirements of gear shafts are generally relatively high, and the processing difficulty is relatively large, so some important links in the processing process must be correctly selected and analyzed, such as materials, involute external splines, benchmarks, tooth profile processing, heat treatment, etc. In order to ensure the quality and processing cost of the gear shaft, various key processes in the processing of the gear shaft are analyzed below.

Material selection of gear shaft

Gear shafts in transmission machinery are usually made of 45 steel in high-quality carbon steel, 40Cr, 20CrMnTi in alloy steel, etc. Generally, it meets the strength requirements of the material, and the wear resistance is good, and the price is appropriate.

Rough machining technology of gear shaft

Due to the high strength requirements of the gear shaft, the use of round steel for direct machining consumes a lot of materials and labor, so forgings are usually used as blanks, and free forging can be used for gear shafts with larger sizes; Die forgings; sometimes some of the smaller gears can be made into an integral blank with the shaft. During blank manufacturing, if the forging blank is a free forging, its processing should follow the GB/T15826 standard; if the blank is a die forging, the machining allowance should follow the GB/T12362 system standard. Forging blanks should prevent forging defects such as uneven grains, cracks, and cracks, and should be tested in accordance with the relevant national forging evaluation standards.

Preliminary heat treatment and rough turning process of blanks

The blanks with many gear shafts are mostly high-quality carbon structural steel and alloy steel. In order to increase the hardness of the material and facilitate processing, the heat treatment adopts normalizing heat treatment, namely: normalizing process, temperature 960 ℃, air cooling, and the hardness value remains HB170-207. Normalizing heat treatment can also have the effect of refining forging grains, uniform crystal structure, and eliminating forging stress, which lays the foundation for subsequent heat treatment.

The main purpose of rough turning is to cut the machining allowance on the surface of the blank, and the machining sequence of the main surface depends on the selection of the part positioning reference. The characteristics of the gear shaft parts themselves and the accuracy requirements of each surface are affected by the positioning reference. The gear shaft parts usually use the axis as the positioning reference, so that the reference can be unified and coincide with the design reference. In actual production, the outer circle is used as the rough positioning reference, the top holes at both ends of the gear shaft are used as the positioning precision reference, and the error is controlled within 1/3 to 1/5 of the dimensional error.

After the preparatory heat treatment, the blank is turned or milled on both end faces (aligned according to the line), and then the center holes at both ends are marked, and the center holes at both ends are drilled, and then the outer circle can be roughed.

Machining Technology of Finishing Outer Circle

The process of fine turning is as follows: the outer circle is finely turned on the basis of the top holes at both ends of the gear shaft. In the actual production process, the gear shafts are produced in batches. In order to improve the processing efficiency and processing quality of the gear shafts, CNC turning is usually used, so that the processing quality of all the workpieces can be controlled through the program, and at the same time, it is guaranteed Efficiency of batch processing.

The finished parts can be quenched and tempered according to the working environment and technical requirements of the parts, which can be the basis for the subsequent surface quenching and surface nitriding treatment, and reduce the deformation of the surface treatment. If the design requires no quenching and tempering treatment, it can directly enter the hobbing process.

Machining Technology of Gear Shaft Tooth and Spline

For the transmission system of construction machinery, gears and splines are the key components to transmit power and torque, and require high precision. Gears usually use grade 7-9 precision. For gears with grade 9 precision, both gear hobbing cutters and gear shaping cutters can meet the requirements of gears, but the machining accuracy of gear hobbing cutters is significantly higher than gear shaping, and the same is true for efficiency; Gears that require grade 8 precision can be hobbed or shaved first, and then processed by truss teeth; for grade 7 high-precision gears, different processing techniques should be used according to the size of the batch. If it is a small batch or a single piece For production, it can be processed according to hobbing (grooving), then through high-frequency induction heating and quenching and other surface treatment methods, and finally through the grinding process to achieve the precision requirements; if it is a large-scale processing, first hobbing, and then shaving. , and then high-frequency induction heating and quenching, and finally honing. For gears with quenching requirements, they should be processed at a level higher than the machining accuracy level required by the drawings.

The splines of the gear shaft generally have two types: rectangular splines and involute splines. For splines with high precision requirements, rolling teeth and grinding teeth are used. At present, involute splines are the most used in the field of construction machinery, with a pressure angle of 30°. However, the processing technology of large-scale gear shaft splines is cumbersome and requires a special milling machine for processing; small batch processing can use The indexing plate is processed by a special technician with a milling machine.

Discussion on Tooth Surface Carburizing or Important Surface Quenching Treatment Technology

The surface of the gear shaft and the surface of the important shaft diameter usually require surface treatment, and the surface treatment methods include carburizing treatment and surface quenching. The purpose of surface hardening and carburizing treatment is to make the shaft surface have higher hardness and wear resistance. Strength, toughness and plasticity, usually spline teeth, grooves, etc. do not need surface treatment, and need further processing, so apply paint before carburizing or surface quenching, after surface treatment is completed, tap lightly and then fall off , quenching treatment should pay attention to the influence of factors such as control temperature, cooling speed, cooling medium, etc. After quenching, check whether it is bent or deformed. If the deformation is large, it needs to be destressed and placed to deform again.

Analysis of Center Hole Grinding and Other Important Surface Finishing Processes

After the gear shaft is surface-treated, it is necessary to grind the top holes at both ends, and use the ground surface as a fine reference to grind other important outer surfaces and end faces. Similarly, using the top holes at both ends as the fine reference, finish machining the important surfaces near the groove until the drawing requirements are met.

Analysis of Finishing Process of Tooth Surface

The finishing of the tooth surface also takes the top holes at both ends as the finishing reference, and grinds the tooth surface and other parts until the accuracy requirements are finally met.

In general, the processing route of gear shafts of construction machinery is: blanking, forging, normalizing, rough turning, fine turning, rough hobbing, fine hobbing, milling, spline deburring, surface quenching or carburizing, central hole grinding, important outer surface and end face grinding The grinding products of the important outer surface near the turning groove are inspected and put into storage.

After a summary of practice, the current process route and process requirements of the gear shaft are as shown above, but with the development of modern industry, new processes and new technologies continue to emerge and apply, and the old processes are continuously improved and implemented. Processing technology is also constantly changing.

in conclusion

The processing technology of the gear shaft has a great influence on the quality of the gear shaft. The preparation of each gear shaft technology has a very important relationship with its position in the product, its function and the position of its related parts. Therefore, in order to ensure the processing quality of the gear shaft, The optimal processing technology needs to be developed. Based on the actual production experience, this paper makes a specific analysis of the processing technology of the gear shaft. Through the detailed discussion on the selection of processing materials, surface treatment, heat treatment and cutting processing technology of the gear shaft, it summarizes the production practice to ensure the processing quality and machining of the gear shaft. The optimal processing technology under the condition of efficiency provides important technical support for the processing of gear shafts, and also provides a good reference for the processing of other similar products.