Mechanical Knowledge

The process of gear manufacturing

In modern machinery, gear drive is the most widely used mechanical transmission method. The function is to transmit motion and power between two shafts. Especially in the automobile production industry, gears are already in a large-scale professional production. In the long-term production practice, a complete set of production processes has been formed.

Typical gear manufacturing

Machining gears with cutting methods is a typical gear machining process. The production process is generally divided into: gear blank manufacturing→ tooth surface processing → heat treatment process → tooth surface finishing. The specific process is: forging or bar forming gear blank → rough machining, cutting off more margin → semi-finishing, turning, hobbing, gear shaping, etc. → heat treatment, tempering, carburizing quenching, high frequency quenching → finishing , Fine-tuning benchmarks, finishing tooth profile, etc.

The gears processed by this process can achieve high precision, generally reaching level 6, and after honing, it can reach level 5 or higher, and can be used in high-speed, low-noise working environments. In the long-term practice, it is found that the failure rate of the tooth body of this type of gear is higher than the failure rate of the tooth surface, which is mainly bending fatigue breakage and overload breakage.

Precision forging process for gear manufacturing

With the development of CNC precision machining technology, precision forging technology and precision mold manufacturing technology have been widely used in mass production of gear parts. The precision forging process is divided into hot precision forging and cold heading forging. After hot forging and trimming, the gears are finished with the residual heat of the forging. The accuracy of such hot forged gears is about 8-9.

Cold heading forging, also known as block forging, is an advanced precision forming technology without flash. When the mold tooth profile accuracy reaches level 6, under mass production conditions, the gear accuracy can reach level 8-9. Such gears can meet the requirements of trucks and light vehicles, and can be used in low-speed, heavy-duty, high-noise working environments. In the long-term use process, it is found that the failure mode of this type of gear, the ratio of tooth surface failure is higher than that of tooth body failure, mainly due to wear and pitting.

Performance analysis of gear manufacturing by two processes

Gears produced by a typical process

Figure 1 Gears produced by a typical process

The gears produced by a typical gear machining process are shown in Figure 1. During the tooth shape processing (hobbing, gear shaping, honing, grinding, etc.), the fiber structure of the part is cut, although relatively high tooth shape accuracy and tooth phase accuracy, surface finish, etc. can be obtained. The stress performance and anti-breaking performance are affected. Under overload conditions, there is a hidden danger of tooth root breaking.

Under the conditions of the precision forging process, the gears produced are shown in Figure 2. During the precision forging process, the metal undergoes plastic deformation under the action of high stress, the gear structure is dense, the metal fiber is continuous, the fatigue strength and wear resistance are much higher than the cutting gear, which is suitable for frequent impact and heavy load Working under normal conditions, but due to its low accuracy, rough surface, high working noise and low working speed, it is easy to produce tooth fatigue damage.

Precision forged gears

Figure 2 Precision forged gears

Technological innovation of gear manufacturing

With the popularization of CNC machining technology, the mature application of CNC gear hobbing machine and secondary automatic tool setting technology, we can effectively combine the two gear machining processes of CNC machining and precision forging, which can get good metal fiber structure and improve In case of force, relatively high gear accuracy can be obtained, reducing the amount of metal cutting and improving production efficiency.

In the actual production process, the gear blanks are produced by the precision forging process, and then the CNC gear hobbing machine is added with a secondary tool setting device for precision gear hobbing. The gears produced in this way have improved various accuracy and performance indicators, and their economic value has also been greatly improved. Compared with the typical gear machining process, because the cutting amount is reduced, the machining efficiency is improved. For example, to produce a batch of gears for vehicles with a module of 3mm, 24 teeth, and 6 to 7 grade accuracy. For the first time, the precision forged gear blanks are produced, and then the precision forged blanks are processed on the high-speed CNC spline milling machine YKH750 (Figure 3) with a secondary tooling process (only about 6s), and the 0.2mm machining is performed on the CNC hobbing machine. The remaining amount is only about 1min. The new process not only improves the production efficiency, but more importantly, it improves the performance of the gears. After a series of tests, the mechanical performance of the gears produced by the new process is significantly higher than the gears produced by traditional methods.

CNC spline milling machine

Figure 3 YKH750 high-speed CNC spline milling machine

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