1. Gear cutting processing
For the gear cutting processing of Gleason spiral bevel gear, “five knife method” has always occupied a dominant position. The large wheel is processed by double-sided method, and rough cutting and fine cutting are separated; The small wheel is processed by double-sided method during rough cutting and single-sided method during fine cutting, that is, convex fine cutting and concave fine cutting. Different cutter heads are used on different machine tools and different machine tool adjustment parameters are used for tooth cutting respectively. The machining efficiency of “five tool method” is low, and the consistency of gear backlash is difficult to control. In the past, the tool inclination method must be used for the processing of Gleason made hypoid gears. With the popularity of domestic NC gear milling machines, many enterprises use the denaturing method to process hypoid gears on domestic four-axis NC gear milling machines, and the tooth surface contact area can meet the requirements of axle manufacturing enterprises. In recent years, the imported six axis linkage CNC gear milling machine has begun to use the “two tool method” to process Gleason spiral bevel gears. Different from the “five tool method”, it is rough and fine cutting. The same cutter head is used on one machine tool. Both large and small wheels are cut by double-sided method, which is also called full process method. The control of tooth surface contact area of spiral bevel gear machined by “two tool method” is much more complex than that of five tool method, which puts forward higher requirements for tooth surface machining design. At present, only a few enterprises use this method, but the tool consumption is very large. In order to save energy and protect the environment, in recent years, many enterprises have adopted dry rough cutting on the newly purchased NC rough cutting machine, which does not need lubricating oil cooling, avoids the pollution of smoke to the environment, maintains the health rights of operators and improves the health status of factories. For example, Shandong Fengrun, qingtezhongli and Dongying Jubang are in good use.
In recent years, the CNC gear milling machines imported from China are mainly Phoenix II gear milling machine produced by Gleason company of the United States and C series gear milling machine produced by klinberg company of Europe. The recommended processing method is “two tool method”. This efficient machining method has been successfully applied in batch in developed countries. The cutting tool can be ground once and can process more than 500 gears. However, when this method is used in China, there are problems: affected by the high impurity content of domestic gear blank material and the large dispersion of gear blank hardness after isothermal normalizing, the tool grinding cycle is very short. Generally, only about 50 pieces can be processed after grinding of gear tools for drive axle of heavy vehicles. Gleason Phoenix II gear milling machine and klinberg C series gear milling machine have serious “acclimatization” in China, which has seriously affected the healthy development of China’s gear industry. For the cutting tools used in the “two tool method”, the “blade” is used to replace the “cutter teeth”. Special sharpening machine and cutter loading machine must be equipped. Re coating is required after each grinding to ensure the durability of the cutting tools. The same cutter head is used for rough cutting and fine cutting. Although the cutter can cut teeth after wear, the roughness of the tooth surface can not meet the requirements. It is necessary to Regrind, coat, install and adjust the cutter. Due to the low efficiency of tool grinding and loading, two gear milling machines need an expensive tool grinding machine and tool loading machine, and the coating needs 1000 ~ 2000 yuan at a time, resulting in a significant increase in the manufacturing cost of gears. At present, the “two knife method” is only used in a few enterprises. In order to reduce the tool consumption, the author puts forward the “four tool method”, which is a new method for machining spiral bevel gears with high efficiency and low consumption. This method uses domestic CNC gear milling machine tools and domestic tools to complete the rough cutting of large and small wheels, which effectively reduces the grinding times and coating times of the tools. The advantages of separating rough and fine cutting are: rough cutting is carried out on a rough cutting machine with good rigidity, and the use of domestic tools not only reduces the tool consumption, but also improves the machining efficiency; The precision cutting is carried out on the imported NC gear milling machine, which not only improves the manufacturing accuracy of the gear, but also prolongs the service life of the gear milling machine.
2. Isothermal normalizing
Isothermal normalizing can optimize the internal structure of gear blank, effectively control the hardness difference and heat treatment deformation of different parts of gear blank, and provide the best dry cutting conditions, so as to reduce the pitch error and tooth surface error of gear after carburizing and quenching. At present, many gear blank forging enterprises have purchased isothermal normalizing continuous production lines to supply gear manufacturing enterprises with isothermal normalizing gear blanks in batches.
3. Hot finishing of driven gear inner hole
In the past, the internal grinding machine was used to grind the inner hole of the driven gear after carburizing and quenching, and the machining efficiency was low. Aligning with the original inner hole requires high technical level of the operator. At present, many enterprises have changed to vertical lathe to finish the inner hole of the passive gear after heat treatment with cemented carbide tools, and use the tooth mold to align automatically, which not only has high processing efficiency, but also reduces the technical requirements for the operator.
4. Strong shot peening
Strong shot peening can produce compressive stress on the tooth surface and improve the bending fatigue life of the gear by about 15% ~ 30%. At present, some enterprises have purchased strong shot peening equipment, which plays an obvious role in improving fatigue strength.
5. Tooth surface error detection
Now many enterprises have purchased gear measurement centers for the tooth surface error detection of spiral bevel gears. However, most enterprises only use it to detect the tooth pitch error, and less enterprises adjust the machine tool and control the tooth surface deviation according to the tooth surface error topology. Many enterprises reflect that the topology diagram meets the design requirements, but the tooth surface contact area is not good. The reason is that we do not master the fine machining design technology of tooth surface, because the topology is only “responsible” for the machining adjustment parameters. Only the processing adjustment parameters designed by TCA, load meshing simulation or virtual manufacturing technology can ensure a good tooth surface contact area. However, it is very simple for the passive gear to control the tooth surface error through the gear measurement center, which can replace the standard gear to ensure the interchangeability of the active and passive gears.