With the increase of wear degree, the cutting performance of gear hob will gradually decline, which will reduce the finish of machined surface, increase cutting force and produce vibration or abnormal noise in the cutting process. At this time, if the gear hob continues to be used, it will not only further deteriorate the machining quality, but also rapidly wear the tool. The gear hob with excessive wear has relatively large regrinding amount and long grinding time, which is easy to heat the cutter teeth and anneal, and reduces the regrinding times and service life of the gear hob. Therefore, a reasonable standard for gear hob grinding should be formulated according to the specific situation to ensure the rational use of tools.
There are different standard ways to blunt gear hobs, such as the number of machined parts, cutting length or tooth surface finish of machined parts. The most commonly used in the production site is the maximum wear width of the flank of the cutter tooth, which is the most commonly used mark in the blunt standard of gear hob.
In the process of formulating the blunt standard of gear hob, the accuracy requirements of the processed gear, the loading and unloading times of gear hob and the difficulty of regrinding should be considered. If the wear amount is too large, it will reduce the accuracy of the machined gear parts, increase the difficulty in regrinding and affect the service life of the gear hob; However, if the wear amount is too small, the loading and unloading times of gear hob will be increased and the auxiliary time will be increased. Generally, the maximum wear of gear hob shall be 0.2 ~ 0.4mm during finish machining and less than 0.5 ~ 1.0mm during rough machining. The maximum wear of gear hob shall not exceed 1.0mm.
Normal grinding hob will maintain the accuracy and consistency of the tool and prolong the service life of the gear hob. Therefore, it is helpful to limit the maximum wear range.
Modulus | Maximum grinding amount of hob (mm) |
0.5-1.25 | 0.15-0.25 |
1.25-2.5 | 0.25-0.38 |
2.5-6.38 | 0.38-0.5 |
The table above shows the maximum grinding amount after the tooth surface is blunt. For involute gear hobs, it can usually be measured at the sharp corner near the top of the tooth. The values in the table only represent the grinding amount used by high-speed steel hobs.