I. Introduction
Hobbing is one of the common methods of machining external gears. Compared with other processing methods such as gear shaping and milling, it has the advantages of high machining efficiency, good tooth profile accuracy, and the same tooth profile error when machining the same modulus but different gears with the same hobbing cutter. , reducing the inventory demand of the tool, so it is the most widely used in actual production.
In addition to the traditional high-speed steel integral hob, blade hobs have been increasingly used in large-module and large-diameter gear processing in recent years. Compared to high-speed steel hobs, they have high cutting speeds, long blade life, several cutting edges per blade, and no need for re-grinding.
However, due to the limitations of the blade hob, its main application range is limited to roughing and semi-finishing of gears. There is no successful case for gear fine rolling in China.
Kenner is committed to the application of high-efficiency blade hobs for the machining of large-modulus gears. It has done a lot of trials and improvements on the basis of the original design, and has made great progress in tool accuracy and blade life. The blade hob can also be successfully applied to the finishing of large modulus gears. The following is a brief introduction to these improvements in conjunction with actual cases.
Second, the workpiece introduction and difficulty analysis
The machined workpiece is an outer ring gear of modulus 36 with a number of teeth of 296, a diameter of 10.8 m and a height of 0.96 m. The accuracy grade AGMA10 is equivalent to the 8-level accuracy in ISO, and the tooth surface finish requires Ra3.2. The material is high alloy steel, after heat treatment, the hardness reaches about HB300.
The previous process is done by milling the teeth, leaving a 1.3mm unilateral margin to the final design profile.
The finishing process in the original process is completed by inserting teeth, and the cycle is more than 10 days, which can not meet the production needs of customers.
There are two difficulties in using a blade hob for the finishing of this workpiece:
â— Tool accuracy: Compared with the accuracy of the 8th gear, the accuracy of the hob is required to reach AA level, and the accuracy of the tooth profile is allowed to be 21 microns. The blade hob is difficult to achieve.
â— Tool life: Due to the special nature of the hobbing process, the blade cannot be changed during processing. The life expectancy of the blade is 284.16 meters, and there is no obvious wear and tear to avoid affecting the tooth surface finish and not reaching Ra3.2. Customers have tried to use high-speed steel and welded carbide hobs, but the tooth surface finish exceeds the standard due to tool life problems.
Figure 1: External gear processing site
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