Machining method and experiment for segmental spiral flute rake faces of hourglass worm gear hob

Abstract

The performance of hourglass worm gear hob is influenced by two features of the rake angle: smaller absolute value and more balanced distribution on the left and right sides of each teeth. To meet the requirements of the rake angle, a method of machining the segmental spiral flute rake faces with a cylindrical milling cutter in different drive ratios is proposed. Firstly, a mathematical model of different drive ratios machining the rake face is established based on the principle of gear meshing. The initial point is determined using the point on the spiral face at the indexing ring position of the cutter tooth machined with a fixed drive ratio. The expression for the drive ratio is then calculated based on the machine movement relationship. Next, the optimum drive ratios were determined by studying the effect of drive ratio on the value of the rake angle and the machining position of the rake face. The design results show a significant improvement compared to the values of the rake angle for the fixed drive ratio. The maximum absolute value drops from 5.3° to 0.57°, and the difference between the rake angles of the two sides on cutter tooth is reduced from 7.47° to 0.15°. This implies that the cutting conditions have been substantially improved. Finally, the machining experiment is conducted. Measurement result shows the minimum difference between the experimental and theoretical values is 0.0167° and the maximum difference is 0.5451°. Verifying the correctness of the theoretical calculation and the feasibility of practical machining.

Keywords

• double enveloping
• hourglass worm gear hob
• rake angle
• spiral flute rake face
• drive ratio