Firstly, the difference Δ n (that is, Δ n = N-N) between the minimum number of effective axial cutter teeth n required by the hob and the number of axial cutter teeth n with complete teeth on the cutting edge of the standard hob is calculated. Generally, the number of large modulus standard hobs n is 3-5. Because the length of complete cutter teeth on both ends of the cutting edge of the standard hob is greater than the metal length of the cutting groove LC, the axial pitch of a reverse movement of the hob does not exceed 1 n. In most cases, a radial feed hobbing can be completed by moving one or two axial pitch at a time.
Next, use the right-hand hob to Hobb theor left-hand in the reverse milling mode, and take the two-stage hobbing as an example to explain:
The standard hob uses the hob “centering” method to find the offset datum point, and makes the cut in end with complete teeth at the starting point. The turning in end of hob blank is as shown in Figure 1. The hob teeth are centered, that is, cut to the end of the length direction of the alveolar metal, and then move Δ n axial pitch to the cutting out end in reverse direction. After the hob is “centering”, the turning out end of hob blank is as shown in Figure 1 2, the radial feed hobbing cycle ends, and the above working process is repeated until it meets the requirements.
For the hobbing machine with automatic tool shifting mechanism, the hob “centering” or isosceles triangle method is used to find the datum point of shifting distance. The complete cutter teeth at the cutting end are at the starting point, and the turning in end of hobbing gear blank is shown in Fig. 1. Then the turning out end of hobbing gear blank is shown in Fig. 2 after the automatic tool shifting Δ n axial pitch As shown in the figure below, every radial feed is one time, tool shifting is one time, and after multiple radial feed, the hobbing of a gear is completed.
Or before hobbing, prepare a corresponding special cutter pad according to the difference Δ n, and the thickness tolerance shall be controlled within 0.002-0.01 mm according to the gear accuracy requirements. If the gear accuracy is higher, take the smaller value, otherwise take the larger value. First, use the hob “centering” or isosceles triangle method to find the offset datum point. The end face of the standard hob and the cutter pad are in series face to face. The cutter pad is close to the cutting end of the hob. The cutting end has complete cutter teeth at the starting point. The turning end of the gear blank is shown in Figure 3 Then the position of the hob and the cutter pad is exchanged, that is, the cutter pad position is replaced by the hob, the hob position is replaced by the cutter pad, and the turning out end of the hobbing gear blank is shown in Fig. 4. The position is exchanged once every radial feed. After multiple radial feeds, the hobbing of a gear is completed.
When using the standard hob with grinding cutting cone or tooth height correction for hobbing, the difference is that when the hob moves axially to the turning out end of the gear blank, a Δ a can be fed radially at the same time In other words, in addition to the axial displacement to the final tooth thickness, the axial displacement and radial feed of the hob can be carried out at the same time during the hobbing process, which significantly improves the efficiency of hobbing and the durability of the hob. Figure 5 illustrates the special cutter pad as an example.