In order to meet the needs of production, the tooth profile of the pre-grinding hob is based on a large number of theoretical analysis, computer simulation hobbing and cutting test. The selection criteria of the tooth profile of the pre-grinding hob are formulated. The head clearance coefficient of the tooth height coefficient hkw carburizing and quenching gear is different from that of the standard gear. It must ensure various special requirements of the grinding process, such as root cutting, so the head clearance coefficient C must be increased. According to these factors, C=0.4 is generally taken, and the tooth height coefficient hkw=1.4 of the tool is taken. In some cases, considering the size structure of the gear and the heat treatment deformation, etc., hkw=1.45.
The residual grinding allowance A of the gear is compiled according to the gear standard. The residual grinding margin A of the gear is: A=(0.42 0.03m)/2(m≤10)A=[0.72 0.012(m-10)]/2(m >10). (1) where: m - the gear modulus. The root cutting amount W of the gear and the height of the tool tip apex Sp gear are selected according to the specific production conditions of our factory and with reference to relevant foreign technical data, because the parameter and the tool tip bulge height Sp Related, so the relationship between Sp and W is analyzed below. The tool tip lob height Sp is: Sp = A W (z ≥ 21). (2)
The tooth thickness on the tool segment line is SwSw=t/2-2A/cosA. (3) where: t—the pitch of the tool 1, t=Pm; A—the pressure angle of the gear, A=20°. In order to meet the geometric requirements of the tooth profile, the small pressure angle B must ensure a certain side blade back angle. After considering the cutting performance and tool durability, the small pressure angle is B=14°. When the knives fillet radius rj is hkw=1.4, in order to ensure the geometric requirements of the cutter teeth, rj needs to be as small as possible, and in order to make the root transition curve smooth, and rj is as large as possible, comprehensively meet the above requirements, take rj =0.3m.
When the number of gear teeth is small (z ≤ 17), in order to avoid the serrated blade marks left by the intermittent cutting on the root transition curve, the radius of the fillet should be larger, then take rj = 0.35 m. When hkw When =1.45, because the top of the knife is sharp, the arc can be used at this time, and the radius of the single arc is used to calculate the model. At this time [(Sw/2 Sp/cosA)/tgA-(hkw-rj)]sinA=rj, solve rj as: rj=[(Sw/2 Sp/cosA)cosA-hkwsinA]/(1-sinA) . (4)
In order to prove the experimental results, some hob parameters were tested, and the hob machining gears made by the calculated hob parameters were used to measure the involute length of the gear after grinding and the tooth thickness on the fixed chordal height. The test results are listed below. There are errors between the calculation and the test results. The main reasons are: 1 manufacturing error of the tool; o various errors in the machining process; measurement error; the difference between the mathematical model and the actual machining process, mainly the mathematical model is An idealized smooth curve, but actually an intermittent, uneven curve.
Conclusion After a large number of tests and production practices, it is confirmed that the pre-grinding hob can be designed according to the data provided to ensure the quality of the machined gear, that is, the effective involute length after grinding and the maximum root cutting amount to meet the design and use requirements. As far as the actual situation of my branch is concerned, this research has satisfactorily solved the problems that have long existed in the design of the hob before grinding.
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