Research On Gear Parametric Modeling Based On Hobbing Machining Errors

Precision gears are key core components of aerospace transmission system, precision machine tool spindle box and automotive transmission, required to have high accuracy to maintain, long service life and high reliability. At present, machining accuracy, quality and life of gear are difficult to meet the performance requirements of high-grade gear in China, high-grade gear used in lots of high-end equipment must rely on the import, moreover, gear machining technology abroad is restrictive to China. In view of this situation, researching gear machining error factors, and building errors compensation, finally to realize the manufacture of high precision gear seems to be imminent.Firstly, this paper introduces the classification of gear machining errors, according to the gear meshing theory, revealing the reason of generating gear machining errors: machining errors damage the certain generating movement between the tool and gear, lead to the location change of transient mesh point and mesh node. Focus on eccentricity errors, error motions of axis of rotation, machine transmission chain errors and tool errors analysis and calculation in the hobbing process, obtaining the mapping rule between respective error factors to gear precision, which provides a theoretical basis to reduce machining errors and improve gear precision.Then analyze the influence of hob installation errors on gear accuracy, from gear hobbing principle, using coordinate transformation method to obtain the gear tooth profile equation, and building the gear modeling by UG. Finally, develop the UG interface under the VS2010 development platform and realize the gear parametric modeling considering hob installation errors. Considering various errors to set up gear parametric model is a trend of accurately modeling in the future, which can make an accurate comparison of the change of gear model by adding machining errors.Conduct the static contact analysis of four different error gear mesh models, to explore the influence of two factors of hob installation errors on gear equivalent stress and contact stress. By comparison, we find that the equivalent stress of gears with errors varies widely and the maximum contact stress doesn’t change significantly. However, the hob mounting angle error and radial error exist, resulting in gears generating machining errors, tooth changing, and gear contact state deteriorating, so the contact fatigue failure is more likely to occur in the gear transmission. In addition, tooth roots are undercut and root curves are asymmetry, which cause the gear bending fatigue strength greatly reducing.Conduct the transient contact analysis of four different error gears with full method, to simulate the actual situation of gear meshing. Compare with error gears transient and static contact analysis, and four kinds of gears transient contact analysis. Because consider the role of inertia and damping in the transient contact analysis, the maximum contact stress compared to the static maximum contact stress increases by 6.9% on average. When there is a single error factor, equivalent to make a modification design to gears, the contact stress and maximum impact stress reduce, but it is very different with the correct modification way, it destroys the normal gear mesh state and parts of tooth root, which Leads to a sharp decline of gear bending fatigue strength. For the practical hobbing process, two error factors existing, the static and transient maximum contact stress, the single and double tooth average contact stress and maximum impact stress are all increasing.