| The large-scale numerical control （NC） gear hobbing machine is mainly used insome extremely important fields such as aviation industry, ship industry, wind powergeneration, heavy-duty vehicles and engineering machinery industry, in which thedemanded gears should be of large size with a low risk and cost and high precision.Accordingly, a large-scale NC gear hobbing machines will be needed high safetyperformance and processing quality, especially the machining precision.Additionally, some factors such as its large structural size, varieties, largedimension between hob and workpiece spindle of gear hobbing machine, thecomplicated system configuration, also the complicated hobbing system and cuttingforce, have the significant influence upon gear of machining precision. Furthermore, theresearch of machining error and capability on the large-scale NC gear hobbing machinehas become increasingly significant to improve machining precision and decreasemachining error of gear.In order to realize the large-scale gears of machining accurately and efficiently, thisthesis has finished some research on the machining error mechanism and correspondingcompensation technique of large-scale gear hobbing machine from the followingaspects:①Research on the effect of spindle deformation which is caused by hobbing forceis an important way to diminish or control the machining tolerance of the large-scalegear. Based on the hobbing gear features, process parameters, the methods of changingcoordinate and theory of beam deflection, several formulae of hobbing and spindledeformation and centre distance variation are established through theoretical analysis.For certain typical gear hobbing machine with particular structure and machiningparameter, its hobbing force and spindle deformation and centre distance variationunder practical hobbing parameter are calculated by adopting the mentioned formulae.Further, the relationship curve of cutting force, spindle rotational speed, hobbing depthand deformation of spindle were obtained, and revealed the law of hobbing and cuttingdeformation. This research provides important basis for optimization design of machinetool structure, processing parameter and machining error prediction and compensationfor gear hobbing machine.②To master the influence of spindle and spindle the centre distance radial deformation caused by dynamical properties of hobbing gear on machining precision forgear hobbing machines. Based on machine tool structure, processing parameter,dynamical properties of the machining gear, dynamical principle and Euler-BernouHibeam vibration theory, the related dynamical mathematical models were established inthis paper. According to the theoretical model, processs parameters and vibrationexperimental datum, this paper focused on the research and analysis of mutual relationbetween the response parameters of vibration displacement and hobbing processparameters for hob and workpiece spindle. By all the above analysis and research, thispaper reveal the radial deformation change law of the centre distance between hob andworkpiece spindle caused by the vibration of hobbing gear, and the influence on whichthe vibration displacement deformation exerts gears’ machining precision.③Research on the deviation of the centre distance between hob and workpiecespindle and this deviation is caused by thermal deformation. Based on the structuralfeatures of large-scale NC gear hobbing machine, the theory of thermal expansiondeformation of metallic materials, the extensional beam theory, non-uniformtemperature distribution of the Euler-Bernoulli beam and Kirchhoff theory ofplane-section assumption, a novel model was proposed in this paper to calculate thebending thermal deformation of lathe bed and upright column of gear hobbing machinetheoretically, then, the research on the axial deformation and bending deformation of theupright column were also carried out by utilizing the deformation theory of thedeformation element and equilibrium element method. According to the theoreticalresearch, the testing system of temperature and thermal deformation for gear hobbingmachines were proposed, further, a experiment platform was established to test andanalyze the temperature and corresponding thermal deformation displacement data,eventually to reveal the theory and practical rule of thermal deformation, and to plot thedeviation curves of the centre distance between hob and workpiece spindle and geartooth trace deviation.④Based on the theoretical research of the vibration mode, harmonic response andhobbing dynamical properties, the finite element of entity simulation model wereestablished about the restriction mode and harmonic response for gear hobbing machine,and proposed the restriction boundary conditions for dynamical simulation. The finitemodel was simulated by adopting the processing and material parameter. According tothe simulation cloud chart and data, the gear machining error and the variation of thecentre distance between hob and workpiece spindle were analyzed. These results of the simulation research provide theoretical basis for the structural optimization design andassembly position adjustment for gear hobbing machine.⑤Based on the research of the thermal deformation theory and experiment, thetesting temperature variables were selected by using the method of fuzzy clustering, thethermal error compensation model of the center distance between hob and workpiecespindle of the Large-scale NC gear hobbing machine was set up by adapting themethods of multi-regressions and the least square regression. Meanwhile, theexperiment of the thermal error compensation for the certain typical Large-scale NCgear hobbing machine was carried out in the numerical control automatic programmingsystem. The result shows that the thermal deformation value of the centre distance ofhob and workpiece spindle reduces substantially and various indexes and precise ofmachining gear improve remarkably. The thermal error compensation model is higherprecision, the method not only upgraded the gear machining accuracy and the efficiencybut also effectively control and forecast the thermal deformation of the large-scale NCgear hobbing machine. Therefore, this compensation system and experiment have greatpractical value.These novel calculation models were established about the hobbing deformation,dynamical vibration displacement and thermal deformation of large-scale NC gearhobbing machine abased on the analysis and research of theory, experiment and finiteelement method in this paper. Meanwhile, the thermal error compensation model of thecentre distance between hob and workpiece spindle of gear hobbing machine was set upby combining processing parameters and experimental datum, numerical machining andcomputer software’s technology, which successfully carried out the experiment ofthermal error compensation. the result show that the machining precision of gears aregreatly improved, Above all these researches lay the theoretical basis and provide keytechnological support for promoting the high speed and efficiency of machiningcapability, and for overall realizing the large-scale gear of high precision of machiningtechnology of large-scale NC gear hobbing machine. |
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