【作者】 李华；

【导师】 闫蓉； 彭芳瑜；

【作者基本信息】 华中科技大学 ， 机械制造及其自动化， 2018， 硕士

【摘要】 飞机起落架整体尺寸大,型腔结构多,材料去除率大,加工表面质量要求高,采用新的加工工艺可有效改善表面加工质量。加工型腔可采取摆线轨迹切削,为避免加工干涉,往往采用细且长的刀具,因此加工系统动态特性较差,不合理的较大的摆线步长常常会导致颤振发生,保守的较小的摆线步长会限制型腔加工效率,需要建立相应的稳定性模型进行预测分析,为起落架型腔加工参数优选提供理论基础。起落架为航空难加工材料,较差的切削加工特性会严重影响表面质量,从而降低整个起落架的服役性能,研究微量润滑加工参数对型腔加工的表面质量影响,可以为优化起落架型腔加工参数、提高表面质量提供研究基础。本文针对上述问题建立了摆线铣削稳定性预测模型,提出了同时考虑主轴转速与摆线步长的方法去预测摆线铣削稳定性边界。根据摆线轨迹的几何模型特点,分析了刀具-工件的啮合角随刀具位置角的不同而变化。基于摆线刀路轨迹的不同刀位点处稳定性边界的最低包络线,获取摆线铣削过程中稳定性预测的下限值,以确保加工稳定性。为了提高型腔切削效率,在加工中心GMC 1600H/2上进行摆线刀路轨迹稳定性模型验证实验,验证了摆线刀路轨迹稳定性预测模型的准确性。在考虑稳定性边界的基础上提出摆线步长优化策略,进行加工仿真分析,仿真结果表明采用优化的摆线步长可有效提高型腔摆线轨迹稳定加工的效率。考虑到起落架的服役性能,采用微量润滑加工工艺,开展对比分析实验,分析了加工润滑条件(干式切削、微量润滑)、切削参数对于型腔加工的表面质量(表面粗糙度、残余应力与显微硬度)的影响,结果表明采用微量润滑条件下的优化工艺参数可提升工件已加工表面质量。基于型腔摆线轨迹加工理论与微量润滑加工工艺,将两者的理论与实验研究结果应用在起落架的型腔实际加工中,实验结果表明在实际加工工况中,采用摆线轨迹加工理论与微量润滑工艺技术可提高起落架型腔的加工效率以及表面质量。更多还原

【Abstract】 The aircraft landing gear is known for large zize,multi-cavity structure,large material removal rate,and its high surface quality requirement.Adopting new processing techniques has become effective methods for improving surface quality.Trochoidal trajectory can be used to machine cavities.To avoid interference during trochoidal milling,it is necessary to use thin and long tools which cause poor processing system dynamics.The irrationally large trochoidal step usually leads to chatter,while the conservative trochoidal step constrains the machining efficiency.It is necessary to establish a corresponding stability model for predictive analysis,which provides a theoretical basis for optimizing the processing parameters of the landing gear cavity.The landing gear is one of the aerospace hard-to-machine material.The poor cutting performance will seriously affect the surface quality,while reducing the service performance of the entire landing gear.The mininum quantity lubrication(MQL)is used to study and analyze the effects of lubrication conditions and cutting parameters on the surface quality of the cavity machining.It provides the basis for optimizing the processing parameters and improving the surface quality of the landing gear cavity.In this paper,a stability prediction model of trochoidal milling is established to solve the above problems.An approach considering trochoidal steps and spindle speeds is presented to predict stability boundary of trochoidal milling.According to the characteristics of trochoidal milling geometric model,the varying cutter-workpiece engagements are analysed.Based on the lowest envelope of the stability boundary at different tool positions of trochoidal tool path,the limit value of the stability prediction during the trochoidal milling process can be obtained to ensure processing stability.In order to improve processing efficiency,verification experiments of trochoidal tool path stability model are performed on the machining center GMC 1600H/2,and the accuracy of the trochoidal milling stability prediction model is verified.Based on the stability boundary,the optimization strategy of trochoidal step is proposed.The simulation analysis is performed,and simulation results show that the use of an optimized trochoidal step can effectively improve the cavity stable machining efficiency of the trochoidal milling.Considering the service performance of the landing gear,MQL is used to conduct comparative analysis experiments.The effects of machining lubrication conditions(dry cutting,MQL)and cutting parameters on the surface quality(surface roughness,surface residual stress,microhardness)of the cavity processing are studied and analyzed,so as to optimize the machining parameters and improve the quality of the machined surface of the workpiece.Based on the trochoidal milling theory of the cavity and the MQL process,the theoretical and experimental results of both are applied to the actual processing of the aircraft landing gear cavity.In this way,the machining stability and surface quality of the landing gear cavity can be improved in the actual processing conditions.更多还原