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题名:
薄壁件高性能铣削加工技术与方法研究
其他题名: Research on the Technologies and Methods for High Performance Milling of Thin-walled Parts
作者: 曲胜
导师: 王天然
关键词: 薄壁件 ; 高性能铣削 ; 切削力 ; 稳定性 ; 参数优化
页码: 108页
学位专业: 机械电子工程
学位类别: 博士
答辩日期: 2016-12-06
授予单位: 中国科学院沈阳自动化研究所
授予地点: 沈阳
作者部门: 装备制造技术研究室
摘要: 薄壁件具有重量轻、结构强度高等特点,航空领域中的许多零件采用薄壁结构从而减少自身重量。铣削加工是决定薄壁件加工质量和加工效率的关键技术。但是由于其结构刚度低、加工工艺性差,薄壁件铣削加工过程中容易发生颤振和加工变形等现象,造成加工表面质量下降以及工件的让刀误差,严重制约着薄壁件的高效加工。为避免发生颤振等不良状况,在实际生产中不得不采用保守的加工参数,造成生产时间延长,制造成本增加。高性能铣削的基本要求就是在保证工件加工质量的同时,最大限度地提高加工效率。为此,本文以薄壁件的高性能铣削加工为研究对象,对其中的切削力预测、薄壁件铣削加工稳定性和铣削参数优化等关键技术进行了研究。1.根据铣刀和工件的相对运动,提出铣刀沿直线和圆弧铣削的切削力预测方法。对于直线铣削,针对传统的切削厚度模型存在逼近误差的问题,根据铣刀轨迹及铣削参数,推导出静态切削厚度模型,其精度高于传统的切削厚度模型。同时,考虑铣削系统动态特性引起的动态切削厚度,将其以反馈的形式添加到静态切削厚度上得到总切削厚度。结合该切削厚度模型,预测直线铣削过程中的切削力。对于圆角铣削,构建圆角铣削的几何模型,以此模型为基础确定圆角铣削时变的切入角和切出角。分析铣刀轨迹曲率效应对瞬时切削厚度的影响,给出瞬时切削厚度的表达式,并将其运用到切削力模型中预测出切削力值。试验结果表明,提出的切削力预测方法能够很好地预测直线铣削和圆角铣削过程中切削力的幅值及其变化趋势,验证了提出的切削力预测方法的有效性。2.对空转和铣削过程中的振动进行检测并对比分析,设计单因素试验研究主轴转速、轴向切深和进给速度等加工参数对加工振动的影响规律,探讨了引起切削振动的原因,并分析了铣削振动随着薄壁件的加工位置高度改变的变化趋势。对薄壁件加工振动的研究,为采取有效措施减小加工振动并保证加工质量奠定了基础。3.预测薄壁件铣削加工稳定性,研究模态参数、铣刀齿数等参数对铣削稳定性的影响规律。建立薄壁件铣削加工的动力学模型,以薄壁件铣削位置动态位移的统计方差作为颤振判断标准,确定不同转速条件下的临界轴向切深。考虑到加工位置会对薄壁件的动态特性造成影响,绘制薄壁件铣削加工的主轴转速、加工位置和轴向切深的三维稳定性叶瓣图。基于稳定性叶瓣图,通过仿真系统分析铣削系统工艺参数对稳定域的影响,为选择适当的铣削条件加工薄壁件提供理论依据。4.为了保证薄壁件加工质量并提高加工效率,对薄壁件铣削参数进行优化。以最小切削力、最小表面粗糙度值和最大加工效率为目标函数,构建薄壁件铣削参数的多目标优化模型,利用多目标优化算法求解优化的薄壁件铣削参数组合。通过试验建立了目标函数的数学模型,并验证了模型的精度。由于目标的冲突性,改善一个目标的同时通常会削弱其他目标。因此,用非支配排序遗传算法NSGA-II作为多目标优化的求解方法,找到Pareto最优解集。根据薄壁件的加工要求,从最优解集中选出符合要求的铣削参数组合,并结合三维稳定性叶瓣图判断优化的参数组合是否能保证稳定铣削。试验结果表明优化后的加工参数组合能保证薄壁件的加工质量并提高加工效率,满足高性能铣削的基本要求。
英文摘要: The thin-walled parts have their advantages, such as less weight, more structure strength. So, large numbers of components used in aerospace field are designed as thin-walled structures. Milling is a key technology that determines the machining quality and efficiency of the thin-walled parts. Due to their low structure rigidity and bad manufacturability, chatter and deformation are liable to occur in milling thin-walled parts, which will reduce surface quality and cause dimension error. And this situation severely restricts high performance milling of thin-walled parts. In order to avoid chatter, conservative milling parameters are usually adopted in actual milling. Consequently, the productivity is depressed and production costs increase. The basic requirements of high performance milling are to ensure machining quality and improve machining efficiency. Therefore, high performance milling of thin-walled parts is taken as the research objective, cutting force prediction, milling stability analysis, and machining parameters optimization are studied. 1. According to cutter-workpiece relative motion, a method to predicting cutting force is proposed for linear milling and circular milling. For linear milling, traditional chip thickness model is not quite accurate for its approximation error. Based on tool path and milling parameters, static chip thickness model is derived, and the model is more accurate than traditional chip thickness model. Meanwhile, cutting process dynamics is taken into account. As feedback, the dynamic chip thickness caused by the cutter-workpiece system subjected to the cutting force is superposed on static chip thickness to acquire total chip thickness. With consideration of the developed total chip thickness model, the cutting force in linear milling is predicted. For circular milling, the geometrical model for circular milling is established to determine the time varying entry and exit angles. The curvature effects of tool path on instantaneous chip thickness are analyzed. Then, its expression is developed and applied to calculate cutting force based on cutting force model. The results of simulation and milling experiment show that the predicted cutting forces are in good agreement with the measurements both in magnitude and in variation trend. Thus, the validity of the proposed approach is confirmed. 2.Milling experiments, including the idling experiments, are carried out to investigate the vibration. The influences of machining parameters (e.g., spindle speed, axial depth of cut, feed rate, etc.) on vibration are discussed by means of single factor experiments. Then, the internal reason of vibration is analyzed. In addition, the variation trend of vibration in milling thin-walled parts under different heights is presented. Generally, the research on vibration lays a foundation for guaranteeing machining quality of the thin-walled structures as well as taking effective measures to reduce vibration. 3.An approach to predict the three-dimensional stability in milling thin-walled parts is put forward, and influences of processing parameters on the stability limits are also researched respectively. Dynamic model of the milling system is built. Based on this model, statistical variances of the dynamic displacements are employed as a chatter detection criterion, the relationship between ultimate axial depth of cut and spindle speed under the condition of stable milling is determined. The dynamic behaviour of the wall depends on the position of the tool, and the variation in the dynamics of the wall due to material removal can not be neglected. Thus, the tool position is introduced in the stability and the three-dimensional stability lobe diagram of the spindle speed, tool position, and axial depth of cut is developed. Based on this stability theory, the influences of processing parameters on the machining stability are analyzed systematically by simulation, which provides theoretical basis for choosing an appropriate machining condition in milling of thin-walled parts. 4.To ensure the machining quality and improve milling efficiency, an optimization procedure to determine the optimum machining parameters in milling thin-walled parts is presented. A multi-objective optimization model of milling parameters is proposed, in which the minimal cutting force, the minimal surface roughness, and the maximal material removal rate are taken as optimization objectives. By dint of multi-objective evolutionary algorithm, the optimum machining parameters are determined. The regression models for objectives are deduced from experiments results, and their accuracy is verified. As the effects of milling parameters on optimization objectives are conflicting in nature, many efforts are made to find Pareto optimal solutions by using non-dominated sorting genetic algorithm (NSGA-II). The optimized combinations of machining parameters are selected from the Pareto optimal solutions and these solutions are verified by the three-dimensional stability lobe diagram to ensure stable milling. Milling experiments results show that the optimized machining parameters help to guarantee the high quality of the machined thin-walled parts as well as improve milling efficiency. This meets the basic requirements of high performance milling.
语种: 中文
产权排序: 1
内容类型: 学位论文
URI标识: http://ir.sia.cn/handle/173321/19455
Appears in Collections:装备制造技术研究室_学位论文

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Recommended Citation:
曲胜. 薄壁件高性能铣削加工技术与方法研究[D]. 沈阳. 中国科学院沈阳自动化研究所. 2016.
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