【作者】 尹震飚；

【导师】 刘飞；

【作者基本信息】 重庆大学 ， 机械制造及其自动化， 2011， 博士

【摘要】 型腔工件在现代工业生产中涉及面非常广泛,如涉及到汽车、家电、机床等制造行业广泛应用的模具系统的核心构件,航天航空、海洋工程等领域高端装备的机舱等结构件,以及复杂金属工艺品的凹型曲面等。型腔工件通常形状复杂、品种多样,致使数控加工过程复杂,易于出现加工效率不高,质量难于保证等实际问题。同时,型腔加工还面临着短工期、高质量、低成本的迫切需求。因此,型腔的高效数控加工是一个亟待解决的问题。刀具优选是实现型腔高效数控加工的关键内容之一,对提高型腔加工的效率和质量,并降低成本有重要作用。为此,本文面向型腔的高效数控加工,对刀具优选技术展开研究,主要内容如下:分析型腔数控加工对刀具要求的特点,明确型腔数控加工刀具优选所包含的主要内容,构建一个包含目标层、优化功能层、技术支持层和数据层的刀具优选技术框架,在此基础上,阐述本文刀具优选的技术过程和关键技术。在分析加工目标、工件、机床和工艺等因素对刀具材料决策过程的影响的基础上,提出一种面向复杂切削实况的刀具材料决策方法。该方法设计并构建若干与常用加工目标相应的、并包含待考察刀具材料性能指标及其初步权重的模板供决策选择;建立工件、机床和工艺的特征体系用于提取实际加工情况下工件、机床和工艺的具体特征;利用知识推理等方法导出工件、机床和工艺的特征对刀具材料性能的约束与侧重,并将约束用于筛选出合格的刀具材料,将侧重用于修正用户所选模板中的刀具材料性能指标权重;在此基础上,利用模板中的性能指标与修正后的指标权重建立刀具材料评价模型,实现对合格刀具材料的评价与择优。应用案例说了该方法的可行性和实用性。在优选型腔加工的刀具直径和刀具组合的过程中,判别加工域是否可以被拆分具有重要的基础意义。为此,提出一种用于判别型腔加工域是否可分的概念及方法——型腔铣削单纯区及其判别方法。首先提出铣削单纯区的概念,给出其定义,指出铣削单纯区是一类当且仅当使用一种刀具就可实现最优加工的特殊区域,并且具有不可再分性、完全覆盖性和效益最优性等三大特点。然后给出并论证铣削单纯区的判别条件,从加工成本的角度建立铣削单纯区的判别模型,并在此基础上设计了铣削单纯区的判别算法。算例结果证明了所提出的概念及方法的理论价值和实用价值。提出一种支持型腔粗加工刀具序列高效优化的刀具筛选方法。通过对比刀具组合过程中因不同刀具的优势互补而产生的效益增量与因换刀带来的相关效益损失量,建立一种用于判断刀具序列是否有效的分析模型;在此基础上,从刀具序列的组合形态的角度构造并证明一种可以判别部分冗余刀具的规则,将该规则与基于几何、设备和工艺等约束的刀具筛选方法相串联,可获得良好的刀具筛选效果。算例结果表明所提方法在去除部分冗余刀具上效果明显。提出一种改进的型腔粗加工可行刀具序列构建方法。对现行的基于有向图的可行刀具序列构建方法进行分析,指出对刀具进行近似纯数学上的排列组合使得解空间偏大,进而制约刀具序列优化效率是该方法的主要不足;通过对刀具序列有效性的分析,发现可行刀具序列构建过程中刀具之间存在的互斥特性,并将该特性引入至现行的可行刀具序列构建方法之中,加强对解空间的约束,实现对大部分无效序列的预先排除。算例结果表明,改进后的方法可明显排除大部分的无效刀具序列,对实现刀具序列的高效优化具有良好的支持作用。更多还原

【Abstract】 Pockets are widely applied in modern industry. For instance, pockets are core components of mould systems of manufacturing industries like automobile, appliances, and machine tools. Pockets are also structural member of high-end equipments in fields like aerospace, aviation, and oceaneering. In addition, pockets refer to modeling faces of complex metal artwork. For the complex shape and high manufacturing quality of pockets, most pockets can only be machined on multi-axis NC machine tools with complex machining process, which is prone to practical problems like low machining efficiency, low quality, and high cost. For these reasons, the study on methods and technologies of high-efficiency NC machining of complex pocket is of great importance. Due to the cutting tool selection affects the machining time, quality and cost greatly in pocket NC machining, in this paper, methods and technologies of cutting tool selection for high-efficiency NC machining of complex pocket are studied.The characteristics of pocket and pocket machining are analyzed to conduct the main task of cutting tool selection of pocket NC machining. In order to support high-efficiency NC machining of pocket, a technology architecture of cutting tool selection is established, which consists of four levels: object level, function level, supporting technology level and data level. Based on the technology architecture, the process of cutting tool selection and the critical technologies of this paper are elaborated.Due to the numerous types of the cutter material in modern NC machining, and the complexity and diversity of the machining site condition (including machining target, workpiece, machine tools and machining process), the optimal selection of cutter material becomes difficult. To solve the problem, the effect of the above four machining site conditions on cutter material decision is analyzed, based on which a cutter material decision method oriented to complex machining site condition is proposed. According to common machining target, this method designs and builds several templates for user to choose, which contain cutter material performance index and initial index weight. The characteristics architecture of workpiece、machine tools and machining process is set up to identify and extract the specific characteristics in practical machining. Methods like knowledge reasoning are applied to derive constraints and correction coefficient of cutter material performance from the three aspects of characteristics. The constraints are used to screen out qualified cutter material, and the correction coefficient is used to revise the cutter material performance index weight of the user chosen template. On the bases of the performance index and revised index weight, the cutter material evaluation model is established, and the evaluation and optimal selection of qualified cutter material is realized. The case study indicates the feasibility and practicability of the method.The geometry of pocket is generally complex, and it is usually necessary to optimize tool sequence (TS) while improving the pocket machining efficiency. As the proper division of machining region is a foundation for high-efficiency TS, whether the machining region could be divided becomes a basic problem. In order to solve the problem, a concept of simplex region (SR) is proposed, and the recognition method of SR is put forward. The concept and definition of SR is given, which indicates that SR is a special region that could be machined in high efficiency by just one cutting tool. Then, the recognition condition of SR is analyzed and demonstrated, the recognition model is set up from the perspective of machining cost, and the recognition algorithm of SR is designed. The given case study of SR recognition proves the theoretical and practical value of the presented concept and method.Cutter screening is an important link in the TS optimization of pocket rough machining, and is aimed at screening out feasible cutters. However, most current cutter screening methods are based on constrains extracted from pocket geometry, machining tools, and machining process, and rarely take constrains between cutters into consideration, thus, redundant cutters appear in feasible cutter set. In this paper, a mathematic model by analyzing benefits increment and benefits decrement in cutters combination process is established for analyzing validity of TS. In addition, a redundant cutter judging rule based on the model is constructed and demonstrated. By connecting the existing cutters screening methods and the new rule for judging redundant cutters, a new cutter screening method for high-performance TS optimization is obtained. The realization techniques of the new method, including the machining ability estimate of cutters and validity calculation of TS, are studied. The case study indicates the ability of the method to eliminate part of the redundant cutting tools.Constructing feasible TS is another important link in the TS optimization of pocket rough machining, which takes certain permutation and combination method to obtain a series of optional feasible TS. This paper analyzes the current feasible TS constructing method based on directed graph, and point out its approximately pure mathematical permutation and combination of cutting tools leads to oversize solution space, thereby restricts the optimization performance. In order to improve the current method, based on analyzing the advantages and disadvantages generated in the process of cutting tools combining, an analytical model for judging the validity of TS is established. By importing this model to the current method, large amount of the invalid TS are eliminated from the solution space, thus the optimization performance is accordingly promoted. The implementing technologies (including the TS validity analysis) of the new method are studied. The case study shows the obvious effect of the improved method on eliminating invalid tool sequences.更多还原