Process planning for sheet metal parts based on information management

Design and manufacturing processes and their mutual interaction are reflected by the Manufacturing Engineering Reference Model. Information management, as the kernel of this reference model, encompasses structures that reflect the information. The three information structures that are discerned refer to products, resources and orders respectively. Originating from the demand for Concurrent Engineering, augmented effort is invested in the integration of the different processes applied in the manufacturing cycle of products. This paper discusses the integration of design and process planning-which is one of the main topics in Concurrent Engineering-along with the demand for Design for Manufacturing. Emphasis is on the application of production method knowledge and design support, especially for sheet metal parts.     

板材数字化成形加工路径规划研究

在板材数字化成形过程中零件的直壁部分常因为金属变形量过大而极易发生破裂,故在加工前需要进行适当的路径规划以控制成形中直壁部分金属过度变形,使板材整体壁厚变化缓慢而均匀,优化其成形过程,最终完成薄板材的直壁部分成形.研究了具体的路径规划方法及其加工轨迹自动生成,主要从工艺角度对直壁部分成形作了有益的探索.     

A WWW-based integrated product development platform for sheet metal parts intelligent concurrent design and manufacturing

This paper presents a WWW (World Wide Web) based integrated product development platform for intelligent concurrent design and manufacturing of sheet metal parts. In order to achieve this platform, several major modules are discussed. These modules mainly include the structure of the WWW-based integrated product development platform, an information integration framework, a RTCAPP (real time computer aided process planning) module, a customer interface module, and a design/manufacturing knowledge-based module for supporting product design and manufacturing. This paper gives the structure of the information integration framework for concurrent design and manufacturing of sheet metal parts. An information integration framework, called 'step structure information framework' is proposed. The principles, called 'zero thickness and zero bend radius' are put forward, which can be used to abstract the geometric entities of sheet metal parts in order to facilitate product design and modelling. Finally, case studies are given.     

金属粉末激光快速成形的工艺及材料成形性

对比了3类金属粉末激光快速成形工艺:选区激光烧结;选区激光重熔,或称选区激光熔覆;以及直接激光沉积,或称激光净成形.提出了其分类依据是金属粉末与激光的作用机制,以及由此导致的金属粉末激光成形机理.综述了上述3类激光快速成形工艺的成形原理、成形材料及工艺优劣,分析了"球化"效应、翘曲变形、以及裂纹等对金属粉末激光成形性的影响规律及相应解决措施.     

An expert system for process planning of sheet metal parts produced on compound die for use in stamping industries

Process planning of sheet metal part is an important activity in the design of compound die. Traditional methods of carrying out this task are manual, tedious, time-consuming, error-prone and experience-based. This paper describes the research work involved in the development of an expert system for process planning of sheet metal parts produced on compound die. The proposed system is organized in six modules. For development of system modules, domain knowledge acquired from various sources of knowledge acquisition is refined and then framed in form of ‘IF-Then’ variety of production rules. System modules are coded in AutoLISP language and user interface is created using visual basic (VB). The system is capable to automate various activities of process planning including blank modeling, blank nesting, determining punch force required, selection of clearance between punch and die, identifying sheet metal operations, and determining proper sequence of operations for manufacturing the part. The proposed system can be implemented on a PC having VB and AutoCAD software, therefore its low cost of implementation makes it affordable even for small scale sheet metal industries.     

多参考点板金零件展开方法研究

针对射线法在展开具有弯曲特征的板金零件时常出现的展开方位错误以及展开区域重叠等问题,在充分考虑了具有弯曲特征的板金零件材料弯曲变形特点的基础上,提出了以多参考点分区展开的思路和方法,建立了能考虑板金零件弯边外法向方向的射线分区展开算法,以此体现材料的弯曲变形特征.通过实例测试,所提出的展开算法高效、实用,并有效解决了展开方位错误和展开区域重叠问题,所得到的零件毛坯形状合理正确,为一步法快速分析优化提供了良好的初值.     

Automatic production planning of press brakes for sheet metal bending

This paper discusses the planning module of system that has been developed in a research project investigating the possibilities for automatic planning of press brakes. Only limited attention has been given to production-planning problems for bending processes in the sheet-metal industry. A well-considered production-planning module provides an important opportunity for cost saving and flow-time reduction. The module will support and may replace an experienced planner. Under certain assumptions, the planning problem can be modelled both ways as a Travelling Purchaser Problem (TPP) and as a Generalized Travelling Salesperson Problem (GTSP). A hierarchical decomposition approach is presented to solve the TPP, while the GTSP is solved using guided local search (GLS). These methods are compared based on a set of problems from a real production environment and perform well.     

薄板件多工位装配尺寸误差建模与仿真

为保证薄板件装配尺寸精度,分析了两种主要误差源夹具尺寸误差和零件尺寸误差,尤其是定位销误差与零件孔间隙对装配尺寸误差的影响.采用状态空间法建立了薄板件多工位装配尺寸误差传递模型,并以某汽车地板薄板样件为例,运用所建立的尺寸误差模型对薄板样件进行仿真计算,仿真结果与实际测量结果进行对比,验证了模型的正确性和实用性.该模型可应用于多工位装配尺寸误差源诊断、装配过程夹具优化设计和装配过程稳定性分析等.     

Automatic determination of bending sequences for sheet metal parts with parallel bends

A method for solving the problem of bend sequencing in sheet metal manufacturing is presented. The algorithm developed divides the part into basic shapes (channels and spirals) and determines the partial sequences associated with them. The complete bending sequences associated with the complete part were obtained from the combination of these partial sequences. To make this combination possible, several strategies were defined to reduce the number of solutions and, therefore, the searching time. All sequences (partial and complete) were checked considering possible part-tool collisions and tolerance constraints. The last stage was to order the sequences by taking into account the total process time. To attain the required process time accuracy, a robot was used for the handling operations. Finally, the sequence associated with the lower process time was selected as the optimal solution.     

柔性薄板件装配误差分析

为简化柔性薄板件装配分析过程和提高计算效率,在自由回弹的基础上,分析在"N-2-1"定位方式下,柔性薄板件夹具偏差经定位夹紧、自由回弹和焊接后对最终装配偏差的影响,建立柔性薄板件装配偏差模型.同时,分析装配过程中外力力矩作用下的偏转所引起的法向变形.最后,用MATLAB结合有限元软件ANSYS进行仿真,与CATIA TAA按传统装配过程分析的结果进行比对,验证装配偏差模型的有效性.     

正交异性板料拉深件快速展开与成形模拟

针对板件初始毛坯形状计算以及正交异性板的快速有限元分析问题,依据拉深件的UG模型,导出了零件的三角网格数据,并采用几何映射方法得到了用于快速有限元分析的拉深件初始展开毛坯.在此基础上,基于理想变形假设以及Hill’48正交异性屈服准则,给出了用于拉深件成形过程快速分析的一步法数学公式和有限元表达,并在Unigraphics系统中进行了有限元分析的后置处理.此外,对TC1钛板筒型拉深件毛坯初始形状进行了优化,并对成形中拉深件厚向应变分布进行了分析,得到了满意结果.     

Grouping parts and tools in flexible manufacturing systems production planning

Batch production in a flexible manufacturing environment is necessary not only to satisfy some technological constraints but also to achieve potential reductions in processing time, to reduce work-in-process and finished goods inventories, and to simplify the production planning process. Central to batch production is the problem of grouping part types and the required tools into families for simultaneous processing. This paper presents a practical and useful algorithm for grouping parts and tools in flexible manufacturing systems (FMSs).This problem is first formulated as a 0-1 linear integer program. A Lagrangian dual formulation is then developed to obtain an upper bound on the optimal objective function value. The Lagrangian dual program is further decomposed into a linear network subproblem and a set of knapsack subproblems. A subgradient algorithm with several enhancement strategies is employed to minimize the upper bound obtained from the dual problem. Computational results for medium and large-scale problems demonstrate that this solution procedure is effective.     

Meso-scaled progressive forming of bulk cylindrical and flanged parts using sheet metal

In microforming, handling and transporting of meso/micro-sized intermediate preforms are difficult due to the influence of adhesive force on preform surfaces. In this research, the fabrication of meso-scaled bulk cylindrical and flanged parts by directly using sheet metal is investigated. The cylinder is made with a single stroke by shearing, while the flanged part is formed progressively via multi-stage shearing and extrusion. In forming of the flanged part, an intermediate preform is fabricated with sheet metal and a pre-pierced hole for positioning. The final part is blanked out from the sheet metal in the last operation. In such a way, the transporting, positioning and ejecting of the flanged part are facilitated. Furthermore, the characteristics of the developed meso-scaled forming process are extensively investigated. The shearing and fractured surfaces on both the cylindrical and flanged parts are found. The surface grains of the blanked cylinder have undergone severe deformation and been hardened, which increases the flow stress of the blanked cylinder. In addition, the longer cylinder and flanged part are obtained with fine-grained material. This implies that a larger amount of material flow to the lateral side of the workpiece in the case of coarse-grained material.     

Process planning for rotational parts using the generalized travelling salesman problem

Process planning for rotational parts can be described as deciding on the order of machining the various features. However, this problem entails more details since each feature, hypothetically, can be machined by a left- or a right-hand tool, and in many cases, the parts can be chucked from either end. Another complicating factor is that some features require machining from both directions (with both left- and right-hand tools) and some can be machined by either tool. Thus, the process planning problem for rotational parts decides on the order of machining the various features, the chucking direction and the tool to be used for each feature. Every time the part is chucked or to a lesser extent when the tool direction is changed, the accuracy of the feature is compromised and productivity is reduced due to time spent on non-cutting operations. A good process plan, therefore, should consider the productivity as well as the overall accuracy of the part. This paper presents an algorithmic graph-theoretic approach towards determining the optimal process plan such that the part's overall accuracy is maximized, given the accuracy of the machine and the features tolerances. In particular, we describe the process-planning problem as a generalized travelling salesman problem and then use known procedures to solve the problem. This solution minimizes the overall impact of rechucking operations and tool changes on the process accuracy. Therefore, in addition to the improved precision, the process plan results in faster and more efficient operations.     

基于CT反求选区激光熔化制造个性化零件研究

为直接制造具有复杂外形的个性化金属结构件,采用"设计-制造"两步成型法,将CT图像反求与正向建模方法结合,获得个性化的股骨、手术模板及舌侧矫正器CAD数据,通过选区激光熔化技术完全熔化316L不锈钢粉末,由正交试验优化成型工艺参数,然后,制取设计构件.讨论了光纤激光器的细小光斑对成型精度的影响,分析了层间错开扫描策略对...     

Feature-based representation for manufacturing planning

Improved integration using product models in a computer aided design and manufacture environment implies that there is an enhanced need to provide information support across a wide range of applications. In a typical situation concerned with mechanical products, these applications are likely to include detail design, process planning and assembly planning. Features have frequently been used to support these and other applications individually, but single feature representations that simultaneously meet the information needs of a number of applications are unusual. Assembly and process planning are two important aspects of an integrated design and manufacture system, and a formal structure for their representation in a feature-based design system is presented. Features are considered to be machined volumes and are described in a hierarchical taxonomy that is designed to be useful across a range of machined components. The assembly structure is also defined hierarchically with the (machining) features forming the basic entities in the assembly. Assembly relationships among features are defined in the form of mating relationships that are carried by the features. A set of mating relationships between pairs of features has been defined after having studied the literature and a number of engineering products. An integrated data structure containing process planning information from earlier research work and the assembly mating relationships is presented and forms the basis of class definitions for each level in the assembly hierarchy. Object-oriented programming techniques have been used to implement a prototype system using the ACIS solid modelling kernel. The research has illustrated the feasibility of using a single feature representation to support a number of activities within a computer integrated manufacturing environment.     

Automated process planning for parametric parts

The available automated CAPP solutions are mostly academic research or specific applications, which cannot be used in different environments. This paper presents a solution for automated process planning for parametric parts included in one CAPP environment with many other software components. It meets the planning requirements of any parts and products in a real industrial environment. This paper provides a brief overview of CAPP and a definition of the parametric parts used. The requirements of the CAPP environment are discussed and its concept and design characteristics are presented. A practical application of the CAPP environment is described in order to validate the proposed solution.     

A model for labour pooling in batch manufacturing

Cross-training workers to perform multi-skilled jobs is one of the modern trends in job design. As companies engage in downsizing, the remaining workforce is expected to do more and different tasks. This paper presents a formal definition and a practical solution for optimizing the size and cost of the pool of multi-skilled workers for production units operated under batch manufacturing. The pool size is optimized through a search procedure applied separately to just-in-time (JIT) and level production plans, which are derived from the stones heuristic. The method allows direct calculation of the cost savings from labour pooling. This paper was inspired by consulting in the food industry, where implementation of these results has significantly reduced labour costs.     

Feature reasoning for sheet metal components

The objective of this paper is to develop a set of principles for extracting, recognizing and reasoning about features from sheet metal parts which are created in the CAD system. Recognition of such features will enable the automatic evaluation of designs and the development of process plans by among other things, mapping form features to tools needed to produce the form. The principles are developed by studying the face-oriented representations of features and deriving concepts which relate the features geometrically and topologically. Subsequently, the processes that relate to the geometrical forms are used to further uniquely identify the features.