Rule and branch-and-bound algorithm based sequencing of machining features for process planning of complex parts

The machining sequence of machining features is vital to achieve efficient and high quality manufacturing of complex NC machining parts. In most feature-based process planning system, the machining features are sequenced as the lowest level unit. However, a single machining feature of complex parts such as aircraft structural parts is usually machined by multiple machining operations. The one-to-many mappings between the machining features and the machining operations cause the increase of the non-cutting tool path. In order to solve this problem, some types of machining features of complex parts are decomposed into several sub-machining features that are associated with a single machining operation individually according to the rules which are abstracted from the machining process of complex parts. Benefitting from the decomposition, the sub-machining features from different machining feature can be assembled into a sub-machining feature in order to avoid the cutting tool marks. The different types of sub-machining features are sequenced in the light of some rules which are also extracted from the machining process of complex parts. And the branch-and-bound algorithm are employed to sequence the same type sub-machining features to minimum the non-cutting tool path. A pilot feature-based process planning system has been developed based on this research, and has been used in some aircraft manufacturers in China.     

基于自定义特征的飞机结构件智能检测规划技术

飞机结构件常用坐标测量机检测形状特征的加工质量。为了满足飞机结构件需要检测复杂形状特征以及便于拓展形状特征检测范围的迫切需求,研究了独立于形状特征类型的特征定义框架及统一的特征识别算法;提出了检测知识驱动的测量点智能分布方法;设计了结合聚类和改进模拟退火算法的测量方向优化算法;实现了基于自定义特征及检测知识的智能检测规划。该技术已在多个重大航空产品的研制中得到应用,显著提升了飞机结构件检测规划的效率和智能化水平。     

An integrated NMT-based CAE environment — Part II: Applications to automated gating plan synthesis for injection molding

The focus of this paper is on the application of the integrated non-manifold-topology-based CAE environment described in the companion paper (Part I). The need for both a geometry-based and a feature-based environment is illustrated through the application of the features modeling utility to automate the procedure for injection mold design and, more specifically, gating design. The gating plan synthesis system described in this paper automatically determines an initial gating configuration based on a features representation of the part and a knowledge-base that captures some of the design rules used in practice. The Features Modeling Utility (FMU), a Topology And Geometry Utility System (TAGUS) and an automatic mesh generator, OCTREE, are used to identify and query features and to perform geometric reasoning about the part. The methodology used, implementation details and examples of test cases are presented.     

Case based reasoning method for computer aided welding fixture design

This paper presents a case-based reasoning (CBR) method for welding fixture design, a critical issue in the manufacturing of large and complicated equipment. However, previous fixture design research has mainly focused on machining fixtures rather than welding fixtures. In this paper, an approach of data abstraction for fixture design information representation is proposed, first to systemize and manage myriads of fixture related resources, e.g., past fixture design solutions, fixture units depository. Based on this approach, a multi-level CBR method for welding fixture design is then presented. This method could help designers, by referencing previous design cases, to make a conceptual fixturing solution quickly and, finally, finish the detailed solution of fixture design.     

Feedback method from inspection to process plan based on feature mapping for aircraft structural parts

The feedback from results of computer aided inspection is used by process planners (though a manual process) to improve machining processes to achieve desired quality. Mapping from inspection features to machining features is a practical method to automate this process. In NC machining of aircraft structural parts, composite machining features, surface joining and complex topological adjacency between free-from surfaces make this kind of mapping (one-to-many mapping mostly) much more complicated. In this research, a new feature mapping based feedback method from inspection to process plan is proposed. The geometry of inspection features are categorized into three kinds of basic inspection elements: Axis, Plane, and Surface. Then, the one-to-many mapping is simplified into one-to-one mapping. The correspondence relationships between basic inspection elements and machining features are abstract as mapping rules to obtain the associations between the basic inspection elements and candidate machining features. Through geometric reasoning, the basic inspection elements are mapped into machining features. Then, the measure data as feedback can be transferred to process planner for improving machining process. The optimized machining process will be stored in knowledge base for reusing. A case study is presented in this paper to demonstrate the proposed method. A prototype feature-based on-line inspection system has been developed and applied for machining aircraft structural parts in a large aircraft manufacturer.     

An integrated form-feature-based design system for manufacturing

Much of the knowledge that is applied in or communicated between design and manufacturing activities is primarily shape based or shape indexed. Previous attempts to acquire and organize shape knowledge have been mostly concentrated on feature recognition from solid models, group technology (GT) coding schemes, and feature-based modeling. This paper presents the development of an efficient form-feature-based modeling system, and addresses the important issue of utilizing feature information for manufacturing, which has not been extensively discussed by previous work. In this paper we first present a Euler operator-based approach for efficient and effective form-feature encoding and manipulation in a feature-based design environment. Subsequently, a hybrid representation scheme called enhanced CSG tree of feature (ECTOF), which integrates feature model with solid model in a tree structure, is discussed. A feature interference resolution methodology to maintain the correct and consistent feature information in an ECTOF is also deliberated. Finally, we present a machinability-checking module, which employs global accessibility criteria to analyze a feature's machinability on a three-axis machining center. By developing feature interference resolving and machinability testing techniques and integrating with an efficient feature-based design system, this research makes the development of an integrated feature-based design and manufacturing system possible.     

Applying RBR and CBR to develop a VR based integrated system for machining fixture design

A fixture is a special tool used to accurately and stably locate the workpiece during machining process. Proper fixture design improves the quality and production of parts and also facilitates the interchangeability of parts that is prevalent in much of modern manufacturing. This study combines the rule-based reasoning (RBR) and case-based reasoning (CBR) method for machining fixture design in a VR based integrated system. In this paper, an approach combines the RBR and fuzzy comprehensive judgment method is proposed for reasoning suitable locating schemes and locating features. Based on the reasoning results, a CBR method for machining fixture design is then presented. This method could help designers, by referencing previous design cases, to make a conceptual fixturing solution quickly. Finally, the implementation of proposed system is outlined and cases study has been used to demonstrate the applicability of the proposed approach.     

Fault diagnosis in assembly processes based on engineering-driven rules and PSOSAEN algorithm

The ability to detect and isolate process fault for product quality control in assembly processes plays an essential role in the success of a manufacturing enterprise in today’s globally competitive marketplace. However, the complexity of assembly processes makes it fairly challenging to diagnose process faults. One novel fixture fault diagnosis methodology has been developed in this study. The relationship between fixture fault patterns and part variation motion patterns is firstly off-line built, then |S| control chart is used as the detector of abnormal signals, and an improved Particle Swarm Optimization with Simulated Annealing-based selective neural network Ensemble (PSOSAEN) algorithm is explored for on-line identifying the part variation motion patterns triggering the out-of-control signals. Finally, an unknown fixture fault is identified based on the output of PSOSAEN algorithm and explored diagnosis rules. The method has excellent noise tolerance in real time, requires no hypothesis on statistical distribution of measurements, and has explicit engineering interpretation of the diagnostic process. The data from the real-world aircraft horizontal stabilizer assembly process were collected to validate the developed methodology. The analysis results indicate that the developed diagnosis methodology can perform effectively for fixture fault diagnosis in assembly processes. All of the analysis from this study provides guidelines in developing selective neural network ensemble and statistical process control-based fault diagnosis systems with integration of engineering knowledge in assembly processes.     

Rule inferencing and object-orientation for boundary elements mesh design

In this paper, object orientation and rule inferencing are used to automate the design of boundary element meshes. The work is part of an effort to develop an object-oriented integrated environment for the damage tolerance design of aircraft stiffened panels and other parts such as fuselage lap-joints. An inference domain class library has been developed. Inference domain objects are used to create symbolic representations for the structural configuration and for production rules that describe the mesh design strategy. An objectoriented inference engine is utilized to apply this rule set to the knowledge base where the symbolic representation of the structural configuration is stored. The technique was implemented using the C++ programming language.     

Feature-based modeling for automatic mesh generation

Automatic meshing algorithms for finite element analysis are based on a computer understanding of the geometry of the part to be discretized. Current mesh generators understand the part as either a boundary representation, an octree, or a point set. A higher-level understanding of the part can be achieved by associating engineering significance and engineering data, such as loading and boundary conditions, with generic shapes in the part. This technique, called feature-based modeling, is a popular approach to integrating computer-aided design (CAD) and computer-aided manufacturing through the use of machinable shapes in the CAD model. It would seem that feature-based design also could aid in the finite element mesh generation process by making engineering information explicit in the model.This paper describes an approach to feature-based mesh generation. The feature representation of a fully functioning feature-based system that does automatic process planning and inspection was extended to include finite element mesh generation. This approach is based on a single feature representation that can be used for design, finite element analysis, process planning, and inspection of prismatic parts. The paper describes several advantages that features provide to the meshing process, such as improved point sets and a convenient method of simplifying the geometry of the model. Also discussed are possible extensions to features to enhance the finite element meshing process.     

Simulation-based methodology for machine cell design

This paper presents a simulation-based methodology which uses both design and manufacturing attributes to form manufacturing cells. The methodology is implemented in three phases. In phase I, parts are grouped into part families based on their design and manufacturing dissimilarities. In phase II, machines are grouped into manufacturing cells based on relevant operational costs and various cells are assigned part families using an optimization technique. Phases I and II are based on integer and mixed-integer mathematical models. Finally, in phase III, a simulation model of the proposed system is built and verified, and the model is run so that data on the proposed system may be gathered and evaluated. The mathematical and simulation models are used to solve a sample production problem. The results from these models are compared, and can be used to justify the final design. By the use of these modeling tools, cellular manufacturing systems can be designed, analyzed, optimized, and finally justified.     

Rapid manufacturing with custom fixturing

Reports research on an experimental system for automated manufacturing with custom fixturing. In this approach, high level, feature-based shape models are transformed automatically into process plans from which computer numeric code for target machining centres is then derived automatically. This approach is targeted initially at parts with 2.5D features, including sculpted-exterior profiles and features requiring four- and five-axis indexing for manufacture. This part class has great practical utility and can be used to build very complex assemblies     

A methodology of forming manufacturing cells using manufacturing and design attributes

This study develops a methodology for forming machine cells using part's design and manufacturing dissimilarities. The proposed methodology is divided into two sequential phases. In phase I parts are grouped into families based upon their design and manufacturing attributes. In phase II, the machines are grouped into manufacturing cells based on relevant operational costs and the various cells are assigned part families using an optimization technique.     

Form tolerance-based measurement points determination with CMM

In an intelligent manufacturing environment, computer aided inspection (CAI) provides a critical role in closing the computer aided design (CAD) to computer aided manufacturing (CAM) loop. A coordinate measuring machine (CMM) is often used as a measurement tool in a mechanical part manufacturing environment. Feature-based measurement (FBM) with CMM plays an important role in the concurrent engineering environment (Fig. 1) (Yau and Menq, 1993). It measures a part and feedbacks the results to the concurrent control center to modify related process attributes. Feature-based computer aided inspection (CAI) systems define various measurement attributes for different features (Jacobohn et al., 1990). Part of the system determines the number of measurement points for a feature. In this research, a computer aided feature-based statistical concept is used to calculate sufficient measurement points for a feature. Circular and cylindrical parts are used to demonstrate the proposed methodology for determining the number of measurement points. The results show that the measurement error is significantly lower with the proposed method in determining the number of measurement points as compared to the method commonly used with a CMM. The proposed methodology is also computerized for on-line applications.     

特征的自动识别规则与提取

在对箱体类零件的加工特征及特征参数进行了分析,归纳和总结,在特征实体造型进行了研究的基础上,制定了各类特征的合理的识别规则和 识别算法,及提取的信息模型,实现了对复杂箱体类零件的加要特征信息自动提取,及CAD／CAPP系统的信息自动传递。     

An application-independent methodology of feature recognition with explicit representation of feature interaction

The existing feature-based design and feature recognition methods cannot fulfil the requirements of automated process planning. It is now recognized that satisfactory modelling of interactions between features is necessary for developing an automated process planning system. The selection of an optimum manufacturing process for a part needs to be considered at the conceptual design phase to incorporate the capabilities and constraints of the process in design. This paper describes a methodology of feature recognition that is independent of manufacturing process and explicitly generates geometric feature interactions in a part. The paper illustrates generation of feature sets for shape-forming processes, and describes a method to convert the process-independent features into machinable volumes and tool paths for material removal processes.     

Extraction of geometric characteristics for manufacturability assessment

One of the advantages of feature-based design is that it provides data which are defined as parameters of features in readily available forms for tasks from design through manufacturing. It can thus facilitate the integration of CAD and CAM. However, not all design features are features required in down stream applications and not all parameters or data can be predefined in the features. One of the significant examples is property that is formed by feature interactions. For example, the interaction of a positive feature and a negative feature induces a wall thickness change that might cause defects in a part. Therefore, the identification of the wall thickness change by detecting the feature interaction is required in the moldability assessment.The work presented in this paper deals with the extraction of geometric characteristics in feature-based design for manufacturability assessment. We focus on the manufacturability assessment of discrete parts with emphasis on a net shape process—injection molding. The definition, derivation and representation of the spatial relationships between features are described. The geometric characteristics formed by feature interactions are generalized as significant items, such as “depth”, “thickness”, “height” etc. based on the generalization of feature shapes. Reasoning on feature interactions and extraction of geometric characteristics is treated as a refinement procedure. High-level spatial relationships—“is_in”, “adjacent_to” and “coplanar” as well as their geometric details are first derived. The significant items formed from feature interactions are then computed based on the detailed spatial relationships. This work was implemented in a computer-aided concurrent product and process development environment to support molding product design assessment.     

Integrated cost/weight optimization of aircraft structures

A methodology for a combined cost/weight optimization of aircraft components is proposed. The objective function is formed by a simplified form of direct operating cost, i.e. by a weighted sum of the manufacturing cost and the component weight. Hence, the structural engineer can perform the evaluation of a design solution based on economical values rather than pure cost or weight targets. The parameter that governs the balance between manufacturing cost and weight is called weight penalty and incorporates the effect of fuel burn, environmental impact or contractual penalties due to overweight. Unlike previous work, the analytical cost model and structural models are replaced by commercially available software packages that allow a more realistic model of the manufacturing costs; further, arbitrary constraints for the structural analysis can be implemented. By means of parametric studies it is shown that the design solution strongly depends on the magnitude of the weight penalty.