Self-organizing migration algorithm applied to machining allocation of clutch assembly

Tolerancing is an important issue in product and manufacturing process designs. The allocation of design tolerances between the components of a mechanical assembly and manufacturing tolerances in the intermediate machining steps of component fabrication can significantly affect the quality, robustness and life-cycle of a product. Stimulated by the growing demand for improving the reliability and performance of manufacturing process designs, the tolerance design optimization has been receiving significant attention from researchers in the field. In recent years, a broad class of meta-heuristics algorithms has been developed for tolerance optimization. Recently, a new class of stochastic optimization algorithm called self-organizing migrating algorithm (SOMA) was proposed in literature. SOMA works on a population of potential solutions called specimen and it is based on the self-organizing behavior of groups of individuals in a “social environment”. This paper introduces a modified SOMA approach based on Gaussian operator (GSOMA) to solve the machining tolerance allocation of an overrunning clutch assembly. The objective is to obtain optimum tolerances of the individual components for the minimum cost of manufacturing. Simulation results obtained by the SOMA and GSOMA approaches are compared with results presented in recent literature using geometric programming, genetic algorithm, and particle swarm optimization.     

基于SolidWorks的虚拟装配路径规划研究

在机械产品制造过程中,装配工作占有重要的地位,其成本可以占到制造成本的30%—50%。装配工作对产品的最终质量也有很大影响。虚拟装配可以提前模拟装配过程,对保障装配质量和最终产品质量有着重要的意义,机械手臂的应用也使得装配工作更可控。本文基于SolidWorks三维模型设计软件,利用SolidWorks提供的API接口,通过.NET编程语言控制机械手臂,对产品零件进行装配模拟、碰撞干涉检查和机械手臂运动空间路径规划,最终生成机械手臂装配最优路径,大大减少了人工对机械手臂运动的调试工作,提高了产品的最终质量,对加速制造业发展具有重要意义。     

Simultaneous parameter and tolerance optimization of structures via probability-interval mixed reliability model

Both structural sizes and dimensional tolerances strongly influence the manufacturing cost and the functional performance of a practical product. This paper presents an optimization method to simultaneously find the optimal combination of structural sizes and dimensional tolerances. Based on a probability-interval mixed reliability model, the imprecision of design parameters is modeled as interval uncertainties fluctuating within allowable tolerance bounds. The optimization model is defined as to minimize the total manufacturing cost under mixed reliability index constraints, which are further transformed into their equivalent formulations by using the performance measure approach. The optimization problem is then solved with the sequential approximate programming. Meanwhile, a numerically stable algorithm based on the trust region method is proposed to efficiently update the target performance points (TPPs) and the worst case points (WCPs), which shows better performance than traditional approaches for highly nonlinear problems. Numerical results reveal that reasonable dimensions and tolerances can be suggested for the minimum manufacturing cost and a desirable structural safety.     

Tolerance design optimization on cost–quality trade-off using the Shapley value method

Part tolerance design is important in the manufacturing process of many complex products because it directly affects manufacturing cost and product quality. It is significant to develop a reasonable tolerance scheme considering the demands of cost and quality to reduce the production risk and provide a guide for supplier management. Traditionally, some kinds of cost objective functions or variation propagation models are often applied in part tolerance design. Moreover, designers usually solve the tolerance design problem by constructing a single-objective model, dealing with several single-objective problems, or establishing a comprehensive evaluating function combining several optimization objectives with different weights. These approaches may not adequately consider the interdependent and the interactional relations of various demands and balance them. This paper presents a kind of tolerance design approach at the early design stage of automotive parts based on the Shapley value method (SVM) of coalitional game theory considering the demands of manufacturing cost and product quality. First the part tolerance design problem is defined. The measuring data in regular production is collected instead of working on specific objective functions or design models. Then how the SVM is adopted to solve the tolerance design problem is discussed. Lastly, a tolerance design example of a vehicle front lamp demonstrates the application and the performance of the proposed method.     

Group technology applications in manufacturing operations through the computer system

The typical manufacturing facility is constantly developing new product designs and related manufacturing processes. The increased volume of new designs and processes causes rapid and inefficient construction of product designs and manufacturing processes. Many parts and manufacturing processes are developed over the life cycle of a production facility with no organized means of cataloging this past and present data. This procedure is extremely ineffective because there is no way to determine if a part or process has been previously developed. The constant “reinventing of the wheel” creates a tremendous waste of manpower and cost.

One approach to solving this problem is through the use of group technoogy. Group technology is the identification and grouping of similar parts and processes in order to take avantage of their similarities in the design and manufacturing process. Parts and processes can be grouped under a classification and implemented with a coding system. Concurrently, the number of parts and processes can be reduced by putting them in a “family.” This “family” has common characteristics such as shape, size, color, tolerance or production operations.

For handling and manipulation of this data, a computer system has been developed. The computer system would set up a reporting format that would classify, code and group the parts and processes, so the user can analyze if a previously designed process or part can be used in the current system and/or if a better layout can be feasible.

Many advantages such as reduced inventory cost, increased facility space and better utilization of manpower are but a few of the benefits from this system.     

Mathematical model for quality cost optimization

Quality engineering uses robust design in order to improve quality by reducing the effects of variability. Variability of the product can be reduced by two stages. One is parameter design which is adjustable to the nominal value so that output is less sensitive to the cause of variability. Other one is tolerance design which is to reduce the tolerance in order to control variability. All costs incurred in a product life cycle can be divided into two categories—manufacturing cost before the sale to the customer and quality loss after the shipment of the product to the customer. It is very important to find the optimum tolerances for each of the characteristics. A balance between manufacturing cost and quality loss should be arrived at in the tolerance design for quality improvement and cost reduction. For the case of Nominal-The-Best, a mathematical model is developed in order to determine the optimum product tolerance and minimize the total cost which includes the manufacturing cost and the quality loss. Since the process capability index (C_pm) shows the balance of quality responsibility between the design and the manufacturing engineers, this is taken as the basis in developing the functional relationship between the variability of the product and the tolerance. Based on these relationships, the total cost of model can be expressed as a function of product tolerance from which the optimal tolerance limits can be found out. Finally, using this model a tolerance design approach that increases the quality and reduces the cost can be achieved in the early stages of the product process design stage itself.     

Design strategy for reducing manufacturing and assembly complexity of air-breathing Proton Exchange Membrane Fuel Cells (PEMFC)

Conventional flat plate Proton Exchange Membrane fuel cell (PEMFC) designs have been under investigation for the last five decades with the majority of the research being conducted in fluid dynamics of the reactants, membrane chemistry, thermal characteristics, stacking, and electrical properties. By rigidly adhering to design characteristics and material choices (graphite flow plates and metal end plates), conventional fuel cell designs have become bulky, fastener intense designs that have a high degree of manufacturing and assembly complexity. The department of energy has recognized the need for economical and efficient manufacturing practices to further the market penetration and end user adoption of fuel cells. Therefore this paper analyzes air-breathing PEMFC's from the perspective of reducing manufacturing complexity, assembly complexity, and costs. Areas of complexity like the flow plates, end plates, sealing methods have been reassessed and this paper proposes alternatives to component functions, and the commonly employed materials along with an alternate assembly strategy. Prototypes built using the new design strategy achieved about 90% reduction in weight and number of components while enjoying an 80% reduction in costs. The new prototypes also possess a superior form factor, along with a 10-fold increase in power density as compared to conventional designs.     

Automating manufacturability evaluation in CAD systems through expert systems approaches

Design for Manufacturability (DFM) represents a new awareness of the importance of product design as an integral part of manufacturing activities. Good design guidelines exist in industry for frequently used manufacturing processes. These guidelines are systematic statements of good design practices, empirically derived over years of design and manufacturing experience. Ensuring that the given product design conforms to each of the guidelines specific to the selected process results in better manufacturability. To meet the objectives of the DFM approach, design and manufacturing planning activities have to be combined into a single engineering effort and applied througout the life cycle of a product. Computer-aided design (CAD) systems offer powerful features such as the ability to develop complex solid models and perform engineering analyses, including stress analysis, interobject interference, collision detection, and inertial analysis. However, a prominent limitation faced by designers in CAD systems is the lack of “intelligence.” Though designs could be developed, analyzed, and perfected from a functional viewpoint in CAD systems, manufacturability consideration may get little or no attention at all. As a result, product designs that are functionally sound may be developed at a high manufacturing cost. Thus, intelligence should be incorporated in CAD systems, whereby product designs could not only be developed and analyzed but also evaluated for cost and manufacturability. This study attempts to perform this task automatically in a CAD system using a knowledge-based approach: the manufacturability criteria are considered for milling and drilling operations performed on a computerized numerically controlled (CNC) milling machine. The results obtained from the application of the expert system suggest that the expert systems methodology is a feasible method for implementing manufacturability evaluation capability in CAD systems.     

Multiple-view feature modelling for integral product development

To allow a designer to focus on the information that is relevant for a particular product development phase, is an important aspect of integral product development. Unlike current modelling systems, multiple-view feature modelling can adequately support this, by providing an own view on a product for each phase. Each view contains a feature model of the product specific for the corresponding phase. An approach to multiple-view feature modelling is presented that supports conceptual design, assembly design, part detail design and part manufacturing planning. It does not only provide views with form features to model single parts, as previous approaches to multiple-view feature modelling did, but also a view with conceptual features, to model the product configuration with functional components and interfaces between these components, and a view with assembly features, to model the connections between components. The general concept of this multiple-view feature modelling approach, the functionality of the four views, and the way the views are kept consistent, are described.     

Modeling automatic assembly and disassembly operations for virtualmanufacturing

A system for evaluating products in their design phase has been developed for virtual manufacturing. It is integrated into a CAD/CAM environment to calculate the cost for assembling and disassembling parts. In our earlier work, a generic assembly and disassembly model was developed to represent operations required for product manufacturing and de-manufacturing. To be useful, the model requires a method for translating high-level instructions from product designers into low-level assembly and disassembly instructions. This paper presents a set of rules for accomplishing this task. The developed rules are used for manipulating strings representing parts and handlers in binary assembly and disassembly operations. A telephone assembly and disassembly simulation is used to illustrate the developed system     

Knowledge-based design for assembly in agile manufacturing by using Data Mining methods

Decision making in early production planning phases is typically based on a rough estimation due to lack of a comprehensive, reliable knowledge base. Virtual planning has been prevailed as a method used to evaluate risks and costs before the concrete realization of production processes. The process of product assembly, which yields a high share in total production costs, gets its particular importance. This paper introduces a new approach and its initial implementation for knowledge-based design for assembly in agile manufacturing by using data mining (DM) methods in the field of series production with high variance. The approach adopts the usage of bulk data with old, successful designs in order to extrapolate its scope for assembly processes. Especially linked product and process data allow the innovative usage of DM methods in order to facilitate the front loading in the product development. The concept presents an affordable assistance potential for development of new products variants along the product emergence process (PEP). With this approach an early cost estimation of assembly processes in series production can be conducted using advanced DM methods as shown in an industrial use case. Furthermore, design and planning processes can be supported effectively.     

A generic deviation-based approach for synthesis of tolerances

In this paper, a generic model for the synthesis of tolerances for manufactured parts is presented. The model uses a method of transforming traditional tolerance specifications (as defined in ASME Y14.5M) to a generalized coordinate system (hereinafter referred to as deviation space). Small displacement torsors (SDTs) have been used for representing the deviations. The tolerance synthesis method is formulated as a constrained nonlinear optimization process. Three different types of constraints have been considered for the optimization process: 1) representation of assemblability; 2) mapping of tolerance specification to deviations; and 3) functional requirements. A new deviation-based cost of manufacturing model has been proposed. A working module of the scheme has been implemented and the process has been elaborated with two examples. The possibility of extension of the model and scope for further generalization have been discussed. Note to Practitioners-This paper presents an optimization method for finding tolerance values for different features of an assembly of manufactured parts. Determination of different types of tolerances and their exact values for critical features of any part has been an ad-hoc process; it has been mostly experience-based till recent time. In this paper, efforts have been made to establish a strong mathematically oriented method for synthesis of tolerances. The procedure attempts to minimize cost of manufacturing while the functionality and assemblability are satisfied. It is a generalized method and could be applied for designing rigid manufacture parts. For practical usage, this method should be integrated with three-dimensional computer-aided design packages as a tolerance synthesis module for integrated tolerance design.     

基于工程约束与权重优化的民机部段柔性调姿算法实现

民用飞机具有产品复杂、气动外形要求严格、产品构型众多、零部件数量巨大等特点,飞机制造过程中装配技术要求和工作量占比远高于其他一般的机械产品加工行业.调姿对接装配是装配工作的重要内容,高精度、低应力的对接装配是飞机成功制造和安全飞行的保证.基于奇异值解算与优化算法,根据民机装配工艺要求,在Python环境下开发并实现无权...     

产品族设计与延迟制造过程决策的主从关联优化

在市场全球化的进程中,延迟仍然是当今企业降低供应链风险的一种有效策略.然而,当前对延迟的研究往往是基于预先已固定好的产品族架构,较少关注到产品族设计与延迟制造过程决策间存在的内在固有耦合关系.鉴于此,提出对这二者的一种主从关联优化方法.首先,通过构建二者间的主从交互评价机制,建立以产品族设计为上层优化、延迟制造过程决策为下层优化的非线性双层规划模型:模型上层为设计产品族架构和决策延迟产品模块类型,从而最大化单位成本的顾客效用;下层分别为非延迟和延迟产品模块决策最优的制造方式以及为终端产品决策最优的组装方式,从而最小化工程成本.然后,设计一种嵌套式遗传算法对模型进行求解,以智能冰箱产品族延迟制造案例验证所提出模型和算法的可行性.最后,通过设计一种嵌套GAPSO算法对嵌套式遗传算法进行改进,并对比分析两种算法的计算过程和结果.     

A knowledge-based approach to design for manufacturability

In the light of growing global competition, organizations around the world today are constantly under pressure to produce high-quality products at an economical price. The integration of design and manufacturing activities into one common engineering effort has been recognized as a key strategy for survival and growth. Design for manufacturability (DFM) is an approach to design that fosters the simultaneous involvement of product design and process design. The implementation of the DFM approach requires the collaboration of both the design and manufacturing functions within an organization. Many reasons can be cited for the inability to implement the DFM approach effectively, including: lack of interdisciplinary expertise of designers; inflexibility in organizational structure, which hinders interaction between design and manufacturing functions; lack of manufacturing cost information at the design phase; and absence of integrated engineering effort intended to maximize functional and manufacturability objectives. The purpose of this research is to show how expert systems methodology could be used to provide manufacturability expertise during the design phase of a product. An object- and rule-based expert system has been developed that has the capability: (1) to make process selection decisions based on a set of design and production parameters to achieve cost-effective manufacture; and (2) to estimate manufacturing cost based on the identified processes. The expertise for primary process selection is developed for casting and forging processes. The specialized processes considered are die casting, investment casting, sand casting, precision forging, open die forging and conventional die forging. The processes considered for secondary process selection are end milling and drilling. The cost estimation expertise is developed for the die casting process, the milling and drilling operations, and the manual assembly operations. The results obtained from the application of the expert system suggest that the use of expert systems methodology is a feasible method for implementing the DFM approach.     

A method for computer-aided specification of geometric tolerances

The paper describes a method for the generation of tolerance specifications from product data. The problem is nontrivial due to the increasing adoption of geometric dimensioning criteria, which call for the use of many types of geometric tolerances to completely and unambiguously represent the design intent and the many constraints deriving from manufacturing, assembly and inspection processes. All these issues have to be modeled and explicitly provided to a generative specification procedure, which may thus need a large amount of input data. The proposed approach tries to avoid this difficulty by considering that most precision requirements to be defined relate to the assembly process, and can be automatically derived by analyzing the contact relations between parts and the assembly operations planned for the product. Along with possible user-defined additional requirements relating to function, assembly requirements are used in a rule-based geometric reasoning procedure to select datum reference frames for each part and to assign tolerance types to part features. A demonstrative software tool based on the developed procedure has allowed to verify its correctness and application scope on some product examples.     

Design for agility: a scheduling perspective

Agility is the ability of a company to produce a variety of products in a short time and at a low cost. This demands that products and manufacturing systems be simple, robust, and flexible to allow for quick response to the changing market. Scheduling of manufacturing systems in a changing environment is complex. This paper attempts to simplify scheduling of manufacturing systems through appropriate design of products and manufacturing systems. An attempt has been made to generate rules that allow to design products and systems for easy scheduling. Four design for agility rules are proposed in the paper. The first rule deals with decomposition of a manufacturing system. The rule simplifies the scheduling problem and reduces the total changeover cost. The second rule is concerned with design of products with robust scheduling characteristics. Product designs with robust scheduling characteristics can improve the response of a manufacturing system to the changes in the product demand and mix and reconfigurability of the system. The third rule results in a streamlined assembly line which has the type of product flow that simplifies scheduling. The fourth rule emphasizes the reduction of the number of stations in an assembly line. Examples are provided to demonstrate the benefits from using these rules. The implementation of the four rules is also discussed.