Cam shape optimisation by genetic algorithm

This article overviews a genetic algorithm based computer-aided approach for preliminary design and shape optimisation of cam profiles for cam operated mechanisms. The primary objective of the work was to create a complete systematic approach for preliminary cam shape design including cam shape design automation and true cam shape optimisation with respect to the simulated computer models of cam mechanisms. Typically, shape optimisation of a cam cross-section is a multiobjective optimisation problem of two-dimensional geometric shape in a heavily constrained environment. In order to illustrate the genetic algorithm based cam shape optimisation approach, a cam shape design example is described, in which a cam shape designed by genetic algorithm is compared with its more conventionally designed counterpart.     

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.     

面向并行设计的特征识别与模型重构方法

在分析现有CAD软件以及产品建模方法不足的基础上，引入广义工程语义特征的概念，应用广义特征对象实现面向并行设计的产品广义信息模型的简化表示；提出一种自动特征识别方法，对识别对象进行分类；以截面复杂的回转体特征为例，着重表述了基于基面的特征识别算法；扼要介绍Pro／E软件中的特征结构树，提出面向Pro／E的特征信息三级提取策略与特征信息模型重构原则，并据此开发了DFX原型系统．     

实现中小企业产品设计重用的若干途径

产品设计知识重用日益受到国内外企业和学术界的关注。根据我国中小企业进行产品设计知识重用需求,讨论了适宜我国中小企业进行产品设计重用的若干途径和方法,主要包括:采用大规模定制、基于PDM等商品化软件、基于Web的零件库资源共享,以及基于CAD知识和工程语义的产品知识重用方法。该方法基于CAD知识和工程语义的双重网,解决一个面向低层次的产品结构的知识表达、查询和重用问题。     

Parameter free shape and thickness optimisation considering stress response

In the parameter free approach, FE-based data are used as design variables, such as nodal coordinates and nodal thickness. During shape and thickness optimisation, this approach provides much design freedom for a limited modelling effort. Stress results are, however, very sensitive to the local shape changes that can occur during parameter free optimisation. When stress results are used as response function, this irregularity can complicate the optimisation. As a solution, the Kreisselmeier-Steinhauser function for the stresses is introduced as a response function for parameter free shape optimisation. In this function, the local stress results are aggregated to obtain a global measure of stress in a structure. This measure can be used as an objective to reduce the overall stress in the structure or as a constraint to limit the stress in the structure to a maximum allowable value. As a result, the optimal structures are smooth and material efficient. Several examples are presented in this paper to illustrate the use of the parameter free design approach in combination with the stress response function.     

The application of ubiquitous multimodal synchronous data capture in CAD

Design is an interactive and iterative process where the designer’s skills and knowledge are fused with emotive rationales aided by design tools. A design solution is thus influenced by the designer’s creativity, experience and emotional perception. Consequently, there is a need within computer aided design (CAD) research for ubiquitous tools to capture the affective states of engineers during design activities to further understand the product design process.This paper proposes a generic framework for ubiquitous multimodal synchronous data capture, based around the capture of CAD system activities, to monitor and log a variety of inputs, interactions, biophysical data and design solutions with a view to providing meta and chronological performance data for post design task analysis. The framework has been employed in two use cases namely, a CAD station activity and a collaborative design review. The results of these trials validated the architecture and use of the ubiquitous data capture approach demonstrating the practical application of time-phased data capture, analysis and the subsequent output of metadata in CAD environments providing a new perspective on, and a new way of investigating CAD-based design activities.This research also extrapolates the framework’s usefulness into future CAD and PLM systems by arguing why and how they need to adopt such ubiquitous platforms. It also subjectively points to potential opportunities and issues that might arise when implementing the ubiquitous multimodal metadata architecture in a real-life environment.     

Shape optimisation for crashworthiness followed by a robustness analysis with respect to shape variables

This paper presents the results of a study on shape optimisation for crashworthiness design of passenger cars based on the software SFE CONCEPT. In contrast to classical morphing approaches, SFE CONCEPT allows for larger geometrical modifications via an implicit parameterisation technique. This is advantageous in particular in the early design phases where different design alternatives are investigated and the optimal and robust geometry needs to be identified. As a first example, the front rail of a standard passenger car is optimised here. This is – as one of the main parts of the body in white – an appropriate example for exploration of optimisation methods. The performance of a classical optimisation approach is analysed and complemented by a robustness analysis where uncertainties in shape parameters are considered.     

Integration of topology and shape optimization for design of structural components

This paper presents an integrated approach that supports the topology optimization and CAD-based shape optimization. The main contribution of the paper is using the geometric reconstruction technique that is mathematically sound and error bounded for creating solid models of the topologically optimized structures with smooth geometric boundary. This geometric reconstruction method extends the integration to 3-D applications. In addition, commercial Computer-Aided Design (CAD), finite element analysis (FEA), optimization, and application software tools are incorporated to support the integrated optimization process. The integration is carried out by first converting the geometry of the topologically optimized structure into smooth and parametric B-spline curves and surfaces. The B-spline curves and surfaces are then imported into a parametric CAD environment to build solid models of the structure. The control point movements of the B-spline curves or surfaces are defined as design variables for shape optimization, in which CAD-based design velocity field computations, design sensitivity analysis (DSA), and nonlinear programming are performed. Both 2-D plane stress and 3-D solid examples are presented to demonstrate the proposed approach. Received January 27, 2000 Communicated by J. Sobieski     

The complementary roles of expert systems and database management systems in a design for manufacture environment

Effective product design that satisfies functional requirements and can be manufactured easily requires vast amounts of knowledge on the part of the design engineer. This paper focuses on the complementary roles of expert systems and database management systems as they relate to the Intelligent Design System (IDS) in a Design for Manufacture (DFM) environment. Each technology complements the other in its strengths and abilities. The database management system provides during the design process. The expert system provides a reasoning mechanism for identifying manufacturing violations and generating meaningful recommendations. These components work cooperatively with a CAD interface to form a unified, intelligent design environment.An information flow analysis of the Intelligent Design System resulted in the development of three distinct classifications of information within the database: CAD data, a design catalog, and a knowledge base. The CAD data tables employ an, object oriented approach to store specific information about the physical contains cost, weight, and strength characteristics of the standard parts and fasteners used within the system. The knowledge base contains rules and heuristics concerning design and manufacturing methodologies.The placement of the expert system rules in the database represents an innovation. As a result, the expansion and updating of the materials, fasteners, standard parts, or manufacturing processes used by the Intelligent Design System is facilitated without increased due to the efficient management of the knowledge base by the database management system. This allows the designer to modify the knowledge and help the system to learn without the need for a knowledge engineer.     

On increasing the developability of a trimmed NURBS surface

Developable surfaces are desired in designing products manufactured from planar sheets. Trimmed non-uniform rational B-spline (NURBS) surface patches are widely adopted to represent 3D products in CAD/CAM. This paper presents a new method to increase the developability of an arbitrarily trimmed NURBS surface patch. With this tool, designers can first create and modify the shape of a product without thinking about the developable constraint. When the design is finished, our approach is applied to increase the developability of the designed surface patches. Our method is an optimisation-based approach. After defining a function to identify the developability of a surface patch, the objective function for increasing the developability is derived. During the optimisation, the positions and weights of the free control points are adjusted. When increasing the developability of a given surface patch, its deformation is also minimised and the singular points are avoided. G⁰ continuity is reserved on the boundary curves during the optimisetion, and the method to reserve G¹ continuity across the boundaries is also discussed in this paper. Compared to other existing methods, our approach solves the problem in a novel way that is close to the design convention, and we are dealing with the developability problem of an arbitrarily trimmed NURBS patch.     

Distributed Integrated Information System for Product Design

A new approach to construct Distributed Integrated Information System for product design(DIIS) is presented. Design knowledge of parts and products is expressed in STEP form, it is neutral and independent to commercial CAD platforms. After compiling by STEP Developer and being pre/post processed, the binary codes of data dictionary model can be sent into the end user's design platform directly and readily supports the product design.     

Automation and optimisation of Family Mould Cavity and Runner Layout Design (FMCRLD) using genetic algorithms and mould layout design grammars

Family Mould Cavity Runner Layout Design (FMCRLD) is the most demanding and critical task in the early Conceptual Mould Layout Design (CMLD) phase. Traditional experience-dependent manual FCMRLD workflow causes long design lead time, non-optimum designs and human errors. However, no previous research can support FMCRLD automation and optimisation. The nature of FMCRLD is non-repetitive and generative. The complexity of FMCRLD optimisation involves solving a complex two-level combinatorial layout design optimisation problem. Inspired by the theory of evolutionary design in nature “Survival of the Fittest” and the biological genotype–phenotype mapping process of the generation of form in living systems, this research first proposes an innovative evolutionary FMCRLD approach using Genetic Algorithms (GA) and Mould Layout Design Grammars (MLDG) that can automate and optimise such generative and complex FMCRLD with its explorative and generative design process embodied in a stochastic evolutionary search. Based on this approach, an Intelligent Conceptual Mould Layout Design System (ICMLDS) prototype has been developed. The ICMLDS is a powerful intelligent design system as well as an interactive design-training system that can encourage and accelerate mould designers’ design alternative exploration, exploitation and optimisation for better design in less time. This research innovates the traditional manual FMCRLD workflow to eliminate costly human errors and boost the less-experienced mould designer’s ability and productivity in performing FCMRLD during the CMLD phase.     

Topology/shape optimisation of axisymmetric continuum structures – a metamorphic development approach

A novel topology/shape optimisation method for axisymmetric elastic solids, based on solid modeling and FE analysis, is presented. Optimal profiles of minimum-mass axisymmetric structures are sought by growing and degenerating simple initial structures subject to response constraints. The rates of the growth and degeneration are controlled based on the current objective and constraint functions of the optimisation problem under consideration. The optimal structures are developed metamorphically in specified infinite design domains using both quadrilateral and triangular axisymmetric finite elements that are ideally suited for modeling continua involving curved boundaries.The robustness of this fully automatic method is studied and validated with the first example of seeking the optimal shape of a centrally suspended axisymmetric object with minimum strain energy caused by self-weight. Then the method is applied to a practical industrial design problem: the design of a turbine disk. The variations of load and boundary conditions caused by shape change in these problems, including the gravitational and centrifugal loads, and temperature distribution are accommodated in the optimisation procedures. Thus, the design model closely resembles the real design problem. The results demonstrate the success of the method in generating optimal but realistic solutions to practical design problems.     

A CAD-based on biological method for designing optimal fatigue life

This paper presents an innovative approach to shape optimisation of three-dimensional, damage-tolerant structures. In this approach, a new and simple method, which we termed Failure Analysis of Structures (FAST), is used to estimate the stress-intensity factor for cracks at a notch. The methodology and software used to automate damage-tolerance calculations are developed using computer-aided design and FAST codes. The worst crack locations are found by modeling many cracks along fractured critical edges of the structure by using FAST. This software is then used to evaluate damage-tolerance objective functions for optimisation algorithms. A particular stress-based biological growth method is employed to study the problem of optimisation with fatigue life as the design objective. This work confirms that a stress-optimised structure does not necessarily give the longest fatigue life by numerical examples.     

Collaborative design: Improving efficiency by concurrent execution of Boolean tasks

Computer-Aided Design (CAD) applications provide design and engineering professionals with various computer-based tools to perform design activities. As efficiency is one of the most important requirements in most design tasks, in this article, we contribute a novel collaborative design approach to improving efficiency, where a complex design task can be divided and executed concurrently by multiple collaborative designers. This approach is particularly effective for design tasks where Boolean operations – widely supported by most CAD applications – are heavily used in design activities, such as architecture design, mechanical design and digital media design. We have designed and implemented a prototype system CoAutoCAD to test the approach and to demonstrate a variety of collaborative design activities.     

An object-oriented constraints-based system for concurrent product development

This research work aims to develop an intelligent constraint-based system that enables designers to consider at the early stages of the design process all activities associated with product’s life cycle. One of the most important aspects of these activities is the evaluation and optimisation of manufacturing processes that require various type of information from the different aspects of product’s life cycle. This research article discusses the development of a prototype system for manufacturing process optimisation using a combination of both mathematical methods and constraint-programming techniques. This approach enables designers to evaluate and optimise feasible manufacturing processes in a consistent manner as early as possible during the design process. This helps in avoiding unexpected design iterations that wastage a great amount of time and effort, leading to longer lead-time. The development process has passed through the five major stages: Firstly, an intelligent constraint-based design system for concurrent product and process design has been developed. Secondly, a manufacturing process optimisation module has been constructed. Thirdly, the product features, processes, cost, time and constraints to be used for carrying out various design tasks has been represented in the format of constraints, frames, objects, and rules. Fourthly, the process optimisation and evaluation rules for the selection of feasible processes for complex features, and finally, the information management system that ensures consistency in information exchange and decision making activities have been developed.     

Similarity assessment of 3D mechanical components for design reuse

Duplicate designs consume a significant amount of resources in most new product development. Search of similar parts for a given query part is the key to avoid this problem by facilitating design reuse. Most search algorithms convert the CAD model into a shape signature and compute the similarity between two models according to a measure function of their signatures. However, each algorithm defines the shape signature in a different way, and thus has its own limitations in discriminating 3D parts. This paper proposes a search scheme that successfully complements various shape signatures in similarity assessment of 3D mechanical components. It considers form-feature, topological, and geometric information in component comparison. Such an integrated approach can effectively solve the feature intersection problem, inherited in any feature-based approaches, and capture the user's intent more precisely in the search, which geometry-based methods fail to accomplish. We also develop a set of algorithms that performs the component comparison in a polynomial time. The proposed scheme is implemented in a product design environment consisting of commercial CAD and PDM systems. The result demonstrates the practicality of this work in automatic search of similar mechanical components for design reuse.