Chapter 3 - Computer-aided fixture design

Configure-to-Order (CTO) assembly systems are becoming pivotal in meeting the rising demand for mass customization. However, enabling rapid and cost-effective system reconfiguration remains a major challenge in manufacturing. Despite the flexibility of general-purpose machines, fixture design introduces significant bottlenecks, often requiring extensive manual effort to access, organize, and interpret fragmented or incomplete data. This leads to inefficient design pipelines that can compromise product functionality and result in costly redesign iterations, even when using advanced Computer-Aided Fixture Design (CAFD) tools. Although the Model-Based Definition (MBD) paradigm offers a promising response to these information-related challenges, its adoption within the CAFD domain remains limited. This work aims to support the broader adoption of MBD in this field through a multi-level contribution. First, a structured literature review identifies the essential semantic information required in an MBD dataset tailored to CAFD. Second, this content is structured in a machine-readable form using the ISO standard STEP AP242. Third, an MBD-driven CAFD framework is proposed. Finally, a proof-of-concept CAFD tool is developed by integrating established methodologies with commercial software to automate non-value-added tasks, such as configuring Computer-Aided Technologies (CAx). The results demonstrate the potential of this approach to streamline CAFD processes and establish a fully connected digital thread.

A review and analysis of current computer-aided fixture design approaches

Fixtures are used to locate, hold and support workpieces in manufacturing operations such as machining, inspection, and assembly. Designing and fabricating fixtures can take up to 10-20% of the total cost of a manufacturing system. Fixture planning is a complex activity restricted by the extreme diversity of workpiece, product batch size, product geometry, part accessibility, and working force. Computer-Aided Fixture Planning (CAFP) has been used to improve the fixture design for over 20 years. CAFP contributes to the reduction of lead-time and human interaction in fixture planning. It helps verification of the fixture quality and integration of fixture design with CAD/CAM systems. This paper summarizes constraints of fixture planning and four phases of CAFP. Various approaches to CAFP are surveyed. Application systems of CAFP including some recent patents are reviewed. The paper concludes with the research trend of CAFP. The global competition and customer demand change lead to greater product variety, smaller product batch size, shorter production time and higher product quality. Industrial organizations have to pursue flexibility and automation in manufacturing systems to remain competitive and profitable. Flexible Manufacturing System (FMS) developed in the past decades is to meet such challenge. FMS usually consists of one or more CNC machines which are capable of machining a variety of workpieces. With the development of Computer- Aided Design and Computer-Aided Manufacturing (CAD/ CAM) technology, product design and machining program- ming have been greatly computerized. However, one of the difficulties in FMS is the fixture design for locating and securing a workpiece during manufacturing operations. Fixture planning is time-consuming as it is customized for workpieces. Computer-aided fixture planning (CAFP) aims to reduce the lead-time and human interaction in fixture planning. It can verify fixture quality to integrate fixture design with CAD/CAM systems by automating the reasoning process. The integration of CAFP with CAD/CAM has greatly reduced the production lead-time and cost for an overall optimal solution in product design and manufacturing (1). Fixtures are used to locate, hold and support workpieces in manufacturing operations such as machining, inspection, and assembly. Fixture design and manufacturing is costly due to the tight tolerance and restricted machining opera- tions. Designing and fabricating fixtures can take up to 10- 20% of the total cost of a manufacturing system. Dedicated fixtures are mostly applied in mass production to gain high efficiency. For smaller batch size, the fixture flexibility becomes more important than efficiency due to the workpiece variety and machining requirements. Flexible and

Fixture design has traditionally been regarded as a manual process due to extensive requirements of heuristic knowledge and skilled craftsmanship. There are many mathematical and scientific formulae which can be used to calculate cutting forces, deflection of structural members, tolerance analysis of locating datum, etc. However many of the good fixture design features such as ease of loading/unloading, safety considerations, ingenuity in securing the workpieces, etc come from the experience and skill of the designers. Due to the extensive requirements of heuristic knowledge and craftsmanship, the automation of fixture design has not been considered possible in the past. Recent developments in artificial intelligence techniques and, in particular, knowledge representation have provided great opportunities in automating this field.

Advances in the technology of flexible manufacturing systems, and the introduction of concurrent engineering of product and process design have propounded the need for computer aided fixture design systems. Computer aided process planning is the interface between design and manufacturing and has a key role in achieving integration between the various modules in an FMS environment. Fixture design is inseparable from process planning, and hence to be of practical use any CAPP system must include fixture design. The past few years have seen great advances in automated fixture design systems and the tools used to achieve them. With the exception of fixture design for a limited range of products with close family similarity, fully automated design of practical fixtures is not yet achievable. The advances described in this book have widened the scope of application of computer aided fixture design and provide enhanced links with other product and process design activities.

Fixture design and planning is one of the most important manufacturing activities, playing a pivotal role in deciding the lead time for product development. Fixture design, which affects the part-quality in terms of geometric accuracy and surface finish, can be enhanced by using the product manufacturing information (PMI) stored in the neutral standard for the exchange of product model data (STEP) file, thereby integrating design and manufacturing. The present paper proposes a unique fixture design approach, to extract the geometry information from STEP application protocol (AP) 242 files of computer aided design (CAD) models, for providing automatic suggestions of locator positions and clamping surfaces. Automatic feature extraction software “FiXplan”, developed using the programming language C#, is used to extract the part feature, dimension and geometry information. The information from the STEP AP242 file is deduced using geometric reasoning techniques, which in turn is utilized for fixture planning. The developed software is observed to be adept in identifying the primary, secondary, and tertiary locating faces and locator position configurations of prismatic components. Structural analysis of the prismatic part under different locator positions was performed using commercial finite element method software, ABAQUS, and the optimized locator position was identified on the basis of minimum deformation of the workpiece. The area-ratio (base locator enclosed area (%)/work piece base area (%)) for the ideal locator configuration was observed as 33%. Experiments were conducted on a prismatic workpiece using a specially designed fixture, for different locator configurations. The surface roughness and waviness of the machined surfaces were analysed using an Alicona non-contact optical profilometer. The best surface characteristics were obtained for the surface machined under the ideal locator positions having an area-ratio of 33%, thus validating the predicted numerical results. The efficiency, capability and applicability of the developed software is demonstrated for the finishing operation of a sensor cover – a typical prismatic component having applications in the naval industry, under different locator configurations. The best results were obtained under the proposed ideal locator configuration of area-ratio 33%.

Investigate on computer-aided fixture design and evaluation algorithm for near-net-shaped jet engine blade

Modular fixture is conventionally designed less concerning the detailed specifications of machine tool. A little of literatures involve the effectively application to the existing CAD systems in CAFD (computer-aided fixture design). The determination of the validity of modular fixture during NC machining lacks for a practical method. This paper put forward that: Firstly, the feature-model repository of elements of modular fixture can be built in CAD packages; the design of modular fixture in NC machining should be accomplished under the concept of NC Manufacturing System (NMS); the Post-NC verification can be applied to check the performance of modular fixture applied in NC machining. Part 1 of the paper focuses on the feature-model repository of the modular-fixture elements. The other jobs will be introduced in the Part 2.

Flexible fixturing is an essential ingredient of flexible manufacturing systems (FMS) and computer-integrated manufacturing systems (CIMS). Computer-aided fixture design (CAFD) has become a research focus in implementing FMS and CIMS. This paper, presents an overview of interactive computer software developed with CAD interface for designing fixtures for machining centers (HMC/VMC). An exhaustive set of structured queries incorporated in the preprocessor prompts the designer to extract qualitative and quantitative part features. The database and decision support system (i.e., the rule base and the knowledge base) built into the design module assist the designer to select and position locators, calculate clamping forces, decide number and types of clamps, their locations and orientations, etc. Finally, in the post processor the bill of material, part and assembly drawings are obtained. A case study for the design of fixture for a Roller-head is presented and results are discussed. The implementation of the system has proved to be a quick and effective tool that reduces the design lead time from a few days to a few hours and requires fractional efforts and expertise on the part of the designer.

Management of fixture design knowledge is vital for improving product quality and reducing product lead time, but there is no efficient and effective mechanism in current computer-aided fixture design systems to integrate fixture design process, to share design resource as well as acquisition and reuse knowledge. Ontology is increasingly seen as a key technology for enabling semantics-driven knowledge processing. On the background of a architecture of fixture design system based on knowledge introduced in the paper, we presented and expatiated a fixture design knowledge acquisition and reuse technology based on ontology, which embeds ontology in current computer-aided fixture design based on knowledge. Finally, the related case study was given.

A crucial factor in the success of developing integrated manufacturing systems lies in the ability to exchange information among the various computer-aided systems. Although a vast amount of research has been conducted on computer-aided fixture design systems, the need for information exchange between a fixture design system and other manufacturing systems has not been dealt with thoroughly. Models for the exchange of information within an enterprise or within an extended enterprise depend on the functionality and behaviour of individual enterprises. One means of developing an information model for an enterprise is to determine the information requirements by modelling the enterprise. However, this results in a monolithic model that is only applicable to that enterprise. As a solution to this drawback, we describe the development of a reference model for fixture design information support, which can be instantiated to be applied to different types of enterprises. We concentrate on machining fixtures and information form the fixture design domain to other domains.

In this paper, the manufacturing software interoperability (MSI) was investigated. The definition of manufacturing software interoperability was proposed on the definition of semantic interoperability. And, some distinctions and correlations between interoperability and integration were analysed. The interoperability problem of manufacturing software was discussed. Furthermore, the Manufacturing Software Interoperability Model (MSIM) and its supported technologies were advocated. To verify MSIM model, the primary study on interoperation between Computer Aided Process Planning (CAPP) system and computer aided fixture design (CAFD) was carried out by the Model Driven Architecture (MDA) methodology. The results showed that the layered MSIM model can be a promise of the product data exchange, sharing and reuse without data loss and corruption among applications.

Amanufacturing systemtransforms rawmaterials to final products through a series ofmanufacturing processes. Manufacturing companies are classified into process manufacturers and discrete manufacturers. A process manufacturer builds something that is not supposed to be taken apart; for example, liquid and powder products. A discrete manufacturer makes discrete goods such as screws, nuts, and handles that can be taken apart and used on something else when needed. Design variables and systemparameters in process manufacturing and discrete manufacturing are quite different. Table 8.1 gives the comparison of the characteristics of these two types of manufacturing processes (Sophen 2019).

In the current metal-forming product design and development paradigm, product cost, time-to-market, and product quality are three overriding issues, which determine the competitiveness of the developed products. In up-front design process, the first 20 % of design activities commits to more than 75 % of product development cost and product quality issues. How to conduct “design right the first time” is critical to ensure low product development cost, high product quality, and short time-to-market. To address these issues, state-of-the-art technologies are needed to support design solution generation, evaluation, and optimization in metal-forming product design and development. Traditionally, computer-aided design (CAD) and computer-aided manufacturing (CAM) technologies provide approaches for representation and realization of design solutions physically [1]. However, how to generate design solution and conduct design solution evaluation and optimization is a non-trivial issue. In metal-forming product design and development, it is difficult to simultaneously address the design issues related to metal-formed part design, forming process determination, process parameter configuration, tooling structure design, material selection, prediction of the properties of deformed part, and finally the product quality control and assurance. In addition, how to reveal, assess, and evaluate the interaction and interplay of different design variables or factors in the above-mentioned different stages and areas is another critical issue. Computer-aided engineering (CAE) technology fills this gap as it helps practitioners generate, evaluate, and optimize design solutions before the best design solution is feasibly and uniquely identified and practically and physically implemented. In the current metal-forming product development paradigm, CAE simulation technology is one of the state-of-the-art technologies, which has been widely used in addressing the above-mentioned technical issues and will be used to solve the emerging bottleneck problems in the next upward trend of technology and product development.

Appropriate fixture design could lower process time, lower cost, and improve the quality of products. This paper proposes a case-based reasoning (CBR) method, with improved indexing and retrieving approaches which are critical issues in machining fixture design systems. A case storage for fixture design case indexing approach is developed so that the database is constructed into two levels—to manage and categorize numerous related fixture designs. The data includes existing workpieces and associated fixture planning and unit depository as solutions. Based on this approach, a CBR method with a two-step case retrieval is presented. The objective is to improve searching results in database for machining fixture design. In this CBR-based fixture design method, the appropriate workpiece in the first level of database by using design requirement is found. Then, the proper conceptual fixture design can be achieved by retrieving related fixture case from the second level. This method facilitates the fixture designing by means of referencing past design cases to generate a conceptual fixture design quickly and easily. It also helps in the finishing design by suggesting some alternative fixture cases. Finally, several case studies are used to validate and present the applicability and usability of the proposed approach.