Fixture Configuration Design Research Articles

Static interactions of surface contacts in a fixture–workpiece system

Static indeterminacy and frictional constraint nonlinearity are common problems encountered in fixture configuration design. In a fixture–workpiece system, the behaviour of contact is influenced by a combination of geometrical, kinematic and elastic relationships. Our objective is to determine clamping force intensities for a given layout of fixels by investigating contact force distribution. In this paper, we present a numerical procedure to accurately determine clamping forces required to satisfy fixturing requirements with good computational efficiency. A system of virtual springs is used to illustrate the states of contact restraints at locating and clamping points. The differences between manual clamping and power clamping are investigated and analysed theoretically. A cone set of virtual springs is introduced to model a frictional contact. We then develop a linear programming model to find a set of minimum clamping force intensities, and to identify their feasible directions for increments. Examples are also given to demonstrate the procedure.

Robust Design of Fixture Configuration

The paper deals with robust design of fixture configuration. It aims to investigate how fixture element deviations and machine tool volumetric errors affect machining operations quality. The locator position configuration is then designed to minimize the deviation of machined features with respect to the applied geometric tolerances.The proposed approach represents a design step that goes further the deterministic positioning of the part based on the screw theory, and may be used to look for simple and general rules easily applicable in an industrial context.The methodology is illustrated and validated using simulation and simple industrial case studies.

Analysis and optimization of fixture under dynamic machining condition with chip removal effect

Dynamic interactions in the tool---workpiece and workpiece---fixture systems significantly impinge on the quality of finished workpieces. The presented simulation system integrates the effects of workpiece fixture dynamics with the other factors contributing to the machining process dynamics. It provides more accurate prediction of the process output which helps in the design of the optimum fixture configuration prior to the production stage. Modelling of the frictional contact behaviour between the fixture element and the workpiece helps to improve the prediction accuracy of the simulation system which accelerates the convergence to the optimum fixture configuration design and consequently improves the machined part dimensional accuracy and geometric integrity. The developed simulation is capable of modelling complicated part geometries by interfacing with commercial ANSYS.V10® packages. This research work minimizes the deformation of workpiece using integrated optimization tool of Genetic algorithm (GA) and ANSYS Parametric Design Language (APDL) of finite element analysis. The same layouts given by the above optimization tool are used in the experimental setup and it is found that the improved geometric tolerance of squarness and flatness of the given workpiece. The chip removal effect and frictional contact between the workpiece and the fixture elements are taken into account based on element death technique and nonlinear finite-element analysis. A Case study of an open slot milling process illustrates the application of the proposed improved geometric tolerance approach.

Study of Computer-Aided Design Process and Methods Based on Welding Fixture

Although various computer-aided fixture design (CAFD) systems have been developed to assist the designer during the various stages of fixture design, most of previous computer aided fixture design research has mainly concentrated on machining fixtures rather than welding fixtures. The development of complicated computer aided welding fixture design (CAWFD) system has received much less attention. Welding fixture can ensure welding dimension, improve assembly precision and efficiency. It can prevent the welding deformation. The function of welding fixture was introduced in this paper. The computer-aided welding fixture design workflow was developed. The design steps include the project creation, setup design, Orientation and position determination, fixture plan design, fixture configuration design, fixture design verification and fixture design output. The classification of welding fixture component has been demonstrated. Information tree and the database tables to save the unit information are designed. The unit information retrieval menu and interface based on UG, Visual C++ and database is realized.

Machining fixture layout design using ant colony algorithm based continuous optimization method

In any machining fixture, the workpiece elastic deformation caused during machining influences the dimensional and form errors of the workpiece. Placing each locator and clamp in an optimal place can minimize the elastic deformation of the workpiece, which in turn minimizes the dimensional and form errors of the workpiece. Design of fixture configuration (layout) is a procedure to establish the workpiece–fixture contact through optimal positioning of clamping and locating elements. In this paper, an ant colony algorithm (ACA) based discrete and continuous optimization methods are applied for optimizing the machining fixture layout so that the workpiece elastic deformation is minimized. The finite element method (FEM) is used for determining the dynamic response of the workpiece caused due to machining and clamping forces. The dynamic response of the workpiece is simulated for all ACA runs. This paper proves that the ACA-based continuous fixture layout optimization method exhibits the better results than that of ACA-based discrete fixture layout optimization method.

A desktop virtual reality-based interactive modular fixture configuration design system

Modular fixture configuration design is a complicated task requiring strong professional background and practical experience. However, automated or semi-automated computer aided modular fixture systems based on CAD packages still are not well accepted by the manufacturing industry due to the lack of intuitive interaction and immediate feedback compared with traditional models such as paper and physical models. In this paper, a novel Virtual Reality-based system for interactive modular fixture configuration design is presented. We use a multi-view based modular fixture assembly model to assist information representation and management. In addition, the suggested strategy is compatible with the principles of virtual environment and it is easy to reutilize the element model. Based on geometric constraints, we propose a precise 3D manipulation approach to improve intuitive interaction and accurate 3D positioning of fixture components in virtual space. Thus, the modular fixture configuration design task can precisely be performed in virtual space.

Towards the development of a desktop virtual reality‐based system for modular fixture configuration design

PurposeModular fixture configuration design is a complicated task requiring both intensive knowledge and experience. Automated or semi‐automated computer‐aided modular fixture systems based on computer‐aided design packages do not appear to have made a significant impact within the manufacturing industry. Modular fixture designers still prefer traditional systems such as paper or physical model; as such models provide a more intuitive interaction and immediate feedback. The objective of the paper is to present an application of the desktop virtual reality (VR) to develop an interactive modular fixture assembly design system.Design/methodology/approachDesktop‐based friendly interface is designed and the low‐system requirement key techniques, namely assembly modeling and collision detection approach, to make proposed system run smoothly on a desktop PC, are presented.FindingsThe paper finds that the proposed system is an efficient tool for modular fixture configuration design.Practical implicationsThe proposed system is a portable and affordable solution for modular fixture design.Originality/valueA low‐cost VR application for modular fixture configuration design is presented.

Dynamic analysis on optimal placement of fixturing elements using evolutionary techniques

In the design of a machining fixture configuration (layout), the stability of the fixture, which influences the dimensional and form accuracy of the workpiece, is an important factor. The optimal placement of the fixturing elements minimizes the dynamic response of the workpiece (elastic deformation of the workpiece under dynamic conditions), which in turn improves the stability of the fixture. In this paper, an Ant Colony Algorithm (ACA) and Genetic Algorithm (GA) are employed to optimize the fixture layout with an objective of minimizing the dynamic response of the workpiece. The different node systems are used on the same workpiece geometry, and the fixture layout is optimized so that the elastic deformation of the workpiece satisfies the accuracy needed on the workpiece. Two different examples are used to compare the performance of ACA- and GA-based fixture-layout optimization methods.

Precise manipulation approach to facilitate interactive modular fixture assembly design in a virtual environment

PurposeThe virtual design environment offers users an opportunity to interact with a virtual prototyping rather than physical models and to build a fixture configuration in a realistic way. But the virtual reality (VR) environment tends to be inaccurate because humans have difficulty in performing precise positioning tasks. Therefore, it is necessary to implement precise object manipulation methods for assembly and disassembly activities, so that users can perform modular fixture configuration design efficiently in VE. The purpose of this paper is to develop a VR‐based modular fixture assembly design system, which supports the design and assembly of modular fixture configuration in a virtual environment.Design/methodology/approachGeometric constraint‐based method is utilized to represent and treat the assembly relationship between modular fixture elements. The paper presents a hybrid method of rule‐based reasoning and fuzzy comprehensive judgment to capture the user's operation intent and recognize geometric constraint. Through degrees of freedom based analysis, a mathematical matrix is presented for representing and reducing allowable motion of fixture elements, and a constraint‐based motion navigation approach is proposed to ensure that the manipulation of a fixture component not violate that the existing constraints.FindingsThe paper finds that the proposed techniques are applicable to the convenient manipulation and accurate positioning of fixture elements in a virtual environment.Practical implicationsComponent manipulation plays a key role in interactive virtual assembly design. The proposed approach in this paper enables interactive assembly design of modular fixture in virtual environment.Originality/valueThis paper presents a geometric constraint‐based approach that realizes automatic assembly relationship recognition, constraint solving and motion navigation for interactive modular fixture assembly design in a virtual environment.

Computer-aided generation of fixture configuration design using polychromatic sets

This paper presents a new approach to the generation of fixture configuration design in manufacturing. First of all, the concept of polychromatic sets is introduced. Then the polychromatic set approach to the generation of fixture configuration design is proposed. This approach first identifies the relationship between fixture elements and then derives a contour matrix and its corresponding Boolean matrix. Furthermore, feasible paths and final alternatives to the fixture configuration design are found using the theory of polychromatic sets. A fixture configuration design example is used to illustrate the approach.

Machining fixture layout optimization using FEM and evolutionary techniques

Design of fixture configuration (layout) is a procedure to establish the workpiece fixture contact through positioning of clamps and locating elements such that the workpiece elastic deformation is minimized. This work is done based on the assumption that the workpiece is an elastic body. Since the fixture layout influences the dimensional and form accuracy of the workpiece during the machining process, the fixture layout has to be optimized to minimize the workpiece deformation. In this paper, the workpiece deformation is modeled using finite element method (FEM), for the problem of fixture layout optimization problems with the objective of minimizing the dimensional and form errors. This paper presents a fixture layout optimization method that uses genetic algorithm (GA) and ant colony algorithm (ACA) separately. In this paper, three different number of node systems are defined on the same workpiece geometry to find the consistency in the performance of GA and ACA. The optimal solution, i.e., the most minimum value among the entire possible layout is determined separately for all three different number of node systems. The solution obtained for each node system using GA and ACA is compared with their respective optimal solution separately and ACA reports faster and accurate solutions.

Solving a fixture configuration design problem using genetic algorithm with learning automata approach

Proper fixture design is crucial to workpiece quality assurance in manufacturing. Incorrect fixture design may lead to workpiece deformation during machining. The fixture configuration design is one of the important aspects of fixture design. This paper deals with fixture layout optimization problem. The objective is to minimize the norm of all the passive contact forces satisfying Coulomb friction constraint, work-piece static equilibrium constraint and contact constraint, for the entire cutting operation. To solve this problem, the paper proposes Genetic Algorithm with Learning Automata (GALA) algorithm, which is a population based interconnected learning automata algorithm incorporating genetic operators. The algorithm enjoys the good characteristics of both GA and LA. It is validated with an example of face milling operation. The optimal layout is found to be in tune with empirical facts. Also, for the further investigation of the algorithm, it has been tested on a different problem sets and a comparative study is carried out.

Automatic Modular Fixture Generation in Computer-Aided Process Planning Systems

Fixturing is the most commonly used manufacturing constraint in setup planning. The computer-aided fixture design technique is being rapidly developed to reduce the lead-time involved in manufacturing planning. An automated fixture configuration design system has been developed to select modular fixture components automatically and place them in position with satisfactory assembly relationships. In this paper, an automated fixture generation system for prismatic components is presented. Sequential steps for automatic fixture layout planning for machining setups, focusing on determining the most suitable locating and clamping positions in accordance with the 3-2-1 configuration, considering geometrical and dimensional constraints are presented. A software has been developed which takes two-dimensional-manufacturing drawings of the prismatic components as input and generates fixture design automatically. The modularity concept is incorporated in the developed software application and enables locating positions to be as wide apart as possible. The clamping positions are obtained directly opposite to the respective locators as far as possible. The software is tested successfully with numerous examples of prismatic parts involving similar design characteristics.

Experimental determination of the friction coefficient on the workpiece-fixture contact surface in workholding applications

Surface flatness, geometric integrity and micro-surface finish characteristics are crucial for automotive industry to properly seal joints, reduce leakage and consequently increasing engines efficiency and reducing emissions. Optimum fixture layout is a key element in achieving this goal. Machining of flexible parts impose further challenges to the selection of a proper fixture scenario. Workpiece motion arising from localized elastic deformation at the workpiece/fixture contacts due to machining and clamping forces significantly affect the workpiece location accuracy and hence the machined part quality. The tangential friction force plays an important role in fixture configuration design as it can be utilized to reduce the number of fixture components, thereby the workpiece features accessibility to machining operations and providing a damping mechanism to dissipate input energy from machining forces out of the workpiece/fixture system. Although the literature is full of research on friction and its application, it lacks research that relates to the contact found in workpiece/fixture systems. This paper presents the results of an experimental investigation of the workpiece/fixture contact characteristics.

Effect of workpiece/fixture dynamics on the machining process output

Selection of fixturing system parameters is a very important part of any manufacturing process. These parameters become more important when machining flexible parts, as the classical trial-and-error approach used in industry leads to more scrapped parts before reaching an acceptable fixture scenario. The presented simulation system integrates the effects of workpiece/fixture dynamics with the other factors contributing to the machining process dynamics and stability. It provides more accurate prediction of the process output, which helps in the design of the optimum fixture configuration prior to the production stage, consequently reducing both cost and lead time. Modelling of the frictional contact behaviour between the fixture element helps improve the prediction accuracy of the simulation system which accelerates the convergence to the optimum fixture configuration design and consequently improves the machined part dimensional accuracy and geometric integrity. The developed simulation is capable of modelling complicated part geometries by interfacing with commercial packages. The workpiece/fixture frictional contact is modelled using the finite element method. The frictional characteristics of the contact were determined experimentally. Face milling was used as a case study. Simulation results showed good agreement with the experimental validation.

Fixture Configuration Design for Sheet Metal Assembly with Laser Welding: A Case Study

The role of assembly fixtures is gaining importance in order to meet the special requirement of metal fit-up for sheet metal assembly with laser welding. Fixture configuration methodologies based on a new proposed locating scheme have been developed. In order to demonstrate the feasibility of the proposed fixture design principles in industrial applications, an industrial case study with cross-members assembly is presented. In order to obtain a physical model with the actual tolerances, reverse engineering technologies are employed for geometric modelling of the assembled parts. For achieving modelling accuracy a CMM-based finite-element model is produced and performance characteristics of the 3D features obtained. In the case study, the assembly weld patterns are designed first, to determine the weld locations. Then the general design, the deterministic optimisation and the robust design of the fixture configuration are carried out sequentially. The results of the case study show that the proposed fixturing principles are applicable and effective.

Machining fixture verification for linear fixture systems

This paper presents a fixture configuration verification methodology that takes into account dynamic machining conditions--including the effect of dynamic gravitational forces--in the verification process. The fixture verification system is modelled as a linear optimization problem with respect to minimum clamping forces. The method provides a simple and effective means for (a) verifying whether a particular fixturing configuration is valid with respect to locating stability, deterministic workpiece location, clamping stability and total restraint; (b) identifying which locator loses contact with the part for an invalid fixture configuration; (c) identifying which clamp needs to be replaced; and (d) determining the minimum clamping forces to restrain the piece during the entire machining process. Since a fixture configuration design is validated not only under a given cutting direction, but also under an inverse cutting direction, this allows designers to understand thoroughly whether the fixture configuration is valid and what the sufficient dynamic clamping forces are for the fixture system to withstand unpredicted machining forces over the entire machining time. Hence, it makes the verification system more robust and reliable. Two case studies are included to demonstrate the effectiveness and the capabilities of the methodology.

Principle and Simulation of Fixture Configuration Design for Sheet Metal Assembly with Laser Welding, Part 2: Optimal Configuration Design with Genetic Algorithm

A fixture plays a key role in ensuring proper metal fit-up in sheet metal assembly with laser welding. In this paper, an optimal fixture configuration design model is proposed based on a new locating scheme which includes both total locating and direct locating on welds. In this model, both the number and the location of the concerned locators are taken as objectives. The proposed prediction and correction method is used for determining the number of direct locators, and a pattern sorting method is developed for determining the number of total locators. Considering the degree of metal fit-up (DMF) to be a fuzzy quantity, a feasible evaluation criterion of DMF is also developed using a fuzzy synthesis evaluation method. A powerful optimisation technique - genetic algorithm - is employed as the optimisation procedure. A case study is presented which demonstrates the effectiveness of the optimal model, and the degree of metal fit-up can be improved compared to the initial locating scheme.

Principle and Simulation of Fixture Configuration Design for Sheet Metal Assembly with Laser Welding, Part 1: Finite-Element Modelling and a Prediction and Correction Method

The quality of the stamping process has a direct effect on laser welded sheet metal assembly. The fixture plays an important role in the satisfactory metal fit-up that laser welding requires. The traditional “3-2-1” locating scheme will no longer suffice for the deformable laser sheet metal assembly process. Because of the often poor stamping quality, a complex die fixture has to be employed to meet the metal fit-up requirements. The die fixture corresponds to an “infinite-2-1” locating scheme where the tooling cost is very high and yet lacks flexibility. This limits the application of laser welding. In this paper, a new locating scheme with both total locating and direct locating for welds is proposed. A total locating scheme is used to locate the overall assembly, and a direct locating scheme is used to locate the weld location, which is critical for ensuring correct metal fit-up. A finite-element model and a prediction and correction method for the direct locator configuration are developed in this paper. A case study is used to show that the proposed method is effective for sheet metal assembly for laser welding.

Fixturing surface accessibility analysis for automated fixture design

Fixturing is an important manufacturing activity in the production cycle. The computer-aided fixture design (CAFD) technique has been developed and become part of CAD/CAM integration. CAFD consists of three major aspects: setup planning, fixture planning, and fixture configuration design. An automated modular fixture configuration design system has been developed and applied to industrial practice. This paper focuses on a technical problem involved in the development of automated fixture planning systems, that is, the accessibility analysis of a fixturing surface on workpiece. The fixturing surface accessibility should be correctly assessed to reflect the extent of ease to place a fixture component in contact with the fixturing surface. The objective of accessibility analysis is to help the fixture planning fulfill the optimum selection of fixturing surfaces and points on workpiece. Firstly, several basic criteria for evaluating the eligibility of a surface being a preliminary candidate fixturing surface are discussed. Secondly, by applying a discretization technique, an accessibility model of fixturing surfaces is established based on an overall evaluation of the accessibility of discrete points on the surface. Finally, the implementation issue and a analysis/ design example are presented.