Optimal Robust Fixture Configuration Design Using Computer Experiment

A new FEA based design approach of optimal robust fixture configuration is proposed in this paper, which employs a surrogate model through computer experiment to significantly reduce the intensive computing effort involving numerous FEA system response evaluations. The effects of the fixture variability to the workpiece performance variability are assessed through an efficient robustness evaluation method, First Order Reliability Method (FORM), based on the surrogate computer model. Not restricted to primary datum surface, this new approach enables simultaneous determination of robust locator/clamp locations and clamping forces for a deformable workpiece and thus captures interaction between locating and clamping. The effectiveness of this approach is illustrated though an application example. The results of robustness analysis reveal new information and suggest that the optimal solution resulted from deterministic optimization may not be the best solution when the design is subjected to variability.

Time and Frequency Domain Investigation of the Static and Dynamic Characteristics of Micro-Drilling

In this paper, the dynamic characteristics of micro-drilling process under different cutting conditions and the resulting correlation to tool wear have been studied. Two types of drills, three spindle speeds and two kinds of workpiece materials were used. In-process cutting forces and accelerations were measured. The signals were analyzed in both the time and frequency domains. Some interesting phenomena were observed in the dynamic time-history response during drilling. Progressive functions with the proper order were obtained to describe the curve of the average thrust force with the number of the holes drilled. Dynamic features which were sensitive to tool wear were found. The changing trends of these dynamic features as the drill wear progresses show a feasibility to develop an on-line drill wear monitoring system by evaluating the changes in dynamic features.

Investigation of the Spark Cycle Effect on Material Removal Rate in Wire Electrical Discharge Machining

The development of new, advanced engineering materials and the needs for precise and flexible prototype and low-volume production have made wire electrical discharge machining (EDM) an important manufacturing process to meet such demand. This research investigates the effect of spark on-time duration and spark on-time ratio, two important EDM process parameters, on the material removal rate (MRR) and surface integrity of four types of advanced material: porous metal foams, metal bond diamond grinding wheels, sintered Nd-Fe-B magnets, and carbon-carbon bipolar plates. An experimental procedure was developed. During the wire EDM, five types of constraints on the MRR due to short circuit, wire breakage, machine slide speed limit, and spark on-time upper and lower limits have been identified. An envelope of feasible EDM process parameters is created and compared across different work-materials. Applications of such process envelope to select process parameters for maximum MRR and for machining of micro features are presented.

Quintic Spline Interpolation With Minimal Feed Fluctuation

This paper presents a parameterization and an interpolation method for quintic splines, which result in a smooth and consistent feedrate profile. The discrepancy between the spline parameter and the actual arc length leads to undesirable feed fluctuations and discontinuity, which elicit themselves as high frequency acceleration and jerk harmonics, causing unwanted structural vibrations and excessive tracking error. Two different approaches are presented that alleviate this problem: The first approach is based on modifying the spline toolpath so that it is optimally parameterized with respect to its arc length. The second approach is based on scheduling the spline parameter to accurately yield the desired arc displacement (i.e. feedrate), either by approximation of the relationship between the arc length and the spline parameter with a feed correction polynomial, or by solving the spline parameter iteratively in real-time at each interpolation step. The two approaches are compared to nearly arc length parameterized C3 quintic spline interpolation in terms of feedrate consistency and experimental tracking accuracy.

Tolerance Analysis and Synthesis for Composite Assemblies of Resin Transfer Molded Components

With the increasing demand for composite products to be affordable, net-shaped and efficiently assembled, tight dimension tolerance is critical. Due to lack of accurate process models, dimension analysis and control for resin transfer molding (RTM) processes are often performed using trial-and-error approaches based on engineers’ experiences or previous production data. Such approaches are limited to specific geometry and materials and often fail to achieve the required dimensional accuracy in the final products. This paper presents an innovative dimension variation prediction approach. First a dimension variation model was developed based on process simulation, the classical laminate theory (CLT) and finite element analysis (FEA). The FEA-based dimension variation model was validated against experimental data. The deformations of common features in typical composite structures were analyzed using the FEA-based dimension variation model. Design parameters were identified and the regression-based dimension variation model was developed. The model provides a fast, practical and proactive tool to predict and control dimension variations in RTM processes. The structural tree method (STM) is presented for design optimization and tolerance analysis/synthesis of composite assemblies.

Development of a Course on Product Design for Environment

This paper outlines the development of a senior undergraduate course concerned with product design for environment. The course sits alongside other well established courses devoted to product design for manufacture and assembly and is aimed at giving students experience of the use of evaluation procedures that enable the environmental impact of products to be taken into account during product design. The course is partially project based and culminates in the students working in small groups to evaluate existing products. Based on this evaluation design changes are developed for improved environmental performance, including ease of recycling.

Experiences of Teaching “Life Cycle Design” Course at Tokyo Metropolitan University

This paper describes the outline of “life cycle design” course the author teaches and illustrates some experiences and findings with results of questionnaires to attendees of the lecture. “Life cycle design” is a half-year course to third-year students at Tokyo Metropolitan University, Japan. The main subject is environmentally conscious design focusing on life cycle thinking. This course intends to establish general and correct viewpoints toward relationship between manufacturing industry and the environmental issues, which are indispensable knowledge as mechanical engineers, rather than to educate environmental specialists. Results of questionnaires indicate that this course succeeded in increasing students’ interest in this area and awareness of importance of the environmental issues. However, some students feel bewildered because of wide variety of topics and, therefore, lack of a central theory.

Contour Controller Design for Cubic Parallel Machine Tool

In machining processes, contouring accuracy is usually more important than tracking performance. In order to reduce the contour error, there have been many contour control algorithms for conventional machine tools, which noticeably improve their contouring accuracy. However, the available contour control algorithms cannot be directly applied to the parallel machine tools. The dynamic characteristics of the parallel machine tools are not consistent inside workspace and unsymmetrical disturbances can be imposed on any axis. Due to these, mismatched dynamics cause unwanted contour error. In this paper, we present a contour control algorithm for the cubic parallel machine tool that employs the parallel mechanism for its moving table, which can be also applied to a general parallel manipulator. The contour error estimation method for free-formed curve trajectory is proposed and the relation between the contour error vectors in joint and Cartesian spaces is considered. In order to show the validity of the algorithm, the contour control simulations and experiments are made for various contour trajectories with the cubic parallel machine tool. The results show that the proposed controller reduces the contour error considerably both in joint and Cartesian spaces.

Development of a Reference Enterprise Model for Fixture Design Information Support in Integrated Manufacturing

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.

Convertibility and Productivity of Manufacturing System Configurations

Conversions between different products manufactured on the same system often require time-consuming shut-downs and thus, incur productivity losses. Producing multiple products on the same line complicates system productivity analysis because production rates, failure rates, and repair rates vary between different part types. Certain manufacturing system configurations have advantages when convertibility is considered. Ideally, manufacturing lines that produce a mix of products or undergo a product rollover would not see any loss in production relative to lines that continuously produce a single product throughout the system lifetime. This paper investigates the interactions between convertibility and productivity for different manufacturing system configurations, using analytical methods. The methods presented in this paper can be applied to assembly or machining stations in dedicated, flexible, or reconfigurable manufacturing systems. When designing such systems, it is important to recognize that more convertible systems are more productive over the long-term, as product designs change.