S. H. Yeo

Processing of Zirconium-Based Bulk Metallic Glass (BMG) Using Micro Electrical Discharge Machining (Micro-EDM)

A zirconium-based bulk metallic glass was machined by micro electrical discharge machining (micro-EDM) to demonstrate its feasibility under discharge energies typical of the microregime. Furthermore, input energies of 13.4 µJ and 0.9 µJ, and three different tool electrodes, namely, tungsten rod electrode, copper, and brass tube electrodes were employed to elucidate the effects of different machining conditions on the machined surface roughness, burr width, and tool wear. Experimental results showed that using the lower input energy reduced surface roughness by 43%–51% and burr width by 63%. Moreover, results also suggested that, at lower input energies, tube electrodes experienced lower tool wear ratios than rod electrodes.

GRINDING OF NICKEL-BASED SUPER-ALLOYS AND ADVANCED CERAMICS

This paper studies grinding of Inconel 718, Hastelloy, and some advanced ceramics. A newly developed ultra-high-speed grinding machine and a conventional grinding machine were used for the experiments. The ultra-high-speed grinding machine is equipped with a specially designed and built spindle unit that can run up to 200 m sec−1 and deliver a maximum output of 12 kW. The surface roughness and residual stress values of the ground super-alloys and advanced ceramics were measured using a profilometer and a residual stress analyzer, respectively. The ground surfaces were also assessed using a scanning electron microscope. The effect of h m (undeformed chip thickness) on surface topography of the difficult-to-machine materials was also investigated. A higher grinding wheel speed produces a smaller cutting depth and undeformed chip thickness, and thus smaller grinding force, decreased residual surface stress, and better surface finish. High productivity and good surfaces with ductile streaks could be obtained by employing ultra-high-speed grinding, even at very large wheel depths of cut such as 400 μm, without cross feed.

Process sequence optimization based on a new cost–tolerance model

Identification of the optimal production sequence and allocation of machining tolerance are important activities in process planning for reducing production cost. This paper presents an approach that is capable of determining the optimal production sequence and its optimal process tolerance to achieve the minimum production costs. A new mathematical model, representing the cost–tolerance relationships and showing significant accuracy improvement over existing models, is introduced to allocate process tolerance. Stock allowance constraints on the selected switching tolerance are also considered to yield practical solutions. A prototype system for hole-making components is used to verify and evaluate the effectiveness of the new approach.

A cost-tolerance model for process sequence optimisation

This paper concerns the modelling of cost-tolerance data for various manufacturing processes and the optimisation of process sequences based on minimum production cost. A natural spline model representing the cost-tolerance relationship is introduced. A methodology to optimise the process sequences is developed using an expert system approach. An example to illustrate the methodology and the optimisation model is presented

A rule-based frame system for concurrent assembly machines

The aim of this research is to develop a rule-based frame system for printed circuit board (PCB) assembly to generate the component feeder arrangement and placement sequence for concurrent chip placement machines. A knowledge base of frames, assertions and rules are used in the methodology to solve the PCB assembly process of SMT components. The system has been implemented using an AI programming environment, GOLDWORKS®. A heuristic approach is used to minimize placement cycle time in PCB assembly. The objective of the solution method is to reduce theX-Y table displacement, movement and component feeder translation movement. Such a system is aimed at obtaining good solutions to the problem as illustrated by an example.

A Feasibility Study on the Micro Eletro-Discharge Machining Process for Photomask Fabrication

A feasibility study of micro electro-discharge machining (micro-EDM) technology has been conducted for its possible contri-bution in the photomask industry. A series of experimental runs was performed on three specimens using a micro-EDM system with built-in wire electro-discharge grinding. Different thicknesses of chromium films were coated on borosilicate glass substrates. Unwanted chromium metal was machined through to the transparent glass substrate, leaving behind the desired pattern. In this study, lines were machined at different voltages, using electrodes of 20 _m in diameter, and no significant wear of electrodes was observed. The machined regions on the specimens were quantified in terms of linewidth deviation and light transmission. The experimental results showed that the linewidth deviations for all three specimens are below the 10% cut-off threshold. The best average light transmission obtained from this experiment was 75.8% at 90 V. The results gathered so far, suggests that the application of micro-EDM to produce a photomask is an acceptable process.

Knowledge-based systems in the machining domain

The purpose of the research work described here is to develop an interactive and user-friendly system to assist shopfloor personnel in the selection of suitable machining conditions and cutting tools. The authors describe a new approach which involves the use of an expert-system development tool for the problem domain of machinability-data selection, with particular reference to turning processes. It employs a frame-based knowledge-representation scheme. The systems knowledge base can be easily updated and modified with the ultimate aim of providing a sophisticated, yet practical, knowledge-acquisition module so as to provide a realistic solution. The problem is formulated in a manner which allows the application of a simple, effective heuristic to find good results.

Kinematic analysis and design optimization of a cable-driven universal joint module

Cable-driven parallel manipulators (CDPMs) are a special class of parallel manipulators that are driven by cables instead of rigid links. So CDPMs have a light-weight structure with large reachable workspace. The aim of this paper is to provide the kinematic analysis and the design optimization of a cable-driven 2-DOF module, comprised of a passive universal joint, for a reconfigurable system. This universal joint module can be part of a modular reconfigurable system where various cable-driven modules can be attached serially into many different configurations. Based on a symmetric design approach, six topological configurations are enumerated with three or four cables arrangements. With a variable constrained axis, the structure matrix of the universal joint has to be formulated with respect to the intermediate frame. The orientation workspace of the universal joint is a submanifold of SO(3). Therefore, the workspace representation is a plane in R2. With the integral measure for the submanifold expressed as a cosine function of one of the angles of rotation, an equivolumetric method is employed to numerically calculate the workspace volume. The orientation workspace volume of the universal joint module is found to be 2π. Optimization results show that the 4-1 cable arrangement produces the largest workspace with better Global Conditioning Index.

TEMPERATURE DEPENDENCE OF MR FLUIDS

The rheological properties of MR fluids, MRF-132LD, are investigated under the steady shear and oscillatory shear for a range of operating temperatures from 20°C to 60°C. This was accomplished by using an advanced rheometer with the parallel-plate configuration. Under the steady shear, the Herschel–Bulkley model is used to model the rheology of the MR fluid. The corresponding parameters namely, τyd, K and n were determined at various temperatures, in an attempt to minimize the discrepancies between the experimental results and that predicted by the model. The results show that τyd, K and n all show decreasing trend with temperature. The results suggest that the MR fluid get thinner with increasing temperatures. Under the oscillatory shear, viscoelastic properties of the MR fluid were studied in the frequency sweep mode. The storage modulus, G′, decreases with increasing temperatures in both the linear viscoelastic region and the nonlinear viscoelastic region. In addition, two critical frequencies, ωcr and ωm, were identified in the latter region. They were found to decrease with increasing temperatures. Finally, thermodynamics are used to explain temperature dependence of MR properties.

Assessment of Health Hazards in Production of Printed Paper Packages

This paper discusses the health hazards faced in a company which produces printed paper packaging. The analysis is based on three main production processes, namely, printing, plate-making and washing. The components in the emissions of these processes are broken down into their chemical compositions and given a hazard rating. The analytic hierarchy process in the health hazard scoring system is introduced to evaluate the level of hazard of each process to the environment. When the hazard level encountered in each process is known, the necessary precautions and measures can be taken.