M. Zulafif Rahim

Electrical Discharge Grinding of Polycrystalline Diamond—Effect of Machining Parameters and Finishing In-Feed

Electrical discharge grinding (EDG) is becoming more prevalent in the manufacturing of polycrystalline diamond (PCD) tools. This paper concerns investigation of the effects of machining parameters, as well as finishing in-feed, to the surface quality obtained when using EDG to erode PCD. With the aid of the morphological findings, different PCD erosion mechanisms are discussed. Experimental results demonstrated that the eroded surface quality of PCD was significantly affected by the selected parameters. High temperature due to the erosion process resulted in the partial conversion of diamond to graphite phase under the surface. Higher finishing in-feed produced better surface quality and caused lower surface graphitization and lower tensile residual stress. A model for the thermal stress prediction was developed and found to have good agreement with the experimental findings.

Electrical discharge grinding of polycrystalline diamond – Effect of wheel rotation

ABSTRACT Electrical Discharge Grinding (EDG) is an advanced machining process that becomes popular in manufacturing of Polycrystalline Diamond (PCD) tools. This research investigated the effects of wheel rotation as well as debris flow direction on the quality of PCD tools based on a series of EDG experiments. Experimental results showed the debris that flowed toward the cutting edge could significantly affect the edge sharpness and symmetry of the tool, which were critical for the smaller edge apex angle. Evidence of spark concentration caused by the debris accumulation phenomenon were found through microscopic analysis on the eroded surfaces. This research also revealed the unexplained phenomenon associated with the undercut that normally formed beneath the PCD cutting edge after erosion. By examining PCD samples using scanning electron microscopy (SEM) and Raman spectroscopy, the formation of the heat-affected layer caused by the high-temperature erosion process in the EDG was analyzed. Results also proved that the surface finish of tungsten carbide (WC) and notch width of the PCD tools, particularly on the tungsten carbide WC/PCD interface, should not be taken as the index to measure PCD tool quality.

Experimental study of wheel rotating speed effect on electrical discharge grinding

Electrical discharge grinding is used to machine polycrystalline diamond layer of cutting tools, which can effectively drill composite/titanium stacks in modern aircraft frames. In the machine, an electrode wheel is rotated to accelerate debris flushing to quickly recover the dielectric fluid between a spark gap. The aim of this study was to investigate the effect of the wheel speed on polycrystalline diamond removal rate for high erosion efficiency. Multiple wheel speeds were applied in a electrical discharge grinding machine under various pulse on-times and the volumetric removal rates were calculated by the precise position feedback of this machine over the time, which was obtained by the electrical waveform of discharges. The experimental results show that the removal rate increases with the wheel speed up to a limit at the low range and then declines at the high range. This indicates that the wheel speed needs to be optimized for high erosion efficiency under various discharge conditions such as different materials and pulse on-times.

Residual Stress Analysis of Polycrystalline Diamond after Electrical Discharge Machining

The extreme hardness of Polycrystalline Diamond (PCD) makes it an ideal choice for the machining of hard materials as a cutting tool. Due to the high hardness, fabrication of PCD tools relies on conventional abrasive grinding which suffers from low machining efficiency. Electrical discharge machining (EDM) is an advanced machining process and can be utilised to fabricate complicated PCD tools. High temperature of sintering and EDM processes creates residual stress inside PCD and can result in unmatured failure of PCD tools. This paper analyses the distribution of residual stress in PCD after electrical discharge machining process.

Preliminary Design of Aerial Spraying System for Microlight Aircraft

Undoubtedly agricultural is an important sector because it provides essential nutrients for human, and consequently is among the biggest sector for economic growth worldwide. It is crucial to ensure crops production is protected from any plant diseases and pests. Thus aerial spraying system on crops is developed to facilitate farmers to for crops pests control and it is very effective spraying method especially for large and hilly crop areas. However, the use of large aircraft for aerial spaying has a relatively high operational cost. Therefore, microlight aircraft is proposed to be used for crops aerial spraying works for several good reasons. In this paper, a preliminary design of aerial spraying system for microlight aircraft is proposed. Engineering design methodology is adopted in the development of the aerial sprayer and steps involved design are discussed thoroughly. A preliminary design for the microlight to be attached with an aerial spraying system is proposed.

Effect of triggering angles on the crushing mechanisms of hybrid woven kenaf/aluminum hollow cylinders

This paper presents the effect of triggering angles constructed on the top of hybrid woven kenaf/aluminium hollow cylinders on the energy absorption performances. The crushing performances of aluminium tubes can be found widely in open literature. However, lack number of work on the hybridizing the aluminium tubes with woven kenaf fibre is found. Woven kenaf mats are produced and bathed with polymeric resin before they are wrapped around the aluminium tubes twice. Different fibre orientations, +-θ° are used where θ = 0, 15, 30 and 45. Once the hybrid composite hardened, one of their end are chamfered using different angles of 0o, 30o, 45o and 60o. The tubes are quasi-statically compressed in order to obtain their force-displacement responses and crashworthiness parameters are extracted and discussed with the relation of fibre orientations and chamfering angles. It is found that the chamfering angles are only affected the force-displacement curves during the first stage of elastic deformation whereas there is no obvious effect in the second stage. However, varying the fibre orientations are slightly increased the force-displacement curves especially when the fibre is orientated with 30o. Based on the fracture mechanism observations, most of composite experienced large fragmentation indicating that the composites absorbed the crushing energy ineffectively.

Numerical modelling of steel tubes under oblique crushing forces

This paper presents the numerical assessment of crushing responses of elliptical tubes under crushing forces. Based on the literature survey, tremendous amount of works on the axial crushing behaviour can be found. However, the studies on the oblique crushing responses are rarely found. Therefore, this work investigates numerically the elliptical tubes under compressions. The numerical model of the tubes are developed using ANSYS finite element program. Two important parameters are used such as elliptical ratios and oblique angles. The tubes are compressed quasi-statically and the force-displacement curves are extracted. Then, the area under the curves are calculated and it is represented the performances of energy absorptions. It is found numerically that the introductions of oblique angles during the crushing processes decrease the crushing performances. However, the elliptical-shaped tubes capable to enhance the energy absorption capabilities. On the other hand, the elliptical-shaped tubes produced the enhancement on the energy absorption capabilities.

Combined mode I stress intensity factors of slanted cracks

The solutions of stress intensity factors of slanted cracks in plain strain plate are hard to find in open literature. There are some previous solutions of stress intensity factors available, however they are not studied completed except for the case of plain stress. The slanted cracks are modelled numerically using ANSYS finite element program. There are ten slanted angles and seven relative crack depths are used and the plate containing cracks is assumed to fulfil the plain strain condition. The plate is then forced uni-axially the stress intensity factors are determined according to the displacement extrapolation method. Based on the numerical analysis, it is found that slanted angles have inverse effects on the behaviour of stress intensity factors. Increasing such angles capable to reduce the mode I stress intensity factors. On the other hand, it is also enhanced the capability of mode II stress intensity factors at the crack tip. Due to difficulty of determining stress intensity factors numerically, a regression technique is used to formulate mathematical expressions which are capable to predict the stress intensity factors in reasonable accuracies.

Electrical discharge machining of polycrystalline diamond using copper electrode – finishing condition

Research on machining process of Polycrystalline Diamond (PCD) is becoming important as the material was believed suitable to be used for cutting tools of advanced aeronautical structure. Electrical Discharge Machining (EDM) was regarded as the suitable method to machine PCD due its noncontact process nature. The objective of this research is to determine the influence of several EDM parameter such as sparking current, pulse duration, and pulse interval to the material removal rate and surface roughness of the machined PCD. Instead of significantly influenced the material removal rate, the sparking current was also highly influenced tha surface roughness. Highest material removal rate of approximately 0.005mm3/s was recorded by the EDM process with the highest current used of 5A, and lowest pulse interval of 1μs. The influence of pulse duration is not clearly seen at the lowest pulse interval used. On the other hand, 0.4μm was the lowest surface roughness value obtained in this research indicated by the highest sparking current, highest sparking duration and lowest sparking interval of 5A, 1μs and 1μs respectively.

Preliminary Study on Kano Model in the Conceptual Design Activities for Product Lifecycle Improvement

Product manufactured with short life cycle had only one major issue, it can lead to increasing volume of waste. Day by day, this untreated waste had consumed many landfill spaces, waiting for any possible alternatives. Lack of product recovery knowledge and recyclability features imprinted into product design are one of the main reason behind all this. Sustainable awareness aspect should not just be implied into peoples mind, but also onto product design. This paper presents a preliminary study on Kano model method in the conceptual design activities to improve product lifecycle. Kano model is a survey-type method, used to analyze and distinguished product qualities or features, also how the customers may have perceived them. Three important attributes of Kano model are performance, attractive and must-be. The proposed approach enables better understanding of customer requirements while providing a way for Kano model to be integrated into engineering design to improve products end-of-life. Further works will be continued to provide a better lifecycle option (increase percentage of reuse, remanufacture or recycle, whereby decrease percentage of waste) of a product using Kano model approach.