Swee-Hock Yeo

On the effects of ultrasonic vibrations on localized electrochemical deposition

This paper studies the effects of ultrasonic vibrations on the localized electrochemical deposition (LECD) process. Nickel micro-columns were locally electrodeposited onto a copper substrate from a nickel sulphamate solution using a non-soluble platinum counter electrode, both with and without ultrasonic vibrations. Three output parameters were investigated in the experiments: rate of deposition, concentricity and porosity of the micro-columns. Results showed that generally, ultrasonic vibrations increased the rate of deposition and improved the concentricity of the fabricated micro-columns. On the other hand, it gives rise to structures with higher porosity as compared to those deposited in the absence of ultrasound. The application of ultrasonic vibrations in the LECD process is a novel effort to utilize a well-studied phenomenon to enhance the capability of a new microfabrication process.

Effect of cutting fluid on the machinability of metal matrix composites

Abstract This paper utilizes models for cumulative tool wear to study the effect of cutting fluid on the machinability of aluminum-based matrix composites reinforced with SiC or Al 2 O 3 particles. Pressurized cutting fluid neither improves nor worsens the tool life because of either effective flushing of the chips or lack of a lubricating film. The surface finish and the cutting forces are insensitive to cutting fluid and cutting speed when machining with a new diamond tool, but deteriorate with greater tool wear.

Magnetic field assisted micro electro-discharge machining

This paper studies the feasibility of application of a magnetic field to obtain higher aspect ratio micro holes on hardened tool steel using the micro electro-discharge machining (micro EDM) process. The magnetic field has been introduced to improve debris circulation. Implementing magnetic force perpendicular to the electrodes rotational force produces a resultant force that is efficient in transporting debris out of the hole during machining. With the magnetic field assisted micro EDM process a hole depth of 1177 µm is achieved in 360 min in tool steel. This is 26% higher when compared with the conventional micro EDM process under similar working conditions. No significant difference is noticed in the side wall surface roughness values in the two cases.

Chip formation in machining particle-reinforced metal matrix composites

Abstract This paper compares the chip forming mechanism in monolithic metals and in particle-reinforced metal matrix composites. A quick stop device was designed to collect the chip-root for microscopic examination. The eutectic silicon and reinforcing particles formed flow lines due to different velocity zones across a chip. The reinforcing particles interfered with plastic deformation of the matrix, retarded crack growth, and were not delaminated from the matrix. High local temperature, induced by high strain rate in machining, improved the material ductility and healed microcracking in a chip. Heat treating a composite to a T6-temper affects the shear deformation at the tool-chip interface, and shortens the tool life.

Process Simulation and Residual Stress Estimation of Micro-Electrodischarge Machining Using Finite Element Method

A mathematical model based on heat transfer principles has been developed for the simulation of single-spark machining during micro-electrodischarge machining (µEDM) of a titanium alloy (Ti–6Al–4V). The model is solved by using a commercially available finite element method. A Gaussian distribution of the heat source and temperature-dependent material properties have been used to perform transient thermal analysis to estimate the crater size, the temperature distribution on the workpiece and the residual stress on and near the crater. Simulated crater dimensions and residual stresses were compared with experimentally obtained values by atomic force microscope (AFM) and a nanoindentation technique. The diameter-to-depth ratios of the crater obtained by simulation and by experiment are 3.45 and 3.99, respectively. The simulated stress exceeds the ultimate tensile strength (860 MPa) of the material near the spark center and gradually diminishes as the distance from the center increases. The stress values measured by nanoindentation of the spark-eroded surface are within 300 MPa.

Effects of powder additives suspended in dielectric on crater characteristics for micro electrical discharge machining

The effects of using powder additives suspended in dielectric on crater characteristics for micro electrical discharge machining (PSD micro-EDM) are investigated through the conduct of single RC discharge experiments at low discharge energies of 2.5 µJ, 5 µJ and 25 µJ. Through the introduction of additive particles into the dielectric, results of the single discharge experiments show the formation of craters with smaller diameters and depths, and having more consistent circular shapes than those produced in dielectric without additive. These craters also possess a noticeable morphological difference compared to those generated in dielectric without additive. In addition, discharge current measurements show a smaller amount of charges flowing between the tool electrode and workpiece, and at a slower flow rate when additives are present in the dielectric. Furthermore, based on the experimental results and findings from studies done in nanofluids, a hypothesis is made on the effects of powder suspended dielectric on the crater formation mechanism. The increased viscosity and enhanced thermal conductivity of a powder suspended dielectric lower the plasma heat flux into the electrode and raise the rate of heat dissipation away from the molten cavity. As a result, a smaller-sized crater having a larger amount of resolidified material within the crater cavity is formed.

A New Pulse Discriminating System for Micro-EDM

A new pulse discriminating technique for monitoring microelectrical discharge machining (micro-EDM) process in real time is proposed. The proposed system employs current pulse as the main detecting parameter as it is considered to be a better representation of the spark energy inside plasma channel as compared to the voltage. Micro-EDM pulses are classified into normal discharge, delayed discharge, arcing, and short circuit. The developed system was tested on micro-EDM drilling and micro-EDM milling, and the pulse distributions throughout these processes were analyzed. The developed pulse discriminator (PD) system is further used in the development of an adaptive speed servo system in micro-EDM. Experiment results show that the system is able to improve the machining time by more than 50%, and the accuracy of the resulting features is increased.

Coolant shoe development for high efficiency grinding

Abstract The combination of ultra hard abrasives and the high speed grinding process enables the fragmentation of chips into smaller size to accommodate a higher feed rate. However, the application of high efficiency grinding depends to a large extent upon the method of grinding fluid delivery. The formation of an air curtain layer around the grinding wheel prevents the entry of coolant to the grinding zone. This paper reports the characteristics of the air curtain layer that encompasses the grinding wheel. Also a new kind of coolant shoe is proposed and the performance output such as the grinding forces, power flux, surface integrity, wheel wear, microstructure and applications are reported. Such shoe possesses three adjustable orifice jets. The upper orifice breaks the air curtain and thus creates a vacuum enabling the sudden flow of coolant to the grinding zone. The middle orifice supply the coolant that leads to the formation of a coolant coating on the grinding wheel. The lower orifice directly impinges onto the grinding zone. Steady and laminar flow of coolant enable an increase of the coolant velocity and ensure the continuous supply of coolant to the grinding zone.

Localized electrochemical deposition: the growth behavior of nickel microcolumns

The development of MEMS has initiated the birth of various types of microfabrication processes. These processes in turn serve as a platform for the invention of newer improve3d processes with increasingly higher fabrication resolution. This paper reports on an investigative study on the growth characteristics of nickel micro-columns grown by localized electrochemical deposition - a new truly 3D micro-rapid prototyping and direct-fabrication process capable of producing extremely high aspect ratio microstructures. Nickel columns were electrochemically formed on copper cathodes form a nickel sulfamate plating solution using a non-soluble microelectrode as the anode. Initial experiments showed that zero, partial or complete growths of the columns were revealed, depending on the vertical traverse speed of the microelectrode away form the horizontal copper surface - the preferred traverse speed profile being a decreasing quadratic function that starts form a low traverse speed value followed by a constant function at a higher speed value with respect to time. Further work conducted based on this finding achieve da constant growth rate with an analog closed-loop feedback control of the process, which produced columns with more even dimensions. Understanding of the growth phenomena will allow increases in the rate of deposition and better dimensional control of 3D micro- components grown via localized electrochemical deposition.

Inclusion of environmental performance for decision making of welding processes

Abstract There are over 40 welding processes in use in our major industries today. The selection of a welding process takes into consideration the cost of the process and versatility, as well as the amount of training required for the process. This paper discusses environmental performance as a factor for consideration when selecting a particular welding process. An analytical hierarchy process in a health-hazard scoring system is introduced to quantify the environmental impact of the processes. The system determines a score based on the emissions of the process. The score serves to assess the degree of impact that the process has on the environment and at the same time provides a factor for consideration in the decision making of welding processes.