Electrical discharge machining (EDM) is one of the earliest non-traditional machining processes. EDM process is based on thermoelectric energy between the work piece and an electrode. A pulse discharge occurs in a small gap between the work piece and the electrode and removes the unwanted material from the parent metal through melting and vaporising. The electrode and the work piece must have electrical conductivity in order to generate the spark. There are various types of products which can be produced using EDM such as dies and moulds. Parts of aerospace, automotive industry and surgical components can be finished by EDM. This paper reviews the research trends in EDM on ultrasonic vibration, dry EDM machining, EDM with powder additives, EDM in water and modeling technique in predicting EDM performances.

A review on current research trends in electrical discharge machining (EDM)

Ultra-precision grinding is primarily used to generate high quality and functional parts usually made from hard and difficult to machine materials. The objective of ultra-precision grinding is to generate parts with high surface finish, high form accuracy and surface integrity for the electronic and optical industries as well as for astronomical applications. This keynote paper introduces general aspects of ultra-precision grinding techniques and point out the essential features of ultra-precision grinding. In particular, the keynote paper reviews the state-of-the-art regarding applied grinding tools, ultra-precision machine tools and grinding processes. Finally, selected examples of advanced ultra-precision grinding processes are presented.

Ultra-precision grinding

This paper provides a comprehensive review of the literature, mostly of the last 10-15 years, that is enhancing our understanding of the mechanics of the rapidly growing field of micromachining. The paper focuses on the mechanics of the process, discussing both experimental and modeling studies, and includes some work that, while not directly focused on micromachining, provides important insights to the field. Experimental work includes the size effect and minimum chip thickness effect, elastic-plastic deformation, and microstructure effects in micromachining. Modeling studies include molecular dynamics methods, finite element methods, mechanistic modeling work, and the emerging field of multiscale modeling. Some comments on future needs and directions are also offered.

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The Mechanics of Machining at the Microscale: Assessment of the Current State of the Science

This study investigates the critical maximum undeformed equivalent chip thickness for ductile-brittle transition (DBhmax-e) of zirconia ceramics under different lubrication conditions. A DBhmax-e model is developed through geometry and kinematics analyses of ductile-mode grinding. Result shows that DBhmax-e decreases with increasing friction coefficient (μ). An experimental investigation is then conducted to validate the model and determine the effect of dry lubrication, minimum quantity lubrication (MQL), and nanoparticle jet minimum quantity lubrication (NJMQL) conditions on DBhmax-e. According to different formation mechanisms of debris, the grinding behavior of zirconia ceramics is categorized into elastic sliding friction, plastic removal, powder removal, and brittle removal. Grinding forces per unit undeformed chip thickness (Fn/h and Ft/h) are obtained. The lubrication condition affects the normal force and ultimately influences the resultant force on workpiece. In comparison with dry grinding (DBhmax-e = 0.8 μm), MQL and NJMQL grinding processes increase DBhmax-e by 0.99 and 1.79 μm respectively; this finding is similar to model result. The theoretical model is then assessed by different volume fractions of nanofluids under NJMQL condition with an average percentage error of less than 8.6%.

Maximum undeformed equivalent chip thickness for ductile-brittle transition of zirconia ceramics under different lubrication conditions

Micro and Nano Machining by Electro-Physical and Chemical Processes

Robotic grinding and polishing for turbine-vane overhaul

The 3D profile airfoil of a turbine vane under overhaul can be severely distorted. The current manual repair to restore its original shape is time and labour intensive, and also produces inconsistent quality. Automation of such a process can lead to a significant cost reduction and improved quality. This paper reports on a system and the process development of a SMART robotic system for automatically grinding and polishing vane airfoils.

SMART robotic system for 3D profile turbine vane airfoil repair

An ultrasonic vibration has been superposed on the normal electrode movement to increase the flushing effect during a micro electro-discharge machining (EDM) process. A systematic study on the effects of ultrasonic vibration on the EDM performance for fabricating microholes in Nitinol has been completed. The introduction of ultrasonic vibration to the micro-EDM process has increased the machining efficiency more than 60 times, without significantly increasing the electrode wear. Numerical simulation reveals that the efficiency improvement is attributed to the strong stirring effect caused by ultrasonic vibration, which results in an excellent flushing in the micro-EDM process.

https://iopscience.iop.org/article/10.1088/0960-1317/13/5/322/pdf

Ultrasonic vibration assisted Electro-discharge machining of microholes in Nitinol

High speed grinding of silicon nitride with resin bond diamond wheels

In this paper, the silicon substrates machined by nanogrinding and chemo-mechanical-grinding (CMG) were characterized using atomic force microscopy, transmission electron microscopy and instrumented nanomechanical tests. It was found that the nanogrinding-generated silicon subsurfaces consisted of an amorphous layer and a damaged crystalline layer underneath, but the CMG-generated subsurface was defect-free. The formation of the amorphous and damaged crystalline layers was dependent on the maximum undeformed chip thickness involved in the nanogrinding process. Nanoindentation and nanoscratch tests revealed that the amorphous silicon exhibited to be more plastically deformed than the damaged crystalline layer under the same loading condition.

Libo Zhou

Papers

Robotic grinding and polishing for turbine-vane overhaul

SMART robotic system for 3D profile turbine vane airfoil repair

Ultrasonic vibration assisted Electro-discharge machining of microholes in Nitinol

High speed grinding of silicon nitride with resin bond diamond wheels

Characteristics of silicon substrates fabricated using nanogrinding and chemo-mechanical-grinding