A comparative study of the dry and wet nano-scale electro-machining

In recent years, a nano-electromachining (nano-EM) process based on a scanning tunneling microscope (STM) platform has been demonstrated. Nano-EM is capable of machining nano-features, under both, liquid dielectric (wet nano-EM) and air dielectric (dry nano-EM) media. The objective of this paper is to present a comparative study between the wet and dry nano-EM processes based on process mechanism, machining performance, consistency and dimensional repeatability of these two processes. The comparison of the two processes has been conducted at near field nano-EM, where the gap between the tool electrode and workpiece is 2 nm and the machining is performed at room temperature and pressure (macroscopically). The major differences in the process mechanism are due to the media at dielectric interface, the breakdown field strength and breakdown characteristics of two dielectrics and therefore, the material removal mechanism. It is reported that the material removal mechanism of wet nano-EM is associated with field emission-assisted avalanche in nano-confined liquid dielectric, whereas, the material removal mechanism in dry nano-EM is associated with field-induced evaporation of material. The differences have also been observed in the machining performance, dimensions of the machined features and repeatability of the nanoscale machined features. The self-tip-sharpening process with the continuation of machining has added several advantages to dry nano-EM over wet nano-EM in terms of dimensions of the nanoscale features, repeatability and machining performance

Cryogenic Machining of Hard-to-Cut Materials

This paper presents a technique for machining of advanced ceramics with liquid nitrogen (LN2) cooled polycrystalline cubic boron nitride (PCBN) tool, titanium alloys, Inconel alloys, and tantalum with cemented carbide tools. With LN2 cooling, the temperature in the cutting zone is reduced to a lower range, therefore, the hot-strength and hot-hardness of the tool remain high, and the temperature-dependent tool wear reduces significantly under all machining conditions. The surface roughness of all materials machined with LN2 cooling were found to be much better than the surface roughness of materials machined without LN2 cooling after the same length of cutting

A stochastic approach to thermal modeling applied to electro-discharge machining

The usual method of making some simplifying assumptions and formulating thermal models that yield results confirmed by experiments does not work in many cases where the problem is complex and random. Electro-Discharge Machining (EDM) is such a process that is not only complicated and random but also physically little understood. The paper illustrates thermal modeling of this process with the help of a recently developed stochastic methodology called Data Dependent Systems (DDS). An equation to the melting iosthermal curve is defined from the DDS (stochastic empirical) model obtained from readily measurable surface profiles of actual machined surfaces created by the random superposition of electrical discharges. This equation of the melting isothermal curve is then combined with the heat conduction equation, under rather realistic and intuitively obvious assumptions, to develop a transient temperature distribution. The form of this (hybrid) thermal model is mathematically much simpler and yet its predictions are much closer to the experimental results, compared to the complicated models proposed in the literature. © 1983 by ASME

Quantitative expressions for some aspects of surface integrity of electro discharge machined components

An on-line adaptive control of the Electrical Discharge Machining (EDM) process needs proper quantitative relationships between output parameters and input variables of the process. This paper presents an attempt to develop mathematically simple expressions for the depth of cracks, the depth of damaged layer, and the depth of martensitic layer in terms of pulse duration and current. The transient temperature distribution developed by Data Dependent Systems analysis of the EDM process is used in obtaining thermal stress expressions. The hypothesis that the cracks are the consequence of thermal stresses exceeding the fracture level leads to the expression for the depth of occurrence of cracks. The estimation of the thickness of martensitic layer is based on the phase transformation temperature isothermal obtained from the temperature distribution. A simple expression for the depth of the damaged layer is also obtained using the experimental conclusions reported in the literature. Regression equations suitable for the on-line adaptive control of the EDM process are developed. The theoretical estimates are compared with the experimental measurements. © 1984 by ASME

Formation and ejection of ed debris

This paper presents a theoretical and experimental investigation into the debris formation and ejection mechanism. An expression for the size of a debris particle is derived using the drop formation energy and the kinetic energy of the ejected debris particle. The velocity of the ejected particle is obtained from expressions derived on the basis of the analysis of hydrodynamic propagation of shock waves generated due to electrical breakdown in dielectric. The debris particles were collected by machining AISI1020 steel under various operating conditions. The projected areas were measured by a microscope following the standard procedure of particle size measurement. The particle size has been found to be log normally distributed. The experimental values of debris size compare well with the theoretical estimation indicating the validity of the proposed analysis. © 1986 by ASME