K.P. Rajurkar

New Developments in Electro-Chemical Machining

Abstract Electrochemical machining (ECM) has traditionally been used in highly specialized fields such as those of the aerospace and defense industries. It is now increasingly being applied in other industries where parts with difficult-to-cut materials and complex geometry are required. In this paper the latest advances are discussed, and the principal issues in ECM development and related research are raised. Developments in tool design, pulse current, micro-shaping, finishing, numerically controlled, environmental concerns, hybrid processes, and recent industrial applications, are covered.

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.

3D Micro-EDM Using CAD/CAM

Abstract It is necessary to integrate CAD/CAM systems with micro-EDM to generate tool paths when simple shaped tools are used to machine three-dimensional (3D) micro parts. Currently available CAD/CAM systems cannot be directly used because of the continuous tool electrode wear during machining. This paper proposes an approach to integrate CAD/CAM systems with micro-EDM while accounting for tool wear using a recently developed uniform wear method. This approach is verified by successfully generating very complex 3D micro cavities. Additionally, the feasibility of the approach is illustrated by generating complex macro cavities using conventional EDM with single simple shaped electrodes.

Electroforming process and application to micro/macro manufacturing

Abstract Electroforming is the highly specialised use of electrodeposition for the manufacture of metal parts. This paper describes the process principles and mechanisms of electroforming, outlining its advantages and limitations. A review of modelling and simulation of electroforming and experimental analysis work is also presented. The metals that can be electroformed successfully are copper, nickel, iron or silver, thickness up to 16 mm, dimensional tolerances up to 1 μm, and surface finishes of 0.05 μm R a . The ability to manufacture complex parts to close tolerances and cost effectively has meant that electroforming has applications both in traditional/macro manufacturing and new micromanufacturing fields. These include tooling; mould making; fabrication of microelectromechanical systems (MEMS) and the combination of lithography, electroforming and plastic moulding in the LIGA process. Applications in micro-optics and medicine are included.

High aspect ratio and complex shaped blind micro holes by micro EDM

Abstract It is difficult to drill high aspect ratio through holes and complex shaped blind holes using micro EDM. The debris concentration in the narrow discharge gap causes abnormal discharges leading to excessive electrode wear and lower machining precision. In micro EDM, the electrode size is too small for internal flushing. This paper presents a new approach for effective self-flushing using planetary movement. Through micro holes with an aspect ratio of 18 have been drilled. This approach is also demonstrated by drilling blind noncircular micro holes with sharp corners and edges. The process performance characteristics are analyzed under different machining conditions.

Hybrid machining of Inconel 718

Abstract A new approach for machining of Inconel 718 is presented in this paper. It combines traditional turning with cryogenically enhanced machining and plasma enhanced machining. Cryogenically enhanced machining is used to reduce the temperatures in the cutting tool, and thus reduces temperature-dependent tool wear to prolong tool life, whereas plasma enhanced machining is used to increase the temperatures in the workpiece to soften it. By joining these two non-traditional techniques with opposite effects on the cutting tool and the workpiece, it has been found that the surface roughness was reduced by 250%; the cutting forces was decreased by approximately 30–50%; and the tool life was extended up to 170% over conventional machining.

A study of the effects of abrasive-flow finishing on various machined surfaces

Abstract Deburring and surface finishing methods represent a critical and expensive segment of the overall manufacturing process. A relatively new non-traditional process called Abrasive-Flow Machining (AFM) is being used to deburr, polish, radius, remove recast layers, or produce compressive residual stresses in a wide range of applications. Material is removed from the workpiece by the flowing of an abrasive-laden viscoelastic compound across the surface to be machined. There currently exists a lack of pertinent data which industry can use in selecting AFM for finishing workpiece surfaces generated by conventional and non-traditional machining processes. This paper presents the results of an investigation of the effects of AFM on surfaces produced by turning, milling, grinding, and wire electrical-discharge machining. The machining characteristics studied included material removal and surface finish improvement. The statistical analysis found that the type of machining process affected both metal removal and surface finish results. The initial surface condition significantly affected the amount of metal removal and was very close to meeting the significance requirement for surface finish improvement. In particular, all of the Wire EDM surfaces were improved greatly by AFM. Media viscosity significantly affected only surface improvement, while extrusion pressure did not have a significant effect in this experiment. Scanning Electron Microscopy (SEM) was used to study the surface characteristics of the workpieces. The photographs showed that AFM smoothed out the effects of the machining processes, leaving a more uniform surface. Data Dependent Systems (DDS), a stochastic modeling and analysis technique, was used to study the surface-roughness profiles before and after AFM. Overall, many similarities were found between grinding and abrasive-flow machining. This suggests that AFM is a very capable finishing process, and that its area of application should be expanded.

Study of Pulse Electrochemical Machining Characteristics

Summary The Pulse Electrochemical Machining (PECM) promises to improve dimensional accuracy control and to simplify tool design in machining hard, high strength, and heat resistant materials into complex shapes such as turbine blades. This paper presents a mathematical model for the PECM process which takes the non-steady physical phenomena in the gap into consideration. A specially-built PECM cell and a high-speed data acquisition device are used to obtain accurate experimental results in the gap for the model verification. The interelectrode gap characteristics, Including pulse current, metal removal rate, effective volumetric electrochemical equivalent and electrolyte conductivity variations, are analyzed based on the model and experiments.

Study of wire electrical discharge machined surface characteristics

Abstract The main goals of wire electrical discharge machine (WEDM) manufacturers and users are to achieve a better stability and high productivity of the process, i.e., higher machining rate with desired accuracy and minimum surface damage. The complex and random nature of the erosion process in WEDM requires the application of deterministic as well as stochastic techniques. This paper presents the results of current investigations into the characteristics of WEDM generated surfaces. Surface roughness profiles were studied with a stochastic modeling and analysis methodology to better understand the process mechanism. Scanning electron microscopic (SEM) examination highlighted important features of WED machined surfaces. Additionally, energy dispersive spectrometry (EDS) revealed noticeable amounts of wire electrode material deposited on the workpiece surface.

Thermal modeling and on-line monitoring of wire-EDM

Abstract This paper reports a WEDM sparking frequency monitor developed to detect the thermal load for on-line control to prevent the wire from rupture. The wire rupture phenomena are also analyzed with a thermal model. An extensive experimental investigation has been carried out to determine the process performances such as machining rate and surface finish with overall control parameters of an ED machine. The relationship between the machining rate and surface finish under optimal machine settings has been determined by means of a multi-objective model.