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Many manufacturing processes, such as lithography, etching, laser, electrical discharge machining (EDM), and electrochemical machining (ECM), are being applied to produce the meso- and microscale parts and products. Materials such as silicon, glass, quartz crystal, and ceramics are being increasingly used in microelectromechanical system (MEMS) devices. Ultrasonic machining (USM) offers an attractive alternative to machine some of the hard and brittle materials. However, the tool wear in micro-ultrasonic machining adversely affects the machining accuracy. Therefore, it is necessary to account for and to compensate the tool wear during machining. This paper reports the feasibility of applying the uniform wear method developed for micro electrical discharge machining and its integration with CAD/CAM to microultrasonic vibration process for generating accurate three-dimensional (3D) microcavities. Experimental results show that the tool shape remains unchanged and the tool wear has been compensated. Keywords: Micromachining, Ultrasonic Machining, 3D Microshapes

The electrical discharge machining (EDM) process performance depends on maintaining an appropriate machining gap with a servo system and discharge pulse parameters with a pulse power generator. The integration of the state-of-the-art monitoring and control technologies can substantially improve the performance of the EDM process. This paper reviews the research and development of advanced monitoring and control systems for die-sinking EDM and wire EDM during the last two decades. Important research activities include different EDM gap monitoring systems, servo and pulse adaptive control systems, and knowledge base control systems.

Jet Electrochemical Machining (ECJM) employs a jet of electrolyte for anodic dissolution of workpiece material. ECJM is extensively used for drilling small cooling holes in aircraft turbine blades and for producing maskless patterns for microelectronics parts. ECJM process drills small diameter holes and complex shape holes without the use of a profile electrode. One of the most significant problems facing ECJM user industries is the precise control of the process. A theoretical analysis of the process and a corresponding model are required for the development of an appropriate control system. This paper presents a mathematical model for determining the relationship between the machining rate and working conditions (electrolyte jet flow velocity, jet length, electrolyte properties, and voltage) of ECJM. This model describes a distribution of electric field and the effect of change of conductivity of electrolyte (caused by heating) on the process performance. A maximum dissolution rate is determined from the allowable increase of electrolyte temperature. Experimental verification of theoretical results is also presented.

This paper presents a dynamic analysis of the ultrasonic machining process based on impact mechanics. Equations representing the dynamic contact force and stresses caused by the impinging of abrasive grits on the work, are obtained by solving the three-dimensional equations of motion. The factors affecting the material removal rate have been studied. It is found that the theoretical estimates obtained from the dynamic model are in good agreement with the experimental results.

The bonding strength of deposited metallic thin films or strips on a hard substrate is investigated through micro-strength tests and micro-mechanics analyses. The combination of Ti:W-Au/Cu deposited directly on Si[O.sub.2]/Si substrate was taken as an example in the experiments conducted. Investigations and analyses resulted in a general model concerning the separation mechanism of thin ductile films from a hard brittle substrate. This separation model leads to some systematic methods of improving strip-substrate interconnection strength. Besides strip-substrate adhesion and internal stresses, strip stiffness turns out to be a key factor for the bonding strength of such a system. Hardening processes such as post-deposition heat treatment and work-hardening are proved to be effective in strengthening the bonding strength. These investigations reveal a principle of mechanical compatibility concerning interface micro-deformation. Instead of thin and flexible strips, thick and rigid strips have better compatibility with a hard substrate if the bonded combination is subjected to mechanical loading rather than thermal loading. As far as interface stresses are concerned, a stress distribution strategy is proposed based on the same principle. This original understanding will help to improve common bonding strength problems of various interconnection structures and materials combinations in manufacturing processes.

This paper reports a monitoring and adaptive integral control strategy for EDM to regulate the cycle time of the periodical retraction (jumping) of the tool electrode according to the gap condition. A digital EDM gap monitor has been developed to detect the time ratios of gap states with a resolution of 0.2 [[micro]second]. The theoretical and experimental analysis of the effect of sensing parameter combinations on control aspects and performance of manual setting integral control and adaptive integral control methods have been carried out. Experimental verification shows that the proposed system results in higher erosion rate, better machining stability, and complete avoidance of arc damage.

Polycrystalline diamond (PCD) tools are now widely used in machining a large variety of advanced materials. However, the manufacture of PCD tool blanks is not an economical and efficient process. The shaping of PCD blanks with conventional machining methods (such as grinding), is a long, labor-intensive and costly process. Wire electric discharge machining (WEDM) promises to be an effective and economical technique for the production of tools from PCD blanks. However, a knowledge base for wire electrical discharge machining of PCD blanks needs comprehensive investigations into the proper parameter setting, metal removal mechanisms, and surface integrity of machined blanks. This paper presents the results of experimental and theoretical investigations of the influence of discharge frequency and discharge energy on the material removal rate of WEDM of PCD blanks. The mechanism of removing diamond grains from the matrix during electrical erosion is also discussed on the basis of thermal stresses between the diamond grain and cobalt phase.

A small interelectrode gap in Electrochemical Machining (ECM) results in improved dimensional accuracy control and simplified tool design. However, using a small gap with conventional ECM equipment adversely affects the electrolyte flow or mass transport conditions in the gap, leading to process instability. The most remarkable breakthrough in this regard is the development of ECM using pulsed current. Pulse Electrochemical Machining (PECM) involves the application of a voltage pulse at high current density in the anodic dissolution process. PECM allows for more precise monitoring and control of machining parameters than ECM using continuous current. Small interelectrode gap, low electrolyte flow rate, gap state recovery during the pulse-off times and improved anodic dissolution efficiency features encountered in PECM lead to improved workpiece precision and surface finish when compared with ECM using continuous current. This paper presents mathematical models for the PECM process which take into consideration the nonsteady physical phenomena in the gap between the electrodes, including the conjugate fields of electrolyte flow velocities, pressure, temperature, gas concentrations, current densities and anodic material removal rates. The principles underlying higher dimensional accuracy and simpler tool design attainable with optimum pulse parameters are also discussed. Experimental studies indicate the validity of the proposed PECM models.

The main advantages of the electrochemical machining (ECM) process, such as high material removal rates and smooth, damage-free machined surface, are often offset by the poor dimensional control and process stability resulting from the complex and stochastic nature of the interelectrode gap (IEG) states. Full economic utilization of ECM will be realized only when reliable dimensional and process control systems are developed. This paper presents an ECM control model based on the basic ECM dynamics that accounts for the dynamic nature of the ECM process. The state space methodology is applied to transform it into the control model applicable to an ECM control system based on a digital computer. The simulations have been made for the model verification and controller design. A new approach is introduced to develop an indicator that detects or predicts the onset of random sparks based on ECM current signal analysis. ECM current and voltage signals have been acquired using a specially-built data acquisition circuit. The signals are digitized and analyzed with an IBM PC. The frequency analysis of the signal leads to a better insight of the physical mechanism of the ECM process. A comprehensive review of the state-of-the-art ECM research and development efforts in the areas of spark and short circuit detection and IEG control is also included in the paper.