Accuracy Enhancement Technologies for Micromachining Processes

The need for micro part is growing drastically because of technology advancement in biomedical, semiconductor, and aerospace industries, etc. Tool-based micromachining is the advanced approach for the production of parts for enhanced functionality with significant size reduction. Part accuracy is dealt with the degree at which the part approximates the true geometrical shape and size. In this chapter, factors that influence the part geometrical and dimensional accuracy in tool-based micromachining are presented. It is divided into six major elements: (a) cutting tool, (b) work material, (c) environment, (d) cutting phenomenon, (e) process parameters, and (f) machine tool. In this study, tool-oriented conventional micromachining processes are considered. The individual sub factors are represented by a fishbone diagram. The influence of parameters and their cause are described with the published literature, and the possible ways for part accuracy improvement in tool-based micromachining are presented.

Advanced materials are not easy to machine due to technological and industrial development and which discover extensive applications in nuclear engineering, aviation industries, etc. The manufacture of complex shape with high-quality surface finish and superior accurateness can be easily obtained by nonconventional machining processes. This manuscript covers the significant issues about the performance improvement of ultrasonic micromachining process. This book chapter also focuses on accuracy of ultrasonic micromachining process with process development. The two types of ultrasonic micromachining processes, i.e., stationary USM and rotary USM, are also discussed. Novel development for accuracy on ultrasonic micromachining (USMM) process has been emphasized and discussed. Strategies for development of ultrasonic micromachining system for performance enhancement are discussed for both stationary and rotary ultrasonic micromachining in this chapter. Micro-type tools developments for ultrasonic micromachining process with various strategies have been presented. In this section, influences of process parameters of USMM on different responses have been studied.

Micro electrical discharge machining (µEDM) is used for fabricating microstructures and micro components such as arrays of micro tools, micropillars, and complex three-dimensional shapes. These micro features are extensively used in the field of micro-electro-mechanical systems (MEMS), bio-MEMS, environmental and information technology, and so on. µEDM variants such as micro electrical discharge drilling (µED-drilling), reverse micro electrical discharge machining (R-µEDM), drilling with in situ fabricated tool, block micro electrical discharge grinding (B-µEDG), micro wire electrical discharge grinding (µWEDG), and micro electrical discharge milling (µED-milling) are equally contributing toward the fabrication of microscale parts and components. For the last few decades, researchers have mainly concentrated on the dimensional accuracy and precision measurement while fabricating microstructures for quantifying the response measures to determine the quality machining in micro level. Several factors such as machining parameters (electrical and non-electrical), tool and workpiece fixation, resolution, and repositioning capacity of the machine control dimensional accuracy and precision altogether. In addition, for machining the micro features, micro tools have been used. So, it is very important to study the tool wear because it directly affects the accuracy of micro features during machining. Tool wear cannot be completely avoided, but it can be minimized up to a significant level. Moreover, it can also be done using tool wear compensation. These errors are highly responsible for getting the inaccurate dimension of the microstructure. It is important to analyze the effect of each factor meticulously to achieve a precise and accurate dimension of micro components.

A thorough investigation on wirelag phenomena was carried out in this study. Here, the effect of wire deflection or wirelag on geometrical accuracy has been explored. A proper control to improve dimensional accuracy of circular job is achieved here. A novel method is presented to measure the wirelag by geometrical analysis. A mathematical model is developed to measure the gap force. Experimental investigations are performed to verify the proposed model.

Micro-channels are generally used in micro-fluidic devices and heat sinks for biomedical, chemical, microelectronics, and micro-electromechanical applications. A number of processing techniques are used for fabricating micro-channels on different materials. Laser-based micro-channeling techniques are now gaining popularity because of simplicity, flexibility, repeatability, and reliability of the process. Laser is a versatile non-contact machining tool, which can be utilized to machine any profile contour on almost every type of materials. In this chapter, the attempt is made to furnish a comprehensive technical know-how about laser-based fabrication techniques of micro-channels. An overview on fabrication of micro-channels and their applications, including a brief discussion on operation principles of commonly used micro-channeling techniques is presented in the initial sections. The subsequent sections elaborate laser micro-channeling process, including process fundamentals and process requirements. Thereafter, underwater laser processing of micro-channels is also discussed, which is a recent development in this field. The improvements achieved in terms of dimensional accuracy and quality of micro-channels, by using laser-based fabrication techniques, are reported and discussed to justify the effectiveness of these techniques, which are evidenced by several research findings.

Laser beam cutting (LBC) demonstrates its superiority over traditional cutting techniques due to its contactless and localized nature between the cutting tool and workpiece surface. Nowadays, pulsed Nd:YAG laser beam cutting is in one of the highly demanded cutting processes for variety of applications in the aircraft, aerospace, marine, defense, etc., sectors. This system is able to cut not only intrinsic and complex shapes for an inclusive variety of materials but also provide higher accuracy and precise cut edge surface. In this chapter, analysis of some key investigations is performed by the previous researchers for pulsed Nd:YAG laser beam cutting of distinct materials like metals, non-metals, and composites have been discussed. The conducted survey has been based on the influence of the variable laser cutting factors on the performance characteristics.

Recently, laser micromachining and micro-fabrication processes have remarkable and diversified applications in the direction to manufacture highly precised and accurate dimensional parts or components which are used in bio as well as technological domains such as biomedical, dental and orthopaedic, aircraft engines, micro-electromechanical systems (MEMS), electronic devices, turbocharger rotor parts and nuclear reactors. The present chapter deals with experimental investigation into micro-turning process using pulsed Nd:YAG laser during machining of aluminium oxide ceramics. A number of experimental schemes were adopted to explore the parametric influences on process characteristics such as surface roughness and depth deviation. Experimental investigation was also carried out to improve the dimensional accuracy and surface characteristics of laser micro-turned components using laser defocusing technique.

Electrochemical micromachining (EMM) has several advantages over its competitive micromachining techniques, and hence, it is one of the best micromachining techniques applied in various fields. However, further investigations are required to augment the machining accuracy for overcuts, taper formation, profile accuracy, and surface excellence, to discover the utility of EMM for various applications. Generally, microstructures like microholes, microslots, microgrooves, and 3D microfeatures are machined on various metallic components by EMM. Geometrical profile, dimension, and tribology of machined microfeatures mainly affect the performance as well as life of these components. Therefore, machining of such microfeatures of few tens to hundreds of microns with correct shape profile and better quality is ever demanding area for exploration. Availability of electrolyte at inter-electrode gap, removal of slush and hydrogen gas bubbles from machining zone, stray-current control, and microtool feed rate control to maintain uniform inter-electrode gap are the major challenges for the researchers to increase the machining accuracy. Machining accuracy can also be upgraded by selecting proper shape and size of the microtool, by insulating the sidewalls of the microtool, and also by utilizing the innovative machining strategies. In addition to these techniques, controlling and optimizing influencing process parameters of EMM and hybrid electrochemical micromachining are some of the areas by which machining accuracy can be enhanced in EMM.

Surface being the outermost layer of a body is the first point of contact between a body and the environment in which it is intended to work. By modifying the surface properties, the characteristics exhibited by a material can be controlled. With the need for reducing the structure sizes for different applications, the conventional machining has been scaled down to micromachining in which micro tool is used and micron-sized structures are created. Among the different types of micromachining techniques, surface micromachining stands out as a process which is intended only for the surface of a workpiece. In contrast to other micromachining techniques which target the bulk of the workpiece, surface micromachining aims at creating patterns, structures or features on the surface of the workpiece thus inducing unique and controllable properties. This chapter discusses different micromachining techniques and methods of characterization. The first section will include brief introduction to well-known processes like photolithography, reactive ion etching, deep reactive ion etching; some advanced processes capable of micron as well as nanometric scale fabrication like focused ion beam fabrication, electron beam lithography. Almost all these techniques are physical in nature, as in they do not involve use of chemical etching for creating the surface structures. Thus, they enable one to achieve high level of accuracy in the process and to actively control the features of the structure. As the fabrication methods have evolved with time, so did their characterization methods. Conventional measurement techniques are not suitable for evaluating the structures fabricated by the advanced surface micromachining methods. The second section of the chapter discusses three measurement and characterization methods. First of which is stereo zoom microscope which is used mostly at macro scale, followed by scanning electron microscopy which is capable of operating at micron and nanometric scale. The last of the characterization methods is scanning tunneling microscopy which is capable of imaging and characterization at atomic scale.

Nowadays, nano-level surface finish is a necessary requirement in different industries. To enhance the performance of a component, nano-level surface roughness is an essential quality. The main drawback of the traditional finishing processes is a longtime requirement for finishing and its dependency on manual labor. The surface morphology requirement of the present era is also very difficult to achieve using conventional finishing processes. Different advanced finishing processes like abrasive flow finishing, elastic emission finishing and magnetic field-assisted finishing processes are developed for achieving nano-level finish. Magnetic field can be used to control finishing forces precisely in magnetic field-assisted finishing processes. Magnetic abrasive finishing and magnetorheological finishing processes belong to this group. Different types of magnetorheological finishing processes are developed to finish a vast selection of components using magnetorheological fluid as the polishing medium. Magnetorheological abrasive flow finishing, rotational magnetorheological abrasive flow finishing, ball end magnetorheological finishing and magnetic field-assisted finishing using novel polishing tool are some of the processes which generate nanometer level surface finishing on flat and free-form surfaces using MR polishing medium. Semiconductor industries use chemical mechanical polishing process due to its planarization capability. Also, CMP process is able to provide nanometer level surface finish in metals and non-metals alike. The required surface characteristics and surface finish in automotive, aerospace, medical and other industries are dependent on the application of the component. These required surfaces can be generated using advanced nano-finishing processes.