Non-traditional Micromachining Processes

The high demand and stringent design requirements in developing fields of microengineering as well as various needs of society and nation require the utilization of suitable techniques of non-traditional machining processes on different existing and newly developed metals, non metals, alloys, polymers, ceramics, rubber and composites, etc. Presently, nontraditional machining techniques have expanded their applicability in the field of micromachining and offer better opportunities with several inherent advantages that make these processes superior as well as more efficient than conventional one. Non-traditional mechanical micromachining processes include abrasive jet machining (AJM), water jet machining (WJM), ultrasonic machining (USM), ion beam machining (IBM), etc. Non-traditional thermal micromachining processes include micromachining by electro discharge machining (EDM), laser beam machining (LBM), electron beam machining (EBM), etc. Non-traditional chemical and electrochemical micromachining processes have been used successfully to generate micro features of high quality. Hybrid micromachining can also be utilized effectively for generating more intricate shapes and complex parts. Advanced finishing processes using non-traditional machining like abrasive flow finishing (AFF), magnetic abrasive finishing (MAF), etc. are also gaining popularity to cope up the steep demand in finishing intricate, complex, durable and sophisticated shapes that are highly economical and posses better surface quality and property. The opportunities and challenges of each non-traditional micromachining and finishing processes are to be investigated considering various practical applications in different micro engineering fields. These non-traditional micromachining techniques as well as advanced finishing processes can be improved further and utilized more successfully in the near future for numerous microengineering applications.

There are a lot of developments in the micro manufacturing methods for the production of the three-dimensional miniaturized products made up of different advanced materials. Ultrasonic micro machining is an essential technique for the fabrication of micro parts on the hard, brittle and non-conductive materials like glass, ceramics and silicon with high aspect ratio. Ultrasonic micro machining is the mechanical type non conventional micro machining process. Material removal mechanism of USMM is similar to macro ultrasonic machining process. Adequate surface finish with stiff tolerances and dimensions can be achieved by ultrasonic micro machining (USMM) on hard and brittle materials. During the last decades, a number of researchers have explored experimentally and theoretically this ultrasonic micro machining (USMM) process technique with different materials. Recent development on ultrasonic micro machining (USMM) process has been highlighted and discussed in details with different types of ultrasonic micro machining (USMM) set up and material removal mechanism. Design and developments of micro-tools for USMM process have also been discussed. Influences of different process parameters on various responses of USMM have been discussed here.

Micro-electrical discharge machining (Micro-EDM) has become one of the promising micromachining processes utilizing which high accurate intricate micro-features can be machined efficiently in shop floor. In this chapter, an overview of micro-EDM process and its capabilities is presented for obtaining different desired shape/profile utilizing various machining techniques. The chapter also deals with differences between EDM and micro-EDM, details of system components and micro-EDM process parameters. The significant performance characteristics of micro-EDM process are also discussed. For improving the machining rate as well as for producing high accurate micro-features in different engineering materials, experimental investigation of micro-hole drilling process on Ti–6Al–4V material is carried out implementing several innovative machining strategies such as comparative study of employing kerosene and de-ionized water as dielectrics, the effects of mixing of boron carbide additive in kerosene and de-ionized water, effects of polarity changing between the electrode and effects of rotating the micro-tool. Detailed parametric analysis is carried out to explore the effects of process parameters utilizing these novel machining strategies. Optical and SEM micrographs taken at different parametric combinations have also been analyzed.

A WEDM process may be called as a Micro WEDM (MWEDM) process when it is used for manufacturing micro parts. The rest underlying theory is same as traditional WEDM. A micro part is machined with good dimensional accuracy and surface finish when the kerf (slot) width becomes considerably smaller compared to that obtainable in conventional WEDM. Truly speaking, the cutting tool in WEDM/MWEDM is not the wire, but it is the pulse (electrical discharge). A minimum kerf is ensured in Micro WEDM, when (i) pulse sizes are made extremely small, (ii) extremely thin wire is used (ϕ = 20–100 μm), and (iii) process inaccuracies along with the discharge gap are minimized. It is required for Micro WEDM to maintain the pulse energy in the order of 10⁻⁵–10⁻⁷ J. Process inaccuracies are minimised by minimising the amplitude of wire vibration and wire lag. Hence, for an MWEDM machine, the following subsystems are modified as compared to a conventional WEDM setup: (a) the machine tool configuration is designed mainly to eliminate stray capacitance or leakage of charges from the gap, (b) the pulse generator produces discharges with pulse energy preferably in the order of 10⁻⁶–10⁻⁷ J, (c) a pulse discrimination system is installed to avoid arc or other abnormal discharges, (d) a closed-loop controlled proper wire transportation system is needed, (e) the wire diameter should be 20–80 μm and preferably of tungsten, (f) a suitable oil dielectric is used and lastly, (g) a precise closed-loop controlled servo mechanism is used for gap and work-table feed control to operate at steps at submicron level.

One of the newly developed laser micromachining processes for generating micro-turn surface on cylindrical work sample is laser micro-turning process. To explore the capability of this laser micromachining process for achieving particular surface profile and dimensional accuracy of machined parts, authors considered a number of experimental investigation to find the effect of process parameters. During investigation and analysis, a number of experimental designs are applied to in-depth analyse the effect of process parameters on surface roughness (Ra and Rz) and depth deviation. The governing equations of spot and circumferential overlap were developed for investigating the effect of these overlaps on surface criteria. By adopting statistical design of experiments approaches such as Response Surface Methodology, the influence of process parameters on process performance were studied. Moreover, novel machining strategy of laser defocusing condition was also implemented for improving the micro-turning surface features. For qualitative assessment of important process parameters, scanning electron microscopic images of machined surface were analysed for better understanding the process.

In the present era, fiber lasers have been successfully replacing Nd-YAG and CO₂ lasers along with other conventional laser systems for various micro-machining applications such as micro-cutting of stents, thin sheet of ferrous and non-metals in terms of cutting speed, cut edge quality and the length of micro cracks. The usage of fiber laser can also be observed in field of micro-machining of various engineering materials owing to the characteristics of short pulse lengths which range from millisecond to picosecond or even femtosecond. The present chapter aims to carry out an in depth study of the fiber laser micro-machining, i.e., micro-cutting, micro-drilling, engraving, marking, etc., of engineering materials ranging from polymer to ceramics. The aim of the chapter is also to include an overall concept of fiber laser micro-machining system in the present scenario and its applications along with the occurring physical phenomena and influence of various process parameters on the fiber laser generated micro-features.

This chapter gives a brief overview of laser beam cutting. An illustration of basic fundamentals of laser material interaction and material removal is given here which considers generation of photon and interaction with electron to generate heat, absorption of heat, phase transformation, plasma generation, ablation and removal mechanism of cut material from the irradiate region at dry condition. An experimental study of laser beam cutting of Inconel 625 superalloy at dry condition is given at the end of this chapter. During this experimental study effect of different process parameters on machining characteristics also discussed in details.

Product miniaturization is the principal driving force for 21st century’s industries because of the escalating demands for compact, intelligent, robust, multi-functional, and low cost products in all fields. As demand of miniaturized products is exponentially increasing, the need to manufacture such products from advanced engineering materials becomes more apparent. Micromachining plays significant role in miniaturization, and consist of machining different microfeatures on products. Design of microtools, tool wear, surface quality, burr and heat removal are the main challenges in various micromachining methods. Electrochemical micromachining is one of the important techniques because of its special material removal mechanism, better precision and control, environmentally acceptable, and mainly it permits machining of any metallic materials irrespective of its hardness. For better understanding of EMM process, the basic concepts such as electrochemistry, Faraday’s laws of electrolysis, electrical double layer, equivalent electrical circuit, and material removal mechanism have been discussed. Significant process parameters which affect the process performance, need of EMM setup development, various subsystems, along with the challenges in setup developments, and important techniques for improving the machining accuracy have been highlighted. Machining, finishing, and surface engineering applications of EMM, as well as recent advancement in EMM for micro and nanofabrication have also been discussed.

Miniaturization has covered every area of modern world. Micromachining is one of the key technologies that can enable the realization of almost all requirements of the microproducts and related domain. However, materials which can micromachined easily and used in present day Microsystems, MEMS and microengineering applications have some limitations such as low strength to weight ratio, corrosion resistance and biocompatibility. Titanium is one of the potential material and arising as alternative to the conventional MEMS materials particularly silicon or silicon based materials or glass. Titanium is known as super metal due to its high strength to weight ratio, excellent corrosion resistance and superior biocompatibility. This chapter highlights the challenges in micromachining of titanium and its alloys as well as potential use of electrochemical micromachining (EMM) technique for micromachining of titanium. Utilization of masked i.e. TMEMM as well as maskless electrochemical micromachining techniques for generation of various microfeatures on titanium has been presented in this chapter. Effect of various EMM process parameters on machining accuracy of microfeatures of titanium as well as most suitable EMM process parameters for fabrication of various complex microfeatures on titanium has also been discussed. This chapter provides comprehensive information on electrochemical micromachining of titanium and its prospective applications in the area of MEMS, Bio-MEMS and microengineering fields.

Electrochemical discharge micro-machining (micro-ECDM) process appears to be very promising as a future micro-machining technique, since in many areas of applications it offers several advantages, which include machining of variety of electrically non-conducting hard, brittle materials including glass, ceramics and composites etc. It is an advanced hybrid micro-machining process that combines the techniques of electrochemical machining (ECM) and electrodischarge machining (EDM). This book chapter focuses on the current researches and developments in micro-ECDM process. The chapter discusses in details about the micro-ECDM system, which includes the mechanical hardware unit, electrolyte supply unit and electrical power supply unit etc. The effects of various factors on different machining performance characteristics such as material removal rate, accuracy, heat affected zone, gas film quality, machining depth, surface topography and tool wear etc. during its application mainly for micro-drilling and micro-cutting operations on engineering materials are represented in this chapter. The chapter also gives a glimpse on the fundamentals, problematic areas and applications of micro-ECDM process and highlights the challenges and future possibilities of research in this area. The recent advancements for improvement of performance of µ-ECDM process by using the rotating and travelling micro-tool, controlling the gap between the tool and the workpiece, changing the shape of micro-tool and also controlling the surface texture and material of tool for micro-spark discharge for required micro-machining operations are also depicted in this chapter. The chapter is expected to open up new insights into the process characteristics for successful application of electrochemical discharge micro-machining (micro-ECDM) process and provides valuable guidance to the applied researchers and manufacturing scientists for setting up unique platform for micro-machining electrically non-conducting engineering materials.

Travelling wire electro chemical spark machining (TWECSM) is a hybrid machining process; TWECSM is combination of electro chemical machining (ECM) and wire electric discharge machining (WEDM). This machining process can be effectively used for machining of difficult to machine non-conductive materials that are not possible to machine by non-conventional machining methods i.e. EDM, ECM and WEDM etc. Now a days the utilization of hybrid machining techniques are very much important to process advanced materials as the different types of advanced materials are developing by the modern research community. The non-conductive materials can be machined with the help of conventional machining processes but compromise with surface texture, accuracy, micron level slicing etc. Keeping in view, this chapter presents the detail overview about the hybrid TWECSM process. The design and development of TWECSM process, potential and effectiveness of the process, parametric optimization for effective application of this process etc. are also explained in the chapter.