A comprehensive investigation on machining of composites by EDM for microfeatures and surface integrity

In electro-discharge machining (EDM), the material removal takes place by precisely controlled sparks that occur between tool and workpiece separated with a spark gap in the presence of a dielectric. Generally, the non-contacting type and less material removal rates are attributed to attain a good surface finish and close dimensional tolerances during an EDM of monolithic metals and alloys. But the dimensional accuracy and surface integrity parameters would considerably affect during EDM of composites due to the existence of more than one material phase constituents. Therefore, the present work aims to study and optimize the performance characteristics under various EDM conditions employed in making rectangular channels on AA6061-B4C composite material. Initially, AA6061-4wt.%B4C composites were fabricated by ultrasonically assisted stir-casting, and the improved properties were obtained from various mechanical characterizations. The EDM experiments were conducted according to the full factorial experimental design. The three levels of input conditions such as discharge Current (I), discharge duration (T On), and discharge idle time (T Off) were considered. The considered output responses are material removal rate (MRR),taper (θ) of the machined channel, tool wear rate (TWR), average surface roughness (R) of the machined surface, and average recast layer thickness (ARLT) of the machined zone. These responses are co-related with multi-objective types in the sense that the MRR has to be maximized with all other responses minimized. Hence, principal component analysis (PCA) coupled with grey relation analysis (GRA) was used for optimization in which the results were normalized, and all the responses were converted into a single response named weighted grey relation grade (WGRG) for each trial. The experimental trial, which had the highest WGRG, was considered as a local optimum. The global optimum parameters were obtained by performing the Taguchi method (TM) (higher-the-better) for the maximization of WGRG. The analysis of variance (ANOVA) was performed to know the contribution of each EDM parameter toward the WGRG. The optimum levels of Current, T On, and T Off were identified as 8 A, 25 µs, and 36 µs, respectively. Results showed that all three input parameters significantly affected the WGRG, and a higher contribution of Current (52.11%) followed by the T On (26.72%) was observed. The interaction between the Current and T Off was found to be greater than other interactions. Taper values were observed to be reduced at the combination of 8 A discharge Current and 25 µs T On. None of the input parameters significantly affected the Ra, except for Current, which showed a slight effect. ARLT values showed an increasing trend of T On from 25 µs to 45 µs but decreased slightly at 65 µs for all Current levels. The moderate Current level 6 A was observed to be favorable in reducing ARLT when compared to low (4 A) and high (8 A) for all Ton values.

Pulsed-flow microchannel heat sink: Simulation and experimental validation

Microchannel heat dissipation devices were first conceptualized in 1981 and since then are at the forefront of cooling techniques for a variety of applications, extending from computer chips and turbine blades to lasers and optical systems. However, much of the research is concentrated on steady flow of a cooling fluid through the channels. In this article, transient two-dimensional (2D) simulation for heat transfer in microchannels under a pulsed-flow condition is carried out. For validation of simulation results, a novel heat sink device is designed and fabricated, using milling and micro-electric discharge machining (EDM) technique. The fabricated device is then tested to evaluate the effect of a variable flow rate on the heat transfer characteristics when the flow is pulsating. It is found that the numerical results underpredict slightly as compared to actual experimental results. Results indicate a higher temperature at the outlet of the heat sink device for lower pulse frequency, and as pulse frequency increases, the outlet temperature decreases.

Design analysis and fabrication of side-drive electrostatic micromotor by UV-SLIGA

In the present work, a micro-electro-mechanical system (MEMS)-based electrostatic micromotor is designed and fabricated. Finite element analysis is done and various parameters affecting the torque are studied. Maximum torque is achieved at 120° phase angle. The effect of change in voltage, micromotor height and frequency is analysed and discussed. UV-SLIGA, a microfabrication technique, is used for the fabrication of electrostatic micromotor of height 30µm and higher. UV lithography is conducted by both positive AZ P4620 and negative (SU-8 10 and SU-8 2150) photoresists. Copper (Cu) is used as a sacrificial layer to release the rotor (the movable part) of the electrostatic micromotor. Electroformed nickel (Ni) is used for making stator, rotor and axle, whereas chromium (Cr) is used as a seed layer. The micromotor is fabricated with a stator-rotor pole having configuration ratio of 3:2. The gap between the rotor and axle is 20 µm. Wet chemical etching is used to etch the deposited metal layers (Cr, Ni and Cu). Challenges such as the adhesion between the photoresist mould and substrate, cracks, seepage and misalignment are faced during the microfabrication. These challenges are overcome by optimizing the various parameters. The fabrication of electrostatic micromotor is done successfully and the results are discussed in the article.

Micro-machining: An overview (Part II)

This article on ‘Micro-machining: An Overview (Part II)’ is in continuation to ‘Micro-machining: An Overview (Part I)’ published in this journal ( Journal of Micromanufacturing). It consists of four parts, namely, electrochemical micro-texturing, electrochemical spark micro-machining, molecular dynamics simulation and sustainability issues of micro-machining processes. Electrochemical micro-texturing (ECMTex) deals with various techniques developed for micro-texturing on different types of workpiece-surfaces, namely, flat, curved and free-form surfaces. Here, basically two categories of techniques have been reviewed, namely, with mask and without mask. It also deals with ‘single point tool micro-texturing’ which turns out to be a single-step technique requiring minimum time, but the accuracy and repeatability obtained after micro-texturing need to be critically analysed. For mass production, one needs to go for sinking kind of ECMTex processes. Electrochemical spark micro-machining (ECSMM) is an interesting hybrid (ECM+EDM) process which can be applied for electrically conducting as well as electrically non-conducting materials. However, the work reported in this article deals only with the electrically non-conducting materials for which this process was initially developed. This process has a lot of potential for theoretical work to be done. In this article, two theories of sparking/discharging have been briefly mentioned: single bubble discharging/sparking and single surface discharging. It also dicusses its applications for different types of electrically non-conducting materials. Molecular dynamics simulation (MDS) of micro-/nano-machining processes is very important, but it is very cumbersome to understand at atomic/molecular scale. In these processes, the material behaviour at micro-/nano-level machining is completely different as compared to bulk-machining (macro-machining) processes. Hence, some fundamentals of MDS have been discussed. It just gives the idea of available techniques, softwares and models for different types of processes. However, there is the need of further research work to be done for clearly understanding the MDS of micro-/nano-machining. In the end, the sustainability of micro-machining issues have been discussed, mainly based on the energy consumption per unit mass of production. It is concluded that the advanced micro-manufacturing processes are highly energy-intensive processes, and they need further studies to be done for making them more suitable from sustainability point of view. At the end of each section, some potential areas of research for enhancing the accuracy and repeatability, and minimising the production time of each process have been discussed.

A numerical model for tool–chip friction in intermittent orthogonal machining

This article presents a novel model to study the influence of surface textured cutting tools in near-micromachining conditions. The model utilizes the Challen and Oxley’s asperity deformation model (Van Luttervelt et al., CIRP Ann Manuf Technol, 1998, vol. 47, pp. 587–626; Arrazola et al., CIRP Ann Manuf Technol, 2013, vol. 62, pp. 695–718) paired with an approach to a priori estimate of the interfacial film formation at the tool–chip interface. The procedure considers the chemical effect of the environment, along with the mechanical aspects of the surface texture of the cutting tool’s rake surface. Model performance, in terms of predicting machining forces and coefficient of friction, was validated with existing experimental data (Anand et al., Proceedings of the international conference on advancements and futuristic trends in mechanical and materials engineering, 5–7 October 2012, pp. 661–666). The outcome trend of the proposed model approximately matches with the experimental results. Further, the model tries to explain the impact of cutting tool’s surface roughness on overall tool–chip friction while performing intermittent cutting in the near-micromachining regime.

Parametric studies on laser additive manufacturing of copper on stainless steel

Laser additive manufacturing using directed energy deposition (LAM-DED) technique is one of the recent techniques for fabricating engineering components directly from 3D CAD model data using high power lasers. In this respect, LAM-DED of copper (Cu) and stainless steel (SS) is an enduring research area. However, LAM-DED of Cu is challenging due to higher thermal conductivity, lower absorption to infrared radiation and oxide formation tendency. The present work reports an experimental investigation to evaluate the effect of process parameters on the track geometry, contact angle, inter-diffusion and micro-hardness of Cu tracks deposited on SS 304L substrate using LAM-DED. Analysis of variance is used to estimate the contribution percentage of process parameters on the track geometry. Further, Cu bulk structures are deposited at an identified combination of process parameters and they are subjected to optical microscopy for microstructural characterisation. Further, finite-element-based numerical simulation is performed to understand the temperature distribution during the processing of Cu bulk structures on SS304L and the temperature results are co-related with the microstructural transformation during the processing. This investigation paves a way to understand the effect of processing parameters for building Cu bulk structures on SS Substrate using LAM-DED.

Plasma polishing processes applied on optical materials: A review

Nowadays, the surface quality of the material is crucial for industry and science. With the development of micro-electronics and optics, the demand for surface quality has become more and more rigorous, making optical surface polishing more and more critical. Plasma polishing technology is conceived as an essential tool for removing surface and subsurface damages from traditional polishing processes. The plasma processing technology is based on plasma chemical reactions and removes atomic-level materials. Plasma polishing can easily nano-finish hard-brittle materials such as ceramics, glass, crystal, fused silica, quartz, Safire, etc. The optical substrate with micro-level and nano-level surface roughness precision is in demand with the advancement in optics fabrication. The mechanical properties of super-finished optics materials are being used to fulfill the requirement of modern optics. This article discusses the processing of different types of freeform, complex and aspheric optical materials by the plasma polishing process used mainly by the optical industry. The plasma polishing devices developed in the last decade are thoroughly reviewed for their working principles, characteristics and applications. This article also examines the impact of various process parameters such as discharge power, rate of gas flow, mixed gas flow ratio and pressure on the plasma polishing process.

Effect of scan pattern on Hastelloy-X wall structures built by laser-directed energy deposition-based additive manufacturing

This article systematically analyzes the effect of scan pattern on the geometry and material properties of wall structures built using laser-directed energy deposition (LDED)-based additive manufacturing. Hastelloy-X (Hast-X), a nickel superalloy, is deposited using an indigenously developed 2-kW fiber laser–based LDED system. The wall structures are built using unidirectional and bidirectional scan patterns with the same LDED process parameters and effect of scan pattern on the geometry, microstructural and mechanical characteristics of Hast-X wall structures built using LDED. The wall width is higher for samples deposited with the bidirectional pattern at the starting and ending points as compared to walls built with the unidirectional pattern. Further, the range of width value is higher for walls built with bidirectional strategy as compared to walls built with unidirectional strategy. Wall height is more uniform with unidirectional deposition at the central region, with the range and standard deviation for walls built using bidirectional deposition at 3 and 2.5 times more than unidirectional deposition, respectively. The deposition rate for bidirectional deposition is two times that of unidirectional deposition. The microstructure of the built walls is cellular/dendritic, with bidirectional deposition showing a finer grain structure. Elemental mapping shows the presence of elemental segregation of Mo, C and Si, confirming the formation of Mo-rich carbides. Micro-hardness and ball indentation studies reveal higher mechanical strength for samples built using the bidirectional pattern, with unidirectional samples showing strength lower than the conventional wrought Hast-X samples (197 HV). This study paves a way to understand the effect of scan pattern on LDED built wall structures for building intricate thin-walled components.

Chemomechanical magnetorheological finishing: Process mechanism, research trends, challenges and opportunities in surface finishing

Chemomechanical magnetorheological finishing (CMMRF) has emerged as a nanofinishing method that combines the characteristics of chemical mechanical polishing (CMP) and magneto-rheological finishing (MRF). The CMMRF process was designed to take into account both the chemical and mechanical effects that occur during the finishing process. In the field of material processing science, this article delves into the fundamentals of the CMMRF method. The potential research patterns linked to CMMRF are assessed and their benefits are determined. Furthermore, the challenges of improving CMMRF process capabilities, as well as the wide futuristic opportunities of the research sector, are emphasised, along with meeting all industrial needs. The findings of this analysis paper will also aid researchers in the field of advanced finishing in identifying process realisation for better results.