Chander Prakash

A Review of Additive Mixed-Electric Discharge Machining: Current Status and Future Perspectives for Surface Modification of Biomedical Implants

Surface treatment remained a key solution to numerous problems of synthetic hard tissues. The basic methods of implant surface modification include various physical and chemical deposition techniques. However, most of these techniques have several drawbacks such as excessive cost and surface cracks and require very high sintering temperature. Additive mixed-electric discharge machining (AM-EDM) is an emerging technology which simultaneously acts as a machining and surface modification technique. Aside from the mere molds, dies, and tool fabrication, AM-EDM is materializing to finishing of automobiles and aerospace, nuclear, and biomedical components, through the concept of material migrations. The mechanism of material transfer by AM-EDM resembles electrophoretic deposition, whereby the additives in the AM-EDM dielectric fluids are melted and migrate to the machined surface, forming a mirror-like finishing characterized by extremely hard, nanostructured, and nanoporous layers. These layers promote the bone in-growth and strengthen the cell adhesion. Implant shaping and surface treatment through AM-EDM are becoming a key research focus in recent years. This paper reports and summarizes the current advancement of AM-EDM as a potential tool for orthopedic and dental implant fabrication. Towards the end of this paper, the current challenges and future research trends are highlighted.

Bio-inspired low elastic biodegradable Mg-Zn-Mn-Si-HA alloy fabricated by spark plasma sintering

ABSTRACT In this paper, biodegradable low elastic Mg-Zn-Mn-Si-HA alloys have been synthesized by element-alloying assisted spark plasma sintering (SPS) process. The main concern of the current investigation is to study the influence of the key SPS-process variables, such as, alloying element, milling/alloying time, sintering temperature, and pressure on the porosity and elastic modulus of the fabricated alloys. Following an L27 OA-based on Taguchi method and accompanying the input parameters, a series of SPS experiments were carried out. Results indicated that sintering temperature and pressure were found to have a significant effect. The SEM observations showed that highest degree of porosity was observed at the lowest level of the parameters and the full dense compact was obtained at the highest level of the parameters. The alloying of HA and Si refined the grain structure and improved the brittleness of the composite. The SPS fabricated alloys exhibited an elastic modulus in the range between 16 and 38 GPa, that is proximate to bone and viably avoid stress-shielding. Moreover, various biocompatible phases, that is, CaMg, Mg-Si, Mn-CaO, Ca-Mn-O, and CaMgSi were observed in the alloy, which are expected to enhance its bioactivity and corrosion resistance. As-synthesized alloy would be considered potential biodegradable material for orthopedic applications.

Electrochemical Discharge Drilling of Polymer Matrix Composites

The applications of nonconductive fibrous composites are increasing significantly over the last few years in numerous industries such as aerospace and marine application due to the unique combination of mechanical properties, i.e., lightweight and high strength. The components of aerospace and marine structures which are made of glass fibers require highly precise machining tasks like drilling for assembly in various parts of automobile and aerospace shuttles. Apparently, microdrilling of these nonconductive materials is still a challenge and critical aspect in the advancement of manufacturing industries. Recently, the utilization of electrochemical discharge drilling (ECDD) has emerged as the potential technique for the effective and precise microdrilling of such type of nonconductive materials. But, the reinforcement of abrasive particles deteriorates the drilling behavior of composites and results in high tool wear, increased cutting forces, and poor surface roughness of drilled hole. To avoid these complications, unconventional machining method like ECDD could provide a better platform for drilling of these types of materials. Keeping this in mind, the overview of electrochemical discharge drilling (ECDD) process including development and parametric optimization of the process parameters for effectual application in fibrous composites has been presented in this chapter. Moreover, an experimental investigation and optimization of ECDD process parameters have been carried out for the drilling of glass fiber reinforced polymer matrix composites.

Multi-objective Optimization of MWCNT Mixed Electric Discharge Machining of Al–30SiCp MMC Using Particle Swarm Optimization

In the present research work, the multi-walled carbon nanotube (MWCNT) mixed electric discharge machining of Al–SiCp-based MMC has been proposed. The effect on MWCNT concentration, peak current, pulse duration, and duty cycle on the surface roughness and material removal rate has been investigated and multi-objective optimization of MWCNT mixed-EDM process parameters has been carried out for the machining of Al–30SiCp substrate using particle swarm optimization (PSO) technique. The SR and MRR increased with peak current and pulse duration in the case of EDM, but SR decreased and MRR increased with the dispersion of MWCNTs in EDM dielectric fluid. The empirical model has been developed by response surface methodology to interpret the relation between input parameters and output characteristics such as SR and MRR. However, the impacts of MWCNT mixed-EDM parameters on SR and MRR are clashing in nature; there is no single condition of machining parameters, which gives the best machining quality. Multi-objective particle swarm optimization technique was used to find the best optimal condition of MWCNT mixed-EDM parameters to minimize the SR and maximize the MRR. The best global solution where, maximum MRR (1.134 mm3/min) and minimum SR (1.097 μm) obtained from the Pareto optimal front is at peak current = 15.59 A, pulse-on = 169.61 μs, duty cycle = 65.17%, and MWCNT powder concentration = 4.08 g/l. The MRR and SR are increased by 14.89 and 15.94%, respectively, after mixing 4.08 g/l MWCNT concentration in dielectric fluid. From the above study, it is recommended for the process engineer to use the proposed optimal setting to achieve maximum MRR and minimum SR.

Machinability Investigations of Inconel-800 Super Alloy under Sustainable Cooling Conditions

With regard to the manufacturing of innovative hard-machining super alloys (i.e., Inconel-800), a potential alternative for improving the process is using a novel cutting fluid approach. Generally, the cutting fluids allow the maintenance of a better tool topography that can generate a superior surface quality of machined material. However, the chemical components of fluids involved in that process may produce harmful effects on human health and can trigger environmental concerns. By decreasing the cutting fluids amount while using sustainable methods (i.e., dry), Near Dry Machining (NDM) will be possible in order to resolve these problems. This paper discusses the features of two innovative techniques for machining an Inconel-800 superalloy by plain turning while considering some critical parameters such as the cutting force, surface characteristics (Ra), the tool wear rate, and chip morphology. The research findings highlight the near-dry machining process robustness over the dry machining routine while its great potential to resolve the heat transfer concerns in this manufacturing method was demonstrated. The results confirm other benefits of these methods (i.e., NDM) linked to the sustainability aspects in terms of the clean process, friendly environment, and permits as well as in terms of improving the manufacturing characteristics.

Synthesis, Characterization, Corrosion Resistance and In-Vitro Bioactivity Behavior of Biodegradable Mg–Zn–Mn–(Si–HA) Composite for Orthopaedic Applications

Recently, magnesium (Mg) has gained attention as a potential material for orthopedics devices, owing to the combination of its biodegradability and similar mechanical characteristics to those of bones. However, the rapid decay rate of Mg alloy is one of the critical barriers amongst its widespread applications that have provided numerous research scopes to the scientists. In this present, porous Mg-based biodegradable structures have been fabricated through the hybridization of elemental alloying and spark plasma sintering technology. As key alloying elements, the suitable proportions of silicon (Si) and hydroxyapatite (HA) are used to enhance the mechanical, chemical, and geometrical features. It has been found that the addition of HA and Si element results in higher degree of structural porosity with low elastic modulus and hardness of the Mg–Zn–Mn matrix, respectively. Further, addition of both HA and Si elements has refined the grain structure and improved the hardness of the as-fabricated structures. Moreover, the characterization results validate the formation of various biocompatible phases, which enhances the corrosion performance and biomechanical integrity. Moreover, the fabricated composites show an excellent bioactivity and offer a channel/interface to MG-63 cells for attachment, proliferation and differentiation. The overall results of the present study advocate the usefulness of developed structures for orthopedics applications.

Fabrication and characterization of Ti-Nb-HA alloy by mechanical alloying and spark plasma sintering for hard tissue replacements

In the present research work, a β-type Ti-35Nb-10HA alloy was successfully fabricated by mechanical alloying of titanium (Ti), niobium (Nb), and hydroxyaptite (HA) powders followed by consolidation using Spark Plasma Sintering technique. The effect of HA on the microstructure and mechanical properties were studied. The microstructure, surface topography, and element composition of the Ti-Nb-HA alloy was investigated using optical microscope, field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The micro-hardness of the specimens was measured on a Vickers hardness tester. The microstructure examination of the compact revealed that the alloy distinctly shows the primary grain boundaries along with secondary grain boundary. It was observed that complex reactions between HA and alloy elements occurred during the sintering process of Ti-35Nb-10HA alloy and biocompatible phases [Ca3(PO4)2, CaTiO3, Nb8P5, CaO, TiP, Nb4O5, and TiO2] were generated in the compact, which is beneficial to form apatite and improved the bioactivity of the alloy for osseiointegartion. The fabricated Ti-35Nb-15HA alloy exhibits maximum micro-hardness (~786 HV), which is very high value as compared to the alloys reported in literature. Based on these above observations, it is expected that the as-fabricated Ti-35Nb-10HA alloy is suggested for dental and orthopaedic applications.