A Soft Computing-Based Analysis of Cutting Rate and Recast Layer Thickness for AZ31 Alloy on WEDM Using RSM-MOPSO

In the present research, the AZ31 alloy is machined by wire-cut electric discharge machining (WEDM). The experiments were designed according to the Box-Behnken design (BBD) of response surface methodology (RSM). The input process variables, namely servo feed (SF), pulse on-time (Ton), servo voltage (SV), and pulse off-time (Toff), were planned by BBD, and experiments were performed to investigate the cutting rate (CR) and recast layer thickness (RCL). The analysis of variance (ANOVA) was performed to determine the influence of machining variables on response characteristics. The empirical models developed for CR and RCL were solved using Multi-Objective Particle Swarm Optimization (MOPSO). Pareto optimal front is used for the collective optimization of CR and RCL. The optimal solution suggested by the hybrid approach of RSM-MOPSO is further verified using a confirmation test on the random setting indicated by the hybrid algorithm. It is found that the minimum RCL (6.34 µm) is obtained at SF: 1700; SV: 51 V; Toff: 10.5 µs; and Ton: 0.5 µs. However, maximum CR (3.18 m/min) is predicted at SF: 1900; SV: 40 V; Toff: 7 µs; and Ton: 0.9 µs. The error percentage of ±5.3% between the experimental results and predicted solutions confirms the suitability of the proposed hybrid approach for WEDM of AZ31.

Characterization of micro hole on super alloy GH4037 and stainless steel 304 by millisecond-pulsed Nd:YAG laser processing

In this study, both super alloy GH4037 and stainless steel 304 were selected as experimental materials to be processed by LASERTEC 80 PowerDrill three-dimensional solid laser machining center. The structure of the micro hole was researched by 3D Laser Scanning Confocal Microscope and Scanning Electron Microscope (SEM). Meanwhile, The holes taper, entrance and exit ends diameter, microcrack, recast layer, orifice deposits and the heat affected zone (HAZ) were also investigated. The single factor experimental method was used to research the influences of defocusing amount, pulse energy, repetition frequency, and pulse duration on quality of micro holes. Experimental results indicated that the holes entrance and exit ends diameter enlarged with increased pulse energy from 3.4 J to 4.2 J. The entrance and exit ends diameter of holes decreased with increased pulse duration from 0.5 ms to 2.5 ms. Besides, the variation of holes diameter and taper were more obvious with repetition frequency changing from 10 Hz to 30 Hz, and variation range for the entrance and exit ends diameters and taper were not obvious with increased defocusing amount from −2 mm to 2 mm. The herein results indicated that pulse energy was one of the most significant influencing elements, and higher pulse energy could bring about lower hole taper within a certain range. Meanwhile, shorter pulse duration reduced splash and debris of holes surface. The recast layer, micro crack and HAZ were existed in the both kinds of experimental materials. Moreover, the microcrack and recast layer on holes wall of GH4037 were less than those of 304, and the HAZ in drilling hole for GH4037 was more than that of 304. The experimental results for the holes size were compared with corresponding simulation results under different defocusing amount respectively, which verified the accuracy of simulation results. Combining the above factors, the quality of micro holes drilling on super alloy GH4037 was better than stainless steel 304.

Enhanced Micro-Electric Discharge Machining-Induced Surface Modification on Biomedical Ti-6Al-4V alloy

In the midst of a huge demand for high-precision miniaturized medical implants made up of potential biomaterials, the biomedical Ti-6Al-4V alloy meets the uncompromising standards for longevity, biocompatibility, and sterilizability required to interact with living cells in medical settings. This research tailored the existing capabilities of a traditional micro-electric discharge machining (μ-EDM) setup by adding 0, 2, 4, 6, 8, and 10 g/l bioactive zinc powder-particle-concentrations (PPCs) to the dielectric. A copper and brass micro-tool electrode (C-μ-TE and B-μ-TE) were employed in association with each PPC, and experiments were executed using one-variable-at-a-time (OVAT) approach. Machining time and dimensional deviation were chosen as the response variables of Zn powder mixed-micro-EDM (Zn-PM-μ-EDM). According to the analytical findings, the combination of C-μ-TE and 6 g/l Zn PPC achieved 23.52 %, 3.29 %, and 17.96 % lesser machining time, dimensional deviation, and recast layer thickness, respectively, compared to the B-μ-TE. The detailed study of this surface endorsed a significant modification in terms of improved recast layer thickness (26.44 μm), topography (Ra = 743.65 nm), and wettability (contact angle < 90°), suggesting its dental application. Additionally, the observation of ZnO and TiO in X-ray diffraction and appealing in vitro cytocompatibility encourage the subsequent biological and therapeutic studies to validate the anticipated anti-viral activity of the modified Ti-6Al-4V alloy surface against coronavirus (COVID-19).

Prediction and analysis of EDM performances considering random multiple-pulse discharges based on geometric optimization modeling

Continuous electrical discharge machining (EDM) is characterized by random discharge positions, uncertain discharge energy, extremely short discharge time, extremely narrow tool-workpiece gaps, etc. Theoretical research into the mechanisms leading to thermal erosion of material and the associated surface morphology has become urgent to allow the continued development and application of EDM technology. Firstly, multi-pulse theory and geometric optimization are utilized to derive an expression for the material removal rate and surface roughness in multi-pulse EDM. Secondly, Based on the characteristics of multi-pulse discharge, a multi-pulse numerical simulation model was established to predict the material removal volume, surface roughness and thickness of recast layer. Finally, the results predicted by the geometric and numerical models are compared with the experimental results. Experimentally, 0.176 mg of material is removed in the multi-pulse EDM; the theoretical calculation and numerical simulation of the same produce errors of 5.11% and 11.36%, respectively. The analogous results for the surface roughness are 1.623 µm, 8.93%, and 1.23%. The experimentally determined thickness of the recast layer was 5.31 µm, which corresponds to an error in the simulation error of 7.53%.

Experimental Research on Discharge Forming Cutting-Electrochemical Machining of Single-Crystal Silicon

During the wire electrical discharge machining (WEDM) process, a large number of discharge pits and a recast layer are easily generated on the workpiece surface, resulting in high surface roughness. A discharge forming cutting-electrochemical machining method for fabricating single-crystal silicon is proposed in this study to solve this problem. On the same processing equipment, single-crystal silicon is first cut using the discharge forming cutting method. Second, electrochemical anodic reaction technology is used to dissolve the discharge pits and recast layer on the single-crystal silicon surface. The machining mechanism of this process, the surface elements of the processed single-crystal silicon and a comparison of the kerf width are analyzed through experiments. On this basis, the influence of the movement speed of the copper foil electrode during electrochemical anodic dissolution on the final surface roughness is qualitatively analyzed. The experimental results show that discharge forming cutting-electrochemical machining can effectively eliminate the electrical discharge pits and recast layer, which are caused by electric discharge cutting, on the surface of single-crystal silicon, thereby reducing the surface roughness of the workpiece.