Powder mixed EDM for biomedical alloys Nurlan Nauryz 2nd Year Master in Mechanical and Aerospace Engineering Supervisor: Assistant Professor Asma Perveen Co-Supervisor: Associate Professor Didier Talamona Outline 2 1 2 3 4 5 6 Introduction Literature review Methodology Results Conclusion References Introduction Existing coating techniques have some demerits [4,5]: Nonuniform and thin coating Unable to generate a nanoporous layer Cannot shape and coat simultaneously 3 Biomedical alloys [1,2] Fractured, lost or diseased parts (bone, teeth, ligaments, and heart) [3] Bio implants Area of application Problem Statement Introduction 4 Electrical Discharge Machining (EDM) A desired shape is obtained by using electrical discharge (spark). Spark machining, spark eroding, die sinking, wire erosion No contact between the workpiece and the tool. Advantages: absence of a cutting force flexibility of machining EDM schematics [6] Introduction 5 Powder mixed EDM Increases inter electrode gap Decreases insulating strength of dielectric Increase in material removal rate Powder in dielectric [7] Introduction 6 Wire EDM Cut internal corners with very small radii. Consistent accuracy of the cutting tool Introduction Objectives: To examine the macro-EDM machining performance with and without the addition of the hydroxyapatite powder into the dielectric fluid for Ti-6Al-4V. To examine the micro-EDM machining performance with and without the addition of hydroxyapatite powder into the dielectric fluid. To examine the bacterial attachment and adhesion after PM wire EDM treatment. 7 PMEDM machining performance on Ti-6Al-4V Aim Literature review 8 Authors Key findings Tanjilul et al. (2018) [6] Novel debris removal method, with simultaneous flushing and vacuum for drilling EDM Reduction in machining time and surface roughness improvement Abu et al. (2018) [8] Review on machining titanium alloys with several EDM methods Summary on theoretical and experimental EDM investigations targeted at enhancing process efficiency Kumar et al. (2018) [9] Various methods, such as introducing cryogenic cooled electrode, addition of magnetic field to the sparking zone and imparting electrode rotation to EDM Optimization of process parameters showed enhancement in material removal rate up to 44% and resulted in the increase of the surface roughness to 51% in comparison with the standard EDM technique Mohanty et al. (2019) [10] Used the powder mixed micro-EDM technique to make a firm and solid-lubricating coating on a surface of a Ti6Al4V work piece Improvement in micro-hardness, thickness of recast layer and wear rate Methodology: Macro EDM 9 Equipment setup Description Machine Drilling EDM DD703.30A Tool electrode Tubular brass electrode Workpiece Ti-6Al-4V alloy Polarity Tool (+), Workpiece (-) Dielectric Deionized water No. exp. Discharge current Time-on Time-off Gap voltage 1 2 2 2 2 2 2 5 5 5 3 2 8 8 8 4 5 2 5 8 5 5 5 8 2 6 5 8 2 5 7 8 2 8 5 8 8 5 2 8 9 8 8 5 2 Experiments on macro EDM conducted on Ti-6Al-4V alloy workpieces Orthogonal array with 4 parameters in 3 dimensions Parameters include pulse current, time-on, time-off, and gap voltage It was repeated 3 times Same procedure was repeated for 5 g/l hydroxyapatite powder addition Methodology: Micro EDM 10 Capacitance Voltage [V] Powder concentration [g/l] 100 pF 90 0 100 pF 90 0 100 pF 90 0 100 pF 100 5 100 pF 100 5 100 pF 100 5 100 pF 110 10 100 pF 110 10 100 pF 110 10 1 nF 90 5 1 nF 90 5 1 nF 90 5 1 nF 100 10 1 nF 100 10 1 nF 100 10 1 nF 110 0 1 nF 110 0 1 nF 110 0 10 nF 90 10 10 nF 90 10 10 nF 90 10 10 nF 100 0 10 nF 100 0 10 nF 100 0 10 nF 110 5 10 nF 110 5 10 nF 110 5 Experimental study was conducted on Hybrid DT-110 μEDM Machine Orthogonal array with 3 parameters in 3 dimensions Capacitance and voltage settings were divided into 3 levels each (100 pF, 1 nF, and 10 nF for capacitance; 90 V, 100 V, and 110 V for voltage). Each experimental trial was conducted using a 0.03 mm/min feed, with the aim of machining 0.050 mm in depth Tungsten carbide electrode diameter tool was decreased from 2 mm to 0.62mm using micro turning tool Methodology: Wire EDM 11 Experimental study was conducted on Hybrid DT-110 μEDM Machine 50-µm diameter tungsten wire to cut 3x20x0.025 mm dimensions on both sides of 9 titanium plates Three discharge energy values: low (100 pF and 90 V), medium (1 nF and 100 V), and high (10 nF and 110 V) Methodology: Hardness test 12 Falcon 300 hardness tester used to investigate hardness of Micro EDM machined samples Vickers 200 g with 10-second dwelling time used for hardness value acquisition Three measurements conducted for each of the 27 experiments to ensure comprehensive statistical dataset Methodology: Surface roughness 13 A Portable Surface Roughness Gauge was used for the measurements of micro Wire EDM machined samples Experiments for each parameter combination was repeated 3 times The height of the probe position was calibrated using the built-in leveling indicator of the Portable Surface Roughness Gauge Methodology: Contact angle 14 Contact angle measurements were conducted using OCA 25 contact angle measurement machine The sessile drop method was employed for contact angle measurement Overall, 27 experiments were performed, with three experiments for each combination of input parameters Deionized water was utilized as the liquid for contact angle measurements Bacterial attachment 15 Antibacterial efficacy of Ti-6Al-4V against S. aureus and E. coli Fresh 24-hour liquid culture of each bacterial species was used to obtain an initial optical density of 0.1. Each metal piece was suspended in a separate 50 mL Falcon tube and was incubated at 37°C and 220 RPM for 48 hours. Samples were stained with crystal violet dye and rinsed three times with distilled water Biofilm coverage was quantified using custom written MatLab code Metals were sterilized using 30% acetic acid, 70% ethanol, and UV light before each biofilm formation test. Results: Macro EDM (MRR and Overcut) Mean of SN ratios for MRR versus Discharge current, Time-on, Time-off, Gap voltage for 0 and 5 g/l concentration 16 Mean of SN ratios for Overcut versus Discharge current, Time-on, Time-off, Gap voltage for 0 and 5 g/l concentration Results: Micro EDM (MRR and Overcut) 17 Mean of SN ratios for MRR versus Capacitance, Voltage, and Powder Concentration Mean of SN ratios for Overcut versus Capacitance, Voltage, and Powder Concentration Results: Micro EDM (Optical microscope) Optical microscope captures of micro-EDM treated Ti-6Al-4V holes for different discharge energies Tungsten carbide electrode tool Constant electrode rotational speed of 1000 rpm 18 a) 0.405 µJ b) 0.5 µJ c) 0.605 µJ d) 4.05 µJ e) 5 µJ f) 6.05 µJ g) 40.5 µJ h) 50 µJ i) 60.5 µJ Results: SEM images of Micro EDM treated samples 19 SEM captures for different discharge energies for micro-EDM of Ti-6Al-4V Tungsten carbide electrode tool a) 0.405 µJ b) 0.5 µJ c) 0.605 µJ d) 4.05 µJ e) 5 µJ f) 6.05 µJ g) 40.5 µJ h) 50 µJ i) 60.5 µJ Results: EDS analysis (Micro EDM) 20 Ti-6Al-4V alloy used had 90 wt.% Ti, 6 wt.% Al, 4 wt.% V, 0.2 wt.% O, and 0.05 wt.% N. Material transfer was observed from tungsten carbide electrode and hydroxyapatite powder in dielectric. Tungsten was identified from electrode and calcium and phosphorus from hydroxyapatite powder. . Element Line Mass% Atom% Al K 2.87±0.01 6.00±0.02 P K 0.18±0.00 0.33±0.01 Ca K 0.02±0.00 0.03±0.00 Ti K 70.46±0.04 82.9±0.05 V K 3.15±0.01 3.49±0.01 Co K 0.17±0.01 0.16±0.01 W M 23.14±0.04 7.09±0.01 Total   100 100     Fitting ratio 0.0450   Element Line Mass% Atom% Al K 5.7±0.01 9.65±0.02 Ti K 89.45±0.04 85.19±0.04 V K 3.82±0.01 3.42±0.01 Na K 0.64±0.01 1.26±0.01 Cl K 0.29±0.00 0.38±0.00 K K 0.10±0.00 0.11±0.00 Total   100 100     Fitting ratio 0.0073   Results: Crater size measurements (Micro EDM) 21 Capacitance Voltage [V] Powder concentration [g/l] Crater area [µm2] 100 pF 90 0 34.116 100 pF 100 5 42.5024 100 pF 110 10 41.8264 1 nF 90 5 217.3106 1 nF 100 10 263.9776 1 nF 110 0 317.8454 10 nF 90 10 1354.6093 10 nF 100 0 2111.6435 10 nF 110 5 2877.3125 Results analyzed by measuring crater area for each experimental set using ImageJ software and captured in x1000 magnification Increase in capacitance and voltage leads to increase in crater size, while effect of powder concentration is moderate SN ratio approach used for further analysis, with capacitance being the most influential parameter followed by voltage and powder concentration Level Capacitance Voltage Powder concentration 1 39.48 535.35 821.2 2 266.38 806.04 1045.71 3 2114.52 1078.99 553.47 Delta 2075.04 543.65 492.24 Rank 1 2 3 Results: Hardness tests (Micro EDM) 22 The highest average hardness value of 445.5 was obtained at capacitance 5, voltage 110, and powder concentration 5 Addition of powder did not always result in an increase in hardness. The response table for signal-to-noise ratios shows that the most consistent and reliable results were obtained at level 3, with a delta of 0.85. Capacitance Voltage Powder concentration Hardness 1 [HV/0.2] Hardness 2 [HV/0.2] Hardness 3 [HV/0.2] Average hardness [HV/0.2] 100 pF 90 0 340.3 347.94 345.34 344.53 3 90 0 340.99 332.9 346.77 340.22 3 90 0 448.96 399.21 398.25 415.47 3 100 5 356.93 349.12 356.82 354.29 3 100 5 355.73 350.23 353.4 353.12 3 100 5 350.4 354.49 356.53 353.81 3 110 10 383.73 343.32 374.74 367.26 3 110 10 423.16 454.32 499.09 458.86 3 110 10 363.92 360.31 359.42 361.22 1 nF 90 5 343.6 368.93 371.15 361.23 4 90 5 373.85 369.78 394.67 379.43 4 90 5 362.24 362.39 375.03 366.55 4 100 10 394.47 404.8 376.05 391.77 4 100 10 397.22 378.3 392.5 389.34 4 100 10 403.73 400.33 415.04 406.36 4 110 0 377.84 354.83 353.46 362.04 4 110 0 386.76 386.68 377.94 383.79 4 110 0 367.33 507.28 444.49 439.7 10 nF 90 10 396.16 422.4 409.7 409.42 5 90 10 408.99 403.32 441.61 417.97 5 90 10 371.12 441.75 408.58 407.15 5 100 0 388.39 394.33 452.68 411.8 5 100 0 396.08 482.6 367.95 415.54 5 100 0 415.29 360.59 369.71 381.86 5 110 5 379.91 416.15 362.87 386.31 5 110 5 389.65 392.88 381.33 387.95 5 110 5 457.91 417.64 460.97 445.51 Level Capacitance Voltage Powder concentration 1 51.32 51.60 51.71 2 51.71 51.67 51.48 3 52.17 51.93 52.01 Delta 0.85 0.32 0.53 Rank 1 3 2 Results: surface roughness (Micro Wire EDM) 23 Surface roughness values varied significantly depending on input parameters. Surface roughness increased with higher discharge energy. Hydroxyapatite powder concentration effect was moderate. Energy Powder Roughness 1 [µm] Roughness 2 [µm] Roughness 3 [µm] Average roughness [µm] Low 0 0.295 0.279 0.243 0.272333 Medium 0 0.667 0.715 0.719 0.700333 High 0 1.763 1.715 1.567 1.681667 Low 5 0.274 0.249 0.343 0.288667 Medium 5 0.642 0.675 0.644 0.653667 High 5 1.71 1.861 1.745 1.772 Low 10 0.247 0.234 0.413 0.298 Medium 10 0.754 0.869 0.627 0.75 High 10 1.832 1.737 1.56 1.709667 Results: Contact angle (Micro Wire EDM) 24 Ti-6Al-4V samples treated with micro wire EDM were analyzed for contact angle using the sessile drop method Average contact angle values varied between 45.53° and 59.57° depending on input parameters used Higher surface roughness generally associated with a higher contact angle value Energy Powder (0, 5, 10 g/l) Contact angle 1 [˚] Contact angle 2 [˚] Contact angle 3 [˚] Average contact angle [˚] Low 0 52.8 49.7 61.5 54.67 Medium 0 52.1 51.4 51 51.50 High 0 55.8 55.8 51.1 54.23 Low 5 54.4 40.3 47.8 47.50 Medium 5 47 51 66.1 54.70 High 5 59.6 58.5 56.2 58.10 Low 10 43.6 47.6 45.4 45.53 Medium 10 64 60.5 54.2 59.57 High 10 44.7 58.3 62.8 55.27 Results: Biological attachments Staphylococcus aureus (Micro Wire EDM) 25 Low Medium High Left Right 0 g/l 5 g/l 10 g/l 0 g/l 0 g/l 5 g/l 10 g/l 10 g/l 5 g/l Results: Biological attachments of Escherichia Coli (Micro Wire EDM) 26 Low Medium High Left Right 0 g/l 5 g/l 10 g/l 0 g/l 5 g/l 10 g/l 0 g/l 5 g/l 10 g/l Results: Bacterial attachment (Micro Wire EDM) 27 Discharge energy and hydroxyapatite settings had a significant effect on bacterial adhesion properties. Unmachined surface of Ti-6Al-4V alloy had a higher tendency for bacterial adhesion compared to the machined surface. Powder mixed Wire EDM machining technique can be an effective method to improve the biocompatibility of Ti-6Al-4V alloy against bacterial strains, particularly for high energy settings and higher hydroxyapatite powder concentrations. Conclusion 28 Optimization of input parameters resulted in improvement of macro and micro EDM performance on Ti-6Al-4V The lowest bacterial attachment on micro wire EDM machined parts was achieved with: medium and high energy input high hydroxyapatite powder concentration low surface roughness Current Voltage Powder Medium and high energy settings are more effective in preventing bacterial adhesion on Ti-6Al-4V for all bacterial strains. Micro wire EDM machining can reduce bacterial adhesion on metallic surfaces. Proper combination of base material, electrode tool, dielectric, and powder additive in micro EDM machining can enhance biocompatibility. Input parameters have a significant effect on bacterial attachment. Thank you for your attention! www.nu.edu.kz References [1] V. D. Bui, J. W. Mwangi, and A. J. J. o. M. P. Schubert, "Powder mixed electrical discharge machining for antibacterial coating on titanium implant surfaces," vol. 44, pp. 261-270, 2019. [2] M. Navarro, A. Michiardi, O. Castano, and J. J. J. o. t. r. s. i. Planell, "Biomaterials in orthopaedics," vol. 5, no. 27, pp. 1137-1158, 2008. [3] C. Lhotka, T. Szekeres, I. Steffan, K. Zhuber, and K. J. J. o. O. R. Zweymüller, "Four‐year study of cobalt and chromium blood levels in patients managed with two different metal‐on‐metal total hip replacements," vol. 21, no. 2, pp. 189-195, 2003. [4] Z. Wang, Y. Fang, P. Wu, W. Zhao, and K. J. J. o. M. P. T. 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