Afzaal Ahmed

Bio: Afzaal Ahmed is an academic researcher from Indian Institutes of Technology. The author has contributed to research in topics: Machining & Polishing. The author has an hindex of 7, co-authored 15 publications receiving 182 citations. Previous affiliations of Afzaal Ahmed include National University of Singapore.

Deposition and Analysis of Composite Coating on Aluminum Using Ti–B4C Powder Metallurgy Tools in EDM

Abstract: The present work investigates the method of depositing a ceramic coating on the surface of aluminum by means of electrical discharge coating (EDC) in electrical discharge machining (EDM). The present study makes use of powder metallurgy (P/M) green compacts made of titanium, boron carbide, and aluminum (Ti + B4C + Al) powder as the EDM tool for surface modification of aluminum workpieces. EDM process was carried out with different tool parameters like composition of the electrode material, compaction pressure of the green compacts, and different settings of the process variables like peak current and pulse duration setting. Responses observed were material deposition rate (MDR), tool wear rate (TWR), and average layer thickness (LT). Experiments were designed and carried out using Taguchi L18 orthogonal array. The most influential parameter for responses MDR, TWR, and LT was found to be peak current (Ip) with a percentage contribution of 60.72%, 59.52%, and 42.09%, respectively. In addition, various other...

A novel approach in high performance deep hole drilling of Inconel 718

Abstract: Application of deep holes is extensively found in the oil and gas industry to manufacture downhole equipment. These deep holes are fabricated in drill collars to deploy delicate sensors downhole for obtaining vital information like temperature, pressure and other geo-physical data from the bottom of the hole. High temperature and corrosion resistant materials like Inconel 718 is often used for drill collars to shield these sensitive communication equipment from the hostile downhole environment. Gundrilling is an established hole making method known for drilling precise and high aspect-ratio (AR>10) holes in conventional materials such as steels, cast iron and aluminium alloys etc. However, gundrilling of Inconel 718 offers unprecedented challenges like excessive tool wear, hole straightness deviation due to poor thermal conductivity and work-hardening tendency of the alloy. Moreover, as the drilling depth increases the deviation is further exacerbated due to the low rigidity of long gundrill shafts. The present study in the Phase 1 introduces a dynamic model using multispan Euler-Bernoulli beam theory to evaluate the effectiveness of coolant pressure and rotation speed during deep hole fabrication in Inconel 718. In addition, experimental investigations have been conducted to validate the model by studying the effects of coolant pressure and rotation speed on straightness of the fabricated holes. It was found that the straightness deviation was 0.37 mm corresponding to 137.89 bar and 1600 rpm coolant pressure and rotation speed respectively. In Phase 2, a non-contacting EDM process was used to fabricate a straight guide hole followed by conventional gundrilling (CG) with optimum pressure (137.89 bar) and speed (1600 rpm) obtained from the Phase 1 trials. The experimental results revealed that the thrust force reduced drastically from 800 N (CG) to 250 N (EDMG). Moreover, a significant improvement in both rake wear and flank wear was also observed. Finally, a straightness deviation of 0.19 mm was recorded for a maximum drilling depth of 350 mm which is 48.65% lesser than CG. From the study, it was found that this novel EDMG process improved the drilling capability of Inconel 718 by reducing the thrust force generated, enhancing tool life and minimizing the straightness deviation.

A comparative study on the modelling of EDM and hybrid electrical discharge and arc machining considering latent heat and temperature-dependent properties of Inconel 718

Abstract: Inconel 718 is one of the most widely used super alloys in industries like oil and gas, aerospace and automobile. However, properties like poor thermal conductivity and work hardening tendency make it difficult to machine, using a conventional machining approach. EDM is one of the effective and efficient ways of machining this exotic material. However, the material removal rate (MRR) is very low. In an attempt to enhance the performance of EDM, an arc machining module has been integrated into the existing EDM system and the compound process is named hybrid electrical discharge and arc machining (HEDAM). Due to the high thermal intensity of the sparks/arcs imparted by this process, the material removal rate is elevated. To understand this process better, a comparative thermal modelling between HEDAM and EDM has been presented in this article. Firstly, a thermal analysis is performed for the EDM and HEDAM processes to understand their respective erosion efficiencies. Finally, the numerical simulation for MRR of both EDM and HEDAM is presented. Unlike other EDM models, in this simulation, the thermophysical properties of the material were considered to be temperature-dependent and the latent heat of fusion was incorporated into the modelling process. A comparative analysis was also performed, which showed that incorporating such variables increases the accuracy of the obtained results. The study revealed that the spark radius in HEDAM is larger in size and more stable. Consequently, this resulted in HEDAM to have about three times more erosion efficiency compared to conventional EDM.

Experimental investigations in powder mixed electric discharge machining of Ti–35Nb–7Ta–5Zrβ-titanium alloy

Abstract: The present research is the first type of study in which the application of powder mixed electrical discharge machining (PMEDM) for the machining of β-phase titanium (β-Ti) alloy has been proposed....

Surface modification of β-phase Ti implant by hydroaxyapatite mixed electric discharge machining to enhance the corrosion resistance and in-vitro bioactivity

Abstract: The study presented an innovative method for surface modification of β-phase titanium alloy using hydroxyapatite mixed electric discharge machining (HAM-EDM). The process enables one to deposit in-situ a biomimetic nano-porous HA-containing layer while shaping the base titanium, hence modifying the surface properties of the original substrate. A series of the dedicated HAM-EDM on titanium alloys have been conducted. Surface integrity, topography, and elemental composition of the modified surface were investigated by FE-SEM, EDS, XRD, and indentation techniques, while in vitro cell study was performed to evaluate biocompatibility and cell attachment of the treated surface. The morphology characterization results revealed that a natural bone-like nano-porous surface topography has been imparted on the β-phae Ti implant surface using the HAM-EDM. The EDS and XRD examinations showed that the deposited layer comprised of Ti, Nb, Ta, Zr, O, Ca and P elements and formed biocompatible phases such as Ca 3 (PO 4 ) 2 , CaZrO 3 , Nb 8 P 5 , CaO, TiP, Nb 4 O 5 , and TiO 2 , TiH on the β-Ti implant surface, which improved the bioactivity of the alloy and beneficial for the promotion of osseointegration. The results revealed that a 18–20 μm thick recast layer containing biocompatible phases was generated, which has excellent metallurgical bonding with the base surface and offered mechanical interlocking to delamination. The HA deposited surface shows am improved hardness of 1275 HV which is 3-fold higher than the untreated surfaces; predominantly owing to the deposition of hard oxides on the modified surface. The HA-deposited bioceramic layer presented an excellent and higher corrosion resistance as compared to EDMed and un-treated specimens in simulated body fluid. The in-vitro bioactivity results confirmed that the nano-porous HA-containing layer exhibited the superior bioactivity and promotes adhesion, growth, proliferation, and differentiation of human osteoblastic MG-63 cells.

Surface Modification of Ti-6Al-4V Alloy by Electrical Discharge Coating Process Using Partially Sintered Ti-Nb Electrode.

Abstract: In the present research, a composite layer of TiO2-TiC-NbO-NbC was coated on the Ti-64 alloy using two different methods (i.e., the electric discharge coating (EDC) and electric discharge machining processes) while the Nb powder were mixed in dielectric fluid. The effect produced on the machined surfaces by both processes was reported. The influence of Nb-concentration along with the EDC key parameters (Ip and Ton) on the coated surface integrity such as surface topography, micro-cracks, coating layer thickness, coating deposition, micro-hardness has been evaluated as well. It has been noticed that in the EDC process the high peak current and high Nb-powder concentration allow improvement in the material migration, and a crack-free thick layer (215 μm) on the workpiece surface is deposited. The presence of various oxides and carbides on the coated surface further enhanced the mechanical properties, especially, the wear resistance, corrosion resistance and bioactivity. The surface hardness of the coated layer is increased from 365 HV to 1465 HV. Furthermore, the coated layer reveals a higher adhesion strength (~118 N), which permits to enhance the wear resistance of the Ti-64 alloy. This proposed technology allows modification of the mechanical properties and surface characteristics according to an orthopedic implant’s requirements.