Papers by Author: A.K.M. Nurul Amin

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Authors: M.A. Mahmud, A.K.M. Nurul Amin, M.D. Arif
Abstract: Soda-Lime glass is a very hard and brittle material which is commonly used as window panels and many other common applications. Due to its low fracture toughness it is very difficult to machine and obtain good surface finish under nornal cutting conditions. Hence, machining has to be done in ways to avoid brittle fracture on the finished machined surface. Such machining is only possible under ductile mode machining conditions when the removal of material is performed in the plastic state. However, ductile mode machining requires that during machining the temperature generated in the cutting zone in the working temperature range of glass to avoid crack formation during machining. This makes all types of machining of glass an extremely challenging affair, given the current state and mode of mechanical machining. This research paper elucidates the results of an experimental study for determination of critical depth of cut as a function of cutting parameters in high speed end milling of soda-lime glass. The critical depth is defined as the depth of cut at which crack formation the material is initiated for a given high speed attachment. In determining the critical depth as well as the ductile brittle transition depth, machining was performed on a tapered surface. Vibration signals from an accelerometer in time domain (amplitude vs. time display) and the surface characteristics were used in identifying the critical depth of cut. The new method has been found to be useful in online determination of the critical depth, as well as the brittle-ductile transition depth, for generating crack-free surfaces with good surface finish in high speed end milling of soda lime glass.
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Authors: A.K.M. Nurul Amin, A.A. Che Omar, M.A. Mohammed Kamal, Mahmoud M.A. Nassar, N.F. Mohd Zaib, Muammer Din Arif
Abstract: Soda lime glass is widely used in optics, chemical apparatus, camera lens, micro gas turbines, light bulbs etc. on account of its high hardness, corrosion resistance, and excellent optical properties. These require high dimensional accuracy and flawless surface finish. However, soda lime glass is inherently brittle leading to subsurface crack propagation and fracture which compromise its functionality. To avoid these defects, the machining needs to be performed under ductile mode conditions. Therefore, this research investigates the viability and requisite conditions for achieving ductile regime machining (DRM) in high speed micro-end milling of soda lime glass. Machining was performed at high cutting speeds (30,000 to 50,000 rpm), feed rate (5 to 15 mm/min), and depth of cut (3 to 7 μm). A surface profilometer was then used to measure the surface roughness and a scanning electron microscope (SEM) used to scrutinize the resultant machined surfaces. The results demonstrate that ductile streaks and rounded gummy chips (without sharp or jagged edges) are produced in all runs. In addition, there are no subsurface cracks and the minimum surface roughness attained is 0.08μm. These indicate that DRM of soda lime glass is obtainable using high-speed micro end milling in a conventional end mill with tungsten carbide inserts.
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Authors: A.K.M. Nurul Amin, Suhaily Mokhtar, Muammer Din Arif
Abstract: Inconel 718 is used for high-temperature applications in aerospace, nuclear, and automotive industries due to its resistance, at high temperatures, to corrosion, fatigue, creep, oxidation, and deformation. Unfortunately, these same qualities also impair its machinability and researchers have investigated on ways to machine it economically. Some unconventional machining practices such as: Plasma Enhanced and Laser Assisted Machining etc. have been applied. However these practices increase the machining cost. This research investigated the viability of high speed end milling of Inconel 718 using circular Silicon Nitride (ceramic) inserts under room temperature conditions. Tool wear (flank and notch wear), machining vibration amplitude and average surface roughness were evaluated for the feasibility analysis. A vertical CNC mill was used to machine Inconel 718 samples using different combinations of three primary machining parameters: cutting speed, feed, and depth of cut. Vibration data acquisition device and Datalog DasyLab 5.6 software were used to analyze machining vibration. Scanning Electron Microscope (SEM) and surface profilometer were utilized to measure tool (flank and notch) wear and surface roughness, respectively. It was observed that the machining vibrations, in high speed machining, was reasonable (0.045 V on the average). This resulted in acceptable tool wear (averages: flank wear = 0.25 mm, notch wear = 0.45 mm) and semi-finished surface roughness (0.30 µm) measured after every 30 mm length of cut. Thus, room temperature high speed machining of Inconel 718 using circular silicon nitride inserts is a practical option.
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Authors: Syidatul Akma Sulaiman, A.K.M. Nurul Amin, M.D. Arif
Abstract: Machining of metals is generally accompanied by a violent relative vibration between work and tool, known as chatter. Chatter is undesirable due to its adverse effects on product quality, operation cost, machining accuracy, tool life, and productivity. This paper presents an innovative approach to chatter control during end milling of titanium alloy Ti-6Al-4V using ferrite permanent magnets to reduce the unwanted vibrations. A special fixture was fabricated and mounted on a Vertical Machining Center‘s spindle for holding the permanent magnet bars, used in suppressing the vibration amplitudes. DASY Lab 5.6 was used for signal analysis and processing to compare the intensity of chatter under normal and magnet application conditions. Fast Fourier Transform (FFT) was subsequently used to transform the vibration data to a function of frequency domain. The experiments focused on monitoring the vibration amplitudes and analysis of chip formation process during metal cutting. It was observed that the magnetic fields contributed to reduction of chatter amplitudes. It was apparent that a reduction of chatter amplitude would result in improved surface finish of the work-piece and lead to uniform chip formation.
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Authors: A.K.M. Nurul Amin, Ummu Atiqah Khairiyah Bt. Mohamad, Muammer D. Arif, Asan Gani Bin Abdul Muthalif
Abstract: This paper presents the improvement in chatter vibration damping using different types and arrangements of magnets, as well as comparison with normal cutting conditions in turning of stainless steel AISI 304. Chatter is defined as the self-excited violent relative motion between the cutting tool and work-piece. It is the common vibration problem that limits the productivity of machining processes, since it leads to shortened tool life, poor surface finish, breakage and premature damage of cutting tool, as well as mechanical deterioration. The occurrence of chatter during metal cutting process also causes instability of the machine tool system. Though there has been a large number of works on identifying the causes of chatter and its behavior, there is still no consensus among researchers on this very vital issue of machining. Previously, the incidence of chatter was thought to be due to forced vibration, BUE formation, cutting speed, and cracking during chip formation. Different ways to overcome this problem have been investigated, such as using piezoelectric inertia actuators, feed-forward neural network controllers, and work-piece preheating methods. In this research, permanent magnets with different size, strength, and composition are mounted around the cutting tool. A vibration sensor (accelerometer) is placed at the bottom of the tool to record the suppression of chatter amplitude in turning operation. It is shown that magnetic force can modify the frequency response function of the cutting tool resulting in improved cutting stability in turning operations. Chatter can then be effectively suppressed due to increased cutting stability.
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Authors: A.K.M. Nurul Amin, A.A. Che Omar, M.A.Mohammed Kamal, Mahmoud M.A. Nassar, N.F. Mohd Zaib, Muammer Din Arif
Abstract: Soda lime glass is used extensively in camera lens, micro gas turbines, light bulbs, tablewares, optics, and chemical apparatus owing to its high hardness, excellent optical properties, and good corrosion and chemical resistance. Such applications of soda lime glass demand high machining and finishing precision. On the other hand, machining of glass poses significant challenges due to its inherent brittleness. The process of removal of material from glass, if not done in ductile mode, can generate subsurface cracks and brittle fractures which have adverse effects on its functionality. This research investigates the high speed micro-end milling of soda lime glass in order to obtain ductile regime machining. It has been found by other researchers that ductile mode machining can avoid sub-surface cracks and brittle fractures. However, in ductile mode machining, the gummy chips settle permanently on the machined surface affecting adversely the surface finish. In order to avoid such chip settlement, compressed air was directed using a special air delivery nozzle to blow away the resultant gummy chips, thereby preventing them from settling on the machined surface. Response surface methodology (RSM) and a commercial NC end mill were used to design and perform the machining runs, respectively. Machining was done using: high spindle speeds from 30,000 to 50,000 rpm, feed rates from 5 to 15 mm/min, and depth of cuts from 3 to 7 μm. Three different diameter carbide tools were used: 0.5, 1, and 2 mm. A surface profilometer was used to analyze the surface roughness of the resultant machined surface. Subsequently, the data was used for finding the best combination of cutting parameters required to obtain the lowest surface roughness. The results demonstrate that high speed machining is a viable option for obtaining ductile regime machining and generating machined surfaces with very low surface roughness in the range of 0.08μm – 0.22 μm, using 0.5 mm carbide end mill cutter.
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Authors: Syidatul Akma Sulaiman, A.K.M. Nurul Amin, M.D. Arif
Abstract: One of the most challenging issues in machining process is understanding the chatter phenomenon. Chatter mechanics is still not fully understood. It is inconsistent in character, making it difficult to analyze and predict. This research work investigates the influence of permanent magnets on chatter suppression in end milling of Titanium alloy (Ti-6Al-4V) using uncoated WC-Co insert. The experiments were designed based on the Response Surface Methodology (RSM) approach using DESIGN EXPERT (DOE) software. The experiments were performed under two different conditions: under normal condition and under the application of magnetic fields from two permanent magnets located in opposite direction. Ti-6Al-4V was used as the work material. The resultant average surface roughness was found to be reduced by a maximum of 50% due to magnet application. Scanning Electron Microscope (SEM) was used to analyze the chip morphology. The microphotographs showed the evidence of more stable chip formation under the influence of magnetic fields.
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Authors: A.K.M. Nurul Amin, Noor Syairah Khalid, Siti Nurshahida Mohd Nasir, Muammer D. Arif
Abstract: Machining of silicon is an expensive affair because its inherent brittleness leads to subsurface crack generation. Research endeavours have therefore focused on ductile mode machining of silicon to obtain crack free machined surfaces with roughness as low as 0.22 µm or even below, hence eliminating the need for subsequent polishing/grinding operations. However, most of these research works utilized expensive ultraprecision machines and tools. This research aimed at determining the viability of using conventional milling machines with diamond coated tools, high speed attachments, and air blowing mechanisms in order to achieve ductile regime machining of silicon. Spindle speed, depth of cut, and feed rate, ranges: 60,000 to 80,000 rpm, 10 to 20 µm, and 5 to 15 mm/min respectively, were considered as the independent machining parameters. Compressed air at 0.35 MPa was also provided to prevent chip deposition on the finished surfaces. The resultant surfaces were analysed using Optical and Scanning Electron Microscopes. Then, the influence of each machining parameter on surface roughness was investigated. From the analyses it was concluded that all three machining parameters and air blowing had significant influence on the surface topography and integrity of silicon.
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Authors: A.K.M. Nurul Amin, Muammer Din Arif, Siti Aminatuzzuhriyah B. Haji Subir, Fawaz Mohsen Abdullah
Abstract: Chatter is a type of intensive self-excited vibration commonly encountered in machining. It reduces productivity and precision, and is more noticeable in the machining of difficult-to-cut alloys like hardened steel. In such cases chatter causes excessive tool wear, especially flank wear, which in turn affects the stability of the cutting edge leading to premature tool failure, poor surface finish, and unsatisfactory machining performance. Nowadays, however, the demand is for fine finish, high accuracy, and low operation costs. Therefore, any technique which significantly reduces chatter is profitable for the industry. This paper demonstrates the viability and effectiveness of a novel chatter control strategy in the turning of (AISI 304) stainless steel by using permanent bar magnets. Reduction in chatter and corresponding tool flank wear are compared from results for both undamped and magnetically damped turning using coated carbide inserts. Special fixtures and keyway were made from mild steel in order to affix the magnets on the lathe’s carriage. The two ferrite magnets (1500 Gauss each) were placed below and beside the tool shank for damping from Z and X directions, respectively. Response surface methodology (RSM) was used to design the experimental runs in terms of the three primary cutting parameters: cutting speed, feed, and depth of cut. A Kistler 50g accelerometer measured the vibrations. The data was subsequently processed using DasyLab (version 6) software. The tool wear was measured using scanning electron microscope (SEM). Results indicate that this damping setup can reduce vibration amplitude by 47.36% and tool wear by 63.85%, on average. Thus, this technique is a simple and economical way of lowering vibration and tool wear in the turning of stainless steel.
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Authors: A.K.M. Nurul Amin, Fawaz Mohsen Abdullah, Muammer Din Arif, Israd H. Jaafar
Abstract: Chatter, a violent and often unpredictable relative oscillatory motion between the tool and work-piece, is a serious concern in turning operations. Its occurrence is usually associated with a loud monotonous sound and usually results in increased surface roughness, reduced material removal rates, shortened tool life, and damaged machine-tool bearings. The established theories for chatter are very limited in scope and are often contradicted by empirical evidences. Therefore, chatter avoidance in the past has relied on inefficient techniques like limiting material removal rates or expensive setups such as actuators and ultrasonic vibration damping systems. However, a deeper investigation into chatter formation reveals that chip morphology and segmentation play a significant role during the incidence of chatter. The novel Resonance theory of chatter combines the concept of mode coupling of the machining setup and serrated chip formation, to explain and predict chatter. To validate the postulates of this theory, models for chip serration frequency are essential. At the same time, a reliable and economical chatter control method is required. With this goal, the current research work has developed an empirical mathematical model of chip serration frequency in turning of stainless steel AISI 304 using Response Surface Methodology (RSM). Also, it investigated the influence of damping provided by magnetic field from a permanent ferrite magnet placed beneath the tool shank. The developed chip serration model is in good accord with the experimental data, demonstrating that the empirical model could be used for further chip morphology and chatter analyses.
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