Sharif Digital Repository

For various types of materials, milling process is extensively used to generate complex shapes with high quality. During the process and to achieve high removal rate, precision and better surface finish, chatter suppression is of great importance. An extended model of the milling process is presented in which the cutting forces are described as a third-order nonlinear function of chip thickness. Uncertainties associated with the process and tool parameters are also included to achieve a more realistic model. To suppress regenerative chatter, an H∞ robust control is designed based on µ-synthesis with DK-iteration algorithm. The controller guarantees the robust stability and performance of... 

To achieve higher accuracy in the prediction of cutting forces in finish milling process of sculptured parts, the curvatures of in-process workpiece surface are necessary to be taken into consideration in the calculation of cutter-workpiece engagement boundaries. These curvatures, however, are not readily available in tool path data, as the main existing source of geometrical information of the process. In this paper, first, a new straightforward algorithm is proposed to extract the principal curvatures and principal directions of the in-process workpiece surface from ball-end finish milling tool path data. These quantities, then, are employed to calculate the boundaries of engagement... 

The desired milling process with high material removal rate (MRR) and low surface roughness of the product can be achieved only if machining chatter is absent. Incorporating chatter into the optimal selection of the machining parameters leads to a complex problem. Therefore, the approach of selecting conservative intervals for the machining parameters is usually employed instead. In this paper, a practical approach is proposed to specify the optimal machining parameters (depth of cut and spindle speed) in order to maximize MRR and minimize forced vibrations by considering machining chatter. Firstly, the worst-case scenario-based optimization problem in terms of the surface quality is solved... 

Nanocrystalline Al-4 wt% Cu alloy reinforced with nanometric Al2O3 particles was synthesized by in situ reactive milling of Al and CuO powder mixture. X-ray diffraction (XRD), differential thermal analysis (DTA) and transmission electron microscopy (TEM) techniques were employed to study the mechanically induced solid state reaction between the blended powders. The mechanical milling stages were studied by scanning electron microscopy (SEM), bulk density measurement and laser particle size analyzer. It was shown that the reaction between Al and CuO occurs progressively as the mechanical milling continues, leading to formation of nanoscaled alumina particles. The grain refinement of the... 

In the present work, ultrafine-grained Al-5vol.% Al2O3 nanocomposite was synthesized through mechanical milling followed by direct powder extrusion method. The characteristics of the processed nanocomposite were examined by electron microscopy (SEM and TEM), Xray diffraction (XRD), tensile test and Vickers hardness measurement. It was shown that the addition of the reinforcement nanoparticles accelerates the milling process of the aluminum matrix and enhances the grain refinement of the aluminum matrix. An improved mechanical strength as compared with Al-Al2O3 microcompoiste was obtained. A dimple-type fracture mode was observed, which is a clear evidence of micro-deformation. In addition,... 

In the present work, the synergetic effect of Ti-based catalysts (TiH2 and TiO2 particles) on hydrogen desorption kinetics of nanostructured magnesium hydride was investigated. Nanostructured 84mol% MgH2-10%mol TiH2-6%mol TiO2 nanocomposite powder was prepared by high-energy ball milling and subjected to thermal analyses. Evaluation of the absorption/desorption properties revealed that the addition of the Ti-based catalysts significantly improved the hydrogen storage performance of MgH2. A decrease in the decomposition temperature (as high as 100°C) was attained after co-milling of MgH2 with the Ti-based catalysts. Meanwhile, solid-state chemical reactions between MgH2 and TiO2 nanoparticles... 

In this study, Cu-TiC nanocomposites were produced by high energy ball milling of elemental powders and in-situ formation of TiC in the copper matrix. Cu-40wt% Ti powder mixture were milled for 60 h, then graphite powder was added, subsequently milling was continued for further 10 h. Based on theoretical calculations, at this composite, the amount of TiC as reinforcement should be 60.25vol% (45.47wt%). The effect of milling time on solution progress of titanium in the copper lattice was studied by X-Ray diffraction analysis (XRD) with CuKα radiation. Considering XRD of Cu-40wt%TiC after 60 h milling data and Williamson-Hall relation, crystallite size and lattice strain of copper were... 

Because of corrosion resistance and antibacterial effects, shape memory Ni-Ti-Ag alloy can be considered for different biomedical applications. Mechanical alloying is used to produce nanostructured Ni-Ti-Ag alloy from elemental powders. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) are used to characterize the product. Results show that after 1h milling, homogenous distribution of the elements occurs; while no intermetallic compounds is observed. After 3h milling, titanium dissolves in nickel to form amorphous and nanostructured solid phases. Peaks of B2 phase appear in the XRD pattern after the 3h milling of the powder mixture. Sintering of the 3h-milled... 

Cu/SiC nanocomposite powders with homogeneously distributed nanosize SiC particles were produced by high energy mechanical milling (MM). Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and micro-hardness and density measurements were performed to understand the effects of microstructure and hardness on compaction behavior during MM. The effects of SiC nanoparticle content and mechanical milling time on apparent density (AD) and tap density (TD) of the nanocomposite powders were systematically investigated. The Hausner ratio (HR), defined as TD to AD, were estimated to evaluate friction between the particles. Increasing MM duration and SiC content resulted... 

Peripheral milling is extensively used in manufacturing processes, especially in aerospace industries where end mills are used for milling of wing parts and engine components. The generation of complex shapes with high quality for various types of materials is the main advantage of milling in contrast to other machining processes. During the milling process, the occurrence of self-excited vibrations or chatter may cause reduction in material removal rate (MRR), damage to the tool and spindle bearing or may result in poor dimensional accuracy and surface finish of the work-piece. In this paper, milling process is modeled as two degrees of freedom (2DOF) system in which the tool wear and... 

In this research, FINEMET alloy with composition of Fe73.5Si13.5B9Nb3Cu1 was produced by mechanical alloying from elemental powders. The effect of milling time on the magnetic and structural properties of alloy has been investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometery. The results showed that milling for 53 hr leads to the formation of Fe supersaturated solid solution which includes Si, B and Nb atoms with mean crystallite size of ~30 nm. The shift of the main peak of Fe to the higher angles indicated that Si and B atoms dissolve in the Fe solid solution, at primary stage of mechanical alloying, up to the... 

Effect of Al2O3 nanoparticles (80 nm) on the grain structure and phase formation in Ni-50Ti system during high-energy mechanical alloying (MA) was studied. While the formation of NiTi B2 phase occurs progressively during MA, it is shown that the hard inclusions cause abrupt phase formation at short milling times, particularly at higher nano-Al 2O3 contents. High-resolution transmission electron microscopy showed significant grain refinement in the presence of alumina nanoparticles to sizes less than 10 nm, which precedes the formation of semicrystalline structure and reduces the diffusion length and thus accelerates the phase formation. The composite powder reached steady-state MA condition... 

In this paper, chatter instability of micro end mill tools is studied by taking into account the process damping effect. The actual geometry of the micro tool including shank, taper part and fluted section is considered in the analysis. Timoshenko beam theory is utilized to consider the shear deformation and rotary inertia effects due to short and thick beam-type structures of each parts of the micro tool. The extended Hamilton's Principle is used to formulate a detailed dynamical model of the rotating micro end mill. The governing equations are solved by assumed mode model expansion. An exact dynamic stiffness method is developed to investigate modal characteristics of the tool including... 

FeNiCo base powder alloy with nominal composition Fe-27Ni-17Co-4Ti (wt%) was prepared from elemental powders by mechanical alloying. The structure of milled powders was characterized by XRD and SEM. The effect of nanosize structure on magnetic properties and shape memory behavior was studied using VSM and DSC. After milling for 240 minutes by high energy vibrational ball mill under argon atmosphere, supersaturated solid solution formed with mean crystallite size of ∼20 nm. Results of VSM examinations showed that by milling for 240 minutes saturation magnetization and intrinsic coercivity reached 304 emu/gr and 21 Oe, respectively. XRD analyses made it clear that transformation from BCC to... 

In this paper, internal resonance and nonlinear dynamics of regenerative chatter in milling process is investigated. An extended dynamic model of the peripheral milling process including both structural and cutting force nonlinearities is presented. Closed form expressions for the nonlinear cutting forces are derived through their Fourier series components. In the presence of the large vibration amplitudes, the loss of contact effect is included in this model. Using the multiple-scales approach, analytical approximate response of the delayed nonlinear system is obtained. Considering the internal resonance dynamics (i.e. mode coupling), the energy transfer between the coupled x-y modes is... 

The effect of high-energy ball milling on the textural evolution of alumina nanopowders (compaction response, sinter-ability, grain growth and the degree of agglomeration) during post sintering process is studied. The applied pressure required for the breakage of the agglomerates (P y) during milling was estimated and the key elements of compressibility (i.e. critical pressure (P cr) and compressibility (b)) were calculated. Based on the results, the fracture point of the agglomerates decreased from 150 to 75 MPa with prolonged milling time from 3 to 60 min. Furthermore, the powders were formed by different shaping methods such as cold isostatic press (CIP) and uniaxial press (UP) to better... 

Peripheral milling is extensively used in manufacturing industry. To achieve more material removal rate, high precision and surface quality and increase tool life, chatter vibration must be suppressed. In this paper, an extended dynamic model of the peripheral milling process including both the structural nonlinearity and nonlinear cutting forces is presented. Using the multiple-scale approach, as a perturbation technique, internal resonance of the milling process is investigated. Transfer of the energy between the coupled x-y modes is studied. According to results obtained, it is possible to adjust the rate at which the x-mode (or y-mode) decays by implementation of the internal resonance... 

The effect of particle size, lattice strain and crystallite size on the hydrogen desorption properties of nanocrystalline magnesium hydride powder was investigated. Commercial MgH2 powder was milled in a Spex 8000M up to 16 h and its structural evolution and desorption characteristics at different time intervals were examined using various analytical techniques. At the early stage of milling, the formation of metastable γ-MgH2 phase was noticed. While the crystallite size gradually decreased to 12 nm with increasing the milling time, the accumulated lattice strain gained a maximum value of 0·9% after 4 h milling. The highest drop in the desorption temperature (∼100°C) was attained at the... 

Mechanical milling proceeded by sintering was used to synthesize nanostructured temperature-resistant TZM alloy. Milling under Ar for different times (1, 2, 3, 5, 10, 15, 20, 25, and 30 h) and sintering at 1500, 1600 and 1700 °C for 30, 45, 60 and 90 min resulted in increasing of low-energy grain boundaries (LEGBs) and dispersion of TiC and ZrC with a size of ~ 65 nm in the matrix near LEGBs. Morphology and grain size of the products were determined from scanning electron microscope (SEM) images and X-ray diffraction (XRD) patterns, almost precisely. Optimum density of nanostructured TZM alloy ~ 9.95 ± 0.01 g/cm 3 was achieved by sintering at 1700 °C for 90 min  

Fungal delignification can be considered as a feasible process to pre-treat lignocellulosic biomass in biofuel production, if its performance is improved in terms of efficiency thorough a few modifications. In this study, Trichoderma viride was utilized to investigate the effect of wet-milling, addition of surfactant (Tween 80) and optimization of operating factors such as temperature, biomass to liquid medium ratio and glucose concentration on biodelignification of rice straw. Next, the enzymatic hydrolysis of pretreated biomass was studied at various pretreatment times. Results revealed that the wet milling and addition of surfactant increases the lignin removal about 15% and 11%,...