Mehrdad Vahdati

Experimental study on the effect of finishing parameters on surface roughness in magneto-rheological abrasive flow finishing process

In this study, a novel precision finishing process for complex internal geometries using smart magneto-rheological polishing fluid is developed. Magneto-rheological abrasive flow finishing process provides better control over rheological properties of abrasive-laden finishing medium that exhibits changes in rheological behavior in the presence of external magnetic field. The finishing fluid used in this study contains SiC and iron particles with a combination of specific volume percentage of glycerin and liquid paraffin as abrasive, magnetizable and base medium parts, respectively. The smart characteristics of magneto-rheological fluid are utilized to precisely control finishing forces to control surface quality. A hydro-mechanical device is used to provide experimental setup in order to investigate the effects of different parameters on surface roughness. This device consists of a hydro-mechanical power unit, abrasive fluid containers, permanent Nd-Fe magnets, workpiece fixtures and a base frame. Experiments were conducted on austenitic stainless steel (AISI304), aluminum (7075 alloy) and copper (unalloyed) with different magnetic field strength, abrasive particle size and finishing time cycles. It is observed that by decreasing magnetic field strength, the surface roughness decreases in all three materials. Besides, with increase in abrasive particle mesh number, surface roughness tends to be higher. However, there is a slight difference observed through different finishing cycle times. The specific applications of this process are finishing fluid guidelines in precise instruments like capillary tubes in drug delivery setups.

An experiment on the shape and depth of air pocket on air spindle vibrations in ultra precision machine tools

In order to achieve nanometer accuracies, low vibration in air spindle is vital. Some parameters affecting air spindle vibration could be mentioned as rotational speed, inlet hole diameter, air pocket geometry, air gap pressure and so on. In this study, the air pocket geometry and depth plus rotational speed are experimentally investigated. Three levels of quantity are selected for each parameter. Vibration movements were considered as experiment output. Then, experimental results were analyzed by design of experiment method. The results showed that the air spindle with an air pocket of rectangular shape and 3 mm depth at low rotational speed has minimum vibrations.

Experimental investigation on effect of number and size of rectangular air pockets on air spindle vibrations in nanomachining

In order to achieve nanometer accuracies, the low vibration of air spindle and air table is vital. Number and size of air pockets in air spindles and air tables are important parameters in nanomachining vibrations. In this article, rotational speed as well as these parameters has been studied. Three levels are selected for each parameter and, in total, 27 experiments have been committed. Also, in this work, air pockets were rectangular. In this study, rotor considered externally which rotates about stator. Experiments were conducted with the help of a lathe machine. For vibration measurements, the VibroTest 60 was used. The results were analyzed using design of experiment method. Experimental results show that the air spindle with two air pockets with 200 mm2 area at a low rotational speed has minimum vibrations.

Effect of Tool Nose Radius on Nano-Machining Process by Molecular Dynamics Simulation

Today, there is a need to understand the micro mechanism of material removal to achieve a better roughness in ultra precision machining (UPM). The conventional finite element method becomes impossible to use because the target region and grids are very tiny. In addition, FEM cannot consider the micro property of the material such as atomic defect and dislocation. As an alternative, molecular dynamics (MD) simulation is significantly implemented in the field of nano-machining and nano-tribological problems to investigate deformation mechanism like work hardening, stick-slip phenomenon, frictional resistance and surface roughness [1]. One of the machining parameters than can affect nano-cutting deformation and the machined surface quality is tool nose radius [2]. In this paper molecular dynamics simulations of the nano-metric cutting on single-crystal copper were performed with the embedded atom method (EAM). To investigate the effect of tool nose radius, a comparison was done between a sharp tool with no edge radius and tools with a variety of edge radii. Tool forces, coefficient of friction, specific energy and nature of material removal with distribution of dislocations were simulated. Results show that in the nano-machining process, the tool nose radius cannot be ignored compared with the depth of cut and the edge of tool can change micro mechanism of chip formation. It appears that a large edge radius (relative to the depth of cut) of the tool used in nano-metric cutting, provides a high hydrostatic pressure. Thus, the trust force and frictional force of the tool is raised. In addition, increasing the tool edge radius and the density of generated dislocation in work-piece is scaled up that is comparable with TEM photographs [6].

Air pocket effects on air spindle vibrations in nanomachining

In this study, factors that affect air spindle vibrations have been investigated experimentally. In order to achieve nanometer accuracies, the low vibration of air spindle is vital. Shape, size, depth, number of air pockets, and rotational speed of air spindles are important parameters influencing nanomachining vibrations. A total of 3 levels are selected for each parameter and in total 243 experiments have been performed. In this study, the rotor is considered externally which rotates about a central stator. Experiments were committed by the help of a lathe machine. For vibration measurements, the VibroTest 60 has been used. Results have been analyzed using the Design of Experiment method. From the results, it has been analyzed that the air spindle with 2 circular/rectangular air pockets and with 300 mm2 area and 3 mm depth at a low rotational speed has minimum vibrations.

Investigation of Frictional Resistance in Nanometric Cutting by Molecular Dynamic Simulation

Recently, the development of machine tools and sub-micron positioning control systems has brought the minimum thickness of ultra-precision cutting to less than 1 nm. The conventional continuum based method (FEM) becomes impossible to use for numerical analysis. As an alternative method, molecular dynamics (MD) method is significantly implemented in the field of nano-machining to investigate cutting mechanism. In this paper, firstly, molecular dynamics simulations of the nanometric cutting of single-crystal copper were performed applying a pin tool. The model was solved with both Morse and Embedded Atom Method (EAM) potential functions to simulate the interatomic force between the work piece and a rigid tool. The nature of material removal, chip formation, and frictional forces were simulated. In order to investigate the coefficient resistance (the ratio of the cutting force to the thrust force), some MD simulations also carried for various cutting velocity and cutting depths. The results show that the Morse potential and EAM method have some difference to model tool forces and frictional resistance. Also, surface properties and atomic displacement in each of these potential functions have some discrepancy. In addition, cutting and trust forces increase with the cutting velocity and the depth of cut, however the effect of cutting speed is not very significant. Finally the value of frictional resistance is not changed with similar tool for various cutting speeds.Copyright

Evaluation of Parameters Affecting Magnetic Abrasive Finishing on Concave Freeform Surface of Al Alloy via RSM Method

The attempts of researchers in industries to obtain accurate and high quality surfaces led to the invention of new methods of finishing. Magnetic abrasive finishing (MAF) is a relatively new type of finishing in which the magnetic field is used to control the abrasive tools. Applications such as the surface of molds are ones of the parts which require very high surface smoothness. Usually this type of parts has freeform surface. In this study, the effect of magnetic abrasive process parameters on freeform surfaces of parts made of aluminum is examined. This method is obtained through combination of magnetic abrasive process and Control Numerical Computer (CNC). The use of simple hemisphere for installation on the flat area of the magnets as well as magnets’ spark in curve form is a measure done during testing the experiments. The design of experiments is based on response surface methodology. The gap, the rotational speed of the spindle, and the feed rate are found influential and regression equations governing the process are also determined. The impact of intensity of the magnetic field is obtained using the finite element software of Maxwell. Results show that in concave areas of the surface, generally speaking, the surface roughness decreases to 0.2 μm from its initial 1.3 μm roughness. However, in some points the lowest surface roughness of 0.08 μm was measured.

Molecular Dynamics Simulation on Nano-Machining of Single Crystal Copper with a Void

Nowadays, the ultra-precision machining with single diamond tools can remove materials at nanometer scale, which has been used to produce surface with high quality finishing. As far as the conventional finite-element method becomes impossible for numerical analysis, as an alternative, molecular dynamics (MD) method is significantly implemented in the field of nano-machining process to investigate cutting mechanism. Although it is well known that even the purest real material contains a large number of defects within its crystal structure, in conventional MD simulation of nano-cutting process the workpiece is assumed as a perfect single crystal. So, there is a need to check the effect of defect inclusion in the workpiece on nano-machining process.

Investigation of Interatomic Potential on Chip Formation Mechanism in Nanometric Cutting Using MD Simulation

Nowadays, the nano-machining process is used to produce high quality finished surfaces with precise form accuracy. To understand and analyze the chip formation mechanism of nano-machining process on an atomistic scale, since the experimentation is not an easy task, numerical simulation such as molecular dynamic (MD) simulation is a very useful method. In this paper, MD simulation of the nano-metric cutting of single-crystal copper was performed with a single crystal diamond tool. The model was solved with both pair wise Morse potential function and embedded atom method (EAM) potential to simulate the inter-atomic force between the work-piece and a rigid tool. The chip formation mechanism, dislocation generation, tool forces and generated temperature were investigated. Results show that the Morse potential cannot perform an appropriate defect formation and plastic deformation in nano-metric cutting of metals. Also, tool forces in Morse potential are more than the forces in EAM potential. Furthermore, the fluctuations of resultant forces in Morse potential are greater than that of EAM. In addition, using many-body interaction potentials like EAM can lead to substantial changes in surface energies, elastic-plastic properties and atomic displacement, compared with the pair-wise potentials like Morse. Finally, the atomic displacement investigation shows that in EAM potential study, only the atoms in a local region near the cutting process are displaced, but in Morse potential a large portion of atoms has affected during cutting process. Subsequently, the chip temperature in EAM potential is more than that of Morse potential.

Vibration Simulation of Air Slide Table in Ultra Precision Machines

The compressed air vibration in air slide table of ultra precision machines is an obstacle for gaining Nano-metric level of accuracies in the products created by these machines. In this article, the vibration behavior of air slide table due to compressed air layer is analyzed. The air slide table fluid and dynamic analytical model has been derived. In order to have air exit velocity from clearance gap, the finite element software FLUENT was applied. Finally, in order to calculate the displacements of table due to vibration and drawing its curves via time at the presence of varieties of air pressure, the second order differential equation was solved by MATLAB. In solving differential equation the Rang-Kutta method was used.