Saeed Daneshmand

Influence of Layer Thickness on the Design of Rapid-Prototyped Models

Today, engineers are aiming for performance, quality, and repeatability, to be reached in a very short delivery time. Rapid-prototyping techniques are applied to concept design and modeling. A typical aircraft development program usually needs at least four to five wind-tunnel models to adequately test the aerodynamics of a new airframe. The models are generally made of steel or aluminum. The models can require months to be manufactured. The dimensional accuracy, surface finish, and strength of such all-metal models have a distinguished history of providing high-fidelity aerodynamics data for both subsonic and supersonic aircraft. However, the fabrication of all-metal wind-tunnel models is very expensive and time-consuming. This paper describes the effects of layer-thickness models on aerodynamic coefficients to construct wind-tunnel-testing models produced with rapid prototyping. These models were fabricated from SOMOS NanoTool by stereolithography. The layer thickness for each model was 0.025, 0.05, and 0.1 mm. Testing covered the Mach range of Mach 0.10 to 0.40. Results from this study show that layer thickness does have an effect on aerodynamic characteristics. The layer thickness is more effective on the aerodynamic characteristics when Mach number is decreased and has the most effect on the aerodynamic characteristics of axial force.

Effect of Tool Rotational and Al2O3 Powder in Electro Discharge Machining Characteristics of NiTi-60 Shape Memory Alloy

Nickel titanium is an intelligent alloy which are used in optical devices, thermal sensors, actuators, medical equipment and aerospace, because memory shape property, high strength, good creep and fatigue resistance. This alloy has features like the response to electrical stimulation, thermal, magnetic and mechanical stimulation. According to hardness and mechanical properties of this alloy, one of the ways it is used for machining, is EDM. EDM is one of the machining of precision and complex parts methods which material removal rate, tool wear rate, surface roughness and thickness of the recast layer one is very important in it. In this study the effect of current, voltage, pulse on time, pulse off time, tool rotational, Al2O3 powder, material removal rates, tool wear rate and surface roughness are examined. The results show that using Al2O3 powder and tool rotational along with increasing current intensity, pulse on time and voltage, increases the material removal rate. Rotation of the tool create a centrifugal force and Al2O3 powder increases the gap and the material removal rate. Rotation of the tool prevents spreading of the plasma channel and Al2O3 powder fills gap between tool and workpiece, decrease kinetic energy of ions and reduced tool wear rate. By adding powder Al2O3, rotation of the tool, reducing current intensity, voltage and time pulse, sparks get smaller and will have less penetration and surface roughness reduces.

Investigation of rapid manufacturing technology with ABS material for wind tunnel models fabrication

Abstract Nowadays, several procedures are used for manufacturing wind tunnel models. These methods include machining, casting, molding and rapid prototyping. Raw materials such as metals, ceramics, composites and plastics are used in making these models. Dimension accuracy, surface roughness and material strength are significant parameters which are effective in wind tunnel manufacturing and testing. Wind tunnel testing may need several models. Traditional methods for constructing these models are both costly and time consuming. In this research, a study has been undertaken to determine the suitability of models constructed using rapid manufacturing (RM) methods for use in wind tunnel testing. The aim of this research is to improve the surface roughness, dimensional accuracy and material strength of rapid manufacturing models for testing in wind tunnels. Consequently, the aerodynamic characteristics of three models were investigated and compared. The first model is made of steel, the second model from FDM-M30, and the third model is a hybrid model. Results show that metal models can be replaced by hybrid models in order to measure aerodynamic characteristics, reduce model fabrication time, save fabrication cost and also to verify the accuracy of aerodynamic data obtained in aerospace industry.

Investigation of Surface Roughness on Aerodynamics Properties

This paper describes the effects of surface finish models on aerodynamic coefficients for constructed wind-tunnel testing models. Three models were evaluated. These models were fabricated from aluminum 2024-T4 by computer numerical control (CNC) machining. The roughness of surfaces for each model was 6.3, 60, and 150 μm, which was determined by PERTHOMETER2. A wing-body-tail configuration was chosen for the actual study. Testing covered the Mach range of Mach 0.3 to 1.2 at an angle-of-attack range of +6 to +26 deg at zero sideslip and an angle-of-sideslip range of -8 to +8 deg at a 16-deg angle of attack; the coefficients of normal force, axial force, pitching moment, and lift over drag are shown at each of these Mach numbers. Results from this study show that surface finish does have an effect on the aerodynamic characteristics in general; the data differ between the three models by less than 5%. The surface finish does have more effect on the aerodynamic characteristics when the Mach number is decreased and has the most effect on the aerodynamic characteristics of axial force and its derivative coefficients.

Optimization of Electrical Discharge Machining Parameters for NiTi Shape Memory Alloy by Using the Taguchi Method

Electrical discharge machining (EDM) is among the most essential nontraditional machining processes. Material removal rate (MRR) and surface roughness are the two main parameters applied in this method. A desired surface roughness can be achieved at the maximal MRR by selecting the optimal input parameters. Because of the mechanical properties and hardness of shape-memory nickel titanium (NiTi) alloy, material can be removed using an EDM method. NiTi alloy is widely used in marine science and aerospace industries. Surface roughness is a critical parameter affecting the machining of this alloy. This study examined the effect the input parameters (pulse current, gap voltage, pulse on time, and pulse off time) on the output parameters (surface roughness and MRR) to determine the minimal surface roughness and maximal MRR for NiTi alloy. Accordingly, the Taguchi method and analysis of variance were employed to optimize the machining parameters. The modeling and experimental results indicate that pulse current and pulse-on time are the most critical parameters affecting MRR and surface roughness.

Design and Production of Wind Tunnel Testing Models with Selective Laser Sintering Technology Using Glass-Reinforced Nylon

In this study, the ability of Selective Laser Sintering (SLS) Technology for production of wind tunnel testing models are evaluated. It has been undertaken to determine the suitability of the Model constructed with SLS method in subsonic and transonic wind tunnel testing. Two models were evaluated in this study. The first model was fabricated from aluminum 5086-H32 by a CNC machining technique. The other model had the same section but was fabricated by the selective laser sintering (SLS) process. Aerodynamic characteristics and times as well as costs of both models were measured in 0.3 to 1.2 Mach and the results were compared. The longitudinal aerodynamic data and the normal force data obtained from SLS model showed good agreement with data obtained from the aluminum model. The greatest difference in the aerodynamic data between two models is the total axial force. The time and the cost of production are considerably reduced with use of SLS model.

On the control of a single flexible arm robot via Youla-Kucera parameterization

In this paper, based on the Youla-Kucera (Y-K) parameterization, the control of a flexible beam acting as a flexible robotic manipulator is investigated. The method of Youla parameterization is the simple solution and proper method for describing the collection of all controllers that stabilize the closed-loop system. This collection comprises function of the Youla parameter which can be any proper transfer function that is stable. The main challenge in this approach is to obtain a Youla parameter with infinite dimension. This parameter is approximated by a subspace with finite dimensions, which makes the problem tractable. It is required to be generated from a finite number of bases within that space and the considered system can be approximated by an expansion of the orthonormal bases such as FIR, Laguerre, Kautz and generalized bases. To calculate the coefficients for each basis, it is necessary to define the problem in the form of an optimization problem that is solved by optimization techniques. The Linear Quadratic Regulator (LQR) optimization tool is employed in order to optimize the controller gains. The main aim in controller design is to merge the closed-loop system and the second order system with the desirable time response characteristic. The results of the Youla stabilizing controller for a planar flexible manipulator with lumped tip mass indicate that the proposed method is very efficient and robust for the time-continuous instances.

Investigation of Weight Percentage of Alumina Fiber on EDM of Al/Al 2 O 3 Metal Matrix Composites

This paper aims to study the influence of Al2O3 particle addition to Al alloys. The effects of reinforcement volumes in a metal matrix alloy on response variables were investigated towards the highlighting of this process with the goal of achieving high process performance. In this study, the comparison between EDM of Al/Al2O3 metal matrix composites with different volumes of reinforcement and 2024 alloys was investigated to determine the influence of weight percentage of Al2O3-reinforced particles on output parameters. The results show that addition of Al2O3 particles in the composites has significant effects on material removal rate, surface roughness and tool wear rate. Tool wear rate and surface roughness were increased with increased Al2O3 ceramic contents. Surface roughness was obviously affected by the discharge current as well as pulse on-time. Rapid increase in tool wear rate was seen when reinforced with higher weight percentage of Al2O3 particles. The pulse on-time and discharge current significantly affect the material removal rate, tool wear rate and surface roughness. Tool wear rate, material removal rate and surface roughness were high if the discharge current and pulse on-time were set at a higher level. In other words, high current and pulse on-time resulted in high tool wear rate, material removal rate and surface roughness. The material removal rate was decreased by increasing the weight percentage of Al2O3 particles.

Investigation and optimization of the electro-discharge machining parameters of 2024 aluminum alloy and Al/7.5% Al2O3 particulate-reinforced metal matrix composite

Abstract Being newly advanced materials, metal matrix composites enjoy the properties of high service temperature, light weight, high specific strength, good wear resistance, high stiffness, and a low thermal expansion coefficient. However, machining these materials by conventional methods is difficult. A key machining process for difficult-to-machine materials like composites is electro-discharge machining, which is widely used in non-conventional material removal processes. The current work aims to identify different parameters, such as voltage, current, pulse on-time, and pulse off-time, which influence the material removal rate (MRR), tool wear rate (TWR), and surface roughness (SR). By applying regression equations, a mathematical model is adopted to estimate MRR, TWR, and SR. The optimum machining parameters are investigated using the Taguchi method with L9 orthogonal array. The optimum values are also analyzed by multi-objective Taguchi method with calculation of total normalized quality loss (TNQL) and multi-signal to noise ratio (MSNR) included. Analysis of the Taguchi method introduced voltage and pulse off-time as the two main significant factors that influence the value of the material removal rate. The discharge current and pulse off-time also have a statistically significant impact on both tool wear rate and surface roughness.

ELECTRICAL DISCHARGE MACHINING OF Al/7.5% Al2O3 MMCs USING ROTARY TOOL AND Al2O3 POWDER

Nowadays, composites are used in different parts of industries and it is one of the most important subjects. The most widely used reinforcements in metal matrix composites are Al2O3 and SiC fibers and particles which may be used in cutting-edge functional and structural applications of aerospace, defense, and automobile industries. Depending on the type of powder used, composite materials are difficult to machine by conventional cutting tools and methods. The most appropriate way for machining of these composites is electro discharge. For the reason of improving the surface quality, tool wear rate and material removal rate and reducing the cracks on the surface, Al2O3 powder was used. In this study, the effect of input parameters of EDM such as voltage, pulse current, pulse on-time and pulse off-time on output parameters like material removal rate, tool wear rate and surface roughness in both conditions of the rotary tool with powder mixed dielectric EDM and the stationary tool excluding powder mixed dielectric were investigated. The critical parameters were identified by variance analysis, while the optimum machining parameter settings were achieved via Taguchi method. Results show that using of powder mixed dielectric and rotary tool reduce the tool wear rate, surface roughness and the cracks on the surface significantly. It is found also that using of powder mixed dielectric and rotary tool improve the material removal rate due to improved flushing action and sparking efficiency. The analysis of variance showed that the pulse current and pulse on-time affected highly the MRR, TWR, surface roughness and surface cracks.