Ahmad Barari

Search-Guided Sampling to Reduce Uncertainty of Minimum Deviation Zone Estimation

Integrating computational tasks in coordinate metrology and its effect on the inspection’s uncertainty is studied. It is shown that implementation of an integrated inspection system is crucial to reduce the uncertainty in minimum deviation zone (MDZ) estimation. An integrated inspection system based on the iterative search procedure and online MDZ estimation is presented. The search procedure uses the Parzen Windows technique to estimate the probability density function of the geometric deviations between the actual and substitute surfaces. The computed probability density function is used to recognize the critical points in the MDZ estimation and to identify portions of the surface that require further iterative measurements until the desired level of convergence is achieved. Reduction of the uncertainty in the MDZ estimation using the developed search method compared to the MDZ estimations using the traditional sampling methods is demonstrated by presenting experiments including both actual and virtual inspection data. The proposed search method can be used for assessing any geometric deviations when no prior assumptions about the fundamental form and distribution of the underlying manufacturing errors are required. The search method can be used to inspect and evaluate both primitive geometric features and complicated sculptured surfaces. Implementation of this method reduces inspection cost as well as the cost of rejecting good parts or accepting bad parts. DOI: 10.1115/1.2798114

Global adaptive slicing of NURBS based sculptured surface for minimum texture error in rapid prototyping

Purpose – This paper aims to propose a global adaptive direct slicing technique of Non-Uniform Rational B-Spline (NURBS)-based sculptured surface for rapid prototyping where the NURBS representation is directly extracted from the computer-aided design (CAD) model. The imported NURBS surface is directly sliced to avoid inaccuracies due to tessellation methods used in common practice. The major objective is to globally optimize texture error function based on the available range of layer thicknesses of the utilized rapid prototyping machine. The total texture error is computed with the defined error function to verify slicing efficiency of this global adaptive slicing algorithm and to find the optimum number of slices. A variety of experiments are conducted to study the accuracy of the developed procedure, and the results are compared with previously developed algorithms. Design/methodology/approach – This paper proposes a new adaptive algorithm which globally optimizes a texture error function produced by ...

Surface Topography of Additive Manufacturing Parts Using a Finite Difference Approach

Inspection of surface integrity in additive manufacturing (AM) parts essentially needs a detailed understanding of their actual surface topography. Todays optical surface topography and roughness measurement sensors only provide information of the discrete points measured from the manufactured surface and not a detailed reconstruction of the surface topography. This paper presents a finite difference approach for reconstruction of the surface topography using sample measured data points. The developed methodology can be used in the surface quality inspection of the additive manufactured parts, their surface texture modeling, surface integrity analysis, and in planning for the required postprocessing or down-stream surface finish processes suitable for them. The methodology is fully implemented, and variety of experiments is conducted. The results show that the developed methodology is successful to reconstructed surface topography of the AM parts.

NURBS representation of estimated surfaces resulting from machining errors

A new approach to model the actual machining result as a NURBS surface is presented, which explicitly expresses the geometry and topology of the final product and increases the clarity in the mathematical representation of quasistatic machining errors. Most of the available models that estimate interaction of quasistatic machining errors present the actual position of individual machined points and are unable to explicitly describe the resulting machined surface. During the machining process, the desired geometry is mapped from the ideal computer-aided design (CAD) vector space into the machine tools vector subspaces. Using a Jacobian of the deformed geometry, it is shown that for a variety of three-axis machine tool configurations, a linear operator can be found to express this transformation. Classified error operators for all different configurations of three-axis machine tools are derived and the applicability of the developed method is illustrated by simulating the machining process using case studies. The developed model can be utilised in virtual machining and simulation of the machining process, modification of the design within a design for a manufacturing platform, and also in on-line error compensation during the machining process.

Design for Manufacturing of Sculptured Surfaces: A Computational Platform

This paper presents a computer aided design for machining (DFMc) platform that enables designers to customize the design for the available machine tools and to estimate the effect of design decisions on the accuracy of the final machined products, particularly those containing sculptured surfaces. The platform contains two modules to model and simulate the actual machined surface and to evaluate the resulting minimum deviation zone compared to the desired geometry. In the first module, based on the configuration of the available machine tool and the limitations imposed by its inherent errors, the machined surface is simulated and presented as a nonuniform rational B-spline (NURBS) surface. In the second module, the minimum deviation zone between the actual and the nominal NURBS surfaces is evaluated when the developed method to do this task efficiently improves the convergence of the resulting optimization process. Utilizing this platform, two different applications are developed; design tolerance allocation based on the minimum deviation zone of the machined surface and adaptation of the nominal design to compensate for the effect of machining errors. Employing these applications during the design stage improves the acceptance rate of the produced parts and reduces the rate of scrap and rework. The DFMc platform and its presented applications can be implemented in any integrated computer aided design/computer aided manufacturing (CAD/CAM) system. The presented methods can be applied to any type of input geometries and are particularly efficient for design and manufacturing of precise components with complex surfaces. Products in this group, such as dies and tools, medical instruments, and biomedical implants, mostly have critical and important functionalities that demand very careful design and manufacturing decisions.

Effect of Adaptive Slicing on Surface Integrity in Additive Manufacturing

In today’s Additive Manufacturing (AM), a part is typically manufactured using layer by layer addition of material from a Computer Aided Design (CAD) model. Traditionally the CAD model is transferred to RP system after exchanging to Stereo Lithography (STL) format which is triangulated tessellation of the CAD model. Then it is sliced using different slice algorithms and machine constraints. The inherent uncertainties in this process have led to development of adaptive direct slicing technique. There are several adaptive slicing techniques but only few researches have been done to calculate an actual surface error factor and the cost aspect of the slicing algorithm. This paper proposes new adaptive algorithm to compute a surface error factor and to find the cost effective approach for slicing. The adaptive slicing algorithm dynamically calculates slice thickness and it is based on the allowable threshold for surface integrity error to optimize the cost and time. The paper also provides comparative study of previously developed adaptive models by the authors based on cusp height and surface integrity.Copyright

Development of a DSM-Based Methodology in an Academic Setting

This paper proposes the use of a design structure matrix/work transformation matrix (DSM/WTM)-based methodology in academic settings to serve engineering educators as a facilitating tool for predetermining the difficulty and feasibility of design engineering projects they assign, given both the time constraints of the academic term and the expected skill level of the respective learners. By using a third-year engineering design project as a case study, engineering students actively participated in this comprehensive use of DSM methodologies. The engineering design process has been thoroughly analyzed to determine convergence characteristics based on the eigenvalues of the system followed by a sensitivity analysis on the originally determined DSM based on data provided by students in terms of task durations and number of iterations for each task. Finally, an investigation of the design process convergence due to unexpected events or random disturbances has been conducted. The obtained predictive model of the design process was compared to the actual dynamics of the project as experienced by the students and the effect of random disturbances at any point in the design process has thereby been evaluated. [DOI: 10.1115/1.4005591]

Handling and safety enhancement of race cars using active aerodynamic systems

A methodology is presented in this work that employs the active inverted wings to enhance the road holding by increasing the downward force on the tyres. In the proposed active system, the angles of attack of the vehicles wings are adjusted by using a real-time controller to increase the road holding and hence improve the vehicle handling. The handling of the race car and safety of the driver are two important concerns in the design of race cars. The handling of a vehicle depends on the dynamic capabilities of the vehicle and also the pneumatic tyres’ limitations. The vehicle side-slip angle, as a measure of the vehicle dynamic safety, should be narrowed into an acceptable range. This paper demonstrates that active inverted wings can provide noteworthy dynamic capabilities and enhance the safety features of race cars. Detailed analytical study and formulations of the race car nonlinear model with the airfoils are presented. Computer simulations are carried out to evaluate the performance of the proposed active aerodynamic system.

Analysis of nonlinear oscillation of circular curved carbon nanotube

The nonlinear vibration of a circular curved carbon nanotube using Euler-Bernoulli beam theory is investigated. The governing equation of motion of the system is developed and the Galerkin method is utilized to obtain the nonlinear ordinary differential equation of the curved carbon nanotube. A quarter-circular curvature is considered for the nanotube and it is assumed to have a single wall with simply-supported boundary conditions. Two semi analytical approaches to study the behavior of the developed nonlinear differential equation are utilized and the frequency-amplitude relationship of the objective system is obtained. Subsequently, a parametric study is performed to study the importance of different parameters, such as the amplitude of oscillation and the curvature radius, on the nonlinear behavior of the system. Finally, numerical simulation is carried out to obtain the results and investigate the accuracy of the analytical solution methods applied.

Study of the Effect of Coating Parameters and Substrates on 3D Surface Roughness in Diamond-Like-Carbon Coating Process

Abstract This paper presents an experimental platform which is used to study the effect of Diamond-Like-Carbon (DLC) coating on surface roughness. Variety of experiments is conducted and the effect of variation of the coating process parameters and type and combination of sub-layers on the surface roughness of the coated part is discussed. It is shown how DLC coating can decrease the surface roughness and the amount of decrease has direct relationship with the coating thickness. It is shown that with a thick enough coating, approximately the same surface roughness results can be obtained from surfaces with different uncoated roughness. This means that if a part is going to be DLC coated to achieve a certain tribological property, the surface finishing process during machining can be reduced.