Papers by Author: Khalil Khalili

Abstract: Robotic machining is an attractive, cost-effective, and flexible alternative for basic machining applications. Having these characteristics, industrial robots are assumed to be the next generation of machine tools. But, due to weaker structure of robotic manipulators in comparison to conventional CNC machines, robotic machining processes are more subject to unwanted detrimental vibrations. At this work, simulations are realized in Time-Domain using the linearized robot structure model as transfer function of chatter block diagram and end milling force as machining force model. This article presents a new technique for simulating and analyzing the possibility of happening chatter vibrations at different values of machining parameters considering structure and configuration of the studied robot. Results show that limit of chatter occurrence is dramatically affected by changing robotic machining configuration.

Abstract: This study was conducted to determine if austempered 4340 steel had different mechanical properties compared to step quenched 4340 steel. Tensile strength and impact energy was determined at room temperature under identical test conditions. The specimens were cut from a bar with 25 mm diameter and austenitized at 800°C for 60 min and followed by quenching at 430°C for the high austempering temperature to achieve the upper bainite morphology and at 360°C for the lower austempering temperature to achieve the lower bainite morphology. In the case of step quenched, the specimens were first austempered at 430°C and then austempered at 360°C to achieve the mixed structure of upper bainite and lower bainite morphology. The another set of specimens for step quenching, after austenitization were quenched to below M_s (martensite start temperature), followed by heating at 400°C to achieve the mixed structure of tempered martensite and lower bainite and 500°C to achieve the mixed structure of tempered martensite and upper bainite. It is also shown that the best combination of strength and ductility can be achieved by the mixed structure of tempered martensite and lower bainite that has been suggested in this investigation.

Abstract: The present study aims to determine the optimum blank shape design for the deep drawing of Elliptical-shape cups with a uniform trimming allowance at the flange i.e. cups without ears. This earing defect is caused by planar anisotropy in the sheet and the friction between the blank and punch/die. In this research, a new method for optimum blank shape design using finite element analysis has been proposed. Present study describes the approach of applying Response Surface Methodology (RSM) with Reduced Basis Technique (RBT) to assist engineers in the blank optimization in sheet metal forming. The primary objective of the method is to reduce the enormous number of design variables required to define the blank shape. RBT is a weighted combination of several basis shapes. The aim of the method is to find the best combination using the weights for each blank shape as the design variables. A multi-level design process is developed to find suitable basis shapes or trial shapes at each level that can be used in the reduced basis technique. Each level is treated as a separated optimization problem until the required objective – minimum earing function – is achieved. The experimental design of RSM method is used to build the approximation model and to perform optimization. MATLAB software has been used for building RSM model. Explicit non-linear finite element (FE) Code Abaqus/CAE is used to simulate the deep drawing process. FE models are constructed incorporating the exact physical conditions of the process such as tooling design like die profile radius, punch corner radius, etc., material used, coefficient of friction, punch speed and blank holder force. The material used for the analysis is Stainless steel St12. A quantitative earing function is defined to measure the amount of earing and to compare the deformed shape and target shape set for each stage of the analysis. The cycle is repeated until the converged results are achieved. This iterative design process leads to optimal blank shape. So through the investigation the proposed method of optimal blank design is found to be very effective in the deep drawing process and can be further applied to other stamping applications.

Abstract: Tube hydroforming process is one of the metal forming processes which uses internal pressure and axial feeding simultaneously to form a tube into the die cavity shape. This process has some advantages such as weight reduction, more strength and better integration of produced parts. In this study, T-shape tube hydroforming was analyzed by experimental and finite element methods. In Experimental method the pulsating pressure technique without counterpunch was used; so that the internal pressure was increased up to a maximum, the axial feeding was then stopped. Consequently, the pressure decreased to a minimum. The sequence was repeated until the part formed to its final shape. The finite element model was also established to compare the experimental results with the FE model. It is shown that the pulsating pressure improves the process in terms of maximum protrusion height obtained. Counterpunch was eliminated as being unnecessary. The results of simulation including thickness distribution and protrusion height were compared to the part produced experimentally. The result of modeling is in good agreement with the experiment. The paper describes the methodology and gives the results of both experiment and modeling.

Abstract: One of the most effective methods of manufacturing conical parts is the hydroforming process. The pressure profile during forming is the most important factor on wrinkling, thinning, and punch wall contact. This paper presents a methodology to determine the optimal profile of hydraulic pressure during hydroforming of conical parts. The objective is to minimize the variation of the thickness throughout the part. Initially, the finite element model is developed and verified. The part being modeled is then subjected to different pressure profiles to examine the effect of each profile on thinning. The Response Surface Modeling (RSM) along with Genetic Algorithm (GA) is employed to obtain the optimum pressure profile. The paper describes the methodology developed and reports the results obtained.

Abstract: Tube Hydroforming Process (THF) is heavily affected by the pressure-displacement diagram, and adjustment of the raw tube. Three common defects of the process are bursting, buckling and wrinkling. In this work, the leading conditions to wrinkling defect have been studied. Proper criteria are required to predict wrinkling condition, and to quantify wrinkling when subjected to various pressure-displacement diagrams. A variety of criteria have been presented by researchers, most of which are suitable to a specific geometry. In current work, two criteria are considered namely, the strain difference and the radius velocity. At first an accurate FEM (Finite Element Model) model of the process have been established and validated. Then based on a number of experiments with different diagram, the process have been simulated and analyzed. According to experiments imbalances between pressure and displacement, improper sitting of tube in the die, poor vacation of the tube and the existence of external tiny particle inside the die, are the reason of wrinkling criterion in the tube. The Response Surface Method (RSM) has been used to model the responses from the finite element analysis. The behavior of the process has been predicted using this model.

Abstract: 3D Scanners are used in industrial applications such as reverse engineering and inspection. Customization of existing CAD systems is one of rapid ways to supplying a 3D Scanning software. In this paper, using AutoLisp and Visual Basic programming languages, AutoCAD has been customized. Also facilities of automatic scanning of physical parts, in the domain of free form surfaces, have been provided. Furthermore, possibilities such as, control of scanner automotive system, representation of registered point clouds, generation of polygon and /or NURBS model from primary or modified point clouds, have been prepared. Triangulation and image processing techniques along with a new fuzzy logic algorithm have been used to extract the depth information more accurate. These, accompanying with AutoCAD capabilities have provided acceptable facilities for 3D scanning.