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Publication Open Access A hierarchical solution approach for a multicommodity distribution problem under a special cost structure(Elsevier, 2012) Koca, Esra; Department of Industrial Engineering; Yıldırım, Emre Alper; Faculty Member; Department of Industrial Engineering; College of EngineeringMotivated by the spare parts distribution system of a major automotive manufacturer in Turkey, we consider a multicommodity distribution problem from a central depot to a number of geographically dispersed demand points. The distribution of the items is carried out by a set of identical vehicles. The demand of each demand point can be satisfied by several vehicles and a single vehicle is allowed to serve multiple demand points. For a given vehicle, the cost structure is dictated by the farthest demand point from the depot among all demand points served by that vehicle. The objective is to satisfy the demand of each demand point with the minimum total distribution cost. We present a novel integer linear programming formulation of the problem as a variant of the network design problem. The resulting optimization problem becomes computationally infeasible for real-life problems due to the large number of integer variables. In an attempt to circumvent this disadvantage of using the direct formulation especially for larger problems, we propose a Hierarchical Approach that is aimed at solving the problem in two stages using partial demand aggregation followed by a disaggregation scheme. We study the properties of the solution returned by the Hierarchical Approach. We perform computational studies on a data set adapted from a major automotive manufacturer in Turkey. Our results reveal that the Hierarchical Approach significantly outperforms the direct formulation approach in terms of both the running time and the quality of the resulting solution especially on large instances.
Publication Metadata only A novel analytical algorithm for prediction of workpiece temperature in end milling(Elsevier, 2022) N/A; Department of Mechanical Engineering; Akhtar, Waseem; Lazoğlu, İsmail; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 179391Temperature is a critical parameter in machining as it directly affects the cutting performance, part quality, residual stresses, distortion, tool life, etc. In this article, a novel analytical algorithm for fast temperature predic-tion in intermittent cutting processes like milling is proposed. For the first time, the temperature drop during the noncutting period is taken into consideration for the workpiece side. The model also takes into account time-varying chip thickness due to the trochoidal motion of the milling tool. Validation tests with Ti6Al4V showed the promise of the algorithm in predicting the milling temperature under various cutting conditions.(c) 2022 CIRP. Published by Elsevier Ltd. All rights reserved.Publication Metadata only A variable neighborhood search for minimizing total weighted tardiness with sequence dependent setup times on a single machine(Pergamon-Elsevier Science Ltd, 2012) N/A; N/A; Department of Industrial Engineering; Kirlik, Gökhan; Oğuz, Ceyda; PhD Student; Faculty Member; Department of Industrial Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 6033This paper deals with the single machine scheduling problem to minimize the total weighted tardiness in the presence of sequence dependent setup. Firstly, a mathematical model is given to describe the problem formally. Since the problem is NP-hard, a general variable neighborhood search (GVNS) heuristic is proposed to solve it. Initial solution for the GVNS algorithm is obtained by using a constructive heuristic that is widely used in the literature for the problem. The proposed algorithm is tested on 120 benchmark instances. The results show that 37 out of 120 best known solutions in the literature are improved while 64 instances are solved equally. Next, the GVNS algorithm is applied to single machine scheduling problem with sequence dependent setup times to minimize the total tardiness problem without changing any implementation issues and the parameters of the GVNS algorithm. For this problem, 64 test instances are solved varying from small to large sizes. Among these 64 instances, 35 instances are solved to the optimality, 16 instances' best-known results are improved, and 6 instances are solved equally compared to the best-known results. Hence, it can be concluded that the GVNS algorithm is an effective, efficient and a robust algorithm for minimizing tardiness on a single machine in the presence of setup times.Publication Metadata only Active damping of chatter in the boring process via variable gain sliding mode control of a magnetorheological damper(Elsevier, 2021) N/A; N/A; Department of Mechanical Engineering; Saleh, Mostafa Khalil Abdou; Ulasyar, Abasin; Lazoğlu, İsmail; PhD Student; Researcher; Faculty Member; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); Graduate School of Sciences and Engineering; N/A; College of Engineering; N/A; N/A; 179391In this article, a sliding mode control of a magnetorheological fluid damper is presented for active damping of chatter in the boring process for the first time. A boring bar is integrated with an in-house developed magnetorheological fluid damper system. The variable gain super twisting sliding mode control algorithm is designed and implemented for suppressing the chatter in the boring process. Simulations of the controller show its fast response and robustness against disturbances and parametric uncertainties. Validation cutting tests performed under various machining conditions showed that the stability limit can be increased significantly with the sliding mode control of the magnetorheological fluid damper.Publication Metadata only An enhanced analytical model for residual stress prediction in machining(Elsevier, 2008) Ulutan, D.; Engin, S.; Kaftanoglu, B.; Department of Mechanical Engineering; Department of Mechanical Engineering; Lazoğlu, İsmail; Alaca, Burhanettin Erdem; Faculty Member; Faculty Member; Department of Mechanical Engineering; College of Engineering; College of Engineering; 179391; 115108The predictions of residual stresses are most critical on the machined aerospace components for the safety of the aircraft. In this paper, an enhanced analytic elasto-plastic model is presented using the superposition of thermal and mechanical stresses on the workpiece, followed by a relaxation procedure. Theoretical residual stress predictions are verified experimentally with X-ray diffraction measurements on the high strength engineering material of Waspaloy that is used critical parts such as in aircraft jet engines. With the enhanced analytical model, accurate residual stress results are achieved, while the computational time compared to equivalent FEM models is decreased from days to secends.Publication Metadata only Analysis of thermal fields in orthogonal machining with infrared imaging(Elsevier Science Sa, 2008) Department of Mechanical Engineering; Department of Mechanical Engineering; Department of Physics; Lazoğlu, İsmail; Serpengüzel, Ali; N/A; Faculty Member; Faculty Member; Department of Mechanical Engineering; Department of Physics; Manufacturing and Automation Research Center (MARC); Manufacturing and Automation Research Center (MARC); N/A; College of Engineering; College of Engineering; College of Sciences; N/A; 179391; 27855The validation of a previously developed finite difference temperature prediction model is carried out for orthogonal machining process with a high precision infrared camera set-up, considering the temperature distribution in the tool. the thermal experiments are conducted with two different materials; al 7075, AISI 1050, with two different tool geometries; inserts having a rake angle of 6 degrees and 18 degrees, for different cutting velocities and feedrates. an infrared camera set-up is utilized for the thermal experiments. the results of the high precision infrared thermal measurements are compared with the outputs of the finite difference temperature model, considering the maximum and the mean temperatures in the tool-chip interface zone and the temperature distributions on the tool take face. the maximum tool-chip interface temperature increases with increasing cutting velocity and feedrate. the relationship between the maximum tool-chip interface temperature and the rake angle of the tool is not distinctive. the experimental results show good agreement with the simulations. (c) 2007 Elsevier B.V. all rights reserved.Publication Metadata only Improving cycle time in sculptured surface machining through force modeling(Elsevier, 2004) Budak, E.; Department of Mechanical Engineering; N/A; Lazoğlu, İsmail; Güzel, Birhan Ufku; Faculty Member; Master Student; Department of Mechanical Engineering; College of Engineering; Graduate School of Sciences and Engineering; 179391; N/AIn this paper, an enhanced mathematical model is presented for the prediction of cutting force system in ball end milling of sculptured surfaces. This force model is also used as the basis for off-line feed rate scheduling along the tool path in order to decrease the cycle time in sculptured surface machining. As an alternative for setting a constant feed rate all along the tool path in rough machining of sculptured surfaces, resultant cutting forces are aimed to be kept under a pre-set threshold value along the tool path by off-line scheduled piecewise variable feed rates. In this paper, it is shown that machining time, depending on complexity of sculptured surfaces, can be decreased significantly by scheduling feed rate along the tool path. The model is tested under various cutting conditions and some of the results are also presented and discussed in the paper.Publication Metadata only Investigation on the performance of SiAlON ceramic drills on aerospace grade CFRP composites(Elsevier, 2015) Celik, Ali; Kara, Alpagut; Kara, Ferhat; Department of Mechanical Engineering; Lazoğlu, İsmail; Faculty Member; Department of Mechanical Engineering; College of Engineering; 179391Carbon fiber reinforced polymer (CFRP) composites are widely used in aircraft structure due to their outstanding physical and mechanical properties. Drilling is one of the most critical operation in the handling of CFRP composites, since the delamination free holes with high dimensional accuracy are required for assembly. The quality of the machined holes strongly depends on machining conditions, tool geometry and tool wear. There are a limited number of tool materials which can survive in the abrasive cutting conditions formed by the fractured carbon fibers during drilling. SiAlONs are promising materials for the machining of CFRP composites due to their superior abrasive wear resistance. SiAlON ceramics have been reported for the first time in the literature as cutting tool materials for drilling of CFRP composites in this study, where alpha/beta-SiAlON drilling tools with four different sets of common drill geometries were manufactured and tested extensively on drilling of aerospace grade CFRP composites. The effects of cutting parameters and geometrical features of novel alpha/beta-SiAlON drilling tools on the cutting forces and the peel-up delamination of the machined holes were investigated. It was observed that the point angle and chisel edge length of the novel SiAlON drilling tools are the main parameters that affect the maximum thrust force and delamination during drilling. The thrust force exhibited an increase during drilling tests, indicating that an abrasive wear occurs at the cutting edges of the SiAlON drilling tools.Publication Open Access Joint gateway selection, transmission slot assignment, routing and power control for wireless mesh networks(Elsevier, 2013) Gökbayrak, Kağan; Department of Industrial Engineering; Yıldırım, Emre Alper; Faculty Member; Department of Industrial Engineering; College of EngineeringWireless mesh networks (WMNs) provide cost effective solutions for setting up a communications network over a certain geographic area. In this paper, we study strategic problems of WMNs such as selecting the gateway nodes along with several operational problems such as routing, power control, and transmission slot assignment. Under the assumptions of the physical interference model and the tree-based routing restriction for traffic flow, a mixed integer linear programming (MILP) formulation is presented, in which the objective is to maximize the minimum service level provided at the nodes. A set of valid inequalities is derived and added to the model in an attempt to improve the solution quality. Since the MILP formulation becomes computationally infeasible for larger instances, we propose a heuristic method that is aimed at solving the problem in two stages. In the first stage, we devise a simple MILP problem that is concerned only with the selection of gateway nodes. In the second stage, the MILP problem in the original formulation is solved by fixing the gateway nodes from the first stage. Computational experiments are provided to evaluate the proposed models and the heuristic method.Publication Metadata only Loss of customer goodwill in the uncapacitated lot-sizing problem(Pergamon-Elsevier Science Ltd, 2007) Department of Business Administration; Aksen, Deniz; Faculty Member; Department of Business Administration; College of Administrative Sciences and Economics; 40308Loss of customer goodwill in uncapacitated single level lot-sizing is studied with a mixed integer programming model extending the well-known Wagner-Whitin (WW) model. The objective is to maximize profit from production and sales of a single good over a finite planning horizon. Demand, costs, and prices vary with time. Unsatisfied demand cannot be backordered. It leads to the immediate loss of profit from sales. Previous models augment the total cost objective by this lost profit. The difference of the proposed model is that unsatisfied demand in a given period causes the demand in the next period to shrink due to the loss of customer goodwill. A neighborhood search and restoration heuristic is developed that tries to adjust the optimal lot sizes of the original no-goodwill-loss model to the situation with goodwill loss. Its performance is compared with the WW solution, and with the commercial solver CPLEX 8.1 on 360 test problems of various period lengths. (c) 2005 Elsevier Ltd. All rights reserved.