Browsing by Subject "CNC"

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Open Access
An analysis of cyclic scheduling problems in robot centered cells
(Elsevier, 2012) Yıldız, Serdar; Karasan, Oya Ekin; Aktürk, M. Selim
The focus of this study is a robot centered cell consisting of m computer numerical control (CNC) machines producing identical parts. Two pure cycles are singled out and further investigated as prominent cycles in minimizing the cycle time. It has been shown that these two cycles jointly dominate the rest of the pure cycles for a wide range of processing time values. For the remaining region, the worst case performances of these pure cycles are established. The special case of 3-machines is studied extensively in order to provide further insight for the more general case. The situation where the processing times are controllable is analyzed. The proposed pure cycles also dominate the rest when the cycle time and total manufacturing cost objectives are considered simultaneously from a bicriteria optimization point of view. Moreover, they also dominate all of the pure cycles in in-line robotic cells. Finally, the efficient frontier of the 3-machine case with controllable processing times is depicted as an example.
Open Access
An analysis of pure robotic cycles
(2008) Yıldız, Serdar
This thesis is focused on scheduling problems in robotic cells consisting of a number of CNC machines producing identical parts. We consider two different cell layouts which are in-line robotic cells and robot centered cells. The problem is to find the robot move sequence and processing times on machines minimizing the total manufacturing cost and cycle time simultaneously. The automation in manufacturing industry increased the flexibility, however it is not widely studied in the literature. The flexibility of machines enables us to process all the required operations for a part on the same machine. Furthermore, the processing times on CNC machines can be increased or decreased by changing the feed rate and cutting speed. Hence, we assume that a part is processed on one of the machines and the processing times are assumed to be controllable. The flexibility of machines results in a new class of cycles named pure cycles. We determined efficient pure cycles and corresponding processing times dominating the rest of pure cycles in the specified cycle time regions. In addition, for in-line robotic cells, the optimum number of machines is determined for given parameters.
Open Access
Bicriteria robotic cell scheduling
(Springer, 2008) Gultekin, H.; Akturk, M. S.; Karasan, O. E.
This paper considers the scheduling problems arising in two- and three-machine manufacturing cells configured in a flowshop which repeatedly produces one type of product and where transportation of the parts between the machines is performed by a robot. The cycle time of the cell is affected by the robot move sequence as well as the processing times of the parts on the machines. For highly flexible CNC machines, the processing times can be changed by altering the machining conditions at the expense of increasing the manufacturing cost. As a result, we try to find the robot move sequence as well as the processing times of the parts on each machine that not only minimize the cycle time but, for the first time in robotic cell scheduling literature, also minimize the manufacturing cost. For each 1-unit cycle in two- and three-machine cells, we determine the efficient set of processing time vectors such that no other processing time vector gives both a smaller cycle time and a smaller cost value. We also compare these cycles with each other to determine the sufficient conditions under which each of the cycles dominates the rest. Finally, we show how different assumptions on cost structures affect the results.
Open Access
Bicriteria robotic cell scheduling with controllable processing times
(Taylor & Francis, 2011) Yildiz, S.; Akturk, M. S.; Karasan, O. E.
The current study deals with a bicriteria scheduling problem arising in an m-machine robotic cell consisting of CNC machines producing identical parts. Such machines by nature possess the process flexibility of altering processing times by modifying the machining conditions at differing manufacturing costs. Furthermore, they possess the operational flexibility of being capable of processing all the operations of these identical parts. This latter flexibility in turn introduced a new class of robot move cycles, called pure cycles, to the literature. Within the restricted class of pure cycles, our task is to find the processing times on machines so as to minimise the cycle time and the manufacturing cost simultaneously. We characterise the set of all non-dominated solutions for two specific pure cycles that have emerged as prominent ones in the literature. We prove that either of these pure cycles is non-dominated for the majority of attainable cycle time values. For the remaining regions, we provide the worst case performance of one of these two cycles.
Open Access
Bicriteria robotic operation allocation in a flexible manufacturing cell
(Elsevier, 2010) Gultekin, H.; Akturk, M. S.; Karasan, O. E.
Consider a manufacturing cell of two identical CNC machines and a material handling robot. Identical parts requesting the completion of a number of operations are to be produced in a cyclic scheduling environment through a flow shop type setting. The existing studies in the literature overlook the flexibility of the CNC machines by assuming that both the allocation of the operations to the machines as well as their respective processing times are fixed. Consequently, the provided results may be either suboptimal or valid under unnecessarily limiting assumptions for a flexible manufacturing cell. The allocations of the operations to the two machines and the processing time of an operation on a machine can be changed by altering the machining conditions of that machine such as the speed and the feed rate in a CNC turning machine. Such flexibilities constitute the point of origin of the current study. The allocation of the operations to the machines and the machining conditions of the machines affect the processing times which, in turn, affect the cycle time. On the other hand, the machining conditions also affect the manufacturing cost. This study is the first to consider a bicriteria model which determines the allocation of the operations to the machines, the processing times of the operations on the machines, and the robot move sequence that jointly minimize the cycle time and the total manufacturing cost. We provide algorithms for the two 1-unit cycles and test their efficiency in terms of the solution quality and the computation time by a wide range of experiments on varying design parameters.
Open Access
An integrated process planning approach for CNC machine tools
(Springer-Verlag, 1996) Aktürk, M. S.; Avcı, S.
In view of the high investment and tooling cost of a CNC machining centre, the cutting and idle times should be optimised by considering the tool consumption and the non-machining time cost components. In this paper, we propose a detailed mathematical model for the operation of a CNC machine tool which includes the system characterisation, the cutting conditions and tool life relationship, and related constraints. This new module will be a part of an overall computer-aided process planning system to improve the system effectiveness and to provide consistent process plans. A hierarchical approach is presented for finding tool-operation assignments, machining conditions, appropriate tool magazine organisation and an operations sequence which results in the minimum production cost. © 1996 Springer-Verlag London Limited.
Open Access
Multiple part-type scheduling in flexible robotic cells
(2009) Batur, Gül Didem
This thesis considers the scheduling problem arising in two-machine manufacturing cells which repeatedly produce a set of multiple part-types, and where transportation of the parts between the machines is performed by a robot. The cycle time of the cell depends on the robot move sequence as well as the processing times of the parts on the machines. For highly flexible CNC machines, the processing times can be adjusted. As a result, this study tries to find the robot move sequence as well as the processing times of the parts on each machine that minimize the cycle time. The problem of determining the best cycle in a 2- machine cell is first modeled as a travelling salesman problem. Then, an efficient 2-stage heuristic algorithm is constructed and compared with the most common heuristic approach of Longest Processing Time.
Open Access
Pure cycles in flexible robotic cells
(Elsevier, 2009) Gultekin, H.; Karasan O. E.; Akturk, M. S.
In this study, an m-machine flexible robotic manufacturing cell consisting of CNC machines is considered. The flexibility of the machines leads to a new class of robot move cycles called the pure cycles. We first model the problem of determining the best pure cycle in an m-machine cell as a special travelling salesman problem in which the distance matrix consists of decision variables as well as parameters. We focus on two specific cycles among the huge class of pure cycles. We prove that, in most of the regions, either one of these two cycles is optimal. For the remaining regions we derive worst case performances of these cycles. We also prove that the set of pure cycles dominates the flowshop-type robot move cycles considered in the literature. As a design problem, we consider the number of machines in a cell as a decision variable. We determine the optimal number of machines that minimizes the cycle time for given cell parameters such as the processing times, robot travel times and the loading/unloading times of the machines.
Open Access
Scheduling in a three-machine flexible robotic cell
(IFAC, 2006) Gültekin, Hakan; Aktürk, M. Selim; Karasan, Oya Ekin
In this study, a three-machine flexible robotic manufacturing cell in which the CNC machines are used is considered. These machines are highly flexible and are capable of performing several different operations. Each machine is assumed to be capable of performing all of the required operations of each part. As a consequence of this assumption, a new class of cycles is defined and three simple and widely used cycles among this class is proposed. The regions of optimality for these cycles as well as the worst case performances are derived.
Open Access
Scheduling in flexible robotic manufacturing cells
(2006) Gültekin, Hakan
The focus of this thesis is the scheduling problems arising in robotic cells which consist of a number of machines and a material handling robot. The machines used in such systems for metal cutting industries are highly flexible CNC machines. Although flexibility is the key term that affects the performance of these systems, the current literature ignores this. As a consequence, the problems considered in the current literature are either too limiting or the provided solutions are suboptimal for the flexible systems. This thesis analyzes different robotic cell configurations with different sources of flexibility. This study is the first one to consider operation allocation problems and controllable processing times as well as some design problems and bicriteria models in the context of robotic cell scheduling. Also, a new class of robot move cycles is defined, which is overlooked in the existing literature. Optimal solutions are provided for solvable cases, whereas complexity analyses and efficient heuristic algorithms are provided for the remaining problems.