Browsing by Subject "Controllable Processing Times"

Now showing 1 - 3 of 3

Open Access
Optimal allocation and processing time decisions on non-identical parallel CNC machines: ε{lunate}-constraint approach
(Elsevier, 2007-12-01) Gurel, S.; Akturk, M. S.
When the processing times of jobs are controllable, selected processing times affect both the manufacturing cost and the scheduling performance. A well known example for such a case that this paper specifically deals with is the turning operation on a CNC machine. Manufacturing cost of a turning operation is a nonlinear convex function of its processing time. In this paper, we deal with making optimal machine-job assignments and processing time decisions so as to minimize total manufacturing cost while the makespan being upper bounded by a known value, denoted as -constraint approach for a bicriteria problem. We then give optimality properties for the resulting single criterion problem. We provide alternative methods to compute cost lower bounds for partial schedules, which are used in developing an exact (branch and bound) algorithm. For the cases where the exact algorithm is not efficient in terms of computation time, we present a recovering beam search algorithm equipped with an improvement search procedure. In order to find improving search directions, the improvement search algorithm uses the proposed cost bounding properties. Computational results show that our lower bounding methods in branch and bound algorithm achieve a significant reduction in the search tree size that we need to traverse. Also, our recovering beam search and improvement search heuristics achieve solutions within 1% of the optimum on the average while they spent much less computational effort than the exact algorithm.
Open Access
Scheduling with controllable processing times in a CNC environment
(2002) İlhan, Taylan
Flexible manufacturing systems give a manufacturer some capabilities to consider and solve different manufacturing problems simultaneously instead of one by one in a sequential manner. Using those makes her more competitive in the market. One of those capabilities is controllable processing times. By using this capability, the due date requirements of customers can be satisfied much more effectively. Processing times of the jobs in a CNC machine can be easily controlled via machining conditions such that they can be increased or decreased at the expense of tooling cost. In this study, we consider the problem of scheduling a set of jobs by minimizing the sum of total weighted tardiness, tooling and machining costs on a single CNC machine. This problem is NP-hard since the total weighted tardiness problem is NP-hard alone. Moreover, the problem is non-linear because of the nature of the tooling cost. We proposed a DP-based heuristic to solve the problem for a given sequence and designed a local search algorithm that uses it as a base heuristic.
Open Access
Single CNC machine scheduling with controllable processing times and multiple due dates
(2004) Atan, Mehmet Oğuz
In order to reflect the characteristics of a modern manufacturing environment, elements of customer satisfaction and the competition between firms should be considered simultaneously. Manufacturers should be careful on deciding which orders to accept, and should pay attention on the weighted earliness and tardiness penalties they will be due, while considering the priorities of the customers. Customers that want to minimize the risk of deviation from a delivery date, offer multiple due dates to the manufacturer, each coming with a distinct price for the order that is decreasing as the date gets later. Manufacturers that use flexible manufacturing systems have the capability to control the processing times of jobs, by changing the machining conditions at the expense of tooling costs. In this study, we consider the problem of scheduling a set of jobs on a single CNC machine, while maximizing the total profit that is composed of sum of prices of scheduled jobs less the sum of total weighted earliness/tardiness cost, tooling cost and machining cost. This problem is NP-hard since the total weighted tardiness problem is NP-hard alone. Furthermore, because of the nature of the tooling cost, the problem is nonlinear. We propose a number of ranking rules and scheduling algorithms. Using these rules and algorithms, we construct a single-pass heuristic algorithm that determines the processing times for each job and schedules them simultaneously, to maximize the overall profit.