Browsing by Subject "Tool Management"

Now showing 1 - 3 of 3

Open Access
Joint lot sizing and tool management in a single CNC environment
(1996) Önen, Siraceddin
111 most of the studies on tool management, lot sizes are taken as pi'edetermined input while deciding on tool allocations and machining |)arameters. In this study, we considered the integration of lot sizing and tool rnaricigement problems for single and multi i:>eriod cases. For the single period case, we proposed a new algorithm. By this algorithm we not only improved the overall solution by exploiting interactions, but also prevented any infeasibility that might occur lor the tool management problem due to the decisions made at the lot sizing level. The computational experiments showed that in a set of randomly generated problems 22.5% of solutions found by a. traditional approach were infeasible and the proposed joint approach improved the overall solution by 6.8%. For the multi period case, we proposed live new algorithms. Among these algorithms, the most promising one was tlie Look Atiea.d-LUC algorithm, which improved the overall solution on the average by 6.5% compared to the best known algorithm, Wa.gner-Whitin, used in traditional approcich, over a set of randomly generated problems.
Open Access
Scheduling with tool changes to minimize total completion time
(1998) Güneş, Evrim Didem
In the literature, scheduling models do not consider the unavailability of tools. The tool management literature separately considers tool loading problem when tool changes are due to part mix. However in manufacturing settings tools are changed more often due to tool wear. In this research, the problem of scheduling a set of jobs to minimize total completion time on a single CNC machine is considered where the cutting tool is subject to wear. We show that this problem is NP-hard in the strong sense. We discuss the behavior of SPT heuristic and show that its worst case performance ratio is bounded above by a constant. A pseudo-polynomial dynamic programming formulation is provided to solve the problem optimally. Furthermore, heuristic algorithms are developed including dispatching heuristics and local search algorithms. It is observed that the performance of SPT rule gets worse as the tool change time increases and tool life decreases. The best improvement over the SPT rule’s performance is achieved by the proposed genetic algorithm with problem space search.
Open Access
Scheduling with tool changes to minimize total completion time under controllable machining conditions
(2001) Köylü, Rabia
In the literature, scheduling models ignore the unavailability of the cutting tools. Tool management literature considers tool loading problem when tools change due to part mix. In practice, tools are changed more often due to tool wear. The studies on tool management issues consider machining conditions as constant values. In fact, it is possible to change the processing time and tool usage rate of a job by changing the machining conditions. However, the machining conditions, such as cutting speed and feed rate e ect the processing time and usage rate of the tool in opposite directions. Increasing the usage rates of jobs will lead to an increase in number of tool switches. Processing times and number of tool switches are two components of our ob jective function. This two-side e ect creates a tradeo between processing time and tool usage rate. Therefore machining conditions should be selected appropriately in order to minimize the total completion time. We proposed a set of single-pass dispatching rules and a local search algorithm to determine the machine conditions for each job and to schedule them on a single CNC machine simultaneously to minimize the total completion time.