Inventory policy and magazine reloading schedule optimisation for cutting tools in pipe manufacturing

In a steel pipe manufacturing industry, several machining centres are used for different purposes, where tool magazines speed up the tool exchange and machine setup. Early tool replacement incurs unutilised tool lives, leading to additional tool purchase. On the other hand, delays in tool replacement may result in sudden tool failure and machine breakdown. A multiple tool holding facility in a tool magazine provides a good opportunity to reduce the number of magazine reloading. However, an increased magazine size eventually leads to an increase in the inventory and operating cost for the tool magazine. To trade-off between the stated conflicting objectives, a non-linear mixed-integer programming problem is formulated to minimise the total cost for cutting tools. The problem is solved both optimally and heuristically to find an appropriate combination of tool ordering size, magazine size and reload timing. The throughput rate is observed to improve when an optimal size of tool magazine is installed. The sensitivity analyses are done to investigate the influence of different parameter(s) on the optimum solution.