Production Planning & Control vol:20 issue:7 pages:649-663
Sheet metal working remains an important industry. It is argued that, to be competitive, the complete production chain needs to be optimised. Therefore, this article focuses on the optimisation of the production plan. The sheet metal shop is configured as a two-stage flow shop with laser cutting and air bending. In the literature, theoretical production planning models can be found for both individual processes. Unfortunately, those planning models have a low applicability in sheet metal working small and medium sized enterprises (SMEs) due to the fact that they only focus on one single production step while in reality the planning decisions taken at the cutting stage affect the production plan for the air bending stage. An integrated production planning methodology is proposed to overcome this problem of individual optimisation by taking into account relevant bending information already at the cutting stage. An integer program is presented, incorporating some important practical requirements: (1) the planning model is suited for normal workpieces, rush orders, special workpieces and multiple-machine sheet metal shops and (2) the computational times to generate the production plan are limited. Ten real-life industrial test cases are used to evaluate the proposed methodology. The integrated production planning methodology results in schedules with a reduced makespan and a reduced set-up time at the press brake compared to the current way of planning. All planning models are developed in close cooperation with sheet metal working SMEs to facilitate the implementation process.