Observe that the optimality of the solutions is proved for a half of the 12 instances in the first two cases (i.e. for the original model (1)–(19), and when valid inequalities (20) are included), and for seven instances in the last twocases (i.e. Model (1)–(19) + Inequalities (21), and Model (1)–(19) + Inequalities (20) and (21)). Each one of these optimal solutions represents the best way for production planning, since all possible preset settings for the molding machine were considered and, consequently, all possible molding patterns could be generated.