Abstract
Lathes with two turrets are often used to get high efficiency of turning. To utilize them, it is important to plan a machining sequence considering simultaneous machining by two cutting tools, since combinations of processes influence practical cutting time very much. But it is difficult for users to determine an optimal machining sequence, because the number of the combinations is great.
A method proposed in this paper divides processes into cycles, during which spindle speed is constant, and distributes divided processes to two turrets. Genetic algorithm is applied to divide processes into cycles. Genes are assigned to processes. Values of genes represent identified cycle numbers, and processes with the same cycle number are simultaneously machined. A chromosome is a series of all processes, and constitutes a machining sequence. As a criterion of the first fitness, total cutting time by machining sequences represented by a chromosome is adopted. And as that of the second fitness, difference of cutting time on two turrets for each cycle is adopted. Preserving crossover, arbitrary crossover and mutation are used as genetic operations. Preserving crossover is multipoint crossover to preserve cycles with the good second fitness. Mutation is intended to break cycles with the bad second fitness. Preserving crossover is mainly used in the first stage, and arbitrary crossover and mutation are in the second stage. A simulation showed that proper use of two kinds of crossover and mutation produces good results.
