Assume that working procedure is only cutting tool′s breakdown,by using the method of probability and the theory of renew process,mathematic model that expected cost per unit time is objective function has been established,we take the interval of check and replacement of cutting tools as policy,the problem is to determine the o.

Current textbooks only discuss the condition under which the optimal quantity ordered should satisfies and do not give the concrete formulas for expected cost,which is an inconvenience for real practical uses.

For solving time-cost optimization problems of PERT(Program Evaluation and Review Technique) network plans,the model was represented with linear programming,and a particle swarm optimization algorithm was used to solve this problem.

Based on analysis of uncertainties in both project completion limit and expense in project negotiation scheduling of virtual enterprise, a multi-issue time-cost stochastic model was put forward.