对于订单式中小生产企业,物料供应是否及时以及生产进度是否按计划进行是影响订单交货期的关键因素。实际中,某些产品的物料价格随时间连续波动并具有规律性,而生产过程中由于插单多、工人流动性大、设备故障、质量返工等,生产完工期有一定的随机性。对于物料订购决策,传统方法主要考虑订单的投产日期以及物料采购成本最小化,而未考虑订单完工期的随机性特点。基于企业内部供应链集成及总成本最小化的系统思想,综合考虑物料价格的变化趋势以及随机生产完工期的统计规律,分别建立单一物料或多种物料订购情形下总生产成本(包括订购成本、制造成本、延迟完工或提早完工成本等)与订购日期的关系模型,并对其最优解进行讨论、分析与求解。当物料种类单一时,采用极值法对模型极小值点的存在性进行讨论;当物料种类较多时,构建了有约束条件的多决策变量非线性优化模型,并采用最优化理论中的拉格朗日乘子法(即PHR算法)进行求解。通过实例分析,得出的结论是物料最佳订购时间点与物料初始价格、价格波动周期、波动幅度、单位延迟或提早完工成本等因素相关。上述采购与生产集成的思想、模型构建的思路以及求解方法等可供有关人员参考。
For the Small and Medium Production Enterprises(SMPEs) under MTO(Make-to-order) environment, materials provision in time and schedules as planed are the key factors, which affect delivery time. In reality, the price of some materials fluctuates over time continuously, and because of other random inserted orders, staff turnover, equipment failures and rework owing to the poor quality of some products etc, the makespan is random. For the decision of materials ordering, the traditional methods mainly consider the beginning date of the order and minimizing the materials purchasing costs but regardless of the random makespan. Based on the system considering about internal supply chain integration and minimizing the total costs, When the materials price fluctuates over time and the makespan is random, it considers how to model, analyze and solve the problem of getting the optimal decision of ordering date, so that the total costs (it includes the costs of materials procurement, manufacturing, delay in delivery or in advance) are lowest. For the case of a single type of materials, the existence of the minimum points by extreme method is discussed.When the types are more than two, a constraint nonlinear optimization model with multi-variables is built by the algorithm of PHR. Then, the numerical examples show the validity of the models. The above ideas about integrated procurement and production, the methods about model building and problems solving would give references to some relevant persons.
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