بهبود بهره وری تحویل مشکل زمان بندی سفارش مشتری در یک تولید کارگاهی

The focus of this paper is customer order scheduling (COS) problem, where each order consists of a set of jobs that must be shipped as one batch at the same time. In COS each job is part of a customer order and the make-up of the jobs in the order are pre-specified. Most of the existing research deals with COS in a single machine or in a parallel machine shop for developing an optimal solution. COS is common in a normal job shop, and the more complex the shop, the more complex the scheduling. Most existing research has focused on trying to reduce the completion time of the batch. That is, the focus is only on the point in time the last job is finished, while ignoring the actual duration of the jobs within the same order. The longer it takes to complete all the jobs within an order the more it increases the stock of finished goods and the more it deteriorates the efficiency of the logistics and the supply chain management. A new dispatching rule, referred to as Minimum Flow Time Variation (MFV), has been proposed for COS in a normal job shop, in order to reduce the total time it takes to complete all jobs within the same order. That is, the individual completion times of all jobs for the same customer order will be controlled in order to improve the shipping performance. In the simulation test and statistical analysis, the level of work in process (WIP) under the MFV rule in the finished goods warehouse is reduced by more than 70% compared to any other method. The MFV method will efficiently reduce the stock level of finished goods, and controls the waiting time required before they can be shipped. Depending on the environmental factors, the performance of our proposed method will become increasingly significant the more complex the system.

In this research, we consider the scheduling of customer orders in a normal job shop. In customer order scheduling, each job is part of a customer order and the composition of the job in the order is pre-specified. Let’s consider a manufacturing facility that produces different types of products. A customer can request a variety of products in a single order. After the entire order is produced, the products are shipped to the customer. Each order is a batch and each product is a job. The composition of a batch is specified by the order. Since 1990, many researches have been done on the issue of customer order scheduling (COS). Most of the existing researches deal with the problem of COS in a single machine or in a parallel machine shop to develop an optimal solution. Besides, most existing research has focused on trying to reduce the completion time of the batch. That is, the focus is only on the point in time the last job is finished, while ignoring the actual duration of the jobs within the same order. The longer it takes to complete all the jobs within an order the more it increases the stock of finished goods and the more it deteriorates the efficiency of the logistics and the supply chain management. For time-based competition, on-time delivery is the most crucial performance factor. How to finish a product at the moment it is required is the modern concept, similar to the just-in-time (JIT) principle. In either concept, inventory should be erased if possible. There are three kinds of inventory in the production system, including materials/parts, work in process (WIP), and finished goods. The materials/parts inventory is controlled by purchasing management and material requirement planning (MRP). WIP is subject to the efficiency of the shop floor control, especially order releasing and scheduling. To reduce the inventory level of finished goods, jobs from the same order should be finished as close as possible at the same time since they will be shipped as a batch at the same time. Hence, in the present study we will try to model a new dispatching rule for COS in a normal job shop in order to minimize the completion time variability of all the jobs for the same order. That is, the individual completion times for all the jobs in the same customer order will be controlled in order to improve the shipping performance. The remainder of this paper is organized as follows. The relevant literature on the COS in a job shop is reviewed in the next section. Section 3 describes the methodology of the proposed dispatching rule. The simulation model and the data collected are presented in Section 4, while the statistical analysis and discussion are summarized in Section 5. Finally, in Section 6 we draw our conclusions and discuss some future works.

In this research, we have considered the problem of scheduling customers’ orders in a normal job shop. The focus of this paper was customer order scheduling (COS), where each order consists of a set of jobs that must be shipped as one batch at the same time. Different from the majority of COS related literature, the present research focused on reducing the stock level of finished goods, with the main objective being to reduce the amount of finished time jobs have to spend among the same customer order. This paper proposed MFV, a new dispatching rule for solving the COS problem, and to enhance the control of the variation in finished time among the jobs for the same order. Two kinds of normal job shop, the simple shop and the complex shop were tested using a simulation model. Seven job-based rules and six order-based rules were considered for comparing and benchmarking. In the simulation test and the statistical analysis, the stock level of finished goods under the MFV rule was reduced by more than 70% compared to the others. MFV can efficiently reduce the stock level of finished goods. The time waiting for shipping can be kept under control, and the performance under different environment factors, will be more significant the more complex the system is. In this research, a new dispatching rule was proposed for controlling the variation in the finished time of jobs for the same order. The jobs are to be released immediately upon arrival of the order. The order review and the decision to release is an important topic in shop floor control. In the future, the control of order releasing can be considered for designing a new control methodology for reducing the jobs’ finished time and the waiting time of the finished goods simultaneously. Besides, the methodology of just in time (JIT), which was introduced into the automobile manufacturing for improving production efficiency, can be included to deal with the COS problem. If most of the jobs for the same order can be finished at the requested point in time (just in time), the efficiency of the logistics and supply chain will be maximized.