زمان ارائه تحویل سفارش مشتری براری تولید بر اساس زمان ارائه محصول و هزینه های تاخیر

In practice decisions regarding customer order lead time and customer order processing are taken in different parts of the organization. Definite lead times are quoted by the sales department and job flow decisions are taken by the production department. This split up of decision responsibilities is in accordance with the differences in scope and control areas in complex organizations like job-shops or engineer-to-order firms. In this paper we present a simple economic model of sales and production in a job shop. Production aims at realizing the jobs by using its capacity to perform the operations of the jobs. Sales, using a model of the performance of production, aimes at maximizing expected profit by quoting lead times to customer orders, given that penalties are put on quoting long lead times and on tardy deliveries. Analysis of the model shows that for any combination of penalties on lead times and tardiness, there exist job flow times distributions for which it is optimal for sales to quote unrealistically short customer order lead times. Specifically if the job flow time has a high mean value and/or a high variance sales tends to quote a lead time with zero lead time penalty. In practice we often observe that the job flow times are long and have a high variance. The research presented in this paper shows why this may stimulate sales to neglect flow time information and to quote unrealistically short lead times. Our model shows that under a wide range of economic conditions a job flow time distribution with a small mean and a small variance seems to be a necessary condition for sales to quote realistic customer order lead times.

In practice decisions regarding customer order lead times and customer order processing are taken in different parts of the organization. Definite lead times are quoted by the sales department and order flow are controlled by the production department. This split up of decision responsibilities is in accordance with the dynamics of the process. Customer orders arrive dynamically over the time, are released to the shop floor and processed according to certain priority rules. At the arrival of a customer order it is impossible to know exactly how the process on the shop floor will evolve. Therefore, order lead time quotations are based on certain assumptions about the shop order flow times. These assumptions contain errors which lead to uncertainty about the exact order flow time. In this paper we study the assignment of economical optimal due dates to customer orders that arrive at a job shop. We study the situation where customer orders arrive dynamically over time and are assigned a due date upon arrival. Each customer order leads to a job which is immediately released to the shop floor and, after processing in the shop, is completed. The job shop consists of a number of functionally organized work centers and each job requires a number of operations in different work centers. The due dates are assigned by a due date assignment system which may take job information into account. The processing of the jobs is controlled by the production department according to certain priority rules. Both the production control problem and the due date assignment problem for job shops have been seperately studied. For a review of the literature we refer to [1]. Also the interaction between the due date assignment rules and the production control rules has been studied (see for instance [2], [3], [4] and [5]). In most of this research the performance is measured in terms of job flow times, job tardiness, or job lateness. In this research we study the due date assignment problem in an economic setting. We study the situation where on the one hand a cost penalty is incurred as a function of the length of the quoted job lead time and, on the other hand, a cost penalty is incurred as a function of the tardiness of the job. This assumes that the firm in some way or the other is penalized for assigning long order lead times; a penalty which decreases by assigning short lead times. Also it is assumed that the firm is penalized for late deliveries. In view of the management literature which reports the strategic importance of short and reliable lead times (see e.g. [6]) it is reasonable to assume that sales operates in such a reward and penalty structure. In this paper we study the situation where this penalty structure is modelled with simple piecewise linear functions. We derive optimal due date policies for various instances of the penalty functions under a simplifying assumption regarding the job flow time distribution. In this research we assume a simple shop structure consisting of work centers each containing a single machine. We furthermore assume that jobs follow random routings on the shop floor and are processed at the work centers according to the first-come-first-served priority rule. The remainder of this paper is organized as follows. In Section 2 we give an overview of recent related literature. In Section 3 we work out the research question in more detail, present a formal model of the problem and derive theoretical results. Section 4 discusses the application of the formal model for two kind of lead time policies: a common lead time for all work orders and a lead time which depends on the number of operations for the order. For various setups of penalty costs and job flow time distributions we compare the total costs of the economically optimal lead times with the total costs incurred when using `conventional’ (95% reliable) lead times. Finally in Section 5 the conclusions and directions for future research are given.

In this paper we presented a model for determining the economical optimal value for the customer order lead time for job shop-like production systems. We modelled the job shop as a symmetrical shop having single machine work centers. The lead time quotation process has been modelled as optimizing the lead time, given knowledge of the order flow time distribution and costs related to the length of the lead time and the costs related to the tardiness. We have shown that the order flow time distribution plays an important role in the setting of the economical optimal job lead time. For any given cost setting order flow time distributions exist for which it is optimal to quote short, unrealiable lead times. This may explain the often heard complaint in industry that sales departments tend to quote unrealistically short lead times. Our model suggests that this might be explained by the existence of long and highly variable order flow times on the shop floor. Put in other words: realistic lead times are only economically optimal in conjunction with short flow times with a small flow time variance. We have investigated the model with common lead times under tardiness costs related to tardiness occurrence and tardiness costs related to the tardiness time. For both costs settings optimal results were derived. Next we have investigated order-dependent lead times, specifically lead times which are proportional to the number of operations of an order. Also for this situation we have derived results which can be used to determine an economically optimal lead time per order type under tardiness costs related to the tardiness occurrence. The results have been used to construct tables which illustrate that for orders with few operations, which have short flow times, the model assigns realistic lead times. For orders with many operations, having a large flow time with a high variance, the model assigns short and unrealistic lead times. For a number of situations the total costs, when using the economic optimal lead times have been compared with the total costs when using conventional 95% reliable lead times. As can be expected for some situations the economical optimal lead times have much lower total costs, which demonstrates the relevance of putting the lead time quotation problem in an economical setting. The results obtained show that the length and predictability of the order flow time have a large impact on the optimal lead time. In this research we have studied a job shop with the FCFS priority setting on the shop floor. It is well known that due date-oriented priority rules can substantially increase the predictability of the job flow time. Therefore, the next phase in our research is to derive results for the situation where the shop floor aims at being reliable by using due date-oriented priority rules. We may expect that under this regime, all other things being equal, the cost optimal lead times will tend to be more realistic than under the FCFS priority rule. Furthermore, we will study the situation where quoting long lead times or unreliable lead times affects the probability of an order being placed. In this way the interaction between the production system and the market will be included in the model.