基於等候時間分配和在製品預算的新派工法則

A New Dispatching Method Based on Waiting Time Allocation and WIP Budgets

林勇伸

指導教授 ： 許棟樑

國立清華大學/工學院/工業工程與工程管理學系碩士在職專班/碩士(2013年)

摘要

半導體廠的生產流程複雜，機台價格昂貴，派工法則對工廠生產效率，生產成本有明顯影響。本研究發展之派工法則，優化達交率、在製品數量、製造週期時間等三項工廠生產之重要指標。
本研究使用『等候時間分配法則(WTA)』為基礎，將『達交率』作為改善的首要目標。並且進一步利用「預算導向的在製品存量調控法」減少在製品數量與生產週期時間。「預算導向的在製品存量調控法」之運作模式，依據前後工作站在製品數量與規劃數量的差異，優先將產品往供給面與需求面相對存貨低的工作站安排，藉此降低在系統內的等候加工的時間，以減少等候時間、製造週期時間來降低在製品數量。本研究在製品的預算，精算到各產品之各製程階，得以精密調控至各產品在各製程階之在製品的數量。
本研究貢獻在於導入預算觀念，將等候時間和在製品存量加以控制與分配，有效改善工廠績效，並提供未來派工研究者一個新的思考面向。本研究派工法則以模擬方法驗證於真實工廠之配置，並以FIFO(先進先出法則) 、CR(關鍵比值法則) 、EDD(最早交期法則) 、WTA(等候時間分配法則)為比較對象。達交率的績效表現與WTA無差異，較 FIFO、 CR 、EDD 改善30.23% 、15.82% 、36.36%。平均生產週期時間的績效分別較 FIFO、 CR 、EDD、WTA短1.48天(4.03%)、3.3天(8.99%)、2.83天(7.71%)、2.64天(7.19%)。在製品數量分別較 FIFO、 CR 、EDD、WTA低72批(5.33%)、122批(9.04%)、129批(9.56%)、114批(8.44%)。證實本研究提出之方法在達交率、在製品數量、生產週期時間都有較優的表現。

關鍵字

派工法則 ； 達交率 ； 生產週期時間 ； 平衡在製品 ； 等候時間分配

並列摘要

The semiconductor factory production processes are complex Dispatching rule has a significant effect on production efficiency and costs. Most dispatching rules, optimized only for a single performance index, and fail to take into account other important indicators. This study developed a dispatching rules to optimize the target hit rate, the Work-In-Process number, and manufacturing cycle time more efficiently.
The research used “Waiting Time Allocation” (WTA) method to optimize the dispatching toward delivery rate improvements as a primary dispatching rule. The difference between the budgeted WIP and actual WIP is used as a supplementary dispatching rule when the batch is on or ahead of its delivery schedule. The concept of WTA is to allocate the waiting time for a batch at the current processing stage based on the remaining acceptable waiting time allocated across all remaining processes. Among the available batches of the products, the one with the lower allocated waiting time will get a higher priority to be processes. The concept of WIP budget is to plan the WIP distribution among all process stages based on the current waiting time allocation scheme, the known delivery dates, the known processing times, and their known transport times. The differences between the budgeted WIP and the actual WIP are then used to determine which lot will get priority to process. To reduce the WIP in the system, A lot with relative over-budget WIP at current station will get higher priority to be processed than the lot with under-budget WIP. Simulation of the proposed dispatching method on a real fab indicated that the proposed WTAWB dispatching performs better than FIFO, CR, and EDD in all three performance measures (Delivery rate, WIP, and cycle time) and is better than the pure WTA in WIP and cycle time performance.

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