製造業生產一個產品，零件與成品為上下游的關係，若彼此生產模式的差異導致生產節拍 (Takt Time, TT)無法一致，容易產生零件庫存或機台閒置等浪費。本研究案例T公司上製程的加工線零件產能遠低於下製程的裝配線領料需求，無法及時供料，只得提早生產大量零件庫存以備生產，產生了高額的庫存成本。
本研究使用外包策略與限制理論，建立自製與外包同時供給零件之二階段同步生產模型。先使用經濟生產批量 (Economic Production Quantity, EPQ)模型對下游裝配線進行排程，上游加工線再根據裝配線排程建立同步生產模型。本研究成功降低了T公司的生產成本，且規劃出可用的產能。本研究結論為：當生產線自製生產成本高時推薦提高外包零件數量，外包生產成本高時推薦提高自製零件數量，庫存成本高時推薦使上下游產能一致將庫存量壓低。其他的成本參數則不會影響策略的選擇，僅影響成本數值高低。

In the manufacturing industry, there is an upstream-downstream relationship between components and finished products. If the differences in production modes between them lead to inconsistent production rates, it can easily result in waste such as component inventory or idle machines. In this research case of Company T, the production capacity of the upstream processing line for components is far lower than the material demand of the downstream assembly line, resulting in an inability to supply materials in a timely manner. As a result, a large amount of component inventory needs to be produced in advance for production, resulting in high inventory costs.
This study utilizes the outsourcing strategy and the theory of constraints to establish a two-stage synchronized production model for simultaneous supply of components through in-house production and outsourcing. Firstly, an Economic Production Quantity model is used to schedule the downstream assembly line, and then the upstream processing line establishes a synchronized production model based on the assembly line schedule. This study successfully reduces the production costs of Company T and plans for available capacity.
The conclusion of this study is as follows: when the in-house production cost of the production line is high, it is recommended to increase the quantity of outsourced components, and when the outsourcing production cost is high, it is recommended to increase the quantity of in-house produced components. When the inventory cost is high, it is recommended to synchronize the production capacity between the upstream and downstream to reduce the inventory level. Other cost parameters will not affect the selection of strategies but only influence the cost values.

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