隧道式烘烤爐烘乾效率精實改善策略－以冒口保溫套的生產為例

Abstract

鑄造工業與食衣住行息息相關，甚至醫學及精密科技發展也需要鑄件，而冒口保溫套是鑄造過程中提升品質的重要工具，因此冒口保溫套的需求量大，對品質也要求嚴謹；加上不同的鑄件需要不同大小或設計的冒口保温套，因此生產線常被要求能快速提供不同種類的產品。冒口保溫套的製程中，烘乾過程是最耗時也最容易出現不良品的瓶頸作業，且當市場需求多樣且大量時，瓶頸站是精實管理中阻礙價值流動的主要爆破點，也造成許多浪費而產生營運上的損失，因此提升烘乾過程的生產效率為本研究主要任務。但是，烘乾是瓶頸工程，因此改善過程中也要盡量維持烘乾原有的產出，才能支持公司營運；本研究除參考相關文獻外，也實際訪查烘乾過程所使用的隧道式烘烤爐的現場，綜合兩者，找出兩項影響烘乾效率的可調整參數，分別為輸送带速度及熱流方向；之後，提出搭配田口方法的改善策略，達成在不影響烘乾產出量的情况下，探尋上述兩參數的最佳設定值，以提升烘乾製程的生產效率。提出的改善策略落實在一間台灣的主要冒口保溫套公司，本研究運用精實管理的五大原則為訂定改善策略，現場對此策略的接受度良好且顯著改善烘乾製程的良率及產出量。

The foundry industry is closely related to the daily life of a human being, the development of medical or high technology and etc. while risers play an important role for improving quality during the casting production process. Therefore, the market demand for casting risers is large, and the requirement of the quality is strict. In addition, different castings require different types or sizes of risers. Thus the production line of risers is often required to quickly provide a wide range of products with high quality. In the process of riser production, the drying process is the bottleneck that is the most time-consuming and most prone to produce defective products. Based on the concept of lean management, the bottleneck station is the obstruction of value stream of the production line when the demand is strong. Therefore, the bottleneck point caused a lot of waste and caused operational losses, so improving the drying efficiency of the production process of risers is the most important task of this research. However, since the drying process is a bottleneck station, the production capacity must be maintained for continuing the daily production schedule during looking for strategy to improve drying efficiency. In addition to consulting the relevant literature, this study also actually investigates the site of the tunnel-type baking oven used in the drying process. Combining the findings of literature and on-site investigation, two adjustable parameters affecting the drying efficiency are proposed, namely the speed of conveyor belt and the direction of heat flow. After that, this study proposes an improvement strategy based on the Taguchi method to find the optimal setting values of the above mentioned two parameters without affecting the daily production scheduling. The proposed improvement strategy was actually implemented in a major casting riser production company in Taiwan. The yield of one product of the case company was upgraded significantly for the drying process.