Application of Lost Foam Process in Development of Hollow Irregular Carbon Fiber Composite Structure

In the composite materials industry, hollow parts, which reduce product weight and improve bending rigidity, are generally manufactured through the bonding and blown film processes. However, the bonding process makes carbon fibers discontinuous, and the blown film process generates excessive wrinkles within tubes. To solve these problems, we developed a new manufacturing process. The difference between the coefficient of thermal expansion of the mold and the material created a difference in the internal and external pressures. Similar to the blown film process, a hot-melt core material was used to smoothen the interior of the tubes and make the shapes of hollow parts complex and diverse. On the basis of the difference between the coefficient of thermal expansion of the mold and the material, we covered the core material with carbon fiber composite materials. The carbon fiber composite materials provided internal pressure during molding. After the molding was completed, the composite structure was placed into a refrigerator to cool. Due to the core material's thermal contraction properties, the core material contracted and could be easily removed. The core material could also be removed by melting and be reused. Through computer-aided engineering (CAE), we simulated the thermal stress of the mold and the core material and verified the simulation results by conducting an experiment. We (1) simulated the heating curves and thermal stress through CAE, (2) conducted an experiment on thermal expansion pressure to measure the actual thermal expansion pressure of the core material and calculated the error between the experimental and CAE results, and (3) successfully manufactured well-structured hollow parts with irregular shapes and manifolds. The optimal processing parameters for the hollow last foam manufacturing process were obtained. The temperature was increased from 25°C to 120°C, maintained at 120°C for 60 min, increased to 150°C, and maintained at 150°C for 45 min. The process capability results revealed that the C_(pk) values for the core material temperature and pressure value were 1.49 and 1.52, respectively, which met the quality standard of the process capability indices. The manufacturing process we proposed in this study substantially improved the quality of current mold manufacturing.

關鍵字

carbon fiber ； coefficient of thermal expansion ； composite materials ； hot-melt core material ； lost form

並列摘要

複合材料（簡稱複材）業界因為需要產品輕量化與提高彎曲剛性，所以使用中空件較多。過去中空件作法使用膠合或是吹袋製程較多，但因膠合製程會使碳纖維不連續，或是吹袋製程使得內部皺摺多。因此本研究開發新製程解決以上問題。藉由模具與材料熱膨脹係數差異，造成內外壓力差成型，使用熱熔性核芯材仿吹袋製程，可讓管件內部均勻，中空件造型也可以複雜多變化。本研究開發新製程，藉由模具與熱熔性核芯材的熱膨脹係數差異，在核芯材外疊成包覆碳纖維複材，使碳纖維複材固化成型過程中給予內部壓力，成型後再利用物理特性熱脹冷縮，將複材結構放進冰箱，核芯材收縮後，便能輕易取出，也可以採取熔解取出，而核芯材能重複使用。結合電腦輔助分析（computer-aided engineering, CAE），模擬模具與核芯材之熱應力，進行驗證模擬分析與理論實作結果。本研究已完成（1）利用CAE模擬製程加溫曲線與熱應力；（2）熱膨脹壓力實驗，量測核芯材受熱膨脹之實際壓力並與模擬分析結果比對進行誤差值計算；（3）造型變化大或是岐管的中空件皆可一體成型。取得最佳加工參數數據，溫度設置從25°C加溫至120°C，於120°C持溫60分鐘，再經二次加溫至150°C，於150°C持溫45分鐘。製程能力分析出核芯材溫度C_(pk)達1.49，壓力值C_(pk)達1.52，皆符合品質水準製程能力指標，研究結果可以實質提升模具製程品質。