飛機複合材料零件於熱壓爐成型之熱傳模擬分析

Abstract

纖維複合材料因其優異的機械性質和質量輕等特性，已經逐漸取代傳統金屬材料而被大量使用在飛機主要結構、內裝與引擎外罩等部位，許多現代的大型客機之複合材料使用比例已超過50%，也就是說複合材料已經成為了現代飛機零件中主要使用的材料。而在航太工業中常見的複合材料零件製造係採用熱壓爐成型製程，此製程可以穩定產出品質較好且形狀複雜之飛機零件，符合了航太工業高品質要求，但是因為製程時間長且需要花費大量的人力進行檢測，藉由不斷的測試方能找出穩定生產的方式，故本論文希望能透過電腦輔助工程減少測試次數以及縮短製程時間，達到節省零件製造成本的目的。 本論文首先建立了熱壓爐模型與邊界條件，並且將通風口所測量到的流速結果代入模擬中，在忽略放置模具架子與複合材料的情形下進行單一模具不包含複材之熱壓爐成型熱傳CAE分析，接著將模擬與實驗結果進行驗證，比對結果發現模擬結果與實驗有相同的升溫趨勢，且模具前、中、後段的升溫效果也與實驗結果接近，驗證結果顯示此組熱壓爐CAE模型能夠完整模擬實際熱壓爐成型中之模具升溫情形。 由於複合材料以非常多材料所組合而成，造成了幾何形狀非常複雜且厚度差異非常大，導致複合材料模型與材料參數的建立需要花費大量時間，故本論文建立了等效複合材料分析模型，採取等厚度的等效複合材料模型，分別討論複合材料之等效熱傳導係數、等效比熱與等效密度共三種關鍵係數之建立方式。最後以此等效複合材料模型在不考慮樹脂成化所產生的放熱反應下進行CAE模擬分析，並針對模具、複合材料和蜂巢共三種位置之測量點分別進行實驗驗證，驗證結果發現以此CAE分析模型所預測到達成化溫度之平均時間誤差小於10%，顯示本論文所建立之CAE分析模型已具實務應用之價值。

Fiber-reinforced composite has gradually replaced the traditional material, such as metallic material, to be used in aircraft structure, interior and nacelle due to its excellent mechanical properties and light-weight. Nowadays, the percentage of fiber-reinforced composite used in airliner has over 50%. In other words, fiber-reinforced composite has become the main material for manufacturing modern aircraft parts. In the aerospace industry, autoclave forming process is commonly adopted for the manufacture of composite parts. This process can stably produce high quality and complex shape parts. Although autoclave forming process can reach the standard of aerospace, it spends a lot of time for trial and error to search for a steady way to produce parts. Therefore, in this thesis efforts were endeavored to reduce the lead time and save the production cost for the autoclave forming process with the use of the finite element analysis. This thesis first establishes the finite element model which can simulate both the air flow and the heat transfer presented in the autoclave forming process. The air flow speeds at different locations around the circumference of the autoclave inlet were measured and used as the initial air flow speeds for the simulation model. A measured temperature at the autoclave inlet was also used as an input data. The finite element simulations were then performed for a simplified model in which the composite layers were not considered. The heating efficiency is represented by the temperature evolution of the die surface at various locations during the heating process and a fast heating rate was anticipated. The temperature evolution of the die surface at various locations obtained from the finite element simulations and measured from the actual autoclave forming process was compared. The comparison reveals that the heating paths resulted from the simulation results and the measured data agree with each other in trend and the quantitative difference is within an acceptable range. It confirms that established finite element model with the specified initial and boundary conditions is capable of predicting the heat transfer during the autoclave process. In addition, this thesis also builds an equivalent material model for the composite in order to decrease the computation time that strongly depends on the complex geometry and the various thicknesses of the composite layers. The equivalent material model considers the composite layers having an equal thickness with the honey-cone structure built in. The equivalent thermal properties such as the thermal conductivity, specific heat and density were also determined by experiments performed and the theoretical derivations. With the equivalent material properties of the composite layers applied to the simulation model aforementioned, the temperature evolution of the die surface at various locations obtained from the finite element simulations differs from that measured from the actual autoclave forming process only within a range of 10%.