明膠玻璃慢速延展成形之模擬分析

Abstract

飛機透明擋風器材係採用明膠玻璃成形，隨著透明擋風器材形狀日益複雜和多變，且越來越多不等曲率透明擋風器材之生產需求，傳統以人工生產之方式逐漸不符合時間與金錢成本，且難以控制成品品質，為了建立相關領域之自動化製程與優化成品品質，本論文採用有限元素模擬做為研究載具，透過建立CAE模型，並分析材料性質、製程參數對不等曲率透明擋風器材產品之影響性，以供相關製程參考應用。 在材料性質方面，本論文透過文獻蒐集、實驗與模擬比較對明膠玻璃之材料特性進行全面的探討，並選擇以彈-塑-黏耦合材料模型做為後續分析之材料模型，因為其考慮材料之彈塑性性質，可以在產品脫模後維持其成形形狀，符合本論文聚焦於脫模後之各項指標表現；此外，也考慮材料之黏性性質，因成形方式為溫間拉伸成形，成形溫度接近玻璃轉化溫度，而文獻也證實明膠材料在高溫的條件下有不可忽視之潛變性質，因此本論文以彈-塑-黏耦合材料模型全面性的考慮材料於高溫下之性質。 於成品品質方面，本論文透過文獻收集歸納出透明擋風器材產品常見的缺陷，包含貼模度不足、回彈缺陷、光線偏折、光線扭曲與霧度等，並利用基本理論推導分析缺陷之成因。其中回彈缺陷主要由產品之內外表面主應力差所造成，光線偏折、扭曲則是產品之折光率分布不均與厚度分布不均所造成，霧度則是表面刮痕或材料內部缺陷所造成。此外還建立缺陷與CAE模擬後處理指標之對應關係，其中貼模度不足與回彈缺陷主要對應至CAD軟體量測成品之曲率分布與回彈量，折光率則與密度分布和殘留應力有關並分別對應至CAE軟體之相關的後處理資訊，厚度分布則也透過CAD軟體進行量測。 於製程參數方面，本論文建立利用電動缸帶動夾爪拉伸板材之一道次成形方式以生產足夠貼模之成品，並針對夾爪之拉伸軌跡進行設計與探討，也同時考慮成形階段後冷卻對於產品品質之影響。而根據實際生產狀況，成品於脫模後有回彈之現象，因此本論文利用機構設備增加板材拉伸量以有效降低各截面之回彈量，最後還探討不同下料尺寸對成品品質之影響，藉由提高材料之使用效率以降低生產成本。 本論文透過CAE模型建立不等曲率透明擋風器材造型之成形方法，也探討透明擋風器材成品常見之缺陷與成因，並利用預拉伸板材之方式降低回彈量，可提供未來相關製程之分析或優化做為參考。

The airplane windshields are made with plexiglass. As the shapes of airplane windshields become more and more complex, and with the growing demand for the production of uneven curvature windshields, traditional manual production methods are gradually becoming inefficient, and difficult to meet the demand for products. To establish automated processes and optimize product quality, this thesis uses finite element simulation and developing a CAE model as a research tool to analyze the impact of material properties and process parameters on the forming of uneven curvature windshields. In terms of material properties, this thesis conducts a comprehensive study on the material characteristics of plexiglass through literature review, experiment, and simulation comparison. The elastic-plastic-visco coupled material model is chosen for subsequent analysis because it considers the elastic-plastic properties of the material, allowing the windshield to maintain its shape after demolding, which aligns with the focus of this thesis on post-demolding qualities. Additionally, it considers the viscous properties of the material since the forming method is warm stretching, and the forming temperature is close to the glass transition temperature. Literature also confirms that plexiglass exhibits non-negligible creep properties under high-temperature conditions. Therefore, this thesis comprehensively considers the material properties at high temperatures using the elastic-plastic-visco coupled material model. As to product quality, this thesis summarizes common defects in windshield products through literature review, including insufficient mold adherence, springback, deflection, distortion, and haze. Basic theories are used to derive and analyze the causes of these defects. Springback defects are mainly caused by the principal stress difference between the inner and outer surfaces of the product. Deflection and distortion are caused by uneven refractive index and thickness distribution of the product, while haze is caused by surface scratches or internal material defects. Furthermore, this thesis establishes post-processing indicators corresponding to the defects and CAE simulation results. Insufficient mold adherence and springback mainly correspond to curvature distribution and springback measurements in CAD software, while the refractive index is related to density and residual stress, corresponding to CAE software post-processing information, and thickness distribution is also measured by CAD software. With respect to process parameters, this thesis establishes a single-pass process using an electric cylinder to drive a gripping jaw which stretches the sheet to produce products that meet the target curvature. The stretching trajectory of the gripping jaw is also designed and discussed, and the impact of cooling on product quality after the forming stage is considered. According to practical production conditions, the product exhibits springback after demolding. Therefore, this thesis effectively reduces the springback by increasing the sheet stretching amount. Finally, the impact of different blank sizes on product quality is discussed to improve material utilization efficiency and reduce production costs. This thesis establishes a forming method for windshields with uneven curvatures through CAE modeling, investigates common defects and their causes in windshield products, and reduces springback by pre-stretching the sheet. This provides a reference for future analysis and optimization of related processes.