3D列印積層製造技術，正改變著我們的生活，翻轉傳統的製造方式，實為一個結合數位科技、材料科學、精密機械與綠色能源等技術的合成，3D列印積層製造技術已被《經濟學人雜誌》譽為「第三次工業革命」。然而，在高能雷射使用時，使得材料在短時間內迅速加熱及迅速冷卻，迅速加熱過程的熱應力及迅速冷卻後的殘留應力相繼出現，往往造成工件產生翹曲變形，甚至工件產生龜裂或脫層，大大地降低工件的強度及最終成品尺寸的精度。本計畫擬以離散元素電腦模擬與選擇性雷射燒結實驗探討3D列印產品之力學與變形行為，本研究提出創新的離散元素模型分析3D列印工件在選擇性雷射燒結過程中的溫度分佈與熱應力分佈，進而預測產品的扭曲變形與殘留應力分佈，同時本計畫亦規劃選擇性雷射燒結實驗列印產品，採用的金屬顆粒為Ti6Al4V金屬，並進行對應的離散元素電腦模擬，探討兩者巨觀變形行為差異的原因，用以修正電腦模擬之理論模式。確定採用之離散元素電腦模擬模式的合理性與可靠性後，再進一步分析產品的殘留應力分佈，同時考慮雷射加工參數(例如雷射移動速度與掃描軌跡)對3D列印產品扭曲變形與殘留應力分佈的影響，進而達到3D列印產品的最佳化設計。本計畫發展相關的離散元素電腦模擬技術，除了基本架構外(三維剛體運動方程式與接觸力模型)，引進顆粒體熱傳理論模擬雷射燒結能量在金屬顆粒體間的傳導，使用顆粒間平行鍵接理論模擬金屬顆粒間燒結的粘接結構，藉以傳遞顆粒間的力量與力矩，本計畫亦使用顆粒應力張量評估3D列印產品殘留應力分佈。為了驗證本計畫所發展的離散元素模型的合理性與可靠性，本計畫進行選擇性雷射燒結實驗列印產品，並採用白光干涉技術量測產品的扭曲變形，藉以驗證離散元素電腦模擬結果。本計畫最後透過驗證合理的離散元素模型計算内部物理量(中觀與微觀行為)，中觀物理量有內部應力與應變 (stress and strain) 及粒子體積佔有率 (solid fraction)，微觀物理量有力量傳遞鏈 (force chain)、配位數 (coordination number) 及顆粒間的組構 (fabric)，進行多尺度 (巨觀、中觀與微觀) 行為之分析，藉以更深入地探究雷射燒結過程中3D列印產品之力學與變形行為。 ;3D printing technology is changing our life and replacing traditional manufacturing methods. In fact, it is a combination of digital technology, materials science, precision machinery and green energy technology. The magazine,「THE ECONOMIST」, reports that the 3D printing technology has initiated the third industrial revolution. However, during the use of high-energy laser, the materials are rapidly heated and rapidly cooled in a very short time. The thermal stress of the rapid heating process and the residual stress of the rapid cooling process occur one after another, often resulting in warpage of the workpieces and even cracking or delamination. This greatly reduces the strength of the workpieces and the size accuracy of the 3D printed product. This project investigates mechanical and deformation behaviours of 3D printed products by using discrete element modelling and selective laser sintering experiment. This study proposes an innovative discrete element model to analyze the temperature and stress distributions of the workpieces during selective laser sintering process, and further to predict their distortion and residual stress distributions. The selective laser sintering experiments are performed and the granular materials used in this study are Ti6Al4V metal particles. The corresponding DEM simulations are carried out. The comparison of the macro distortion between numerical simulation and physical experiment is made and discussed. The proposed DEM model is validated and then modified. In addition, the effects of the laser processing parameters on the distortion and residual stress are further explored.The innovative discrete element model uses the theory of particle heat transfer to model the heat conduction amongst metal particles induced by the high-energy laser. The parallel bond is employed to model the melted structure between metal particles and to transmit the interactive forces and moments. In addition, the particle stress tensor is also adopted to evaluate the residual stress distribution in the 3D printed products. The white light interference technology is used to measure the distortion of the 3D printed products. After careful validation for the proposed DEM models, the meso and micro behaviours (meso properties: solid fraction, strain and stress; micro properties: force chain, coordination number and fabric) will be evaluated. The effects of the laser scanning speed and path on macro, meso and micro behaviours of 3D printed products will be systematically explored. This project will provide useful and valuable strategies for DEM applications to realistic engineering problems in manufacturing industries.
