| 摘要: | 選擇性雷射熔融(SLM)製造屬於積層製造，為新興的重要製程技術。對於金屬零件的原型製作或複雜工件的製作，較傳統製程有明顯的加工優勢。本研究以Inconel 718為對象，以機械性質為目標，進行雷射粉床式熔融積層製造的製程參數最佳化，並探討製程條件、金相組織、機械性質間之因果關係。研究內容分成兩部分，首先以較大的製程參數範圍設計先期研究，以成形性與機械性質為考量，確定合理的參數範圍。再利用單目標與多目標最佳化分析方法進行製程參數最佳化研究。製程參數的控制因子為雷射功率、掃描速度、掃描間距與層間角度。機械性質目標為抗拉強度、衝擊能、伸長率及硬度。單目標最佳化為使用田口方法進行分析。多目標最佳化採用田口方法搭配主成分分析。
研究結果顯示，單目標最佳化分析中，以抗拉強度為目標，使用雷射功率140 W、掃描速度800 mm/s、掃描間距70 m、層間角度45可得最佳抗拉強度，驗證實驗中最高的抗拉強度為1190 MPa。多目標最佳化分析中，發現衝擊能與抗拉強度同時強化的主成分方向佔總和的28.4 %，代表兩項性質可以同時強化，抗拉強度與伸長率同時強化的方向向量佔總和的1.9 %，代表兩項性質難以同時強化。以四種機械性質為綜合目標的最佳製程參數組合與單獨採用抗拉強度為目標者相同。在多目標的驗證實驗中，抗拉強度1190 MPa，衝擊能82 J，伸長率27%，硬度HRC 33。在金相組織方面，若製程的體積能量密度相似，使用高功率搭配高掃描速度者會過度累積能量，形成大量樹枝狀或細胞狀結晶。而使用低功率搭配低掃描速度者，會產生較少樹枝狀結晶。過多的樹枝狀結晶會造成抗拉強度下降。此外，使用過低的能量密度則會產生大量孔洞，使衝擊能下降。
;Selective laser melting (SLM) manufacturing belongs to additive manufacturing and is one of the important emerging process technologies. Obviously, SLM has processing advantages over traditional manufacturing processes in prototyping of metal parts or manufacturing of complex shaped parts. A study of SLM manufacturing of Inconel 718 was carried out with four parameters namely laser power, scanning speed, hatching space and build orientation. The research is divided into two parts. Firstly, a larger process parameter range was designed for the prestudy test, and a reasonable parameter range was determined based on the formability and mechanical properties. Secondly, Taguchi and principal component analysis were used for single-objective and multiobjective optimizations respectively for optimizing tensile strength, impact energy, elongation, and hardness. The causal relationship among the process condition, metallographic structure, mechanical property and failure mechanism was discussed.
The results show that the optimal tensile strength of product can be obtained by using laser power 140 W, scanning velocity 800 mm/s, scanning spacing 70 m, and build orientation 45º in the single-objective optimization analysis. Tensile strength in the verification experiment was 1190 MPa. The results of multi-objective optimization analysis revealed that tensile strength and impact energy can be reinforced simultaneously. But tensile strength and elongation can’t be reinforced simultaneously. The optimal combination of process parameters with four mechanical properties as the strength index is exactly the same as that with tensile strength alone as the target. In the multi-objective verification experiment, the tensile strength was 1190 MPa, impact energy 82 J, elongation 27%, hardness HRC 33. If the volume energy density of the SLM process was similar, the one with higher power and higher scanning speed over-accumulated energy and form a large amount of dendritic or cellular crystals. Too much dendritic crystallization resulted in a decrease in tensile strength. In addition, the process using too low volume energy density led to porosity arising, so that the impact energy declined. |
