積層製造擁有生產期程短、能客製化生產、節省材料、能製作具有複雜幾何外觀工件等的優勢；其中，能夠以金屬作為材料，提供產品足夠剛度、抗疲勞能力、耐高溫化學性的定向能量沉積製程(Directed energy deposition，DED)與粉床熔融成型製程(Powder bed fusion，PBF)更是在這十多年內飛速地發展起來。本研究便是以定向能量沉積製程為主軸，使用鎳基合金IN 718金屬粉末為材料，進行實驗觀察製程因子對品質影響並取得最佳因子組合；再將優化結果應用於路徑規劃與沉積製作實驗，最後完成具有懸空扭轉幾何的類機翼工件之製作。
　　本研究使用田口灰關聯分析方法(Taguchi-grey relational analysis)做為實驗設計方法進行多品質之製程因子組合優化實驗；由結果分析得到五個控制因子：雷射功率、重疊程度、供粉量、掃描速度及雷射離焦距離對三個品質：沉積效率、表面粗糙度及孔隙率之影響，最後決定出能兼顧各品質之最佳因子組合。也以實驗數據進行變異數分析(ANOVA)，找出對各品質影響最顯著之因子當作變因建立迴歸模型，並測試各模型之預測能力，確認是否可做為初步預測製程產品品質之工具。
　　優化後的因子組合被應用在工件製作的研究上，使用NX CAM軟體進行路徑規劃，輔以後處理器與Matlab程式進行路徑延長與雷射系統專用M碼之添加等特殊處置，最後生成可以實際上機執行之NC程式。本研究先以一個正方體測試工件分別對薄殼輪廓與實心填補路徑進行測試；路徑測試的結果提出可以依所要製作工件的形貌選擇「固定每層抬升並調整雷射頭抬升距離(Z-offset)法」或「螺旋上升法」這兩種方法進行輪廓路徑沉積；而填補路徑則可以使用「往復式水平/垂直鋸齒狀方法」，依照工件截面調整填補的角度以避免未填補之空隙產生。最後結合在因子優化與路徑規劃兩部分之研究成果，設定Z-offset為50%之「螺旋上升法」完成薄殼類機翼工件之製作；而實心機翼工件則是以「固定每層抬升距離並調整Z-offset法」與「45°往復式水平/垂直鋸齒狀方法」完成製作。使用上述的路徑在工件形貌與沉積效率上都有得到改善並有不錯的成效。
　　此外也透過實驗探討Z-offset設定與稀釋率之關係，得出可以透過「由熱變形所造成之舊層高度收縮量與單層沉積稀釋率兩者相同」的想法，將Z-offset設定為首層層高乘以舊層層高受熱縮減程度，進而讓沉積成品獲得較好的外觀形貌與沉積效率之結論。搭配稀釋率曲面擬合模型，提出系統性調整Z-offset之方法來提高DED產品之沉積品質。

關鍵字：定向能量沉積製程、田口灰關聯分析、沉積效率、表面粗糙度、孔隙率、沉積路徑規劃、雷射頭每層抬升距離(Z-offset)、具懸空扭轉幾何的機翼製造

In this study, a multi-objective optimization of directed energy deposition (DED) process was conducted with Taguchi-grey relational analysis. In this optimization, the effects of five control factors (laser power, overlap ratio, powder feed rate, scanning speed and laser defocus distance) on three DED product qualities (cladding efficiency, surface roughness and porosity) were analyzed and an optimal factor setting which can take all qualities into account was found. ANOVAs were also conducted to find out significant factors of each qualities. By using the significant factors as variations, three regression predictive models for qualities were created.

The optimized factor setting was applied to deposition toolpath planning research and part fabrications. The deposition toolpath in this study was decomposed into contour and field toolpaths. First of all, a cuboid part model of which geometry was simpler was created to test toolpath planning approaches. The results recommended to use "Fixed rising height per layer with proper laser head rising height (Z-offset setting)" or "Spiral" approaches to plan contour toolpaths. For field toolpaths, "Reciprocating zigzag” planning approach was suggested and it needed to adjust the cladding angle to fit the cross-section of parts. According to the test results of cuboid part fabrications, the contour of target blade part was successfully manufactured with 50% Z-offset setting and spiral toolpath. The solid blade fabrication was also finished with fixed rising height per layer with 50% Z-offset setting and 45° reciprocating zigzag toolpath.

In addition, the relationship between the Z-offset setting and the dilution was investigated through experiments. A conjecture that a height shrinkage of an old layer caused by thermal deformation is equal to the single-layer deposition dilution was proposed. Based on this conjecture, user can improve DED deposition results by setting Z-offset as "the product of single-track height and the degree of shrinkage of the old layer height." By combining predictive value of dilution surface fitting model with the conjecture, it can be easier to get better DED deposition qualities.

Keywords: Directional energy deposition, Taguchi-grey relational analysis, Cladding efficiency, Surface roughness, Porosity, Deposition toolpath planning, Laser head rising height (Z-offset) and Blade fabrication

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