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標題: | 新穎擠形模及擠壓墊的設計模擬與驗證實驗 Design Simulations and Verification Experiments of the Novel Extrusion Die and Dummy Blocks |
作者: | Cheng-Hsien Liu 劉正賢 |
指導教授: | 林新智 |
關鍵字: | 直接擠形,有限元素法,表面粗晶層,尾端缺陷, Direct Extrusion,Finite Element Method,Surface Coarse Grain Layer,Back-End Defect, |
出版年 : | 2016 |
學位: | 博士 |
摘要: | 摘要
直接擠形存在著一些許久未能解決的問題,例如表面粗晶層(Coarse Grain Layer)、尾端漏斗缺陷(Back-end Funnel Defect)、以及擠件(Extrudate)內部氧化物環(Inner Oxide Ring)等等缺陷。這些缺陷造成擠件的報廢、線上廢料的增加、以及引起品質問題。這些缺陷的形成,事實上都與擠錠(Billet)、擠件材料的流動行為有關,因此如果可以控制材料的流動行為,就可以控制這些缺陷的形成。就表面粗晶層的部分,我們開發Ex-ECAE (Extrusion + ECAE)製程,利用傳統的直接擠形機來執行ECAE製程,以細化擠件的晶粒大小,並藉此評估工業化(Scale up)ECAE製程的可行性。為考量現有擠形機的能量,以及現有生產線的動線,Ex-ECAE的模具角訂為120度,並選擇兩道次的ECAE路徑C製程,實驗材料選用AA 6063。實驗結果顯示,第一段擠出擠件(條錠)的心部與表面粗晶層的晶粒,在Ex-ECAE製程中,都因為不同來源的剪應力而細化。因為模具內通道面的高摩擦力,再加上Ex-ECAE中路徑C的結構,造成相當於在通道出口施加背向壓力一樣,使得模具通道的內、外彎角處(Inner and outer Corner),均被條錠材料填滿。接下來也因為通道高摩擦力的存在,促使在通道的彎角處產生了滯留區(Dead Metal Zone)。這個現象使得條錠的表面層材料,在通過通道轉彎處時,沿著滯留區的邊界前進。為了維持與滯留區材料之間的連續性,在通過這個滯留區的表面時,表層材料將會承受高強度的剪切應力,晶粒因而被細化。另外條錠心部晶粒的部份,因為擠形製程而出現長軸晶,此時內部已建立相當數量的次結構(Substructure),之後這些長軸晶在通過模具通道轉彎處時,因為ECAE製程的簡單剪應變(Simple Shear)作用,使得這些次結構大量的發展成為高角度晶界的次晶粒,心部組織因而由長軸晶細化成細小的等軸晶。Ex-ECAE試片各段的織向分析顯示:就心部區域而言,Ex-ECAE第一段的織向是完美的纖維組織,由兩個織向分量所組成,就是強<001> + 弱<111>。第二段試片由於變形機構改變,前一段的纖維織向被破壞,新的織向被建立。第二段試片顯示的是強{1 1 0} <1 -2 1> + 弱{0 1 1} <2 -1 0>的混合織向。由於ECAE路徑C的變形是在同一剪切面上,只是簡單剪切力反向進行而已,所以第三段試片的織向,有回復到纖維織向的趨勢,但是因為擠形與ECAE變形機構有極大的差異,所以形成的是不完全的纖維織向,主要是由強{0 0 1} <-1 -1 0> + 弱{1 1 1} <1 -1 0>。 採用Ex-ECAE製程來工業化ECAE製程的優點,除了上述組織的調整之外,還包括因為擠形進料可以採用錠接錠(Billet-to-billet)的方式,使得Ex-ECAE製程能夠成為連續式的製程,生產效率會遠高於傳統的ECAE製程。再者Ex-ECAE製程可以經由擠形的部分,生產各種異形的條錠,然後再進入ECAE的部分。傳統ECAE若要做異形材料,異形條錠的製作,恐怕是難以機械加工而得,製作成本也會相當的高。 直接擠形有一些先天性的缺陷,這些缺陷包括了尾端漏斗缺陷及內部氧化物環。在直接擠形當中,很少人關心或注意到壓餅(亦即擠壓墊-Dummy Block)的設計。在此實驗中我們希望藉由壓餅的設計來克服上述的缺陷。我們設計了熱套壓餅(Hot Top Dummy Block)來解決尾端漏斗缺陷,也設計了斜邊壓餅(Beveled Edge Dummy Block)來解決內部氧化物環的缺陷。實驗結果也顯示了這兩種壓餅,都如預期地分別的解決或改善了這兩個缺陷的問題。 在設計Ex-ECAE、熱套壓餅及斜邊壓餅時,我們也利用FEM(Finite Element Method)電腦模擬的協助,以快速地了解各設計參數的影響。最後就是只要擠形機設備能量足夠,更嚴苛的ECAE條件(例如90度的模具角、ECAE製程道次的增加),都可以經由直接擠形機來執行,以達到ECAE工業化的目標。 Abstract In the past, there were many defects occurred in the direct extrusion process has not been solved for a long time. Such as surface coarse grain layer, back-end funnels or axial hole defect, inner oxide ring, etc. These defects will cause scrap increased and quality problem. We developed the Ex-ECAE (Extrusion + ECAE) process using the conventional direct extrusion press to scale up ECAE process and eliminate the surface coarse grain layer of the extrudate. Consider the capacity of the existed extrusion press and the arrangement of the production line, the Ex-ECAE process with die angle of 120° and route C were a choice. The billet was AA 6063. The experimental results show that the surface coarse grain layer and the grain in the core of the rod billet were refined by the different causes of shear stress. Both of the inner and outer corners of the die channel were filled with the extruded material, because the rod billet was supplied continuously and the high friction of the channel surface (equivalent to back pressure) in the Ex-ECAE process. Therefore a dead metal zone cause by the friction of the channel was built at the corners. This brought about the surface coarse grain layer flowed through the channel along the boundary of the dead metal zone. To keep the continuity with the dead metal zone along the boundary, the surface coarse grain layer was imposed by the high intensity shear stress. The grain of the surface coarse grain layer would be refined. As part of the grains in the core of the rod billet would be refined and became elongated grains by the extrusion process. There were many substructures has already been built inside these elongated grains. With the help of the simple shear, the substructure built during the extrusion process would translate into subgrains of high angle grain boundaries. Then those elongated grains would become fine equiaxed grains. Except the grain refinement, adopt the Ex-ECAE process to scale up the ECAE process includes the other advantages. First, the billet-to-billet loading method makes the Ex-ECAE process become as a continuous process. Secondly, it may be difficult via ECAE process to produce an extrudate with a specified shape. As we need a rod billet of a specified shape first. But this kind of rod billet may be hardly to produce by machining, or maybe the cost of the machining is too high. The textures of the Ex-ECAE sample at various segments are measured. The results reveal that the first segment of the Ex-ECAE sample has a perfect fiber texture which consists of a mixture of strong <001> and weak <111>. The texture of the second segment is a mixture of strong {1 1 0} <1 -2 1> and weak {0 1 1} <2 -1 0>. Finally, the texture of the extrudate (the third segment) is reversed to an incomplete fiber texture which consists of the strong {0 0 1} <-1 -1 0> and the weak {1 1 1} <1 -1 0>. Using the direct extrusion press to perform the Ex-ECAE process, some congenital defects, e.g. back-end funnel defect and inner oxide ring, will occur. No one tried to eliminate or avoid these defects by the design of the dummy block. However, we designed a hot top and beveled edge dummy blocks to eliminate or avoid back-end funnel defect and inner oxide ring, respectively. And the experimental results showed that these two designed dummy blocks could eliminate or solve these two defects as expect, respectively. In the design of the hot top and beveled edge dummy blocks, with the help of FEM (Finite Element Method) simulation, we could obtain the effect of the design parameters quickly. Finally, more severe conditions of ECAE (such as die angle of 90° and increase process passes) can be performed and scaled up by the direct extrusion if the capacity of the press is high enough. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/51552 |
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顯示於系所單位: | 材料科學與工程學系 |
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