傘齒輪擺輾熱鍛之有限元素模擬與實驗之研究

Finite Element Simulation and Experiment of Orbital Hot Forging for Bevel Gear

鄭焜隆(Kun-Long Cheng)

指導教授 ： 許源泉

國立虎尾科技大學/工程學院/創意工程與精密科技研究所/碩士(2010年)

摘要

本研究針對傘齒輪擺輾熱鍛進行研究，先以AISI-1045結構用鋼進行材料性質分析，並對傘齒輪成形模式進行實驗及模擬之比對。隨後利用有限元素模擬來分析傘齒輪熱間擺輾製程，比較擺輾製程與傳統製程之成形負荷、變形模式、等效應力、等效應變及微觀晶粒的差異。並進ㄧ步探討胚料預成形、擺動角度、擺頭速度、進給速度、成形溫度及介面摩擦因子等製程參數對傘齒輪擺輾塑性成形與微觀組織的影響。此外，本文亦對傘齒輪鍛件進行不同冷卻方式之相變態探討，獲得實際難以預估的金相演變行為，以預測傘齒輪鍛件在熱機行為之變化。

研究分析結果顯示，有限元素模擬所獲得之各階段傘齒輪變形模式與實驗有相當的ㄧ致性，由分析比較得知擺輾製程之成形負荷約為傳統製程1/3~1/5，擺輾製程產生之等效應力分佈小於傳統製程，等效應變分佈以擺輾製程所獲得較平均，且大於傳統製程，而晶粒細化以擺輾製程較均勻，傳統製程則大集中於齒型部。改變胚料幾何外型或適當選擇擺動角度、擺頭轉速、進給速度等製程參數均能改善材料之流動變形，並避免摺料等缺陷的產生。由各製程參數進行分析得知，選用較大擺動角度、較快擺頭轉速、較慢進給速度及較高成形溫度均可減少成形所需負荷。在等效應力方面，以心軸根部所受等效應力最大，並隨較小擺動角度、較慢擺頭轉速、較慢進給速度及較低成形溫度而有所提升。等效應變方面，在各製程參數下心軸部所產生之等效應變相當ㄧ致，主要在於齒型部遭受不同參數條件而影響較大，整體而言，隨較快擺頭轉速、較慢進給速度以及較低成形溫度而變大，而不同擺動角度對齒型部所產生的等效應變則有所不同。微觀晶粒尺寸方面，得知在各製程條件下均有細化現象，而隨較快擺頭轉速、較大介面摩擦因子細化結果越佳，不同擺動角度、進給速度及成形溫度對微觀晶粒尺寸的影響則有所不同。熱機冷卻相變態方面，隨冷卻方式不同，所產生的相變態也有所差異，鍛製後進行水冷、油冷，齒型部均能由沃斯田鐵組織變態為硬度較高的麻田散鐵組織，心軸部則有些許變態為波來鐵組織。而進行空冷則將使原沃斯田鐵組織變態為波來鐵組織。

關鍵字

傘齒輪 ； 擺輾熱鍛 ； 有限元素分析 ； 微觀組織 ； 相變態

並列摘要

The current study aims to explore the orbital hot forging process of bevel gears. Firstly, the material properties of AISI-1045 steel were analyzed, and the experiments and simulation of the forming models of bevel gear were also compared. Then, the finite element simulation was applied to analyze the orbital hot forging process for bevel gear, and the differences in forming load, deformation type, effective stress, effective strain, and microstructure grain between orbital forging and traditional forging were compared. The effects of the process parameters, such as pre-form, inclination angle, rotational speed, temperatures, feed rate, and the interface friction factor, on the plastic forming and microstructure of bevel gear were further explored. In addition, to predict the change of thermo-mechanical behavior of bevel gear forgings, the phase transformation on the bevel gear forgings in different cooling manners were also investigated to explore the microstructure evolution of the actual behavior.

The analysis results show that the deformation modes in various stages of bevel gear between finite element simulation and experiments have extensive consistency. Through analysis and comparison, the forming load of the orbital forging is about 1/3 to 1/5 of that of the traditional forging. The effective stress distribution in bevel gear generated by orbital forging is less than by traditional forging. The effective strain distribution by orbital forging is more regular and also larger than by the traditional forging. The grain refinement by orbital forging process is more uniform than by the traditional forging, in which the grain refinement is almost located at the tooth section. In addition, the flow of materials could be improved, and the fold defects of materials could also be avoided when reasonably changing the geometric shapes of billet or appropriately selecting the inclination angle, rotational speed, and feed rate. Through analysis of process parameters, the forming load could be reduced by using larger inclination angle, higher rotational speed, slower feed rate, and higher forming temperature. As for the effective stress, the spindle root section suffers the maximum stress, and the stress increases with smaller inclination angle, slower rotational speed, slower feed rate, and higher forming temperature. In addition, the effective strain generated by the process parameters has considerable consistency, mainly because the section of tooth has suffered a greater impact with different parameters. Generally, the effective strain increases with higher rotational speed, slower feed rate, and lower forming temperature. Different inclination angles will generate different effects on the effective strain in the tooth section. The microstructure grain size has refined in various process conditions. Study results show that the refinement effect of grain size increases as the rotational speed and interface friction factor increase. With different inclination angle, feed rate, and forming temperature, the influences on micro grain size are different. The phase transformations of thermal-mechanical cooling are different in various cooling ways. By water-cooling and oil-cooling after forging, the austenitic structure can all be transformed to high hardness martensite structure at the tooth section of bevel gear, but some transformed to the pearlite structure at spindle section. However, the original austenitic structure has transformed to pearlite structure in air-cooling.

並列關鍵字

bevel gear ； orbital hot forging ； finite element analysis ； microstructure ； phase transformation

參考文獻

[1]Y. K. Lee, S. R. Lee, C. H. Lee, D. Y. Yang, Process modification of bevel gear forging using three-dimensional finite element analysis, Journal of Materials Processing Technology 113, 2001, 59-63.

[2]J. H. Song, Y. T. Im, Process design for closed-die forging of bevel gear by finite element analyses, Journal of Materials Processing Technology 192–193, 2007, 1–7.

[3]許源泉、林恆勝、彭御芳，傘齒輪塑性成形技術及其研究趨勢，鍛造，第十六卷第三期，2007年。

[4]Juan Liu, Zhenshan Cui, Hot forging process design and parameters determination of magnesium alloy AZ31B spur bevel gear, Journal of Materials Processing Technology 209, 2009, 5871–5880.

[5]S. Choi, K. H. Na, J.H. Kim, Upper-bound analysis of the rotary forging of a cylindrical billet, Journal of Materials Processing Technology, 67, 1997, 78–82.