熱沖壓模冷卻系統之設計與分析

Design and Analysis of Cooling System for Hot Stamping Die

周育祺(Yu-Chi Chou)

指導教授 ： 陳立緯

國立虎尾科技大學/工程學院/機械與電腦輔助工程系碩士班/碩士(2017年)

摘要

熱沖壓是將金屬板材的成形製程與淬火製程互相結合的技術。熱沖壓加工後，板件的強度可提高2-3倍。熱沖壓板件的品質取決於麻田散鐵組織的分佈。而板件成形後的麻田散鐵組織的品質取決於模面的冷卻狀況。本研究利用有限元素分析軟體Fluent分析冷卻系統對於熱沖壓製程的影響，並以SKD61為模具材料，S45C和CSC-15B22為測試板件進行熱傳影響分析。首先建立熱沖壓模具及冷卻水道等幾何模型，透過不同的流速、冷卻水溫度，驗證此軟體的可行性並探討對熱沖壓製程的影響。模擬分析與實驗結果比對發現，在模擬時因為胚料與模具的接觸條件完美，所以在模擬的量測點距離模面和板材越近，實驗和模擬的誤差就越大，最大達到42%；在實驗時，因為胚料的平整度、夾持過程及移動過程、熱電耦線的安裝等因素造成誤差，使得量測點的溫度曲線較為平緩。經過模擬後發現，冷卻水道距離模面20mm比28mm低4℃，在模面上各點的溫差4℃；水道之間距離與直徑之比值3.5比4.5低2℃，在模面上各點的溫差到2℃，由此可知水道距離模面越近、分佈越密集，冷卻效果最好，但是加工的成本也相對提高。為了能夠瞭解不同流速及冷卻水溫度對板材的影響，本研究進行微觀組織、硬度的分析。結果顯示，胚料熱源是從板件中間的高溫區域向外側擴散，越靠近胚料的地方熱傳影響越大；將原始素材與試件的硬度轉換為抗拉強度來進行比對分析，發現15B22從原本的640MPa提升至1995MPa，S45C則是從465MPa提升至2070MPa。從金相試驗發現，微觀組織由肥粒鐵與波來鐵轉變成麻田散鐵組織，但是分佈不均勻，甚至看不太清楚。本研究藉由金相試驗與硬度試驗轉換抗拉強度去對照其相對應的強度。希望本文得到的結果可以作為熱沖壓模具冷卻系統設計的參考。

關鍵字

熱沖壓 ； 冷卻水道 ； 熱傳遞 ； 有限元素法

並列摘要

Hot stamping is a technology which combines forming process and quenching process. After the hot stamping process, the strength of the plate can be increased by 2-3 times. The quality of the hot stamping plate depends on the distribution of the martensite. The quality of the martensite depends on the cooling situation in the die surface. In this study, the influence of the cooling system on the hot stamping process was analyzed by the Fluent. The die material was set as SKD61 and the S45C and CSC-15B22 were set as sheet materials for the analysis of heat transfer during hot stamping process. First, hot stamping die, cooling channel and other geometric models were developed, then different flow rate, cooling water temperature, were analyzed to verify the feasibility of this software and investigate the impact of hot stamping process .Analysis and experimental results were compared and found that in the analysis, in the simulation because the workpiece and die contact conditions perfect, so the simulation measurement point from the die surface and workpiece closer, the greater the error of the experiment and simulation, up to 42%;In the experiment, the workpiece flatness ,clamping process and the moving process or the installation of thermocouple lines and other factors caused by the error, so the cooling rate curve is more ease. After the simulation found that the cooling channel from the die surface 20mm lower than the 28mm 4℃, the die surface temperature difference of 4℃; The ratio of distance between the channel and the diameter of 3.5 than the ratio of 4.5 low 2℃, the die surface temperature difference to 2℃, it can be seen that the closer the channel is to the die surface, the more dense the distribution, the best the cooling effect, but the processing cost is also relatively higher. In order to understand the different flow rates and cooling water temperature on the plate, the microstructure, hardness were analyzed. The results showed that workpiece heat source was from the middle of the high temperature region of the workpiece to the outside of the spread, the closer to the plate, the greater and the heat transfer is. From the hardness test to compare the tensile strength, compared with original material, it was found 15B22 reached 1995MPa from the original 640MPa , S45C reached 2070MPa from. From the metallographic test it was found that the ,microstructure has turned into martensite, but the distribution was not uniform ,or even can be seen clearly, hardness test and tensile test could be used to verify the corresponding strength. It was hoped that the results obtained in this study could be used as a reference for the cooling system design of the hot stamping die cooling system.

並列關鍵字

Hot stamping ； Cooling channel ； Heat transfer ； Finite element analysis

參考文獻

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