工件與電極接觸型態對差溫電氣端鍛之影響分析

An Influence Analysis of Contact Characters between Billet and Electrode on Thermal Differential Electric Heading Processes

鄭又瑄(You-Shyuan Jheng)

指導教授 ： 許源泉

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(2012年)

https://doi.org/10.6827/NFU.2012.00087

摘要

目前用於電氣端鍛的零件加工，主要用於高徑比大的零件加工，如汽、機車之軸盤類汽門零件等，而隨著交通及機械業的迅速發展，對於汽門與軸類零件的數量及種類需求也越來越多。電氣端鍛技術具有設備投資低，鍛件桿部尺寸精度高與各項品質優異等特點，缺點是變形方式為自由鍛粗，對一些塑性差的材料變形不利，容易產生過熱與過燒、裂痕等缺陷，導致製品不良率高，所以必須透過模擬軟體來分析差溫電氣端鍛的成形過程，此過程必須依照電氣端鍛的特性來規劃製程參數，並且處理好電壓、溫度、成形力，三種耦合問題，才能獲得準確性高的分析結果。
本研究分為工件接觸型態及電極接觸型態與電氣端鍛成形應用研究三部分，並利用有限元素軟體DEFORM-2D對AISI 1045中碳鋼之棒材進行差溫電氣加熱與端鍛成形的模擬分析，工件接觸型態研究方面為探討棒材在不同接觸面積、接觸面數及接觸位置等條件下，其溫度分佈與變化之情形，接著進行不同接觸面積與面數之端鍛成形，以了解其棒材在不同接觸面積與面數的條件下變形之情形。電極接觸型態研究為探討電極在不同體積外形與接觸方式下，對差溫電氣加熱的影響。棒材成形應用部分，為探討棒材成形時之應力、應變、溫度分佈與輪廓外型變化等研究，並分析棒材在差溫電氣端鍛及成形後之晶粒大小與硬度分佈等微觀組織變化。經由分析結果顯示，在短時間電氣加熱下，當工件接觸面積範圍變小時，瞬間加熱溫升速率會加快，同理工件倒角愈大時亦是，因工件傳熱範圍縮小所致，但均溫性較不佳，材料塑流應力相對增大。當工件接觸位置改變時砧子電極的電流方向亦跟著改變，其溫度也會隨著電流場的不同而不同，所以溫度的變化取決於電流場的大小。當工件接觸面積固定時，增加工件接觸面則使溫度降低，主要是因為環面增加導致電流分散所致。而電極接觸型態研究結果顯示，體積外形小且平面接觸之電極加熱速度會比側面接觸之電極快，此乃電流所走路徑較短，導致相同時間下所獲得電通量較大，所以溫度較高。
由電氣端鍛實驗與有限元素模擬之分析比較，研究結果顯示，差溫電氣加熱模擬與實驗所量得之溫度，誤差值皆在1%以下。而差溫電氣端鍛成形模擬與實驗，針對棒材成形後的輪廓外形與最大徑的量測值，實驗與模擬的趨勢相當符合，因此，更加驗證有限元素模擬軟體DEFORM-2D應用於差溫電氣成形之可靠性。

微觀組織研究結果顯示，在棒材端部的金相顯微組織呈現出麻田散鐵分佈，但因本研究為差溫電氣成形，所以溫度梯度大，因此產生部分麻田散鐵，所以量測所得到的硬度值比文獻低。在棒材直部的金相顯微組織呈現出肥粒鐵與波來鐵，所以直部微觀組織與原素材微觀組織頗為相似。硬度量測結果顯示，棒材接觸面積比例為12.5%、倒角為15˚、30˚端部所量測出的硬度值皆比直部大，其硬度值約在600~700HV之間，而倒角為45˚之棒材端部所量測之硬度值約在260~380 HV之間，造成此差異之原因，推測乃因棒材倒角大、接觸面積範圍小，以致水冷時的溫度已經沒有前面兩者高，所以此區所量測之硬度值反而比較小，而所得的微觀組織也比較不同。在直部所量測之硬度值，因差溫的關係，所以溫度普遍集中於局部變形之區域，直部未變形之區域溫度較低。

關鍵字

電氣端鍛 ； 差溫加熱 ； 有限元素分析

並列摘要

This study is divided into contact with the workpiece type and electrode contact morphology and electrical terminations forging the three parts of the applied research and the use of finite element software DEFORM-2D differential temperature of electrical heating and side forging of AISI 1045 medium carbon steel bars simulation analysis, contact with the workpiece type of research to explore the bar in a different contact area, contact surface number and the contact position and other conditions, the temperature distribution and changes in circumstances, then a different contact area with the number of faces of the end of forging forming Learn bar deformation in the contact area and the number of faces under the conditions of the case. Electrode contact type of electrode in different volume shape and contact mode, the differential temperature electrical heating. The bars forming the application part of the study to explore the bars forming the stress, strain, temperature distribution and the contour shape change, and analyze the microstructure of the bars in the differential temperature electrical terminations forging and forming grain size and hardness distribution changed.

Through the analysis showed that the range variable hours, when the workpiece contact area in a short period of electrical heating, instantaneous heating temperature rise rate will accelerate Similarly workpiece chamfer larger range of workpiece heat transfer narrow due, but alltemperature than poor material flow stress is relatively increased. When the contact with the workpiece position to change the direction of the anvil electrode current change with temperature will be different with the current field, so the change of temperature depends on the size of the current field. When the workpiece contact area fixed, the increase in contact with the workpiece surface temperature lower, mainly because of the torus increases due to the current spreading. Electrode contact type, the volume of small size and planar contact electrode heating rate faster than the side of the contact electrode, which was current to take the shorter path, resulting in the same time the electric flux is large and have more respectable, so temperatures in high.

From the electrical side forging experiments and analysis of finite element simulation results show that the temperature measured by the differential temperature electrical heating simulation and experimental errors were within 1%. Differential temperature electrical terminations forging forming simulation and experiment, the bars forming the contour and the maximum diameter of the measured value, the trend of the experiment and simulation is quite consistent, therefore, more to verify the finite element simulation software DEFORM-2D used in differential temperature reliability of electrical forming.

The microstructure results, showing in the bar end of the metallographic microstructure of martensite distribution, but this study is the differential temperature electrical forming, so the temperature gradient, resulting in some martensite, so the measurement The hardness value is lower than the literature. Bars direct the Department of metallographic microstructure showing ferrite and pearlite, so straight microstructure and the microstructure of the original material is quite similar. Hardness measurement results show that the bar contact area ratio of 12.5%, the chamfer is 15˚, 30˚ end of the measurement the hardness values are better than straight Ministry, and its hardness value of about 600 ~ 700HV, while chamfer 45 ˚ bar end measured hardness value between about 260 ~ 380 HV, resulting in the reason of this difference, presumably due to the bar chamfering, the scope of the contact area, resulting in water-cooled temperature not in front of the two, so the measured hardness values in this area but relatively small, while the microstructure of the obtained compare. Direct the department of the measured hardness values, due to the difference of the relationship between temperature, so temperature is generally concentrated in the region of localized deformation, the undeformed straight Ministry of Regional temperature is low.

並列關鍵字

Electric heating ； Thermal differential forming ； Finite Element Method

參考文獻

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