H65黄铜管冷轧变形模拟分析与实验研究(续)

图3-b可以看出,孔型脊部区域的管坯内表面温度明显高于外表面,这主要是由于外表面摩擦较小,而内表面的摩擦相对较大,产生的摩擦热远远大于外表面。由此可知,对于减壁量不大的皮尔格冷轧管,引起金属温度变化的主要因素不是塑性功的转化而是由于摩擦所引起的,因此实际生产中应加强对管坯表面的润滑,以免产生过高的温升。H65黄铜在200℃～700℃会发生脆性转变,如果实际冷轧管生产中,管坯变形区的温度出现如图3所示的情况,即使工作应力较小,也可能超过材料此时的强度极限,从而产生如图4所示的周期性横向裂纹。

Numerical Simulation of Cold Rolling Deformation of H65 Brass Tube and Experimental Research

3 -D thermal mechanically coupled FEM modeling was established to analyze cold pilgering process of H65 brass tubes by the finite element method software DEFROM -3D. The distribution of temperature and thermal stresses fields were acquired. The research shows that ingots with good microstructure and properties are the key to realize the cold rolling of H65 brass tube. The ratio of 13 phase in ingots should be controlled within 0% - 20%. If the cold rolling process was controlled unreasonable, the periodic horizontal cracks of cold rolling tubes are caused by temperature rise that due to the plastic deformation heat and friction heat which is as high as 300 ℃. The axial stress az is tensile in the groove flange area, which is one of the reason for the periodic horizontal cracks of cold rolling tubes. The rotation angles were 60° -90°and feed amount was 2mm- 6mm in the cold pilgering process for relatively low plasticity brass （such as H65 brass ）, which can effectively reduce the additional tension stresses in the groove opening area.