镦粗是大锻件制造工艺中最重要的基本工序与常用工序.镦粗变形是由其坯料内部的速度场(或位移场)确定的,进行镦粗变形研究的关键是得到其真实速度场(或位移场),为此,利用塑性力学变分原理,对其进行了研究.根据试验与生产得到的镦粗变形基本规律,预设镦粗变形的运动学容许的速度场,进而求得应变速率场,借助刚塑性材料的第一变分原理求得其真实速度场的解析式.为检验真实速度场的合理性,考察了端面摩擦因子m分别为0、0.25、0.5和0.75时镦粗坯料的变形情况,结果合理.又进一步将解析计算结果与数值计算结果对比,两种计算结果十分接近.表明研究得到的镦粗真实速度场解析式是正确的.利用建立钢锭镦粗的真实速度场,计算分析了钢锭镦粗的难变形区,可为制定大锻件工艺提供参考.%Upsetting is a basic operation of the greatest importance.It is commonly used in the heavy forging process.Upsetting deformation is determined by the billet's internal velocity fields (or displacement fields),therefore,the key to the research on the upsetting deformation is to get its true velocity field (or displacement field).The variation principles for plastic mechanics are employed to study upsetting here.Based on the upsetting deformation's fundamental rules that were achieved from experiments and shop-floor production,kinematic permissible velocity fields are assumed and the strain rate fields are obtained.Finally, the first variation principle for rigid-plastic materials is used to acquire the mathematical expression of the true velocity field.The investiga-tions on upsetting cases with end face friction factors of 0,0.25,0.5 and 0.75 are carried out in order to verify their correctness.The calculation results show that it is reasonable.Further comparisons between the analytical results and numerically simulated results indicate that they agree well with each other.The achieved mathematical expressions for the true velocity fields of upsetting are correct.The true velocity filed for ingot upsetting is established to analyze the Dead Metal Zones (DMZs) during ingot upsetting, which provides reliable reference for heavy forging makings.
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