Developmental Study of Expert Systems for Die-Life Estimation in Hot Forging

热闭塞锻造模具的寿命主要取决于模具表面的软化。模具内温度场的准确估计对机械零件的精密锻造至关重要。温度场由模具表面的热接触和冷却条件控制，但模具-零件界面的接触导热系数的真实值或实用值尚不清楚。为此，在车间锻造过程中，使用了7个热电偶来测量锻造过程中的亚表面温度。模具表面用水、水基润滑剂和油基润滑剂冷却和润滑。并利用自行设计的模具寿命试验装置，对六种刀具材料的抗软化性能进行了评价。通过比较芯片内的实验温度和理论温度来估算接触导热系数。在这些数据的基础上，开发了五个辅助模具寿命估算的程序。它们是：1)4节点、8节点四边形单元和8节点六面体单元有限元分析的自动网格生成器；2)解决锻模中热传导问题的程序，包括估计模具的软化状态；3)求解锻模热应力的程序；4)估计模具与工件之间的导热系数的程序；5)用三维图形显示锻模的几何形状和温度、应变、应力、硬度等的分布情况。所有程序都是在NEC-9801-VM2 PC机上运行的。

The life of forging die in hot closed forging is mainly governed by the softening of the die surface. The precise estimation of the temperature field within the die is of essential importance to close tolerance forging of machine elements. The temperature field is controlled by the thermal contact and cooling conditions of the die surface, but the realistic or practical values of the thermal contact conductance of the die-orkpiece interface is not well known yet. In upset-forging process in workshop,therefore,seven thermocouples are used to measure the sub-surface temperatures during the forging run. The surface of the dies were cooled and lubricated with water, water-based lubricant and oil-based lubricant. And also, a specially designed die life testing apparatus was used to estimate the softening resistance of six kind of tool materials. The contact thermal conductance were estimated by comparing the temperatures in the die due to experimental and theoretical. On the bases of these data obtained, five programs to aid the estimation of die life are developed. These are:1)Automatic mesh generator for finite element analysis for 4- and 8- nodes quadrilateral element and 8-nodes hexahedron element.2)Program for solving heat conduction problems in the forging diewhich includes the estimation of softening state of the die.3)Program for solving thermal stress of forging die.4)Program for estimating the thermal conductance between die and workpiece.5)Three dimensional graphics to display the geometry of the forging dies and the distribution of the temperature, strain, stress, hardness etc.All programs are executed on a personal computer of NEC-9801-VM2 with NDP8087.