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

热封闭锻造中锻模的寿命主要取决于模具表面的软化。模具内温度场的精确估计对机械零件的近公差锻造具有重要意义。温度场是由模具表面的热接触和冷却条件控制的，但模具工件界面的热接触电导的现实或实用值尚不清楚。因此，在车间镦锻过程中，使用7个热电偶来测量锻造过程中的次表面温度。采用水、水基润滑剂和油基润滑剂对模具表面进行冷却和润滑。并利用专门设计的模具寿命试验装置对6种刀具材料的抗软化性能进行了评估。通过对模具内温度的实验和理论比较，估算了接触导热系数。在此基础上，开发了五种辅助模具寿命估算的程序。这些是：1)用于4节点和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)解决锻模热传导问题的程序，包括模具软化状态的估计。3)锻模热应力求解程序。4)模具与工件热传导估算程序。5)三维图形显示锻模的几何形状及温度、应变、应力、硬度等的分布。所有程序均在带有NDP8087的个人计算机NEC-9801-VM2上执行。

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.