模锻锤载荷谱和应力谱的确定方法

模锻锤是承受多次冲击载荷的金属成形机器。现有的最大载荷设计理论已不符合锤机主要构件的实际承载情况,而应以载荷谱和应力谱为基础进行疲劳强度设计,目前从理论上直接建立这两种谱尚有一定困难。作者采用测试、调研统计、类比和理论计算相结合的方法建立了模锻锤的载荷谱。此外,作者在多次试验中发现锤杆上首次峰值应力与模锻锤打击力之间的相关关系,通过大量的实验数据建立了相应的回归方程。因此从模锻锤的打击负荷分布可求出锤杆上首次峰值应力分布,再借助于减幅系数和无效变程,运用峰值计数法建立了锤杆上的应力谱,尤其是危险区的应力谱,这是一条可行和有效的金属成形机器的编谱方法。

On Determination of Load and Stress Spectra of Die-Forging Hammer

In order to make clear the new contributions of this paper, it is necessaryfirst to review briefly past research. The pioneering work on the experimental investigation of the dynamic loadand service life of die-forging hammer was carried out by Flasof 13]. Beliaefanalyzed the maximum blow load of die-forging hammer 14]. Kogan measuredexperimentally the dynamic stresses of the hammer rod of 16 ton die-forginghammer 5]. Lukeanof measured experimentally the dynamic stresses of thehammer rod of counterblow hammer 15]. Karpenko 6], Fursof 7], and Cerw-in 16] studied the dynamic strength, the vibration of the frame of die-forginghammer, and the dynamic load on ram respectively. Kerdief appraised the dy-namic strength specification of the component materials of forging-stampingmachine 17], But the load and stress spectra of die-forging hammer, the foun-dation of fatigue-strength design,have not been investigated in the above Refs.(in fact, no such investigation on any forging equipment has been reported inthe open literature). The new contributions of this paper are believed to be the following: (1) Load spectra for various sizes of die-forging hammer are presentedin Table 2. These are believed to be the first of their kind. In preparing thesespectra, the authors considered carefully several factors such as the statisticalstudy of real working conditions of die-forging hammer, the statistical analysisof much experimental data, and the first author's previously published theoreticalcalculation method11]. (2) Equation(2) established the regression correlation of stress in the ham-mer rod and the blow of the die-forging hammer. The authors have discoveredin experiments that stress varies along hammer rod height and there are twohigh-peak zones: one tensile and the other compressive. Figs.2 and 3 and Table4 give respectively the stress spectra of hammer rod in these zones. The authors have discovered in investigations that more than 60% of failureoccur in the high-peak zone of tensile stress, a lesser percentage in the high-peakzone of compressive stress. Other failures do not belong to repeated impact fatigue,and they are caused by fatigue damage known as bite, defect of material, bad instal-lation, etc. It is believed that with the load spectra and stress spectra presented in thispaper, the designer is provided with the data necessary for the strength designagainst occurrence of repeated impact fatigue.