压铸模数学模型及测温试验研究

发布时间：2018-09-08 14:16

【摘要】：压铸模具的使用寿命是压铸成本的重要组成部分。热疲劳失效是影响压铸模寿命的主要因素。压铸模型腔表面所受热负荷主要来源于压铸时压铸件的热传导及脱模剂的冷却作用,模具表面层温度随压铸周期的进行呈现出有规律的变化,周期性的温度变化则会导致周期性的热应力产生,当所受热应力超过材料的屈服强度时模具产生塑性变形,再经过足够多的循环周期后,裂纹萌生,最终导致疲劳失效。因此,研究模具表面层温度场、热应力场、热疲劳寿命、热疲劳区深度对摸清模具的失效机理有着重要意义。本文首先概述了压铸的特点及工艺参数的选择;介绍了国内外对模具失效机理的研究现状。发现温度梯度是导致热疲劳产生的关键因素。利用非稳态传热理论,建立一维半无限大物体的表面接触传热模型,进而构建出多次连续压铸时压铸模型腔表面的温度场模型。以锌合金、铝合金、铜合金为例,绘制出温度变化曲线。根据热弹塑性理论,建立符合压铸模热应力变化规律的薄板模型。结合温度场模型,进而构建出连续压铸时模具型腔表面的热应力场模型。绘制出三种不同合金压铸时热应力变化曲线。通过对热疲劳产生机理的研究,得到热疲劳寿命计算公式,并给出热疲劳区深度的计算方法。结果表明:铜合金压铸时模具表面层热疲劳区深度为3mm。最后利用金属型模具对锌合金、铝合金、铜合金进行浇注试验,分别测量出距离模具表面0.2、1.5、3.0和5.0mm处的温度变化曲线。与温度场理论模型相对比,验证了温度场模型的正确性。
[Abstract]:The service life of die-casting die is an important part of die-casting cost. Thermal fatigue failure is the main factor affecting die casting die life. The heat load on the surface of the die casting die is mainly from the heat conduction of the die casting and the cooling of the release agent. The temperature of the surface layer of the die casting varies regularly with the period of the die casting. The periodic temperature change will lead to periodic thermal stress. When the thermal stress exceeds the yield strength of the material, the mold will produce plastic deformation, and then after enough cycle period, the crack will initiate and eventually lead to fatigue failure. Therefore, it is of great significance to study the surface temperature field, thermal stress field, thermal fatigue life and depth of thermal fatigue zone in order to find out the failure mechanism of die. In this paper, the characteristics of die casting and the selection of process parameters are summarized, and the research status of die failure mechanism at home and abroad is introduced. It is found that temperature gradient is the key factor leading to thermal fatigue. Based on the theory of unsteady heat transfer, the surface contact heat transfer model of one-dimensional semi-infinite body is established, and the temperature field model of the cavity surface of die casting is constructed. Taking zinc alloy, aluminum alloy and copper alloy as examples, the curve of temperature change is drawn. According to the thermoelastic-plastic theory, a thin plate model is established, which accords with the changing law of thermal stress of die casting die. Combined with the temperature field model, the thermal stress field model of die cavity surface during continuous die casting is constructed. The curves of thermal stress change during die casting of three different alloys were plotted. Based on the study of thermal fatigue generation mechanism, the formula for calculating thermal fatigue life is obtained, and the method for calculating the depth of thermal fatigue zone is given. The results show that the depth of thermal fatigue zone on the surface of the die is 3 mm during die casting of copper alloy. Finally, the casting test of zinc alloy, aluminum alloy and copper alloy was carried out by using metal mould, and the temperature change curves were measured at the distance of 0.2 ~ 1.5N ~ 3.0 and 5.0mm from the surface of the die respectively. Compared with the theoretical model of temperature field, the correctness of the model is verified.
【学位授予单位】：武汉科技大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG241

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