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通过对未印刷的覆膜铁板材进行热处理,研究了加热温度和保温时间变化与冲压成形后圆角处出现白痕之间的规律。结果表明,加热温度为100℃,保温时间不超过30min时,圆角处无白痕。加热温度超过100℃,随着温度的升高,圆角处出现白痕的时间不断减小,当温度提高到140℃时,保温时间仅3min即可出现严重的白痕。随着保温时间的增加,圆角处将由无白痕、轻微白痕向严重白痕过渡。冲压工艺不变的前提下,热处理工艺对圆角处白痕的出现具有明显的影响。较高的加热温度和较长的保温时间,促进了覆膜铁表面透明膜中球晶组织的转变,在之后的冲压成形过程中,圆角处的球晶组织在复杂应力作用下发生破裂并最终形成纤维结构,降低了薄膜的透明度而呈白痕现象。
Through the heat treatment of unprinted coated iron plate, the law between the change of heating temperature and holding time and the appearance of white marks at the fillet after press forming was studied. The results show that the heating temperature is 100 ℃, holding time does not exceed 30min, no white marks at the corners. Heating temperature exceeds 100 ℃, with the increase of temperature, fillet whitening time decreases, when the temperature is raised to 140 ℃, holding time of only 3min to appear serious white marks. As the holding time increases, rounded corners will be no white marks, slight white marks to severe white marks transition. Stamping process under the premise of the heat treatment process on the appearance of white marks have a significant impact. The higher heating temperature and longer holding time promoted the transformation of spherulitic structure in the transparent film on the coated iron surface. In the subsequent stamping process, the spherulitic structure at the fillet ruptured under complicated stress The final formation of fiber structure, reducing the transparency of the film was white marks phenomenon.