工艺参数对聚甲醛微注塑制品力学性能的影响机理EI北大核心CSCD

基于单因素实验,研究工艺参数对不同厚度聚甲醛(POM)微注塑制品屈服应力、弹性模量、断裂强度和断裂伸长率等力学性能指标的影响,并基于制品形态结构分析工艺参数对制品力学性能的影响机理。实验结果表明,随着注射速度的增大,1.0mm厚微制品的皮层厚度减小,过渡层厚度增加,结晶度增大,综合效应使得屈服应力、断裂强度和弹性模量增大,断裂伸长率减小;0.2mm厚微制品的皮层厚度占主导地位,其力学性能是由皮层的力学性能决定,皮层厚度先增大后减小使得屈服应力、断裂强度和弹性模量先增大后减小,断裂伸长率先减小后增大。随着熔体温度的升高,1.0mm厚微制品的分子链取向度减小,皮层厚度减小,收缩量增大,使得屈服应力、断裂强度和弹性模量减小,断裂伸长率增大;而0.2mm厚微制品的皮层减小,但过渡层增加,结晶度增大,且补料更充分,综合作用使得屈服应力、断裂强度和弹性模量增大,断裂伸长率减小。随着模具温度的升高,1.0mm厚微制品的皮层比例减小,结晶度增大,结晶度影响占主导,使得屈服应力、断裂强度和弹性模量逐渐增大,断裂伸长率减小;而0.2mm厚微制品的皮层厚度占主导,皮层厚度明显减小使得屈服应力、断裂强度和弹性模量减小,断裂伸长率增大。

Mechanism of the Influence of Processing Conditions on Mechanical Properties of Micro Injection Molded polyformaldehyde Parts

Based on the single factor experiment method,the micro injection molded polyformaldehyde tensile specimens with the thickness of 1.0 rnm and 0.2 mm were molded by micro-injection molding experiments.The tensile testing of the micro specimens was conducted and the effect of process parameters on the mechanical properties indices of different micro specimens such as yield stress,modulus,fracture strength and fracture elongation was investigated,and influence mechanism was analyzed based on the morphology and structure of the micro specimens.The results show that with the injection speed increasing,for the micro parts with the thickness of 1.0 mm,the thickness of the skin layer decreases,the thickness of the transition layer increases,and the crystallinity increases.The synthetic effect result in that yield stress,fracture strength and modulus increase and the break elongation decreases gradually;for the micro parts with the thickness of 0.2 mm,the skin layer is dominant in the thickness direction,and the mechanical properties of the parts are determined by the mechanical properties of the skin layer;with the injection speed increasing,the thickness of the skin layer increases at first and then decreases,which result in that the yield stress,fracture strength and modulus increase at first then decrease,and the break elongation decreases at first and then increases.With the melt temperature increasing,for the micro parts with the thickness of 1.0 mm,the orientation degree of molecular chain decreases,the thickness of the skin layer decreases,and the shrinkage increases,which result in that the yield stress,fracture strength and modulus decrease gradually,and the break elongation increases gradually;however,the integrated effect of the enough compensation of the melt,the increase of the transition layer and the increasing of the crystallinity of the micro parts with the thickness of 0.2 mm makes the yield stress,the fracture strength and modulus increase,and the break elongation decreases gradually.With the mold temperature increasing,for the parts with the thickness of 1.0 mm,the thickness of the skin layer decreases,the crystallinity increases,and the influence of crystallinity is dominant for the 1.0 mm parts,which result in that the yield stress,fracture strength and elastic modulus increase,and the break elongation decreases gradually;for the micro parts with the thickness of 0.2 mm,the skin layer is dominant in the thickness direction,and the thickness of the skin layer decreases with the mold temperature increasing,result in that the yield stress,the fracture strength and modulus decrease,and the break elongation increases gradually.