Research On Online Monitoring Method Of Crystallinity Of Injection Molding Products

Injection molding is the most common method to obtain high performance plastic products.For crystalline materials,the quality and properties of plastic products are affected by the crystallinity.However,there are few studies on online monitoring of crystallinity of injection molding products.Both the measurement method and the accuracy of the results need to be improved.The method of crystallinity measurement is usually off-line,which is inefficient and cumbersome to operate.In order to alleviate this situation,a new monitoring method of crystallinity is proposed in this paper.Based on the characteristics of capacitance sensor,the online measurement of crystallinity of injection molding products is realized.The main research contents include:(1)According to the crystalline and dielectric properties of polymer materials,a new method for monitoring crystallinity is proposed.The monitoring principle of variable permittivity capacitance sensor is briefly introduced.The main working stages of capacitance sensor in injection molding process are pre injection stage,injection filling stage,pressure maintaining and cooling stage.According to the new method of crystallinity monitoring,the orthogonal experiment scheme of on-line monitoring crystallinity is designed.(2)The mathematical relationship between the crystallinity and the dielectric constant of the material was established.The orthogonal experiment was used to set different injection molding process parameters to produce injection samples.The crystallinity of the samples was measured by DSC;The dielectric constant of the sample was measured by a dielectric constant measuring instrument;The mathematical model between crystallinity and dielectric constant was fitted by least square method,and the reliability of fitting polynomial was verified.(3)According to the orthogonal test scheme and the mathematical model,the online monitoring experiment of the crystallinity of injection molding products was carried out.The crystallinity data measured by the capacitance sensor measurement system is compared with the crystallinity data measured by DSC.The results show that the output voltage waveform of each process parameter combination can be measured by the capacitance sensor measurement system.The output voltage data collected by usb3102 data acquisition card is transformed into crystallinity curve by MATLAB.Compared with the data measured by DSC differential thermal analysis,the value and trend of the transformed curve are basically consistent.The average absolute error was 0.5625 and the average relative error was 1.79%.The validity of the capacitance sensor measurement system is verified,and the online measurement of crystallinity is finally realized.(4)Based on the orthogonal experiment of crystallinity measurement,the influence of these process parameters on the crystallinity of injection molded parts was studied.In order to understand the influence of crystallinity on the mechanical properties,the mechanical properties of the plastic products were tested.The relationship between the process parameters crystallinity mechanical properties of injection molding is mastered,which is of great significance for the on-line quality control of plastic products.The most important factor affecting the crystallinity of plastic products is injectionpressure.The effect of packing pressure is low.The melt temperature and injection time have the lowest influence on the orientation tensor.This can be used as the basis for controlling the crystallinity.