Research On Long Conveying PP Shrinkage Ratio And Forming Property

The plastic parts are widely used in automotive industry,and automotive industry is advocating light weight.The first thing of automobile lightweight is increase the plastic use in the automobile.So it is required that the plastic parts should have good quality.The plastic parts in automobile mainly includes instrument panel,door panel and so on.These parts are all have a large size and all this kind of products usually use polypropylene(PP).So it is necessary to research these quality issue.And this paper is trying to find the root cause from these respects.In this paper,we take the self-made strip mold as the research object,which has the advantages of adjustable wall thickness,simple structure,preset temperature and pressure sensor.This paper will find out the which factors will affect the percentage of the shrinkage and how to deduce it by using the exchange experiments and Taguchi orthogonal experiments.The researched steps are as followed.At first,this paper studies the melt temperature,mold temperature,packing pressure,packing pressure time,v-p switching point,cooling time,screw speed and other factors on the impact of PP shrinkage.The result show that packing time,packing pressure and molding temperature are the most significant factors for PP shrinkage.The experiment proved that Taguchi orthogonal test can quickly determine the size of the influence of each factor on the shrinkage rate.Secondly,this paper collected by the sensor mold cavity temperature and pressure data,more meticulous research of packing parameters and mold temperature on the rate of contraction,analysis a linear relationship between the pressure parameters and ensure the existence of the weight of the product,and when other parameters do not change the situation between the weight of the product and molding the shrinkage rate also exist linear correlation,and the correlation coefficient of the experimental fitting out.Then through many experiments and collect temperature and pressure data,the experiments obtained shrinkage temperature pressure correction data rate,the results show that in the 3 experiment,after correction the shrinkage rate of results is not more than 0.02%.Verify that this method of determining shrinkage have repeatability.At last,considering the relationship between sink mark and shrinkage,this paper also briefly studies the process parameters and the structure of reinforcement of the plastic products surface sink mark.The results showed that the changes of process parameters to improve the sink mark defects and reinforcement effect is not remarkable,and the root thickness and the angle has great influence to sink mark.This results in reducing the surface sink marks with defects certain guiding significance.