Calculation Model Of Injection Molding Products’ Ejection Force And Experimental Research

The ejection force of the injection molding products is important basis for design of mold ejection mechanism, accurate calculation of ejection force could improve the reliability of ejector mechanism and ensure a good quality of the products after ejection. However, the the existing formulas of ejection force have lower precision and fewer consideration of impact factors, the value of the ejection force in engineering practice was reduced. In this paper, on the basis of a comprehensive analysis of the research about ejection force, theoretical derivation was combined with molding experiment. Through measurement platform of ejection force and measurement device of friction coefficient, the relationship between several factors and ejection force and the mechanism of enveloping force affected by these factors were studied. Numerical simulation technology and data fitting method were used to establish a more easier use and higher accuracy calculation model of ejection force on the basis of experimental results.The impact of six process parameters such as ejection temperature on the ejection force were studied by carrying out single factor and orthogonal experiments with a rectangular box product as its target, and the experimental materials are High-Density Polyethylene (HDPE), Polypropylene (PP) and Acrylonitrile-Butadiene-Styrene(ABS).The experimental results of three experimental materials show ejection temperature is the main factor affecting the ejection force, and other process parameters could be neglected.Based on the above research, the impact of the core surface roughness on the ejection force was studied by carrying out molding exeriments, the results show that, the lower core surface roughness causes an increase of the ejection force, because the lower core surface roughness will increase the actual contact area of the products with the core, resulting in enhanced adhesion effect. The impact of the wall thickness on the ejection force was studied at the same time, the experimental results show that, the relationship between the wall thickness and the ejection force was influenced by ejection temperature, but in a certain ejection temperature, when the wall thickness is large, the enveloping force between products and core decreases because of slow cooling of the products. On the basis of a rectangular box part, the impact of local characteristic structures on the ejection force were studied by adding internal characteristic structures, the results show that, when the local characteristic structure of the products is closer to the shrinkage center of main structure, it will have a larger shrinkage and a greater impact on whole ejection force. The impact of product size and shape on the ejection force were studied with a rectangular box product as its target, the results show that, in same wall thickness and size, the ejection force of cylindrical products is as approximately0.785times as rectangular box products.In order to obtain real value of ejection friction coefficient between products and core, a measurement device was designed and manufactured to measure the ejection friction coefficient under different ejection temperature and different core surface roughness, the results show that, higher mold temperature and lower mold core surface roughness cause an increase of friction coefficient.Finally, the theoretical calculation model of ejection force is improved through data fitting of measurement data obtained by experiments. The ejection force of experimental product was calculated by improved model in this paper and another model in textbook, the results show that the calculation results of the model established in this paper is closer to experimental values.