Molding Mechanism And Key Technology Of Water Projectile-Assisted Injection Molding Process

Fluid Projectile-Assisted Injection Molding(F-PAIM)is a new injection molding process,in which the pressurized fluid is used to drive a projectile to penetrate a molten polymer to mold a hollow pipe.This process can be used to produce pipe that has thinner,more uniform wall thickness and smoother surface.Based on the research of the process parameters of Water Projectile-Assisted Injection Molding(W-PAIM),what will be studied further is the penetration behavior of the projectile,the relationship between the material and morphology of the projectile and the molding quality in the research,whose purpose is to reveal the differences between different processes and the impact of the projectile to the molding quality so that the technology can be extended to practical production applications.The main contents of this research were summarized as follows:(1)The molding principle and characteristics of W-PAIM process are explained.And the research status of WAIM technology and W-PAIM technology at home and abroad are introduced briefly.Finally,the research content and ideas are determined.(2)A flow model of W-PAIM is built and the relevant parameters in Fluent are set to simulate the penetrating process of the W-PAIM process.It is found that the turbulence intensity is the larger around the entrance of the pipe.And the closer to the inner wall of the pipe the position is,the larger the turbulence intensity is.The shearing effect is mainly concentrated between the profile of the projectile and the melt.During the penetration process,the temperature of the pipe and the high-pressure water decrease gradually along the opposite direction of the melt flowing.The simulation results can match the actual flowing conditions better.The rationality and reliability of the model and method are verified.(3)Based on the simulation technology,the shape geometry and size of the projectile are selected and optimized.It is mainly based on the residual wall thickness and standard deviation of RWT.It is found that the projectile whose the front-end shape is parabolic has a better smooth and centering characteristic.After penetrating,the residual wall thickness is more uniform.When the length of the straight section of the projectile is too small,a large eccentricity and overturning phenomenon occurs when it penetrates to the end of the cavity.When the diameter of the projectile is too small,eccentricity phenomenon also occurs.When the diameter is too large,the average residual wall thickness is too small,which weakens the mechanical properties of the pipe.(4)In terms of residual wall thickness,velocity field,pressure field,strain field etc,the WPAIM process is analyzed.Comparing with the WAIM process,it is found that the penetration of water in WAIM and the projectile in W-PAIM are relatively stable in the front of curved section of the pipe.The RWT of both has a declining tendency along the flow direction in the behind of curved section of the pipe.On the other hand,The central speed of W-PAIM and WAIM are faster than 0.34 m / s.In W-PAIM and WAIM,the closer to the center of the mold cavity the position is,the lower the strain rate is.And the peak of both is around the inner wall of pipe.(5)An experimental platform is built and the different projectiles are made to mold pipe.By measuring and observing the residual wall thickness,standard deviation of the wall thickness,and the quality of the inner wall surface,it is found that the order of the deformation of the projectile is ranked as PP> PTFE> ABS> PA6 after penetration molding.However,the thermal deformation temperature of these is ranked as PA6> ABS> PP> PTFE.Except the PP material,the rule which the higher the thermal deformation temperature is,the smaller the deformation is,is followed basically by the rest of three materials.At the same time,according to a certain measurement method to measure the RWT of different number of pipe,it was found that materials with higher thermal deformation temperature are more suitable for making projectiles.A better quality-pipes with 16 mm-diameter might be molded by projectile whose front end is parabolic,straight length is 7mm,and diameter is 13 mm.(6)PA6 and PP projectile-molding pipe and WAIM-O-molding pipe are chosen as samples to observe their microscopic morphology and analyze causes.It found that a lamellar crystal structure is shown generally in the micro-morphology of the samples of the W-PAIM-O process,while a long filamentous and massive structure is shown generally in the micro-morphology of the samples of the WAIM-O process.On the other hand,a rectangular and laminar structure is present in the microstructure of the PP projectile molding pipe,which was mainly caused by the adhesion of the matrix material to the outer contour of the projectile.