Analysis Of The Influencing Factors Of The Residual Thickness Of Water Projectile-assisted Injection Molding Pipes

Fluid projectile-assisted injection molding(F-PAIM),as a novel and unique injection molding technology used to produce complex bending pipe with uniform wall thickness,was developed by inducing a projectile in the fluid-assisted injection molding(FAIM)technology.The projectile was driven by with a high pressure fluid to push the molten polymer in the mold cavity,and obtained complex bending pipes with uniform wall thickness.Based on the fluid used,F-PAIM can be divided into gas projectile assisted injection molding(G-PAIM)and water projectile assisted injection molding(W-PAIM).To the best knowledge of us,there were hardly any researches on this technology.In this paper,an experimental equipment for F-PAIM was set up based on a lab-developed platform of FAIM.And the effects of processing parameters and other factors on the residual thickness of F-PAIM pipes were investigated by experiments and numerical simulations.The study of F-PAIM would provide theoretical and practical supports for the further development of the technology,and promote its application.The main contents of this research were summarized as follows:(1)The paper described the forming principle,characteristics and classification of the F-PAIM and analyzed the current situation and development trend of fluid assisted injection molding(FAIM)and fluid projectile assisted injection molding(F-PAIM).The research contents and approaches were also confirmed.(2)An experimental equipment for W-PAIM was set up based on a lab-developed platform of FAIM according to the characteristics of W-PAIM.The W-PAIM process equipment was designed and optimized on the basis of the experiment of the original FAIM:(1)Increasing the volume of mold projectile placement area was to ensure that the melt was completely wrapped the projectiles and water jet nozzle,and achieved full seal effect.(2)Design of water needle.On the one hand,it provided supports for fixing the projectile.On the other hand,it can help ensure that the fluid(water)jetted at stable,uniform speed and pressure.(3)Drawing on the shape of military missile,combined with the requirements of W-PAIM molding,the shape of the projectile was confirmed.(3)The effect of processing parameters on residual wall thickness of W-PAIM pipes was investigated by an experimental study.Aiming to the minimum residual wall thickness of pipes,single factor experiment and orthogonal experiment for overflow W-PAIM were carried out.In the single factor experiment,the influence of process parameters on the residual wall thickness of pipes was investigated.It was found that the water injection pressure and water injection holding time had little effect on the wall thickness.While the factors influencing it greatly were the melt temperature,injection pressure,water injection delay and mold temperature.When the melt temperature was below 240?,the wall thickness of pipes decreased with the increase of melt temperature.While the injection pressure was below 8 MPa,the wall thickness of pipes decreased with the increase of melt injection pressure.The longer it delayed,the greater the residual wall thickness of pipes was.When the mold temperature was below 85 ?,the wall thickness of pipes decreased with the increase of the mold temperature.The orthogonal test of the six factors and five levels was carried out,and the influence of each factor on the wall thickness of pipes was determined.The results were as follows: water injection delay time > the melt temperature > mold temperature > injection pressure > water pressure > pressure holding time.Meanwhile,the optimum process parameters for obtaining the thinnest wall thickness of pipes were also determined as follows: the melt temperature was 240 ?,the water pressure was 6 MPa,the injection pressure was 8MPa,the pressure holding time was 20 s,the water injection delay time was 0 s,and the mold temperature was 90 ?.(4)The influence of the shape of the projectile,the material it used,the process method,the processing material and the geometry of the cavity on the residual wall thickness of pipes were investigated experimentally.It was found that there was little difference in the residual wall thickness of the straight part of the samples with the projectiles of same diameter and different lengths,and there was little difference in the thickness of the inner and outer side walls of the 12 mm and 15 mm projectiles produced at the corner.Meanwhile,the difference between the thickness of the inner and outer side walls of the projectile with the length of 18 mm was obviously increased.At the same time,comparative tests were carried out using Q235,PLA and POM samples,respectively.The results showed that the first half part of a metallic projectile had obvious scratches,and the second half was of good quality.While,the wall thickness of PLA material was thin.The results of the experimental samples by short shot method showed that there was an inverse relationship between the amount of plastic and the length of penetration.The end of pipes appeared the shrinkage hole,and two penetration phenomena was not found.WAIM and W-PAIM experiments were carried out using HDPE,LDPE,ABS,GPPS,TPE,TPU,PBT,PP materials and so on,respectively.The results showed that W-PAIM can be fully applied to the above materials,and showed the excellent material practicability compared with PAIM.Three kinds of mould cavities with different structures were used in the experiments.It was found that the smaller the geometric mutation of mold cavity was,and the less obvious the difference between the inner and outer side wall thickness of pipes was,the better the uniformity of the wall thickness of pipes was.(5)A mathematical model for W-PAIM was built and numerical simulations were performed based on the Fluent module of ANSYS with 6 DOF.The fields analysis during the projectile penetration in cavities with different shape revealed the mechanisms of the effects of the projectile,bending angle and radii on the residual thickness.The simulation results were in good agreement with the experimental data quantitatively,which proved the feasibility of the numerical simulation method.