| Gas-Water-Assisted Injection Molding(GWAIM)is a new Injection Molding process which based on the research of Gas-Assisted Injection Molding(GAIM)and Water-Assisted Injection Molding(WAIM).The process of GWAIM is as follows: First,high temperature melt is injected to fill the cavity,and then high pressure gas is injected from the fluid injector.The high temperature melt moves forward under the push of high pressure gas until the whole gas filling process is completed.Secondly,high pressure water is injected from the fluid injector,and the high pressure water flows in the hollow channel formed by the high pressure gas.Finally,after a period of cooling and pressure retention,the hollow parts are obtained after draining.Therefore,it is expected that the GWAIM process not only maintains the uniformity of the residual wall thickness of the GAIM process,but also has good cooling performance and inner wall surface quality of the WAIM process.GWAIM technology not only combines the advantages of GAIM and WAIM technology,but also overcomes their limitations,so that this process has a wider applicability.In order to master the forming mechanism of the new process and guide its application practice,in this research,CAE technology is used to systematically study the penetration behavior and flow field distribution characteristics of overflow GWAIM process,The influence law of process parameters on the residual wall thickness of straight pipe parts was investigated,and the optimal process parameter combination of GWAIM process was studied.The influence law and mechanism of bending Angle and process parameters on the hollow rate and deviation rate of curved pipe parts were studied in depth.The main contents of this research were summarized as follows:(1)The forming principle and technical characteristics of GWAIM process are described,the forming principle,characteristics and research status of GAIM process and WAIM process at home and abroad are briefly introduced,and the research content and ideas of this article are determined.(2)The dynamic and heat transfer mathematical models of transient,non-isothermal and non-Newtonian fluids were established for the filling penetration process unique to the GWAIM process.The continuity equation,motion equation and energy equation in the forming process of the GWAIM process were deduced according to the three conservation laws.Cross-WLF viscosity model was selected to describe the relationship between melt viscosity and temperature and shear rate in GWAIM process.The SST k-w turbulence model which can obtain more accurate results is adopted.Volume of fluid was used to track the forming process of GWAIM technology with free interface.The finite volume method was used to discretize the governing equations,and the discrete solution method(PISO algorithm)was used to solve the discretized governing equations.Choosing a suitable discrete format for different control equations.(3)Through fluid analysis software,and based on the two-dimensional axisymmetric model,the numerical simulation and mechanism analysis of the filling penetration process of GWAIM for straight pipe were carried out.It is found that the simulation results of the residual wall thickness of GWAIM process are in good agreement with the experimental results.In the process of penetration,the gas/water/melt interface presents a parabolic shape under the condition of constant velocity inlet,while the water presents a wave and jet shape.In the GWAIM process,a stable residual wall thickness is maintained along the direction of fluid penetration.By analyzing the temperature field of filling penetration process,it is found that the cooling effect of gas injection on the parts is small,but the cooling effect of water injection is very significant.By analyzing the velocity field,it is found that the axial velocity is relatively disordered when the gas is just injected,while the axial velocity is stratified obviously when the water is injected.By comparing the numerical simulation results of GWAIM process with those of GAIM and WAIM process,it is found that the order of residual wall thickness of each process part from large to small is GAIM> GWAIM> WAIM process;By comparing the flow field,it is found that the flow field change of GWAIM process is more complex.(4)The influence of process parameters on the residual wall thickness of straight pipe GWAIM process was studied by single factor method.It was found that the residual wall thickness tended to increase with the increase of gas injection delay time;With the increase of delay time,the residual wall thickness of the parts increases slightly and tends to be stable.With the increase of gas injection speed and mold temperature,the residual wall thickness becomes smaller.Increase the water injection speed and melt injection temperature,and the residual wall thickness of the part will decrease slightly.The primary and secondary order of the factors affecting the residual wall thickness was studied by orthogonal experiment.It was found that the primary and secondary order of the factors affecting the residual wall thickness was gas injection delay time> Gas injection speed> Injection delay time> Injection speed> Mold temperature> Melt injection temperature;The optimal combination of process parameters is gas injection delay time of 3s,water injection delay time of 3s,gas injection speed of 3m/s,water injection speed of 2m/s,mold temperature of 320 K,melt injection temperature of 503 K.(5)The single factor method was used to study the influence of bending Angle on the hollow rate.It was found that: when bending Angle was between 30° and 60°,the hollow rate increased with the increase of bending Angle;When the bending Angle was between 60° and120°,the hollow rate decreased with the increase of bending Angle.The influence of process parameters on the hollowness was studied by orthogonal experiment.It was found that the primary and secondary order of factors affecting the hollowness was gas injection delay time>Gas injection speed> Mold temperature ? delay time of water injection> Injection speed> Melt injection temperature;Increase the gas injection delay time and reduce the gas injection speed,the smaller the hollow rate of the part.The water injection delay time,water injection speed,mold temperature and melt injection temperature have little effect on the hollow rate of the part.The influence rule of bending Angle on the deviation rate was studied by single factor method.It was found that the mean deviation rate of the curved pipe increased with the increase of bending Angle.It can be seen that the larger the bending Angle,the more uneven the distribution of the wall thickness at the bending section of the part.The influence of process parameters on the deviation rate was studied by orthogonal experiment.It was found that the order of factors affecting the deviation rate was melt injection temperature ? gas injection delay time> Mold temperature> Gas injection speed> Water injection speed ? Water injection delay time;Reduce the gas injection delay time,increase the gas injection speed,mold temperature and melt injection temperature,the greater the deviation rate at the bending section of the part.The water injection delay time and water injection speed have little effect on the deviation rate at the bending section of the part. |
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