Simulation and Experiment Research on the Proportional Pressure Control of Water-assisted Injection Molding

Water-assisted injection molding（WAIM）,a newly developed fluid-assisted injection molding technology has drawn more and more attentions for the energy saving,short cooling circle time and high quality of products.Existing research for the process of WAIM has shown that the pressure control of the injecting water is mostly important for the WAIM.However,the proportional pressure control for the WAIM system is quite complex due to the existence of nonlinearities in the water hydraulic system.In order to achieve better pressure control performance of the injecting water to meet the requirements of the WAIM,the proportional pressure control of the WAIM system is investigated both numerically and experimentally.A newly designed water hydraulic system for WAIM is first modeled in AMEsim environment,the load characteristics and the nonlinearities of water hydraulic system are both considered,then the main factors affecting the injecting pressure and load flow rate are extensively studied.Meanwhile,an open-loop model-based compensation control strategy is employed to regulate the water injection pressure and a feedback proportional integrator controller is further adopted to achieve better control performance.In order to verify the AMEsim simulation results WAIM experiment for particular Acrylonitrile Butadiene Styrene（ABS） parts is implemented and the measured experimental data including injecting pressure and flow rate results are compared with the simulation.The good coincidence between experiment and simulation shows that the AMEsim model is accurate,and the tracking performance of the load pressure indicates that the proposed control strategy is effective for the proportional pressure control of the nonlinear WAIM system.The proposed proportional pressure control strategy and the conclusions drawn from simulation and experiment contribute to the application of water hydraulic proportional control and WAIM technology.

Thickening and Rheological Properties of Crystalline Polyester Used in Low Pressure Sheet Molding Compounds

Low pressure sheet molding compound （LPMC,1.0-3.0 MPa,95-103 ℃） is a new kind of thermosetting material with crystalline polyester as a physical thickenner.LPMC is different from conventional SMC using an earth oxide thickening agent （e.g.MgO） as chemical thickenner,it relies on the physical thickening of crystalline polyester.Crystalline polyester resin is the key material to mold LPMC parts.Currently there was no report about the thickening mechanism of crystalline polyester in LPMC.In this article,crystalline polyester resins,whose melting points were between 45 ℃ and 89 ℃,were synthesized by a two-step esterification.The melt points of crystalline polyesters are controlled by regulating the mol ratio of the two glycols and the two acids.And by means of varying the content of crystalline polyester resin,the thickening effect on resin paste is investigated.In addition,the thickening mechanism of crystalline polyester in LPMC was investigated by FTIR and DSC analysis.The effects of the diameters and viscosity of crystalline polyester on the rheological property and fiber distribution of LPMC sheets were studied,too.Results show that the thickening effect is excellent when the weight content of crystalline polyester resin is 3%.And there exists three kinds of functions acting in the process of thickening：swelling,hydrogen bonds and induction crystallization.During the preparing process of resin paste in LPMC,the temperature of resin paste must be kept at 90 ℃.In addition,crystalline polyester make LPMC have a perfect fluid property.When the viscosity of LPMC sheet is beyond 1 kPa s,the fiber orientation is not obvious.But when the viscosity of LPMC sheet is about 500 Pa s,the fiber shows a certain degree of orientation.Moreover the study of physical and chemical thickening mechanism of crystalline polyester and the rheological discipline of LPMC sheets in the hot mould will provide the researchers and enterprises with theory guidance.

Effects of Forming Pressure on the Porosity of Polyimide Porous Materials

Based on a series of experiments, the theory of relationship between normal pressure and pores＇ characters fit for polymer was set up for the first time. On the study of relation between normal pressure and porosity, experience model of polyimide porous materials was proposed which is similar to the traditional expe- rience model of the metal porous material. While being pressed, polyimide was found soon to come into elasto- plastic deformation progress in this paper, so the theory model of metal porous material based on Hooker＇s law was not fit for the polymer any more. A new elasto-plastic deformation and exhausting model is proposed which shows better agreement with polymer material＇s pressing process.

Influence of Initial Value of Transient Time Step on Numerical Simulation of Blow Molding Balloon

The correlation between the initial time value of transient iterative parameters and the blowing pressure in the numerical simulation process of blowing balloon is investigated by POLYFLOW. The results show that: 1) As the blow molding pressure increases, the boundary value of the iterative time step decreases rapidly at first and then slowly. At the end of the first step of iterative calculation for each boundary value, the balloon parison is in the mold core cavity. 2) If the initial time value of transient iterative parameters is smaller than the boundary value of the iterative time step, the balloon parison is still in the mold core cavity at the end of the first iteration. However, if the iterative calculation continues, the calculation process may be interrupted when the time step is smaller than the initial time value of the transient iterative parameters, which makes the blow molding simulation of balloon unable to continue. 3) It is suggested that the initial time value of transient iterative parameters is one order of magnitude smaller than the boundary value of the iterative time step to complete smoothly the simulation of blow molding balloon.

The Banded Spherulites of iPP Induced by Pressure Vibration Injection Molding

Isotactic polypropylene（i PP） samples obtained by pressure vibration injection molding（PVIM） and conventional injection molding（CIM） were studied by polarized-light microscopy（PLM）, respectively. It was found that the alternating bright and dark banded spherulites were generated in the transitional region of PVIM parts. It is the first time that the banded spherulites of isotactic polypropylene were observed in polymer processing. What＇s more, the banded spherulites were proved to be constituted of α-form crystal by hot stage polarized-light microscopy（HT-PLM） and wide angle X-ray diffraction（WAXD）. Morphology of the banded spherulites was also studied by scaning electronical microscopy（SEM）.

Active Air Venting of Mold Cavity to Improve Performance of Injection Molded Direct Joining

A surface micro-/nano-structured metal plate can be joined with an injection molded plastic piece in a mold,which has been named injection molded direct joining(IMDJ).The injected plastic melt infiltrates the micro-/nano-structure,e.g.,a porous structure with micro/nano pores,on the metal plate while flowing in the mold cavity where the metal plate is inserted.After solidification of the plastic,the metal and plastic materials are directly joined via the micro-/nano-structured metal surface.Since air is trapped by the plastic melt,it is easily imagined that the air in the mold cavity prevents the melt plastic from contacting the metal surface and infiltrating the micro-/nano-structure,which could result in poorer joining performance.To avoid the prevention of the air for the better joining performance,the present study proposes a system actively venting the mold cavity during injection molding.To apply the active venting to IMDJ,venting and sealing systems were newly developed.In addition,a system measuring air pressure of the mold cavity was developed.The proposed system was evaluated by a measurement of joining strengths of IMDJ specimens that were produced under various conditions.From the results,it is concluded that the active venting does not necessarily have a positive effect in any cases:the effect depends on the type of surface micro-/nano-structure.