Abstract
Water-projectile-assisted injection molding (W-PAIM) is a novel molding process for plastic pipes with complicated shape. It utilizes high-pressure water as a power to push a solid projectile to penetrate through the melt to form a hollow space. In order to investigate the penetration behavior of the projectile during the water injection stage of W-PAIM process, numerical simulation of the water injection stage of a W-PAIM pipe with straight and curved segments was carried out. A turbulent flow for the driving water was considered in the motion equation, and the dynamic mesh technology was used to deal with the moving solid projectile. The simulation results, including RWT and the flow fields, were compared with those of water-assisted injection molding (WAIM) pipe with the same outer dimensions. It was found that the residual wall thickness (RWT) of the W-PAIM pipe is much thinner than that of the WAIM pipe. The projectile has a crucial influence on the RWT. The pressure fields of W-PAIM and WAIM are very similar in both straight and curved segments. The velocity field and strain rate field near the penetration front in W-PAIM are quite different from those in WAIM due to the drag flow caused by the projectile penetration.
Highlights
Fluid-projectile-assisted injection molding (FPAIM, PIT in German) process, which is one process variant of fluidassisted injection molding (FAIM, including water-assisted injection molding (WAIM) and gasassisted injection molding process (GAIM)), can overcome the limitations of FAIM such as thicker residual wall thickness (RWT), fluctuation of RWT, and material selection
It was found that the residual wall thickness (RWT) of the water-projectile-assisted injection molding (W-PAIM) pipe is much thinner than that of the WAIM pipe. e projectile has a crucial influence on the RWT. e pressure fields of W-PAIM and WAIM are very similar in both straight and curved segments. e velocity field and strain rate field near the penetration front in W-PAIM are quite different from those in WAIM due to the drag flow caused by the projectile penetration
A W-PAIM pipe with straight and curved segments was used as a test case, and numerical simulation of the water injection stage of it was conducted. is study includes the following: (1) the influence of projectile on the size of penetrating section and the distribution of RWT; (2) the characteristics of velocity field, pressure field, and strain rate field when the projectile is penetrating through the straight segment; and (3) the flow field when the projectile is penetrating through the curved segment. e research results are helpful to understand the penetration mechanism of the projectile in melt and provide a theoretical basis for the process control of W-PAIM and quality improvement of W-PAIM part
Summary
Fluid-projectile-assisted injection molding (FPAIM, PIT in German) process, which is one process variant of fluidassisted injection molding (FAIM, including WAIM and GAIM), can overcome the limitations of FAIM such as thicker residual wall thickness (RWT), fluctuation of RWT, and material selection. To simplify the model and facilitate the simulation, the simplification assumptions are as follows based on CFD method: the water and melt are incompressible; the melt flow meets no-slip boundary; the body forces and surface tension are ignored; the melt fills mold cavity uniformly at the initial state, and the melt injection process does not affect the projectile penetration; and the plastic projectile with a high melting point was regarded as a moving solid boundary without thermal properties. Governing equations include the continuity equation, motion equation, energy equation, constitutive equation, viscosity model, and volume fraction equation
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