| Author | Prapol Chivapornthip |
| Note | A dissertation submitted in partial fulfillment of the requirements for the
degree of Doctor of Philosophy in
Industrial and Manufacturing Engineering |
| Publisher | Asian Institute of Technology |
| Abstract | Bulk viscosity has been neglected from the flow analysis of injection molding based on the assumption that the melt flow in the process was divergence-free. However, several experiments and simulations have shown that the melt flow during the packing-holding stage was compressible and non-divergence free. In this research, we aimed to investigate the effect of the bulk viscosity on the melt during the packing-holding stage via the simulation of 2D flow in a cylindrical cavity. A new hybrid 1D/2D finite volume-finite difference method was developed to specifically solve the packing-holding stage models with the bulk viscosity. An isotactic polypropylene (iPP) was used as the material for the packing-holding stage simulation. The bulk viscosity of iPP was measured from the uniaxial compression experiment with a capillary rheometer. From the experimental results, the bulk viscosity of melt might be associated with the ability of molecules to replace free interstitial spaces. This molecular replaceability depended on the process conditions, for instance, the compression deformation, the compression rate, and the melt temperature. The bulk viscosity increased with the increase in the compression deformation, decreased gradually and exponentially with the increase in the melt temperature and the compression rate respectively. From the simulation results, the bulk viscosity influenced the cavity pressure more highly than the temperature distributions. The dilatational viscous heat dissipation due to the bulk viscosity was very small during the packing-holding stage. The bulk viscosity reduced the cavity pressure during the packing stage, increased the back pressure and induced the pressure gradient reversal effect when the holding pressure decreased during the holding stage. Moreover, the bulk viscosity retarded the speed of the melt flow without the preferred directions. With the effects of the bulk viscosity, the new location and distribution of the maximum compressive stress was found at the corner of the cavity’s end wall. This was contrary to conventional models without the bulk viscosity from the commercial software in which the maximum compressive uniformly distributed over the cavity cross-sectional area at the end wall. The negligence of the bulk viscosity might result in an underestimation of the pressure gradient reversal effect and misplacement of the maximum compressive stress location which was later on associated with the development of shrinkage or warpage during the cooling stage. |
| Year | 2017 |
| Type | Dissertation |
| School | School of Engineering and Technology (SET) |
| Department | Department of Industrial Systems Engineering (DISE) |
| Academic Program/FoS | Microelectronics (ME) |
| Chairperson(s) | Bohez, Erik L. J.; |
| Examination Committee(s) | Mongkol Ekpanyapong ;Keun, Song Weon;Makhanov, Stanislav S.;Tanner, Roger Ian ; |
| Scholarship Donor(s) | AIT Fellowship; |
| Degree | Thesis (Ph.D.) -- Asian Institute of Technology, 2017 |