Papers by Author: A.J. Pontes

Abstract: In this study the influence of nanoclay and glass fibre in the shrinkage and ejection forces in polypropylene matrix in tubular parts moulded by injection moulding were analysed. An instrumented mould was used to measure the part surface temperature and ejection forces in tubular parts. The materials used were a polypropylene homopolymer Domolen 1100L nanoclay for polyolefin nanocomposites P-802 Nanomax in percentages of 2%, 6% and 10% and a polypropylene homopolymer with content of 10% of glass fibre Domolen P1-013-V10-N and 30% of glass fibre Domolen P1-102-V30-N with 2% of nanoclay. The shrinkage and ejection forces were analysed. The results show that the incorporation of nanoclays decreases the shrinkage and ejection forces whereas glass fibre decreases the shrinkage and increase ejection forces due to the increase of the elastic modulus. The nanoclays decrease the ejection force when compared with glass fibre and pure PP. The effects of nanoclays are less pronounced than those of glass fibre. The effect of the mould temperatures on the ejection forces in the mouldings produced with the mentioned materials were also analysed. The ejection force decreases with the increase of the temperature of the mould.

Abstract: Warpage and poor dimensional stability of rotomoulded products are two of the main obstacles to the use of this technique in the production of engineering parts. The knowledge of the effect of the processing conditions on the shrinkage of rotomoulded parts will allow overcoming some of the restrictions of this process. In the present work the influence of the processing conditions on the development of shrinkage and warpage of rotomoulded parts was studied. The moulding of the parts was performed using a rotational moulding machine build at the University of Minho. The shrinkage and the warpage of the moulded parts were assessed using 3D MMC (3D measuring Machine Control) equipment, and understanding the microstructural development.

Abstract: Microinjection moulding is one of the key technologies for the mass production of plastics microcomponents. Recently, significant effort has been made to test the limits of applicability of existent numerical codes for simulating the polymer flow at the microscale. However, the modelling precision in what concerns polymer flow in microimpressions depends on factors which may not be properly accounted for in the process simulation. In this study, a micropart with variable thickness was designed, and the moulding block fabricated and instrumented. Short shots and complete filling of the cavity were carried out and the flow front progress was subsequently evaluated. These data were also assessed numerically by 3D-finite element modelling. A flow simulation considering the polymer as incompressible was carried out to investigate how the mesh size and density affected the prediction of the flow field in the microimpression, using the same processing conditions of the experimental study. The reduction of the mesh size as well as the increase of the mesh density are consistent with better representativeness of the experimental flow front progress in the microimpression. Moreover, the weld line prediction also tends to be improved. This study suggests that the mesh adaption and domain discretization is important in numerical studies of the polymer flow at the microscale.

Abstract: During the injection moulding process, the material is subjected to successive transformations, being submitted to a thermo-mechanical environment that determines the final dimensions of the part. This environment is characterized by several parameters which are related to material properties, the mould design, equipment and process variables. As a result, deviations of the dimensions of the moulded parts from the dimensions of the cavity cannot be avoided. If differences on shrinkage occur, caused for example by anisotropies of the material or non-uniform cooling, distortions will happen. In order to predict this two effects on the injection cycles is require one strategy to monitoring and control the process variables. The aim is to achieve highest quality control of all manufacture parts. This paper presents the effect of different holding pressures and mould temperatures on shrinkage and warpage in two different materials, one amorphous (PC) and another semi crystalline (PP). An instrumented mould was manufactured. During the injection moulding process sensors signals were continuously monitored by a Data Acquisition System. The experimental results were compared with predictions made by commercial software.

Abstract: In this study, the as-moulded shrinkage and pressure data are obtained experimentally and compared with numerical simulations. The mouldings were produced in polypropylene (PP). The effect of pressure on viscosity in the predicted pressure evolution was analyzed and also its influence on the shrinkage. The results show that the rise of holding pressure determines the reduction of the shrinkage. Also, it was observed that the pressure predictions are qualitatively in good agreement with the experimental data. However noticeable quantitative discrepancies can be observed when the effect of pressure on viscosity is not considered. If the effect of pressure on the melt viscosity is considered the deviation between predicted and the experimental pressure evolution is substantially reduced.