| 1. |
- Aronsson, Gunnar, 1939-
(author)
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Five Geometric Principles for Injection Molding
- 2003
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In: International polymer processing. - Munich, Germany : Carl Hanser Verlag GmbH. - 0930-777X .- 2195-8602. ; 18:1, s. 91-94
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Journal article (peer-reviewed)abstract
- A condensed presentation of some results of a geometric character, concerning the injection molding of plastics, is given here. The author has derived these results from mathematical arguments and some simplifying assumptions, besides the usual Hele-Shaw flow conditions.The presentation here is intended for readers with an interest in polymer processing, rather than mathematics, so that the mathematical derivations are omitted in some cases, and sketchy in other cases. Instead we try to explain the results using figures, intuitive arguments and a few inevitable formulas. Since the experimental verification of the results is still very incomplete, we prefer to present them as proposed principles. Comments and suggestions for improvement are very welcome.
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| 2. |
- Lundström, Staffan, et al.
(author)
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Modelling of residual stresses and warpage in sandwich injection moulding
- 2003
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In: International polymer processing. - : Walter de Gruyter GmbH. - 0930-777X .- 2195-8602. ; 18:1, s. 95-106
-
Journal article (peer-reviewed)abstract
- Sandwich injection moulding offers the possibility of combining materials with different properties and, for instance, hide a recycled constituent within a virgin ditto. This attractive potential puts great demands on the manufacturing and therefore also on the process modelling. In particular the effect on the final stress state and the deformation of the part due to the heterogeneity of the material must be clarified. This topic is addressed in this study. To start with it is confirmed that expressions for the temperature field can be much simplified without major loss of accuracy in the solution. This enables us to take an analytical approach to the modelling and the resulting equations can be solved on a spread-sheet or with a simple code. It is also shown that the derived models compare well to experiments made with a two-layered structure, indicating that the models presented can be used to estimate changes of processing conditions or material properties for sandwich structures.
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| 3. |
- Pisciotti, F, et al.
(author)
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Evaluation of a model describing the advancing flow front in injection moulding
- 2002
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In: International polymer processing. - 0930-777X .- 2195-8602. ; 17:2, s. 133-145
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Journal article (peer-reviewed)abstract
- The simulation of the advancing flow front during mould filling in the injection moulding cycle is important as a way of anticipating manufacturing defects, particularly different types of welds, air traps, cold spots and hot spots. The purpose of the present work was to evaluate a model (the distance model) simulating the advancing flow front and predicting potential issues related to the progression of the flow front such as welds and air traps. The distance model is based on a mathematical theory of Hele-Shaw flow for strongly shear-thinning fluids, i.e. fluids with a power-law index, n, equal to 0,3 or preferably less. Two grades of general-purpose polystyrene were selected according to their abilities to shear thin (weakly or moderately strong) at the selected processing temperature and in the typical shear rate range of the injection moulding process. The two grades were injection moulded into twelve mould configurations derived from two similar single-gated moulds. The flow length from the gate to the weld was measured in the mouldings obtained at three distinct rates of filling (conventional, slower and faster) and compared to the flow lengths obtained by the distance model. Good agreement was found between the predicted flow lengths and the experimental flow lengths at the conventional and faster filling conditions. Larger deviations between simulation and experiment were found at the slower filling rate, particularly for the weakly shear-thinning polystyrene grade. Some comparisons were also made with the predictions obtained using the commercial simulation code Moldflow. A comparison between the advancing front predictions of the distance model and experimental short shots of a commercial polypropylene grade in a lure-box type of mould geometry showed that the distance model, despite its simplicity, could probably be used to detect welds and air traps in more complex and practice-related mouldings.
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| 4. |
- Vahlund, C. F., et al.
(author)
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Squeeze flow rheology of glass mat thermoplastic (GMT) in large tools and at high closing velocities
- 2002
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In: International polymer processing. - : Walter de Gruyter GmbH. - 0930-777X .- 2195-8602. ; 17:2, s. 158-165
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Journal article (peer-reviewed)abstract
- Rheological measurements on materials with fibre-like inhomogeneities will be significantly affected by sample size when the in-plane dimensions of the sample are comparable with the length of the fibres. In this paper, a 310 t hydraulic press has been modified for squeeze flow rheology studies so that large tools that will minimize the influence of sample size can be used in combination with high closing velocities. Isothermal squeeze flow rheology experiments of GMT have been performed for closing velocities up to 30 mm/s corresponding to maximum closing forces of 1000 kN. Successful power law fits of closing velocity versus closing force have been performed for the velocity interval. Four different analytical models have been fitted to the experimental data and the accuracy in these has been investigated. The force prediction of the biaxial extension model is acceptable for the major part of mould closure, but better fits during the last part of mould closure were obtained using an additive model incorporating both shear and extensional flow.
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