Przemysław Poszwa

Influence of Processing Parameters on Residual Stress in Injection Molded Parts

Residual stresses are the source of shrinkage and warpage of the parts manufactured with injection molding technology and strongly influences its final dimensions. In complicated parts residual stresses are very difficult to predict without numerical tools, along with the warpage, what leads to problems with manufacturing parts that meet the expected tolerances. Residual stresses have also strong influence on mechanical performance of the part, where its high value can results with self-cracking during ejection from the mold. In this work numerical simulations injection molding process were performed to analyze the presence of residual stresses in manufactured plastic parts by this technology. Numerical simulations were used to find the relations between the processing parameters and the distribution and magnitude of residual stresses. Occurrence of residual stresses were analyzed with new 3D residual stress model implemented in Autodesk Moldflow® software. Qualitative strain-optics observations were performed to verify the differences between different sets of processing parameters. From investigated parameters the strongest influence on residual stresses was observed with packing time, while the weakest influence was observed with injection time.

Numerical Study of Rapid Cooling of Injection Molds

Rapid heat cycle molding (RHCM) technology has become an alternative for classic injection molding and it is consist of the rapid control of the temperature of mold or forming surfaces. Despite widely used in the plastics industry, there are some problems with rapid, balanced cooling. The primary problem during the cooling stage is to ensure the balanced and uniform heat removal from cooled material and suitable dynamic of the entire process, as to avoid molding’s defects. This article presents the simulation research of various geometry of cooling channels, which can be used in RHCM technology to improve the efficiency of a cooling process. Authors proposed the use of finned channels, which can guarantee the most effective heat transfer. The analysis and comparison of proposed channels show the advantage over conventional channels commonly used in injection molds. To more clearly show the correlation between the geometry of cooling channels, the flow state of working fluid and the heat transfer, the dependencies of the Nusselt and the Reynolds number are evaluated and presented. The investigation results lead to possibility of reducing the cooling phase and thus the production time of entire injection cycle.

Influence of Fill Imbalance on Pressure Drop in Injection Molding

During injection molding process melted polymer is introduced into mold cavity due to the pressure delivered from injection unit. Mold design principles suggests that filling of the cavity should be balanced. It means that the furthest regions of cavity (measured from injection point) should be filled at the same time to avoid problems with differential shrinkage and injection pressure drop. Fill imbalance can lead to the significant increase of pressure drop and needed clamp force, that can be compensated with more powereful injection molding machines. In this paper the relation between fill imbalance and injection pressure needed for cavity filling were investigated with Autodesk Moldflow Insight software. In this research several different shapes with thickness change of analyzed parts were performed to measure the significance of imbalance on injection pressure drop. It was found that it is possible to find a gate location even for geometrically imbalanced part, where significant pressure drop reduction can be obtained. Additionally, It was found that lowering V/P switchover point can provide significant reduction of needed injection pressure even if gate location must be placed in unfavorable location

Wpływ modeli materiałowych na jakość wyników analiz wytrzymałościowych wyrobów z tworzyw sztucznych

Nowadays, more and more elements originally made of metal are replaced with plastic parts. This is due to the low density of polymer materials, their high relative strength, as well as the ease of forming (complicated elements can be produced in one operation). The disadvantages of plastics are low rigidity and very non-linear material properties. To increase rigidity, a glass fiber filler is used above all. Its addition to the polymer allows to increase the rigidity from four to six times (depending on the type and amount of fiber added, in the case of carbon fiber, it is possible to achieve up to 10-fold improvement in rigidity), due to which the manufactured elements have less deformability with a slight increase in basis weight [1, 2]. The disadvantage of using glass fibers is to reduce the maximum elongation of details and their impact strength. In addition, the introduction of glass fibers into the polymer matrix results in the anisotropy of the material depending on the orientation of the fiber, which in turn depends on the method of filling the cavity forming the mold. In addition, it complicates the mathematical description of the phenomenon of deformation under the influence of applied loads.