Nafi Yesildag

Opportunities and challenges of profile extrusion dies produced by additive manufacturing processes

The design and manufacture of profile extrusion dies is characterised by costly running-in trials. Significant cost and time savings can be achieved by replacing the experimental running-in trials by virtual ones. A simulative optimisation, however, often leads to complex, free-formed flow channels. A feasible manufacture of such dies is only possible with additive manufacturing processes such as the Selective Laser Melting (SLM). Against this background, the manufacture of profile extrusion dies by SLM is investigated. A major challenge is to ensure a specific surface quality of the extruded plastics profiles. The roughness of SLM surfaces does not meet the high demands that are placed on the surface quality of extrusion dies. Therefore, in case of the SLM die a concept for the surface finishing of the flow channel is required, which can be applied to arbitrarily shaped geometries. For this purpose, plastics profiles are extruded both with a conventionally and an additively manufactured die. In case of the SLM die only the die land of the flow channel was reworked by polishing. The comparison of PP profile surfaces shows that the SLM die with polished die land leads to the same surface quality of the extruded profile as the conventional die (Ra ≈ l μm). Another important task in the design of profile dies by SLM is the optimisation of the die topology. The efficiency of the SLM process largely depends on the volume of the part being produced. To ensure the highest possible efficiency, it is necessary to adapt the die geometry to its mechanical loads and minimise its mass. For this purpose, the internal pressure in the die was numerically calculated and used for a first optimisation of the die topology. The optimisation, however, leads to a free-formed outer die wall so that the die cannot be tempered with heating tapes anymore. This problem is solved by using the high potential of SLM for functional integration and integrating contour adapted tempering channels into the extrusion die.The design and manufacture of profile extrusion dies is characterised by costly running-in trials. Significant cost and time savings can be achieved by replacing the experimental running-in trials by virtual ones. A simulative optimisation, however, often leads to complex, free-formed flow channels. A feasible manufacture of such dies is only possible with additive manufacturing processes such as the Selective Laser Melting (SLM). Against this background, the manufacture of profile extrusion dies by SLM is investigated. A major challenge is to ensure a specific surface quality of the extruded plastics profiles. The roughness of SLM surfaces does not meet the high demands that are placed on the surface quality of extrusion dies. Therefore, in case of the SLM die a concept for the surface finishing of the flow channel is required, which can be applied to arbitrarily shaped geometries. For this purpose, plastics profiles are extruded both with a conventionally and an additively manufactured die. In case of t...

Numerical investigation of the temperature influence on the melt predistribution in a spiral mandrel die with different polyolefins

Abstract The main goal in the design of spiral mandrel dies for blown film extrusion is to achieve a homogeneous velocity distribution of the plastics melt at the die outlet. However, thermal inhomogeneities in the die can lead to an uneven flow distribution despite a rheologically optimized design of the die. The thermal inhomogeneities are especially dominant in the predistributor of spiral mandrel dies. Against this background, the temperature influence on the melt distribution in the predistributor is investigated for different polyolefins with the help of flow simulations in Polyflow (Ansys). The simulation models the whole predistributor and takes both the heat transfer in the predistributor and the shear heating in the melt into account. Afterwards, simulations are conducted in which the thermal design measures for the homogenization of the flow in the die are applied. With the combination of heating cartridges, brass inserts, and isolating gaps in the die, a significant homogenization of the predistribution can be achieved. Finally, the simulation results are validated in practical tests, whereby a good agreement between simulation and measurement can be observed.

Properties of polyamide 6-graphene-composites produced and processed on industrial scale

The use of graphene as a filler in thermoplastics has already been investigated extensively. The mechanical properties as well as electrical and thermal conductivity of thermoplastics can be improved due to graphene. However, these studies were carried out in experimental scale, which allows a good dispersion of graphene because of a long residence time during melt mixing and because of the use of almost ideal graphene, which has a high specific surface and low number of layers. In this study the scientific findings are transferred into industrial practice. For that purpose, a co-rotating intermeshing twin screw extruder with limited residence time and limited shear energy input is used to produce graphene based polyamide 6 composites and short carbon fibre reinforced graphene based polyamide 6 composites. These composites are further processed by injection molding to produce specimens in order to determine the mechanical properties. In addition to the scale-up to industrial production, two types of graphene platelets are used, which are commercially available. This investigation reveals that the addition of 1 wt.-% commercially available graphene platelets to polyamide 6 improves Younǵs modulus and tensile strength. Compared to pure polyamide 6 an improvement up to 20 % with regard to Younǵs modulus and up to 15 % with regard to tensile strength can be achieved. The combination of short carbon fibre with graphene platelets in polyamide 6 enables an increase of Younǵs modulus, which is higher than the additive effect.The use of graphene as a filler in thermoplastics has already been investigated extensively. The mechanical properties as well as electrical and thermal conductivity of thermoplastics can be improved due to graphene. However, these studies were carried out in experimental scale, which allows a good dispersion of graphene because of a long residence time during melt mixing and because of the use of almost ideal graphene, which has a high specific surface and low number of layers. In this study the scientific findings are transferred into industrial practice. For that purpose, a co-rotating intermeshing twin screw extruder with limited residence time and limited shear energy input is used to produce graphene based polyamide 6 composites and short carbon fibre reinforced graphene based polyamide 6 composites. These composites are further processed by injection molding to produce specimens in order to determine the mechanical properties. In addition to the scale-up to industrial production, two types of graph...

Mold-Based Production Systems

Mold-based production systems are vastly common in mass production processes, due to the high investment costs of production equipment. In order to address the challenge of a strong tendency towards individualized customer demands, companies in high-wage countries are forced to react towards these changes. This chapter describes recent advances in the field of individualized production for mold-based production systems regarding plastics profile extrusion and high-pressure die casting. A holistic methodology for an integrated product and mold design is presented based on the principles of simultaneous engineering. In addition, recent advances in the field of numerical optimization are shown. The advances in numerical optimization will be carried out based on the processes mentioned above. The monitoring and simulation of the viscoelastic swell will be shown for plastics profile extrusion. For the field of high-pressure die casting the strategy to optimize the entire process will be outlined and current experimental results shown. For both application cases the potential benefit of additive manufacturing technologies—such as Selective Laser Melting (SLM)—will be evaluated and validated inasmuch as possible.