Christian Windeck

Simulative design and process optimization of the two-stage stretch-blow molding process

The total production costs of PET bottles are significantly affected by the costs of raw material. Approximately 70 % of the total costs are spent for the raw material. Therefore, stretch-blow molding industry intends to reduce the total production costs by an optimized material efficiency. However, there is often a trade-off between an optimized material efficiency and required product properties. Due to a multitude of complex boundary conditions, the design process of new stretch-blow molded products is still a challenging task and is often based on empirical knowledge. Application of current CAE-tools supports the design process by reducing development time and costs. This paper describes an approach to determine optimized preform geometry and corresponding process parameters iteratively. The wall thickness distribution and the local stretch ratios of the blown bottle are calculated in a three-dimensional process simulation. Thereby, the wall thickness distribution is correlated with an objective funct...

Design Criteria in Numerical Design of Profile Extrusion Dies

Abstract. The rather unintuitive and non-linear behavior of plastics melts is a well-known obstacle in the design and manufacturing cycle of profile extrusion dies. This is reflected, for example, in the so-called running-in experiments, in which the already manufactured die is modified up to 15 times until the final product, shaped by the die, matches the quality requirements. Besides a homogeneous outflow velocity and thus homogeneous material distribution, an appropriate die swell is a second design objective which complicates the reworking of the manufactured die. We are conducting work to shorten the manual running-in process by the means of numerical shape optimization, making this process significantly less costly and more automatic. From a numerical point of view, the extrusion process is not as challenging as high-speed flows, since it can be described by steady Stokes equations without major loss of accuracy. The drawback, however, is the need for ac- curate modeling of the plastics behavior, which generally calls for shear-thinning or even viscoelastic models, as well as for 3D computations, leading to large computational grids. The intention of this paper is to investigate the application of specific geometry features in extrusion dies and their influence on objective functions in an optimization framework. However, representative objective functions concerning die swell and the incorporation of known geometry features, as used by experienced die designers, into the optimization framework still remain a challenge. Hence, the topics discussed are the influence of the mentioned geometry features on existing objective functions as well as an outlook on an algorithmic implementation into the optimization process with regard to representative objective functions.

Design methodology for modular tools

Serving individual customer needs at reasonable prices can be a profitable target market in high-wage countries. The dilemma between scale and scope-oriented production is one major research topic within the Cluster of Excellence “Integrative Production Technology for High-Wage Countries” at the RWTH Aachen University. One main objective of this project is to bridge the existing gap between individual manufacturing and mass production. Modularization is a widely accepted approach in tool-based manufacturing processes. In this paper, we propose a flexible design methodology for modular tools and dies. The methodology will assist the design engineer in setting up a series of modularized tools in a conceptually closed manner. The described methodology covers modularization in a broad sense, i.e. it includes hardware modularization as well as modularization of the construction process. The methodology consists of three phases: initiation, analysis and design phase.

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...

Extrusion foaming of thermoplastic cellulose acetate from renewable resources using a two-component physical blowing agent system

Thermoplastic cellulose acetate (CA) is a bio-based polymer with optical, mechanical and thermal properties comparable to those of polystyrene (PS). The substitution of the predominant petrol-based PS in applications like foamed food trays can lead to a more sustainable economic practice. However, CA is also suitable for more durable applications as the biodegradability rate can be controlled by adjusting the degree of substitutions. The extrusion foaming of CA still has to overcome certain challenges. CA is highly hydrophilic and can suffer from hydrolytic degradation if not dried properly. Therefore, the influence of residual moisture on the melt viscosity is rather high. Beyond, the surface quality of foam CA sheets is below those of PS due to the particular foaming behaviour. This paper presents results of a recent study on extrusion foamed CA, using a two-component physical blowing agent system compromising HFO 1234ze as blowing agent and organic solvents as co-propellant. Samples with different co-propellants are processed on a laboratory single screw extruder at IKV. Morphology and surface topography are investigated with respect to the blowing agent composition and the die pressure. In addition, relationships between foam density, foam morphology and the propellants are analysed. The choice of the co-propellant has a significant influence on melt-strength, foaming behaviour and the possible blow-up ratio of the sheet. Furthermore, a positive influence of the co-propellant on the surface quality can be observed. In addition, the focus is laid on the effect of external contact cooling of the foamed sheets after the die exit.

Improving the automated optimization of profile extrusion dies by applying appropriate optimization areas and strategies

The rheological design of profile extrusion dies is one of the most challenging tasks in die design. As no analytical solution is available, the quality and the development time for a new design highly depend on the empirical knowledge of the die manufacturer. Usually, prior to start production several time-consuming, iterative running-in trials need to be performed to check the profile accuracy and the die geometry is reworked. An alternative are numerical flow simulations. These simulations enable to calculate the melt flow through a die so that the quality of the flow distribution can be analyzed. The objective of a current research project is to improve the automated optimization of profile extrusion dies. Special emphasis is put on choosing a convenient starting geometry and parameterization, which enable for possible deformations. In this work, three commonly used design features are examined with regard to their influence on the optimization results. Based on the results, a strategy is derived to s...

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.

Multi-technology products

Development of technical solutions that lead to widening the use of multi-technological products as well as in assessing ecological and economic potentials of multi-technological products have not yet been studied intensively. The activities conducted in the context of this research area focus on these aspects. The aforementioned aspects have been examined, evaluated and quantified on the basis of three example products resulting from the first funding period. The research activities conducted on the example components deliver the basis for the layout of different integrated multi-technology production systems. Technical solutions that enable coupling of different process steps with each other as well as the integration of different functionalities and different materials in final multi-technology products have been proposed. The complex interdependencies of the products themselves and their associated production processes have been researched and evaluated intensively. Finally, a profitability assessment of the proposed solutions was conducted and future research topics identified.

Microstructuring polycarbonate films by variothermal extrusion embossing

The variothermal extrusion embossing process enables a high quality replication of microstructures in plastics films. In this advancement on regular flat film extrusion a polymer melt is shaped by a flat film die and cast on an embossing roll. The surface of the embossing roll has the negative form of the desired microstructure. A counter pressure roll is used to apply the line force needed for embossing, thereby transferring the microstructure into the polymer melt. The melt stays in contact to the embossing roll allowing for a rapid cooling of the film and a solidification of the microstructures inside the molds on the embossing roll’s surface. At the haul-off point the cooled down film is removed from the roll. The governing process parameters for successful embossing are the melt temperature, the viscosity, the surface temperature of the embossing roll and its rotation speed. By tempering the embossing roll to a low base temperature while using an electrical inductor or a high-power infra-red laser as...