Johannes Wortberg

Influence of surface characteristics on fatigue behaviour of laser sintered plastics

Purpose – The purpose of this paper is to provide macromechanical insight into the fatigue behaviour of laser sintered parts and to understand the influence of the laser sintered surface structure on this behaviour.Design/methodology/approach – A background on the technological maturity of manufacturing processes and the demand for structural and aesthetic properties of laser sintered plastic products is given. As the contribution of surface structure on part quality was the focus, laser sintered specimens with and without surface finishes, as well as injection moulded specimens were used. The latter simply served as a comparison and was not intended to qualify injection moulding. The study comprises the determination of short‐term tensile properties, the load increase method for investigating fracture and deformation behaviours, and fatigue crack propagation analysis.Findings – According to the test results, the contribution of laser sintered surface structures to relevant mechanical properties can be ne...

Numerical and experimental investigation of a counter flow cooling system for the blown film extrusion

Conventional cooling systems for the blown film extrusion govern the cooling airflow only in one direction. In contrast, a counter flow system uses two individual jet flows. One jet flow provides the air in draw up direction like used in conventional systems. The other one guides the airflow towards the die. It is possible to cool the film over a longer film surface intensively. In addition, the interaction of the jet flow and the ambient air can be reduced which is responsible for an unsteady heat transfer. In this paper, such a cooling system is investigated in detail, numerically as well as experimentally. The experimental work is done using a modular system for a laboratory blown film line. For the simulation, a process model is used which is able to compute a realistic blown film behavior depending on the actual cooling condition. Therefore, a CFD-analysis computes the temperature of the film and flow phenomena of the jets. A contour calculation model is used to predict the bubble shape. It is based ...

Online Quality Prediction in Injection Molding Processes (ICM 2006)

Many mechatronic parts are produced using the injection molding technology. The product design of today, not only in the automotive sector, requires highly integrated and high performance plastic parts with at the same time low production costs. To achieve this aim modern technologies have to be introduced to track the running production. The benefit of the online quality prediction is mainly based on the reduction of the scrap rate. A deviation in parts dimensions for example is already noticeable while producing the lot and corrections can be instantly done to the machine parameter

Effects of laser sintering processing time and temperature on changes in polyamide 12 powder particle size, shape and distribution

In laser sintering (LS) un-molten Polyamide 12 (PA12) powder is usually re-used (recycled) in further processes. However, LS processing time at powder bed temperature leads to material property changes. As a consequence, un-molten PA12 powder that is re-used or recycled in further processes leads to process and part properties deviations. In this context, powder particle size, shape and distribution is assumed to affect surface roughness and porosity of LS parts. In order to investigate this process effect on changes in powder size, shape and distribution, PA12 powder was systematically aged in a vacuum oven at conditions close to the LS process. According to this procedure, polymeric powder was obtained with aging times up to 120 hours and analyzed by dynamic image analysis. At first, fresh powder was investigated as a reference. The effect of LS processing time and temperature, i.e. powder bed temperature of approx. 174°C was measured with respect to changes in size distribution and shape whereas partic...

Knowledge-based approach for an automatic rheological optimization of injection-molded parts

The motivation for the presented approach results from the absence of an integrated method of supporting the designing of injection-molded parts. Thereby, the focus lies on the rheological optimization, which is ensured by knowledge transfer from the production engineer to the designer, i.e., the mentioned aim is achieved by creating a knowledge base including the expert knowledge. This method is based on an integrated product simulation containing the interconnection of CAD and CAE-systems. The first step in the process is a filling simulation done by a standard injection molding process simulation software. The gate location is considered as fixed and optimal. Nevertheless, it is still possible that a uniform mold filling is not reached. To determine an uneven mold filling the results of the simulation are exported as scalar values to a post processing software tool. Thus, a knowledge based analysis of the results using user defined parameters based on flow length, pressure distribution, etc., is enabled. To enhance the filling, the original part design is modified by adding flow leaders or deflectors. Their positioning is calculated by the post processing software tool and this result is returned to the CAD-system. There the preliminary design is done by an analytical approach. By iterations of the mentioned method, the geometry of the flow leaders or deflectors and thus the mold filling are improved. The presented approach is illustrated exemplarily by an injection-molded part. As a result, the designer is supported methodically designing injection-molded parts by implementing and using expert knowledge. So, the number of iterations and the development time (costs) are reduced.The motivation for the presented approach results from the absence of an integrated method of supporting the designing of injection-molded parts. Thereby, the focus lies on the rheological optimization, which is ensured by knowledge transfer from the production engineer to the designer, i.e., the mentioned aim is achieved by creating a knowledge base including the expert knowledge. This method is based on an integrated product simulation containing the interconnection of CAD and CAE-systems. The first step in the process is a filling simulation done by a standard injection molding process simulation software. The gate location is considered as fixed and optimal. Nevertheless, it is still possible that a uniform mold filling is not reached. To determine an uneven mold filling the results of the simulation are exported as scalar values to a post processing software tool. Thus, a knowledge based analysis of the results using user defined parameters based on flow length, pressure distribution, etc., is enable...

Advantages and potentials of a blown film cooling system with a complete housing of the tube formation zone

In a prior work, a novel cooling approach for the blown film application was developed, called Multi-Jet. In contrast to a conventional cooling ring, this alternative cooling system guides the air vertically on the film surface, using several slit nozzles over the whole tube formation zone. In addition, the bubble expansion zone is surrounded by a housing. In this context, the cooling jets penetrate the boundary sublayer on the film surface that is developed by the fast flowing cooling air. The advantage of the housing can been seen in the disablement of the interaction of the cooling jet and the static ambient air. Besides the exhausting of the monomer loaded air, the housing allows to realize a heat recovery of the warmed cooling air. In this paper, an experimental and numerical investigation of the novel cooling system is shown. Here a comparison is done for several different process conditions with and without the use of the housing for the tube formation zone. By the means of a CFD-simulation, the co...

Characteristics of the mold filling simulation for a variothermal injection molding process with highly filled thermoplastics

Bipolar plates, repetition parts in a fuel cell, have to be preferably produced due to cost efficiency reasons by a mass production technique like injection molding. In order to meet thermal and electrical conductivity requirements as necessary product features, state of the art research focuses on highly filled thermoplastic compounds with carbon filler loadings of up to 65 percent by volume. Operating temperatures of the fuel cell (100-200 °C), corrosion stability in the chemical setting (hydrogen, water) and mechanical stability lead to the selection of the high performance thermoplastic polymer polyphenylene sulfide (PPS) as a matrix material. However, due to high filler loadings injection molding machines have to operate close to their stress limits. Only significant machine operating stress reduction allows the production of bipolar plates with injection molding machines for standard applications (injection pressures ≤ 2500 bar). Hence, the potential of operating stress reduction by means of a dynam...

Analysis of batch-related influences on injection molding processes viewed in the context of electro plating quality demands

The injection molding process is mandatorily influenced by the viscosity of the material. By varying the material batch the viscosity of the polymer changes. For the process and part quality the initial conditions of the material in addition to the processing parameters define the process and product quality.A high percentage of technical polymers processed in injection molding is refined in a follow-up production step, for example electro plating. Processing optimized for electro plating often requires avoiding high shear stresses by using low injection speed and pressure conditions. Therefore differences in the material charges’ viscosity occur especially in the quality related low shear rate area. These differences and quality related influences can be investigated by high detail rheological analysis and process simulation based on adapted material describing models.Differences in viscosity between batches can be detected by measurements with high-pressure-capillary-rheometers or oscillatory rheometers...

An experimental comparison between a novel and a conventional cooling system for the blown film process

The blown film extrusion is a significant manufacturing process of plastic films. Compared to other extrusion processes, the productivity is limited by the cooling of the extrudate. A conventional cooling system for the blown film application provides the cooling air tangentially, homogeneous over the whole circumference of the bubble, using a single or dual lip cooling ring. In prior works, major effects could be identified that are responsible for a bad heat transfer. Besides the formation of a boundary sublayer on the film surface due to the fast flowing cooling air, there is the interaction between the cooling jet and the ambient air. In order to intensify the cooling of a tubular film, a new cooling approach was developed, called Multi-Jet. This system guides the air vertically on the film surface, using several slit nozzles over the whole tube formation zone. Hence, the jets penetrate the sublayer. To avoid the interaction with the ambient air, the bubble expansion zone is surrounded by a housing. B...

Inline calculation tool for the determination of the changeover time for color and material changes in polymer processing

A change of extruded plastic products into a different material or color is connected to a wasteful process, regarding the loss of material, energy and system availability. Because of this, plastic processing companies want to reduce the required time between the basic and the target product. In the extrusion processes there are two possibilities to change from one material to another. The first option is the manual cleaning of the extruder and extrusion die, which leads to with a production stop and a high personnel effort. The second option is to perform a direct material or color change. The disadvantage of this method are the produced rejects during the change. Further, it is difficult to detect the end of the changing process, based on the product color, without expert knowledge.The LabVIEW inline calculation tool allows to detect the progress of the material change dynamically and to predict the needed time to reach the end of the changing process. Therefore an inline color measurement system ACS 70...