Maximilian Schöngart

Injection molding of products with functional surfaces by micro-structured, PVD coated injection molds

Molding of micro structures by injection molding leads to special requirements for the molds e.g. regarding wear resistance and low release forces of the molded components. At the same time it is not allowed to affect the replication precision. Physical vapor deposition (PVD) is one of the promising technologies for applying coatings with adapted properties like high hardness, low roughness, low Young’s modulus and less adhesion to the melt of polymers. Physical vapor deposition technology allows the deposition of thin films on micro structures. Therefore, the influence of these PVD layers on the contour accuracy of the replicated micro structures has to be investigated. For this purpose injection mold inserts were laser structured with micro structures of different sizes and afterwards coated with two different coatings, which were deposited by a magnetron sputter ion plating PVD technology. After deposition, the coatings were analyzed by techniques regarding hardness, Young’s modulus and morphology. The geometries of the micro structures were analyzed by scanning electron microscopy before and after coating. Afterwards, the coated mold inserts were used for injection molding experiments. During the injection molding process, a conventional and a variothermal temperature control of the molds were used. The molded parts were analyzed regarding roughness, structure height and structure width by means of laser microscopy.

Hybrid Production Systems

While virtual product development allows great freedom in terms of design, actual development processes are rather restricted. Those boundary conditions are at best hardly possible to exert influence on. Therefore, future research has to focus both on the realisation of the concept of one-piece-flow while simultaneously increasing flexibility and productivity and on the technological advancement. Hence, hybridisation of manufacturing processes is a promising approach, which often allows tapping potentials in all the aforementioned dimensions.

A concept for non-invasive temperature measurement during injection moulding processes

Current models of the injection moulding process insufficiently consider the thermal interactions between melt, solidified material and the mould. A detailed description requires a deep understanding of the underlying processes and a precise observation of the temperature. Because todays measurement concepts do not allow a non-invasive analysis it is necessary to find new measurement techniques for temperature measurements during the manufacturing process. In this work we present the idea of a set up for a tomographic ultrasound measurement of the temperature field inside a plastics melt. The goal is to identify a concept that can be installed on a specialized mould for the injection moulding process. The challenges are discussed and the design of a prototype is shown. Special attention is given to the spatial arrangement of the sensors. Besides the design of a measurement set up a reconstruction strategy for the ultrasound signals is required. We present an approach in which an image processing algorithm...

Manufacturing of micro-structured parts for mass production purposes

Micro-structured and thus functionalized surfaces offer high potentials for new approaches in processing techniques and product design. However, for mass production purposes quite a few challenges regarding the manufacturing of these surfaces have to be overcome. For the fast and economic production of large quantities of structured polymer films the extrusion embossing process is suitable. For embossing microstructures there are special requirements on temperature control because of the double function of the embossing roll. On the one hand the roll is used as an embossing roll with a high surface temperature to improve the embossing accuracy. On the other hand it is used as a cooling roll with a low surface temperature. Only by using variothermal heating systems these contradictory demands on the temperature control can be met. In order to achieve a high quality of the produced micro-structured films an integrative analysis and optimization of the entire process chain is required. This includes the manufacturing of suitable embossing rolls, the development of coating systems and the adaption of the extrusion process. This paper deals with the entire process chain for functionalized, super hydrophobic plastic parts with contact angles up to 165°. Therefore, conelike surface structures, mimicking the structure of lotus leaves, are replicated. Functionalized parts are produced in the injection molding as well as in the extrusion process; however, this paper focuses on the process chain of the extrusion process.

Tensile impact testing on polymer materials considering the force-oscillation phenomenon

Thermoplastic materials are extensively used as a light weight replacement for metal alloys, especially in automotive applications. Furthermore polymer materials can be used to enhance the safety of passengers and pedestrians in a car accident. The state of the art design process for plastics parts is based on Computer Aided Engineering (CAE). Using Finite Element Analysis (FEA), highly dynamic systems can be simulated with a very high accuracy. Considering crash applications, the influence of strain rate on the mechanical behaviour is of paramount importance. To determine the effect of strain rate on the mechanical behaviour, tensile impact tests are conducted at different haul-off velocities. With an increase of the haul-off velocity, the force-oscillation phenomenon becomes significant. The force-oscillation phenomenon is an artifact caused by the dynamic load application in highly dynamic tests. It can be monitored as a superimposition of measured force data with oscillations which increase in amplitude to higher impact velocities.This study looks at the phenomenon of force oscillation in tensile impact testing on viscoelastic materials and its dependency on longitudinal stress wave propagation. Aside a detailed analysis of its origin, a new approach is presented to measure a nearly oscillation free force signal in tensile impact testing on polymer materials, basically independent of the considered haul-off velocity. For this purpose a modification of a standard dumbbell specimen was designed.Thermoplastic materials are extensively used as a light weight replacement for metal alloys, especially in automotive applications. Furthermore polymer materials can be used to enhance the safety of passengers and pedestrians in a car accident. The state of the art design process for plastics parts is based on Computer Aided Engineering (CAE). Using Finite Element Analysis (FEA), highly dynamic systems can be simulated with a very high accuracy. Considering crash applications, the influence of strain rate on the mechanical behaviour is of paramount importance. To determine the effect of strain rate on the mechanical behaviour, tensile impact tests are conducted at different haul-off velocities. With an increase of the haul-off velocity, the force-oscillation phenomenon becomes significant. The force-oscillation phenomenon is an artifact caused by the dynamic load application in highly dynamic tests. It can be monitored as a superimposition of measured force data with oscillations which increase in amplitu...

Laser transmission welding of foamed thermoplastic injection moulded parts

The laser transmission welding is one possibility to join parts, which have been produced in the special injection moulding process structural foam-moulding. Besides reduced weight such parts with reduced density show a reduced cycle time as well as improved size accuracy. Up to now there are no empirical values regarding the laser transmission welding of foamed injection moulded parts. For the use of the laser transmission welding process in a larger scale it is important to acquire knowledge in how far the structure of the foam influences the welding process, the bond strength and the structure of the joint. These knowledges allow an application-specific adjustment of the injection moulding process and the joining process. As part of a current research project the dependence of the foam structure to the injection moulding parameters have been determined using a breathing cavity. That way it is possible to produce parts, which have a defined thickness of the surface layer as well as specified average cel...

Welding of bio-based plastics for applications in the field of injection moulding

Due to intensive research in the field of material development considerable progress in terms of processing and performance characteristics could be achieved during the last years. Therefore, bio-based plastics are increasingly being used for the production of durable injection moulded components. Several applications can be found in the automotive sector, in the field of consumer electronics or the sports industry. For an economic production, joining technology often plays a key role to realise modular designed components. Detachable connections, which are frequently used in plastics processing (e. g. snap hooks or screw connections), often reach their limits with respect to reliability and tightness of the joint. In order to meet the increasing requirements on the joint, plastics joining processes can allow suitable component assembly. Bio-based plastics may differ from conventional plastics regarding their processing properties, such as the melting and solidification behaviour. For these reasons, inves...

Spatially resolved temperature measurement in injection moulding using ultrasound tomography

Current simulation of the injection moulding process insufficiently consider the thermal interactions between melt, solidified material and mould. To improve the prediction accuracy in terms of shrinkage and warpage these interactions cannot be neglected and requires a precise observation of the temperature field within the ongoing process. Nowadays temperature measurements at the transition of the polymer melt to the mould or near the surface of the polymer melt are applicable and do not allow either a non-invasive analysis or a determination of the temperature field. In the approach of ultrasound tomography, presented here, an ultrasound beam is emitted into the melt and the time-of-flight (TOF) is detected by a set of transducers, which are radially arranged around the melt. Subsequent the measurement is repeated from different directions. Using algebraic reconstruction techniques, a distribution of the ultrasound velocity can be calculated based on the TOF-dataset. With additional information about th...

Examination of the weld line strength of stagnating and flowing weld lines in unreinforced thermoplastics

Weld lines lead to a significant reduction of the mechanical properties of injection moulded parts. To provide a reliable method for the mechanical design of parts with weld lines, a calculation concept must be developed to predict the weld line strength. For this purpose, a semi-empirical model to describe a reduction factor depending on relevant process influences will be derived from the results of a variety of experimental investigations on stagnating and flowing weld lines. A simulation chain is developed to employ the model in an integrative simulation chain for injection moulded parts.

Determination of the strain rate dependent thermal softening behavior of thermoplastic materials for crash simulations

Thermoplastic materials are increasingly used as a light weight replacement for metal, especially in automotive applications. Typical examples are frontends and bumpers. The loads on these structures are very often impulsive, for example in a crash situation. A high rate of loading causes a high strain rate in the material which has a major impact on the mechanical behavior of thermoplastic materials. The stiffness as well as the rigidity of polymers increases to higher strain rates. The increase of the mechanical properties is superimposed at higher rates of loading by another effect which works reducing on stiffness and rigidity, the increase of temperature caused by plastic deformation. The mechanical behavior of thermoplastic materials is influenced by temperature opposing to strain rate. The stiffness and rigidity are decreased to higher values of temperature. The effect of thermal softening on thermoplastic materials is investigated at IKV. For this purpose high-speed tensile tests are performed on ...