Prof. Dr. Dietmar Drummer

Compared to many optical grades of glass, plastics have a high dispersion. This means that the refractive index of the material decreases more strongly with increasing wavelength. As a result, different wavelengths of light (light colors), which are focused by an optical lens, have different focal positions. This leads to image errors and blurred images, which is why imaging optics are usually composed of several combined lenses. In illumination optics, the dispersion is shown by a color veil on the edge of the light cone.By combining two lenses made of materials with different dispersions to form an achromatic lens, this chromatic aberration, can be reduced, resulting in a significant increase in imaging performance. To improve image quality, plastic lens systems are usually assembled from several lenses. This requires the production of several components, exact positioning and further assembly steps.The project therefore focuses on injecting a second component onto a preform with low warpage and shrinkage to produce an achromatic lens from different transparent plastics. Possible plastics for the combination are polycarbonate (PC) and poly(methyl methacrylate) (PMMA). In addition to reducing further processing and assembly steps, two-component injection molding also increases transmission by reducing reflections at the interfaces.From the application of an achromatic lens, the general derivation of a production strategy for low-shrinkage and low-warpage two-component injection compression molding with large contact surfaces is to be carried out in the research project. In addition to optics, this knowledge is relevant for numerous other applications. Nevertheless, the prerequisites for this two-component injection moulding of optical components are particularly challenging. The second component must be injected onto the preform with very little shrinkage, the injection process of the second component should not deform the first component surface and sufficient adhesion of the two plastics over a large surface must be ensured. These points are to be achieved by an adapted injection compression molding process. An adapted compression of the melt in the process by means of embossing should reduce subsequent shrinkage of the injected component as far as possible. The influences of the process parameters on adhesion, shrinkage, the shape of the interface and the refractive index as well as the component properties are systematically investigated.

The aim of theproject is the systematic investigation of the process-geometry-interaction ofthin-walled components for the production of locally adapted properties as wellas the modeling of this effect in finite element simulations and structuraloptimization. In experimental tests, the main influencing factors areidentified and mapped in relation to the building position in the process. Newexposure technologies and strategies are used to manipulate the melting pooland homogenize component properties. The findings are incorporated into a wallthickness dependent material model for structural optimization, which isinvestigated in the project. The participating industrial partners willvalidate the results over the course of the project. The experimental findingsand the wall thickness dependent material model will be used to develop amethodology for the product development of thin-walled structures. In thefuture, the product development process can be accelerated, and the economicefficiency increased. Based on these findings, new application areas for theselective laser beam melting of plastics can be opened up in the future.

The use of pin-like structures for the generation of form-fit joints in welding processes represents an innovative approach to combine adhesion incompatible polymers and thus broadens the possible polymer combination spectrum. Without the use of additives or extensive surface pre-treatments, locally adapted part properties can be achieved by joining incompatible semi-crystalline thermoplastics. In addition, the use of pin-like structures allows the combination of semi-crystalline and amorphous thermoplastics, to enable for example a permanent functionalization by an optically transparent element. Besides joining adhesion incompatible polymers, the benefits of the process can be applied on bonds with low weld strength, e.g. fibre-reinforced thermoplastics. In this case, the pin-like structures could contribute to a modification of the fibre orientation, perpendicular to the joining plane, and thus to higher bond strengths.The aim of the proposed project is the fundamental investigation of interdependencies of the joining mechanism by means of pin-like structures in welding processes. For this purpose, vibration welding as well as ultrasonic welding technology are applied, which are both based on energy input by means of friction. Despite the high potential, interdependencies between material, process and resulting bond properties are currently unknown for this novel joining technique. The comprehensive experimental investigations within the research project, in combination with a model-based analysis, enable the development of general requirements for the material combinations as well as for the process handling. Therefore, the effects of decisive process parameters, of the structure geometry as well as of the occurring thermomechanical interactions on the resulting joint are fundamentally analysed.In comparison to the vibration welding technology, the use of the ultrasonic welding technology enables the production of smaller pin structures whereby the load capacity of the joint can be increased and the process can also be made accessible for smaller parts. Furthermore, ultrasonic welding continues to differentiate itself from the vibration welding principle since different oscillation directions are used for the energy input and the structure generation. This allows an improved identification of process-specific interactions during structuring.With the help of the knowledge gained within this project, a comprehensive understanding of the joining by means of pin-like structures as well as general structuring and joining strategies can be established. These allow the transfer of the methodology to further materials and joining processes.

The goal of process-oriented tolerance management is to define permissible deviations of components on the basis of knowledge about the achievable accuracies in manufacturing processes in such a way that the product function is guaranteed during the product lifetime and cost-effective production is made possible. In practice, this consideration is often limited to dimensional, shape and position deviations. However, material-structural deviations also have a strong influence on the component behaviour. Therefore, in the first phase of the project, the influence of the manufacturing process on the shape and structure deviations and their effect on the running-in behaviour of plastic/steel gear pairs was determined. In principle, this made it possible to derive recommendations for their tolerance and design with regard to optimised running-in behaviour, taking into account material-structural aspects. The aim of the second phase of the research group is to extend this knowledge with regard to a comprehensive consideration of the operating behaviour. In the subproject the influence of material-structural and dimensional deviations on the operating behaviour shall be investigated comprehensively. The subproject therefore contributes substantially to the achievement of the objectives in the research group by providing the fundamental and general relationships between component tolerances and structures and the resulting component behaviour, e.g. with regard to load-bearing capacity and wear-bearing capacity, which are necessary for process-oriented tolerance. In addition, an efficient procedure for determining these interrelationships will be developed, which will make it possible to characterize the operating behaviour on the basis of model and material investigations. In cooperation with the other subprojects, a comprehensive and efficient methodology will be developed to enable the design of components and processes as well as the definition of tolerances in line with operational requirements. The objectives of the second phase for this subproject can be summarized as follows: • The influences of geometric and morphological component properties on the deformation behaviour and the functionality in operation under varied load conditions are identified and understood with regard to tolerance management.• The effects of geometric deviations, in particular different surface topographies of extruded pinions, on the operating behaviour of plastic-steel pairs have been determined and can be described comprehensively.• An extended methodology for the efficient determination and assessment of the operating behaviour, based on the correlation of material, model and component investigations, in particular by means of in situ measurement technology, has been developed and validated.

The aim of this project is to conduct fundamental scientific research into joining without auxiliary element using metallic pin structures produced by forming technology, which are pressed into the joining partner or caulked after insertion into a perforated joining partner, and the joint properties that can be achieved with this. This includes the development of a fundamental understanding of the acting mechanisms with a focus on feasibility in phase 1, the optimisation of the pin structure with regard to geometry and arrangement as well as the joining process for the targeted adjustment of joining properties in phase 2 and the transferability of the technology to an extended range of applications in phase 3. The aim in phase 1 is therefore to develop a fundamental understanding of the extrusion of defined metallic pin geometries from the sheet plane using local material accumulation in order to be able to determine local changes in the material properties, such as strength. Simultaneously, different process control strategies for joining metal and FRP as well as different metals will be fundamentally researched and process windows will be derived.In the case of FRP, various process routes will be investigated with a focus on fibre-friendly injection of the pin structures or hole forming for caulking of the pin structures without delamination of the FRP. Ultrasound, vibration, infrared radiation or combinations of these methods are used to melt the matrix with the goal of identifying suitable process routes and generating an understanding of the mechanisms at work.  Based on the findings of the pin manufacturing and the results regarding the joining processes, a fundamental understanding of the process will be developed, which will allow the further development of the pin geometry and the definition of suitable simple, regular pin arrangements and dimensions in the next step. In order to meet the different requirements of the pin manufacturing process and the joining method, the adaptability of the tool and joining technology is essential. Accordingly, the adaptation on the tool side and the specific process control during pin production will be investigated in order to demonstrate the possible variations. In addition, the adaptability of the joining operation will be achieved by adapting the process control, especially in the case of metal-FRP joints, in order to react to different conditions, such as the fibre layer and layer structure of the FRP. Finally, the direction-dependent joint properties and the application behaviour of the multi-material joints joined with the developed pin geometries will be characterised and evaluated depending on the pin dimensioning and arrangement in order to identify the decisive influencing factors on the joint properties.

The comprehension of geometric part deviationsand their manufacturing and assembly related sources as well as the investigationof their effects on the function and quality of technical products builds theframework for the planned research group “process-oriented tolerance managementbased on virtual computer-aided engineering tools”. The aim of this researchgroup is the provision of holistic methods and efficient tools for thecomprehensive management of geometric deviations along the product originationprocess, which are to be validated in a model factory. In doing so, aparticular focus is set on the development of a procedure for the fruitfulcooperation of all departments involved in geometric variations management,from product development, to manufacturing, to assembly and to metrology, whichwill enable companies to quickly specify functional tolerances, which aremanufacturable and measurable, and consequently to save costs and to reduce thetime to market.

In this regard, the vision of the researchgroup is to enable the close collaboration of product development,manufacturing, assembly and metrology in computer-aided tolerancing, i. e.the joint formulation of functional tolerances, which are manufacturable andmeasurable. By enabling this close collaboration, all manufacturing andassembly related sources of later problems regarding the product function andquality can be considered already during early phases of virtual product andprocess development. As a consequence, tolerances can be specified efficientlyand optimized inspection plans as well as robust manufacturing and operatingwindows can be identified, which allows the development of robust products tobe manufactured and measured at low costs.  

Since geometric part deviations are inevitableand affect the function and quality of technical products, their managementalong the product origination process is essential for the development offunctioning products, which conform to the quality and usage requirements ofcustomers and are successful on international markets. As a consequence,tolerance management is a fundamental task in product development and reachesvarious fields of industry, from consumer to industrial goods. Due to steadilyincreasing requirements on quality and efficiency, it strongly gains importancenot only with large, but also small and medium-sized enterprises. In thiscontext, the industrial application of the scientific findings of the researchgroup will contribute to the success of the German economy.  

The goal ofsub-project A6 is to generate graded part properties by local insertion offillers and polymer blend powders by vibration nozzles in selective laser beammelting. In addition, methods for orientating fibers along z-direction togenerate a higher strength will be implemented. In doing so, new degrees offreedom in setting part properties will be enabled. Thereby, the effects oflocally inserted as well as oriented particles on process control will be thesubject of research.

Unter den Begriffen additive, respektive generative Fertigungsverfahren, werden Technologienverstanden die Körper schichtweise aufbauen. Sie ermöglichen die Herstellung komplexerGeometrien aus Kunststoff und Metall ohne Form und Werkzeug, und machen somit einekonstruktionsorientierte Fertigung von individuellen Produkten möglich. Wesentliche Vorteile sinddie Aufhebung vieler konstruktiver Restriktionen (z.B. Realisierung von Hinterschnitten) und dieflexible Fertigung von individuellen Bauteilen mit nahezu beliebig komplexen Geometrien in einemBauprozess. Additive Verfahren ermöglichen daher bisher technisch nicht zugängliche Konstruktions-und Gestaltungsweisen, wie z.B. die Komprimierung von montierten Baugruppen auf ein einzelnesBauteil. Alle diese Aspekte lassen erwarten, dass sich die additive Fertigung zukünftig zueiner in der Industrie wesentlichen neuen Fertigungstechnologie heranbilden kann. Trotz des rasantentechnologischen Fortschritts der letzten Jahre ist es bisher nicht gelungen, diese Verfahrenzu serientauglichen Produktionstechnologien weiter zu entwickeln. Gründe hierfür sind vor allemeine bislang eingegrenzte Materialverfügbarkeit, die mangelnde Prozessstabilität und -simulationsowie das Fehlen von prozessspezifischen Konstruktionsweisen. Ein zusätzliches Defizit der additivenVerfahren besteht in der noch nicht ausreichenden Präzision bezüglich Geometrieabbildungund Detailtreue. Neue Verfahrensansätze zielen auf die Herstellung gradierter und hybrider Komponentenab. Die durchgängige Nutzung im Sinne des Computer Integrated Manufacturing (CIM)erfordert darüber hinaus die Erarbeitung werkstoff- und prozessspezifischer Simulations- undKonstruktionstools.Der Erforschung dieser Herausforderungen will sich die Gruppe der Wissenschaftler dieses Sonderforschungsbereichsstellen. Fokussiert auf strahl- und pulverbasierte Technologien der AdditivenFertigung ist es Ziel der Initiative ein vertieftes Prozessverständnis zu erarbeiten und eine breitereWerkstoffpalette im Bereich der Kunststoffe und der Metalle mit optimierten Eigenschaften fürProzess und Anwendung nutzbar zu machen, um auf dieser Basis neue Multi-Materialbauteile(gradierte und hybride Körper) zu generieren. Es soll ermöglicht werden, multifunktionale Verbundwerkstoffeund Werkstoffverbunde mit neuen werkstofflichen Eigenschaften und neuen konstruktivenLösungen auf Basis reproduzierbarer, robuster, messbarer und in der Simulation abgebildeterProzesse verarbeiten zu können. Aus den speziellen Gegebenheiten bei der additivenFertigung lassen sich zahlreiche übergreifende wissenschaftliche Fragestellungen ableiten, beispielsweisezur Herstellung und Funktionalisierung von Pulvern (Gasverdüsung vonPolymerschmelzen, allgemeine Erhöhung der Schüttdichte), zum Schmelz- und Erstarrungsverhaltenim Pulverbett (epitaktisches Anwachsen neuer Schichten, zeitabhängiges Kristallisationsverhaltenvon Polymeren), zum Fließen flacher Schmelzepools (Verspritzen von Schmelze bei Metallen,„Balling“, allgemein zu raue Oberfläche), zur Entstehung von Eigenspannungen und Verzug.Dabei erwarten wir gerade von der parallelen Betrachtung der beiden Werkstoffgruppen (Kunststoffeund Metalle) sowie der breiten Anwendung von Simulationsverfahren zahlreiche neue Einblicke.

Within sub-project B3,the basic influences of the process control of selective laser beam melting ofpolymers on the resulting part properties are analyzed. Therefore, thesub-processes powder coating, laser exposure and consolidation as well as thetemperature control are scientifically investigated. Innovative processstrategies, which fulfill the material specific requirements ofsemi-crystalline thermoplastics, are studied to produce parts with reproducibleand defined properties.

The object of this sub-project is the scientificdetection, the quantitative determination and the development of a fundamentalunderstanding of essential material-related process variables, which explicitlydescribe the solidification behavior and the energy input during the lasermelting process of polymers. The manufacturing of components with low internalstresses and high mechanical strength requires optimized process parameterswhich are derived from the process-oriented characterization of the powder materialswith regard to their thermo-mechanical and optical properties.