Stephan F. Jahn

Polymer Microsieves Manufactured by Inkjet Technology

Liquid sessile drops can be used as sacrificial templates for the creation of pores in polymeric microsieves. Using inkjet printing, we deposit sessile drops of a water-based liquid onto a hydrophobic solid support and cover them with a thin liquid layer of a polymer solution in such a way that the sessile drops penetrate through the top interface of this layer. The liquid layer is solidified, and the sessile drops imprint their shape into it, acting as templates for the creation of pores. Finally, the polymer layer is separated from the substrate, and a freely suspended polymer microsieve is obtained.

Joining by forming of piezoceramic macro-fiber arrays within micro-structured surfaces of aluminum sheets

Functional integration of smart materials in sheet metal enables lightweight composite parts which are enhanced by new functionalities. Locally integrated piezoceramic/metal composites consist of a prefabricated array of ten parallel piezoceramic macro-fibers with dimensions of 0.277 mm by 0.232 mm by 10 mm which are joined in micro-formed cavities within the surface of an aluminum sheet metal. By the use of joining by forming, the interference–fit, preload and form–fit of macro-fiber arrays are achieved in a single process step. The paper describes investigations of the joining by forming process in formal planned experiments using the design of experiments method. The influence of the dimensions and preparation of the joining partners, the maximum forming force and the velocity of the forming stamp are varied. The interference–fit and preload depend on the maximum forming force. In contrast, the quality of the form–fit is primarily related to the geometric dimensions and the forming force. Fiber fractures and incipient cracks are the major failure mechanisms during joining by forming of the macro-fibers. The number of cracks is significantly reduced by the use of lower die velocities, lower maximum joining forces and the introduction of additional geometric elements in the microstructure of the metal surface. Concluding, constraints with regard to the design of parts and the process are derived from the experiments.

Evaluation of Tribological Properties of AlMg4.5Mn0.7 in Massive Microforming Using the Barrel Compression Test

Tribology is one of the major issues in forming processes. It is influenced by many factors such as workpiece and tool material, lubrication, process parameters, geometric scale etc. Especially in microforming processes, friction plays an important role due to an increased surface to volume ratio and the domination of open over closed lubricant pockets. A simple and sensitive method to quantify the friction factor under realistic conditions of massive forming is the barrel compression test. The friction factor is calculated out of the friction-dependent barreling of cylinder samples while being compressed between two parallel tool surfaces.In these investigations, the barrel compression test was applied to determine the friction factor between cylindrically shaped samples made of the aluminium alloy AlMg4.5Mn0.7 (EN AW 5083) and polished surfaces made of the tool steel 1.3343. The specimen diameter was varied between 0,5 mm and 10 mm. The focus of investigations was the size-dependence of the friction factor under the variation of the parameters such as forming degree, lubrication conditions, and die velocity. In addition to the calculation of the friction factor, surfaces were evaluated by microscopy and roughness measurements.

Investigation of Tribological Properties of AlMg4,5Mn0,7 in a Warm Forming Process Using the Barrel Compression Test

Within the German Collaborative Research Center 39 PT-PIESA the forming of micro cavities into aluminum sheets is one challenging task. During this forming process high forces and stresses occur which lead to a high tool wear. Hence, the actually applied cold forming process should be replaced by a warm forming process. This paper shows the tribological investigations for the warm forming process. Within the experiments the barrel compression test is used to determine the friction conditions by varying the size of the cylindrically shaped samples of AlMg4,5Mn0,7, the forming degree and the lubrication condition (dry, graphite, forming oil). The flat punches were made from hardened steel 1.3343. The friction factor was calculated, and surface roughness was evaluated by 3D-laser microscopy. The experiments show that the friction factor increases, especially at forming degrees below 1 and for small specimen size, compared to cold forming processes. In addition to that, an influence of the lubrication condition onto the surface roughness was observed. For experiments conducted with graphite, the surface roughness is significantly higher than for samples, which were formed dryly or with forming oil.