Up to date the evaporation process in laser beam welding of alloys with volatile elements is not completely understood. This paper discusses the phenomena occurring at the welding process of brass with 37m% zinc. Since copper has a solidification temperature of 1,087°C and zinc vaporizes at a temperature of 907°C, a strong evaporation takes place and an elongation of the keyhole can be observed. Depending upon welding velocity, the ratio of keyhole length to width is between one and six. Furthermore it is observed that a defect free weld seam is formed. Since the melt pool does not leak also for high ratios of keyhole length to width, the conventional keyhole model with a dynamic flow around the laser beam has to be adapted to a model in which the melt flow at the side of the capillary is stabilized also outside of the interaction zone of the laser beam with the melt due to strong evaporation at the flank of the keyhole.
The application of piezoelectric transducers to structural body parts of machines or vehicles enables the combination of passive mechanical components with sensor and actuator functions in one single structure. This approach has high potential for smart lightweight constructions. To obtain the highest yield, the piezoelectric transducers need to be integrated into the flux of forces (load path) of load bearing structures. Application in a downstream process reduces yield and process efficiency during manufacturing and operation, due to the necessity of a subsequent process step of sensor/actuator application. The die casting process offers the possibility for integration of piezoelectric transducers into metal structures. Particularly favorable are aluminum castings due to their high quality and feasibility for high unit production at low cost. Such molded aluminum parts with integrated piezoelectric transducers enable functions like active vibration damping, structural health monitoring or energy harvesting resulting in significant possibilities of weight reduction, which is an increasingly important driving force of automotive and aerospace industry due to increasingly stringent environmental protection laws. In the scope of those developments, this paper focuses on the entire process chain enabling the generation of lightweight metal structures with sensor and actuator function, starting from the manufacturing of piezoelectric modules over electrical and mechanical bonding to the integration of such modules into aluminum (Al) matrices by die casting. To achieve this challenging goal, piezoceramic sensors/actuator modules, so-called LTCC/PZT modules (LPM) were developed, since ceramic based piezoelectric modules are more likely to withstand the thermal stress of about 700 °C introduced by the casting process. The modules are made of low temperature cofired ceramic (LTCC) tapes with an embedded lead zirconate titanate (PZT) plate and are manufactured in multilayer technique. For joining conducting copper (Cu) wires with the electrode structure of the LPM, a novel laser drop on demand wire bonding method (LDB) is applied, which is based on the melting of a spherical CuSn12 braze preform with a liquidus temperature Tliquid of 989.9 °C providing sufficient thermal stability for a subsequent casting process
This paper applies a combined precision stage to fabricate micro-structures by two-photon polymerization (TPP). The combined stage consists of PZT and stepper-motor stages to achieve precision positioning in long displacements. First, we derive the models of the stages by identification experiments. Second, we apply robust loop-shaping techniques to improve the positioning performance of the stages. Third, we integrate the stages and develop a multi-loop control structure to provide long-stroke and high precision. In addition, we propose coordinate transformation and anti-locking functions for further improvement of the system performance. Last, we apply the combined stage to a TPP system for fabricating micro-structures, and define performance indexes based on image processing and optical qualities. The obtained performance criteria can be used to adjust controller design to improve precision manufacturing.
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