Dependency of laser pulse length on the effectiveness of laser engraving 304 stainless steel with nanosecond pulses was investigated. Ytterbium fiber laser with pulse lengths from 4 to 200 ns was used at a constant average power of 20 W. Measured criteria for effective laser engraving were high material removal rate (MRR), good visual quality of the engraved surface, and low processing temperature. MRR was measured by weighing the samples prior and after the engraving process. Visual quality was evaluated from magnified images. Surface temperature of the samples was measured by two laser spot-welded K-type thermocouples near the laserprocessed area. It was noticed that MRR increases significantly with longer pulse lengths, while the quality decreases and processing temperature increases. Some peculiar process behavior was noticed. With short pulses (<20 ns), the process temperature steadily increased as the engraving process continued, whereas with longer pulses the process temperature started to decrease after initially jumping to a specific level. From visually analyzing the samples, it was noticed that the melted and resolidified bottom structure had cracks and pores on the surface when 50 ns or longer pulse lengths were used.
Different monitoring methods for the laser additive manufacturing process were studied in this study. Possibilities and downfalls of three different methods were compared to each other to define their applicability in future on-line and adaptive monitoring use in LAM processes. The material used on all the LAM process tests was EOS StainlessSteel PH1 in fine powder form. In this study, e.g. parameters like scanning speed, layer thickness and hatch space were tested. Based on the results of this study, the pyrometer seems to be more easily adaptable to continuous monitoring than the spectrometer or systems based on active illumination imaging system. It seems that the pyrometer is a promising method for quality control. The ability to control quality through on-line measurements can be further utilized in future e.g. for on-line quality control and dynamic process control, i.e. the ability to change and correct parameters on the fly.
Time pressure is not usually seen as an advantage in front end innovation (subsequently referred to as “FEI”), but rather it is believed that ideas should be left to develop freely without a tight schedule. Instead of strictly formalized operations, creating ideas generally necessitates a certain level of freedom. The starting point for this research was to challenge this general view by imposing severe time pressure in FEI. The FEI process was reviewed from recognizing problems/creating ideas up until the selection of the best concept for further development. The research was executed as a qualitative in-depth investigation of a case. In the case, FEI took place over a three-week period, and the target for the FEI was to generate concepts of digital jewelry with business potential. The time pressure was seen as appropriate – with certain conditions – in FEI. The results also present the advantages and disadvantages of time pressure, combining it to the stress theory.
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