Mechanical Properties of Laser Beam Melting Components Depending on Various Process Errors
Additive Manufacturing processes are constantly gaining more influence. The layer-wise creation of solid components by joining formless materials allows tool-free generation of parts with very complex geometries. Laser Beam Melting is one possible Additive Manufacturing process which allows the production of metal components with very good mechanical properties suitable for industrial applications. These are for example located in the field of medical technologies or aerospace. Despite this potential a breakthrough of the technology has not occurred yet. One of the main reasons for this issue is the lack of process stability and quality management. Due to the principle of this process, mechanical properties of the components are strongly depending on the process parameters being used for production. As a consequence incorrect parameters or process errors will influence part properties. For that reason possible process errors were identified and documented using high resolution imaging. In a next step tensile test specimens with pre-defined process errors were produced. The influence of these defects on mechanical properties were examined by determining the tensile strength and the elongation at break. The results from mechanical testing are validated with microscopy studies on error samples and tensile specimens. Finally this paper will give a summary of the impact of process errors on mechanical part quality. As an outlook the suitability of high resolution imaging for error detection is discussed. Based on these results a future contribution to quality management is aspired.
Compound quality assessment in laser beam melting processes using layer images
Laser beam melting (LBM) is an additive manufacturing (AM) technology that allows the layer-based production of geometrically complex parts from metal powder. Non-destructive evaluation of part quality is a pre-requisite for widespread application of this promising technology and an ongoing research topic. In-process measurement of part layer compound quality will be beneficial during optimization of process parameters for best part quality. We inspect the part surface in high resolution layer images acquired after laser exposure. Based on a fast Fourier transform (FFT) we decompose surface images into laser scan lines (oriented component) and underlying powder structure (not oriented component). By computing the signal energy ratio we obtain a measure for the prominence of laser scan lines which is correlated with the compound quality. For 25 parts with varied laser power and scan velocity the signal energy ratio is compared to the computed energy input. A linear model achieves a root-mean-square error (RMSE) of 9.76Jmm−3. Additionally we automatically classify part regions as good/not good and compare our results to a manual selection based on light microscopy.
Engineering bio-inks for 3D bioprinting cell mechanical microenvironment
Three-dimensional (3D) bioprinting has become a promising approach to construct­ing functional biomimetic tissues for tissue engineering and regenerative medicine. In 3D bioprinting, bio-inks are essential for the construction of cell microenviron­ment, thus affecting the biomimetic design and regenerative efficiency. Mechanical properties are one of the essential aspects of microenvironment, which can be char­acterized by matrix stiffness, viscoelasticity, topography, and dynamic mechanical stimulation. With the recent advances in functional biomaterials, various engineered bio-inks have realized the possibility of engineering cell mechanical microenviron­ment in vivo. In this review, we summarize the critical mechanical cues of cell micro­environments, review the engineered bio-inks while focusing on the selection princi­ples for constructing cell mechanical microenvironments, and discuss the challenges facing this field and the possible solutions for them.