Thomas Niendorf, Florian Brenne, Mirko Schaper, Andre Riemer, Stefan Leuders, Wilfried Reimche, Dieter Schwarze and Hans J. Maier
As additive manufacturing techniques, such as selective laser melting, allow for straightforward production of parts on basis of simple computer-aided design files only…
Abstract
Purpose
As additive manufacturing techniques, such as selective laser melting, allow for straightforward production of parts on basis of simple computer-aided design files only, unauthorized replication can be facilitated. Thus, identification and tracking of individual parts are increasingly vital in light of globalized competition. This paper aims to overcome the susceptibility of additive manufacturing techniques for product piracy by establishing a method for introducing and reading out product identification markers not visible by naked-eye inspection.
Design/methodology/approach
Lasers of different nominal power were used for altering the solidification mechanisms during processing in distinct areas of the samples. The resulting local microstructural characteristics and mechanical properties, respectively, were determined by scanning electron microscopy and hardness measurements. The applicability of an advanced eddy current technique for reading out local differences in electro-magnetic properties was examined.
Findings
The findings show that distinct microstructural features are obtained in dependence of the locally applied laser power. These features manifest themselves not only in terms of grain morphology, texture and hardness but also induce changes in the local electro-magnetic properties. The inscribed pattern can be non-destructively visualized by using an advanced eddy current technique.
Originality/value
Conventional copy protection basically consists in supplementary labelling or surface modification. In the present study, a new method is proposed for additively manufactured parts, overcoming the drawbacks of the former methods through process-induced microstructure manipulation. Slight alterations in the electro-magnetic material properties can be detected by advanced eddy current method allowing for identification of arbitrary and inimitable component information in additively manufactured parts.
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Agnieszka Chmielewska, Bartlomiej Adam Wysocki, Elżbieta Gadalińska, Eric MacDonald, Bogusława Adamczyk-Cieślak, David Dean and Wojciech Świeszkowski
The purpose of this paper is to investigate the effect of remelting each layer on the homogeneity of nickel-titanium (NiTi) parts fabricated from elemental nickel and titanium…
Abstract
Purpose
The purpose of this paper is to investigate the effect of remelting each layer on the homogeneity of nickel-titanium (NiTi) parts fabricated from elemental nickel and titanium powders using laser powder bed fusion (LPBF). In addition, the influence of manufacturing parameters and different melting strategies, including multiple cycles of remelting, on printability and macro defects, such as pore and crack formation, have been investigated.
Design/methodology/approach
An LPBF process was used to manufacture NiTi alloy from elementally blended powders and was evaluated with the use of a remelting scanning strategy to improve the homogeneity of fabricated specimens. Furthermore, both single melt and up to two remeltings were used.
Findings
The results indicate that remelting can be beneficial for density improvement as well as chemical and phase composition homogenization. Backscattered electron mode in scanning electron microscope showed a reduction in the presence of unmixed Ni and Ti elemental powders in response to increasing the number of remelts. The microhardness values of NiTi parts for the different numbers of melts studied were similar and ranged from 487 to 495 HV. Nevertheless, it was observed that measurement error decreases as the number of remelts increases, suggesting an increase in chemical and phase composition homogeneity. However, X-ray diffraction analysis revealed the presence of multiple phases regardless of the number of melt runs.
Originality/value
For the first time, to the best of the authors’ knowledge, elementally blended NiTi powders were fabricated via LPBF using remelting scanning strategies.
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Lan Li, Tan Pan, Xinchang Zhang, Yitao Chen, Wenyuan Cui, Lei Yan and Frank Liou
During the powder bed fusion process, thermal distortion is one big problem owing to the thermal stress caused by the high cooling rate and temperature gradient. For the purpose…
Abstract
Purpose
During the powder bed fusion process, thermal distortion is one big problem owing to the thermal stress caused by the high cooling rate and temperature gradient. For the purpose of avoiding distortion caused by internal residual stresses, support structures are used in most selective laser melting (SLM) process especially for cantilever beams because they can assist the heat dissipation. Support structures can also help to hold the work piece in its place and reduce volume of the printing materials. The mitigation of high thermal gradients during the manufacturing process helps to reduce thermal distortion and thus alleviate cracking, curling, delamination and shrinkage. Therefore, this paper aims to study the displacement and residual stress evolution of SLMed parts.
Design/methodology/approach
The objective of this study was to examine and compare the distortion and residual stress properties of two cantilever structures, using both numerical and experimental methods. The part-scale finite element analysis modeling technique was applied to numerically analyze the overhang distortions, using the layer-by-layer model for predicting a part scale model. The validation experiments of these two samples were built in a SLM platform. Then average displacement of the four tip corners and residual stress on top surface of cantilever beams were tested to validate the model.
Findings
The validation experiments results of average displacement of the four tip corners and residual stress on top surface of cantilever beams were tested to validate the model. It was found that they matched well with each other. From displacement and residual stress standpoint, by introducing two different support structure, two samples with the same cantilever beam can be successfully printed. In terms of reducing wasted support materials, print time and high surface quality, sample with less support will need less post-processing and waste energy.
Originality/value
Numerical modeling in this work can be a very useful tool to parametrically study the feasibility of support structures of SLM parts in terms of residual stresses and deformations. It has the capability for fast prediction in the SLMed parts.
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Lukas Englert, Stefan Dietrich and Pascal Pinter
The purpose of this paper is to understand the relationship between defect properties and the tool path used for generating additively manufactured parts. The correlation between…
Abstract
Purpose
The purpose of this paper is to understand the relationship between defect properties and the tool path used for generating additively manufactured parts. The correlation between processing strategy and porosity architecture is one of the key aspects for a precise understanding of defect formation and possibilities for defect reduction.
Design/methodology/approach
The authors present a new combined geometry, processing path and porosity analysis procedure based on the use of x-ray computed micro tomography image data and numerical control programming code. The procedure allows for a covisualisation of the track of the respective processing head with the three-dimensional microstructure data.
Findings
The presented method yields statistical results about defect distribution and morphologies introduced by the respective process characteristics in parts. The functionality of the proposed procedure is demonstrated on an aluminum (AlSi10Mg) and a polylactide test sample to show the additional insight found for both additive manufacturing processes and the resulting microstructural properties.
Originality/value
The novelty of this paper is the analysis of the porosity with respect to the underlying additive process zone and the sample geometry.