Search

Polymeric parts produced by Laser Sintering (LS) present a consistent amount of pores with a wide pore size distribution. The knowledge about the porosity value and its distribution within the part allows to perform a quality control of the LS process, and gives insights in how to improve it. In this work the influence of the sample size on the porosity measurement is discussed, as well as its representativeness of the LS process itself. The reliability of porosity measurement of those parts using X-ray Computed Tomography (CT) is assessed taking into account the influence of the CT scanning parameters, the reconstruction and noise reduction algorithms using a design-of-experiment approach. The quality of the CT datasets obtained is assessed by calculating Contrast-to-Noise Ratio (CNR) and Signal-to-Noise Ratio (SNR) on representative reconstructed images. Repeatability of the measurements is also assessed along the entire workflow: CT acquisition, reconstruction and porosity measurement using commercial software packages.

© 2017 Elsevier Ltd Laser Sintering (LS) of polymers is an Additive Manufacturing technique progressively used to produce functional parts. However, LS parts still present a certain quality variability. Efficient consolidation of the polymeric powder, necessary to obtain a dense part, mainly depends on the viscosity of the molten polymer and on the time given for the polymer to coalesce. The polymer viscosity is a function of the temperature and, consequently, of the energy density (ED) input by the laser. The sintering time strongly depends on the surface area to be laser-scanned in each layer, which in turn is strongly related to the product complexity and the number of parts within one build. The aim of this work is to investigate how this thermo-temporal effect, influenced by the ED and the inter-layer time, influences the resulting LS PA12 part quality at both micro-level (e.g., porosity, crystallinity) and macro-level (e.g., dimensional accuracy, mechanical performance). ispartof: POLYMER TESTING vol:61 pages:386-395 status: published

The ability to align ex-situ inspection data of an additively manufactured (AM) part to its build geometry can be helpful, for example, to correlate observed in-situ monitoring events or features to measured discontinuities, such as pores and cracks, in ex-situ inspection. In some cases, the original part design does not lend itself to such an alignment due to the absence of datum surfaces. In this study, the concept of incorporating inclined, cylindrical protrusions as reference fiducials in the design of cylindrical AM test coupons is investigated. Six coupons with proposed fiducials were built and inspected using X-ray computed tomography (CT). Dimensional measurements performed on the fiducials expose shortcomings in the proposed fiducial design—mainly a result of limited dimensional fidelity of small features by AM—and allow us to make suggestions on how the design can be improved. Nevertheless, an alignment scheme based on the reference fiducials is compared with an approach based on inherent coupon surfaces on layer-wise porosity measurements by X-ray CT on one of the test coupons.

Porosity is a key parameter determining the functional application limits of polymeric parts produced by laser sintering (LS). In this paper, X-ray computed tomography (CT) is used to investigate the influence of the LS scanning parameters (laser power, hatch spacing, and scan speed) and part or feature size on the distribution and size of pores within polyamide-12 (PA12) laser sintered parts. CT model slices are created parallel to the original LS manufacturing layers in order to determine the porosity distribution and variation within each layer as well as along subsequent layers. Mapping the porosity distribution within these slices onto the laser scanning trajectory moreover allows investigating the influence of LS scanning parameters. Correlation of these porosity data with results from mechanical testing allows identifying optimal LS scanning parameters.

X-ray computed tomography (CT) has an increasing number of industrial applications in the field of dimensional metrology. In the first part of this chapter, an overview of the general measurement tasks that can be performed by using industrial CT is provided. Subsequently, specific measurement examples are given for different manufacturing fields (including casting, forming, machining, injection moulding and additive manufacturing). Then, trends and industrial demands are analysed to determine the current challenges of industrial CT and the future improvements. Finally, a special case study of CT for dimensional measurement in the medical field is presented.

Laser Sintering (LS) is an Additive Manufacturing (AM) technology for polymers processing which is increasingly being used to produce functional products with designs not achievable with traditional manufacturing technologies. Lightweight cellular structures are a good example of complex designs which are increasingly finding applications in AM parts. However, it is not yet clear how the LS process affects the porosity and geometrical characteristics of the cell structural elements. Getting this information allows to perform quality control of the LS process, gives insights into how to improve it, and might help to take into account manufacturing process variability during the design phase. In this work a test artifact containing cylindrical elements with diameters in the range typically used in lightweight cellular structures is used to investigate the influence of features’ size and printing orientation on the porosity and shape deviation of each feature. In order to assess the reproducibility of the process, several replicas of the test object are produced in polyamide-12 (PA12) using the same LS process conditions. An X-ray Computed Tomography (CT)-based quality control approach, which uses both image processing of CT-slices and porosity analysis (porosity content, pores count and pores volume distributions) is used to gather the information. ispartof: Case Studies in Nondestructive Testing and Evaluation vol:6 pages:62-68 status: published