Abstract
PurposeThis paper aims to introduce a novel method for the analysis of open cell porous components fabricated by laser-based powder bed metal additive manufacturing (AM) for the purpose of quality control. This method uses photogrammetric analysis, the extraction of geometric information from an image through the use of algorithms. By applying this technique to porous AM components, a rapid, low-cost inspection of geometric properties such as material thickness and pore size is achieved. Such measurements take on greater importance, as the production of porous additive manufactured orthopaedic devices increases in number, causing other, slower and more expensive methods of analysis to become impractical.Design/methodology/approachHere the development of the photogrammetric method is discussed and compared to standard techniques including scanning electron microscopy, micro computed tomography scanning and the recently developed focus variation (FV) imaging. The system is also validated against test graticules and simple wire geometries of known size, prior to the more complex orthopaedic structures.FindingsThe photogrammetric method shows an ability to analyse the variability in build fidelity of AM porous structures for use in inspection purposes to compare component properties. While measured values for material thickness and pore size differed from those of other techniques, the new photogrammetric technique demonstrated a low deviation when repeating measurements, and was able to analyse components at a much faster rate and lower cost than the competing systems, with less requirement for specific expertise or training.Originality/valueThe advantages demonstrated by the image-based technique described indicate the system to be suitable for implementation as a means of in-line process control for quality and inspection applications, particularly for high-volume production where existing methods would be impractical.
Highlights
Amongst other applications, open cell porous coatings are used in orthopaedic implant design to improve fixation, and have replaced cement and bone screws as the favoured method of attaching implants to existing bone (Friedman et al, 1993)
Resolution analysis tested the accuracy of measurements made by the photogrammetric system and quantified the minimum measurable feature possible with the system by comparing the measured thickness of line sets on the target test graticule to the stated values
Material thickness analysis was performed to determine the measured value produced by the system and how these were compared to values acquired for scanning electron microscopy (SEM) and focus variation (FV)
Summary
Open cell porous coatings are used in orthopaedic implant design to improve fixation, and have replaced cement and bone screws as the favoured method of attaching implants to existing bone (Friedman et al, 1993). The use of porous structures allows for bone in-growth to improve security, increasing the lifetime of the device (Bobyn et al, 1999; Jeyapalina et al, 2014). Porous structures can be fabricated using a number of methods, such as plasma spraying and sintering. The full terms of this licence may be seen at http://creativecommons.org/licences/by/4.0/legalcode
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