Additive manufacturing inert gas flow path strategies for multi-laser powder bed fusion systems and their impact on lattice structure mechanical responses.

Multi-laser Additive Manufacturing systems hold great potential to increase productivity. However, adding multiple energy sources to a powder bed fusion system requires careful selection of a laser scan and inert gas flow strategy to optimize component performance. In this work, we explore four different laser scan and argon flow strategies on the quasi-static compressive mechanical response of Body Centered Cubic lattices. Three strategies employ a swim lane method where laser pathing tends to progress parallel to argon flow. Method one only uses a single laser while method two uses four, both with the laser path working against the argon flow. The third method uses four lasers, each operating in their own lane like the second method, but the laser pathing progresses with the argon flow. The fourth method has all four lasers operating in quadrants and the laser pathing trends against the argon flow.The single-laser strategy generally had the lowest mechanical responses compared to the other three strategies. A quadrant strategy generally had the highest quasi-static mechanical responses and was at least 25% greater in stiffness, yield force, ultimate force, and energy absorption when compared to the single laser strategy. However, the four-laser swim strategy where the laser pathing tends against the argon flow was found to be statistically similar to the quadrant strategy. It is hypothesized that spatter introduced onto the powder layer from the melt pool and particle entrainment may be worse for laser pathing which trends with the argon flow direction. Additionally, the additional energy added to the build volume helps to mitigate inter-layer cool time which reduces temperature gradients. This shows that multi-laser AM systems have an impact on part performance and potentially shows lattices built with multi-laser AM systems may have certain advantages over single-laser AM systems.

Build parameter influence on strut thickness and mechanical performance in additively manufactured titanium lattice structures.

Additively manufactured lattices have been adopted in applications ranging from medical implants to aerospace components. For solid AM components, the effect of build parameters has been well studied but comparably little attention has been paid to the influence of build parameters on lattice performance. For this project, the main aim was to evaluate static compressive mechanical performance of regular and stochastic lattices as a function of build parameters. The second aim was to compare strut dimensions of the metal lattice structures as build parameters were changed. Both regular and stochastic lattices were fabricated with a designed strut diameter of either 200 µm or 300 µm on a laser powder bed fusion machine. A range of laser power (140-180 W), scan speed (1700-2100 mm/s), and laser offset (0-45 µm) were used in fabricating each lattice. Compression tests were performed following the ISO 13314 (2011) standard to measure modulus, yield strength, and ultimate compressive strength values. Laser power adjustments produced the most significant effect on lattice performance. A change of 50 W resulted in roughly a 2X increase in maximum load and modulus for both regular and stochastic lattice structures. Regular lattice structures had a higher mechanical response during the mechanical evaluation. Internal strut diameters varied between build parameters as well, with laser offset adjustments producing the most noticeable change in strut geometry between lattice samples. These findings suggest that build parameter optimization, in lieu of using OEM parameters developed for solid structures, is necessary to ensure the optimum mechanical performance of AM lattice structures.

Dimensional variability characterization of additively manufactured lattice coupons.

BACKGROUND: Additive manufacturing (AM), commonly called 3D Printing (3DP), for medical devices is growing in popularity due to the technology's ability to create complex geometries and patient-matched products. However, due to the process variabilities which can exist between 3DP systems, manufacturer workflows, and digital conversions, there may be variabilities among 3DP parts or between design files and final manufactured products. The overall goal of this project is to determine the dimensional variability of commercially obtained 3DP titanium lattice-containing test coupons and compare it to the original design files. METHODS: This manuscript outlines the procedure used to measure dimensional variability of 3D Printed lattice coupons and analyze the differences in external dimensions and pore area when using laser and electron beam fabricated samples. The key dimensions measured were the bulk length, width, and depth using calipers. Strut thickness and pore area were assessed for the lattice components using optical imaging and µCT. RESULTS: Results show a difference in dimensional measurement between printed parts and the computer-designed files for all groups analyzed including the internal lattice dimensions. Measurements of laser manufactured coupons varied from the nominal by less than 0.2 mm and results show averages greater than the nominal value for length, width, and depth dimensions. Measurements of Electron Beam Melting coupons varied between 0.4 mm-0.7 mm from the nominal value and showed average lengths below the nominal dimension while the width and depths were greater than the nominal values. The length dimensions of Laser Powder Bed Fusion samples appeared to be impacted by hot isostatic press more than the width and depth dimension. When lattice relative density was varied, there appeared to be little impact on the external dimensional variability for the as-printed state. CONCLUSIONS: Based on these results, we can conclude that there are relevant variations between designed files and printed parts. However, we cannot currently state if these results are clinically relevant and further testing needs to be conducted to apply these results to real-world situations.