An open-architecture laser powder bed fusion system and its use for in-situ process measurements

Design and development of an open-architecture laser powder bed fusion (LPBF) system for in-situ process measurements of the build process during additive manufacture is described. The aim of this work is to create new knowledge and contribute towards further understanding of complex laser powder interaction through in-situ process monitoring. The designed system is sufficiently automated to enable single tracks and high density multiple layer components to be built. It is easily transportable to enable measurements at different measurement facilities and its modular design enables straightforward modification for specific measurements to be made. The system produces components with >99% density, hence, the build conditions are representative to observe process fundamentals and to develop process control strategies. Open-architecture design enabled access to the build area allowing a range of insitu measurements such as high energy flash x-ray imaging, camera-based high-speed imaging, schlieren imaging and temperature measurements. High speed imaging of the LPBF process results reveal that the process is more dynamic than is generally appreciated and can involve considerable motion of powder particles and agglomerates in and above the powder bed. Many critical process regimes were observed for the first time, such as changes in inclination of the laser with varying power and scan speed; and denudation became less severe with respects to an increase in layer number. Schlieren imaging results enabled the visualisation of the argon gas flow and laser plume propagation in the atmosphere above the powder bed. In-situ monitoring has been extended to study the effect of ambient pressures from a high vacuum to 5 bar positive pressure on the LPBF. Considerable disruption to the powder bed is observed at pressures below 20 mbar. As the pressure decreases, the expansion of the laser plume prevents particles reaching the melt pool: profiles and crosssections of the track reveal a drastic reduction in its cross-sectional area. At above atmospheric pressure, argon (up to 5 bar), the process was further disrupted by severe plasma formation along with an increase in size and number of spatter. The particle entrainment and resulting denudation was reduced, and single-track continuity was enhanced. In further study, it has been found that helium, used as shielding gas at higher pressure, mitigates negative effects of argon; generates smooth and uniform tracks and islands. The smoothness and continuity of built layers at 5 bar in helium was comparable to argon at atmospheric pressure, with considerable increase in scan speed.School of Engineering and Physical Sciences - James Watt Scholarshi

Powder-based laser hybrid additive manufacturing of metals:a review

Recent advances in additive manufacturing (AM) have attracted significant industrial interest. Initially, AM was mainly associated with the fabrication of prototypes, but the AM advances together with the broadening range of available materials, especially for producing metallic parts, have broaden the application areas and now the technology can be used for manufacturing functional parts, too. Especially, the AM technologies enable the creation of complex and topologically optimised geometries with internal cavities that were impossible to produce with traditional manufacturing processes. However, the tight geometrical tolerances along with the strict surface integrity requirements in aerospace, biomedical and automotive industries are not achievable in most cases with standalone AM technologies. Therefore, AM parts need extensive post-processing to ensure that their surface and dimensional requirements together with their respective mechanical properties are met. In this context, it is not surprising that the integration of AM with post-processing technologies into single and multi set-up processing solutions, commonly referred to as hybrid AM, has emerged as a very attractive proposition for industry while attracting a significant R&D interest. This paper reviews the current research and technology advances associated with the hybrid AM solutions. The special focus is on hybrid AM solutions that combine the capabilities of laser-based AM for processing powders with the necessary post-process technologies for producing metal parts with required accuracy, surface integrity and material properties. Commercially available hybrid AM systems that integrate laser-based AM with post-processing technologies are also reviewed together with their key application areas. Finally, the main challenges and open issues in broadening the industrial use of hybrid AM solutions are discussed. 2021, The Author(s).The authors would acknowledge the support received from the ESIF/ERDF Smart Factory Hub (SmartFub) programme in West Midlands. The authors also acknowledge the support received from Yamazaki Mazak, DMG MORI, LASEA and Systems 3R for establishing the hybrid AM facilities at the University of Birmingham.Scopu

A numerical model for predicting powder characteristics in LMD considering particle interaction

In this work, a numerical model is proposed to analyze the influence of particle–particle interaction in laser directed energy deposition or LMD (laser metal deposition) of CM247 Ni-based superalloy. The model is based on the analysis of contact between particles and the potential agglomeration of powder to predict powder conditions at the nozzle exit. Simulation results were experimentally validated and a good agreement was observed. At the nozzle exit mainly large particles (>100 lm) are found and small ones (<10 lm) tend to flow away from this region. This was also observed in the experimental PSD. Additionally, based on the relative velocity of particles, simulations are able to predict the formation of dents. In comparing virgin powder PSD and the one at the nozzle exit, it was observed that largest particles are collected at the exit. In order to explain this phenomena, particle agglomeration was analysed numerically. It was seen that small particles tend to adhere to the big ones due to their higher adhesive forces, which would explain the change in PSD