Keyhole-mode or Conductive-mode Melt-pool formation?
Look at the process parameters above. In your opinion, does the proposed parameter-set cause a (A) keyhole-mode or a (B) conductive-mode melt-pool formation and why?
Recently we published a post asking metal AM enthusiasts their opinion about a set of AM process parameters and whether they would cause (A) a keyhole-mode or (B) a conductive-mode melt-pool formation and why.
We performed a metal AM process simulation via the Scanning-path module in the AdditiveLab software and concluded the correct answer is A, it causes a keyhole-mode melt-pool formation.
The results are depicted in the image above; the picture is composed of the experimental results from the reference study by King et al. and the simulated thermal field with the indication of the melting temperature (blue) to the left and right, respectively.
The keyhole forms predominantly due to the (relatively) high laser power which is being applied to a very small spot size (laser radius). This subsequentially leads to high energy densities which eventually cause the material to evaporate underneath the laser and form a keyhole. This keyhole leads then to higher absorption rates and therefore larger melt-pools.
We counted the answers from the poll of this post and concluded the following distribution in answers:
66% voted for A and 24% voted for B, thus, the majority guessed the correct answer and identified that the presented parameter set to cause keyhole melt-pool formation. (Note: the votes were counted on 07/15/2022).
But let's back up a little and address some valid comments that were brought up in the poll:
The laser diameter presented is fairly small (at the lower end of what current metal AM machines can produce) and thus a lot of energy is applied on a small volume. In practice, such small diameters are used in combination with higher scanning speeds to allow for producing of very detailed features. The presented process parameters may have limited value for high-volume manufacturing outputs.
The laser power is relatively small compared to what is commonly used in an industrial environment. However, as presented in the reference study by King et al., reducing the power together with reducing the laser diameter was a necessity to force keyhole formation in the experimental setup.
Taking full control of metal additive manufacturing processes and being able to produce the highest-quality parts efficiently, requires users to predict, evaluate and understand the difference between conductive- and keyhole-melt-pool formation properly. Once a metal AM machine operates in keyhole mode, the way of how laser power is being absorbed completely changes compared to the conductive mode. While the significantly increased laser absorption in keyhole presents a great opportunity to increase the process performance, it can also cause challenging problems such as keyhole-pore formation.
While studies such as the one presented above can be done experimentally, utilization of simulation tools such as AdditiveLab RESEARCH allows for predicting melt-pool shapes in minutes enabling very effective process developments.
If you would like to teach us how to use our software to efficiently create melt-pool predictions please reach out at firstname.lastname@example.org.