Modelling the Nickel Electroforming Process of a Mechanical Vane Fit for Industry 4.0
Authors: Andreou Eleni , Roy Sudipta 
Published: December 2024

Electrochemical forming is a chemical additive manufacturing process employed for the development of a variety of niche components, from micro-manufacturing to “heavy industry”. As the Industry 4.0 era unfolds, there is a need to develop models for electroforming which are based on electrochemically sound data. For modelling to be useful, physical and electrochemical parameters which could play a significant role in process optimisation and scaling up should be examined, followed by continuous cross-validation through appropriate experiments and measurements. That way a model can be a valuable aid, allowing predictability in tooling, piloting, and manufacturing in a reliable manner, while minimising the number of manufacturing trials and process waste [1].

In this presentation we aim to discuss the experimental and modelling studies conducted as part of an attempt to predict the electroforming of a vane part used in aerospace applications. Mechanical vanes play an integral role in gas turbine engine design and, therefore, are of great industrial interest. Since their main function is to guide and optimise the air flow as the fluid moves through the engine, their design must abide by strict profile and thickness requirements, followed by low tolerances during manufacturing [2]. As near net shape parts, vanes are an interesting challenge for the electroforming process.

In that effort, the effect of physical and electrochemical parameters on an electroformed vane was studied and a well-informed modelling tool, using COMSOL Multiphysics, was developed for modelling its industrial electroforming process. The model was subsequently validated through experiments.

Following comprehensive scaling-up studies of nickel electroforming on a lab-scale rotating disk electrode (RDE), it was previously established that secondary current distribution could adequately simulate the forming process [3]. Subsequently, experiments were carried out in an industrial piloting tank utilising an industrial vane mandrel. Qualitative analysis of experimental results was carried out to determine process characteristics such as the deposition rate, the direction in which material deposition takes place on the surface, as well as to determine the process predictability. Moving forward, simulations of deposition at current densities up to ~ 5 A/dm2 were run and validated against experimentally achieved thicknesses. Attention was especially focused on the rate with which deposition evolves at the tip of the vane mandrel (“nose”) and the rate at its front and side faces (sides) to determine whether industry requirements for a thick “nose” against thinner sides could be met. The last part of the investigation included the micro-structural characterisation of the electroformed vanes.

Simulations of the process at applied currents ≤5 ASD predicted thickness distribution at the sides in reasonably good agreement with the experimentally observed one. However, thickness at the “nose” area was under-predicted by almost 30%. On the other hand, simulations of the process at applied currents >5 ASD underpredicted both the thicknesses at the “nose” and those at the sides of the part. Nevertheless, it is proposed that the model can still be used for qualitative predictions of the growth of the deposit.

Scanning electron microscopy was used to determine the microstructure of the electroform and the purity of nickel. Imaging suggested that pyramid-shaped nickel particles evolve during deposition. Another interesting observation revealed a periodicity in the growth mechanism which leads to “necklace”-like zones of ~ 100 μm in thickness at the “nose”. It is proposed that these periodic zones might coincide with a periodic regeneration of the active NiOHads intermediate.

Lastly, a qualitative assessment of the COMSOL Multiphysics model’s ability to simulate the effect of “masks on the electroforming process was carried out. Even though the relevant modelling results were not validated through practical experiments, the simulations strongly indicated that current distribution and, consequently, thickness distribution of demanding geometries could be efficiently controlled by the use of “masks” which could potentially be an important aid in the efforts to decrease dendritic growth at mandrel leading edges, just through modifications of the process setup configuration. Specifically, a “shell-type mask” configuration studied in this work was found to be significantly effective, “guiding” the current towards the “nose” and away from the leading edges. That way the desired thickness profile of the final product could imitate the target thickness profiles much closer than in the case when no “mask” is used.

References:

1. E. Andreou & S. Roy, Trans. IMF (2021) 99:6, 299-305

2. L. Hogner et al., Proceedings of ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition (2016)

3. E. Andreou & S. Roy, Front. Chem. Eng. (2022) 4:755725

Figure 1