In August 2014, TWI was invited to showcase a 3D printed component at the International Digital Sculpture and Engineered Forms Exhibition in Austin, Texas. The exhibition featured original 3D-printed artworks from around the world by pioneers in the digital arts and engineered functional forms. TWI’s contribution became a central talking point and was the only metallic object at the exhibition.
The art of 3D welding
The exhibition organisers initially approached TWI to invite them to showcase a helicopter combustion chamber casing built by Laser Metal Deposition (LMD) because of the unique way in which the part was manufactured. However, experts at TWI Technology Centre in South Yorkshire offered to build something more befitting an art exhibition. They decided to build a Rubin vase and attempted probably one of the largest thin-walled net shape components ever built by LMD, standing nearly 400mm tall with a consistent wall thickness of 0.9mm.
In LMD, a weld track is formed using metal powder as a filler material which is fed, through a coaxial nozzle, to a melt pool created by a focused high-power laser beam. Using an approach developed by TWI, the precise synchronisation of the movements of rotation and tilt of the substrate with incremental movements of the coaxial nozzle (predominantly in the +Z direction) allows a continuous spiralling weld track to be deposited or ‘grown’, layer on layer, out of the substrate.
This helical multi-layering technique allows a thin-walled 3D contour to form which accurately follows the specification of the original CAD surface profile.
Profiling the Master of Suspense
To enable the manufacture of the vase, it was necessary for TWI engineers to write a plugin to their ToolCLAD software solution that would automatically generate a 3D triangulated surface model directly from a 2D bitmap image. This enabled the selection and conversion to CAD of a famous face. ToolCLAD software was then used to map a vector toolpath with deposition parameters to guide a three-axis coaxial LMD nozzle across a moving substrate manipulated by a two-axis CNC rotary table. This ground-breaking technique is a novel method of LMD manufacturing.
The vase was built in a single stage using Inconel 718 powder: a consistent track weld of width 0.9mm, depth 0.2mm and a total length of nearly 1.8km, covering 2400 rotations in a 26-hour build time. Four kilograms of powder was used and 3.2kg was fused in the vase, giving 80% powder efficiency. The vase stands nearly 400mm tall with a maximum diameter of 380mm. To improve the aesthetics of the vase for the purpose of the exhibition, the external surface was lightly shot blasted, primarily to remove excess powder, and the internal surface of the bowl was polished.
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This technology is also covered in another case study: Revolutionary development cuts manufacturing times using Laser Metal Deposition . The process can be seen in a video at http://youtu.be/yKnlmfuMSgo.
For more information on LMD technologies, please contact us.