Dubai workshop 3D-prints a 26 kg ship propeller from a scan

The client needed a propeller that matched an existing one, and needed it fast. There were no drawings. The only record of the blade curvature, the pitch and the join between each blade and the hub was the physical part itself. JOME Engineering's answer was to scan it, print the copy, and finish it by hand.

The method is wire arc additive manufacturing, or WAAM: an electric arc melts a metal wire, which is laid down bead by bead until a shape builds up. JOME printed the replacement in SS316L stainless steel on a Vipra AM system, a robotic WAAM platform for large metal parts made by the Italian firm Caracol. The work took place at JOME's facility in Dubai, close to the vessel the propeller was built for. The result weighs 26 kg and measures 685 mm in diameter.

The build went in stages. The central hub, or boss, was machined first, and a dye penetrant test, which reveals surface cracks, confirmed it was sound before the three blades were deposited on it. Machining took about 100 hours and was the hardest step: blades are twisted freeform surfaces with few reference points to align against. To keep errors in check, the team re-scanned the part after each stage and compared it with the digital master. Deposition took about 20 of the roughly 120 hours in total. Caracol says that split is typical for precision metal parts.

The approach has precedents. In 2017 the Dutch naval maintenance company MKM described the same problem, with parts that had no drawings, and used Artec 3D scanners to build digital models. Damen Shipyards' WAAMpeller project went the other way, starting from a CAD file to print a 400 kg tugboat propeller in nickel aluminum bronze before milling it. JOME's job combines both: scanning a part that has no drawings, then rebuilding it by WAAM and machining. Caracol's figures on lead time and cost describe this one propeller, not a production run, and the sources do not show the part's performance in service.

For an operator whose only spare is a metal object on a shelf, the gain is time. A vessel waits for its propeller, and skipping the mould and the foundry queue brings it back to work sooner. JOME now holds the geometry as a file, so a future replacement can go straight to printing without a new scan. Caracol also says WAAM melts only the wire it deposits and needs no steel die, which it argues lowers the carbon footprint of single-unit parts. Those are the maker's claims. Whether the 60 percent and 40 percent figures hold for the next propeller, or for a series of them, is something the sources do not yet show.