Strict conditions on hexavalent chromium for corrosion and wear protection coatings to hit EU manufacturers of highly stressed metal components particularly hard.
The strict conditions on the use of hexavalent chromium for corrosion and wear protection coatings, which will take effect in the EU in September 2017, hit the manufacturers of highly stressed metal components particularly hard. One such company is IHC Vremac Cylinders in the Dutch city of Apeldoorn. The hydraulic cylinders it manufactures, which often measure many meters in length, have to withstand rough maritime conditions for years. With its choice of an alternative to hard chrome plating, this Dutch manufacturer has become the first company in the world to coat its components using the EHLA technique developed by the Fraunhofer Institute for Laser Technology ILT in Aachen, Germany.
Because of the upcoming admission restriction on coatings which are produced with hexavalent chromium, IHC Vremac Cylinders had long been searching for a fast and economical alternative to hard chrome plating. The Dutch company ultimately opted for the EHLA technique (extreme high-speed Laser Material Deposition), which was awarded the 2017 Joseph von Fraunhofer Prize in May. In the patented EHLA method, a laser beam melts the powder particles already above the melt pool.
Coating at up to 500 m/min
Because the particles no longer have to be heated and melted in the melt pool, process speeds can be accelerated from previous levels of between 0.5 and 2 meters per minute to as much as 500 meters per minute. EHLA can also reduce layer thickness: whereas the minimum thickness of layers used to be 500 micrometers, layers as thin as 25–250 micrometers can now be achieved cost-effectively. Moreover, the layers are smoother, with roughness reduced to a tenth of typical values for Laser Material Deposition.
The concept and the first industrial-standard system in Aachen impressed IHC Vremac Cylinders, so the company contracted Hornet Laser Cladding — a manufacturer of laser material deposition systems in Lexmond, Netherlands — to build an EHLA system. The advantage of using EHLA to coat rotationally symmetric parts is that the necessary components can be integrated into a lathe, according to Fraunhofer. It took less than six months to procure and convert a lathe for the roughly 14-meter-long EHLA system, and thereafter install and commission it.
EHLA significantly faster than thermal spraying
For a hydraulic cylinders, IHC Vremac Cylinders say they currently applies a protective layer of Inconel 625 ca. 400 micrometers thick, which then requires grinding rework. The final layer thickness is around 200 micrometers. EHLA is significantly faster than high-velocity oxygen fuel spraying or HVOF and entails much less post-processing.
The Dutch company is already using EHLA in production manufacturing. After completing several projects, the company is certain that EHLA currently costs roughly the same as thermal spraying. In his view, EHLA will become more economical once the rework processes have been optimized.