Just like boats need to be protected from rust, components need to be protected against wear and corrosion. There are special products you can apply to a boat to keep it rust-free, and you should also make sure to store it in a place that’s free from moisture; in the same vein, there are multiple ways of protecting components, such as thermal spraying, hard chrome plating, and laser material deposition. But, none of these three processes are foolproof, and there are drawbacks to each one. But researchers from the Fraunhofer Institute for Laser Technology ILT and the RWTH Aachen University, both in Germany, have been working to find an answer that can get rid of these downsides.
Last year, Fraunhofer presented a new manufacturing process for high precision screen printing of metal parts; now, its researchers have developed an additive manufacturing process that offers eco-friendly, cost-effective corrosion and wear protection and also gets around all of the drawbacks experienced with thermal spraying, chrome plating, and laser material deposition. The patented extreme high-speed laser material deposition method, known by its German acronym of EHLA, is able to overcome the obstacles typically found in coating technology and repair. Not only that, at this week’s Fraunhofer General Assembly Meeting in Dresden, the research team was awarded the Joseph von Fraunhofer Prize for its innovative work.
The annual prize, which has been awarded by the Fraunhofer-Gesellschaft since 1978, is given to honor and recognize its staff members’ outstanding scientific work that leads to solving application-oriented problems. The prize has an award of €50,000, and four prizes will be awarded this year.
Dr. Andres Gasser, group manager at Fraunhofer ILT, said, “We can now use EHLA to apply thin layers in the range of a tenth of a millimeter over large surfaces within a short time, while being resource-efficient and economical.”
So, why is EHLA better at corrosion protection than the typical three techniques? In terms of thermal spraying, EHLA offers a much more efficient and economical use of resources – while the new process uses about 90% of the coating material, thermal spraying wastes a lot of the material and gas. Only about 50% of the material used during thermal spraying actually coats the surface of the component, and the layers only have a weak bond to the substrate; in addition, because thermal sprays are so porous, you need to apply several 25-50 micrometer thick layers. Comparatively, the individual layers of the EHLA process are non-porous, and have a firm substrate bond.
Hard chrome plating is one of the most common processes when it comes to applying corrosion and wear protective coatings, but it also consumes a large amount of energy. Not only that, but because chromium(VI) is harmful to the environment, it can only be used with specific authorization starting this September. For companies that want an eco-friendly alternative, the EHLA process is the way to go. It offers chemical-free application: each layer is metallurgically bonded to the base material and won’t delaminate like hard chrome layers will. EHLA-produced layers offer more efficient long-term protection because they’re non-porous, as opposed to the cracks and pores that riddle hard chrome plating layers.
EHLA is also quicker than deposition welding processes, which are typically used to make firmly bonded, high-quality coatings. But the 2-3 mm layers produced by conventional processes, such as plasma powder deposition and tungsten inert gas (TIG) welding, are usually too thick, and while laser material deposition has much thinner layers (between 0.5-1 mm), the process is far too slow to be efficiently used for large components. A certain melt pool size is also necessary to create a layer that’s free of any defects – the component has to be melted locally, “while a powder nozzle directs a powdery additive into the melt pool.”
“With EHLA, the laser melts the powder particles while they are above the melt pool,” explained Dr. Gasser.
EHLA allows the layers to become more homogeneous, since drops of liquid material fall into the weld pool instead of solid particles of powder. Also, only a few micrometers of base material need to be melted, instead of a millimeter. This means that the component can be coated much quicker using EHLA: up to 100-250 times faster than laser material deposition, and the substrate only requires minimal heating. So not only can the new process facilitate the coating of heat-sensitive components, which was not possible before because of high heat input, it can also be used in conjunction with new material combinations, like coatings for cast iron and aluminum-based alloys.
At the LASER World of PHOTONICS trade fair in Munich next month, the research team will be presenting its new EHLA process at stand A2.431. In addition, Dutch company Hornet Laser Cladding B.V. and Germany’s ACunity GmbH will soon deliver Fraunhofer ILT’s first EHLA system to China, where it will be used for industrial applications and research at the Advanced Manufacture Technology Center, located at Beijing’s China Academy of Machinery Science & Technology (CAMTC). Discuss in the Anti-Corrosion forum at 3DPB.com.