SURFACE TREATMENT DRIVING


New high-speed laser cladding technologies are being developed that rival more traditional techniques, as Matthew Dale discovers


A


high-speed laser material deposition process developed by Fraunhofer ILT has the potential to capture a portion of the chrome plating market worth €2


billion, according to researchers at the institute. Known by its German acronym EHLA, the new laser cladding technology can reach a deposition rate of up to 500 metres a minute, compared to 0.5 to 2 metres per minute for standard laser metal deposition (LMD). Te technology was developed at


Fraunhofer ILT in Aachen and RWTH Aachen University to overcome some of the drawbacks of both conventional cladding methods and laser cladding in an economical way. While standard LMD injects


DEPOSITION


process is far from optimal, as the hard chrome layers are known to delaminate easily, and microcracks can form. Te process also consumes a lot of energy and the chromium (VI) material used has such a negative impact on the environment that, as of September 2017, the substance has been added to an EU directive, meaning it can be only used with special authorisation or a permit. Alternative coating methods such as


thermal spraying, where only about half of the material used ultimately forms a coating, and conventional deposition welding, where multiple layers are required to counteract any mixing between base and cladding layers, also have drawbacks. Even LMD, while enabling thinner layers to be used, has proven too slow for use on large components, as the low surface deposition rates make it suited only for certain anti-corrosion and wear applications. In addition to addressing the speed issues of


a powdered filler material into a laser-induced melt pool on the surface of the component, in EHLA the powder is injected directly into the laser beam, causing it to melt before it reaches the pool. By not having to wait for the powder to liquefy in the melt pool, the processing speed is dramatically increased to 500 metres a minute. Such speeds mean the process can be used for large-scale component coating, including those that aren’t currently coated because of their size. One common cladding technique is hard


chrome plating, where chromium from a chromic acid solution is deposited on components in an electrochemical bath. Te


12 LASER SYSTEMS EUROPE ISSUE 37 • WINTER 2017


capture a 10 per cent share of the surface refining market [it] could account for an annual market volume of €2 billion


If EHLA could


both conventional and laser cladding methods, the EHLA process also solves the inefficiencies of spray technologies by using approximately 90 per cent of the cladding material, making it far more resource-effective and economical. Also, the layer formed by the new method is particularly dense, meaning only one layer gives sufficient protection. Complex pre-treatment of the substrate is no longer needed either, as


EHLA is able to form a firm bond between the coating and substrate. Further benefits include being able to form smoother, thinner layers than standard LMD, 10 times less rough and measuring 25 to 250µm thick – previously, layers less than 500µm were not possible at high deposition speeds. ‘A significant advantage [also] lies in the


heat input,’ explained Tomas Schopphoven, head of productivity and system technology at


EHLA has a new powder feed nozzle that can operate up to 10 times longer than conventional LMD


the LMD group at Fraunhofer ILT, and one of the creators of the new process. ‘Using EHLA shrinks the heat-affected zone by a factor of 100, from between 500µm and 1,000µm in conventional LMD down to just 5-10µm.’ EHLA thus makes it possible to coat heat- sensitive components, which excessive heat input had made impossible up until now. ‘Tis new process can also be used for entirely new material combinations, such as coatings on aluminium base alloys or cast iron,’ said Schopphoven. As well as the mechanics offered by EHLA,


the process also has a new powder feed nozzle that can operate up to 10 times longer than those used in conventional LMD. According to Schopphoven, this new nozzle


had to meet certain requirements in order for EHLA to be viable for industry: an adjustable powder gas beam caustic for optimal injection


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