Canadian Finishing & Coatings Manufacturing Magazine March/April 2022 - 31

PLATING AND ANODIZING: EHLA
Everything On Extreme High
Speed Laser Application
BY ALYSSA KERSLAKE
I
n order to improve upon laser cladding, as a replacement
for chrome plating, and as a substitute for spraying
technologies, Extreme High Speed Laser Application
EHLA was developed. EHLA coatings may be sprayed
to small and large components at speeds up to 10-100 times
quicker than laser cladding, making them ideal for high-volume
production. To learn more about EHLA, we reached out to TWIGlobal
to gain more expert insight.
Could you explain how the EHLA process works?
Extreme High Speed Laser Application (EHLA) is a novel
technology, first developed by Germany's Fraunhofer Institute
for Laser Technology (ILT) in 2012 and becoming commercially
available in 2016 [1]. EHLA takes its idea from laser material
deposition (LMD) but uses a modified powder laser gas jet focus
which is the key to delivering material at high surface coverage
rates with a low dilution and a small heat affected zone (HAZ).
In the EHLA process, metallic powder, within a carrier gas, is
fed through a nozzle and into the path of a focused laser beam.
Melting of the powder occurs a few millimetres above the
substrate to ensure the powder is fully melted before making
contact with the substrate (see Figure 1).
The laser, being partially masked by the melted powder
stream, still has enough energy to create a small melt pool
on the surface of the substrate. This ensures a strong fusion
bond between deposited material and substrate, but with a
significantly reduced dilution and HAZ. This gives the ability
to produce much thinner coatings (20-500µm) that exhibit the
desired chemistry and microstructures. To take full advantage
of the high deposition rates of EHLA, substrates are generally
cylindrical in shape (bar, tube or disc) which rotate at high speed
under a linearly traversing nozzle.
How is EHLA an improvement from laser cladding?
EHLA coatings can be applied to small and very large
components (several meters in length) with area coverage
rates of 10-100 times faster than laser cladding. Laser cladding
generally operates at a deposition speed of around 1m/min.
EHLA can operate at 100m/min and beyond, where laser power
ultimately governs the process speed. Research into deposition
speeds approaching 500m/min using laser powers as high as
6-12kW, or greater, is being conducted to find out if EHLA has
process limits.
Nevertheless, it is important to note that the high process
speeds do not necessarily translate into high material deposition
rates (Kg/hour). This is because the applied layer thickness
Figure 1: schematic of the LMD (laser cladding process) (left) and EHLA process (right) showing the differences in power laser focus, melt-pool
formation and HAZ. (Source TWI Ltd)
March/April 2022
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Canadian Finishing & Coatings Manufacturing Magazine March/April 2022

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