Laser and welding
methods
Hard chrome alternatives
summary – laser treating and weld coating*.
|
Alternative |
Compliance |
Usage |
Notes |
|
Laser cladding |
RoHS, WEEE, ELV, OSHA Cr |
Turbine blades, worn shafts |
Localized high temperatures. Can build very thick
and near-net structures |
|
Weld cladding |
RoHS, WEEE, ELV, OSHA Cr |
Rebuilding turbine engine blades and other parts |
High surface heating. Some alloys must be re-heat
treated after processing. Good for large areas.
Note: welding of stainless steel can be an OSHA Cr
problem. |
|
Explosive bonding
|
RoHS, WEEE, ELV, OSHA Cr |
Thick cladding under evaluation for gun barrels |
Old technique enjoying a resurgence for cladding gun
barrels and joining dissimilar metals |
|
Electrospark deposition (alloying)
|
RoHS, WEEE, ELV, OSHA Cr |
Aircraft engine part repair, repair of corroded or
damaged areas |
Very low deposition rate. Useful for small area
repair of nicks and damage. Not used for
fatigue-critical parts |
|
* Note: These are more for
repair and rebuild rather than coating. |
Some of
these welding methods have been in use for many years – weld
cladding has long been a simple do-it-yourself method for
repairing and reducing wear of farm machinery, while
explosive welding used to be used for welding railroad
track. However, these methods have been modernized and some
of the newer technologies, such as laser cladding, are
beginning to make headway as hard coating and repair methods
in place of chrome plate.
Laser
cladding
is a technology that has only become industrially viable on
a large scale in the past few years as more robust and
reliable lasers, such as diode lasers, have become widely
available. The technique uses a laser to melt a powdered
metal onto the surface. This heats the surface but not the
bulk of the material, so it does not have the limitations of
most heat treatments, but this can an issue for aerospace
parts.
ESD coating (Courtesy
ASAP, Inc.)
Electrospark deposition
(alloying) (ESD, ESA) is a microwelding technique in which
an electrode is used to weld coat the surface or fill in
small damage areas. The heat-affected zone is very small
and the method is used for repairing some aircraft engine
components that are not fatigue-critical. Its primary use
is the repair of damage and wear in molds and dies. The
equipment is very inexpensive and easy to use with minimal
training, and there are several suppliers across the world.
Facts
about laser and weld methods:
-
Welding involves melting the material to be welded.
This limits the alloys and products that can be treated
to materials that can be welded and products that can
withstand the heating involved or can be heat treated
back to their original properties.
-
The
various standard torch and electric arc welding methods
input the most heat. They are ideal for large items.
However, welding of stainless steel can generate Cr6+
in significant quantities because of evaporation from
the weld rod.
-
Laser
welding is best for external surfaces. It can be highly
controlled and automated and can even be used to produce
3-dimensional near net shapes.
-
ESD
can be done in such a way that it has almost no effect
on fatigue. It is a very small area, slow deposition
process and is primarily used for repair rather than
coating.
These
methods are all RoHS-compliant. Weld coating with any
Cr-containing electrode material or laser cladding with
Cr-containing powder could be OSHA non-compliant. |
