Finishing - July-August 2022

26 PROFILE
12 step
programme
Taking it back to basics, at CWST we are
experts in metal surface finishing
treatment processes. But what does this
really mean?
Simply, that we have vast knowledge in a
range of industrial processes that alter the
surface of metal to achieve a certain property,
for example, to improve appearance,
adhesion, corrosion resistance, hardness and
much more. These can be categorised by how
they affect the subject, either
removing/reshaping the finishing, or
adding/altering the finishing.
At CWST we offer 12 key metal surface
finishing treatment processes, each increasing
performance and life of metal components by
protecting against premature failure, due to
fatigue, corrosion, stress, fretting, friction and
galling, as well as support against
environmental and thermal variation.
Our high-performance metal surface
finishing treatments include the following.
Controlled Shot Peening
Tensile stresses induced during welding,
grinding, machining and heat treatment are
replaced with beneficial compressive stresses
proven to prevent fatigue and stress corrosion
cracking.
This cold working process is applied using
spherical media known as ‘shot’, as each piece
hits the surface it creates an indentation where
the surface will attempt to yield but is
restrained by the substrate material. This in
turn causes the material to compress, creating
added stress – making the surface crack
resistant and removes any prior
manufacturing tensile stress.
Shot Peen Forming
Creates curvature in aircraft wing skins to
enhance lift and efficiency and to protect
against fatigue. Also used to correct the
distortion of components following
manufacturing.
Within this process, material is fired at the
surface, creating indentations causing the
material to elastically stretch, however it is
restrained by the substrate. This causes the
surface to arc towards the peened side,
resulting in curvature. This method can induce
stress to greater depths, with a tighter radius
of curvature as well as being able to be
performed on thicker materials.
Laser Shock Peening
Laser peening induces compressive stress
with precision accuracy into key areas of a
component up to 5 to 10 times deeper than
other conventional cold working techniques.
Laser shock peening uses an output beam
at 25 joules at 18 nanoseconds from a glass
laser, a thin stream of water is made to flow
across the surface and the laser transparently
passes through the water, and a pulse is
absorbed on the metal surface. The rise in
pressure creates a shock wave that penetrates
into the metal, straining the surface layer.
C.A.S.E. Isotropic Finishing
Super finishing
Removes surface asperities to create a
mirror like finish, reducing macro and micropitting,
oil temperature and noise whilst
promoting lubricant retention.
This process uses controlled shot peening,
followed by chemical surface superfinishing.
This removes any metal asperities, retaining
valleys for optimum oil retention, reducing
surface friction and operating temperatures.
Thermal Spray Coatings
Wear resistant and barrier coatings such as
HVOF, arc and flame spray, protecting against
Finishing - July/August 2022
continues on p28