Every day, there seem to be more and more ‘knock off’ products that look
similar on the outside but are cheaper in price than the original. In our
business, quality is sometimes a tough sell. Objections range from “I want to spend as little as possible
up front” to “I don’t understand why I need to spend more”. That’s when the discussion turns to
value. Deciding what to buy should always include a product life cycle cost
analysis that looks deeper into
the value proposition and the initial product price. Important considerations
include labor costs associated with production , and the time and money the
customer must spend to get the job done. It boils down to learning how to recognize
the benefits of using an efficient, quality product. But quality goes beyond
what’s apparent on the outside; it’s reflected in design, engineering, and even
tech support—the whole product package. When customers think about the products
they make, we expect they do just that.
Fortunately, within the shot peening community, the trend is one of
increasing concern with quality. We hear that customers seek great design and engineering,
tech support, and an equipment system that consistently gets their job done
right as quickly and efficiently as possible. They appreciate good advice and experience-based
knowledge. We’ve noticed that customers are taking a much more serious look at
the companies they do business with because they seek expertise, reliability,
and trustworthy partners. The reasons more and more customers are taking such a
hard look are numerous, but very high on the list is safety and liability. Is
it worth the risk of producing a product that may jeopardize safety or the
company’s reputation?
When it comes to shot peening, expertise is critical. The process of shot
peening is exacting. It is used on metal parts that are subjected to frequent
cycle stress, stress reversal, twisting, and torsional stresses. To prolong
life and avoid early failure caused by a fracture that begins at the surface,
controlled shot peening is applied. The shot peening process alters the metal
surface through repeated striking with a high-velocity stream of spherical
particles. These particles are peening media, most often steel shot, ceramics
or glass beads. The media produce round indentations on the surface, causing a
stretching of the surface and a rising of the edges of the indentations above
the original surface. Complete peening produces a compressive stress layer, the
depth of which will vary from application to application. Beneath this depth, a
tensile stress layer develops and achieves equilibrium and provides for longer
fatigue life of the shot-peened part.
How does shot peening improve quality?
Shot
peening increases fatigue life.
It does so
in parts subjected to dynamic loading, which is a repetitive, cyclical loading
that causes bending and twisting. Parts like fuel injector components, aircraft
landing gear, helicopter blades, leaf and coil springs, gear teeth, drive
shafts, torsion bars, axles, rotor, compressor, and turbine blades, and many
others see better fatigue life after shot peening.
Shot
peening reduces stress corrosion cracking.
Residual
stress leaves metals more susceptible to corrosion, particularly in
high-strength materials, from a complex interaction of corrosives on sustained
tensile stress in the metal surface. Components such as landing gear and
hydraulic tubing benefit from shot peening.
Shot
peening prepares parts for plating.
Plating
often develops fine cracks and preparing a surface with shot peening prior to
plating can prevent the cracks in the plating from affecting the substrate in
items such as landing gear cylinders, among others.
Shot
peening straightens parts deformed during manufacturing.
Selective
peening can to a certain degree straighten critical areas. Some applications
include bulkheads, large machined structural shapes, and deformed heat-treated
parts.
Shot
peening reduces tensile stresses after grinding.
The process
can convert residual stresses from tensile stress to compressive stress,
producing a uniform compressive layer, which increases fatigue life and
lengthens the service life of
high-strength steel parts.
Shot
peening reveals poor bonding in electroplated parts.
When
incorporated into a rigorous quality-control program, shot peening can be used
to detect adhesion problems and expose imperfections.
Shot
peening reduces casting porosity.
Castings are
often porous, and shot peening with the right media size can close the pores,
compress the surface, and reduce hydraulic leakage in die-cast parts,
transmission housings, and gear boxes.
Shot
peening can alter part dimensions.
Useful
either when first designing and manufacturing a product or when rebuilding one,
shot peening can increase or reduce part size. Shot peening can be used to
increase the diameter of a shaft or decrease the diameter of a hole.
Shot
peening improves lubricity and oil retention.
Because of
its effect on the surface, shot peening reduces friction and can improve oil
retention, thereby also improving lubricity in parts such as engine pistons and
cylinder walls.
Shot peening reduces notch sensitivity in high-strength steel.
High-strength
steel is susceptible to fatigue cracking, also called notching. The stronger
the steel, the more likely it is to crack. With shot peening, the steel surface
is improved, giving it a longer life cycle. Shot peening is often used to treat
steel with a strength rating of more than 200,000 psi. It is commonly used on landing gear and
springs.
Safety- and quality –conscious manufacturers understand the benefits of
shot peening and carefully follow specifications. They accurately document the
process to ensure consistency and repeatability. Proper controls over peening intensity, arc
height, and coverage produce consistent results. And sophisticated equipment
for monitoring, measuring, and documenting such variables enhance the value of
shot peening.
Bottom line: shot peening is complex. Learning everything you can about it, so that you can properly apply it to your particular application, takes time and dedication. Take it from someone who has spent years learning, just follow a few simple steps— make sure your shot peening system is of high quality and engineered to incorporate the features dictated by your application, consult
with an experienced practitioner, like me, and attend the EI Shot Peening Workshop.
© Clemco Industries Corp.
