Understanding Shot Peening

Q: What are the benefits of shot peening and for what applications is it typically used?

A: Shot peening, the “hammering” of workpieces with precisely defined blast
media is an indispensable operation in industries such as automotive and
aerospace. By inducing a residual compressive stress into the workpieces,
the shot peening operation substantially improves their long-term
resistance against tensile and bending loads.

The process is used for treating toothed, steering and transmission
components, as well as for springs, drive- and crankshafts and all kinds of
turbine blades. A significant advantage of the shot peening operation is
that the component weight can be reduced without impacting its mechanical
load capabilities. This is particularly beneficial in electric vehicles,
because it increases their operating range and reduces their energy
consumption. Due to changing workpiece structures and shapes E-mobility
frequently necessitates the alteration of manufacturing processes.
Moreover, customers are demanding significantly higher energy, resource and cost-efficiency — in other words, significant improvements in
productivity and sustainability. One company specializing in such optimization projects is Rösler (Untermerzbach, Germany; Battlecreek, Mich.).

Compressed air blast systems have been the predominant shot-peening tools
to consistently achieve the specified residual compressive stress values. A
downside of the compressed air method is that it requires a lot of energy.
Today innovative technical improvements of the turbine technology allow the
precise and high-quality shot peening of a broad range of components with
energy-efficient, highly productive turbines. For many peening applications
costly compressed air blast systems are no longer required.

The most important factors to be considered in peening operations are the workpiece shape and size, the required peening results and the blast media. Based on these factors, Rösler runs computer simulations of the blast pattern, as well as the entire process. The simulations are followed by actual peening
trials in Rösler's Customer Experience Center (CEC). Since the CEC is equipped
with a broad range of turbine and compressed air blast systems, the shot
peening trials can be conducted under actual production conditions. With an
in-house X-ray diffractometer the peening trials can be quickly evaluated
to determine which process parameters and blast media will generate the
required results.

A joint optimization project between a leading European automobile
manufacturer and Rösler resulted in energy savings of 30% and a 50%
increase of the shot blast capacity.

Sometimes a review of the existing shot blasting parameters can help to
significantly improve the entire peening process. Once they are
established, the process parameters are frequently no longer questioned.
Such carelessness can result in high equipment wear and unused potential for process improvement.

Perfectly calibrated process parameters, including the optimal media
selection, guarantee high peening qualities, less equipment wear and low
operational costs. If a review of the shot blasting parameters in an
existing machine is not sufficient, a retrofit can be the right solution.
Among other things, this includes upgrading the machine with more productive components such as more powerful turbines or the development of workpiece fixtures for new or modified workpieces. Optimization of the blast pattern must always be considered.

Shot peening trials in the CEC, along with the evaluation
of the results by X-ray diffraction, special tests of the peening coverage
and, if needed, surface roughness and light-microscopic measurements, will
ensure that the required peening specifications are achieved. Critical to the resource and cost efficiency of the process is selecting the right blast media. A blast media analysis will always help to
determine if the current media is right for the respective application.

Shot peening with compressed air blast guns can be run as a wet or dry
process. The advantages of the dry peening method are a higher blast intensity and the targeted blasting of specific surface areas. In addition, the
entire process and the blast media can be precisely controlled. The wet
blasting technology prevents the media from embedding in the workpieces and produces a lower surface roughness. Since wet blasting is
gentler than dry blasting, it is the ideal method for treating delicate
workpieces with thin walls without warping them. Each of the two peening
methods has its advantages. Therefore, the chosen method must be a perfect
fit for the respective application, especially concerning cost-
efficiency and quality of the peening results. Rösler offers a broad
spectrum of different machine types. This allows an objective
equipment selection and ensures that customers get the best possible
solution for their specific requirements.

All steps regarding process alteration and optimization, including the
processing trials and process evaluation, can be modified so that the shot
peening equipment can be quickly adapted to changing production conditions. This ensures consistent, high-quality peening results throughout the entire equipment life. And it guarantees that all demands for energy, resource and cost-efficiency are fully met. For more information visit rosler.com.