VOL. 22 March ISSUE YEAR 2021

Shot Peening in the Automotive Industry

in Vol. 22 - March Issue - Year 2021
AM, Shot Peening And Automotive: A Matter Of Costs
Mario Guagliano

Mario Guagliano

In spite of the several supposed potential advantages and improvements, additive manufacturing processes are finding obstacles and problems in replacing traditional substrative processes, in particular in mass production, such as in the automotive industry.
I think I am not wrong if I affirm that AM for production is limited to some peculiar and niche sectors where the ability to build highly customized and functionalized products is the priority (orthopedic implants are a typical example), and that real industrialization must pass through the solution of several still open issues. 
Among these latter, maybe the most relevant one is related to the costs, since it is still true that in most cases, the challenge of offering the most affordable cost is generally won by traditional processes. Why?
Let’s say that the total AM cost is the sum of three different terms. The first is related to the cost of the powder: the cost of 1kg of the powder can be even 5-10 times more expensive than the raw material. This means that the AMed part should be 5-10 times lighter than the part produced with subtractive processes, or that the buy-to-fly ratio of the existing part must be 5-fold that or more to make AM competitive. 
The second term is related to the hourly cost of an AM machine. The general perception is that the cost of these plants is quite high while the production rate is rather low, and this makes the hourly cost increase. However, a recent market analysis shows that the cost of the plants, even if still important, is constantly decreasing, and that the deposition rate is on the way to being improved by using dual or quad-laser machines, so this cost should not be such a worry.
But there is also the third term of the total cost of additive manufacturing, and it is related to the pre- and post-processing. We all know that the quality of AMed parts is generally not satisfactory and that the defects, the surface state and the mechanical properties are a real problem that make post-processing necessary before these parts can be used; however, people might not be aware that, according to a report published on the Wholers Reports, the costs related to pre/post-processing are around 40% of the total cost of an additive manufactured part. This is impressive, and is a serious obstacle for extensive AM introduction in the automotive industry.
At the same time, shot peening can be seen as an attractive process to improve the properties of AM parts (btw, my group and I have done some studies concerning this, so please ask me for information if you are interested) and reduce the total post-processing time and cost. 
But to achieve this goal, we need to address research projects aiming to understand how shot peening affects the behavior of these materials: indeed, the initial status of the AM parts is quite different with respect to traditional ones, and it is not clear what are the best combinations of peening parameters to get the maximum increment of fatigue strength or other properties of interest, while the relative importance of the main effects of shot peening on these materials is also undetermined.  Another point is that effort must be devoted to the development of plants able to efficiently implement shot peening in an AM production line. From an economic point of view, this point could be even more important.
If we will be able to move in this direction, we will be probably able to skip some post-treatment step, making shot peening more and more attractive in this new and important manufacturing route.

Shot Peening in the Automotive Industry
by Mario Guagliano
Contributing Editor MFN and
Full Professor of Technical University of Milan
20156 Milan, Italy
E-mail: mario@mfn.li