VOL. 22 November ISSUE YEAR 2021

MFN Trainer Column

in Vol. 22 - November Issue - Year 2021
Profound Aspects To Shot Blasting Of Non-Ferrous Castings And Forgings

Even as a young boy, I had my first experiences in the processing of metals when I was allowed to watch my grandpa making sheet metal assemblies. I was so fascinated and enthusiastic about it that it was clear to me that I would also like to work with metals later. And that is how it happened, when I started my dual-education as a Die- & Toolmaker after I had finished high-school. However, I only found my entry in blasting business years later, when I started at Frohn GmbH in 2019. At that point in time, blasting was more of a work step for me that was known as deburring, deflashing or de-rusting, but when I got to know the blasting industry in all its facets with many interesting and experienced experts, I recognized the real reasons why components are bombarded with solid particles, either by means of shot peening or shot blasting.
In the past two and-a-half years, I have had the opportunity to get to know many large and interesting companies in this field, and I was able to take a closer look at their blasting processes. But especially when it comes to shot blasting in the aluminum, zinc, magnesium casting or forging industry respectively, an interesting topic kept coming up more profoundly; namely, the balancing between efficient and chemically neutral blasting at the same time. As we all know, the entire automotive industry is currently changing rapidly, and we are moving away from normal combustion engines to hybrid engines or purely electric motors in the drive-train.
 However, changes in the power-train are linked to a major disadvantage that car manufacturers are struggling with. The cars are being equipped with increasingly heavy components such as high-capacity batteries. As a result, other components in a vehicle must be reduced in weight and or redesigned in lighter and or stronger alloys; therefore, the manufacturers of lightweight components are under enormous pressure, not only that as more and more components are being built, the high pressure die-cast parts must also be made lighter and at the same time, more stable and stiffer without quality suffering. Perhaps that is the reason why many companies have taken a closer look at their blasting process in recent years and found a lot of potential. Among other things, investments were made in new and better blasting machines and work processes like automatic loading and unloading. Now it is time to continue progressing and use blasting media that are better tailored to the needs of the customer.
In this respect, the requirements are also growing in several points:
Surface appearance, surface roughness, deburring performance, lifetime & efficiency, and non-corrosive or non-staining properties, 
Over the last couple of months, many customers have asked more frequently about what kind of blasting media can be used, especially in respect to chemically neutral blasting. It seems that this topic will become more and more important in the future. When we talk about chemically neutral blasting, the main topic is how to minimize or better-avoid contact corrosion on the surface of the die-cast parts. But why is this topic becoming more and more important? In my opinion, this is due on the one hand to surface quality issues from the past, and on the other hand, to the currently increasing quality requirements. And for example, today´s end customer also places high demand on the appearance of the parts installed e.g. in a vehicle. 
But to answer the customer question, if this aspect is the focus, we have two options; namely, the use of zinc- or aluminum-alloy cut wire, if it comes to non-ferrous parts made of Zinc-, Al- or Mg-Alloys, and asking me in this regard, I would always prefer these two media to steel or stainless-steel abrasives, for example. Why? Because of the risk of contact corrosion on the surface, leading to discoloration and reduced anchor pattern for possibly coatings. If we look at the electrochemical potential series of metals, we can clearly see that zinc and aluminum abrasives are better-suited than steel or stainless-steel abrasives for shot-blasting substrates and components made of zinc, aluminum or magnesium alloys. 
By the way, if we take a closer look at the properties of zinc- or aluminum-alloy cut wire, we will see the further advantages. For example, the very long lifetime is a great advantage despite the higher procurement value. Furthermore, we have a significantly lower system wear-and-tear! Additionally, the risk of tool breakage in further mechanical processing due to wedged (hard) shot, sticking shot blast particles (made of mild or stainless steel) or shot-grains being carried over has also decreased significantly, eliminating the need for tool replacement and re-calibration.
All things considered, zinc- and aluminum-alloy cut wire are superior to the steel or stainless-steel abrasives despite their lower hardness and / or density, if the equipment- and operational parameters have been adjusted accordingly.
And last but not least, a positive side effect when consumption decreases due to the long lifetime is that the very high freight costs nowadays also decrease besides the regionally varying costs for waste disposal.
To be continued…

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