Comparative analysis of the Shot peening effect on the dynamic root strength of gears, treated with different parameters in different heat treatment methods [Part 1]

Hello, dear FerroECOBlast Blog readers!
Time and new communication technologies are a huge challenge for my generation, and I can honestly say that despite my almost seven decades, writing my first blog feels quite challenging. It is a great test for me and I’m curious to hear your response, the readers’ and followers’ of our blog.
In this series of posts, I want to describe and explain some of the practical challenges and truths about the shot peening of gears and gear shafts, the most heavily loaded transmission elements in the automotive, aerospace and many other industries.

Why start with this topic?

Throughout my long career, there have been and still are countless questions from our customers and professional experts about the problems and new challenges of surface treatment of heavily loaded metal parts.

The first dilemma we want to clear up with the client is, where does their product and it’s use rank in the market? Is it a large-scale and non-demanding group of gears and reducers (this is still dominant), or is it among the highly technologically demanding, heavily loaded, higher precision, more reliable, and repeatable products? Which kind of shot peening process is more suitable for their product? Processing with a turbine (wheel blast) or with compressed air (nozzle)? The answer to this first question is not easy.

Shot peening with a turbine is simpler and has its advantages in high processing capacity and lower energy consumption, but the basic principles of micro forging in terms of accuracy and controlled processing and repeatability do not correspond to the internationally accepted term for shot peening. The process is suitable for high-consumption and less demanding products, which improve their mechanical properties in a certain average range, but the characteristics of the product differ significantly from product to product and occasional fractures during operation are not excluded and are unpredictable.

A more suitable procedure is shot peening with compressed air and a controlled flow of medium through the nozzle. Here, all key processing parameters (air pressure, size, shape, and quantity of abrasive, distance, angle,…) are fully adjustable and controlled. The process is 100% repeatable and documented for each piece separately. As a result, the equipment for shot peening with compressed air is highly demanding and the process itself is slower, as nozzle shot peening is performed individually – piece by piece with a precisely directed and controlled moving nozzle on a specific surface.

Another dilemma we need to resolve with the client is the question of their gear and shaft improvement process, i.e. the “heat treatment process”. At this stage, we can already advise the optimal methods and also the right shot peening equipment; so, the client can do his own economic study and make his decision independently.

Shot peening is the common technology of surface treatment of gears after heat treatment. It’s a very old process, about as old as I am, but it is a big challenge for new companies and new generations of engineers who want to improve mechanical properties and produce first-class, lightweight gears that run as quietly as possible and have maximum elongation lifespan. The eternal question that follows in the first contacts with potential customers is, in addition to the choice of appropriate shot peening equipment, to advise them about the appropriate technology and materials and prescribe the right procedures for which we stand behind and guarantee.

Well, this is usually where it gets complicated: there are as many, often specific, manufacturing processes and heat treatments of gears as there are manufacturers. Shot peening usually benefits gears a lot, but it can also deteriorate them, depending on the previously applied improvement technology. So, who can – regardless of the vast available literature, studies, and professional articles – correctly identify each specific case and give sovereign advice? Here, first and foremost, we clearly see the advantage of our accumulated knowledge and decades of experience, and above all our own research and tests.

In future sequels, I will present the three most common heat treatment processes and prove the effects of shot peening on samples from our own two-year study, which we completed in 2019 with the help of the most eminent partners and institutions, assuming that 85% of gear manufacturers use virtually the same base material, DIN 18CrNiMo7-6 structural steel with special properties.

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