The Michelin plant located in Cuneo is the largest plant of the group in Europe for the production of car tires. The entire tire production cycle takes place there: from raw material processing, to the production of semi-finished products, to the assembly and vulcanization of the finished product.
Given such a structured process, there is a large amount of machinery, which in turn uses a large quantity of consumables. Among these machines, at the beginning of the production chain, are the Previero mills, each using 12 blades (6 fixed and 6 rotating) made of special steel to shred natural rubber bales and prepare them for subsequent processing steps.
These blades, in contact with a viscous and abrasive material like rubber, are subject to violent impacts and rapid wear, which requires, in the colder periods of the year, resharpening the blade every 10 days and the definitive disposal of the component after about 30 days.
Such a rapid turnover has various negative aspects: the need for a large stock of components in the warehouse, supply from a single manufacturer, and finally the continuous disposal of a quantity of valuable steel that could be destined for other purposes.
The company’s drive for innovation has led to the search for solutions that could provide improvements over the current scenario while preserving the product’s quality level. In this context, Michelin, with the support of the CIM Competence Center, decided to perform an additive repair using one of the machines in the Additive Manufacturing Pilot Line, the Directed Energy Deposition (DED).
The solution involved selecting the best material available on the market that was also compatible with the base material, researching a set of process parameters that would ensure a good microstructure while also achieving the hardness target, and developing strategies to avoid hot cracking in a material with extreme characteristics. AISI H13 steel was chosen, from the same family as the base material but with superior mechanical properties. Following experimental tests, a process capable of regenerating a blade in 2.5 hours while meeting all required specifications was achieved.
The induction hardening step that normally occurs for new blades was skipped because the additive process compensates for the hardening, already reaching the required hardness target during the deposition of the overlay.
CIM provided the expertise and assets to conduct both the feasibility study and the prototype production. The Additive Manufacturing Line seeks to spread additive technology where it makes sense to use it, and in this case, the results seem to confirm the legitimacy of this approach.
During the testing phase, which took place in the winter period (representing the worst case for this specific application), the prototype of the repaired blade, of the rotating type, was mounted in a Previero mill along with 5 other new blades, showing half the wear in the same working time.
It was then requested to provide 6 identically repaired blades, which were tested in the same way, confirming the previous result.
In this specific case, the repair exceeded expectations, elevating the initial product from scrap to a component with characteristics superior to the new one, with the possibility of repeating the treatment multiple times, transforming a linear product life cycle into a circular one.
The partnership between CIM and Michelin continued in further plant improvement projects, involving other components and other production areas.
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