Politecnico di Torino | Servizi per la didattica

KEYWORD

Comparative analysis of coatings applicable to large sheet-drawing dies, for the replacement of hexavalent chromium

azienda Thesis in external company

Reference persons PAOLO MATTEIS, RAFFAELLA SESANA

External reference persons Guido Ferrarese, MA Srl.

Description The larger components of the car body are normally made by deep drawing, starting from steel sheets, using cast iron molds, possibly subjected to local surface hardening treatments and/or equipped with steel inserts. To ensure high wear resistance to low friction with the sheet metal, these molds are normally coated with chromium, using low-temperature processes made with baths containing hexavalent chromium ions. In the coming years, the use of hexavalent chromium will be banned in the European Union due to its toxicity; therefore, possible alternative coatings are examined.
These coatings will have to satisfy the requirements of high wear resistance and low friction with the sheet metal, but they will also have to be made at low temperatures so as not to interfere either with the previous local hardening treatments, or with any welding overlays, which often are necessary for the empirical setup of the molds.
(In fact, the deformation path of the sheet metal during molding and its elastic return when the mold is opened cannot be calculated a priori with such precision as to guarantee compliance with the design tolerances already on the first molded piece. Therefore, after the manufacturing of the molds, but before their coating, an empirical adjustment is carried out, by means of molding tests and corrections made on the mold itself, not only by removing material by milling, but also by adding material by welding.)
In this context, the thesis student will carry out a theoretical examination of the problem and contribute to the evaluation of different types of coatings. These coatings will be made (by third-party companies) on small simulacra, which will be manufactured with the material of the molds and in some cases subjected to local hardening and/or welding overlays before coating. During the thesis work, the coated simulacra will be subjected both to functional tests, performed in the company, and to laboratory characterizations, mainly performed in the polytechnic laboratories; the latter may include both metallographic and hardness tests and tribological tests of friction and wear.
The work in the company will mainly take place in the plant of the CLN group in Rivoli (TO). At the request of the student, the thesis can be combined with an internship in the same company. The thesis proposal is open to both national and international students, and the work can be carried out, at the student's choice, in Italian or English.