Case History: Attachment frame for snow groomer with parallel tiller in ADI1050-6

Articulated arm for snow cat in austempered ductile cast iron

But what was the driving force behind the change in technology? The collaboration with Prinoth AG/SPA was guided by two objectives: firstly, to increase the mechanical performance of the articulated attachment to obtain greater freedom of movement and, secondly, to reduce assembly time. In fact, the manufacture of the S355J2 welded steel attachment required the assembly of several parts, resulting in long assembly times. The objectives were achieved by manufacturing the component in ADI austempered ductile cast iron. This has superior mechanical and fatigue strength properties compared to S355J2 steel, with the additional and important benefit of greater design freedom and a more streamlined and simplified procurement and production process for the customer. The ADI1050-6 cast iron therefore allowed the joint to be designed and manufactured as a single cast iron casting (monolithic component). The design benefit then translated into a more streamlined, more stable production process and greater manufacturing precision.

The ADI1050-6 solution also provides a component that is more resistant to the static and dynamic stresses that the vehicle must withstand during use, thanks to the elimination of weld seams and thermally modified areas. The ADI1050-6 monolithic solution also benefits maintenance activities. How? The cross-sections of the coupling holes with the tool arms are obtained by casting and chip removal, rather than by fitting of bushes that are subject to wear. As a result, ADI’s surface hardness ensures reduced wear of the working area, preserving the geometry of the housings over time and avoiding frequent replacement of the bushes in the workshop.

The excellent castability of ductile cast iron and the flexibility of the heat treatment process for ductile cast iron make it possible to meet all application requirements.

The freedom with which the component is designed is at the basis for obtaining a single element ready for assembly. This characteristic of cast iron made it possible to obtain an optimised geometry, particularly in relation to the critical points of the component, in order to guarantee the required structural strength. Consequently, the choice of monolithic casting in austempered cast iron (ADI1050-6) also increased the load bearing capacity. Not only is the foundry process more stable and repeatable than welding, but it also eliminates weld seams, thermally modified areas that are often a critical and fracture point in welded components.

Tensile and fatigue test performed on test specimens obtained from separately cast samples Ø25 mm. The fatigue limit on smooth surfaces (R-1) was obtained by testing Ø6.5 mm smooth test specimens machined with the Short Stair Case method (run out at 5ML of cycles). In reality, the workpiece has a variable thickness.

The co-design activity was fundamental in helping the customer to choose the most suitable material for this application, according to the technical requirements.
Previous experience with technological solutions in steel had highlighted the critical points just mentioned, which led the customer to evaluate austempered ductile iron as the best alternative for the manufacture of the attachment frame for snow cats.

Previously manufactured by welding as many as 21 plates in S355J2 with bushes keyed into the joint holes, this console is now manufactured as a monolithic component in EN-GJS-1050-6 (ADI1050-6), eliminating welding altogether.