Case History: axle pin
Axle pin in ADI for modular vehicles, self-propelled vehicles, trailers and heavy loads
Applications, construction technique and benefits of an axle pin produced by Zanardi Fonderie
The case history describes the development and construction of an axle pin in austempered ductile iron ADI800-10 (or lifting pin) for self-propelled modular vehicles, modular trailers for heavy loads, special self-propelled vehicles for industrial applications, commonly used to carry extremely large and heavy objects of various nature and shape (boats, space modules, wind power equipment, mining machinery and more), either on-road or in work sites or factories. Moreover, we provide a qualitative comparison between an axle pin in austempered ductile iron ADI and another in steel.
The sector of reference is off-road vehicles.
Industrial applications of axle pin
The industrial application of an axle pin allows self-propelled vehicles and trailers to move and support the transferred loads. They are equipped with dozens of wheel axles composed of ‘compass’ hydraulic suspension systems. These suspension systems allow the axle not only to support the transported weight, but also to lift or lower the height of the self-propelled system or trailer depending on logistical or transport needs. The axle pin in ADI800-10 plays a key role in allowing this type of support and lifting/lowering of the platform.
Benefits of an axle pin constructed in austempered ductile iron ADI
The axle pin in austempered ductile iron ADI offers clear benefits with respect to the same part made from quenched and tempered steel. The table shows the benefits of the part manufactured in ADI.
Increased maximum capacity of axle +25%
Increased maximum capacity of axle The capacity of each axle increased from 40 t to 50 t
Reduced manufacturing costs
The unique solution in ADI ductile iron allowed an important reduction in manufacturing costs and the complexity of the supply chain, eliminating the additional heat treatment and significantly reducing the cost of mechanical processing
No increase in weight
Minimum difference in weight with respect to the previous solution (from 99 kg to 101 kg)
Elimination of stress zones
The development of a single component allowed the almost complete elimination of the stress zones typically present in the weld points, which required additional inspection.
Improved fatigue behaviour
The solution in steel did not guarantee fatigue strength such as to increase the capacity to 50 t per axle
Problem solved with axle pin in ADI
The client’s main aim was to achieve a capacity of 50 t for each axle (hence equal to +25%) without increasing the weight of the pin and in respect of the geometric limits already defined for the ‘compass’ hydraulic suspension system. The problem was solved thanks to the development of the part in austempered ductile iron ADI.
In fact, prior to the version in ADI ductile iron, the axle pin was made from welded steel, comprised of 8 different components, some in S690QL steel and others in S355JR steel, combined to obtain the complex design shape, all for a total weight of 99 kg. This solution allowed each axle to have a capacity of 40 t (20 t per suspension system and therefore per axle pin).
Starting solution – with axle in steel
To achieve the client’s objective (+25% capacity for a total of 50 tonnes per axle) without increasing the total weight of the part and in respect of the geometric limits already defined for the ‘compass’ hydraulic suspension system, there were two possibilities:
- maintain the current process, switching to higher performing S890QL steel
- change the technology and material, opting for a single casting in austempered ductile iron grade ADI800-10
The two possible solutions to achieve the objective
- Mechanical strength
- Final cost of part
The solution in austempered ductile iron ADI800-10 allowed first and foremost, a single foundry casting, thus remarkably simplifying the supply chain and development process. The result was in fact the elimination of the machining, preparation and welding stages of 8 parts in steel (S690QL and S355JR) and relative inspection of the welded zones.
The FEM analysis of the two solutions demonstrated that the solution in ADI800-10 was the higher performing of the two, for the following reasons:
- improved fatigue behaviour
- improved fatigue behaviour- elimination of stress concentrations (zones that were typically created in the joints between the two welded parts)
This allowed the development of an improved component without increasing its weight, despite the mechanical properties of the S890QL steel being superior to those of the ADI800-10.
Construction methods and techniques of the axle pin: a comparison between ADI ductile iron and steel
The austempered ductile iron technology allowed the development of a single casting in ADI800-10 unlike the previous version in welded steel, which required the assembly of no less than 8 components.