Case History: conversion of track axle from steel to ADI

Track axle in ADI for combine harvesters

Manufacturing techniques, uses and benefits of a track axle for combine harvesters in ADI ductile iron compared with steel

A case history that describes how it was possible to convert (and relative benefits) a track axle for combine harvesters in ADI1050-6 ductile iron previously produced in forged steel. This axle plays a very important role. It connects the two right and left tracks to the frame of the combine harvester, supporting its weight.

Industrial applications of track axle: large combine harvesters

The track axle is suited for large sized combine harvesters. This type of machine is used in the agricultural sector, in particular to treat large areas.
Combine harvesters can be equipped with a classic wheel system or, when necessary and depending on the type of work to be carried out, they can be equipped with a tracked system with rubber track, allowing the vehicle to travel both off-road, even on wet earth (because it doesn’t overly compact the soil) and on-road.

Advantages and benefits of the track axle in austempered ductile iron ADI

Weight reduction -22%

The solution in ADI1050-6 reduces the weight of the machined part from 90 kg to 70 kg

Less fuel consumption

By reducing the total weight of each vehicle by 40 kg (20 kg per track axle), it is possible to save on fuel used to operate the vehicle.

Material waste

The net-to-shape approach makes it possible to obtain a raw profile in ADI close to that of the machined part, thus minimising waste resulting from mechanical machining

Lower mechanical machining costs

The net-to-shape approach therefore reduces the overall amount of mechanical machining and therefore the relative costs.

Lower Total Cost

The solution in ADI therefore resulted in a total cost less than that of the steel solution, starting from the production of the raw casting through to the machined part.

Reasons for conversion of track axle from steel to ADI

The reasons that drove the client to consider the conversion from forged steel to ADI ductile iron were manifold. The most important were no doubt the reduction in weight and reduced manufacturing costs. The solution in 42CrMo4V quenched and tempered steel was limited due to the technological process (forging 150 kg of raw steel requires very powerful and costly presses), making it difficult to achieve these objectives, in addition to the high number of mechanical processes necessary to achieve the final desired shape.

Starting solution – track axle in forged steel

Fatigue limit
σAG; PS50%
42CrMo4V + Bonificato (trafilato)
650 MPa
900-1100 MPa
420 MPa

Thickness ≥ 100 mm (in reference to old thickness in steel)

Based on the client’s objectives, at Zanardi Fonderie we assessed whether austempered ductile iron ADI would be able to replace the steel, before going on to define the required shape.

Final solution – track axle in ADI1050-6 ductile iron

Fatigue limit
σAG; PS50%
700 MPa
970 MPa
360 MPa

Values ​​by piece – thickness 30-60 mm (in reference to the new thickness in ADI from where the test-tube is obtained)

The following graph shows the comparison between 42CrMo4V + quenched and tempered (rolled) steel and grade ADI1050-6. As can be seen, ADI1050-6 ductile iron has equivalent and in some cases superior characteristics to those of the current steel.

After comparing the materials, together with the client we analysed how to redesign the part in an ADI1050 austempered ductile iron casting, seeking to exploit all the benefits of this material such as:

  • lightness: thanks to a specific weight 10% lower than that of steel
  • free design: the improved “castability” of cast iron makes it possible to obtain complex design shapes very close to the final shape of the part
  • it was possible to discharge the central axis, not stressed, using a sand core; this allowed a significant reduction in weight.

Selection criteria

  • Mechanical strength
  • Fatigue
  • Lightening of part
  • Final cost of part

The solution in ADI1050-6 austempered ductile iron therefore allowed the part to be redesigned in a net-to-shape perspective, with a raw profile very close to that of the machined casting, thus also reducing the amount of mechanical machining required to obtain the external profile. Thanks to the greater design freedom of casting compared to forging, it was also possible to create the internal hole in the core.

Thanks to similar mechanical properties, lower specific weight and revised and improved shape, it was possible to obtain a high-performance, lightweight and more affordable component.

Manufacturing techniques of track axle: comparison of ADI ductile iron and steel

From a technical and economic point of view, the steel forging process may not be ideal for medium-small series production and very heavy units. The process effectively involved forging a 150 kg component and therefore the mechanical removal of almost 40% of unnecessary material. The solution in ADI1050 ductile iron on the other hand made it possible to obtain a raw casting very similar to the machined part.

Table of comparison between the two solutions

Previous solution
Solution in ADI
42CrMo4V + Reclaimed
Final component weight
150 kg
90 kg
-45 %
90 kg
70 kg
-22 %

Case History

Real cases explaining the development of client projects