Metal Additive Manufacturing: Advances in technology

Additive manufacturing has emerged as a credible alternative to conventional processes. However, there are still many questions surrounding the most suitable materials, methods and applications for the use of additive manufacturing in conventional mechanical engineering. When should you adopt these technologies? Which methods should be chosen for which applications? Cetim’s cross-cutting thematic project on additive manufacturing has provided some initial answers for manufacturers.

On 21 March 2023, 71 manufacturers attended a day-long event in Saint-Etienne (France) to present the results of this cross-cutting thematic project. The project, which began in 2021, has yielded 18 technology watch notes that identified potential applications for each type of part and for various material-process pairs. In addition, five demonstrators based on real-life industrial cases have been produced, providing a better understanding of certain metal additive manufacturing processes.

Promising features of WAAM

Wire Arc Additive Manufacturing (WAAM) is well-suited to the production of large metal structures. The first demonstrator of the cross-cutting thematic project applied WAAM to the creation of eighty structural steel flanges, adding a new function to a part that was customarily made using mechanical welding, followed by an assessment of their fatigue strength.

Two wire deposition configurations were assessed: string bead welding (several string beads per deposited layer) and weave bead welding (a single weave bead per deposited layer). The findings were that both strategies had similar fabrication times, but that the surface finish obtained with these bead deposition enabled non-destructive inspection of the part, unlike the configuration with string bead deposition. This is a promising result for future qualification of the processes. In addition, the residual stresses generated by WAAM delay the appearance of fatigue cracks. Above all, these parts have twice the service life of the welded models. Lastly, comparisons between flanges made from steel and those made from high yield strength steel show that the high yield strength steel exhibits fatigue behaviour similar to that of a forged or machined part.

Metal Binder Jetting is going big

Metal Binder Jetting (MBJ) technology consists of two main stages: firstly, manufacturing the part and then consolidating it by de-binding and sintering. In connection with the cross-cutting thematic project, two demonstrators, based on real parts were made available by manufacturers who are members of the working group. These demonstrators have tested the limits of the MBJ method. The first is a cap and lock nut system supplied by Lisi Aerospace and the second is a hydraulic block from Liebherr France, designed for public works machinery.

Three MBJ machine architectures and their individual characteristics were assessed in the studies of these two parts. The results, based on the printing of 204 caps, show that the cost of production is still high, at around twenty euros per part. In the case of the hydraulic block, the part produced using MBJ exhibited poorer fatigue performance than its counterpart made with selective laser melting. This data can be used to identify the strength and limitations of design-material-process combinations and to improve the fatigue calculation models developed by Cetim. The study also showed that by addressing the design, MBJ technology could be used for more than just very small parts.

New functions for forging tools 

Two demonstrators of the cross-cutting thematic project helped to show the feasibility of the powder metallurgy method for producing complex forgings. The first involved producing a part with internal channels to cool the die during the forging process. The second was based on the printing of five steel jaws with a copper insert to increase the diffusion of heat to the active surface of the tool.

In this study, Cetim developed a reproduceable design-manufacturing approach, which demonstrates the benefits of taking into account the product-process pair in additive manufacturing. This approach is centred on proposing an “optimal” geometry for the part, which is gradually tailored in order to balance the constraints of the process with the expected functionalities of the part. The next stage will be to test the parts in production, in order to determine whether they can extend the service life of the tooling.

A dedicated database under development

In addition to producing demonstrators, this project has led to the creation of a dedicated metal additive manufacturing database which will initially be available in 2023 as a set of material-process performance datasheets. A new cross-cutting thematic project is also in the pipeline. Its aim is to work on low-cost processes for everyday mechanical engineering and standardisation.