A Portugal-based consortium led by equipment manufacturer Adira Metal Forming Solutions seeks to facilitate the enlargement of the selective laser melting (SLM) additive manufacturing process for large-format metal parts. The project, SLM-XL, brings on partners from the Instituto Superior Técnico, the Universidade Nova de Lisboa Faculdade de Ciência e Tecnologia and end user Manuel Conceição Graça (MCG), a Portuguese producer of automotive parts.
One of the main challenges facing selective laser melting processes—also known as laser powder bed fusion (LPBF) or direct metal laser sintering (DMLS)—is scale. Currently, the process is well suited to the economical production of small metal parts with up to 99.9% relative density, but there has been little success in printing large-scale components. Most attempts to do so have resulted in compromised mechanical properties.
The SLM-XL consortium, however, addresses these challenges by proposing a comprehensive methodology for selecting parameters for printing large-format metal parts. As part of the project, the research and industry partners are tasked with the production of 316L stainless steel materials with a prototype SLM machine developed by Adira. At this stage, the project is investigating a methodology for selecting parameters for parts printed from 316L as well as advancing the development of the final prototype machine.
In the SLM process, thin layers of metal powders are melted by a precision laser layer by layer, gradually building up a complex geometry. The process is recognized for its capacity to produce complex shapes with high structural integrity as well as to affordably achieve low volume production for metal parts.
The ability to 3D print large-format parts using the SLM process creates opportunities for quickly and efficiently producing low volume parts of any length and height that leverage the benefits of SLM (design freedom and production flexibility). One particularly interesting application area could be in producing and prototyping molds—a process which is currently time and cost intensive.
One of the primary difficulties in scaling the process up has to do with the microstructure and mechanical properties of 3D printed metal parts, as they show anisotropy and position-depending properties. In large-format LPBF systems, the position-depending changes in microstructure and mechanical properties are more pronounced compared to smaller machines.
Adira is making headway in addressing the challenge and has moved from the design stage into the prototyping stage. The prototype system being used in the SLM-XL project to produce samples has already been showcased at a number of expos. In 2017, the technology won in the Product Innovation category at COTEC-ANI because of its Tiled Laser Melting (TLM) printing approach.
Currently, the SLM-XL consortium is exploring the influence of an enlarged build envelope on the porosity and mechanical properties of 316L stainless steel samples. The research aims to fill gaps that exist in the understanding of correlations between process parameters and mechanical properties in high-power LPBF systems with increased build rates. For example, extended power lasers of up to 1 kW create solidification conditions that change a part’s microstructure in terms of size of dendrites and grains.
The SLM-XL project is now focused on investigating the relationship between process parameters—such as laser power, scan speed, layer orientation, hatch distance, etc.—on the density, microstructure and mechanical properties of 316L samples with varying geometric characteristics and produced in different parts of the powder bed.
Results from the research show that in order to assure at least 99% density across the entire build envelope of a system with a volume of 1 m3, the users must adjust parameters throughout the print process, as the outer zones of the bed are reached. The research partners are proposing a methodology to perform these adjustments.