Advances in Mould Making through L-PBF Additive Manufacturing: From Geometric Freedom to New Materials Design ^†

Laser Powder Bed Fusion (L-PBF) is a powerful powder-based additive manufacturing (AM) technology that can complement conventional mould manufacturing. This breakthrough technology has dramatically changed the manufacturing process by improving resource efficiency, opening the possibility of innovative designs, reducing weight and waste, and developing new microstructures. The incorporation of conformal cooling channels into moulds has been possible since the 1990s, when the first metal powder-based AM systems were introduced to the market. Since manufacturing the cooling system is the most time-consuming step in the production of injection moulds, reducing this step can increase production speed while enabling higher-quality moulded parts with less scrap. To date, however, the use of AM in mould making has remained a niche area compared to conventional subtractive technologies, largely due to a conservative industry’s resistance to such a transformative approach. For this reason, it is necessary to thoroughly understand the benefits that can be achieved by integrating this technology. In addition to geometric freedom, it is possible to design new microstructures that differ from those of conventional materials, which can have a direct impact on material properties. Our comparative study with a low carbon maraging steel 18Ni300 showed that the microstructure of this material manufactured with L-PBF is highly refined and consists of cells and dendrites that are drastically different from those produced by conventional methods such as casting. This result had a great impact on the mechanical properties and wear resistance. The steel with refined microstructure had a specific wear 33% lower than that of cast material.

Due to its exceptional wear resistance, AISI H13 carbon tool steel is normally used for mould making. However, processing of this steel by L-PBF is generally problematic due to cracking and low wettability. Despite this, our small-scale experiments have shown that processing by L-PBF is possible in a narrow processing window if carefully optimised parameters are used, i.e., low scanning speed and low laser powers to reduce thermal gradients.

The development of nanocomposites by L-PBF using low-carbon steels as matrix and nanometric reinforcement phases that have high hardness and refractoriness remains a more reliable approach to obtain materials with suitable properties for moulds and high processability by L-PBF. With reinforcement concentration up to 7.0% by volume, 18Ni300/TiC nanocomposites were successfully manufactured by L-PBF with about one order of magnitude improvement in wear resistance compared to the unreinforced matrix. The combined effect of reinforcement due to the presence of TiC in the microstructure and grain refinement due to rapid cooling during L-PBF are responsible for this result. Despite the increased wear resistance of the 18Ni300/TiC nanocomposite compared to the unreinforced material, our study showed that its wear resistance is lower than that of the H13 steel processed with L-PBF. Nevertheless, and due to the need to find economical and reliable solutions for the industry, these nanocomposite materials are considered to have a high potential. In this sense, the steps under investigation focus on the application and real tests of 18Ni300/TiC nanocomposites in plastic injection moulds.