AddKoSt

Additive manufacturing of high-carbon steels using Laser Powder Bed Fusion

2023, 70 pages

Project no. 510
Final report

Abstract:

The aim of the project was the qualification of high-carbon steels for the PBF-LB/M process and the application of these materials in the additive manufacturing of tool holders, base bodies and clamping devices. High-carbon tool steels, which are commonly used in conventional production in the tool industry, have so far hardly been used in additive manufacturing due to their high tendency to cold cracking. In the project, the three materials 1.2343, 1.2714 and 1.2885 were investigated in close cooperation with the industrial partners accompanying the project and successfully qualified for the PBF-LB/M process using various process routes. An additive structure at a processing temperature of 350 °C - 450 °C is favored, which specifically exploits the transformation gaps in the materials. With this processing temperature, which is set via a build plate preheater, the carbon-martensitic hardenable materials could be processed without cold cracking and with few pores. As a result, the components are hardened immediately after the additive build-up and have a fine cellular structure characteristic of additive processing due to the rapid solidification. Thermal post-processing is therefore limited to annealing treatment. Compared to conventional heat treatment, the material systems show improved tempering resistance and an increased secondary hardness maximum, if present. Dimensional and surface tolerances achievable in additive manufacturing were optimized through the development of edge exposure parameters and tested in a geometry study on tool-characteristic features. They meet the requirements of industrial tool manufacturers but, as expected, require mechanical reworking on functional surfaces such as plate seats. The process and material-related findings of the project have been applied in two industrial application scenarios. In both cases, rotating milling tools were functionally optimized with the degrees of freedom of the additive manufacturing process, whereby design recommendations from the results of the geometry study were incorporated. The functional target variables were optimized cooling channels, a reduction in weight and an increase in rigidity through topology optimization as well as the hybrid structure of the tool body on tool interfaces. Both tools were successfully manufactured and functionally tested.

The project also identified interesting approaches for further optimization of the process routes. Promising research potential is seen in particular in selective in-situ heat treatment through targeted laser energy input during additive construction. This allows graded material properties to be generated within a component, which reduces the effort required for mechanical reworking and increases the functional benefits of the tool bodies.

The aim of the research project has been achieved.