Alexander Leicht (photo by Marcus Folino)
Constant efforts are being made to improve product performance across all sectors of industry, ranging from consumer goods to space applications. To achieve this, innovative components are required that can provide better functionality through improved material properties and design. Additive manufacturing, or 3D printing, is a technique that offers a solution to some of these demands. The process supports the realization of advanced geometrical designs without the need for extensive machining in addition to the possibility of producing designs that would be impossible with other manufacturing methods.
Additive manufacturing covers many different technologies for a wide range of materials, from thermoplastics to metals, ceramics and composites. The process has existed for almost four decades and has primarily been used for rapid prototyping due to poor quality. Today, additive manufacturing has matured and can be used for the fabrication of high-end, fully functional parts with properties comparable to or better than those obtained through conventional manufacturing methods. Powder-based metal additive manufacturing is the sector of additive manufacturing technologies that has demonstrated the largest growth in the past decade. Laser powder bed fusion is one of most common powder-based metal additive manufacturing technologies. The process utilizes a high-power focused laser beam to selectively fuse metal powder particles and create compiles of 3D-shaped components.
This thesis focuses on the design possibilities and resulting material properties of the laser powder bed fusion processed components in relation to the process parameters. Focus is placed on stainless steel parts, and the thesis investigates the correlation between the microstructure and the properties, component quality and productivity. It is demonstrated that complex-shaped high-quality parts with properties as good as or better than materials produced via conventional technologies can easily be achieved at the current state of the art. The good mechanical properties are connected to a hierarchical microstructure, with features that span from millimeters to as small as nanometers, such as large elongated grains, melt pool boundaries, cells and precipitates. This thesis demonstrates a strong effect of the part design and build
orientation on both the microstructure and properties. Furthermore, by adjusting the process parameters, a four-fold increase in productivity was achieved without a significant change in the part quality. Such improved productivity increases the competitiveness of the process and allows for expansion into new, more price-sensitive sectors.