Additive manufacturing (3D printing) has developed rapidly in recent years and is increasingly used for small batch production in industry. Due to a wide variety of application fields, the material portfolio of the diverse 3D printing technologies is steadily growing. The particularly pronounced material flexibility of the powder bed-based laser process LBM (Laser Beam Melting) makes it the most widespread metallic 3D printing process. Thin layers of metal powder are applied to a substrate in this process, locally melted by laser energy and bonded to the previous layer. In this way, many layers create a three-dimensional object. This additive principle results in new degrees of freedom in design. In addition, complex shapes for materials can be generated, which are conventionally very difficult to machine, for example because of their high hardness. Further advantages of the LBM include flexibility, the possibility of integral construction and functional integration, improved logistics, reduced development times and individual products. Basically, LBM offers comparable material density and excellent material properties compared to conventional processes. The technology is therefore very well suited for the production of highly stressed, optimized parts for lightweight construction or for functional applications in military technology.

So far, few alloys for a wide range of applications

Due to the currently complex parameter development of new alloys for LBM-based 3D printing, a few selected alloys are used for a wide range of applications. Aluminum and titanium alloys serve the lightweight construction market. Nickel-based alloys are suitable for high-temperature applications, stainless steel for mechanical engineering and the production of art objects, cobalt-chrome and titanium alloys cover the medical technology market, and high-strength steels are used for the production of tools. Areas of application with a need for alternative materials are currently only served to a limited extent. Especially for dynamic applications, such as in the field of vehicle crashes and especially in many areas of defense technology, there are currently no commercially suitable materials. The Fraunhofer EMI is therefore developing its own production parameters for processing special materials. One focus here is the defense technology area of ​​protection and effectiveness.

High quality heavy metals from the 3D printer

For example, parameters for the production of high quality tungsten have been developed. The element is characterized by its high density and the highest melting point of all metals. The processing of refractory metals such as tungsten shows that the LBM process can also process conventionally difficult-to-process metals, although these are generally regarded as poorly weldable and the LBM process basically resembles a laser welding process. The parameter development for tungsten presented the scientists at EMI with particular challenges. Due to the high local energy yield and high cooling rates when working with a laser beam, cracking processes occur in the microstructure. The formation of microcracks was successfully minimized in the course of the work. The result is a brittle material with a density of about 19,2 grams per cubic centimeter, a highly micro-crack reduced and dense-optimized pure tungsten from the 3D printer. The material is suitable for example for ammunition applications or special applications, such as collimators for X-ray detectors. Further areas of application are electrical engineering, medical technology and application fields with the highest thermal requirements.

Efficient parameter development and optimization thanks to in-house methodology

An efficient, in-house method is used to develop the parameter sets. This enables the process parameters to be developed comparatively quickly and with little effort. In this way, particularly expensive special materials can also be developed much more cheaply. The methodology is based on the consideration of the interaction between the laser beam and metal powder as well as on statistical test plans. The knowledge gained will later also be used for application-specific parameter optimization and for parameter adjustment for specific components and their requirements for production. For the first characterization of the resulting materials, fast methods such as determining the density are used. Once the parameter set is fully developed, the material is characterized using the most modern measuring equipment, such as electron backscattering (EBSD) or micro-CT images, and the parameters are further refined.

The development of an in-house methodology for parameter development for LBM materials enables the efficient generation of production parameters and thus the use of optimal materials for specific fields of application. It was shown that even difficult-to-process materials can be produced in high quality in this way. It is also conceivable in the future to develop new types of alloys that cannot be realized conventionally. For example, the high cooling rate of the process could enable a higher solubility of alloying elements and thus new material properties. When selecting future alloys, however, not only the area of ​​application must be taken into account, but also the expanded scope for solutions with regard to the newly available design freedom. If requirements are, for example, solved conventionally by geometries based on half-tools (for example on plates), these may be solved more efficiently with the use of additive processes using alternative geometries (for example using grid elements). Based on the new geometry, it is important to select a suitable material.

Source: Fraunhofer EMI