3D-Printing – Metals
Metals are used almost everywhere in many industrial sectors for a wide variety of purposes. Apart from construction and vehicle manufacturing, metals are also used primarily as conductors and semiconductors, coatings, electronic components or housing parts in electrical engineering. Especially here, in the automotive, medical, and aerospace sectors, the applications are often very special and require small, precisely fitting structures. In order to realize these, more and more modern manufacturing methods have been developed in the past, each bringing higher precision at lower costs and also lower material consumption. The so-called 3D printing processes in particular represent a significant step forward in this development.
Metal 3D printing processes include, above all, Direct Laser Metal Sintering (DMLS, also LPBF – Laser Power Bed Fusion), which is based on the powder bed melting process. In this process, the metal is presented as a powder and melted locally with pinpoint accuracy by an energy source, usually a laser, to create a 3D structure.
In CLAD (laser deposition or cladding, also DED – dorect emergy deposition – process), a metal powder is applied from a nozzle, similar to the ink of a real printer, in a quite similar process. However, at the nozzle exit, the powder is melted directly with a laser, so that quasi directly the liquid metal can be printed.
A combination of additive manufacturing and additive processing is the so-called cold cutting process or cold spraying. Here, fine metal particles are pressed with a carrier gas (usually helium) at high pressure through a fine nozzle, so that these deform plastically when they hit a substrate and thus form a layer without real melting, which can be processed directly. However, this process is rarely used due to its high cost.
In addition, there is also metal binder jetting. Similar to the plastic powder bedding process, here the metal is mixed with a binder and bonded to form a homogeneous mass. The resulting green part is then freed from the binder by thermal processes, i.e. by firing or laser heating, and given its final shape.
Also similar to the plastic process is the so-called fused deposition modeling (FDM), in which a metallic filament (usually made of low-melting metals or alloys) is simply heated until it softens and then applied in layers via a nozzle.
All of the above processes have in common that they do not work with every metal. The common metals for metallic 3D printing are aluminum and its alloys, steels and iron alloys, as well as materials such as gallium, indium, titanium, cobalt or chromium. Despite comparatively high costs, precious metals such as gold and silver are now also being used. Here, however, shaping is somewhat more difficult. Heavy metals and very hard or refractory metals are used little or not at all.
The most common applications of metallic 3D printing are primarily prototyping and research and development, especially when only individual parts and not series are to be produced. Here, mold making for a cast part is often very expensive and can be cleverly avoided with 3D printing. The energy costs saved compared to a cast workpiece are also not insignificant. So are the material savings on the often expensive metallic raw material. In addition, the advantages of metallic 3D printing cannot be dismissed, especially in the case of individually manufactured implants in medical technology or specially adapted machine spare parts.
In contrast to ceramic or polymer 3D printing, not all shapes or structures can be readily implemented in metal sintering or cold gas printing, since different metals have very different melting zones and it is therefore not always possible to apply mixtures or specific layers. Nevertheless, further research is currently being conducted on these methods in order to open up even more flexible and diverse applications in the future.
Thermal analysis can use its methods to characterize the metals produced in terms of their properties and help to identify deviations and differences between solidly manufactured and 3D-printed components. Melting points and phase transitions can be determined by means of DSC and the alloys can thus be optimally designed for use in 3D printing. Dilatometry can be used to show expansion behavior, as well as hardness and phase transitions. The thermal conductivity and heat transport properties of both the cured products and the powders and alloys can be well characterized using THB and laser flash techniques. And the thermo-electric properties such as electrical resistance, conductivity and also Seebeck coefficient can also be accurately determined using the methods of modern thermal analysis.