Effect of edge preparation.

In line with this holistic approach, Surcoatec Deutschland, coating experts from Düren, have developed multipurpose coatings (MpC). These intelligent and self-adapting coatings are versatile, multi-alloyed and nano-structured. Thanks to their adaptive character, they are ideally suited to the requirements of different applications. They score points for their high temperature and phase stability, low thermal conductivity, high hardness combined with good toughness and low coefficients of friction. The specific production process and the unique concept are based on a phase mixture and the nano-structured layer design. This allows the adaptive and therefore multifunctional character of the coatings to be specifically adjusted.

As all-rounders, they are widely used for machining unalloyed, alloyed, stainless and high-strength steels, but also for so-called "exotic" difficult-to-machine materials such as Ni-based or Ti alloys. They can be fine-tuned for machining aluminum, non-ferrous metals and stainless steels by micro-alloying. Intelligent tool concepts consisting of coordinated micro-geometry, surface structuring and adaptive MpC coating therefore offer equally powerful solutions for these materials with a high tendency to adhere. The multifunctional use of tools makes it possible to streamline production processes and reduce the number of variants.

Customized tetrahedral amorphous carbon layers (ta-C)

The use of lightweight materials such as aluminum and composite materials is increasingly becoming the focus of production. Where classic hard material coatings are not sufficient and diamond coatings are actually "overdressed" or unsuitable for the tool materials, the ta-C coating, a tetrahedrally coordinated, hydrogen-free amorphous DLC (Diamond-Like Carbon) coating, fills the gap.

Due to the combination of high resistance to abrasion and low adhesion tendency, ta-C coatings are recommended for machining, for example, aircraft aluminum (_AlZn5.5MgCu with high strength), soft aluminum with a tendency to adhere, highly abrasive aluminum alloys with a high Si content and composite materials. The micrometer-thin ta-C coatings adapt to the given tool contour and impress the user with their dimensional accuracy, integrity and precision. Sharp cutting edges of cutting tools are coated evenly and reliably.

Left: Self-adaptive multifunctional coatings: MpC-coated precision tools. Right: ta-C: contour-true and precise tool coating for machining Al alloys up to 12 % Si, MMCs, wood and paper. © Surcoatec Germany

ta-C coatings are characterized by a high sp3 content or diamond content, which is 70 to 85 percent depending on the application-specific process control. Hardness values of 45-80 GPa, very low coefficients of friction, chemical inertness and a pressure or load-independent temperature stability of approx. 500 °C are further properties that have a positive influence on tool use. A unique production and process technology results in smooth coatings. The choice of carbide for coating tools with ta-C is not restricted, which is an additional benefit for users. Even tools and functional components made of HSS and materials with low tempering resistance can be coated with ta-C due to the low deposition temperature of < 200 °C.

Surface structuring as a design element

In the future, coating and surface structuring will be considered more than ever as a design element in the optimal design of coated composite bodies such as precision tools. In view of the rapid development of innovative manufacturing processes such as additive manufacturing, 3D metal printing by laser beam melting (LBM), selective laser sintering (SLS) or metal printing and subsequent microwave sintering and various other processes, completely new design possibilities are emerging for composite components designed to be suitable for coating. In many cases, the surface quality of printed metal components is still not good enough for many applications or for thin layers to be applied without sometimes complex post-processing. Processes such as the "Micro Machining Process" for optimizing surfaces and contours or post-processing using lasers will come into focus here. In the course of their future development, however, the additive processes themselves will certainly offer the possibility of optimizing in-situ surfaces in the micro and nano range and structuring them for the application, which will further perfect such designed components in combination with multifunctional layers. New constructive possibilities for plasma surface technology are opened up by the new innovative manufacturing processes.

Dr.-Ing. Georg Erkens, Managing Director Surcoatec Germany /ag

Literature:

Holsten, S.: Schneidkantenpräparation Ziele, Verfahren und Messmethoden. Page 25, Kassel University Press GmbH, ed. F. Tikal, 2009.