Process Integrated Production of WC-Co Tools with Local Cobalt Gradient Fabricated by Binder Jetting

Abstract

Producing complex shaped tungsten carbide cobalt (WC-Co) tools by classical technologies is difficult and often impossible due to their high hardness and brittle fracture behavior. Additive Manufacturing (AM) is a suitable technology for creating complex structures and simultaneously shortening expensive machining processes. Binder Jetting (BJ) is an innovative AM technology that offers several advantages over laser-based processes, for example low manufacturing costs and high build-up rates. Binders with nanoparticle additives have already proven to be effective in increasing the packing density of the powder bed and improving the sintering properties. Additionally, they offer the possibility of selectively changing the material composition in the part. This paper presents a concept for the use of nanoparticles to generate gradients in the green compact, which leads to a cobalt gradient in the part after sintering. The possibility of introducing particles locally into complex structures allows local modification of the material properties. Introduction Due to their high hardness, superior wear resistance and acceptable toughness, tungsten carbide cobalt (WC-Co) tools are primarily used for turning, milling or drilling. However, during these machining processes, high temperatures reduce the cutting ability and decrease the wear resistance of the tool so that a cooling lubricant is required. Integrated cooling channels in the tool are essential to ensure that the cooling lubricant can be fed into the process zone as required. Owing to the very high hardness and brittle fracture behavior of hard metals, only a few manufacturing technologies are suitable for processing them. Until now it has only been possible to produce complex integrated cooling channels at very high cost. AM offers a simple and cost-effective alternative: the layer-by-layer generation of parts enables the production of complex structures, which cannot be fabricated by conventional powder metallurgical manufacturing methods. Near-netshape production reduces or shortens complex machining processes, because less material has to be removed during post-processing and there is no need for tooling. This leads to more resourceefficient production [1, 2]. Binder Jetting is a promising additive manufacturing process for the fabrication of WC-Co parts. It has advantages over laser-based processes because of its low unit costs and high build-up rates. During BJ, a binder selectively bonds the powder layers to create a green part, which is then densified in a thermal process, similar to the powder metallurgical production of WC-Co parts. A disadvantage of BJ is the low green part density, which results in high finished part porosity. A suspension of binder and nanoparticles increases the packing density of the powder bed and improves the sintering properties [3], resulting in higher part density. The particles can also introduce specific composition changes in the part resulting in gradients that can improve the mechanical properties and wear resistance. 109 Solid Freeform Fabrication 2019: Proceedings of the 30th Annual International Solid Freeform Fabrication Symposium – An Additive Manufacturing Conference Reviewed Paper