Substitution of solid carbide saw teeth by the use of WC-CoCr coated HSS saw teeth

• Applicants: Professor Dr.-Ing. Dirk Biermann; Professor Dr.-Ing. Wolfgang Tillmann
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering ; Coating and Surface Technology
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 397758646

In the previous project, Investigation and Qualification of HVOF-WC-Co-Coated Cutting Parts for the Substitution of Cemented Carbide Cutting Materials, it was possible to successfully qualify the high velocity oxy-gen fuel spraying process with a subsequent grinding process for the production of the final contour as a new manufacturing route for carbide cutting elements. This qualification enables a significant increase in resource efficiency by substituting solid carbide tools. In the project, a conventional, liquid fuel-driven HVOF system (C-CJS, Thermico Engineering GmbH) with a warm spray function, i.e. the possibility of additional injection of nitrogen, was first investigated. Fine WC-12Co powders (-10 + 2 µm) and WC-10Co4Cr powders (-22 + 5 µm) with small carbide sizes of WCFSSS ≈ 400 nm (Fisher Sub Sieve Sizer) were used, as an increase in the mechanical properties, especially the hardness, which is a very relevant property for use as a cutting material, was observed with these in our own preliminary work. In this way, the coating process could be specifically designed for the downstream grinding process with regard to the surface roughness on the basis of the setting variables of spray distance, nozzle length and nitrogen flow. However, the previous project also revealed numerous challenges in the use of this torch technology for the coating and finishing of cutting tools, which need to be examined and solved in more detail for a successful implementation of the concept and transfer to real tools. These will be examined in more detail by the cooperative work of the Institute of Machining Technology (ISF, Prof. Biermann) and the Chair of Materials Technology (LWT, Prof. Tillmann). The focus is on the interactions and resulting properties of both the coating and the downstream grinding process, which are to be analysed in detail. In detail, optimised path planning and coating strategies will be developed to improve the residual stress state, with the aim of reducing the residual stresses at the cutting edge. In addition to the measures for optimising the coating process, mechanically and thermally induced cracking in the coating and the resulting coating spalling and chipping are to be avoided by the adapted grinding process. For this purpose, process strategies must be developed and investigated that result in low thermomechanical stresses.

• DFG Programme: Research Grants