Analysis of die compaction of tungsten carbide and cobalt powder mixtures

Abstract

pression is not yet available in the literature and conventional models which have been developed to describe the This paper investigates die compression of tungsten compressibility of powder never refer to WC-Co mixtures. carbide-cobalt powder mixtures, which is an import-In this context, the present study is an attempt to obtain a ant step in the processing route of cemented carbides.better characterisation and understanding of the pressing Simple action compression of miscellaneous mixtures of these mixtures. It focuses on die pressing, which is the has been investigated with an industrial type press most classical pressing technique. allowing measurement of the force applied on both Because of the friction between the powder and the die, upper and lower punches. In addition, an original the state of stress within the powder is not homogeneous apparatus was used to measure the average radial during die pressing. Thus, the interpretation of data drawn stress applied upon the die, and the frictional shearing from this test requires a mechanical analysis. A simple force at the powder/die interface was determined model, which has already been used by Mosbah et al.1 for through a powder/wall friction apparatus. A mechaninvestigating the compressibility of iron powder, is proposed ical analysis of the data obtained for various tungsten for this purpose. This analysis, which is supposed to provide carbide-cobalt powder mixtures provided the intrinthe intrinsic compressibility law of the material, is validated sic stress v. density compressibility relation as well by comparing results of tests performed with several as the radial stress transmission coefficient and the devices, as well as data obtained with compacts of different powder/die friction coefficient. In this framework, the geometries. effect of several material and process parameters on With the help of this model, the influence of material the densification is discussed.PM/0825 parameters (cobalt content, carbide grain size) and process parameters (granulation, compression rate) on the com-At the time the work was carried out Dr Roure pressibility of WC-Co systems is investigated and the was with the Centre Europe ´en de Recherches en mechanisms responsible for this behaviour are discussed. Me ´tallurgie des Poudres,

Modelling Powder Compaction

“…Experimental studies indicate that friction depends on several factors including: contact pressure, local powder density, sliding velocity, sliding distance, temperature, and wall roughness. (Pavier and Doremus, 1997;Mallender et al, 1974;Ernst and Barnekow 1994;Mosbah et al, 1997;Wikman et al, 1997;Roure et al, 1999). In Section 6.2, we adopt the instrumented die method and present a number of case studies below where the friction coefficient is dependent on contact pressure and die wall condition.…”

Correlation between the morphology of cobalt oxalate precursors and the microstructure of metal cobalt powders and compacts

“…Metal cobalt powders have many applications, notably in steels for cutting tools, abrasion strengthened composites [1,2] and also, in alkaline rechargeable batteries [3] or heterogeneous catalysis [4]. The mechanical performances of the final materials closely depend on the quality of the green powder compacts.…”

Hot Pressing of Spherical, Polycrystalline 3Y‐TZP Particles

“…Increased die wall friction with decreasing particle size has been observed and attributed to the increased number of particle point contacts with the die wall. 16 To obtain the magnitude of the frictional loss during die pressing, Roure et al 17 experimentally measured the difference between the applied force to the top plunger of a fixed coldpressing die containing WC powder and the measured force at the bottom plunger. They observed a significant increase in the die wall friction with a decreasing particle size.…”