Investigation of Pressing and Ejection Performance of Friction-Reducing Powder-Compaction Tool Coatings

Abstract

Pressing in dies followed by sintering is the most commonly used process for shaping metal powders into components. The mechanical properties (e.g. tensile and fatigue strength) of the final sintered component depend on the green-compact properties resulting from the compaction process. Apart from the powder material used, process-specific factors, such as geometry complexity, compaction pressure and lubrication strategy, have a major impact on the properties of the green compact. The lubrication strategy is also decisive for the economic efficiency of the process as it influences the service life of the tools. Friction-reducing powder-compaction tool coatings (e.g. diamond-like-carbon-based / DLC) provide the potential to positively influence the lubrication conditions during compaction and ejection, thus simultaneously improving product quality and service life. In this study, experimental investigations on the performance of friction-reducing coatings in the die pressing of steel powder (Fe + 0.6 wt% C) with and without admixed lubricant (AncorLube, GKN Hoeganaes) are presented. The results are evaluated by force-displacement measurements, which allows for a more profound analysis of compaction and ejection behaviour. It is shown that the application of the coatings reduces the ejection loads significantly when no admixed lubricant is used, and moderately when lubricant is admixed. However, without lubricant, wear still occurs after a few pressing cycles, so it cannot be completely avoided.