Experimental approaches to powder filling and lubrication in powder die pressing
Doctoral thesis, 2004
There is a continuous need to improve the mechanical properties of steel parts produced through powder metallurgy in order to ensure the market growth of this sector and competitiveness against alternative production techniques. One of the more promising routes able to achieve this is to aim for components with higher densities. Two potential areas for such improvements are deepened understanding of the powder filling process and lubricant behaviour during uniaxial pressing. These steps have received limited attention due to their complexity thus more easily achievable developments with larger impact on final properties, such as optimisation of alloy content, compaction pressure and sintering conditions, have so far always been present. During the time such aspects have been optimised, the need for more systematic investigations of filling and lubricant behaviour, has become increasingly apparent. There is a lack of experimental equipment able to study these problems and potential analysis techniques have not been adapted for the application. The aim of this project has been to develop and verify new techniques to make experimental data available, and use them to acquire new knowledge. An experimental device has been constructed which has been able to identify several factors within the filling process as responsible for density variations observed in the filled powder. A microscopic approach has been adopted in order to study the function and behaviour of lubricant during powder compaction. X-ray photoelectron spectroscopy, interference microscopy and scanning electron microscopy have been used to study the topography and lubricant distribution both at the surface of the compacted powder parts and at the surface of the compaction tools. From the results it has been possible to draw several new conclusions about lubricant behaviour during compaction and the results have indicated which variables that have to be considered in future investigations of lubricant behaviour and which microscopic factors that currently is limiting the compactability of powders containing a homogenously distributed lubricant.