Experimental Investigation of Endogenous Lubrication during Cold Upsetting of Sintered Powder Metallurgical Components

Abstract

Lubrication is essential in metal forming processes. As an example, it has a significant effect on the extent of homogeneity of forming and the resulting component surface. Thus, an adequate lubrication technique is required for a consistent part quality. In this contribution a new lubrication approach for cold bulk metal forming is presented. By exploiting the process-related porosity of powder metallurgical (PM) components as a lubricant storage, the resulting pressure of a forming process forces the stored oil to leak out lubricating the process. As a result, advantages like a decrease of process time because of the omission of the additional lubrication step, and an increased deformability due to compensation of lubricating film break are expected. Besides that, the porosity of the PM component is reduced leading to improved mechanical properties. Experimental investigations with cylindrical PM components were carried out by compression tests in dependence of initial porosity, impregnation time and lubricant. It was found that the required maximum load is reduced by up to 39 % by applying the new lubrication method. In addition, relative densities up to 99 % are reached after deformation.