Approach for reducing variation in weight of PM green parts in mass productive pressing line by addition of nanoparticle to raw material powder

Variation in weight of green compacts is one of the issues to be resolved in PM parts production lines. This variation is correlated with fluctuation of apparent density of powder in a filler shoe that moves continuously. In this study to understand this phenomenon and find out the solution, the fluctuation of apparent density of the iron powder mixture during shaking was investigated, and correlations between the fluctuation and adhesive factors obtained from direct share test were evaluated from the view point of the effects of additive materials. The apparent density of the powder mixture with wax-lubricant decreased drastically after multiple shakes, and this prominent decline could be suppressed by the addition of a small amount of nanoparticles. Both adhesive force and friction angle of the powder with wax-lubricant were larger than the other powder mixtures without wax, and declined by the addition of nanoparticles. These results indicate that wax lubricant can form an unstable particle bridge structure through repeated shakes because of its adhesive property, and nanoparticles have the role to inhibit the formation of the bridge structure. This nanoparticle addition can be a key to productivity in the compacting line of PM parts.