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Abstract
Small cylindrical iron powder compacts have been produced in series of ∼ 75 000 specimens, using an automatic compacting press running at a speed of 33 strokes/min. Die-wear rates were determined, as influenced by powder type, compacting pressure, compact density, type and hardness of die steel, and punch/die clearance. Simultaneously, the ejection forces were continuously recorded.
No substantial difference was found between the die-wear rates of common iron powder grades of an atomized or a sponge type, but an electrolytic grade of especially compact particle structure gave a lower rate. Die wear increases in roughly linear proportion both with the number of compacts and with the compacting pressure.
Steel type and hardness of the die had a pronounced influence upon die-wear behaviour, dies of higher hardness yielding lower wear rates. Unsuitable heat-treatment can cause high wear rates even though it might produce high die hardnesses.
A punch/die clearance of 10 μm resulted in the most favourable die-wear behaviour. At a clearance of only 5 μm the punches became stuck in the die very quickly; at clearances of 25 and 45 μm severe cladding of the die-bore surface with iron from the compacts occurred after 40 000-50 000 strokes.
The following, partly interacting, phenomena were found to be contributory factors in the die-wear mechanism: abrasion, cladding, surface cracking, and chipping. It proved impossible to establish a reliable correlation between ejection forces and die-wear rates.
Notes
* Manuscript received 25 June 1969. Contribution to a Symposium on “Lubrication, Friction, and Wear (Tribology) in Powder Metallurgy” to be held in Eastbourne on 24-26 November 1969.