Paper Based Material vs. Sintered Metal in Automotive Automatic Transmissions

Sintering metal is a manufacturing process that involves the compacting of a powdered metal material into a mold by means of pressure or heat. Sintered metal first appeared in automatic transmissions in the 1950’s. There are applications where sintered metal is the preferred choice; however, in automotive automatic transmissions, compliance of paper based materials resulting in excellent load distribution and favorable friction characteristics make paper materials a much better and more durable choice. Sintered metal is much stiffer than paper based material and thereby poorly compensates geometry imperfections of clutch components; because of high stiffness it tends to produce hot spots and create substantially higher local surface temperatures than a paper based material. This often results in coning, warping and fluid degradation which leads to premature clutch failure. Sintered metal typically has a lower friction coefficient than paper based materials with an endpoint friction coefficient that is typically higher than the midpoint causing harsh shifts. Sintered metal is aggressive towards mating steel which creates surface wear. As metal wears it produces hard debris that is harmful to other components and systems in the transmission and can lead to electronic failure. The use of sintered metal materials also necessitates more frequent transmission service to eliminate the debris and proves to be more costly overtime.Coned Sintered Metal PlatesTest Cycles SurvivedCoefficient of FrictionE/M Ratios