Method for the controlled mechanical working of sintered porous powder metal shapes to effect surface and subsurface densification

A method for producing an annular bearing ring by powder metallurgy which comprises,

• forming a sintered porous metal ring having a porosity corresponding to a density of about 70% to 90% of true density,
• coaxially supporting said ring on a rotatable mandrel including applying clamping pressure to opposite sides of said ring while supported on said mandrel,
• roll-forming a raceway onto a circumferential bearing face of said ring using a circular die having a continuous projecting rib in the form of a male counterpart of the raceway being formed while said mandrel is rotating,
• and continuing the formation of said raceway to a suitable depth to support rolling elements therein,
• said raceway depth being formed in less than 10 revolutions of said ring,
• whereby a highly densified subsurface is obtained adjacent said raceway of average density of at least about 95% of true density while the remaining portion of said ring is maintained substantially porous over the range of about 80% to 92% of true density,
• the amount of clamping pressure being at least sufficient to inhibit the growth of said ring during the formation of said raceway while substantially inhibiting the cracking of said ring during the roll-forming of said raceway.

A method for producing an inner annular bearing ring by powder metallurgy which comprises,

• forming a sintered porous metal ring having a porosity corresponding to a density of about 70% to 90% of true density,
• coaxially supporting said ring on a rotatable mandrel including applying clamping pressure to opposite sides of said ring while supported on said mandrel,
• roll-forming a raceway onto the outer circumferential bearing surface of said inner ring by feeding radially towards said ring and perpendicular to the axis thereof a plurality of radially spaced circular roll-forming dies each having a continuous projecting rib in the form of a male counterpart of the raceway being formed while said mandrel is rotating,
• and continuing the formation of said raceway to a suitable depth to support rolling elements therein,
• said raceway depth being formed in less than 10 revolutions of said ring,
• whereby a highly densified subsurface is obtained adjacent said raceway of average density of at least about 95% of true density while the remaining portion of said ring is maintained substantially porous over the range of about 80% to 92% of true density,
• the amount of clamping pressure being at least sufficient to inhibit the growth of said ring during the formation of said raceway while substantially inhibiting the cracking of said ring during the roll-forming of said raceway.

A method for producing an inner annular bearing ring by power metallurgy which comprises,

• forming a sintered porous steel metal ring having a porosity corresponding to a density of about 70% to 90% of true density,
• coaxially supporting said ring on a rotatable mandrel including applying clamping pressure to opposite sides of said ring while supported on said mandrel, roll-forming a raceway onto the outer circumferential bearing surface of said inner ring by feeding radially towards said ring and perpendicular to the axis thereof three substantially equally radially spaced circular roll-forming dies, each having a continuous projecting rib in the form of a male counterpart of the raceway being formed while said mandrel is rotating,
• one of said roll-forming dies having a circumference of about 5% to 15% less than the circumference of the remaining dies such as to provide die slippage during the formation of said raceway,
• and continuing the formation of said raceway to a suitable depth to support rolling elements therein whereby shear forces are simultaneously applied during formation of said raceway to remove pores therefrom,
• said raceway depth being formed in less than 10 revolutions of said ring,
• whereby a highly densified subsurface is obtained adjacent said raceway of average density of at least about 98% of true density while the remaining portion of said ring is maintained substantially porous over the range of about 85% to 92% of true density,
• the amount of clamping pressure being at least sufficient to inhibit the growth of said ring during the formation of said raceway while substantially inhibiting the cracking of said ring during the roll-forming of said raceway.