FUNDAMENTALS OF METAL FORMING：金属成型原理.ppt

Ring Rolling Deformation process in which a thick?walled ring of smaller diameter is rolled into a thin?walled ring of larger diameter As thick?walled ring is compressed, deformed metal elongates, causing diameter of ring to be enlarged Hot working process for large rings and cold working process for smaller rings * Basic Bulk Deformation Processes Ring rolling used to reduce the wall thickness and increase the diameter of a ring: (1) start, and (2) completion of process. Ring Rolling * Basic Bulk Deformation Processes Applications: ball and roller bearing races, steel tires for railroad wheels, and rings for pipes, pressure vessels, and rotating machinery Advantages: material savings, ideal grain orientation, strengthening through cold working * * * We cannot model the relationship between stress and strain in plastic range by Hooke’s Law * * * K = strength coefficient; and n = strain hardening exponent * C = strength constant; m = strain?rate sensitivity exponent * Mills are designed in different types of configurations, with the most basic being a two-high non-reversing, which means there are two rolls that only turn in one direction. The two-high reversing mill has rolls that can rotate in both directions, but the disadvantage is that the rolls must be stopped, reversed, and then brought back up to rolling speed between each pass * the three-high mill was invented, which uses three rolls that rotate in one direction; the metal is fed through two of the rolls and then returned through the other pair. The disadvantage to this system is the workpiece must be lifted and lowered using an elevator. All of these mills are usually used for primary rolling and the roll diameters range from 60 to 140 cm * To minimize the roll diameter a four-high or cluster mill is used. A small roll diameter is advantageous because less roll is in contact with the material, which results in a lower force and energy requirement. The problem with a small roll is a reduction of s