Abstract: A dynamic force model of the ball screw used for electric operated injection molding machine was established using contact angle, velocity, acceleration, and others as structure parameters. Relationship between the velocity and acceleration of nut and screw was obtained. The contact stress at the nut and screw sides was described in terms of Hertz stress formula, and the effect of the structure and motion parameters on the contact stress of ball screw was further analyzed. It showed that, for a ball screw, increase in either velocity or acceleration could cause increase in contact stress significantly.

Key words: dynamic force model, acceleration, centrifugal force, Hertz contact stress, injection molding machine, ball screw