Abstract: The method of steel ball surface quality detection is to rely on the mechanism friction to expand the ball surface completely. The friction has an important influence on the detection efficiency and effect. For the analysis of friction effect on steel ball expansion, according to the geometric constraint relationship between wheel and the steel ball contact, to carry out the motion and position analysis, then obtain the position variation of contact point between wheel and the steel ball; Because all components of expansion device depend on the dry friction constraint, based on the classical Coulomb friction model, establishes the modified Coulomb friction model in combination with device features, and establishes the movement differential equation between steel ball and unfolding wheel, obtains the change law of friction for contact points of steel ball and unfolding wheel, and analyzes the influence factors of contact force; At the same time, according to the unfolding principle, the entity model is built for virtual simulation, and the physical prototype is built for test. The results show that the driving wheel speed directly affect the normal contact force changes of contact point between steel ball and unfolding wheel, which affects change features in friction of contact point, the principle of steel ball surface unfolding by unfolding wheel can be explained through changing friction characteristics.

Key words: dynamic, steel ball, the modified Coulomb friction, unfolding wheel