Chapter 14 - Friction, Lubrication and Surface Response in Wire Drawing

Abstract

This chapter reviews the basic concepts regarding friction, lubrication, and surface response in wire drawing. The range and phenomenology of the coefficient of friction in metalworking is discussed in terms of the Stribeck curves. These curves encompass the coefficient of friction range generally observable with the use of liquid lubricants in wire drawing. At slow drawing speeds, low apparent viscosities, and relatively high pressures, one encounters a very thin lubricant film, and coefficients of friction in the range from 0.1 to 0.2.The lubricant film may not be completely established, and conditions of sticking friction may arise, leading to coefficients of friction greater than 0.2, though rarely approaching the theoretical limit of 0.5. The condition of sticking friction, involving coefficients of friction beyond 0.2 and corresponding to the left extreme of the Stribeck curves, results in wire surface material being left on the die surface. Hence, the wire surface contains deep longitudinal striations, as evidence of a “shear fracture” vis-a-vis the metal stuck to the die.