Friction-related size effect during IN718 tube drawing: Realization of ultra-low friction

Drawing process, with the advantages of high accuracy and efficiency, is a common process for tube production. The high friction in tube drawing leads to high drawing forces, easy breakage of tube and high production costs, etc. It is urgent to reduce friction coefficient during the tube drawing. However, the effect of contact area on friction (friction-related size effect) along with the coupling effects of surface roughness, lubricants, and coatings is still unclear or even contradictory, which causes the reduction of the friction coefficient in tube drawing to become a challenge. In this study, taking IN718 tube drawing as the research object, the influence mechanism of contact area (1.25–12.06 mm2) as well as the coupling effects of surface roughness (0.513–0.622 µm), lubrication status, and coatings on friction was explored to reduce the friction coefficient as much as possible. Firstly, a new multi-sensor drawing device is designed to obtain contact pressure and drawing force, combined with finite element model, to characterize friction coefficient during the tube drawing. Secondly, the finite element model considering pits and lubricant is designed to reveal the friction mechanism in tube drawing. The results indicate that as the nominal contact area increases, the proportion of actual contact area decreases, leading to a decrease in friction coefficient, from 0.1102 to 0.0502, a decrease of 54.36%. The reduction of roughness leads to the weakening of plough effect, the coating leads to a transformation of the friction pair, and the lubricant bears some pressure, all of which can lead to a decrease in the friction coefficient, from 0.1203 to 0.0351, a decrease of 70.79%. By designing appropriate contact area (12.06 mm2), surface roughness (0.513 µm), lubrication status (graphite), and coating (sodium fluoride), the friction coefficient is sharply reduced from 0.1203 to 0.0014, a decrease of 98.79%. This in turn leads to a significant increase in the deformation amount, viz., the single pass drawing deformation amount is greatly improved from 14.22% to 49.65%. The research results have significantly reduced production costs.