Forced Lubrication Method and the Quantitative Evaluation of Friction Coefficient during Deep Drawing

The friction in the sheet forming process is characterized by high contact pressure, large actual contact area and constantly changing friction surface, and the lubrication condition is very severe.In this paper, a forced lubrication process that relies on pressure from external power is proposed and applied to sheet forming.The process has the technical advantages of high efficiency, low cost, controllable and adjustable lubrication conditions.Deep drawing tests were conducted at 35 kN blank holder force (BHF) and 0-12 MPa lubricant pressure.The experimental results demonstrate that the increase of lubricant pressure significantly reduces the forming force, improves the forming performance and reduces the coefficient of friction (CoF).At a lubricant pressure of 12 MPa, the forming height of the box-shaped part is increased by 16.3%.In order to quantitatively evaluate the effect of forced lubrication, the average CoFs under different process conditions were obtained by using the finite element (FE) inverse method.The results show that the CoF tends to decrease as the lubricant pressure increases.The CoF is reduced by 30.6% at a lubricant pressure of 12 MPa.The superiority of forced lubrication is verified through experiments and simulations, which provides a certain reference for practical production.