A large number of process industries are dependent on tribology. By taking advantage of the new surface, materials and lubrication technologies for friction reduction and wear protection in vehicles, machinery and other equipment worldwide, energy losses due to friction and wear could potentially be reduced by 40% in the long term and by 18% in the short term. Besides the reduction of CO2 exhaust, an adapted lubrication regime in machinery can save 1.4% of the Global Domestic Product annually and 8.7% of the total energy consumption in the long term. One of the applications, which want to achieve friction decrease and wear reduction, is wire drawing. Moreover, it contains a challenging technology concerning tribology.
Figure 1: Metallic wire pulled through a series of dies.
The process of wire drawing is a cold work hardening process. A metallic wire is pulled through a series of dies, in order to reduce its cross-section, while changing the crystal structure of the material and thus the related mechanical properties as strength and hardness. In dry wire drawing, the wire is lubricated with a carrier agent and is pulled at high speed (about 10-20m/s) through a bath of dry soap granules, which may contain different additives. The application of the produced wires is highly diverse, from cables used to support bridges to springs used in the automotive sector.
Figure 2: Steel cables supporting a bridge Figure 3: Clutch steel wire
The primary purpose of the lubricant is to reduce friction between the wire and the die by avoiding adhesive bonding of the metal with the die wall. This will obtain reduced heat generation and energy consumption. Moreover, the production costs will decrease. Secondary the lubricant reduces the wear at the die and will extend its service life. By applying a custom lubricant a reduced production cost will be achieved while ensuring the surface quality of the wire by making the deformation uniform.
In this case, the dry drawing process operates on high drawing speeds conditions, under the plasto-elastohydrodynamic lubrication regime, referring to the plastic deformation of at least one of the two surfaces. In this process, the surfaces are assumed to be entirely separated by the lubricant.
The project under consideration is focused on a 3D modeling of this plasto-elastohydrodynamic lubrication in the dry drawing process, using Finite Volume Method (FVM) and Fluid-Structure Interaction (FSI). The main goal of the 3D modeling of the fluid film is to understand the vibrations generated by the lubricant under specific drawing conditions.
In order to achieve the different goals, first, the student has to master the existing FSI axisymmetric case that will be used as a base with the complete mapping between the structural and fluid solver. Both solvers make use of the open-source CFD package OpenFOAM. In this demonstration, the lubricant is approached as an incompressible flow with arbitrary values. The wire is defined as an axisymmetric rectangle.
The first step of this approach is to make a 3D soap film and 3D wire model as such, the soap fits perfectly around the undeformed wire, to obtain an initial film thickness. A first simulation represents a 3D simulation where the wire radius and the die diameter stay constant before reaching the FSI-interface. An investigation of pressure build-up in the soap and stress development in the wire is carried out of the FSI-simulation.
The second step of the second bullet is to start with the initial state, as approached in the first step. However, after several time step the die diameter decreases gradually. The purpose is to achieve a 3D FSI-simulation with a focus on the pressure build-up and film thickness of the lubricant and stress development of the wire. Finally, the calculated drawing force will be compared with experimental data.
To achieve the last bullet of the goals a literature study has to be performed concerning different models that are used for numerical simulation of tribology parameters. Moreover, the data of a lubricant soap are available from experimental tests executed in an external lab. These characteristics of the lubricant will be implemented in the model. An important notification is that the lubricant always has to be operating in the plasto-elastohydrodynamic regime (PEHL). Finally, the three-dimensional model in combination with the identified parameters of the lubricant will be used to investigate the phenomena occurring in the lubricant film, including the film thickness, pressure and flow-induced vibrations along the wire.