The Effect of Rheological Lubricant Properties on Manufacturing Process of Thin-Walled CuBe2 Alloy Tubes

In the manufacturing process of high-precision thin-walled tubes with diameters of less than 3 mm, the deformation conditions at the contact area between the die, the tube and the floating plug are the decisive factor in the stability of the drawing process. These conditions depend, amongst other things, on the rheological properties of the lubricants, temperature and friction conditions. Industrial drawing trials of ultra-thin beryllium bronze tubes have demonstrated a correlation between the physico-chemical properties of the lubricants and the susceptibility of the tubes to breakage, as well as the efficiency of the drawing process. The maximum drawing speed that guarantees stable process conditions depends on the dynamic viscosity coefficient, the thermal stability of the lubricant, the drawing force, the temperature and the amount of lubricant on the tube surface. As the tube drawing speed increases, the temperature at the material/tool interface rises. This leads to a gradual decrease in the viscosity of the lubricants, a reduction in the thickness of the lubricant film, and an increase in friction, drawing force and the strength properties of the tubes. Once the critical speed is exceeded, the tube breaks in the drawing die. The results indicate that the maximum stable drawing speed is not governed by a single lubricant property, but by the combined effects of dynamic viscosity, its temperature sensitivity, and thermal stability; both an excessively viscous oil and a very low-viscosity emulsion limited process stability. The highest drawing efficiency under industrial conditions was achieved with mineral oils (v = 15 m/min). The use of polymer-based lubricants in drawing enables the drawing process to be carried out at a speed of v = 1 m/min, and these can be used for drawing under laboratory conditions. In contrast, when drawing tubes using potassium soap-based emulsions, unstable drawing conditions occur, leading to very rapid tube breakage.