Friction Evaluation for Combined Drawing and Ironing Process With Thick Sheet by Ball Ironing Test

Abstract

Ball ironing test (BIT) was proposed to evaluate the tribological conditions of the combined drawing and ironing process for thick sheets. This process was used to produce the products with controlled thickness at the sidewall, such as pulleys. Finite element modeling (FEM) was utilized to study the effects of the main geometrical parameters on friction from the BIT results and thereby design suitable tooling geometries. Clearance-to-thickness ratio (c/t), inner die radius (rd), and inner diameter of specimen (di) were adopted as process and specimen parameters. The results of the BIT comprised the maximum load and final height of the specimen. Slope sensitivity (λ) in the results was introduced to evaluate the friction sensitivity. According to the simulation, the maximum load was highly sensitive to the friction and was thus used as a friction indicator. Friction calibration curve (FCC) was established and fitted on the basis of a simplified mathematical model as a function of the maximum load and friction factor (m). The BIT with various types of lubricants was performed experimentally to evaluate the performances of the lubricants and approximate the friction factors. The solid lubricant, Zn-Ph coating, provided the least forming with m of 0.03. The liquid lubricant, oil with extreme pressure (EP) additives, performed similarly to the Zn-Ph coating with m of 0.07. In conclusion, the BIT test performed very well in ranking the lubricants and determining the friction value of the combined drawing and ironing process for thick sheets.