Investigation of the effect of workpiece surface treatments and coating type on formability in cold forging process

Friction is of great importance in metal forming operations as it directly affects the material flow during deformation, the stress and strain distribution on the workpiece, the forming load and as a result, the tool and die life. In the study, the effects of surface treatments, coatings and lubricants applied before cold forging of axle tulips used in automotive axles on formability together with friction were investigated. In this context, the effects of lubricants and coatings used in cold forging processes on the process and the effects of the sandblasting process performed before were investigated. With the increase in friction in the cold forging operation of the axle tulip, the surface quality of the workpiece deteriorates, and hairline cracks are observed. This poses a risk in terms of product safety. In the study, the effects of surface treatments, coatings and lubricants affecting the friction between the mold and workpiece surfaces on the friction coefficient were investigated experimentally and the most suitable surface treatment, coating and lubrication conditions for this process were investigated. The Columbian friction coefficients of coatings and lubricants were measured, and wear depths and widths were compared. SEM and EDS analyses of the coated samples were performed to examine the distribution of the elements forming the coating on the surface and their mass ratios. Simufact Forming software was used to create simulations with 6 different shear friction coefficients and 8 different extrusion ratios and to create calibration curves. In DCET tests, forward and reverse extrusion ratios were calculated and the positions of the coating and lubricants within the calibration curve were determined. According to the results obtained from the experimental studies, the tests were tested on the automotive axle tulip this time. In the first stage, simulations of the axle tulip were performed at different shear friction coefficients using finite element software. In the second stage, the cold forging process of the product was performed and compared with the simulation results. According to the results obtained, it was determined that the friction coefficient, which was around 0.6 in coatings made without soap coating, decreased to 0.18 because of coatings made with soap. The friction coefficient decreased to 0.12 with new generation coatings. While the shear friction value "m" was obtained between 0.02 and 0.025 from the simulation results, the "m" value was obtained as 0.022 in the DCET test, thus the simulation results were confirmed with the experimental results. In addition, it was seen that the shear friction value obtained from the experimental results and the results obtained from the cold forging of the axle tulip agreed with each other.