Flashless forging is classified as a precise metal forming technology. The main advantages of this technology are the reduction of the flash allowance and the shortening of the manufacturing time by eliminating the flash trimming operation. The article presents the process of one-step forging of a stepped shaft made of aluminum with the use of split dies. The process was carried out in cold and hot metal forming conditions. The forging process was analyzed numerically using the Simufact.Forming 15.0 software. The geometrical parameters of the obtained product were analyzed, the distribution of effective strain, temperature and the standardized cracking criterion were determined. The process force parameters were also determined. Numerical tests were verified in real conditions with the use of a specially designed device for forging in vertical split dies. Comparison of hot and cold forging in vertical split dies is presented.