230 J. Mater. Sci. Technol., Vol.23 No.2, 2007 High Velocity Forming of Aluminum Cylindrical Cups-Experiments and Numerical Simulations Mustafa YASAR † and Ibrahim KADI Faculty of Technical Education, ZKU/Zonguldak Karaelmas University, Karabuk, Turkey [Manuscript received January 13, 2006, in revised form April 14, 2006] A new two stage detonation forming machine was developed and cylindrical aluminum cups were formed by using gas detonation forming technology. The forming process was analyzed with the explicit finite element method with various parameters and ANSYS/LS-DYNA software. Defects of wrinkling and rupture were predicted for some forming conditions. The strain and the thickness distribution results were in good agreement with the experimental results. It was seen that thinning and forming mainly take place during the one fourth of the time. The effects of detonation pressure and blank holding force on the deformation of the work pieces were discussed. The numerical results were compared with those obtained in the experiments. KEY WORDS: Detonation forming; Explicit finite element; Detonation pressure 1. Introduction Gas detonation forming (GDF) technology has been used in forming various shaped sheet metal parts. For example, cylindrical cups are one of the typical work pieces formed with this process [1–4] . The main advantage of GDF technology to form cylindri- cal cups is that the cylindrical cups can be formed in one step, while six steps are typically necessary by using conventional deep-drawing technology. In addi- tion, the dimensional accuracy of the products is re- markably improved with GDF technology. The other advantages of GDF could be listed as follows: surface quality is improved; the structure of the tooling sys- tem is very simple and the number of tool components is reduced, and thus the tooling costs are lowered sig- nificantly. However, body wrinkling and premature rupture often occur if the process parameters are not used properly. Process and tool design normally re- quires a lot of trial and error work. Numerical simu- lations have proven very useful in the design of tools and process layout, which can help to find the opti- mal process parameters and reduce the trial and error work. It was found that the detonation velocity is in- dependent of tube diameter. It was also found that for sufficiently long tubes, the velocity is the same for ignition either at the open or closed end [5,6] . The detonation velocity is little affected by the physical state of the gas mixture before ignition— the pressure and temperature—but depends on the mixture composition. It turned out that the detona- tion velocity always increases with the addition of H 2 , whereas decreases with the addition of O 2 or N 2 [5] . Figure 1 illustrates the change of detonation veloci- ties with mixture composition for air excess coefficient (AEC) and Fig.2 illustrates the change of detonation pressure with mixture composition [7] . Figure 1 shows that in case of AEC<1 (rich mixture), initial value of detonation velocity re- duces with decreasing AEC. In rich mixtures, it † Ph.D., to whom correspondence should be addressed, E-mail: myasar@karaelmas.edu.tr, Yasar.mustafa@gmail.com. Fig.1 Measurement of detonation velocity with AEC Fig.2 Measurement of detonation pressure depending on AEC is seen that distance for detonation velocity to reach its peak is inversely proportional to AEC. When AEC decreases, distance to reach maximum detonation in- creases and maximum detonation velocity also rises. This figure reflects that in case of AEC<1, at each AEC value, detonation velocity reaches a certain max- imum. After reaching such a peak detonation velocity, it drops down to a velocity that is lower than the max- imum detonation velocity and then stabilizes within particular tolerances [7] . It is seen clearly from Fig.2 that detonation pres- sure fluctuates over the full length of the pipe. This paper is aimed to investigate the GDF pro- cess of cylindrical cups experimentally and numeri- cally. An explicit finite element (FE) code was used