We propose an efficient method to produce multi-particle Schrodinger cat states of ions in an ion trap. The ions are prepared in quantum entangled internal states for which a wide range of interesting effects and applications have been suggested. Our preparation scheme exploits the collective vibrational motion of the ions, but it works in such a way that this motion need not be fully controlled in the experiment. The ions may, e.g., be in thermal motion and exchange mechanical energy with a surrounding heat bath without detrimental effects on the internal state preparation.