Abstract
Study describes principles of diesel effect creation during thermoplastic injection moulding as a consequence of wrong injection conditions and poor venting system design. On real example, study shows sequence of all steps to eliminate this sort of material degradation with minimal costs in phase when mould is already made. As a first, process parameters were optimized by CAE simulation to minimize cavity internal gasses creation. Finally the specific mould modifications were suggested to improve the effectiveness of venting system.