I think there are no automatic tools to convert solid to mid-plane in the market at all. Some software developers declare that their programs can do it. But really it is possible only for very simple models. We already some years are engaged with converting of solid models to mid-plane models (mainly for Moldflow analysis)but it still remains by labour-consuming process. I don't see essential progress in the software for this purpose.
Igor Jogla
3D Point IK
Mechanical Design and Consulting