Aerospace represents the development of a national science and technology. It is an important foundation for exploring space and an important guarantee for the construction of aerospace power. There are many large workpieces in the aerospace field. The box insulation layer of large workpieces is an important processing problem. A piece of special equipment with a 1:1 ratio is no longer in line with the development trend of processing the end-surface insulation layer of the large box. This article proposes a new thick processing scheme, which consists of the XYZ shaft long guide rail and the processing unit. The processing unit is a redundantly actuated parallel robot, which is composed of 3T2R(T represents translation, R represents rotation) redundantly actuated parallel mechanism (RAPM). This paper focuses on the type synthesis of five degrees of freedom (5-DOF) redundantly actuated parallel mechanisms (RAPMs). Based on Lie group theory and configuration evolution, three classes of the RAPMs are synthesized by designing the moving platform I and the limbs. This work lays the foundation for solving the processing method of the end surface of the large box.