Investigation of Revolute Joint Clearances Created by an In-Mold Assembly Process

Revolute joints are frequently used in articulated structures. Traditionally, such a joint is formed by assembling two components. As an alternative, revolute joints can be created inside the mold using an in-mold assembly process. This process eliminates the need for post-molding assembly, thus significantly reducing the cycle time and part count. The functional performance of a revolute joint depends on the clearance in the joint. The clearance in turn depends on the part shrinkage and the mold deformation during the molding process. The presence of a polymer part during the second molding stage makes an in-mold assembly process significantly different from the traditional molding process due to the difference in heat transfer and deformation characteristics. This paper presents experimental data and a preliminary model to explain the differences in clearance produced by an Aluminum mold and an Aluminum mold with an Acrylonitrile butadiene styrene (ABS) insert. Our data indicates that there is a significant difference between the clearances observed from these two different types of molds. We believe that clearances produced depend strongly on the thermal history of the parts.