Minimise joint clearance in rapid fabrication of non-assembly mechanisms

Layer-based rapid fabrication technologies have two distinct advantages: (1) build parts without geometry restriction; (2) build sub-systems (static or mobile) without the need for assembly. Many previous papers have reported various applications that could benefit from the first advantage. Yet, very limited researches have investigated the applications that can benefit from the second advantage. One of the major reasons is the limited accuracy of current layer-based fabrication technologies that can only make mechanism joint with large clearance. This limitation has prohibited the fabrication of sensible joints in mobile sub-systems such as mechanisms, because large clearance at joints is the major source for excessive impact force, resulting in wear and tear of the joints, and consequently the malfunction/degradation of a mechanism's performance. Thus, how to reduce the joint clearance is a major research issue for layer-based rapid fabrication of non-assembly mechanisms. In this paper, different pin joint designs are analysed. It was found that drum shaped pin joint design gives the minimum joint clearance in layer-based fabrication, and at the same time, without weakening the joint strength compared to the traditional cylindrical pin joint design. A number of sample joints and mechanisms have been made by a layer-based fabrication machine Objet Eden 350V to test the effectiveness of the proposed drum shaped joint design.