Effect of datum system and datum hierarchy on the design of functional components produced by additive manufacturing: a systematic review and analysis

The evolving technology of additive manufacturing (AM) is posing novel challenges in manufacturing practice since nowadays functional, end-use components, and assemblies are produced by commercially available AM equipment. In order to safeguard the functionality and the interchangeability of a part, the designer must clearly denote a set of Geometrical Product Specifications (GPS) in the 3D model or in the engineering drawing by using the existing standards, e.g., ISO 1101, ISO 5459, and ISO 1660. Apparently, the family of ISO GPS standards that are currently used in design, manufacture, and verification has been developed so as to address the needs of traditional manufacturing processes rather than AM. Supported by numerous recent publications, the argument that current standardization does not sufficiently support the geometrical specification and verification of AM parts is getting more and more popular. The paper investigates and questions the need for the development of AM process-specific standards, related to the tolerancing and verification of mechanical components, as encountered with castings, forgings, and composites. Focusing on the most critical issue of datum establishment and datum hierarchy, the capability of existing tolerancing tools, as provided by the ISO GPS standards, to serve the process-specific AM needs is systematically examined. Moreover, major AM process-specific parameters such as build direction, layer thickness, support structure, and hatching plan are linked with the datum system designation and datum hierarchy tasks through a design case study and analysis. The major findings of this research pointing towards the establishment of AM-specific design-for-accuracy good practices are presented and discussed.