Geometric Models and Standards for Additive Manufacturing: A Preliminary Survey

Short abstract: The implementation of Additive Manufacturing (AM) digital flow and product data management system rely more on data formats and standards that nowadays convey Geometric Dimensioning and Tolerancing (GD&T) information directly in the 3D model. The consideration of geometric deviations and variations is an important issue for tolerancing and geometric quality assessment in AM through product and manufacturing information (PMI). This paper reviews current challenges of geometric models and standard formats for AM technologies, which largely impede its advancement. Two criteria to enhance AM geometric models and standards are presented in this paper: tolerancing and compatibility of PMI. The analysis presented in this paper highlights that STEP standard can be a good basis for future research to integrate geometric models and standards for AM. Additive manufacturing (AM) technologies have been applied to the automotive, aerospace and medical industries for many years [1-2]. However, it is a difficult technology for AM that geometric models describe precision and accuracy of product shape, dimensioning and tolerancing. Geometric models have become ubiquitous and offered essential and different tools for the digital product development [3]. In the 1960s Herbert Voelker considered the possibilities of using computer-aided machine to operate machine through CAD geometry. In the 1970s mathematical tools for describing 3D solid modelling had been invented in the early algorithms [4]. At present, geometric deviation has become a major issue on the tolerancing research [5]. Skin model concept has been applied to describe tolerancing representation and analysis [6]. Standards play an important role in the adoption of many technologies. Some of standardized formats include Stereo Lithography (STL), Additive Manufacturing File (AFM) and Standard for Exchange Product (STEP) [7-8]. The theoretical geometrical model has been developed to consider geometric deviations [9]. And the developing and using standards (i.e. ASTM AMF, 3MF, ISO 10303 STEP) and tolerances (ASME Y14) [10-11] have integrated information related to AM process [12]. In order to realise this AM process: design, simulation, build plan, monitoring and control and verification, standard organizations have begun to establish AM file format for data exchange[4]. The design and manufacturing of high performance product may lead to an inevitable need for geometric deviations and tolerancing management [13-14]. The geometric tolerancing models have been proposed [15-18]. Tolerancing analysis has been used in predicting inevitable geometric deviations on the function and quality of product [19]. Skin model shapes can extract valuable information for geometric deviation [20]. Product manufacturing information (PMI) includes the geometric dimensioning and tolerancing (GD&T) [21]. These PMI standards, such as ISO TC213, ASME Y14.5, can define tolerancing [22]. Next sections will highlight challenges of geometric models and standards for AM technologies. These challenges mainly focus on two issues: geometric deviations and tolerancing management, and refer to two criteria: tolerancing and compatibility with PMI for AM formats. In section 3, skin model is introduced, and PMI standard can define tolerancing in AM systems. In section 4, different AM standards (i.e. STL, AMF, STEP) are compared and we emphasize on STEP in future works. In section 5, a conclusion and outlook are given.