Dimensional Tolerances for Additive Manufacturing

Additive manufacturing processes are future technologies. They provide special benefits such as reduced production and process costs, shorter production time or demand-driven production of components.

Additive manufacturing processes create parts and assemblies of metal and plastic materials layer by layer and without formative tools, wherefore great design freedoms exist. For instance, parts can be designed and manufactured with undercuts, complex internal structures or free-form shapes. The freedom of design provides great benefits to users of additive manufacturing processes. In order to profit from these benefits, it is necessary to know and to take into account the manufacturing limits of the processes. This applies in particular to the geometrical accuracy of the components.

Initially, a technical part is designed computer-aided at its nominal shape, which corresponds to the ideal shape. However, such a nominal shape does only exist theoretically. So the manufacturing always leads to geometrical deviations from the nominal shape. For instance, geometric deviations of size, form and position result, which can harm the fulfillment of a function of two combined parts. Thereby, the functionality of technical parts in terms of its assembling ability is significantly influenced by the interaction of various geometric deviations. For this reason, it is essential that the geometric shapes meet their requirements. Because geometric deviations in technical components are unavoidable limits need be given. This is typically done by tolerances that have to be complied the physical manufacturing of the technical parts.

For additive processes, it is not known how large such tolerances can and have to be. Reliable and comprehensive information about tolerances for additive manufacturing processes are neither known in literature nor in applicable standards. Although tolerances are increasingly specified by users, these values mostly come from individual experience and are not empirically justified. Furthermore, these tolerances are limited in their application because they are dependent on a large number of influential factors. At time, neither the reasons for the occurrence of the deviations nor the tolerances to limit the deviations are known.

Thus, the project has two different aims. First dimensional tolerances will be systematically determined that can be stated if additive manufacturing is workshop-commonly used. A workshop-commonly usage describes the application of often used and unchanged standard parameters, materials and machine settings. Secondly, it will be considered, how dimensional deviations and the derived tolerances can be reduced. Therefore, relevant process parameters and manufacturing influences will be identified first. Next, optimized settings will be examined for process parameters and manufacturing influences that can be used to minimized dimensional deviations and dimensional tolerances.