Part Orientation and Support Structure Generation

INTRODUCTION:

Additive manufacturing is a process increasingly used in all industries: automobile, aerospace , medical and electronics. The principle of this manufacturing consists in stacking layers of materials on the top of each other to create the desired part. Materials like metal, plastic or composite can be used in the form of powder, liquid or solid form for plentiful process assembly. In additive manufacturing, a part will always be printed according to Z-axis, however its positioning on the machine's tray, called part building orientation, is not unique. This positioning has to respect some important rules established for additive manufacturing.

Below are the main rules:

·         Support must be built for overhangs with a low angle value. This value depends on the process but is mainly set around 45 degrees (angle between horizontal and material)

·         Holes axis should be oriented under manufacturing's direction to avoid supports in holes during a printing

·         Contacts between part and supports must be minimised to save time during post-processing and to obtain an acceptable surface quality

·         Fillets with a low radius need to be removed to avoid manufacturing defaults and add ones between the tray and part to avoid part's material removal during its cleaning

·         A wall must have a minimum thickness to be printed which depends on its tilt. In post-treatment cases, it is advised to have more thicken wall for functional surfaces

·         Part positioning on the tray should have the lowest height to be quickly printed

Before the printing of a part, the user must defne the part building orientation. It is not trivial because the orientation has an impact on several parameters. Among those, you can find part accuracy and surface finish generated by the staircase effect; the volume and complexity of supports created to support the part's overhangs during the printing and its building time and building cost. To find a part building orientation which will help to satisfy all criteria above is not an easy task. In fact, an orientation which gives a very satisfactory surface finish can lead to a long printing time, thus, to a bigger cost. The methodology tackled in this article aims to find a compromise between these diferent criteria. It aims to help the user to position his part on the machine according to his wish. After a literature review, this paper will present a methodology for part building orientation in additive manufacturing. The selected criteria used in this methodology will be examined. Then applications and case study will be presented. Finally, a conclusion and a future scope will be discussed.