Significant adoption barriers for additive manufacturing (AM) for aerospace applications are low yield and high unit cost to produce flightworthy parts. Users often rely exclusively on final inspection methods like CT scans which are slow, costly, size limited and sometimes geometry limited. Critical flaws detected only after final inspection require rejecting the part in its most expensive state, after all AM operation costs have already occurred. This paper describes an in-process inspection method called Layer Topographic Mapping (LTM) used initially with the laser powder bed fusion (L-PBF) process. Every melt Layer in the part is measured immediately upon creation, generating a detailed map or dataset of the layer surface height. Precise, high density measurements are generated using a commercial laser profilometer mounted in the AM machine. This data is processed to locate and identify melt flaw conditions such as unfused or poorly fused powder, porosity and layer distortion that frequently occur in the L-PBF process. Detecting flaws at the Layer level has direct cost and yield benefits. If a Layer flaw is fatal (i.e. cannot be repaired) the part is immediately terminated at the lowest possible cost. If the flaw is repairable (as several L-PBF flaw types are) inline repair can be performed prior to formation of the next melt Layer, thereby salvaging the part. In both instances yield is improved and unit cost is significantly reduced. The paper describes experimental LTM results obtained with L-BPF of Inconel 625 samples performed under a NASA contract. LTM detected flaw types and locations correlated well with known and CT results for pre-seeded flaws. Future directions for development of the LTM method are also addressed.
展开▼
