Abstract
Additive manufacturing is strongly stimulated by upcoming laser technologies especially in the field of direct metal laser fabrication (DMLF). The main driving force of rapid prototyping (RP) technology has now been shifted from rapid prototyping (RP) to rapid tooling (RT) and rapid manufacturing (RM). Direct metal fabrication techniques, especially those involving the use of laser as a source of energy, are being widely used to fabricate net-shaped parts required for various application sectors including automotive, aerospace and biomedical industries. Such widely used techniques include selective laser sintering (SLS), selective laser melting (SLM), 3D laser cladding and laser engineered net shaping (LENS). These techniques offer several incomparable advantages but in parallel there are numerous mechanical as well as metallurgical-based difficulties which are still need to be overcome. Surface quality, density improvement, powder flowability, solidification, microstructure evolution, dimensional inaccuracies, shrinkage and deformations are some of these difficulties in direct metal fabrication. Large-scale and thin-walled products are still challenging during additive manufacturing. The present paper reviews the research work carried out in the area of direct metal laser fabrication and their various challenges evolved during part fabrication consisting of different metals and alloys. In order to overcome some of the challenges, various hybrid processes are being developed such as electrophoretic deposition, plasma laser deposition, selective laser gelation, 3D micro-welding and laser free-form fabrication which are also discussed in this review. Since additive manufacturing is significantly contributing to biomedical field in the form of fabricating various biomedical implants and scaffolds, therefore several difficulties related to metal fabrication in biomedical sector and their possible remedial solutions are also discussed in this review. The article also highlights the research gaps and future research directions in the context of critical challenges which are still existing in front of direct metal fabrication techniques.