# A Comparative Study of the CMT+P Process on 316L Stainless Steel Additive Manufacturing
## 5 Conclusions  
This study presented and evaluated a line energy method to carry out single channel multilayer continuous deposition of 316L stainless steel wire based on CMT+P process of GMAW. The morphology, microstructure, properties of arc-welding deposited samples, and the conclusions were drawn as follows:  
1. The novelty of this study is that multiple welding parameters are integrated into the single parameter named linear energy which as the unique parameters related to heat input during arc-welding deposition process, through adjusting the linear energy parameter and carrying out the comparative experimental method to find the best linear energy for 316L stainless steel AM. The results show that linear energy of 2.37 kJ/cm is the best for CMT+P process. 2. Only when the wire feeding speed and welding speed were in a proper matching range during CMT+P arc-welding deposition additive manufacturing, could the deposited samples with good deposition wall appearance be guaranteed. The difference between the actual and the optimal wire feeding speed matching the specific welding speed was too large, which led to an unstable deposition process and caused the flow of weld bead metal and collapse, thus seriously deteriorated the appearance of the deposition samples, so in appearance, sample #1 was the worst in the four deposited samples. 3. Oxide and microstructure defects increased with the increase of linear energy, even the obvious and extremely wide cracks formed in sample #4 under the highest linear energy (2.85 kJ/cm), so it is necessary to avoid depositing parts at high linear energy by CMT+P process. Although sample #1 perform well in micromorphology, in terms of micromorphology and saving costs of machining, sample #2 are the best in the four as-deposited samples in this study, and the linear energy of 2.37 kJ/cm is the most appropriate parameter for 316L CMT+P-AM. 4. The micro-hardness fluctuated periodically due to the change of grain structure of the deposition layer, as well as decreased first and then increased in the bottom, middle and top regions of the deposited wall. The reason for this can be attributed to the fine-grain-strengthening caused by the rapid cooling effect of substrate result in high microhardness at the bottom of samples; however, successive heat accumulation made the values go down at the middle, and high dislocation density and solution strengthening effect due to rapid solidification caused the microhardness to rise again at the top. The average microhardness of four samples decrease with the increase of line energy. 5. With linear energy gradually increased, the tensile strength values in the horizontal and vertical direction showed a downward trend, and the average values of YS and UTS in the two direction of the four as-deposited samples all satisfied the industrial standard requirement for 316L forgings, and except for sample #4 (linear energy of 2.85 kJ/cm), the UTS of the other three samples are all higher than that of parts produced by SLM with hot-isostatic pressed, thus, in terms of cost savings and production efficiency, compared with SLM process, CMT+P is more suitable for manufacturing the parts with non-high dimensional accuracy requirements. 6. The bearing capacity of the austenite dendrite grew along the construction direction was stronger than that of the dendrite side boundary, which made the strength of the tensile samples in the vertical direction higher than that in the horizontal direction, and the mechanical properties of the deposited samples were obviously anisotropic. In addition, the higher linear energy reduced the saturation of solid solution to reduce the precipitated spherical particles, which caused the decrease of tensile strength of as-deposited samples. 7. The results of this experiment show that the excessive linear energy will have a negative effect on the mechanical properties of the as-deposited parts.