# A Comparative Study of the CMT+P Process on 316L Stainless Steel Additive Manufacturing
## 1 Introduction  
Additive manufacturing (AM) is a new technology for manufacturing components by continuously depositing material on the substrate. This method is considered as an alternative, cost-effective method for the production of traditional metal components, and can save delivery time and costs [1]. In recent years, many scholars have devoted themselves to researching additive manufacturing technologies including selective laser sintering (SLS) [2; 3], selective laser melting (SLM) [4; 5; 6; 7], electron beammelting (EBM) [8], wire arc additive manufacturing (WAAM) [9], etc. Among them, WAAM has the advantages over traditional parts manufacturing methods in that it can reduce the waste of raw materials, has better performance, low cost, high molding efficiency [10], and is easy for commercial production. In past decades, WAAM has become an important research hotspot all over the world [11]. [PERSON] et al. [12] used a molten electrode gas shielded welding method to deposit C-Mn steel upright walls with the mechanical properties similar to welds. [PERSON] et al. [13] proved that the gas metal arc welding (GMAW) process could deposit AZ91D alloy walls with a higher corrosion resistance than the AZ91D castings. [PERSON] et al. [14] used the WAAM to deposit Al-7 Si-0.6 Mg alloy with well-formed upright walls in which almost no obvious anisotropy was observed. [PERSON] et al. [15] adopted the melt inert-gas welding (MIG) process to deposit Al-6.3% Cu alloy thin-walled and bulk parts in which pore content could be controlled effectively. [PERSON] et al. [16] used inert gas welding process to deposit the vertical wall of martensitic stainless steel 17-4 PH without obvious defect, and the deposition rate reached 9.5 kg/h. GMAW additive technology can achieve low-cost, high-efficiency manufacturing and repairing of large components [17], however, unsuitable process parameters will result in serious heat accumulation, which will deteriorate the molding accuracy and performance [18]. The above research was mainly based on the traditional pulse current to study the influence of various process parameters such as current, voltage, scanning speed and inter layer cooling time on the surface dimensional stability and microstructure of the as-deposited parts, which made it difficult to accurately control the heat input, realize the smooth transition of the droplet, and finally obtain the workpiece with good dimensional accuracy. The cold metal transfer plus pulse (CMT+P) process is a combination of pulse welding process and traditional CMT welding process (that is, in a welding cycle, several pulse welding droplet transitions follow some traditional CMT welding droplet transitions, and then the cycle is repeated). Most studies have shown that, CMT+P has obvious advantages over double pulse current, in terms of improvement of fusion zone width, grain size and liquefying crack [19; 20; 21]. Meanwhile, with the help of reverse wire drawing, the droplet smoothly transits into the molten pool depending on surface tension, thus ensuring the stability of deposition process and improvement of the heat input during the welding process. To sum up, CMT+P has many advantages over other processes, but most of the current research focuses on the comparative study of the weld structure formed by this process and other processes under specific welding current conditions. However, there are few reports on the research of stainless steel additive manufacturing by unifying the process parameters as a single factor of linear energy. 316L stainless steel has the advantages of good formability, moderate price, easy access, high strength, good corrosion resistance, etc., which makes it widely used in industrial fields [22].