Pure copper is widely used for complex shapes, high thermal conductivity and good conductivity parts, such as heat exchangers, welding nozzles, injection molds, and various conductive parts. However, traditional manufacturing techniques are difficult to design complex pure copper parts into the most effective thermal and conductive structure. Selective Laser melting(SLM) can fabricate parts with complex shapes directly. However, due to the characteristics of easy oxidation, high optical reflectivity and high thermal conductivity, 3D printing pure copper by SLM is extremely challenging. In this study, the feasibility of fabricating pure copper by low-laser energy was studied by both numerical simulation and printing experiments, and the characteristics of the molten pool (molten pool structure, temperature flow and velocity flow) were studied. The results showed that due to its high thermal conductivity, heat spread out quickly in the molten pool, temperature rise rate and cooling rate reached as high as 1.36 × 10⁷ K S⁻¹, 2.99 × 10⁵ K S⁻¹ respectively. And it took only about 1.7 × 10^–4 S for the process time of powder melting and solidification. Additionally, by reducing the particle size, the absorption rate for pure copper was improved, pure copper parts were successfully fabricated with low-laser energy: laser power 500 W, hatching space 0.07 mm, layer thickness 0.03 mm, laser scanning velocity 2500 mm s⁻¹.

Selective Laser Melting (SLM) has become one of the most promising technologies in Metal Additive Manufacturing (MAM), which is a complex dynamic non-equilibrium process involving heat transfer, melting, phase transition, vaporization and mass transfer. The characteristics of the molten pool (structure, temperature flow and velocity flow) have a decisive influence on the final forming quality of SLM. In this study, both numerical simulation and experiments were employed to study molten pool structure, temperature flow and velocity field in Selective Laser Melting AlCu5MnCdVA alloy. The results showed the structure of molten pool showed different forms (deep-concave structure, double-concave structure, plane structure, protruding structure and ideal planar structure), and the size of the molten pool was approximately 132 μm × 107 μm × 50 μm: in the early stage, molten pool was in a state of deep-concave shape with a depth of 15 μm due to multiple driving forces, while a protruding shape with a height of 10 μm duo to tension gradient in the later stages of forming. The metal flow inside the molten pool was mainly driven by laser impact force, metal liquid gravity, surface tension and recoil pressure. For AlCu5MnCdVA alloy, metal liquid solidification speed was extremely fast (3.5 × 10⁻⁴ S), the heating rate and cooling rate reached 6.5 × 10⁷ K S⁻¹ and 1.6 × 10⁶ K S⁻¹, respectively. Choosing surface roughness as a visual standard, low-laser energy AlCu5MnCdVA alloy optimum process parameters window was obtained by numerical simulation: laser power 250 W, hatching space 0.11 mm, layer thickness 0.03 mm, laser scanning velocity 1.5 m s⁻¹. In addition, compared with experimental printing and numerical simulation, the width of the molten pool was about 205 um and about 210 um, respectively, and overlapping between two adjacent molten tracks was all about 65 um. The results showed that the numerical simulation results were basically consistent with the experimental print results, which proved the correctness of the numerical simulation model.

A new two-step selective laser remelting (SLR) process was proposed to fabricate 316L stainless steel. The density, surface roughness, and mechanical properties were investigated by a multifunctional density tester, surface roughness meter, and tensile testing machine. Compared with the single-melting selective laser melting (SLM) process, the relative density, surface roughness (R_a), ultimate tensile strength, yield strength, elastic modulus, and elongation reached 99.31%, 6.67 μm, 725 MPa, 643 MPa, 13.95 GPa, and 40.8%, respectively. In addition, the microstructure and fracture characteristics were studied by OM, SEM, and EDS. The results showed little unmelted powder and fewer defects (balling, spatter, and cracks). In addition, a closer and smoother connection between the welds and equiaxed cell were obtained by the SLR process.

In this paper, high-silicon Al–42Si alloy was prepared by selective laser melting (SLM) with different process parameters. Microstructures evolution and defects formation were studied and process parameters were optimized. The results shown that the density of SLM-fabricated Al–42Si alloy increases as input energy density increases. The highest and lowest density of SLM-fabricated Al–42Si alloy are obtained, when input energy density is 42.9J/mm³ and 33.8J/mm³ respectively. The microstructures of Al–42Si alloy fabricated by selective laser melting is mainly composed of primary silicon phase and eutectic silicon phase, which is distinct from casting alloy because of diffient grains size and shapes of the primary silicon. With higher energy density, larger size of the primary silicon observed during process due to higher heat released by powder. The size of primary silicon phase particles is in the range of 2.9–9.4μm, and the size of molten pool during SLM process is in the range of 125 ± 10μm–140 ± 10μm in this study. Also the hardness of SLM-fabricated Al–42Si alloy increases as input energy density increases between 40.0J/mm³ and 42.9J/mm³. After heat treatment, the residual stress is eliminated, microstructure stability and homogeneous of SLM-fabricated Al–42Si alloy are improved. The silicon distribution is more uniform and sizes increases about 1∼2μm, and the hardness decreases after heat treatment. The optimal SLM parameters for Al–42Si alloy are laser power of 320W, scanning speed of 1355 mm/s, layer thickness of 50μm and scanning space of 110μm.

Additive Manufacturing(AM) is an advanced direct-manufacturing technology, based on the discrete-stacking principle. Laser Powder Bed Fusion (L-PBF) is one of the most promising technologies in the field of metal AM, with the characteristics of fabricating parts with complex shapes directly. For L-PBF equipment , the core device is lasers, and almost all L-PBF printers are currently equipped with infrared laser. However, due to too low absorption rate of the pure copper surface to infrared laser and high thermal conductivity between pure copper, it is extremely challenging to fabricate pure copper by traditional infrared-laser powder bed fusion(IR L-PFB). In this work, green-laser was applied to replace traditional infrared laser during L-PBF process, molten pool structure and temperature flow behavior of Green-Laser powder bed additive manufacturing pure copper was studied by mesoscopic simulation. Here we show that green-laser greatly improved the absorption rate of the pure copper surface, and the result showed that with lower cost laser process parameters (lower laser power 300W and larger hatching space 0.08 mm), pure copper parts with smoother surface, no-remelting and no obvious defects could be fabricated successfully.