Selective Laser Melting Additive Manufacturing Research Articles

Microstructural and mechanical properties study of various lattice structures of SS316L-CNTs nano composites fabricated through additive manufacturing

Abstract In this work, various lattice structures, such as FCC (face-centered), BCC (body-centered), GD (Gyroid), and BGD (bare gyroid (without CNTs)) with four different porosities (60%, 70%, 80%, and 90%), were prepared through the SLM (selective laser melting) additive manufacturing process. Stainless Steel (SS) 316L alloy was utilized as the base material, while 0.2 wt.% functionalized CNTs (Carbon Nanotubes) were employed as reinforcement. The uniform dispersion of CNTs was analyzed using FESEM, TEM, and Raman spectroscopy. The results indicated that the plateau stress increases with the addition of CNTs, as well as with relative density, whereas energy absorption increases with the addition of CNTs. However, with increasing relative densities, energy absorption nature changes from increasing to decreasing. The results showed that among all lattice structures formed with CNTs addition, the Gyroid lattice exhibited the highest plateau stress, while the BCC lattice exhibited the lowest plateau stress.

Selective laser melting of 2507 duplex stainless steel: Effect of energy density on microstructure and corrosion resistance

Duplex stainless steel (DSS) is widely used in the marine, petroleum, chemical, automotive, and other fields owing to its excellent mechanical properties and corrosion resistance. However, the research on duplex stainless steel prepared by additive manufacturing is still limited. In this paper, high-density 2507 DSS was successfully prepared by selective laser melting (SLM) additive manufacturing. The effects of energy density on the formability, phase composition, microstructure and corrosion properties of SLM 2507 DSS were investigated. The results showed that with the decrease of the energy density, the density of the specimen increases first and then decreases, and the density achieves 99.18% with the energy density of 190.5 J/mm3. The types of phases are not affected by the energy density, i.e., all 2507 DSS samples prepared by SLM showed a ferrite phase. The YOZ (parallel to the building direction) plane of the SLM 2507 DSS samples showed predominantly columnar grains attributed to the high temperature gradient and epitaxial growth characteristics. With the increase of energy density, the average grain size decreases slightly from 16.97 μm to 15.78 μm, the KAM value decreases slightly from 1.15 to 1.05, and the low angle grain boundaries (LAGBs) increase significantly from 68.4% to 74.8%. The SLM 2507 DSS sample exhibited excellent corrosion resistance. The self-corrosion potential of the sample is 136 mV and the self-corrosion current density is 2.066 × 10−8 A/cm2 at the maximum density. This investigation provides a new approach for the preparation of super duplex stainless steel, which can provide a theoretical basis and guidance for industrialized application.

Evolution of microstructure and mechanical properties in multi-layer 316L-TiC composite fabricated by selective laser melting additive manufacturing

Evolution of microstructure and mechanical properties in multi-layer 316L-TiC composite fabricated by selective laser melting additive manufacturing

Effect of heat treatment on electrochemical behavior of biocompatible Ti–Ta–Nb–Zr alloys prepared by selective laser melting

In this paper, cytotoxicity-free Ti-10Ta-2 Nb-2Zr titanium alloy was prepared by selective laser melting additive manufacturing. The effect of solution and annealing heat treatment on the structure and microhardness were investigated. Electrochemical performance in Ringer’s solution at 37℃ was evaluated. This electrochemical evaluation was performed through the open circuit potential variation as the immersed time, potentiodynamic polarization curves, and electrochemical impedance spectroscopy tests. The results show that main phase composition of as-built and heat-treated specimens was the α/α′ phase. The specimen annealed at 500℃ presented a small amount of β phase. The solutionized and annealed specimens had basket-weave microstructure with distributed micro-scaled α/α′ lamellas. The microhardness of as-built specimens was 400.48 ±12.31 HV. After solution and water quenching, the microhardness dramatically increased to 533.85 ±24.67 HV. The microhardness slightly decreased to 495.46 ±4.85 and 488.8 ±13.84 HV after annealing at 300 ℃ and 500 ℃, respectively. Compared with the as-built specimen, the solutionized and annealed specimens had much lower corrosion current density and higher corrosion resistance.

Mechanical characterization of lattice structures fabricated by selective laser melting via an image-based finite cell method with a damage model

Lattice structures fabricated by the selective laser melting (SLM) additive manufacturing process hold great potential for diverse applications. However, their actual mechanical behaviors often deviate from their counterparts with the as-designed geometries due to manufacturing defects. In this study, we presented an in-depth mechanical characterization of imperfect octet lattice structures via an image-based finite cell method (FCM) in combination with the multi-level hp refinement scheme for resolving the local defects and a Lemaitre damage model to conduct the damage analysis. Micro-computed tomography scanning was utilized to scan six SLM-fabricated octet lattice cells to obtain their as-built geometries. Based on the obtained geometry, the force-displacement curves and the damage distribution of the octet lattice cells and struts under given loads were predicted. The numerical results indicate that external defects significantly affect the struts' damage distribution, while internal voids have a lesser influence due to their low volume fraction. It is identified that the SLM-fabricated octet lattice cell presents better elastoplastic behavior along the loading direction perpendicular than parallel to its build direction. These insights into the mechanical performance of imperfect octet lattice cells underscore the defects' adverse effects and advance the understanding of their significance in SLM components.

Fracture and Wear Behavior of Functionally Graded 316L–TiC Composite Fabricated by Selective Laser Melting Additive Manufacturing

Herein, the tribological and fracture behavior of multilayer 316L–TiC composites produced by the selective laser melting additive manufacturing process is investigated. The results show a robust interface between the layers and no cracks are detected even after a flexural strain of 0.4. The hardness of the composite layers with 5 and 10 wt% TiC increases by 75.5 and 104.8% compared to the hardness of the pure 316L stainless steel layer. Transverse rupture strength measurements show that a layer of pure 316L significantly improves the rupture strength of the multilayer samples. Wear test results show that the inclusion of TiC particles increases wear resistance, with the composite layer containing 10 wt% TiC demonstrating the highest wear resistance.

Effects of process parameters on microstructure properties of WE43 magnesium alloy by selective laser melting

Magnesium alloys have broad application in aerospace, biomedicine and automobile, et al. Selective Laser Melting (SLM) additive manufacturing of magnesium alloy can fabricate complex components with acceptable properties. However, the low evaporation heat of magnesium alloy at ambient temperature leads to vaporization instead of melting during the SLM forming process, posing significant challenges for achieving successful SLM fabrication of magnesium alloys. Hence, the objective of this paper is to analyze the impact of various process parameters on the distribution of macroscopic defects and the relative density during SLM additive manufacturing test of WE43 magnesium alloy samples. Additionally, it investigates the effect of forming parameters on the microstructure by examining molten pool morphology, grain size, and material composition. Mechanical property tests are conducted to establish correlations between relative density, microhardness, strength, and energy density in printed samples. Consequently, optimal SLM manufacturing parameters for WE43 magnesium alloy are determined as follows: laser power 200 W and scanning speed 800 mm/s. This study successfully achieves high-performance additive manufacturing of magnesium alloy materials.

A novel additive manufacturing strategy with high hydrogen production for ordered-porous stainless steel catalyst support

This paper proposes to improve hydrogen production performance of ordered-porous stainless steel by increasing its forming structure parameters. Firstly, selective laser melting additive manufacturing of ordered-porous stainless steel is carried out through designed orthogonal experiment table, to obtain its forming structure parameters under different manufacturing process parameters. Then, different forming structure parameters of ordered-porous stainless steel are converted into a comprehensive index by grey relation theory, which is grey relational degree (GRD). When powder thickness, scanning speed, scanning space and laser power are 30 μm, 800 mm/s, 90 μm and 60 W, respectively, the highest GRD of 0.930 is obtained, when those are 40 μm, 1200 mm/s, 70 μm and 60 W, respectively, the lowest GRD of 0.410 is gained. Finally, catalyst bonding strength and hydrogen production performance of the ordered-porous stainless steels with the above GRDs are verified. It is found that the ordered-porous stainless steel with the highest GRD has higher catalyst bonding strength and higher hydrogen production performance. When 12 mL/h injection rate of methanol–water solution and 250 ℃ reaction temperature are used, CH3OH conversion, H2 flowing rate and CO selectivity of the above ordered-porous stainless steel are 64.3%, 0.396 mol/h and 6.75%, respectively.

Parallel batch processing machines scheduling for SLM additive manufacturing in cloud manufacturing

For the scheduling problem of parallel batch processing machines for Selective Laser Melting (SLM) additive manufacturing in cloud manufacturing environments, an Improved Discrete Artificial Bee Colony algorithm(IABC) is proposed by considering the service time of the product as well as introducing the mathematical model of the problem. Firstly, a population initialization strategy is introduced to improve the quality of initial solutions and accelerate the convergence of the population.Secondly, through three neighborhood search operators, the transition from the original nectar source to the new nectar source is achieved for employed bees and following bees. Furthermore, a local search strategy and a modified abandonment pattern are proposed to increase population diversity and prevent the algorithm from falling into local optima.Finally, the performance of the algorithm is analyzed, and the IABC algorithm was applied to 36 examples. The effectiveness and advantages of IABC in solving the studied problem are verified through a large number of simulation experiments.

Impact of Heat Treatment and Building Direction on Tensile Properties and Fracture Mechanism of Inconel 718 Produced by SLM Process

In the selective laser melting (SLM) additive manufacturing process of Inconel 718, the emergence of Laves and δ precipitate phases in the γ matrix during or after heat treatment is a critical consideration. This study comprehensively assesses the microstructures and mechanical properties of Inconel 718 alloy produced through SLM under varied conditions: as-built (AB), homogenization + solution + aging (HSA), homogenization + aging (HA), and solution + aging (SA). Additionally, the impact of building orientation, whether horizontal (H) or vertical (V), is investigated. The AB specimens oriented horizontally display a columnar melt pool structure, with dimensions roughly between 300 and 400 μm. In contrast, the AB specimens aligned vertically show an elongated river-like structure of melt pools, with their sizes approximately at 250 μm. From the detailed microstructural analysis, the findings reveal that the as-built specimens lack γ′ and γ″ precipitates in their microstructure. Conversely, in heat-treated specimens, both the γ′ and γ″ phases are evident. Notably, Inconel 718 alloy specimens subjected to SLM fabrication and SA heat treatment demonstrate optimal mechanical performance. Notably, SA exhibits an average hardness of 476 HV for the horizontal specimen, which is 51.1% higher than that of AB specimens. The morphology and distribution of the δ phase in the γ matrix emerge as decisive factors influencing high-temperature performance. In SA specimens, the dissolution of brittle Laves phases occurs, and the presence of the δ phase at the grain boundary imparts superior properties during high-temperature tensile testing, including excellent yield and ultimate tensile strength. The presence of the granular-δ phase in the SA specimens resulted in a tensile strength of 1422 MPa and a yield strength of 1236 MPa, which are the highest values among all the specimens. SA has a tensile strength of 1120 MPa and a yield strength of 974 MPa at 650 °C.

Effect of heat treatment on the microstructure and mechanical properties of biocompatible Ti–Ta–Nb–Zr alloys prepared by selective laser melting

Abstract In this paper, a low elastic modulus, non-cytotoxic Ti-10Ta-2Nb-2Zr titanium alloy was prepared by selective laser melting additive manufacturing. The effect of annealing and solution heat treatment on the structure, mechanical properties, and tribological behavior were investigated. The results show that the microstructure was composed of the main α′ phase and a small amount of β phase. Heat treatment improved strength and elongation. The ultimate tensile strength (UTS) and elongation of the deposited specimen were 807 ± 8.74 MPa and 6.6 ± 0.75 %, respectively. After annealing, the UTS was nearly the same, but the elongation increased to 15.3 ± 0.95 %. After solution and aging, the UTS and elongation increased to 873 ∼ 813 MPa and 9.25–11.9 %, respectively. The elastic modulus of the deposited specimen was 120 ± 6.81 GPa. The elastic moduli of heat treated specimens ranged from 74 ± 4.04 to 96 ± 5.13 GPa. The elastic moduli of heat treated specimens were close to that of β-type titanium alloys. The wear mechanism was mainly abrasive wear and oxidative wear. Compared with the deposited and annealed specimens, the solution and age treated specimens had low friction coefficients and much better wear resistance. In terms of properties and cost, the designed alloy has great potential in the medical implant field.

Compressive properties of AlSi10Mg lattice structures with novel BCCZZ and FCCZZ configurations fabricated by selective laser melting

PurposeThis paper aims to examine the static compression characteristics of cell topologies in body-centered cubic with vertical struts (BCCZ) and face-centered cubic with vertical struts (FCCZ) along with novel BCCZZ and FCCZZ lattice structures.Design/methodology/approachThe newly developed structures were obtained by adding extra interior vertical struts into the BCCZ and FCCZ configurations. The samples, composed of the AlSi10Mg alloy, were fabricated using the selective laser melting (SLM) additive manufacturing technique. The specific compressive strength and failure behavior of the manufactured lattice structures were investigated, and comparative analysis among them was done.FindingsThe results revealed that the specific strength of BCCZZ and FCCZZ samples with 0.5 mm strut diameter exhibited approximately a 23% and 18% increase, respectively, compared with the BCCZ and FCCZ samples with identical strut diameters. Moreover, finite element analysis was carried out to simulate the compressive response of the lattice structures, which could be used to predict their strength and collapse mode. The findings showed that while the local buckling of lattice cells is the major failure mode, the samples subsequently collapsed along a diagonal shear band.Originality/valueAn original and systematic investigation was conducted to explore the compression properties of newly fabricated lattice structures using SLM. The results revealed that the novel FCCZZ and BCCZZ structures were found to possess significant potential for load-bearing applications.

Microstructure and compression performance of novel AlSi10Mg composite auxetic structures fabricated by additive manufacturing

In order to further increase the mechanical properties of auxetic structures, a novel enhanced composite (NEC) auxetic structure was proposed and characterized by the combination of the enhanced re-entrant anti-trichiral and double arrow structures. The NEC structures were fabricated from AlSi10Mg powders through selective laser melting (SLM) additive manufacturing technology. The grain morphology and microstructure characteristic of the AlSi10Mg sample were comprehensively analyzed. Results indicate that both columnar and equiaxed grains can be observed in the SLM-fabricated sample. Columnar grains with the size around 52 μm are mainly distributed in the melt pool and equiaxed grains exist at the boundary of the melt pool. The columnar grains are approximately perpendicular to the boundary of the melt pool and grow towards the center of the melt pool, exhibiting <100> filamentous texture. The melt pool boundaries can be divided into three distinct regions, i.e., coarse grain zone, fine grain zone, and heat affected zone. The microstructure of the as-built sample consists of elongate cellular α-Al matrix decorated with eutectic Si network boundaries. The mechanical properties and energy absorption performance are systematically investigated by means of Finite Element Analysis (FEA) verified by the experimental results. It is found that the elastic modulus, compression strength, Poisson's ration and energy absorption of the NEC structures are sensitive to the structure parameters. i.e., the compression stress and energy absorption present an increasing trend with the increasing of α, decreasing of l1 and β, while l1, α and β exhibit opposite effect on the Poisson's ratio. Moreover, the rotational combination of varied structures can lead to an excellent energy absorption capacity of the NEC structures, which is significantly higher than that of other auxetic structures. The results will provide guidance for the structure design of lightweight auxetic structures with enhanced performance and outstanding auxeticity.

Room Temperature Corrosion Behavior of Selective Laser Melting (SLM)-Processed Ni-Fe Superalloy (Inconel 718) in 3.5% NaCl Solution at Different pH Conditions: Role of Microstructures

Inconel 718 (UNS N07718) is a nickel-base superalloy containing iron that is used at cryogenic temperatures (arctic pipe components) and at high temperatures (gas turbines). This alloy is also used in off-shore oil drilling due to its high overall strength and resistance to corrosion. Inconel 718 components are created by a selective laser melting (SLM) additive manufacturing route and result in isotropic fine-grained microstructures with metastable phases (such as Laves phases) that are not usually present in conventional manufacturing processes. In this work, SLM Inconel 718 alloy specimens were investigated in four different conditions: (1) As-manufactured (AS-AM), (2) Additively manufactured and hot isostatically pressed (AM-HIP), (3) As-manufactured and heat-treated (solution annealing followed by two-step aging), and 4) AM-HIP and heat-treated. Localized corrosion behavior was evaluated at room temperature in a 3.5% NaCl solution at three different pH conditions (pH 1.25, 6.25, and 12.25). Electrochemical tests, including linear polarization, cyclic polarization, potentiostatic conditioning, electrochemical impedance spectroscopy, and Mott–Schottky analyses, were used to compare the corrosion behaviors of the SLM specimens with that of the conventionally wrought IN718 samples. The results showed that the additively manufactured specimens showed better corrosion resistance than the wrought material in the acidic chloride solution, and the AM-HIP specimens exhibited superior corrosion resistance to the as-manufactured ones. Hot isostatic pressing resulted in the visible elimination of the dendritic structure, indicating compositional homogeneity as well as a significant decrease in porosity. In addition, the deleterious secondary phases, such as Laves and δ phases, were not observed in the microstructure of the HIPed samples. The AM-HIP material showed the highest corrosion resistance in all the pH conditions. The two-step aging treatment, in general, resulted in the deterioration of corrosion resistance, which could be attributed to the formation of γ′ and γ″ precipitates that increased the cathodic reaction catalytic activities. In the additively manufactured samples, the presence of the Laves phase was more detrimental to corrosion resistance than any other phases and MC carbide and grain boundary δ phase increased the susceptibility to corrosion in wrought materials.

Design optimization of 3D-manufactured monolithic stage for biomedical polishing applications by neural artificial network and teaching learning studying based optimization algorithm

Ultra-precision polishing engineering is a current trend in ensuring the good surface quality for biomedical applications. In precision engineering, compliant mechanism, so-called monolithic mechanism, has an increasing trend in alternating conventional rigid counterparts which can be utilized for biomedical polishing application. Therefore, this article proposes an optimal design for the monolithic stage. The stage is employed in driving the polishing head. The stage is operated within from several millimeters to hundreds of millimeters. In this article, the stage was tended to guide the head to polish the biomedical samples. Hypercube sampling design is combined with finite element method to collect the data. The teaching learning-based optimization algorithm is firstly coupled with the artificial intelligence in modeling the behaviors of the stage (resonant frequency, displacement, strain energy, and stress). Next, the teaching learning studying based optimization algorithm is extended to search the optimal parameters of the stage. Three single objective optimization scenarios and two multiobjective optimization scenarios of the monolithic stage are conducted to show the effectiveness of the offered method. The predictors were well-formed by using the teaching learning-based optimization-coupled artificial neural network. The results found that the performance indicators (R and R2) are almost equal to one with the mean square error (MSE) and root MSE values are very small. The optimal results that the stage can work with a highest frequency of 760.7903 Hz, a largest stroke of 0.7325 mm (about 732.5 μm), and a strain energy of 2.5999 mJ. Meanwhile, the von Mises stress is almost much lower than the yield strength of AL 7075-T73. The designed method can effectively use in designing the stage. The stage can be fabricated by using selective laser melting additive manufacturing technology, and it can be employed to guide the polishing head for biomedical samples.

Fatigue behavior of notched and unnotched AM Scalmalloy specimens subjected to different surface treatments

In the present work, the fatigue resistance values of Scalmalloy specimens obtained by selective laser melting (SLM) additive manufacturing (AM) are experimentally studied. The fatigue levels of specimens with and without notches after applying different surface treatments, such as sand blasting, shot peening, isotropic finishing, and polishing alone or in combination, are analyzed. To understand the fatigue behavior of this material, the surface finishes and internal residual stresses of the specimens are analyzed. Moreover, the fracture surface of each sample is observed by electron microscopy to determine the failure mechanism. There is a clear separation between two different types of failure: (1) rupture by a crack generated on the surface associated with high applied stress values and (2) failure by a crack generated on an internal defect associated with low applied stress values.

Influence of oxygen content on selective laser melting leading to the formation of spheroidization in additive manufacturing technology.

Selective laser melting (SLM) additive manufacturing technology with different oxygen contents leads to the appearance of spherical solids of different sizes on the surface of the part, which affects the mechanical properties of the part, surface roughness, etc. In this study, the SLM molding technique was applied using three different 316L metal powders with different oxygen contents. The spheroidization properties and morphology of the samples were observed using a Quanta 200 environmental scanning electron microscope (ESEM), and the samples were observed microscopically and subjected to EDX spectroscopy using metallographic microscopy, and the mechanical properties were investigated. The results of the study showed that when using gas atomized powders, no spheroidization occurred when the oxygen content of the powders was 5.44 ± 0.01% in all cases, whereas using water atomized powders produced spherical structures with larger dimensions. This observation was closely related to the shape and particle size of the powder. When 316L metal powder with an oxygen content of 4.52 ± 0.01% was used for molding, small spherical structures appeared on the surface of the samples. When metal powder with an oxygen content of 5.44 ± 0.01% was used for the molding, larger spherical structures appeared on the surface of the samples. When the powder with an oxygen content of 5.90 ± 0.01% was used for the molding, more small spherical structures and some large spherical structures appeared on the surface of the samples. This suggests that higher oxygen levels may inhibit the occurrence of spheroidization. EDX spectroscopic analysis revealed that the white matter on the surface of the samples without spheroidization was mainly composed of Fe and Cr, whereas the white matter on the surface of the large-sized spherical structures was mainly composed of Si and Mn, which may be related to the oxygenophilicity of the various substances.

Deep learning-enabled design for tailored mechanical properties of SLM-manufactured metallic lattice structures

The lattice structures obtained by combining repetitive light cellular forms provide superior high strength to weight capabilities compared to monolithic solid bodies. These properties of lattice structures can be further enhanced by improving the design and manufacturing process. However, the process of creating aluminum alloy lattice structures with tailored mechanical properties is still challenging due to the wide range of possible designs and their complex structure-property relationships. This paper proposes a new methodology that uses the deep learning-based 3D Generative Adversarial Network (3DGAN) model to solve this complex engineering problem. Unlike previous studies on deep learning-based lattice design, the dataset obtained through parametric design and Simulated Annealing techniques enables GAN to create new 3D lattice structures with improved mechanical strength properties. The designs generated with the GAN algorithm were produced using Selective Laser Melting Additive Manufacturing (SLM-AM) technology. The mechanical properties of SLM-fabricated (SLMed) AlSi10Mg unit cell samples were examined by a series of compression and impact tests. The results reveal that the lattice configurations generated using the generative model exhibit improved mechanical properties (e.g., a remarkable increase in normalized energy absorption and extension capacities of up to 57% and 26%, respectively). This study shows that designs generated with the 3DGAN model in lattice structures improve the design space by improving their mechanical properties. Moreover, the successful integration of deep learning and SLM-AM opens up new possibilities for creating custom parts with improved strength-to-weight ratios, dimensional accuracy, and mechanical performance.

Experimental investigation on microstructure and properties of Al alloy-PEEK joint with different surface structure obtained by hot-pressing

In this study, selective laser melting (SLM) additive manufacturing was used for the fabrication of Al alloy with the surface structure based on the construction of mechanical interlocking mechanism to complete the joining with polyetheretherketone (PEEK). The application of hot-pressing process provided a direct joining between Al alloy-PEEK at 460 °C for 40 min. This work characterized the forming of both cylindrical and trapezoidal structures, indicating that the structures were formed completely, and the gaps were clear. Although some dimples or micropores were generated in the forming solid, these defects in the forming were beneficial for the flowing and filling of PEEK during hot-pressing joint. The microstructure of Al plate fabricated by SLM showed typical parallel columnar grains perpendicular to the deposition direction and stacked and fish scale like feature in the deposition direction, respectively. The microstructure characterizations of Al alloy-PEEK joints showed that both materials were joined without gaps and formed a strong mechanical interlocking, guaranteeing a firm bond with maximal tensile shear strength up to 81 MPa for trapezoidal structure. By comparison, the joint with cylindrical structure possessed a low 65 MPa shear strength due to weak cuneiform anchor interlocking. Fracture surface was investigated in more detail. The result showed that the joint with cylindrical structure mainly showed interfacial failure and pulling-out, tilting deformation and fracture of the supporting, while the joint with trapezoidal structure exhibited a separation between the top surface of the supporting and the PEEK and brittle cohesive fracture of the PEEK between the gaps.

Influence of forming directions on surface quality of 316L produced by selective laser melting additive manufacturing

Different forming directions have significant impact on surface quality in additive manufacturing. This study is aimed at exploring how different forming directions influence surface quality in additive manufacturing (AM). First, experiments were designed to prepare 316L stainless steel by selective laser melting additive manufacturing (SLAAM) in different forming directions. Moreover, the surfaces of samples manufactured by AM were tested using a three-dimensional (3D) surface profiler and a scanning electron microscope. Furthermore, the surface quality was characterized using four parameters, maximum height, S z ; maximum valley depth, S v; standard deviation of height, S q ; and arithmetic average height, S a. The following results were obtained: (a) different forming directions corresponded closely to upper surface roughness S a values, the values of S a being 7.16 and 8.20 μm, respectively. S a was the smallest among the four parameters; it showed good stability and statistical significance. (b) In the same forming direction, the upper surface roughness values followed the order S z &gt; S v &gt; S q &gt; S a. S z was the largest, exceeding 800 μm; the average value S a was the smallest, reaching 7.36 μm. The values of S q , S z and S v vary when the forming direction changed. Specifically, all of them increased when the forming direction changed from a vertical direction to planar and lateral directions in turn. (c) In different forming directions, the values of S z , S v, S q and S a varied on different surfaces but their variations were basically similar. Meanwhile, the S z , S v, S q and S a values of the free surfaces were at least ten times greater than those of the printed surface. In the SLAAM process, it was necessary to select a forming direction reasonably for parts with different dimensional parameters on each side.