Laser Sintering Process Parameters Research Articles

Dry sliding wear behavior of energy density dependent PA 12/Cu composites produced by selective laser sintering

Abstract The selective laser sintering process is widely used to fabricate polyamide matrix composites. Although various reinforcements are used to produce polyamide matrix composites, metallic-based reinforcements are used to improve the mechanical properties of the structure. Also, selective laser sintering process parameters significantly affect the microstructural and mechanical properties of the composite products. In this study, polyamide 12 (PA 12) matrix composites were produced with Cu particulates by selective laser sintering methods using various energy density values. Moreover, dry sliding wear of the energy density dependent PA 12/Cu composites was investigated. Worn samples were characterized by scanning electron microscopy and 2D profile analysis. The examinations revealed that the lower energy density values improve the microstructural properties and wear behavior of the PA 12/Cu composites. It was obtained that the lowest energy value provides the highest wear resistance for the PA 12/Cu composites.

On failure analysis of three-dimensional printed functionally graded material prepared by direct metal laser sintering

In the past decade, some studies were reported on the successful three-dimensional printing of meta-structure-inspired functionally graded material with two different alloys (having a wide difference in melting range ≈ 450–500 °C) by direct metal laser sintering. But hitherto little has been reported on failure analysis of such meta-structure-inspired three-dimensional printed functional prototypes of dual alloys (17-4 precipitate hardened (PH) stainless steel (SS) and Ti-6Al-4V) with direct metal laser sintering (while fabrication). This study reports the failure analysis of meta-structure inspired dual alloys printing (as FGM) at different processing parameters of direct metal laser sintering. Initially, a pilot study was performed in which a solid structure of Ti-6Al-4V and 17-4 PH SS was successfully printed by selecting the suitable direct metal laser sintering process parameters as functionally graded material (stage 0). In the next stage, specimens of dual alloys were printed with dodecahedron and octet meta-structure of Ti-6Al-4V as a sandwich between the 17-4 PH SS and Ti-6Al-4V layers (stage 1). It has been observed that the octet-based specimen was successfully printed, while the dodecahedron-based sample failed after attaining some height. After successfully octet meta-structure printing of dual alloys (Ti-6Al-4V and 17-4 PH SS), direct metal laser sintering process parameters were further explored for optimization (stage 2). For failure analysis, the specimens with octet meta-structure were fabricated by fixing energy density (in stage 3), hatching distance (in stage 4), laser power (in stage 5), and energy density, hatching distance, laser power, scanning speed (in stage 6). Finally, for confirmation (stage 7), a single specimen was successfully printed by taking process parameters of the successful octet-based sample of stage 2. All the printing failures as per porosity analysis (such as balling phenomenon, caves, and cervices formation) concerning the number of sintered layers in this study are supported with photomicrographic analysis (based on scanning electron microscopy images).

On three-dimensional printing of 17-4 precipitation-hardenable stainless steel with direct metal laser sintering in aircraft structural applications

The martensitic 17-4 precipitation-hardenable stainless steel is one of the commercially established materials for structural engineering applications in aircrafts due to its superior mechanical and corrosion resistance properties. The mechanical processing of this alloy through a conventional manufacturing route is critical from the dimensional accuracy (Δ d) viewpoint for development of innovative structural components such as: slat tracks, wing flap tracks, etc. In past two decades, a number of studies have been reported on challenges being faced while conventional processing of 17-4 precipitation-hardenable stainless steel for maintaining uniform thickness of aircraft structural components. However, hitherto little has been reported on direct metal laser sintering of 17-4 precipitation-hardenable stainless steel for development of innovative functional prototypes with uniform surface hardness (HV), Δ d, and surface roughness ( Ra) in aircraft structural engineering. This paper reports the effect of direct metal laser sintering process parameters on HV, Δ d, and Ra for structural components. The results of study suggest that optimized settings of direct metal laser sintering from multifactor optimization viewpoint are laser power 100 W, scanning speed 1400 mm/s, and layer thickness 0.02 mm. The results have been supported with scanning electron microscopy analysis (for metallurgical changes such as porosity (%), HV, grain size, etc.) and international tolerance grades for ensuring assembly fitment.

Optimization of Selective Laser Sintering Process Parameters Based on PA12 Powders for Bone Tissue Scaffolds.

In selective laser sintering (SLS), process parameters are essential to fabricate outstanding mechanical properties products. In this research, process parameters of porous Polyamide 12 (PA12) scaffold were investigated for the sake of obtaining superior mechanical properties. The area energy density (AED) determined by laser power, scanning speed, and scanning space was employed as the main index to assess process parameters. Six groups with different AED were planed, and then cubic and cylindrical samples were modeled and fabricated with PA12 powders via SLS. Afterward, mechanical properties of the samples were measured and studied to achieve optimum parameters. After a detailed comparison of micrograph, density, dimensional accuracy, and mechanical properties of samples under different AED, laser power of 16 W, scanning speed of 2500 m/s, and scanning space of 0.12 mm were found to be the optimum parameters. Further, a 60% uniform porosity scaffold was fabricated with the optimum parameters to measure mechanical properties for evaluating the optimized results, which were elastic modulus of 87.79 MPa, yield strength of 8.25 MPa, and Poisson's ratio of 0.3. Finite element simulation was also performed, and the results exhibited a good agreement with the experimental behaviors.

17-4 PH stainless-steel as a material for high resolution laser metal deposition

Additive manufacturing (AM) is a type of manufacturing technologies whereby the material is added a layer upon layer to produce a 3D object. Produced 3D parts are applied in such industry sectors as space, aviation, automotive, building and has excellent future promises. These days, the commercially promised technique for metal manufacturing are laser metal deposition (LMD), direct metal laser sintering (DMLS). Our study concentrated on the investigation of mechanical properties of 17-4 PH stainless-steel parts produced by laser sintering. The effect of the laser sintering process parameters (laser power, scanning speed and energy density) on the ultimate stress, yield stress and Young’s modulus was determined. We showed an evolution of the microstructure. The detected defects were classified. This study allowed to determine optimal process parameters for laser sintering of SS 17-4 PH and to describe mechanical properties of the produced parts as well as helped to show future possibilities of the development of laser sintering technology.

Influence of selective laser sintering process parameters on microstructure and physicochemical properties of poly(vinyl alcohol) for the production of scaffolds

Purpose This study aims to investigate the production of scaffolds by selective laser sintering (SLS) using poly(vinyl alcohol) (PVA) polymer, for in vitro studies, a relatively new and growing area in which scaffolds could be used in the design of three-dimensional models for in vitro disease model or tissue equivalent for safety and effectiveness tests. Design/methodology/approach The influence of the SLS process parameters laser power, 26 W and 32 W, and number of laser scans, 1, 2, 4 and 6, on the surface microstructure of the samples and on the degree of crystallinity and chemical stability of PVA material, was investigated using powder with particle size of 20-320 µm. Laser sintered PVA samples were subjected to cell culture tests using osteoblastic cells derived from human osteosarcoma (SaOs-2). Findings The laser power has no significant influence on the microstructure of the laser-sintered samples, however the number of scans has a considerable influence on the sintering degree; the SLS process causes a decrease in the degree of crystallinity and changes the chemical structure of the as-received PVA, especially when using higher laser power and more number of scans. Preliminary in vitro cell culture tests show that the laser-sintered PVA material is biocompatible with SaOs-2 cells. Originality/value SLS offers good potential for the fabrication of scaffolds and thus, may be applied as an alternative to conventional scaffold fabrication processes to overcome their limitations.

Emerging trend in manufacturing of 3D biomedical components using selective laser sintering: A review

Additive manufacturing (also known as 3D printing) process is an emerging technique for the fabrication of biomedical components. Selective laser sintering or melting is one of the widely used additive printing technology for manufacturing of metallic and non-metallic components used in the industry. This review paper presents, a summary of the published research papers on the fabrication of biomedical components using selective laser sintering technique. Therefore, author meticulously attempted to investigate individual biocompatible material-wise review which includes Ti6Al4V, Ti-7.5 Mo alloy, β-Ti35Zr28Nb, PEEK, PA2200, and Polyamide/Hydroxyapatite. In addition, this article also explores the effects of the various laser sintering process parameters such as laser power, scanning speed, density of the material on the mechanical properties, tribological properties, porosity and surface roughness of the fabricated alloy. Moreover, the author also investigated challenges and future prospective of the laser processing of biomedical implants.

Evaluation of processing variables in polymer projection sintering

PurposeProjection sintering, a system for selectively sintering large areas of polymer powder simultaneously with a high-power projector is introduced. This paper aims to evaluate the suitability of laser sintering (LS) process parameters for projection sintering, as it uses substantially lower intensities, longer exposure times and larger areas than conventional LS.Design/methodology/approachThe tradeoffs in sintering outcomes are evaluated by creating single layer components with varied exposure times and optical intensities. Some of these components were cross-sectioned and evaluated for degree of densification, while the single-layer thickness and the maximum tensile force was measured for the rest.FindingsShorter exposure times and higher intensities can create thicker and therefore stronger parts than when equal energy is applied over longer exposures. This is different from LS in which energy input (Andrew’s Number) is accepted as a reliable process variable. This difference is likely because significant thermal energy is lost from the sintering region during the exposure time – resulting in reduced peak temperatures. These thermal losses can be offset by imparting additional energy through increased exposure time or light intensity.Practical implicationsMost methods for evaluating LS process parameters, such as the energy melt ratio and Andrew’s Number, estimate energy input from basic process parameters. These methods do not account for thermal losses and assume that the powder absorbs all incident light. These methods become increasingly inaccurate for projection sintering with visible light where exposure times are much higher (>1s) and a larger portion of the light is reflected from the power’s surface. Understanding the appropriate sintering criteria is critical for the development of long-exposure sintering.Originality/valueA new method of selectively sintering large areas is introduced that could sinter a wider variety of materials by enabling longer sintering times and may increase productivity relative to LS. This work shows that new processing parameters are required for projection sintering as traditional LS process parameters are inadequate.

Direct metal laser sintering of TiN reinforced Ti6Al4V alloy based metal matrix composite: Fabrication and characterization

In the present research, direct metal laser sintering (DMLS) method was chosen to fabricate titanium nitride (TiN) reinforced Ti6Al4V alloy based metal matrix composites (MMCs) under an argon atmosphere using continuous wave (CW) fiber laser having a capacity of 400 W. Laser sintering process parameters, such as layer thickness (0.4 mm), laser beam spot diameter (0.4 mm), and hatching gap (0.2 mm) were kept constant throughout the experiments. Effects of input variable process parameters, such as laser power (50–65 W), scanning speed (3500–4500 mm/min), and volume % of TiN (5–15% v/v) on density, microhardness, and coefficient of friction of the fabricated MMCs were analyzed. The obtained results show the improvement in the physical properties of the fabricated MMCs and FESEM images evidently confirm the presence of TiN particulates and also revealed the uniform distribution of the TiN reinforcement in Ti6Al4V matrix. It was found that the microhardness measured by Vickers test was improved from 388 to 590 HV0.2 with an increase in the volume percentage of TiN. The results showed the coefficient of friction for fabricated samples were in the range of 0.33–0.42. The density (3.40–4.10 g/cm3) of the MMCs was found to increase with increasing the volume percentage of TiN reinforcement in the powder mixture. X-ray diffraction (XRD) analysis of the fabricated MMC confirmed the presence of different in-situ phases, such as Ti, TiN, TiO2, VN, AlV, Ti3Al2N2, and V6N2.7 as a consequence of a series of a chemical reaction between TiN and different elements of Ti6Al4V in the argon atmosphere.

Quasi continuous wave laser sintering of Si-Ge nanoparticles for thermoelectrics

Silicon-germanium is an important thermoelectric material for high temperature applications. In this study, thin films composed of SiGe nanoparticles were synthesized in a plasma reactor and sintered by a millisecond pulse width, quasi continuous wave, near infrared laser of wavelength 1070 nm. We demonstrate that laser sintered SiGe thin films have high electrical and low thermal conductivity, dependent on the surface morphology and dopant concentration. Substrate wetting of laser heating induced molten SiGe was found to play an important role in the final surface morphology of the films. Interconnected percolation structures, formed when proper substrate wetting occurs, were found to be more conductive than the balling structure that formed with insufficient wetting. Laser power was adjusted to maximize dopant reactivation while still minimizing dopant evaporation. After optimizing laser sintering process parameters, the best electrical conductivity, thermal conductivity, and Seebeck coefficient were found to be 70.42 S/cm, 0.84 W/m K, and 133.7 μV/K, respectively. We demonstrate that laser sintered SiGe thin films have low thermal conductivity while maintaining good electrical conductivity for high temperature thermoelectric applications.

Optimization of selective laser sintering process parameters to achieve the maximum density and hardness in polyamide parts

Density and hardness of selective laser-sintered parts are influenced by the different sintering parameters. The selection of sintering parameters plays a vital role to achieve the high precision of end use functional parts. These parts are widely used in the industries such as automobile, aerospace, and for medical applications [Sustarsic et al. (Mater Manuf Process 24:837–841, 2009), Shah et al. (Mater Manuf Process 25:1372–1380, 2010)]. In this study, laser power, scan spacing, bed temperature, hatch length, and scan count were the parameters taken into account for experimentation. Face-centered central composite design was used as a statistical design of experiment technique to set the optimal laser sintering parameters. A relationship between these parameters had also been developed with the generation of different mathematical models. The adequacies of these models were confirmed using analysis of variance. The study concluded that laser power, scan spacing, bed temperature, and hatch length have higher influence on density and hardness of polyamide laser-sintered parts. Among these parameters, scan spacing is the most significant parameter for both density and hardness measures. Laser power—24.05 mm, scan spacing—0.1 mm, bed temperature—173.65 °C, hatch length—114.64 mm, and scan count—2 are the optimum levels to maximize the density and hardness.

Analysis of different infiltration effect for selective laser sintering process through Taguchi method

In this work, an attempt is made to improve the performance of the selective laser sintering process for the production of stainless steel part infiltrated with copper and its alloys. The main aim was to experimentally investigate the influence of selective laser sintering process parameters on hardness. Samples are produced for each experimental condition based on Taguchi’s orthogonal array. It is noted that the infiltration material, laser scan distance, laser power and orientation angle are the process parameters that make considerable enhancement in hardness. The optimum selective laser sintering condition is found through the Taguchi method and mathematical model is also developed for the process. It is noted that the components produced for the optimum condition reveal considerable enhancement in hardness.

Processing and characterization of a polylactic acid/nanoclay composite for laser sintering

In this work, the feasibility of processing polylactic acid (PLA) and a PLA/nanoclay composite by laser sintering (LS) were investigated. The morphology of both the PLA and PLA/nanoclay powder was examined by scanning electron microscopy. LS process parameters, especially powder bed temperature, laser power, and laser scan count were studied. The effect of the addition of nanoclay on the thermal and flexural properties of LS PLA parts was examined. The results showed that PLA/nanoclay required a lower processing powder bed temperature compared with neat PLA. Under the same powder bed temperature, PLA/nanoclay parts exhibited an improvement in flexural modulus compared with neat PLA. Flexural modulus was increased significantly with double scan for both neat PLA and PLA/nanoclay LS parts. POLYM. COMPOS., 38:2570–2576, 2017. © 2015 Society of Plastics Engineers

Effects of micro laser sintering process parameters on quality of nickel-titanium single tracks and thin walls

Micro laser sintering is a promising additive manufacturing process for production of parts with micro features and complicated geometries. Micro laser sintering of mechanically alloyed NiTi was performed in the present work. The effects of powder and laser defocusing distances and also process parameters on the surface quality of single tracks and thin walls were investigated by scanning electron microscopy and optical profilometry. A modified model was described in this research to calculate the height of thin walls produced by micro laser sintering. The experimental results showed that a high melting efficiency can be obtained when the focal point of the laser is situated 200 µm above the working plane of the specimen. Optical profilometry revealed a good agreement between the proposed model for thin wall’s height estimation and experimental results.

Influence of Layer-by-Layer Laser Sintering Modes on the Roughness and Thickness of Sintered Layer of Copper Powder

Quality improvement problem has been considered for a laser sintered surface layer. Purposely built experimental setup was described together with a four-factor experiment design on laser sintering PMS-1 copper powder. A mathematical model describing the effect of laser sintering process parameters on the surface roughness has been proposed. Practical recommendation for improving the quality of the surface layer is given.

The Effect of Laser Sintering Process Parameters on Cu Nanoparticle Ink in Room Conditions

Copper is an interesting material for printed electronics inks because, for example, of its good conductivity and lower raw material price compared to silver. However, post-processing Cu inks is challenging because of non-conductive copper oxide. In this work, inkjet-printed Cu nanoparticle structures were sintered on a polyimide substrate with a continuous-wave 808-nm diode laser. Laser sintering was tested by varying the sintering parameters (optical power and scanning velocity), and the electrical resistance of the samples was measured. A minimum sheet resistance of approx.90 mΩ/□ was obtained. All tests were run in room conditions. Sintered structures were then analyzed from SEM images. Results showed that laser sintering produces good repeatability, that a scanning velocity increment positively affects the process window, and that multiple sintering cycles do not increase conductivity.

Influence of the Energy Density on the Porosity of Polyamide Parts in SLS Process

This paper presents an experimental study about the influence of the Selective Laser Sintering process parameters on the surface and cross-section porosity of parts sintered in polyamide PA2200 material two times recycled. Using of recycled powder affects the part structure and mechanical properties. Therefore, the paper aims to develop a suitable strategy to improve the part structure by controlling the most important SLS process parameters. The main process parameter whose influence was studied is the energy density of the laser beam. Special sample was designed and prototyped using EOS P100 prototyping machine. Three repetition jobs with different energy density of the laser beam were performed. Scanning Electron Microscopy was used to analyze the surface morphology and microstructure of the sintered benchmark parts. The relationship between the SLS parameters and part quality will extend the use of PA2200 recycled material.

Investigation of laser sintering for freeform fabrication of zirconium diboride parts

This paper presents a study wherein the Laser Sintering (LS) process is used to perform additive manufacturing of zirconium diboride (ZrB2) parts. Experiments were conducted to determine values of LS process parameters (laser power, scan speed, energy density, line spacing, and layer thickness) that can be used to improve building of ZrB2 parts. A sacrificial plate with a proper number of layers was first constructed in order to reduce thermal gradients in building the main part. The sacrificial plate was found to eliminate cracks that would otherwise occur in the bottom of the main part. The fabricated green parts went through post-processing steps, including binder burnout and sintering at appropriate heat treatment schedules, to remove the binder and sinter the ZrB2 particles. The test bars after sintering had an average relative density of 87% and an average flexural strength of 250 MPa.

The Optimization Design Study of Selective Laser Sintering Process Parameters on the Pro-Coated Sand Mold

This paper presents experimental investigations on influence of important process parameters viz., laser power, scan speed, layer thickness, hatching space along with their interactions on dimensional accuracy of Selective Laser Sintering (SLS) processed pro-coated sand mold. It is observed that dimensional error is dominant along length and width direction of built mold. Optimum parameters setting to minimize percentage change in length and width of standard test specimen have been found out using Taguchi’s parameter design. Optimum process conditions are obtained by analysis of variance (ANOVA) is used to understand the significance of process variables affecting dimension accuracy. Scan speed and hatching space are found to be most significant process variables influencing the dimension accuracy in length and width. And laser power and layer thickness are less influence on the dimension accuracy. The optimum processing parameters are attained in this paper: laser power 11 W; scan speed 1200 mm/s; layer thickness 0.5 mm and hatching space 0.25 mm. It has been shown that, on average, the dimensional accuracy under this processing parameters combination could be improved by approximately up to 25% compared to other processing parameters combinations.