Direct Metal Laser Sintering Technique Research Articles

An experimental investigation on surface quality of 3D metal printed SS316L by direct metal laser sintering technique

An experimental investigation on surface quality of 3D metal printed SS316L by direct metal laser sintering technique

Effect of Different Metal Bonding Agents on Shear Bond Strength of Ceramic to Direct Metal Laser Sintering

Introduction: laser sinter Cobalt Chromium metal replacing traditional casting processes of dental alloys for metal ceramic restorations, appropriate bonding of ceramic to metal is an important factor for long survival time. Twenty laser sinter cubic metal 10 mm for each sides was fabricated by software designing and CAD\CAM direct metal laser sintering technique. The twenty cubics were classified according to the type of metal to ceramic bonding agents into two groups (n=10), Ceram bond apply for group A and Crea alloy bond for group B. Samples fabricated using custom made silicon index was used to act as standardized mold for metal bond application and porcelain buildup. Instron with chisel indenter and special holding device were involve to measure the strength of bond for ceramic to laser sinter metal. The mean shear bond load of group A (688.8N) was significantly higher than that of group B (303.2N). Application of Ceram bond to metal laser sinter produces more bond strength when compare to usage of Crea bond material.

The impact of print orientation on the fracture resistance and failure patterns of additively manufactured cobalt-chromium post and cores.

The aim of this study was to evaluate the impact of the print orientation of direct metal laser sintering (DMLS) posts and cores on the fracture resistance and failure patterns of endodontically treated mandibular premolar teeth. Sixty intact human mandibular premolars were endodontically treated. The teeth were then randomly divided into four groups (n = 15). Cobalt-chromium (Co-Cr) metal posts were fabricated by traditional casting (Group C), and DMLS method in 0-, 45-, and 90-degree print orientations (Group DMLS 0, Group DMLS 45, and Group DMLS 90). The posts and cores were cemented with composite resin cement and subjected to compression test at a crosshead speed of 1mm/min. Data was analyzed by using one-way analysis of variance ANOVA and multiple comparison post hoc Tukey tests (α = 0.05). Specimens were viewed under a stereo microscope with x20 magnification to evaluate the fracture types. No significant differences were found among the groups tested in terms of fracture resistance (p>0.05). Group C and Group DMLS 0 group exhibited similar fracture patterns. It is possible to produce post and core restorations with the DMLS technique and use them clinically. Print orientation did not influence the fracture resistance. However, fracture patterns were different. Group C outperformed all DMLS groups in terms of fracture patterns.

Impact of an Aluminization Process on the Microstructure and Texture of Samples of Haynes 282 Nickel Alloy Produced Using the Direct Metal Laser Sintering (DMLS) Technique.

In this study, we examined the effects of an aluminization process on the microstructure and texture of Haynes 282 nickel samples fabricated using the direct metal laser sintering technique. The aluminization process involved the use of chemical vapor deposition with AlCl3 vapors in a hydrogen atmosphere at a temperature of 1040 °C for 8 h. Following the 3D printing and aluminization steps, we analyzed the microstructure of the Haynes 282 nickel alloy samples using light microscopy and scanning electron microscopy. Additionally, we investigated the texture using X-ray diffractometry. A texture analysis revealed that after the process of direct laser sintering of metals, the texture of the Haynes 282 nickel alloy samples developed a texture typical of cast materials. Then, in the aluminization process, the texture was transformed-from foundry-type components to a texture characteristic of recrystallization.

Influence of Ion Nitriding on Microstructure and Properties of Haynes 282 Nickel Superalloy Specimens Produced Using DMLS Technique.

The paper investigates the influence of the ion-nitriding process on the microstructure, corrosion resistance, and tensile strength at elevated temperatures of Haynes 282 nickel superalloy specimens produced by the Direct Metal Laser Sintering (DMLS) technique. The study was performed for two conditions, i.e., as-built by DMLS method and as-built by DMLS method + covered by a layer containing CrN + Cr2N phases. An analysis of the surface morphology revealed that the ion-nitriding process significantly affects the physical and chemical phenomena occurring on the specimen's surface. The XRD measurement of the specimens showed that preparing them with the DMLS method as well as following a nitriding process produced residual tensile stresses. Based on the measurement of the nanohardness distribution through the layer approximatively of 7 μm in width and the superalloys substrate, the results of the nanohardness showed the maximum values of 27 GPa and 13.5 GPa for the nitrided layer and the substrate, respectively. The surface protection from the nitrided layer proved a positive effect on the corrosion resistance of the DMLS specimens in the solution of 0.1 M Na2SO4 + 0.1 M NaCl at room temperature. The results of the tensile tests at 750 °C showed that the ion-nitriding process did not significantly affect the elevated-temperature tensile strength of the superalloy specimens produced with the DMLS technique.

Estimation of surface roughness of direct metal laser sintered AlSi10Mg using artificial neural networks and response surface methodology

ABSTRACT Direct metal laser sintering (DMLS) is a metal-specific additive manufacturing (AM) technique that has grown in efficiency and precision due to compelling advancements in high-power lasers and fiber optics. This study examines the surface roughness of AlSi10Mg specimens manufactured additively using the DMLS technique. First, DMLS experiments were conducted with a range of control variables, including laser power, laser speed, orientation, and post-heat treatment temperatures. Later, surface roughness prediction models were developed using machine learning techniques and statistical methods such as artificial neural networks (ANN) and response surface methodology (RSM). The ANN model with an architecture of 4-9-9-1 is identified as the optimal network. The predictions of the ANN models were compared to those of the RSM models, and performance was quantified using the correlation coefficient (R-value) between predictions and the experimental data. The R-value of 0.96218 with experimental data and the least mean absolute percentage error (MAPE) of 0.9804% indicated that ANN predictions were more accurate than the RSM model estimates. Conclusive results prove that the developed ANN model accurately estimated the relationship between DMLS process parameters and surface roughness.

Experimental Characterization of an Additively Manufactured Inconel 718 Heat Exchanger for High-Temperature Applications

This work presents the experimental results of a novel, air-to-air, additively manufactured manifold-microchannel heat exchanger with straight fins on both sides. The heat exchanger was made of Inconel 718 using a direct metal laser sintering technique. The overall core size of the heat exchanger was 94 mm × 87.6 mm × 94.4 mm, with a fin thickness of 0.220 mm on both the hot and cold sides. The heat exchanger was tested with pressurized nitrogen gas at 300 °C and 340 kPa for the hot side, while air at an ambient condition was used for the cold side. An overall heat transfer of 276 W/m2K was obtained for Reynolds number values of 132 and 79 for the cold and hot sides, respectively. A gravimetric heat transfer density (Q/m∆T) of 4.7–6.7 W/kgK and a volumetric heat transfer density (Q/V∆T) of 6.9–9.8 kW/m3K were recorded for this heat exchanger with a coefficient of performance value that varied from 42 to 52 over the operating conditions studied here. The experimental pressure drop results were within 10% of the numerical values, while the corresponding heat transfer results were within 17% of the numerical results, mainly due to imperfections in the fabrication process. Despite this penalty, the performance of the tested heat exchanger was superior to the conventional plate-fin heat exchangers: more than 60% of improvements in both gravimetric and volumetric heat transfer densities were recorded for the entire range of experimental data.

Comparative Evaluation of Retention and Vertical Marginal Accuracy of Co-Cr Copings Fabricated Using Three Different Techniques: An In Vitro Study.

This study was conducted to comparatively assess the retention and vertical marginal fit of cobalt-chromium copings fabricated by the conventional casting technique, 3D-printed resin pattern, and with direct metal laser sintering (DMLS) technique. Out of the total 60 test samples, 20 copings were obtained from inlay-casting wax and 20 from casting of 3D-printed resin patterns. In total, 20 copings were obtained from the laser sintering technique. All 60 test samples were then cemented serially on the prepared maxillary-extracted premolars and were evaluated for vertical marginal gap in 8 pre-established reference areas. Retention was evaluated using a universal testing machine. Results obtained for both marginal gap and retention were statistically analyzed, and the values fall within the clinically acceptable range. The DMLS technique proved precedence over the other two techniques used, as it exhibited maximum retention and marginal accuracy, which is an area of prime concern. The results from this study encourage further research with different pattern-forming materials and techniques and the need to identify the factors that facilitate better marginal fit and retention of cast restorations. This study has myriad of applications in clinical dentistry mainly in decision-making for casting procedure to provide better retention and marginal accuracy for fabrication of Co-Cr crowns. It also aims to aid the clinician to minimize errors by using different techniques for fabrication of wax pattern as well as the coping, keeping abreast with the recent technology to evaluate the accuracy of 3D-printed resin pattern over conventional wax pattern.

The Impact of Plastic Deformation on the Microstructure and Tensile Strength of Haynes 282 Nickel Superalloy Produced by DMLS and Casting.

The article presents the results of research on the influence of plastic deformation on the microstructure and tensile strength of Haynes 282 nickel superalloy produced by direct metal laser sintering (DMLS) and a conventional technique (casting). Samples were tested for dimensional accuracy using a 3D scanner. Then, the samples were subjected to plastic deformation by rolling. The microstructures of the DMLS and the as-cast samples were analysed using a scanning electron microscope. The strength properties of the samples were determined in a static tensile test. Microhardness measurements of the samples were also performed. Based on the analysis of the dimensional accuracy, it was found that the surface quality of the components produced by DMLS is dependent on the input parameters of the 3D printing process. Using the DMLS method, it is possible to produce Haynes 282 with a fine-crystalline microstructure containing dendrites. The fine-crystalline dendritic microstructure and low porosity showed very good tensile strength compared to the as-cast material. It was also found that the increase in the degree of plastic deformation of the as-cast Haynes 282 and the samples produced by the DMLS technique resulted in an increase in the strength of the tested samples, with reduced ductility.

Structural characterization and biocorrosion behaviour of direct metal laser sintered Ti6Al4V–ZrO2 tracks: Influence of processing parameters

Titanium (Ti–6Al–4V) and Zirconia (ZrO2) have proven to be candidate materials for use in the biomedical industry. This present study investigates the effect of processing parameters on microstructural and corrosion performance of Ti–6Al–4V– ZrO2 laser tracks processed via direct metal laser sintering technique. The starting powders were mixed using a turbula mixer. The morphology of the admixed Ti–6Al–4V– ZrO2 powders and the laser melt tracks were examined under a field emission electron microscope (FE-SEM) equipped with energy dispersive X-ray (EDS). X-ray diffraction (XRD) analysis was carried out on the starting powders and laser tracks to ascertain the phases formed before mixing and after laser sintering, respectively. Potentiodynamic polarization and electrochemical impedance spectroscopy technique (EIS) were used to investigate the resistance of the laser tracks to corrosion in Hanks simulated body fluid. The FE-SEM examination showed a homogeneous mixture of the powders, while the laser melt tracks processed at lower scanning power revealed the presence of discontinuities. The corrosion analysis of the laser tracks in Hanks solution showed synergy between the results obtained from the potentiodynamic polarization and EIS analysis. This research established that the specimen fabricated using a laser power of 340 W, a scanning speed of 1 m/s, and a layer height of 100 μm exhibited the most improved corrosion resistance in the test environment used in this study.

Influence of tool rotational speed on the microstructural characterization and mechanical properties of friction stir welded Al-Si10Mg parts produced by DMLS additive manufacturing process

Present study investigate the joining of precipitation hardened AlSi10Mg alloy, developed using direct metal laser sintering technique of additive manufacturing using friction stir welding. Consequently, three, single-pass, square butt-welded joints were fabricated from 3 mm thick plates of this alloy, using friction stir welding process at different tool rotational speeds (low, medium and high). Each welded joint was fabricated at the same transverse speed of 50 mm/min, H13 tool steel possessing scrolled shoulder and 3° tilt angle. Microstructural observations show a significant grain refinement within the stir zone, which reduced with the increase in tool rotational speed. This variation was accredited to the significant dynamic recrystallization in the weldment, and change in the morphology and size of the Si-particles. The transverse tensile test results show a considerable drop in the joint efficiency of the welds from ≈48% to ≈42% with the increase in tool rotational speed from low to high.

Lost-wax or laser sintering? Findings on marginal and internal adaptation of metallic copings

Marginal and internal adaptation are parameters of crucial importance to the success of prosthetic crowns. Automatized process creates an expectative of superior or equivalent results compared to restorations manufactured ​​by conventional lost-wax technique. The purpose of this study was to evaluate the marginal adaptation and internal adaptation (cement space) of metal-ceramic crown copings produced by lost-wax (LW) and direct metal laser sintering (DMLS) techniques. An artificial lower first molar was prepared for a full crown, duplicated in plaster and scanned. Twenty metal-ceramic crown copings were fabricated in cobalt-chromium by the two techniques (n=10). The copings were filled with low viscosity silicone and seated on the prepared tooth, resulting in a replica of the internal space. The pellicle formed was embedded in heavy body silicone, sectioned and captured by means of a stereomicroscope at 50x magnification, according to replica technique (RT). Shapiro-Wilk test followed by Holm-Sidak test were used for statistical analysis (α=.05). Marginal adaptation presented no difference between LW (101.5 ± 41.6) and DMLS (86.3 ± 39.9) groups (p=0.24). Conventional LW technique showed significantly lower occlusal (p<0.008) and axial spaces (p<0.03). Measurements of all regions showed numerically larger adaptation values than that defined during design​​ for DMLS group. Both the LW technique and the DMLS technique are within the clinically acceptable.

Design and development of a novel additively manufactured geothermal heat exchanger

The existing geothermal heat exchangers pose a complex installation process and occupy large spaces which can potentially be cost-prohibitive to many potential users. In the present study, an additively manufactured heat exchanger was designed and developed to address this issue. The designed heat exchanger can be integrated with conventional geothermal heating and cooling systems for improved efficiency and easy installation. The additively manufactured heat exchanger developed in the present study eliminates the current need to excavate the soil and install the long piping as conventionally required for the existing geothermal systems. The prototype of the proposed geothermal heat exchanger was designed using CREO software and fabricated using the direct metal laser sintering technique (DMLS) to be integrated into a heat pump to exchange heat between a constant temperature of a water bath circulator and a water heat sink. Furthermore, the support structure model generated for metal printing of the proposed geothermal heat exchanger was exposed and discussed. Two customized geothermal heating and cooling modes were separately developed to evaluate the heat transfer performance of the heat exchanger analytically and numerically. Using the analytical approach, the system sizing was designated based on the metal additive manufacturing and thermal considerations, and then average heat transfer coefficients and pressure drops were estimated for a range of mass fluxes lying in the transitional and turbulent regimes. The distributions of wall temperature, fluid's bulk temperature, and fluid's velocity along the helically-coiled channel of the heat exchanger was also investigated numerically using the COMSOL-Multiphysics. Lastly, a detailed cost analysis was conducted to estimate the total cost per part for the prototype fabricated using the DMLS technology. Novelty Statement A novel ground-source heat exchanger was additively fabricated using the direct metal laser sintering (DMLS) technique. The unique compact screw-type design eliminates the need of excavating soil and features easy installation with less maintenance costs. Heat transfer characteristics of the proposed design were evaluated analytically and numerically. The proposed geothermal heat exchanger contributes effectively to the deployment of sustainable energy systems.

Influence of post-heat treatment on microstructure, mechanical, and wear properties of maraging steel fabricated using direct metal laser sintering technique

The post-heat treatment of direct metal laser sintered parts is expected to have superior mechanical properties. Therefore, the purpose of the present study is to investigate the post-heat treatment effect on the microstructure, mechanical and wear properties of direct metal laser sintering processed maraging steel. Hence, a systematic methodology for microstructural characterization, mechanical properties, and tribological performance evaluation was performed. The microstructural examinations were performed using optical and scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction technique. The micro-hardness and tensile properties were determined. The unidirectional sliding wear test was performed using a pin on disc wear testing machine for three different sliding velocities (0.8, 1.2, and 1.6 m/s) and three different normal loads (5, 10, and 15 N). The present study’s findings establish that the post-heat treatment techniques significantly altered the microstructural morphology and features. The results showed that the heat-treated sample had finer and non-continuous microstructure and more complex intermetallic precipitate phases, leading to higher hardness (∼64%) and higher tensile strength properties (70–80%) compared to the as-printed sample. The unidirectional sliding wear test results showed that the sliding velocity significantly affected frictional and wear characteristics of direct metal laser sintering processed maraging steel. The wear resistance of the heat-treated sample was three times higher than the as-printed sample, particularly at higher sliding velocities. In addition, the lower coefficient of friction values (∼24%) was observed for heat-treated sample compared to as-printed sample at higher sliding velocities. The post-heat treatment aids as an effective method to enhance mechanical properties of direct metal laser sintered parts and qualify them for tribological applications. The results endorse the suitability of the heat-treated direct metal laser sintered maraging steel in practical tool and die applications involving extreme tribological operating conditions such as higher sliding velocities and contact stresses.

Copper nickel alloys made using direct metal laser sintering method for assessing corrosion resistance properties

Direct Metal Laser Sintering (DMLS) is an additive manufacturing technique, a novel processes in vogue recent times, as it has the supreme advantage of producing near net shape component having low porosity levels and superior mechanical properties. The main thrust of the work focuses on the development of coppper-nickel (Cu-Ni) alloys using 3D printing for studying the rate of corrosion in sea water and in acidic conditions, as such work has not been reported in the literature. In this context, the Cu-Ni alloy with varying thickness 20, 40 and 60 μm was prepared by the DMLS technique at different scan speeds. The composition of the alloys was confirmed using X-ray diffraction technique (XRD), and energy dispersive spectroscopy (EDAX). The analysis of microstructure was done using light and scanning electron microscopy (SEM). Hardness was measured for all the prepared alloys using Vickers hardness tester and energy densities was analysed.Further, to study the durability, the samples were tested for corrosion resistance by average weight loss method. The weight loss trials were carried out in seawater condition i.e., 3% sodium chloride (NaCl) and in acidic medium (1 M HCl), at room temperature. The results show that the Cu-Ni alloy exhibits extreme resistance to corrosion in 3% NaCl but is found to be less resistant in 1 M HCl solution. The average weight loss of the sample is 0.72% in seawater whereas, in 1 M HCl, is 9.73%. Also, it reveals that the least thickness samples prepared at the lowest scan speed by DMLS technique are better resistance towards corrosion to that of the higher thickness samples made at higher scan speed. The corrosion data are well supported by microstructures, the surface of the samples was subjected to light and SEM before and after corrosion. This high resistance in NaCl makes copper-nickel alloys made by DMLS process ideal to use in marine locations.

The impact of surface treatment in 3-dimensional printed implants for early osseointegration: a comparison study of three different surfaces

3D printing technology has been gradually applied to various areas. In the present study, 3D-printed implants were fabricated with direct metal laser sintering technique for a dental single root with titanium. The 3D implants were allocated into following groups: not treated (3D-None), sandblasted with a large grit and acid-etched (3D-SLA), and target-ion-induced plasma-sputtered surface (3D-TIPS). Two holes were drilled in each tibia of rabbit, and the three groups of implants were randomly placed with a mallet. Rabbits were sacrificed at two, four, and twelve weeks after the surgery. Histologic and histomorphometric analyses were performed for the evaluation of mineralized bone-to-implant contact (mBIC), osteoid-to-implant contact (OIC), total bone-to-implant contact (tBIC), mineralized bone area fraction occupancy (mBAFO), osteoid area fraction occupancy (OAFO), and total bone area fraction occupancy (tBAFO) in the inner and outer areas of lattice structure. At two weeks, 3D-TIPS showed significantly higher inner and outer tBIC and inner tBAFO compared with other groups. At four weeks, 3D-TIPS showed significantly higher outer OIC than 3D-SLA, but there were no significant differences in other variables. At twelve weeks, there were no significant differences. The surface treatment with TIPS in 3D-printed implants could enhance the osseointegration process in the rabbit tibia model, meaning that earlier osseointegration could be achieved.

Evaluation of Bacterial Adhesion to the ZrO2 Atomic Layer Deposited on the Surface of Cobalt-Chromium Dental Alloy Produced by DMLS Method.

The main purpose of the research was to analyze the influence of surface modification of the cobalt-based alloy used in dental prosthetics by applying zirconium oxide (ZrO2) layers using the ALD (Atomic Layer Deposition) method. The samples were made using the DMLS (Direct Metal Laser Sintering) technique, and their surfaces were prepared in accordance with the principles of removable partial dentures (RPDs). A 50 nm-thick zirconium oxide coating was applied to the prepared substrates. This paper deals with the issues of prosthetic stomatopathy, which is a complex of pathological changes occurring in approx. 40% of the Polish population using removable dentures. Often, these changes, occurring on the mucosa, are related to improper performance, allergic reactions or the multiplication of bacteria on the surface of partial dentures. An innovative method of surface modification was proposed, together with the analysis of its influence on the physicochemical properties of the alloy and the adhesion of bacteria to the surface.

A Comparative Study between Polymer and Metal Additive Manufacturing Approaches in Investigating Stiffened Hexagonal Cells.

Recent polymer and metal additive manufacturing technologies were proven capable of building complex structures with high accuracy. Although their final products differ significantly in terms of mechanical properties and building cost, many structural optimization studies were performed with either one without systematic justification. Therefore, this study investigated whether the Direct Metal Laser Sintering (DMLS) and Fused Deposition Modelling (FDM) methodologies can provide similar conclusions when performing geometrical manipulations for optimizing structural crashworthiness. Two identical sets of four shapes of stiffened hexagonal cells were built and crushed under quasi-static loading. The results were compared in terms of collapsing behavior, load-carrying performance, and energy-absorption capability. Although the observed failure modes were different since the base-materials differ, similar improvement trends in performance were observed between both fabrication approaches. Therefore, FDM was recommended as a fabrication method to optimize thin-walled cellular hexagonal parameters since it was 80% more time-efficient and 53.6% cheaper than the DMLS technique.

Evaluation of the marginal discrepancy of cobalt chromium metal copings fabricated with additive and subtractive techniques

Aim: The aim of this article was to compare the marginal discrepancy of CoCr metal coping fabricated by three techniques, namely (A) direct CAD/CAM milling, (B) casted milled CAD/CAM wax, and (C) direct metal laser sintering (DMLS) technique. Materials and Methods: A comparative study between additive and subtractive manufacturing techniques was made. The study involves three groups; 15 metal copings were made for each group. Standardization was done by using the same STL file for all groups. With group A, direct milling was done to the CoCr blank. Group B follows the conventional casting method for wax framework milled by a CAD/CAM machine. Group C metal coping was made by the DMLS technique. The measurement of marginal discrepancy was done to four aspects: buccal, palatal, mesial, and distal using a digital light traveling microscope with magnification power of 200×. Statistical analysis used was one-way analysis of variance test and Tukey’s test. Results: The mean vertical marginal discrepancies for groups A, B, and C were 19.070, 23.470, and 38.533 μm, respectively. Statistical analysis shows a very high significant difference among groups (P < 0.001). Conclusion: All the tested groups showed an acceptable marginal discrepancy. The direct CAD/CAM metal milling method results in minimum marginal gaps when compared with additive and subtractive techniques.

Influence of manufacturing technique on marginal fit of cobalt chromium restorations: An in-vitro Study.

For porcelain fused to metal restorations, computer-aided designing (CAD) / computer-aided manufacturing (CAM) systems claim to provide improved marginal fit than conventional casting systems. The present in-vitro study was conducted to compare the marginal fit of cobalt-chromium alloy copings fabricated with milled wax/lost wax, CAD/CAM milling/sintering and direct metal laser sintering (DMLS) techniques. A metal die simulating a prepared tooth was fabricated and scanned using an optical scanner. A standardized coping design was used to manufacture 30 alloy copings divided into three groups of ten copings each i.e., milled wax/lost wax, milling/sintering and DMLS. A modified replica technique was used to measure the silicone film thickness at four pre-designated points on the margin under a digital stereo-microscope. The mean values for marginal gap were compared using one-way Analysis of Variance (ANOVA) followed by Tukey-Kramer test for all pair-wise comparisons. The mean marginal gap values obtained by using milled wax/lost wax technique, milling/sintering technique and DMLS technique were 88.44 μm, 61.135 μm and 55.39 μm, respectively. One-way ANOVA showed a significant difference for marginal fit between the lost wax group and the other two test groups (P < 0.05). The cobalt-chromium alloy copings fabricated using DMLS techniques displayed significantly better marginal fit than the milled wax/lost wax technique which may contribute to their improved clinical performance. DMLS technique produces restorations with an improved marginal fit and may be preferred by clinicians over milling and conventional casting techniques.