Laser Sintering Of Metal Powder Research Articles

Laser Sintering of Metal Powders: Failure Analysis and Implementation of Solutions for Aluminium and Stainless Steel Parts

Abstract In this research, the failures and possible solutions of direct metal laser sintering (DMLS) have been investigated, with the aim of presenting an overview of the current state of science and possible technical solutions to the various challenges and potential solutions. DMLS technology allows to produce high density parts and has proven to be suitable for the cost-effective production of both mass-produced and individual parts in the automotive, aerospace, medical and hydrogen technology industries. This study reveals the fundamental principles, potential benefits, and limitations of metal 3D printing. The defects are categorized into those related to raw materials and those caused by the manufacturing process. The properties of the parts fabricated by this method are mainly depending on the quality of the raw material and the intensity of the laser beam. Clusters of raw materials have a negative impact on the whole manufacturing process, requiring their investigation and avoidance. Another critical defect identified is the significant internal stress generated during the manufacturing process. Various methods are developed to quantify and mitigate these internal stresses. This study provides a detailed analysis of these defects and their impacts, along with a review of literature-based solutions. Among the evaluated and implemented solutions, emphasis is placed on the effects of preheating the build plate and post-process heat treatment. Future objectives and research directions are proposed, presenting and assessing alternative solutions such as Vibratory Stress Relief (VSR) and Thermo-Vibratory Stress Relief (TVSR), which combine heat treatment with vibration. In the scope of the research, the process by which the most common failures occur, and their potential outcomes was reviewed. Special attention was given to deformation caused by internal stress and the possibilities for its mitigation. The feasibility of applying a new approach was investigated, and future research objectives were outlined. SEM imaging was employed to conduct and analyse the grain size of stainless-steel raw material, and agglomerates were observed in the post-print recycled powder.

Inverted laser sintering of metal powders

We demonstrate the ability of the inverted laser sintering process to manufacture parts composed of metal powder. We fabricate a 10-layer part by depositing a layer of copper powder onto a sapphire plate, then pressing the plate against the part being built and sintering the powder onto the part by shining a 14W 445 nm laser through the glass. The process was then repeated multiple times, each time adding a new layer to the component being printed until completion. We discuss the potential applications and impacts of this process, including the ability to directly fabricate multi-material metallic parts without the use of a powder bed.

Zgodność cyfrowego projektu koron protetycznych z uzupełnieniami wykonanymi w technologii laserowego selektywnego spieku proszków metalowych

Zgodność cyfrowego projektu koron protetycznych z uzupełnieniami wykonanymi w technologii laserowego selektywnego spieku proszków metalowych

Relationship between the Size and Inner Structure of Particles of Virgin and Re-Used MS1 Maraging Steel Powder for Additive Manufacturing.

Additive manufacturing (AM) is today in the main focus—and not only in commercial production. Products with complex geometry can be built using various AM techniques, which include laser sintering of metal powder. Although the technique has been known for a quite long time, the impact of the morphology of individual powder particles on the process has not yet been adequately documented. This article presents a detailed microscopic analysis of virgin and reused powder particles of MS1 maraging steel. The metallographic observation was performed using a scanning electron microscope (SEM). The particle size of the individual powder particles was measured in the SEM and the particle surface morphology and its change in the reused powder were observed. Individual particles were analyzed in detail using an SEM with a focused ion beam (FIB) milling capability. The powder particles were gradually cut off in thin layers so that their internal structure, chemical element distribution, possible internal defects, and shape could be monitored. Elemental distribution and phase distribution were analyzed using EDS and EBSD, respectively. Our findings lead to a better understanding and prediction of defects in additive-manufactured products. This could be helpful not just in the AM field, but in any metal powder-based processes, such as metal injection molding, powder metallurgy, spray deposition processes, and others.

Анализ теплопрочностного состояния цилиндрической камеры сгорания, изготовленной с использованием аддитивных технологий

Additive technologies based on layer-by-layer and direct laser sintering of metal powders make it possible to produce objects of complex shapes with high accuracy and at acceptable material and time costs. However, the implementation of additive technologies is associated with a number of technical difficulties caused by a decrease in strength characteristics of the material obtained as a result of laser sintering. The negative trend associated with deterioration of the material strength characteristics and its influence on the structure performance is most pronounced in heat-stressed units, in particular, in combustion chambers of power plants. The paper proposes and tests a computational and experimental method for estimating the stress-strain state of a regenerative cooled cylindrical combustion chamber manufactured using additive technologies. The authors present experimental data on the decrease in the material strength when laser sintering of power is used. The change in the safety factor of the cylindrical combustion chamber is estimated depending on its geometric characteristics and operating modes. The possibility of application of the developed method when choosing the configuration of a combustion chamber with regenerative cooling channels is shown.

ANALYSIS OF SURFACE MICROGEOMETRY AND STRUCTURE OF LAYERED BIOMATERIALS USED FOR PROSTHETIC CONSTRUCTIONS IN DIGITAL TECHNOLOGIES

Veneering layers of prosthetic substructures are responsible for tribological cooperation with opposite teeth in the stomatognathic system (SS). Investigations of microgeometry and structure of veneering layers are aimed at checking to what extent these layers replicate enamel parameters, which, under complex load conditions, are characterized by the phenomenon of resistance to tribological wear. Ceramic veneering layers are dedicated for substructures made in digital technologies from factory fittings by milling and laser sintering of metal powders. Using a confocal microscope, contactless tests of the surface layer stereometry were performed and surface roughness parameters were determined on samples of ceramics veneering of prosthetic substructures. The analysis was performed in comparison to the natural enamel of premolars and molars. The shaping of the surface of materials veneering the substructures is similar to the regularity determined in the statistical analysis of the enamel roughness. Layers facing samples from milling technology are characterized by lower values of roughness parameters than layers created on substructures made of SLM technology.

Модель, методика расчета и визуального представления остаточных напряжений при лазерном спекании металлических порошков

Модель, методика расчета и визуального представления остаточных напряжений при лазерном спекании металлических порошков

Wpływ nagniatania strumieniowego na właściwości eksploatacyjne stopu Ti-6Al-4V uzyskanego technologią przyrostową DMLS

The state of the surface layer and biocompatibility are the key parameters contributing to successful implantation of prostheses such as bone implants which are now increasingly often produced by means of DMLS technologies. The analysis of these factors and proper selection of material are required in order to determine the most favourable technological parameters contributing to long term functioning in course of their presence in human body. Therefore, the purpose of the present paper is to investigate the effect of shot peening on the state of the surface layer and corrosion resistance of specimens made of Ti-6Al-4V titanium alloy produced in Direct Metal Laser Sintering (DMLS) process. The specimens have been produced by means of EOSINT M280 system dedicated for laser sintering of metal powders and their surfaces have been subjected to the shot peening process under three different working pressures (0.2, 0.3 and 0.4 MPa) and by means of three different media i.e. CrNi steel shot, crushed nut shells and ceramic balls based on ZrO2. It has been found that the process conditions i.e. working pressure in course of shot peening and proper selection of applied shot will make it possible to achieve the properties in modified material sufficient to ensure that assumed functions associated with the improvement of surface layer condition are invariable during required period in specified implant operation conditions. In such case, these factors have been determined in course of microhardness tests, evaluation of surface development degree as well as potentiodynamic tests. The increase of working pressure caused deteriorated corrosion resistance. Simultaneously, it has been found the corrosion resistance was most satisfactory for the surfaces modified by means of: ceramic balls based on ZrO2 > crushed nut shells > CrNi steel shot correspondingly.

The effect of shot peening on the corrosion behaviour of Ti-6Al-4V alloy made by DMLS

Abstract Additive Manufacturing processes are being used increasingly in the scope of medicine and dentistry. As indicated by literature data, the durability and quality of medical implants is decisively influenced by surface modification. Insufficient quality of surface finishing leads, among others, to reduced service life of applied implants and to increased number of necessary revision surgeries. Furthermore, various types of finishing processes e.g. cleaning, shot peening or abrasive techniques are suggested by the manufacturers of products made by means of DMLS processes. Due to this fact, the analysis of proper formation of the surface layer of titanium products made by means of the method consisting in the direct laser sintering of metal powders (DMLS) was the subject matter of our research. Therefore, Ti-6Al-4V titanium alloy has been used for tests. The samples have been produced by means of EOSINT M280 system dedicated for laser sintering of metal powders. The surfaces of prepared samples have been subjected to shot peening process at three different values of working pressure (0.2, 0.3 and 0.4 MPa) by means of three different working media i.e. CrNi steel shot, crushed nut shells and ceramic balls. The characteristics of the materials used for shot peening process have been determined by means of Zeiss Ultra Plus scanning electron microscope. The samples have been subjected to profilometric measurements on Bruker Contour GT optical profilometer and the corrosion behaviour of Ti-6Al-4V titanium alloy in Ringer solution has been determined in electrode impedance spectroscopy (EIS) measurements by means of Atlas 0531 set dedicated for corrosion testing. The overall results of all tests indicate to favourable influence of the shot peening process on the corrosion behaviour of titanium alloy.

Temperature Field Simulation of Powder Sintering Process with ANSYS

Aiming at the “spheroidization phenomenon” in the laser sintering of metal powder and other quality problems of the forming parts due to the thermal effect, the finite element model of the three-dimensional transient metal powder was established by using the atomized iron powder as the research object. The simulation of the mobile heat source was realized by means of parametric design. The distribution of the temperature field during the sintering process under different laser power and different spot sizes was simulated by ANSYS software under the condition of fully considering the influence of heat conduction, thermal convection, thermal radiation and thermophysical parameters. The influence of these factors on the actual sintering process was also analyzed, which provides an effective way for forming quality control.

Flow analysis of the laminated manufacturing system with laser sintering of metal powder. Part I: flow uniformity inside the working chamber

Selective laser melting (SLM) as a part of 3D printing technology has been a novel industrial manufacturing process nowadays. However, the collection of metal powders emitted from the working plane is significant for the SLM process. The uniformity of the flow passing through the SLM working chamber, which helps collect emitted powders, has been considered as a key solution. In this study, for the purpose of improving the flow uniformity, a blow-to-suction device composed of a trapezoid push nozzle, a working chamber, and a suction tunnel was applied. Various parameters, such as the width of trapezoid push nozzle, the width of suction tunnel, and the nozzle-to-plane distances, were examined experimentally and computationally. Hot-wire velocity measurement and smoke flow visualization were used to verify the reliability of the simulation. Through the results of degree of uniformity (DOU), the momentum exchange between the suction and blow sides plays an important role for producing a uniform flow through the working chamber. In addition, higher suction velocity as well as larger nozzle-to-plane distance result in relatively better uniformity of the flow.

Surface microgeometry after selective laser sintering of metal powder

A multifactorial model is proposed for the surface microgeometry after selective laser sintering of metal powder. The dependence of the microgeometry on the following dominant factors is established: the laser power, the speed of the laser beam, and the scanning increment.

Computer Simulation of Robotic Device Components in 3D Printer Manufacturing

The paper considers a relevant problem Computer simulation of robotic device components in manufacturing on a 3D printer and highlights the problem of computer simulation based on the cognitive programming technology of robotic device components. The paper subject is urgent because computer simulation of force-torque and accuracy characteristics of robot components in terms of their manufacturing properties and conditions from polymeric and metallic materials is of paramount importance for programming and manufacturing on the 3D printers. Two types of additive manufacturing technologies were used: 1. FDM (Fused deposition modeling) - layered growth of products from molten plastic strands; 2. SLM (Selective laser melting) - selective laser sintering of metal powders, which, in turn, create: • conditions for reducing the use of expensive equipment; • reducing weight and increasing strength through optimization of the lattice structures when using a bionic design; • a capability to implement mathematical modeling of individual components of robotic and other devices in terms of appropriate characteristics; • a 3D printing capability to create unique items, which cannot be made by other known methods. The paper aim was to confirm the possibility of ensuring the strength and accuracy characteristics of cases when printing from polymeric and metallic materials on a 3D printer. The investigation emphasis is on mathematical modeling based on the cognitive programming technology using the additive technologies in their studies since it is, generally, impossible to make the obtained optimized structures on the modern CNC machines. The latter allows us to create a program code to be clear to other developers without cost, additional time for development, adaptation and implementation. Year by year Russian companies increasingly use a 3D-print system in mechanical engineering, aerospace industry, and for scientific purposes. Machines for the additive production, well integrated in the production cycle, allow not only to reduce costs and save time, but also to begin performing more complex tasks. The ability for quick understanding the program code written by other users and adaptation to other projects creates the preconditions for a good economic effect, strength through the use of already existing projects or models of standard forms. This is possible because, based on the data on three-dimensional detail layout scanning, the 3D technology allows us to have a digital copy to be adapted for further implementation on the 3D-printer in any potential project, taking into account the specification of each project. Analysis of these problems gives impetus for further research in the field of mechanical engineering and robotics technology. Conclusion : A process of simulation and bionic design of the case has been done; fixation was across frontal cross-section. Margin of safety for the case (option 1) made from metallic powder is sufficient. As seen from the two proposed options of the device case the first option is more preferable since there is a collapse potential in fixing points of the option 2 made from the ABC plastic.

Discrete element modeling of particle-based additive manufacturing processes

A critical element for the design, characterization, and certification of materials and products produced by additive manufacturing processes is the ability to accurately and efficiently model the associated materials and processes. This is necessary for tailoring these processes to endow the associated products with proper geometrical and functional features. In an effort to address these needs in a computationally elegant and at the same time physically realistic manner, this paper presents the development of a methodology for simulating particle-based additive manufacturing processes, which employs the Discrete Element Method (DEM) extended to incorporate thermal physics. The details of the DEM-based methodology are presented first and the approach is demonstrated on a pair of test problems involving laser sintering of metal powders. The paper concludes with a discussion on how this approach may be generalized to broader classes of additive manufacturing systems, and details are given regarding future work necessary to further develop the present methodology.

ИССЛЕДОВАНИЕ СВОЙСТВ СПЛАВА ЭП648, ПОЛУЧЕННОГО МЕТОДОМ СЕЛЕКТИВНОГО ЛАЗЕРНОГО СПЛАВЛЕНИЯ МЕТАЛЛИЧЕСКИХ ПОРОШКОВ

ИССЛЕДОВАНИЕ СВОЙСТВ СПЛАВА ЭП648, ПОЛУЧЕННОГО МЕТОДОМ СЕЛЕКТИВНОГО ЛАЗЕРНОГО СПЛАВЛЕНИЯ МЕТАЛЛИЧЕСКИХ ПОРОШКОВ

Optimization on Selective Fiber Laser Sintering of Metallic Powder

Purpose – The objective of this study is to investigate the effect of various parameters on rapid prototyping parts for processes of sintering metallic powder by using fiber laser via the design of experiments (DOE) method. Design/methodology/approach – Experiments based on the DOE method were utilized to determine an optimal parameter setting for achieving a minimum amount of porosities in specimens during the selective laser sintering (SLS) process. Analysis of variance (ANOVA) was further conducted to identify significant factors. Findings – A regression model predicting percentages of porosities under various conditions was developed when the traditional Taguchi’s approach failed to identify a feasible model due to strong interactions of controlled factors. The significant factors to the process were identified by ANOVA. Research limitations/implications – Four controlled factors including pulse frequencies and scan rate of laser beams, laser power and scan line spacing with particle sizes of 5µm of the powder base material had significant influence on the sintering process. Future investigation planned to be carried out for achieving multiple quality targets such as the hardness and the density for 3D parts. Originality/value – The implementation of the DOE method provided a systematic approach to identify an optimal parameter setting of the SLS process; thus, the efficiency of designing optimal parameters was greatly improved. This approach could be easily extended to 3D cases by just including additional parameters into the design. Additionally, utilization of the normality analysis on the residual data ensured that the selected model was adequate and extracted all applicable information from the experimental data.

Analysis of Infiltration, Solidification, and Remelting of a Pure Metal in Subcooled Porous Preform

The parts fabricated by selective laser sintering of metal powders are usually not fully densified and have porous structure. Fully densified parts can be obtained by infiltrating liquid metal into the porous structure and solidifying the liquid metal. When the liquid metal is infiltrated into the subcooled porous structure, the liquid metal can be partially solidified. Remelting of the partially solidified metal can also take place and a second moving interface can be present. Infiltration, solidification, and remelting of metal in a subcooled porous preform obtained by laser sintering of metal powders are analytically investigated in this article. The governing equations are nondimensionalized and the problem is described using six dimensionless parameters. The temperature distributions in the remelting and uninfiltrated regions were obtained by an exact solution and an integral approximate solution, respectively. The effects of porosity, Stefan number, subcooling parameter, and dimensionless infiltration pressure are investigated.

Direct laser metal sintering as a new approach to fabrication of an isoelastic functionally graded material for manufacture of porous titanium dental implants

Objectives This work focuses on a titanium alloy implants incorporating a gradient of porosity, from the inner core to the outer surface, obtained by laser sintering of metal powder. Surface appearance, microstructure, composition, mechanical properties and fractography were evaluated. Methods All the specimens were prepared by a selective laser sintering procedure using a Ti–6Al–4V alloy powder with a particle size of 1–10 μm. The morphological and chemical analyses were performed by SEM and energy dispersive X-ray spectroscopy. The flexure strength was determined by a three-point bend test using a universal testing machine. The surface roughness was investigated using a confocal scanning laser microscope. The surface roughness variation was statistically evaluated by use of a Chi square test. A p value of <0.05 was considered statistically significant. Results The original surface microstructure consisted of roughly spherical particles, diameter range 5–50 μm. After exposure to hydrofluoric acid some of these were removed and the microsphere diameter then ranged from 5.1 μm to 26.8 μm. Following an organic acid treatment, particles were replaced by grooves 14.6–152.5 μm in width and 21.4–102.4 μm depth. The metal core consisted of columnar beta grains with alpha and beta laths within the grains. The alloy was composed of 90.08% Ti, 5.67% Al and 4.25% V. The Young's modulus of the inner core material was 104 ± 7.7 GPa; while that of the outer porous material was 77 ± 3.5 GPa. The fracture face showed a dimpled appearance typical of ductile fracture. Significance In conclusion, laser metal sintering proved to be an efficient means of construction of dental implants with a functionally graded material which is better adapted to the elastic properties of the bone. Such implants should minimize stress shielding effects and improve long-term performance.

Laser sintering of metal powders on top of sintered layers under multiple-line laser scanning

A three-dimensional numerical model for multiple-line sintering of loose powders on top of multiple sintered layers under the irradiation of a moving Gaussian laser beam is carried out. The overlaps between vertically deposited layers and adjacent lines which strengthen bonding are taken into account. The energy equation is formulated using the temperature transforming model and solved by the finite volume method. The effects of the number of the existing sintered layers, porosity and initial temperature coupled with the optimal combination laser intensity and scanning velocity are presented. The results show that the liquid pool moves slightly towards the negative scanning direction and the shape of the liquid pool becomes shallower with higher scanning velocity. A higher laser intensity is needed to achieve the required overlaps when the number of the existing sintered layers increases. Increasing porosity or initial temperature enhances the sintering process and thus less intensity is needed for the overlap requirement.

Optimization on selective laser sintering of metallic powder via design of experiments method

Purpose – The objective of this study is to investigate the effect of various parameters on rapid prototyping parts for processes of sintering metallic powder by using Nd:YAG laser via the design of experiments (DOE) method.Design/methodology/approach – Experiments based on the DOE method were utilized to determine an optimal parameter setting for achieving a minimum amount of porosities in specimens during the selective laser sintering (SLS) process. Analysis of variance (ANOVA) was further conducted to identify significant factors.Findings – A regression model predicting percentages of porosities under various conditions was developed when the traditional Taguchi's approach failed to identify a feasible model due to strong interactions of controlled factors. The significant factors to the process were identified by ANOVA.Research limitations/implications – Four controlled factors including pulse frequencies and pulse durations of laser beams, times of strikes of a pulse applying on a single laser spot a...