Computational Analysis of Selective Laser Sintering of Inconel 625

A two-dimensional multi-physics finite element model is developed to simulate the Selective Laser Sintering(SLS)process using Inconel 625 powders.The validity of the developed model is first assessed by comparing its results with experimental data.Various factors such as phase transition,recoil pressure,surface tension,and theMarangoni force are considered.The study’s findings underscore that the morphology and thermal-fluid dynamics of the molten pool in the SLS process are predominantly shaped by the influence of the Marangoni force and recoil pressure acting on its surface.The recoil pressure at the front of the laser spot rises exponentially with temperature,making the liquid metal move downward,and creating a depression at the pool’s head.It also causes particles to splash from the pool’s rear edge.The study explores the influence of the backward Marangoni force,where hightemperature liquid flows from the front to the rear of the molten pool,creating a vortex and moving the pool in the rear.Process parameters like laser intensity,scan speed,and spot size were analyzed.The findings indicate that higher laser power lower scanning speed and laser beam spot size lead to increased width and depth of the molten pool.

NUMERICAL SIMULATIONS OF TEMPERATURE FIELD IN DIRECT METAL LASER SINTERING PROCESS

A mathematical model is developed for simulating the heat transferring behavior in a direct metal laser sintering process. The model considers the thermal phenomena involved in the process, including conduction, radiation, and convection. A formula for the calculation of the heat conductivity of a sintering system containing solid phase, liquid phase, and gas phase is given. Due to the continuous movement of the laser beam, a local coordinate system centered on the laser beam is used to simplify the analytical calculation. Assuming that it is approximately a Gaussian laser beam, the heat conduction equation is resolved based on the assumption of the thermal insulating boundary conditions and the fixed thermal physical parameters. The FORTRAN language is employed to compile the program to simulate the temperature field in the direct copper powder sintering process. It shows a good agreement with the preliminary experimental results.[KH3/4D]

Effects of laser energy density on forming accuracy and tensile strength of selective laser sintering resin coated sands

Baozhu sand particles with size between 75 μm and 150 μm were coated by resin with the ratio of 1.5 wt.% of sands. Laser sintering experiments were carried out to investigate the effects of laser energy density(E = P/v), with different laser power(P) and scanning velocity(v), on the dimensional accuracy and tensile strength of sintered parts. The experimental results indicate that with the constant scanning velocity, the tensile strength of sintered samples increases with an increase in laser energy density; while the dimensional accuracy apparently decreases when the laser energy density is larger than 0.032 J·mm-2. When the laser energy density is 0.024 J·mm-2, the tensile strength shows no obvious change; but when the laser energy density is larger than 0.024 J·mm-2, the sample strength is featured by the initial increase and subsequent decrease with simultaneous increase of both laser power and scanning velocity. In this study, the optimal energy density range for laser sintering is 0.024-0.032 J·mm-2. Moreover, samples with the best tensile strength and dimensional accuracy can be obtained when P = 30-40 W and v = 1.5-2.0 m·s-1. Using the optimized laser energy density, laser power and scanning speed, a complex coated sand mould with clear contour and excellent forming accuracy has been successfully fabricated.

Morphology and Mechanical Properties of PS/Al_2O_3 Nanocomposites Based on Selective Laser Sintering

Selective laser sintering （SLS） is a new process to prepare the polystyrene （PS）/Al2O3 nanocomposites. In this paper, with different laser power and other processing parameters unchanged, the morphology, density and mechanical properties of the sintered specimens were investigated. It was found that nano-sized inorganic particles are uniformly located in the PS matrix and the maximum density of the sintered specimens with pure PS powder reaches 1.07 g/cm^3, higher than 1.04 g/cm^3 that of the sintered specimens with mixture powder. Due to strengthening and toughness of the nano-sized Al2O3 inorganic particles, the maximum notched impact strength and tensile strength of the sintered part mixed with nano-sized inorganic particles are improved greatly from 7.5 to 12.1 kJ/m^2 and from 6.5 to 31.2 MPa, respectively, under the same sintering condition.

Investigating on casting mold (or core) making with coated sand by the selected laser sintering

Using a special coated sand as the material of the selected laser sintering (SLS), the authors test and investigate the strength change of the test samples in terms of different sintering parameters (scanning speed, laser power, sintering thickness, and so on). The characteristics of coated sand hardening by laser beam are analyzed. The sintered mold (or core) for given casting is poured with molten metal.

Accuracy analysis of the part made by selected laser sintering

The effects of different factors, including the precision of selected laser sintering (SLS) equipment, sintering temperature, sintered thickness of individual layer and laser scanning route, on the SLS part accuracy have been analyzed and studied. Some measures are suggested in order to improve the part accuracy made by SLS.

SOFTWARE SYSTEM FOR SELECTIVE LASER SINTERING

The advent of rapid prototyping & manufacturing techniques represents a major breakthrough in production engineering. This paper is concerned with the software system aspects of the selective laser sintering (SLS),i.e.the issues that deal with an external geometric CAD model to automatically control the physical layering fabrication process as directly as possible ,regardless of the source of the model. The general issues are described and some key methods are given in this paper.

Advances in selective laser sintering of polymers

Polymers are widely used materials in aerospace,automotive,construction,medical devices and pharmaceuticals.Polymers are being promoted rapidly due to their ease of manufacturing and improved material properties.Research on polymer processing technology should be paid more attention to due to the increasing demand for polymer applications.Selective laser sintering(SLS)uses a laser to sinter powdered materials(typical polyamide),and it is one of the critical additive manufacturing(AM)techniques of polymer.It irradiates the laser beam on the defined areas by a computer-aided design three-dimensional(3D)model to bind the material together to create a designed 3D solid structure.SLS has many advantages,such as no support structures and excellent mechanical properties resembling injection moulded parts compared with other AM methods.However,the ability of SLS to process polymers is still affected by some defects,such as the porous structure and limited available types of SLS polymers.Therefore,this article reviews the current state-of-the-art SLS of polymers,including the fundamental principles in this technique,the SLS developments of typical polymers,and the essential process parameters in SLS.Furthermore,the applications of SLS are focused,and the conclusions and perspectives are discussed.

Prediction of Sintering Strength for Selective Laser Sintering of Polystyrene Using Artificial Neural Network

In the present work,a study is made to investigate the effects of process parameters,namely,laser power,scanning speed,hatch spacing, layer thickness and powder temperature, on the tensile strength for selective laser sintering( SLS) of polystyrene( PS). Artificial neural network( ANN) methodology is employed to develop mathematical relationships between the process parameters and the output variable of the sintering strength. Experimental data are used to train and test the network. The present neural network model is applied to predicting the experimental outcome as a function of input parameters within a specified range. Predicted sintering strength using the trained back propagation( BP) network model showed quite a good agreement with measured ones. The results showed that the networks had high processing speed,the abilities of error-correcting and self-organizing. ANN models had favorable performance and proved to be an applicable tool for predicting sintering strength SLS of PS.

Rapid casting technology based on selective laser sintering

Selective laser sintering(SLS),as a kind of additive manufacturing technology,which uses a laser beam to scan and heat powder material layer by layer to form parts(models),is widely used in the field of casting,mainly for preparing casting coated sand cores,investment casting patterns,etc.The SLS technique facilitates rapid casting and shortens the casting production periods by eliminating mold preparation.In this study,we reached conclusions for the basic principles and characteristics of SLS methods,and focused on the research status,key technology and development trend of SLS in the fields of forming coated sand-casting molds and investment casting patterns.

Compact Co3O4/Co in-situ nanocomposites prepared by pulsed laser sintering as anode materials for lithium-ion batteries

With the development of portable electronic devices, electric vehicles, and power storage systems, the demand for rechargeable batteries with high energy density is growing rapidly [1–5]. In the field of lithium-ion batteries, the unconventional anode materials such as tin, silicon, metallic lithium, and transition-metal oxides have been extensively studied due to the high capacity, but they are still inapplicable because of the low initial coulombic efficiency(ICE) and/or the poor cycling stability [5–9].

A comparison of the microstructure-dependent corrosion of dual-structured Mg-Li alloys fabricated by powder consolidation methods:Laser powder bed fusion vs pulse plasma sintering

In this study, powder metallurgy methods were used to fabricate Mg-7.5Li-3Al-Zn alloys from repowdered extruded alloys. Extruded alloys were powdered using ultrasonic atomization, and then laser powder bed fusion(LPBF) and pulse plasma sintering(PPS) were used to consolidate the bulk materials. A comparison of the properties of the fabricated alloys with those of a conventionally extruded one was carried out using methods that characterized the microstructure and corrosion resistance. When compared to their conventionally extruded counterpart, LPBF and PPS materials exhibited refined microstructures with low enrichment in Al Li and coarse Al, Zn, Mn precipitates. The main drawback of the LPBF alloy, printed for the needs of this study, was its porosity, which had a negative effect on its corrosion. The presence of unrecrystallized particle boundaries in the PPS alloy was also unbeneficial with regard to corrosion. The advantage of the LPBF and PPS processes was the ability to change the proportion of α(Mg) to β(Li), which when the complete consolidation of the material is achievable, may increase the corrosion resistance of dual-structured Mg-Li alloys. The results show that powder metallurgy routes have a wide potential to be used for the manufacture of Mg-Li based alloys.

Fe-Zn supersaturated solid solution prepared by mechanical alloying and laser sintering to accelerate degradation

The slow degration of iron limits its bone implant application.The solid solution of Zn in Fe is expected to accelerate the degradation.In this work,mechanical alloying(MA)was used to prepare Fe-Zn powder with supersaturated solid solution.MA significantly decreased the lamellar spacing between particles,thus reducing the diffusion distance of solution atoms.Moreover,it caused a number of crystalline defects,which further promoted the solution diffusion.Subsequently,the MA-processed powder was consolidated into Fe-Zn part by laser sintering,which involved a partial melting/rapid solidification mechanism and retained the original supersaturated solid solution.Results proved that the Fe-Zn alloy became more susceptible with a lowered corrosion potential,and thereby an accelerated corrosion rate of(0.112±0.013)mm/year.Furthermore,it also exhibited favorable cell behavior.This work highlighted the advantage of MA combined with laser sintering for the preparation of Fe-Zn implant with improved degradation performance.

IGNITING SHS BY LASER AND ITS APPLICATION TO SELECTIVE LASER SINTERING OF METALLIC POWDER MATERIAL

How to directly fabricate metallic functional parts with selective laser sintering (SLS) process is a potential technique that scientists are researching. Existent problems during directly fabricating metal part by use of SLS are analyzed. For the sake of solving the problems, a new idea of adding self-propagating high-temperature synthesis (SHS) material into metallic powder material to form new type of SLS metallic powder material is put forward. This powder material can release controllable amount of heat during its interaction with the laser beam energy to reduce the requirement to laser power during directly sintering metallic part, to prolong the time of metallic liquid phase existing, and to improve the intensity and accuracy of SLS part. For this reason, SHS material′s interaction with the CO2 laser beam energy is researched, which proves that CO2 laser beam energy may instantly ignite SHS reaction. On the basis of the above-mentioned researches, the effect of sintering the metal powder material mixing SHS material with CO2 laser is also researched, which shows: there is an optimal blending ratio of various material in the new metallic powder material. Under the optimal blending ratio and SLS process parameters, this new metallic powder material can indeed release amount of heat and SHS reaction may be controlled within the laser sintering. This research result makes it possible that the metallic part is directly sintered with small CO2 laser (less than 50W), which may greatly reduce the volume, cost and running expenditure of SLS machine, be propitious to application.

A method to fabricate small features on scaffolds for tissue engineering via selective laser sintering

Purpose: Selective laser sintering (SLS) is a rapid pro- totyping technique applied to produce tissue-engineer- ing scaffolds from powder materials. The standard scanning technique, however, often produces struts of extensive thickness, which means fabrication of high- ly porous scaffolds with small overall dimensions is quite difficult. Nevertheless, this study aims to overcome this shortfall. Design/methodology/approach: To this end, three scanning methods were evaluated in terms of minimum feature size and freedom of design, using a test polyamide (PA) material. Polycaprolactone (PCL) was then employed to create highly porous 3D scaffolds using the preferred scanning me- thod to produce thin struts. Findings: While in normal scanning mode some features were well above the laser spot diameter, strut thicknesses below the laser spot diameter were achieved when using the “outline scan” function for PA material. Those achieved for PCL were slightly higher and in the 500-800 ?m range, with an average pore size of 400 μm. Investigations on the properties of the scaffolds revealed an effective compression modulus of the PCL scaffold of 6.5 MPa. Furthermore, there was no change in physical or che- mical properties when the scaffolds were stored in a physiological environment for 7 weeks. Originality/ value: Though SLS is considered as a fabrication te- chnique for tissue engineering scaffolds, actually pro- duced scaffolds did not comply with porosity requirements and limitations of the SLS process in produ- cing features at the size of the laser beam spot have not been discussed. The present paper shows the capabilities of the SLS process based on two materials and presents a method to minimize feature size in scaffolds.

Prediction and Analysis of Post-Treatment of Sustainable Walnut Shell/Co-PES Parts by Laser Sintering

In order to enhance the strength of sustainable walnut shell/Co-PES(WSPC)sintered parts,wax-filtrated posttreatment was carried out.The effects of treating fluid temperature,preheating time and immersion time on the bending strength of WSPC wax-filtrated parts were analyzed by single factor analysis method.To obtain an accurate model for predicting the bending strength of the WSPC wax-filtrated part,the experiments were involved by using Box-Behnken design(BBD).Main parameters,such as treating fluid temperature,preheating time and immersion time,and their interactive effects were analyzed through analysis of variance(ANOVA)and graphical contours.The results demonstrated that all parameters’direct effects were significant to bending strength of the WSPC wax-filtrated part.Its optimum value was 5.0 MPa when the treating fluid temperature of 70°C,preheating time of 50 min,and immersion time of 20 s.The predicted models effectively validated had good predicting accuracy.The WSPC wax-filtrated part using optimal processing parameters was processed by investment casting,and then the metal casting of dimensional stability and smooth surface was obtained.Investment casting was done using WSPC wax-filtrated parts under optimal process parameters and then metal parts with stable structure size and smooth surface can be obtained,which indicates that WSPC material can be used for investment casting.

STUDY ON SELECTIVE LASER SINTERING OF METALLIC POWDERS

A series of experiments are carried out with selective laser sintering(SLS) for copper,copper-nickel powder matetials.The phenomena of the sintering process is ana-lyzed,the influence of techmological parameters is dis-cussed in detail,By means of SEM with energy spectrum system and X-ray diffraction spectrum,the morphology of the microstructure and the compositions of the different zones are analyzed,the mechanism of the laser sintering metallic powders is preliminarily explored,All those above lay the foundations for the forming metal parts by laser sintering metallic powders.

Selective laser sintering mechanism of polymer-coated molybdenum powder

A type of polymer-coated molybdenum powder used in selective laser sintering technology was prepared by coating polymer on molybdenum particles and frozen grinding techniques, with the maximum particle diameter of 71 μm. The laser sintering experiments of polymer-coated molybdenum powder were conducted by using the self-developed selective laser sintering machine (HLRP-350I). The method of microscopic analysis was used to investigate the dynamic laser sintering process of polymer-coated molybdenum powder. Based on the study, the laser sintering mechanisms of polymer-coated molybdenum powder were presented. It is found that the mechanism is viscous flow when the laser sintering temperature is between 100 ℃ and 160 ℃, which can be described by a two-sphere model; and the mechanism is melting /solidification when the temperature is above 160 ℃.

Numerical simulation of temperature field during selective laser sintering of polymer-coated molybdenum powder

The technology of length-alterable line-scanning laser sintering was introduced. Based on the research of laser heating property, powder thermal physics parameters and laser sintering process, a numerical model of the temperature field during length-alterable line-scanning and laser sintering of polymer-coated molybdenum powder was presented. Finite element method (FEM) was used to simulate the temperature field during laser sintering process. In order to verify the simulated results, a measuring system was developed to study the laser sintering temperature field. Infrared meter was introduced to measure the surface temperature of sintering powder; the temperature of its inside part was measured by thermocouple. The measured results were compared with the numerical simulation results; the conformity between them is good and the relative error is less than 5%.

Microstructure and property of sub-micro WC-10 %Co particulate reinforced Cu matrix composites prepared by selective laser sintering

The WC-10%Co particulate reinforced Cu matrix composite material with a WC-Co∶Cu mass ratio of 20∶80 was successfully fabricated by selective laser sintering(SLS) process. The following optimal processing parameters were used: laser power of 700 W, scan speed of 0.06 m/s, scan line spacing of 0.15 mm, and powder layer thickness of 0.3 mm. The microstructure, composition, and phase of the laser processed material were investigated by scanning electron microscopy(SEM), X-ray diffraction(XRD), and energy dispersive X-ray(EDX) spectroscopy. The results show that the bonding mechanism of this process is liquid phase sintering. The Cu and Co act as the binder phase, while the WC acts as the reinforcing phase. The non-equilibrium effects induced by laser melting, such as high degrees of undercooling and high solidification rate, result in the formation of a metastable phase CoC0.25. The WC reinforcing particulates typically have three kinds of morphology. They are agglomerated and undissolved, incompletely separated and partially dissolved, separated and dissolved, which indicates that particle rearrangement acts as the dominant sintering mechanism for the larger WC, while dissolution-precipitation prevails for the smaller WC particles. Microhardness tester was used to determine the Vickers hardness across the cross-section of the laser sintered sample, with the average value being HV0.1268.5. However, the hardness varied considerably, which might be attributed to the WC segregation and the high solidification rate experienced by the molten pool.