Commercial Selective Laser Sintering Research Articles

Cold Laser Sintering of Medicines: Toward Carbon Neutral Pharmaceutical Printing.

Selective laser sintering (SLS) is an emerging three-dimensional (3D) printing technology that uses a laser to fuse powder particles together, which allows the fabrication of personalized solid dosage forms. It possesses great potential for commercial use. However, a major drawback of SLS is the need to heat the powder bed while printing; this leads to high energy consumption (and hence a large carbon footprint), which may hinder its translation to industry. In this study, the concept of cold laser sintering (CLS) is introduced. In CLS, the aim is to sinter particles without heating the powder bed, where the energy from the laser, alone, is sufficient to fuse adjacent particles. The study demonstrated that a laser power above 1.8 W was sufficient to sinter both KollicoatIR and Eudragit L100-55-based formulations at room temperature. The cold sintering printing process was found to reduce carbon emissions by 99% compared to a commercial SLS printer. The CLS printed formulations possessed characteristics comparable to those made with conventional SLS printing, including a porous microstructure, fast disintegration time, and molecular dispersion of the drug. It was also possible to achieve higher drug loadings than was possible with conventional SLS printing. Increasing the laser power from 1.8 to 3.0 W increased the flexural strength of the printed formulations from 0.6 to 1.6 MPa, concomitantly increasing the disintegration time from 5 to over 300 s. CLS appears to offer a new route to laser-sintered pharmaceuticals that minimizes impact on the environment and is fit for purpose in Industry 5.0.

Design of an In-situ microscope for selective laser sintering

• Demonstration that polymer melting and coalescence lags behind the location of laser – material interaction. This suggests that absorption of the laser energy and subsequent melting is slow relative to the scan speed. • This instrument has captured phenomena which would otherwise not be possible with slower camera frame rates, less magnification, and in a non-heated build environment. The phenomena responsible particle fusion during selective laser sintering (SLS) have been modeled, but attempts at experimental validation have been limited to unrealistic conditions compared to those used in commercial SLS processes. We have designed, implemented, and tested an instrument that is capable of performing in situ microscopy to image particle-scale dynamics of the SLS process at realistic scan speeds, temperatures, and gas environments. The instrument uses a combination of purchased and manufactured components to capture video at length scales of ∼1 µm and timescales of ∼1 ms. Spatial and temporal calibration is performed so that the laser position can be mapped onto the recorded video. Results show that laser melting of polymer is accompanied by particle rearrangement that occurs over an extended time (∼10 ms) after the laser scans a particular location. The findings highlight the importance of performing in situ microscopy under realistic conditions for SLS.

Weld seam morphology and bond strength of infrared and vibration welded SLS parts of polyamide 12 as a function of the layer build-up direction and the welding process

Selective laser sintering (SLS) offers the possibility of manufacturing complex parts without tools and thus enables the cost-effective production of individualized products. In contrast to this advantage, the producible component dimension is restricted due to the dimensions of the building chamber of commercial SLS systems. Furthermore, a great amount of cost-intensive powder is necessary for the production of large SLS parts. In order to overcome these limitations, reliable joining processes, which enable high mechanical bond properties in SLS assemblies, are indispensable. Especially welding processes are suitable in this case. However, there is only limited knowledge available about the welding of SLS parts. In particular, the influence of the characteristics of the SLS process on the resulting bond quality has not been analyzed so far. Within this paper, the influence of the SLS layer build-up direction on the resulting weld seam morphology and bond strength as a function of the welding process is investigated. Infrared and vibration welding, which differ in the method of energy input into the joining zone, are used.The investigations carried out show that high weld seam strengths can be achieved in SLS assemblies for both welding processes. The resulting bond strength is thereby largely independent of the SLS build-up direction. Vibration welded SLS parts exhibit high bond strengths in the range of the base material strength. SLS joints produced via infrared welding have lower bond strengths, which is expected to be caused by an already beginning recrystallization in the generated melt layer during the changeover phase. Furthermore, the investigations show that the weld seam morphology for SLS parts deviates from the characteristic structure of polymeric weld seams, as welded SLS samples do not show the typical separated multi-layer structure. The weld seam shows a very fine spherulitic, partly optically amorphous structure. This is probably the case because of additives contained in the SLS powder (e.g. pyrogenic silicon dioxide), which have an accelerating effect on crystallization. Deformed spherulites in the transition area to the base material are only visible for vibration welded SLS specimens. Due to larger occurring spherulites within the SLS samples compared to injection molded parts, their deformation takes place over a much wider area. The analysis of the weld seam morphology further substantiates the assumption that recrystallization already begins during the changeover phase in the infrared welding process. A highly oriented area with growing spherulites can be detected in the area of the joining plane. In summary, however, it can be noted that both welding processes are well suited for joining SLS parts.

A prototype powder deposition system for an open Selective Laser Sintering machine

Commercial Selective Laser Sintering (SLS) machines possess their own embedded powder deposition systems (PDS), most of which are based on the principle of powder containing piston in combination with a roller for powder spreading. These systems are factory-calibrated and do not offer the possibility to actively modify any pertinent powder deposition parameters. However, beyond the spreading method itself, notably a counter or forward rotating roller with or without a doctor blade, many of these parameters affect the quality of the non-sintered powder layer, such as the particle size distribution and geometry of the grains, rotary speed of the roller, feed of the roller, percentage of excess powder fed to the roller etc. Aiming at facilitating such experimentation, a prototype PDS was designed and manufactured. In this paper, the developed system is described and its utilities are presented. Standard deviation of layer thickness achieved is low enough to ensure system usefulness.

Investigation of Mechanical Properties and Binding Mechanism of Metal Based SLS Prototype Coated with Ceramics using High Velocity Oxy Fuel

Abstract In recent times, there has been a growth in use of Rapid Prototyping and Manufacturing (RPM) in various industries globally. Selective Laser Sintering (SLS) used with coated metallic powders has been of special interest as it has widespread application for direct manufacturing especially in the Automotive, Aerospace and Injection Molding industries. This study aims at analyzing the mechanical properties of the fabricated samples at the various stages of a commercial SLS process developed by 3D Systems. Further, a few samples have been coated with a mixture of SiC and Al2O3 using HVOF coating process to improve the mechanical properties and surface properties of the samples. Simultaneously, a study of the surface of the samples was done using SEM analysis. This was aimed to understand the binding mechanism during the various stages of SLS. Finally, we have attempted to establish how the binding mechanism affects the density and the mechanical properties. This will not only establish which industries can directly use the SLS process in its current form with the appropriate coating process, but also lay the groundwork for future research in the variation of machine parameters and powder based raw material for improved mechanical properties

Surface roughness of polyamide 12 parts manufactured using selective laser sintering

Selective laser sintering (SLS) is an additive manufacturing technique that has become increasingly prevalent in today's rapidly advancing production industries. SLS utilizes a layer-by-layer processing technique that allows for complex geometries to be produced without expensive tooling or molding. Because of the technology's widespread use in fulfilling functional demands, parts produced by SLS should have a good surface quality. However, parts manufactured via SLS have a comparatively higher surface roughness than alternative manufacturing methods. To better understand the various factors that affect surface roughness, a design of experiments was implemented which investigated the effects of four process parameters using a Sinterstation 2500, a commercial SLS printer: laser power, roller speed, powder type, and scan spacing. To draw a comparison with other SLS systems, two process parameters were investigated on a Sinterit Lisa, a desktop SLS printer: power ratio and powder type. These effects were studied across the entire powder bed, a study of which has not been previously conducted. Since many other factors play a role such as layer height, this study concentrated on the top surface of the SLS printed part. The surface roughness of the produced parts was studied using Focus Variation (FV) technology. Conditional formatting was used to show the surface roughness and area ratio of the powder bed, and an analysis of variance (ANOVA) is performed on the data collected from the Sinterstation.

Crystallization Kinetics of Polyamide 12 during Selective Laser Sintering.

Selective laser sintering (SLS) of thermoplastic materials is an additive manufacturing process that overcomes the boundary between prototype construction and functional components. This technique also meets the requirements of traditional and established production processes. Crystallization behavior is one of the most critical properties during the cooling process and needs to be fully understood. Due to the huge influence of crystallization on the mechanical and thermal properties, it is important to investigate this process more closely. A commercial SLS polyamide (PA12) powder was measured with differential scanning calorimetry (DSC) to model a wider temperature range. To model isothermal crystallization between 160 and 168 °C, the Avrami model was used to determine the degree of crystallization. For non-isothermal crystallization between 0.2 and 20 K/min, different models were compared including the Ozawa, Jeziory, and Nakamura equations.

Selective Laser Sintering of Porous Silica Enabled by Carbon Additive.

The aim of this study is to investigate the possibility of a freeform fabrication of porous ceramic parts through selective laser sintering (SLS). SLS was proposed to manufacture ceramic green parts because this additive manufacturing technique can be used to fabricate three-dimensional objects directly without a mold, and the technique has the capability of generating porous ceramics with controlled porosity. However, ceramic printing has not yet fully achieved its 3D fabrication capabilities without using polymer binder. Except for the limitations of high melting point, brittleness, and low thermal shock resistance from ceramic material properties, the key obstacle lies in the very poor absorptivity of oxide ceramics to fiber laser, which is widely installed in commercial SLS equipment. An alternative solution to overcome the poor laser absorptivity via improving material compositions is presented in this study. The positive effect of carbon additive on the absorptivity of silica powder to fiber laser is discussed. To investigate the capabilities of the SLS process, 3D porous silica structures were successfully prepared and characterized.

Open-Source Selective Laser Sintering (OpenSLS) of Nylon and Biocompatible Polycaprolactone.

Selective Laser Sintering (SLS) is an additive manufacturing process that uses a laser to fuse powdered starting materials into solid 3D structures. Despite the potential for fabrication of complex, high-resolution structures with SLS using diverse starting materials (including biomaterials), prohibitive costs of commercial SLS systems have hindered the wide adoption of this technology in the scientific community. Here, we developed a low-cost, open-source SLS system (OpenSLS) and demonstrated its capacity to fabricate structures in nylon with sub-millimeter features and overhanging regions. Subsequently, we demonstrated fabrication of polycaprolactone (PCL) into macroporous structures such as a diamond lattice. Widespread interest in using PCL for bone tissue engineering suggests that PCL lattices are relevant model scaffold geometries for engineering bone. SLS of materials with large powder grain size (~500 μm) leads to part surfaces with high roughness, so we further introduced a simple vapor-smoothing technique to reduce the surface roughness of sintered PCL structures which further improves their elastic modulus and yield stress. Vapor-smoothed PCL can also be used for sacrificial templating of perfusable fluidic networks within orthogonal materials such as poly(dimethylsiloxane) silicone. Finally, we demonstrated that human mesenchymal stem cells were able to adhere, survive, and differentiate down an osteogenic lineage on sintered and smoothed PCL surfaces, suggesting that OpenSLS has the potential to produce PCL scaffolds useful for cell studies. OpenSLS provides the scientific community with an accessible platform for the study of laser sintering and the fabrication of complex geometries in diverse materials.

Open-source Selective Laser Sintering (OpenSLS) of nylon and biocompatible polycaprolactone

Event Abstract Back to Event Open-source Selective Laser Sintering (OpenSLS) of nylon and biocompatible polycaprolactone Ian S. Kinstlinger1, Andreas Bastian1, Daniel H. Hwang1, Anderson Ta1, Samantha J. Paulsen1, Tim Schmidt2 and Jordan S. Miller1 1 Rice University, Bioengineering, United States 2 Lansing Makers Association, United States Introduction: Selective Laser Sintering (SLS) is an additive manufacturing process in which a laser patterns powdered starting materials into solid 3D structures in a layer-by-layer manner. Features which are challenging to fabricate using other additive processes (e.g. overhangs, underhangs, branches, and bifurcations) are readily accessible using SLS. SLS has found great utility in the fabrication of scaffolds for bone tissue engineering[1] and patient-specific splints for human airway stabilization[2]. Despite the potential for fabrication of complex, high-resolution structures with SLS using diverse materials (including biomaterials), prohibitive costs of commercial systems have hindered the wide adoption of this technology in the scientific community. We hypothesized that a consumer laser cutter could be used in conjunction with open-source hardware and software to inexpensively perform SLS. Here, we implemented and characterized sintering with polymers and biomaterials, introduced post-processing techniques for sintered parts, and demonstrated biocompatibility of sintered polycaprolactone (PCL). Methods: We implemented OpenSLS by installing a custom powder handling module inside a laser cutter and overriding the native electronics[3]. Sintered parts were assessed by scanning electron microscopy (SEM) and microcomputed tomography (µCT). PCL biocompatibility was evaluated by seeding human mesenchymal stem cells (hMSC) labeled with GFP and H2B-mCherry on sintered PCL surfaces and imaging with epifluorescent microscopy. Results and Discussion: Nylon was sintered into structures with sub-millimeter features and overhanging/branching regions (Figure 1). Sintered surfaces appear similar to those of nylon parts fabricated on commercial SLS systems[4]. Nylon filaments exhibit a mostly fused core but show small irregular interior cavities. PCL was also sintered into lattice structures, which could be useful as bone scaffolds. Finding that coarse PCL grains yielded rough, poorly connected lattices, we developed a vapor smoothing technique (Figure 2) which reduced the average surface roughness from 120µm to 5µm and increased the elastic modulus from 30MPa to 60MPa. The stiffer scaffolds more closely match bone mechanics while the smoothed surfaces enhance cell adhesion. hMSCs attached, survived, and exhibited characteristic spindle-like morphology on both vapor-smoothed and unsmoothed sintered PCL (Figure 3), suggesting that sintered PCL will be useful for cell studies. Conclusions: Architecturally complex, physiologically relevant structures can be fabricated at high resolution using a low-cost, open-source platform. The use of biomaterials in this system is straightforward and produces structures that are compatible with cell studies. OpenSLS could serve the scientific community as an accessible platform for fabricating structures composed of a wide range of materials, including non-traditional materials not supported by commercial SLS suppliers. We gratefully acknowledge the many open-source and related projects that critically facilitated this work, including Arduino.cc, RepRap.org, Ultimachine.com, Python.org, Blender.org, NIH ImageJ, Fiji.sc, slic3r.org, netfabb.com, pronterface.com, enblend.sourceforge.net, thingiverse.com, and openscad.org.; We are grateful to SeeMeCNC for assisting with the acquisition, installation, and configuration of the laser cutter that was converted into OpenSLS.

Direct Selective Laser Sintering/Melting of High Density Alumina Powder Layers at Elevated Temperatures

Abstract Direct selective laser sintering (SLS) or selective laser melting (SLM) are additive manufacturing techniques that can be used to produce three-dimensional ceramic parts directly, without the need for a sacrificial binder. In this paper, a low laser energy density is applied to SLS/SLM high density powder layers of sub-micrometer alumina at elevated temperatures (up to 800 C ). In order to achieve this, a furnace was designed and built into a commercial SLS machine. This furnace was able to produce a homogeneously heated cylindrical zone with a height of 60 mm and a diameter of 32 mm. After optimizing the layer deposition and laser scanning parameters, two ceramic parts with a density up to 85% and grain sizes as low as 5 μ m were successfully produced.

Multiphase Polymeric Materials for Rapid Prototyping and Tooling Technologies and Their Applications

Rapid prototyping (RP) and tooling (RT) are the technologies for quickly fabricating functional components and tooling inserts directly from CAD data by selectively adding material layer by layer. In this paper, multiphase polymeric materials for RP and RT technologies and their applications, which are developed by the Rapid Manufacturing (RM) Center of Huazhong University of Science and Technology (HUST) in China, were introduced. Selective laser sintering (SLS) is a powder-based RP process. Multi-types of multiphase polymer materials for SLS process were successfully developed in the RM center, and the SLS components were formed from these materials by using the commercial SLS machines HRPS series for various applications. High impact polystyrene (HIPS)/wax blend SLS parts were used as lost patterns for the investment casting process to make complex metal parts rapidly; nylon-12/organically modified rectorite and nylon-12/nanosilica composite powders were used to fabricate functional parts, which showed higher thermal and mechanical properties than neat nylon-12 SLS parts. As a RT application, Fe/epoxy composite tooling inserts were rapidly fabricated by SLS and post-processing. Stereolithography (SLA) uses photocurable resins to rapidly manufacture components with high accuracy and mechanical properties. A freeradical and cationic mixed-type radiation curable composite resin was also successfully developed, and SLA parts without obvious distortion were built on the SLA machines HRPL series from this hybrid resin, successfully and efficiently.

Fusion behavior of TrueFormTM/SiO2 composite powders during selective laser sintering

PurposeThis paper aims to study the effects of solid additives and compounding processes on the selective laser sintering (SLS) behavior of composite powders.Design/methodology/approachComposite powders were prepared from TrueForm™ acrylic‐styrene co‐polymer and SiO2 powder. Dry mixing and melt extrusion were used as the blending processes to produce the composite powders. Some SiO2 powder was ground and treated with silane coupling agent before blending to study the effects of particle size and surface treatment of the filler, respectively. The temperature of the powder bed was monitored using an infrared thermometer. The fusion behaviors of the powders were investigated in situ using an optical microscope and the sintered specimens were examined by scanning electron microscopy.FindingsFor a given volume fraction of the filler, reducing its particle size will hinder fusion between the polymer particles and weaken the sintered specimens. Surface treatment of the filler by silane coupling agent had little effect on the morphology of the sintered specimens; however, it slightly improved their strength. The blending method plays an important role in the sintering behavior of the composite powders. Although melt blending improved the polymer‐to‐polymer contact between the composite powder particles, the high‐resultant viscosity of the material adversely affected the densification of the powder bed, leading to a highly porous structure of the sintered specimens.Research limitations/implicationsThe sintering experiments were conducted in ambient conditions using a laser engraving machine instead of a commercial SLS machine with atmospheric control. The temperature gradient within the powder bed was expected to be higher than that in normal SLS processes.Practical implicationsThe SLS behavior of a composite powder not only depends on its composition but also on the powder preparation method or powder morphology.Originality/valueThis paper provides some useful information for future development of composite powders for SLS applications.

Development and performance evaluation of solid freeform fabrication system by using dual laser sintering process

A solid freeform fabrication (SFF) system using selective laser sintering (SLS) is currently recognized as a leading process and SLS extends the application to machinery and automobiles due to the various materials employed. In order to develop a more elaborate and rapid system for fabricating large objects compared to existing SLS, this study employs a new selective dual-laser sintering process. It contains a three-axis, dynamic focusing scanner system for scanning large areas instead of the existing fθ lens used in commercial SLS. Therefore, the unique scanning path generation is necessary to eliminate the factors of quality deterioration in case of fabricating larger objects. Also, this paper will address development of a SFF system which employs the dual laser system and the unique scanning device. In the SLS, the sintering temperature, laser beam power and layer thickness have a great influence on sintering of the polymer. Experiments were performed to evaluate the effect of a scanning path and fabrication parameters on the sintering process and to fabricate the various three-dimensional objects using polymer powders.

Reflectance and transmittance of TrueFormTM powder and its composites to CO2 laser

PurposeThe purpose of this paper is to report on a study of the effect of glass microsphere (GMS) and potassium bromide (KBr) powder as an additive on the reflectance and transmittance of TrueFormTM acrylic‐styrene co‐polymer (TF) powder to CO2 laser during selective laser sintering (SLS).Design/methodology/approachGMSs and KBr powder were chosen because glass is opaque to CO2 laser while KBr is transparent. The GMSs were treated with silane coupling agent and hydrofluoric acid to study the surface effect on the optical properties of TF/GMS blends. KBr powder was blend with TF powder in an attempt to modify the penetration depth of the laser in the powder bed. An integrating sphere was used to measure the reflectance of the powder bed. In the measurement of transmittance, a power meter was placed below the powder layer, which was supported by a KCl disc, to register the transmitted laser energy through the powder layer.FindingsFor the TF/GMS blends, smaller GMSs gave a higher reflectance while the surface treatments had little effect. The transmittance of both the polymer and the blends were very low. Although bulk KBr is highly transparent to CO2 laser, adding 30 vol% of KBr powder to TF hardly increased the transmittance of the powder bed.Research limitations/implicationsExperiments were carried out on a modified laser engraving machine rather than a commercial SLS machine. The laser energy density used was lower than that for normal SLS processes and no significant changes of physical condition of the powder bed were inflicted. The results only indicate the optical properties in the initial state.Practical implicationsThe effects of transparent and non‐transparent fillers on the optical properties of the powder bed are presented.Originality/valueThis work furthers the understanding of heat absorption behavior of the powder bed during SLS.

Development of industrial SFF system using dual laser and optimal process

Selective laser sintering (SLS) is currently recognized as a leading process in the new field of solid freeform fabrication (SFF). SLS extends the applications to machinery and automobiles due to various employing materials. In order to develop more elaborate and speedy system for fabricating large objects compared to existing SLS, this study employs a new selective dual-laser sintering (SDLS) process. It contains three-axis dynamic focusing scanner system for scanning large area instead of the existing f θ lens used in commercial SLS. The optimal fabrication parameters such as sintering temperature, laser beam power and layer thickness should be determined when sintering polymer and metal powder. In this paper, we will address methods for the effective laser scanning path generation, the suitable temperature and the accurate z-axis control. Also, experiments have been performed to evaluate the effect of fabrication parameters on process and to fabricate the various 3D objects using polymer.

Selective Laser Sintering of Tissue Engineering Scaffolds Using Poly(L-Lactide) Microspheres

This paper reports a study on the modification of a commercial selective laser sintering (SLS) machine for the fabrication of tissue engineering scaffolds from small quantities of poly(L-lactide) (PLLA) microspheres. A miniature build platform was designed, fabricated and installed in the build cylinder of a Sinterstation 2000 system. Porous scaffolds in the form of rectangular prism, 12.7×12.7×25.4 mm3, with interconnected square and round channels were designed using SolidWorks. For initial trials, DuraFormTM polyamide powder was used to build scaffolds with a designed porosity of ~70%. The actual porosity was found to be ~83%, which indicated that the sintered regions were not fully dense. PLLA microspheres in the size range of 5-30 μm were made using an oil-in-water emulsion solvent evaporation procedure and they were suitable for the SLS process. A porous scaffold was sintered from the PLLA microspheres with a laser power of 15W and a part bed temperature of 60oC. SEM examination showed that the PLLA microspheres were partially melted to form the scaffold. This study has demonstrated that it is feasible to build tissue engineering scaffolds from small amounts of biomaterials using a commercial SLS machine with suitable modifications.

A Study of the Solid Freeform Fabrication (SFF) System with Dual Laser System

A solid freeform fabrication (SFF) system using selective laser sintering (SLS) is currently recognized as a leading process and SLS extends the applications to machinery and automobiles due to the various materials employed. In order to develop a more elaborate and rapid system for fabricating large objects compared to existing SLS, this study employs a new selective dual-laser sintering (SDLS) process. It contains a 3-axis, dynamic focusing scanner system for scanning large areas instead of the existing fθ lens used in commercial SLS. Therefore, the unique scanning path generation is necessary to eliminate the factors of quality deterioration in case of fabricating larger objects. Also, this paper will address development of an SFF system which employs the dual laser system and the unique scanning device. Experiments were performed to evaluate the effect of a scanning path and fabrication parameters on sintering process and to fabricate the various 3D objects using polymer powder.

Study of laser‐sinterability of ferro‐based powders

PurposeTo find the suitable parameters for selective laser sintering (SLS) of selected ferro‐based powders. These parameters will help to create products having appreciable strength shown by the highest density and good surface property.Design/methodology/approachDesign of experiment (L9 Taguchi design) has been used to obtain the parameters in the minimum possible number of experiments. For finding the range of various parameters selected such as scan speed, scan spacing and layer thickness, some preliminary experiments have been performed. In order to carry out varied characterization for a given type of experiment, a number of samples have been made.FindingsAn attempt has been made to observe the correlation between applied laser energy and the properties of the laser‐sintered parts. Taguchi design has been useful and has given the optimized parameters. It has also been found that the infiltration increases the strength of the part substantially compared with the property of end‐used sintered product.Research limitations/implicationsThe present set of experiments was limited by the range of supplied laser energy to the powder system, as the laser power could not be increased.Originality/valueThere is a need to search for alternative powders for manufacturing parts through SLS, which can alleviate the need to depend on customized powders, as these customized powders are limited to be used only with prescribed commercial SLS machines for their best performance. This drawback restricts their general use independent of any particular machine and it is, therefore, required to develop know‐how of powders and related process parameters for SLS. The present work is an effort in this direction in which laser sintering of a specially developed iron‐based powder mixture (Fe, Ni, Cu and Fe3P) has been tested on an SLS machine.

Movement of powder bed material during the selective laser sintering of bisphenol‐A polycarbonate

PurposeThe purpose of this paper is to report on a study of the movement of the powder bed material during selective laser sintering (SLS) of bisphenol‐A polycarbonate (PC) powder and its effect on the morphology of the sintered specimen.Design/methodology/approachTwo sintering experiments, i.e. single‐spot laser sintering and raster‐scan laser sintering, were carried out and the material movement mechanisms were investigated in situ and subsequently by scanning electron microscopy.FindingsDuring the raster‐scan laser sintering process, the movement of the powder was found to be primarily perpendicular to the scanning direction. When sintering at a high laser power, it significantly affected the surface morphology of the sintered specimens and parallel surface bands occurred along the scanning direction.Research limitations/implicationsExperiments were carried out on a modified laser engraving machine rather than a commercial SLS machine.Practical implicationsA schematic model of the material movement mechanism for each of the sintering strategies is presented.Originality/valueThe results further the understanding of the sintering behaviour of the powder bed.