Selective Laser Sintering Machine Research Articles

Fabrication of 13-93 bioactive glass scaffolds for bone tissue engineering using indirect selective laser sintering

Bioactive glasses are promising materials for bone scaffolds due to their ability to assist in tissue regeneration. When implanted in vivo, bioactive glasses can convert into hydroxyapatite, the main mineral constituent of human bone, and form a strong bond with the surrounding tissues, thus providing an advantage over polymer scaffold materials. Bone scaffold fabrication using additive manufacturing techniques can provide control over pore interconnectivity during fabrication of the scaffold, which helps in mimicking human trabecular bone. 13-93 glass, a third-generation bioactive material designed to accelerate the body's natural ability to heal itself, was used in the research described herein to fabricate bone scaffolds using the selective laser sintering (SLS) process. 13-93 glass mixed with stearic acid (as the polymer binder) by ball milling was used as the powder feedstock for the SLS machine. The fabricated green scaffolds underwent binder burnout to remove the stearic acid binder and were then sintered at temperatures between 675 °C and 695 °C. The sintered scaffolds had pore sizes ranging from 300 to 800 µm with 50% apparent porosity and an average compressive strength of 20.4 MPa, which is excellent for non-load bearing applications and among the highest reported for an interconnected porous scaffold fabricated with bioactive glasses using the SLS process. The MTT labeling experiment and measurements of MTT formazan formation are evidence that the rough surface of SLS scaffolds provides a cell-friendly surface capable of supporting robust cell growth.

S041024 チタン粉末のレーザ積層造形([S04102]粉末成形とその評価(2))

The fabrication conditions of titanium powder were investigated using a selective laser sintering machine which has a 50 W Yb-fiber laser, a galvanometer scanner and a powder delivery and build system. The optimum laser power, scan speed and scan pitch were investigated by experiments. It was found that the smooth single-scan track can be fabricated at a laser power between 30 and 40 W and at a scan speed between 5 and 10 mm/s, and the width of the smooth single-scan track is around 450 [tm. The smooth surface could be successfully fabricated at a laser power more than 30 W.

Development of direct metal laser fabricating machine

Examples are given to establish the experiment platform for studying the direct metal laser fabricating (DMLF) as a variant of selective laser sintering (SLS). Taking into account of the special requirements for DMLF, by means of the low power SLS machine (CO2, 50 W) and high power laser processing machine (CO2, 2000 W) in the authors' institute, the system integration of two machines is realised after the improvement or rebuilding of light route system, functional units, machinery and electrical system, and control software in the primary SLS machine. After the system integration, the direct metal laser fabricating machine with the laser power up to 1000 W has been developed successfully. At the same time, the primary functions or performances of both low power SLS machine and high power laser processing machine are preserved entirely. The material suitable for DMLF machine ranges from non-metal powders to metal powders, including polystyrene, polyamide, sands and a large number of metal powders. Primary results show that the ability for DMLF of Cu based powder is much better than that of Fe based powder. DMLF parts or materials have some characteristics different from conventional methods in microstructure, phase and microhardness. Sintering environment still need to be improved especially including the seal ability of prototyping cabinet and preheating equipment in DMLF machine. The academic application of DMLF machine is on its way. Metal samples based on copper and 316L powders can be fabricated with the relative density of about 80 and 100% respectively utilising developed DMLF machine. All of advantages of primary two machines are utilised fully after system integration. A novel modification of the freeform technique selective laser sintering machine via system integration is put forward in this paper, developing a direct metal laser fabricating machine suitable for both non-metal and metal materials successfully.

Novel use of an aerospace selective laser sintering machine for rapid prototyping of an orbital blowout fracture

The authors describe the novel use of a selective laser sintering (SLS) machine, commonly used in the aerospace industry, to produce an accurate model of an orbital blowout fracture. Standard stereolithographic apparatus (SLA) technology failed to reproduce either orbital floor of a patient with a blowout fracture. The use of SLS technology using the same CT dataset to produce a superior model, highlights potential limitations of routine SLA technology and the high accuracy of SLS models. A custom-made titanium implant was constructed by hand using the SLS model as a template, it was positioned surgically and the patient's symptoms resolved uneventfully.

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.

Direct metal laser fabrication: machine development and experimental work

A novel modification of the freeform technique selective laser sintering machine via system integration to develop a direct metal laser fabrication machine suitable for both nonmetal and metal materials is put forward in this paper, the aim of which is to establish an experiment platform for studying the direct metal laser fabrication (DMLF) as a variant of selective laser sintering (SLS). The system integration of two machines is realized by use of the low-power SLS Machine (CO2, 50 W) and high-power laser processing machine (CO2, 2,000 W) in our institute after the improvement or rebuilding of light route system, functional units, machinery and electrical system, and control software in the primary SLS machine, which means that direct metal laser fabrication machine with the laser power up to 1,000 W has been developed successfully. Functional tests of two machines and DMLF experiments of a large number of metal powders including Cu-based mixture and 316L-based mixture of powder have been done in detail. The results show that the material suitable for direct metal laser fabrication machine ranges from nonmetal powders to metal powders, including polystyrene, polyamide, polycarbonate, sands, and a large number of metal powders. At the same time, the primary functions or performances of both low-power SLS Machine and high-power laser processing machine are preserved entirely. Metal samples based on copper and 316L powders can be fabricated with the relative density of about 80% and 100%, respectively, by use of developed DMLF machine. The macro appearance and microstructure and processing mechanisms of DMLF are analyzed minutely. The academic application of DMLF machine for metal powders with high melting point has been making its mark.

Manufacturing of WC–Co moulds using SLS machine

Tungsten carbide–cobalt composite is widely used as a wear-resistant material for cutting tools, molds and other applications. Its production by Selective Laser Sintering (SLS) technique promises to combine the material properties of a composite with the flexibility of a production process. The present paper deals with SLS of a powder mixture of tungsten carbide and cobalt with an aim to make functional parts using a modified Rapid Prototyping (RP) machine (100 W DTM Sinterstation 2000). The associated manufacturing problems and their solutions are discussed. Various compositions of powders have been tried before being settled to a particular composition of WC–9 wt.% Co for making final parts. Bronze infiltration is done on laser sintered parts to enhance their mechanical properties. Fretting wear test is taken as a main characterizing test which is used for estimating the wear resistance of samples.

Experimental investigations for improving part strength in selective laser sintering

Selective laser sintering (SLS) is a powder-based rapid prototyping process in which parts are built by sintering of selected areas of layers of powder using laser. Nowadays, SLS is emerging as a rapid manufacturing technique, which produces functional parts in small batches, particularly in aerospace application and rapid tooling. Therefore, SLS prototypes should have sufficient strength to satisfy functional requirements. Apart from the energy density which is the combination of laser power, beam speed and hatch spacing, various other parameters like refresh rate, layer thickness and hatch pattern influence part strength. In the present work, relationship between strength and the various process parameters namely layer thickness, refresh rate, part bed temperature and hatch pattern have been investigated. Experiments are conducted based on Taguchi method using L16 modified orthogonal array. Tensile specimens of polyamide (PA2200) material as per the standard ‘ASTM D638’ are fabricated on SLS machine with constant energy density and tested on a universal testing machine for tensile strength. Optimum strength conditions are obtained by maximising signal to noise (S/N) ratio and analysis of variance (ANOVA) is used to understand the significance of process variables affecting part strength. A regression model to predict part strength has been developed. Confirmation test conducted subsequently has revealed that the results are within the confidence interval.

Effect of delay time on part strength in selective laser sintering

Selective laser sintering (SLS) is one of the most popular layered manufacturing processes used for making functional prototypes of polymers and metals. It is a powder-based process in which layers of powder are spread and laser is used to sinter selected areas of preheated powder. In the present work, experimental investigations have been made to understand effect of delay time on SLS prototypes. Delay time is the time difference for laser exposure between any two adjacent points on successive scanning lines on a layer. Tensile specimens of polyamide material as per the ASTM standard are fabricated on SLS machine keeping delay time range constant for the entire specimen. Specimens are fabricated for different ranges of delay time and tested on universal testing machine for tensile strength. An optimum value of delay time range is obtained experimentally. As delay time depends on part build orientation, an algorithm has been developed and implemented to find out optimum part build orientation for improving tensile strength. The obtained results from developed code are validated experimentally for tensile specimen. Case study for a typical 3D part is also presented to demonstrate the capabilities of developed algorithm.

Selective Laser Sintering of Poly(L-Lactide) Porous Scaffolds for Bone Tissue Engineering

The aim of this study was to investigate the feasibility of utilizing selective laser sintering (SLS) to build 3D porous tissue engineering scaffolds from small quantities of poly(L-lactide) (PLLA). PLLA microspheres with suitable particle sizes for the SLS process were produced by the oil-in-water emulsion solvent evaporation technique. A miniature build platform was designed, fabricated and incorporated in an existing Sinterstation® 2000 system to enable small quantities of polymer powder to be used for the production of 3D porous scaffolds. Trial runs were first performed using the DuraForm™ polyamide powder and interfacing problems between the miniature build platform and the existing machine were solved. Then 3D porous scaffolds were successfully built from the PLLA microspheres using the modified SLS machine. This study paved the way for further comprehensive studies on selective laser sintering of tissue engineering scaffolds using expensive biopolymers and their composites.

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.

Design and freeform fabrication of deployable structures with lattice skins

PurposeFrontier environments – such as battlefields, hostile territories, remote locations, or outer space – drive the need for lightweight, deployable structures that can be stored in a compact configuration and deployed quickly and easily in the field. This paper seeks to introduce the concept of lattice skins is introduced to enable the design, solid freeform fabrication (SFF), and deployment of customizable structures with nearly arbitrary surface profile and lightweight multi‐functionality.Design/methodology/approachUsing Duraform® FLEX material in a selective laser sintering machine, large deployable structures are fabricated in a nominal build chamber by decomposing them into smaller parts. Before fabrication, lattice sub‐skins are added strategically beneath the surface of the part. The lattices provide elastic energy for folding and deploying the structure or constrain expansion upon application of internal air pressure. Nearly, arbitrary surface profiles are achievable and internal space is preserved for subsequent usage.FindingsA set of virtual and physical prototypes are presented, along with the computational modeling approach used to design them. The prototypes provide proof of concept for lattice skins as a deployment mechanism in SFF and demonstrate the effect of lattice structures on deployed shape.Research limitations/implicationsThe research findings demonstrate not only the feasibility of a new deployment mechanism‐based on lattice skins – for deploying freeform structures, but also the potential utility of SFF techniques for fabricating customized deployable structures.Originality/valueA new lattice skin mechanism is introduced for deploying structures with nearly arbitrary surface profiles and open, usable, internal space. Virtual and physical prototypes are introduced for proof of concept, along with an optimization approach for automated design of these structures.

Selective laser sintering of porous tissue engineering scaffolds from poly(l-lactide)/carbonated hydroxyapatite nanocomposite microspheres

This study focuses on the use of bio-nanocomposite microspheres, consisting of carbonated hydroxyapatite (CHAp) nanospheres within a poly(L: -lactide) (PLLA) matrix, to produce tissue engineering (TE) scaffolds using a modified selective laser sintering (SLS) machine. PLLA microspheres and PLLA/CHAp nanocomposite microspheres were prepared by emulsion techniques. The resultant microspheres had a size range of 5-30 microm, suitable for the SLS process. Microstructural analyses revealed that the CHAp nanospheres were embedded throughout the PLLA microsphere, forming a nanocomposite structure. A custom-made miniature sintering platform was installed in a commercial Sinterstation((R)) 2000 SLS machine. This platform allowed the use of small quantities of biomaterials for TE scaffold production. The effects of laser power; scan spacing and part bed temperature were investigated and optimized. Finally, porous scaffolds were successfully fabricated from the PLLA microspheres and PLLA/CHAp nanocomposite microspheres. In particular, the PLLA/CHAp nanocomposite microspheres appeared to be promising for porous bone TE scaffold production using the SLS technique.

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.

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 °C and 160 °C, which can be described by a two-sphere model; and the mechanism is melting/solidification when the temperature is above 160 °C.

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.

Compound scan mode developed from subarea and contour scan mode for selective laser sintering

Scan mode is an important parameter for selective laser sintering (SLS) processing. The improved mode will optimize scan path and improve the precision, strength and fabrication efficiency of a SLS part. A compound scan mode, which combines subarea scan mode and contour scan mode, is proposed. The principle of its hatch (path-planning) algorithm and implementation are presented. To testify the effectiveness of this compound mode compared to that of subarea scan mode, it has been utilized for researches at a SLS machine developed at Huangzhong University of Science and Technique (HUST). The results from the researches indicate that the degree of precision of a SLS part with the compound scan mode is higher than that with subarea one. There is little difference in the tensile strength, flexural strength, shock strength and fabrication efficiency of a SLS part under the compound scan pattern and the subarea scan mode. Therefore, implementation of the compound scan mode is of importance to improve the precision of a SLS part.

A linear drive system for the dynamic focus module of SLS machines

This paper presents a linear drive system that implements the high-accuracy reciprocating motion of the dynamic focus module in selective laser sintering (SLS) rapid prototyping manufacturing. The linear drive system consists of a moving-coil type PM linear DC motor (LDM), a DSP-based digital controller, a pulse-width modulated servo amplifier, and a linear optical encoder. The special configuration and dynamic model of the LDM are presented, the transfer function of the control system is derived, and a PID feedback controller including a low-pass filter with the derivative term and a model-based feedforward controller are designed. The present experiment proves that the tracking performance of the control system is satisfactory. The experimental results show that the linear drive system has fast dynamic response and acceptable tracking error in the driving dynamic focus module of SLS machines.

INVESTIGATION ON THE PREHEATING TEMPERATURE CONTROL BASED ON PART'S SLICING IN SELECTIVE LASER SINTERING

In the current selective laser sintering(SLS) machines, the curl distortion of SLS part is reduced by adding support or manually adjusting preheating temperature, which results in the big working strength, waste of SLS material, low fabrication efficiency, and difficulty to exactly control preheating temperature. For this reason, a new control method based on part's slicing is presented in this paper, which can automatically adjust the preheating temperature according to the different section shape of a part. This new control method is validated in the SLS machine developed by Huazhong University of Science and Technology. The results of experiment and application show that the surface quality, dimensional accuracy and shape accuracy of the part fabricated with this new control method are better than the ones of the part fabricated with the current control method, and this new control method puts the SLS process into automatization successfully.

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.