Selective Laser Sintering Parts Research Articles

Selective laser sintering adaptation tools for cost effective fabrication of biomedical prototypes

PurposeIn recent years, selective laser sintering (SLS) has been used in the biomedical field, including building small‐scaled biomedical devices such as tissue engineering scaffolds and drug delivery devices. A compact adaptation system for the SLS is needed to obtain a more effective and efficient way of sintering small‐scale prototypes so as to reduce powder wastage. Limitations of available smaller‐scale adaptation devices include the need of additional electrical supplies for the device. The purpose of this paper is to report the development of such a system to be mounted at the SLS part bed without any additional energy supply.Design/methodology/approachThe compact adaptation device works on the concept of transferring the motion of the SLS part bed onto the part bed of the compact adaptation device. The device is an integrated attachment that is fixed onto the building platform of the SLS. The gear system of the device lifts the powder supply bed at both sides of the device simultaneously when the part bed at the center of the device is lowered. To further increase powder saving, an improved powder delivery system named alternative supply mechanism (ASM) is mounted on top of the roller to be coupled together with the compact adaptation device.FindingsPowder saving up to 6.5 times compared to using full build version of the Sinterstation 2500 has been achieved by using the compact adaptation device. Furthermore, powder wastage has been reduced by 84 percent when using the ASM compared to the compact adaptation device alone.Originality/valueThe paper demonstrates the development and viability of adaptation devices for SLS to significantly reduce powder consumption by using solely mechanical means to build small parts without using external power supply.

The effect of processing parameters on characteristics of selective laser sintering dental glass‐ceramic powder

PurposeThe purpose of this paper is to report a study about the rapid prototyping method of dental glass‐ceramic restoration.Design/methodology/approachDental glass‐ceramic restoration materials have excellent physical and chemical, mechanical, aesthetic and biocompatibility characteristics. However, casting methods adopted at present have complicated procedures and high costs; the forming qualities are especially difficult to control. These problems greatly restrict their clinical application and promotion. Therefore, a new forming process based on selective laser sintering (SLS) technology is proposed. First, dental glass‐ceramic is processed into fine powder through a special heat treatment process. Then, the dental restoration parts are manufactured using SLS without any moulds. In this paper, the effects of processing parameters including laser power, scan speed, scan spacing and preheating temperature on the relative density and mechanical properties of the sintered parts are studied.FindingsThe experimental results have shown that for the composite powder of epoxy resin binder E‐12 and K2O‐Al2O3‐SiO2 series of dental glass‐ceramics, when preheating temperature, layer thickness, laser power, scan speed and scan spacing are, respectively, 30∼35°C, 0.08 mm, 21 W, 1,800 mm/s and 0.10 mm/s, the relative densities of dental glass‐ceramic parts are relatively high; the mechanical properties and forming effect are excellent. The relative density and bending strength of SLS parts under the optimized processing parameters are 37.40 per cent and 2.08 MPa, respectively.Research limitations/implicationsThis study only concerns the preparation and SLS of the dental glass‐ceramic powders. Further investigations are planned to be conducted on post processing, such as binder decomposition, isostatic press and high temperature sintering.Originality/valueThis study will provide a theoretical and technical basis for dental glass‐ceramic restorations of SLS.

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.

Preparation and Selective Laser Sintering of Nylon-12-Coated Aluminum Powders

The dissolution—precipitation process was developed to prepare nylon-12-coated aluminum powders, and functional parts were directly made using selective laser sintering (SLS) process from the composite powders. The microcosmic appearances of the composite powders and fractured surfaces of the SLS parts were observed by scanning electron microscope. The effect of the aluminum powder on the thermal properties of nylon-12 resin was studied by differential scanning calorimetry. The influences of the contents and particle sizes of the aluminum powders on the mechanical properties and dimensional accuracy of the SLS parts were investigated. The results show that: the aluminum particles are well coated with nylon-12 in the composite powders; the aluminum particles have good interfacial adhesion with nylon-12 and are homogeneously dispersed in the SLS parts; the aluminum particles can increase the melting and crystalline temperatures and crystalline rate of nylon-12; dimensional accuracy of the SLS parts can be improved by increasing the mass fraction of the aluminum powder; the tensile strength, flexural strength, and flexural modulus increase by about 10.4%, 62.1%, and 122.3% respectively when the mass fraction of the aluminum powder increases from 0 to 50%, while elongation at break and impact strength decrease by about 65.0 and 74.4% respectively; the tensile strength, elongation at break and impact strength all increase with decreasing particle sizes of the aluminum powders.

The microstructural characterization of PA6/PA12 blend specimens fabricated by selective laser sintering

This study investigates the processing of blends of polyamide 6 (PA6) and polyamide 12 (PA12) by selective laser sintering (SLS) using a CO 2 laser. Powder properties of undiluted polymers, mixture composition, and processing parameters, as well as their influence on the microstructure of the specimens manufactured, were evaluated. Polyamides showed higher absorption of laser energy during the sintering of blend specimens, with subsequent thermal energy transfer to the melting of the polymeric phases. The structure of parts obtained by SLS is dependent on the process parameters and the characteristics of the powder material to be processed. The microstructures of PA6/PA12 blend specimens were heterogeneous, with co-continuous and disperse phases depending on the quantity of PA12. The porosity and crystallinity also changed as a function of the component proportions. The use of polymeric blends can increase the range of structures and properties of SLS parts.

ANN model for the prediction of density in Selective Laser Sintering

The effects of process parameters on density of the part prepared by Selective Laser Sintering (SLS) were modelled, using an Artificial Neural Network (ANN) with a feed forward topology and a back propagation algorithm. The inputs of the ANN are the process parameters, including layer thickness, hatch spacing, laser power, scanning speed, temperature of working environment, interval time and scanning mode. The output of the ANN is the density. The experimental investigation results show that the ANN model may be used to analyse the relationship between the process parameters and the density of the SLS part quantitatively. [Received 12 September 2007; Revised 14 March 2009; Accepted 24 March 2009]

Density prediction of selective laser sintering parts based on support vector regression

The support vector regression （SVR） approach combined with particle swarm optimization for parameter optimization, is proposed to establish a model for estimating the density of selective laser sintering parts under processing parameters, including layer thickness, hatch spacing, laser power, scanning speed, ambient temperature, interval time and scanning mode. A comparison between the prediction results and the results from the BP neural networks strongly supports that the internal fitting capacity and prediction accuracy of SVR model are superior to those of BP neural networks under the identical training and test samples; the generation ability of SVR model can be efficiently improved by increasing the number of training samples. The minimum error value is provided by leave-one-out cross validation test of SVR. These results suggest that SVR is an effective and powerful tool for estimating the density of selective laser sintering parts.

A Nanosilica/Nylon-12 Composite Powder for Selective Laser Sintering

Nanosilica was used to reinforce the selective laser sintering (SLS) parts of nylon-12. A dissolution—precipitation process was successfully developed to prepare a nanosilica/nylon-12 composite powder (containing 3 wt% nanosilica) for SLS process. The dispersion of nanosilica in the SLS specimens of the composite powder was examined by scanning electron microscope (SEM), and the effects of nanosilica on the thermal and mechanical properties of the SLS parts were investigated. The results show that: nanosilica disperses uniformly on a nano-scale level in the SLS parts of the composite powder; nanosilica has a heterogeneous nucleation effect on nylon-12; the composite powder has much higher thermal stability than neat nylon-12; the tensile strength, tensile modulus, and impact strength of the SLS specimens made from the composite powder are 20.9, 39.4, and 9.54% higher than those of neat nylon-12 SLS specimens, respectively, and the elongation at break decreases by about 3.65%.

Plasma nitriding to selective laser sintering parts made of SCM430 powder

Selective Laser Sintering (SLS) is an attractive Rapid Prototyping process for rapidly manufacturing dies and mechanical parts. Some recent studies have applied the SLS process to molding dies but few have applied it to stamping dies because some of the mechanical properties of SLS parts, such as strength and hardness, are inadequate for stamping dies. Plasma nitriding is widely used for hardening machine components and stamping dies to give them better wear resistance.In this study, SLS parts that are strong enough to be used as stamping dies were produced by plasma nitriding parts that had been sintered from an alloyed steel powder, JIS-SCM430 (corresponding to AISI 4130). The specimens were nitrided in N2–H2 gas mixtures at various temperatures, which hardened the surface layer. The properties of this hardened layer were then investigated.The specimens sintered from SCM430 powder had very low porosity and very high density, much like wrought materials. The porosity of the SLS specimens was 1.2%. After plasma nitriding, the surfaces of the specimens had a compound layer, the so-called “white layer,” composed of ε-Fe2-3N and γ'-Fe4N. The surface hardness of the specimens plasma nitrided at 773 K and 823 K were about 680 HV and 600 HV, respectively and were much higher than that of the original SLS parts — about 330 HV. Moreover, the parts sintered from SCM430 powder and then plasma nitrided showed better wear resistance than the original SLS parts. Therefore, plasma nitriding improved the wear resistance of the SLS parts.

Rapid manufacturing of PA/HDPE blend specimens by selective laser sintering: Microstructural characterization

The structure and properties of parts made by selective laser sintering (SLS) depend on the process parameters and the characteristics of the powder material to be processed. The use of polymeric blends can increase the range of structures and properties of SLS parts. This study investigates the processing of blends of polyamide (PA2200) and high-density polyethylene (HDPE) by SLS using a CO 2 laser. Powder properties of undiluted polymers, mixture composition, processing parameters and their influence on the microstructure of the specimens manufactured, were evaluated. PA2200 showed higher absorption of laser energy than HDPE during the sintering of blend specimens, with subsequent thermal energy transfer to the melting of the HDPE phase. The microstructures of PA2200/HDPE blend specimens were heterogeneous with co-continuous and disperse phases depending on the quantity of HDPE. The porosity and crystallinity also changed as a function of the component proportions. These results suggest that it is feasible to manufacture blend parts using SLS, with control over the structure and properties being achieved through selecting the polymer properties (laser absorption and melt flow), powder characteristics (form and size distribution) and the optimum process parameters according to the blend composition.

Study of the selective laser sintering of polycarbonate and postprocess for parts reinforcement

Polycarbonate (PC) powder, a common and low-cost amorphous polymer, can be moulded easily by the process of selective laser sintering (SLS). However, the sintered parts cannot be used as functional parts because of their poor mechanical properties. In this article, epoxy resin was applied to improve the mechanical properties of PC SLS parts. Specimens for testing dimensional accuracy, tensibility, flexibility, and impact strength were made by SLS with 75-100 μ PC powder. Some of the specimens were posttreated with two types of epoxy resins. Dimensional accuracy and mechanical properties of the specimens were measured. Microstructures of tensile fracture were observed by scanning electron microscopy. The result shows that the mechanical properties of the specimens are reinforced greatly after the epoxy resin has been infiltrated. Extent of the reinforcement depends on curing agents of epoxy resins. For example, with curing agent W, it is increased to 13.82, 8.00, and 3.69 times, respectively, in tensile, flexural, and impact strength and with curing agent Y, it is increased to 19.87, 7.43, and 1.55 times, respectively, in the same properties. The reinforcement in mechanical properties of PC SLS parts can be improved a step further by means of optimizing the epoxy resin system. Therefore, the PC SLS parts reinforced by epoxy resin can be used as functional parts, if the requirement on mechanical properties is not very high.

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.

Design for environment analyses applied to rapid manufacturing

This paper explores the potential to combine rapid manufacturing (RM) technologies and design for environment (DFE) software with an automotive application. The work focuses on the redesign of a door handle assembly for the Jaguar XJ Saloon. The original 11-piece assembly, comprising eight different materials, was subject to a redesign with an RM technology in mind as the method for final manufacture. In this case the suggested method for manufacture was selective laser sintering (SLS). The design freedoms afforded by the SLS process had a profound effect on the potential to redesign the product. Two different redesigns were proposed, and these, along with the original design, were subjected to analyses of environmental burden and financial profits/costs for end-of-life recycling and reuse using Boothroyd Dewhurst DFE software. The first redesign incorporated the entire assembly as a single prefabricated unit and consequently rendered a DFE analysis impossible. The second redesign was a four-piece assembly retaining three metallic components from the original product and, when subjected to the DFE analysis, showed a significant reduction in environmental burden and cost for disassembly. The surface finish of the SLS parts proved to be inadequate for visual components on a luxury car, but the potential to apply RM for applications with less stringent aesthetic requirements remains.

Improving accuracy through shrinkage modelling by using Taguchi method in selective laser sintering

Selective laser sintering (SLS) is a powder-based rapid prototyping process in which parts are built by selective sintering of layers of powder using CO 2 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 high accuracy in order to satisfy functional requirements. Shrinkage is one of the major factors which influence the accuracy of the SLS parts. To compensate for shrinkage, the material shrinkage coefficient or scaling factor is to be calculated in each direction and is to be applied to STL file. The amount of shrinkage encountered is found to be governed by the process parameters during processing and cannot be kept constant as it is a usual practice in today's SLS technology. In the present work, the relationship between shrinkage and the various process parameters namely laser power, beam speed, hatch spacing, part bed temperature and scan length in SLS have been investigated. Cuboids with suitable dimensions are fabricated rather than fabricating long parts along X, Y and Z directions in order to study shrinkage as it is expected that the shrinkage along X, Y and Z direction is not independent. Optimum shrinkage conditions are obtained by maximizing signal-to-noise (S/N) ratio and analysis of variance (ANOVA) is used to understand the significance of process variables affecting shrinkage. Laser power and scan length are found to be most significant process variables influencing shrinkage in X- direction. Along Y-direction laser power and beam speed are the significant parameters and along Z-direction beam speed, hatch spacing and part bed temperature are found to be most significant factors influencing shrinkage. Empirical models for predicting shrinkage along X, Y and Z directions are derived using regression. Obtained results are validated and they are found in good agreement with experiments. One case study of bench marking part is also presented to show that shrinkage model developed in the present work confine more accurate parts.

Influence of process parameters on part shrinkage in SLS

Shrinkage, one of the typical phenomena in the selective laser sintering (SLS) process, affects the final dimensional accuracy of SLS products. We investigated the relationship between the shrinkage and the process parameters of SLS in order to improve dimensional accuracy. According to the characteristic of SLS, the following process parameters are considered: layer thickness, hatch spacing, laser power, scanning speed, temperature of working environment, interval time and scanning mode. A neural network model on the relationship between the processing parameters and shrinkage was built on the basis of a series of experiments. The experimental investigation results show that the neural network model is possible to be used to predict the effects of the process parameters on the shrinkage with reasonable accuracy and to analyze the relationship between the shrinkage and the process parameters of SLS quantitatively. So it is suitable to apply neural networks approach to study the SLS process. This model will allow us to produce the SLS parts with the desired quality attributed by selecting the appropriate parameter values prior the processing. This paper proposes a promising approach to improve the accuracy of the SLS part.

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 on self-heating metallic powder for the selective laser sintering process

Fabricating metallic functional parts directly using the selective laser sintering (SLS) process is a promising technique which is engaging many researchers. Existing problems during direct fabrication of a metallic part using SLS are analysed. To solve the problems, a new self-heating metallic powder material for SLS direct rapid fabrication is developed. This new material can release a controllable amount of heat during its interaction with laser beam energy, resulting in a reduction of the requirement to use laser power during direct sintering of the metallic part, prolonging the time in the metallic liquid phase and improving the strength and precision of the SLS part. A self-propagating high-temperature synthesis (SHS) material is selected as a self-heating component. For this reason, interaction of the SHS material with CO2 laser beam energy is researched, which proves that CO2 laser beam energy can instantly ignite the SHS reaction. On the basis of these investigations, the effect of sintering the metallic powder material mixed with SHS material using a CO2 laser is also researched. The results show that there is an optimal blending ratio of various materials in the new metallic powder material. Under the optimal blending ratio and SLS process parameters, this new metallic powder material can release a large amount of heat and the SHS reaction can be controlled within the laser sintering. This work shows that it is possible for the metallic part to be directly sintered using a small CO2 laser power (less than 50 W), thus greatly reducing the dimensions, price and running expenditure of an SLS machine and making it suitable for many applications.

Development of a polymer alloy of polystyrene (PS) and polyamide (PA) for building functional part based on selective laser sintering (SLS)

Polystyrene (PS) powder materials may be directly used for selective laser sintering (SLS). The part sintered with PS has high dimension precision, but its tensile strength is very low, only 5-6 MPa, and its solvent resistance capability is not good, which cannot meet the demands of the functional parts. The part sintered with polyamide (PA) has high mechanical properties and excellent resistance capability, so PA is suitable for building functional parts. However, the precision of the SLS part sintered with PA is low crystallinity. Also, PA's price is very high (relative to PS powder). Colligating the properties of the two materials, PS and PA, a polymer alloy of PS and PA for building functional parts is developped. Using this alloy as the sintering material, some parts are sintered successfully and the tensile strength of the parts increases to about 14 MPa, which can meet the demands of some functional parts.

Effect of the properties of the polymer materials on the quality of selective laser sintering parts

Effect of the properties of the polymer materials on the quality of selective laser sintering parts

Effect of the properties of the polymer materials on the quality of selective laser sintering parts

The effect of the properties of the polymer materials, such as molecular weight, molten viscosity, crystallization rate and the particle size of the powder, on the quality of selective laser sintering (SLS) parts is researched. The results indicate that the molecular weight affects the quality of the SLS parts through the melting viscosity. SLS parts of higher density can be fabricated with polymer materials of lower melting viscosity. Crystallinity largely affects the precision of the SLS part—shrinkage is more serious with increasing crystallinity. SLS parts sintered with polymer powder materials, whose melting peak and crystalline peak differ greatly, have high dimensional precision. The particle size of the powder affects not only the precision but also the density of the SLS part. The appropriate particle size is about 75-100 μm.