Selective Laser Sintering Components Research Articles

Fracture mechanisms of selective laser sintered parts manufactured in build direction

Selective laser sintering (SLS) is an additive manufacturing process that, in addition to rapid prototyping, is becoming increasingly popular to produce end-use parts. Predictable mechanical properties of the produced parts through this process is a desired primary goal. It has long been known that the mechanical properties especially the elongation at break of SLS components decrease in the build direction. In various test series with tensile specimen fabricated in build direction by SLS, it was found that, on the one hand, these have a very large scatter of the elongation at break, and, on the other hand, it was noticed that these frequently break outside the test range in the upskin radius. The upskin area describes regions that point in a positive build direction relative to the building plate. The fracture occurs at a point where, due to the specimen cross-section, a lower fracture stress occurs than in the test area of the specimen. This fracture leads to a much lower elongation at break than in the case of specimens that fracture in the test area. This study investigates which mechanism triggers this behavior. It turns out that different roughnesses can be determined in the upskin and downskin radius and different defects can be seen in the fracture surfaces, especially in the edge areas. It cannot be predicted based on surface roughness measurements or surface profiling exactly where, or in which layer the fracture occurs. However, the defects lead to a local stress spike, at which the failure of the specimen begins.

Mixed modes crack paths in SCB specimens obtained via SLS

The paper presents experimental results of the crack path in Semi-Circular Bend (SCB) specimens obtained through additive manufacturing using Selective Laser Sintering (SLS) process. Determination of fracture parameters for components obtained via Additive manufacturing is a challenging topic, due to the influence of manufacturing parameters on the mechanical properties. Several researches provided the fracture toughness of SLS components, however there are not yet available results regarding the crack paths in such materials. The SCB specimens were designed with different crack orientations (0°, 15°, 30°, 45°, and 54°) and manufactured using EOS Formiga – SLS equipment (energy density 0.066 J/mm2, chamber temperature 169.5 °C, layer thickness 0.1 mm) using PA2200 material. The specimens were tested in symmetric three point bending configuration, creating 6 mode mixity from mode I (0° – crack orientation) to pure mode II (54° – crack orientation). Tests were performed at room temperature using 2 mm/min loading speed in a Zwick ProLine Z005 testing machine. For each crack orientation five specimens were tested. Crack initiation angle and crack propagation were measured by image digitization after the mechanical testing and presented in accordance to the initial orientation of the crack. Also, numerical simulation of crack path was conducted in the same way like the experiment and results were compared to the measured one.

Effects of copper fillers on mechanical and electrical properties of selective laser sintered PA 12-Cu composites

ABSTRACT Selective Laser Sintering (SLS) is a widely used additive manufacturing (AM) technique for creating 3D geometries by adding materials in layers. Although neat polymer is mainly used in powder forms for production, organic or inorganic fillers can be added to produce polymer composites by SLS method. In this study, Polyamide 12 (PA 12) matrix composite parts filled with two different copper particles, dendritic and spherical shaped, were produced, and their mechanical, structural and electrical properties were investigated. The present study outlined that by increasing incident energy densities during sample fabrication, changes in mechanical and electrical characteristics were examined. The findings were analysed in terms of filler type and energy input, which were discovered to have a slight change in the bending behaviour of SLS components. Furthermore, the impact strength was shown to increase constantly with increasing energy density. Furthermore, whereas the electrical conductivity of spherical Cu-filled parts rose considerably, no significant change was seen in dendritic-shaped Cu-filled parts.

Estimation of the compression strength and surface roughness of the as-built SLS components using weibull distribution

Selective laser sintering (SLS) is a process of fabrication of three-dimensional structures by fus- ing powder particles using a guided laser source. The uncertainty in the mechanical properties of the SLS parts fabricated at the same time and with the same process parameters can affect the repeatability of the SLS process. A vast difference in the mechanical properties of the concurrently processed parts can lower the production quality of the batch. Therefore, the param- eters are required to be design based on the most probable outcome of the desired properties. Weibull distribution is one such statistical-based probability distribution method to measure the likelihood of the occurrence of a value of any random variable falling within a particular range of values. Here, the Weibull distribution was used to measure the relative likelihood (90% probability) of the surface roughness and the compressive strength values of the SLS-built polyamide PA2200 components in the given sample space that was obtained from 20 random samples. The results show that the variance in the surface roughness (scan and built plane) and the compressive strength values were in the range of 6–7 μm and around 10 MPa, respectively. Moreover, the surface roughness of the two orthogonal planes with 90% reliability was measured at 14.81 μm (scan plane) and 12.15 μm (built plane). Similarly, the yield strength and the compressive strength with 90% reliability were found 25.87 MPa and 62.64 MPa, respectively.

Development of an automated laser control system for improving temperature uniformity and controlling component strength in selective laser sintering

It has been shown that quality of components built using selective laser sintering (SLS) are strongly affected by the thermal history of the building process. Temperature variations of a few degrees across the powder surface can alter the mechanical properties of components and render them unsuitable for their intended purpose. Therefore, to improve the quality of SLS components and ease their adoption into the marketplace, temperature fluctuation issues must be addressed. Some success has been demonstrated in the past at reducing temperature non-uniformity by improving the heater system that pre-heats the polymer powder prior to sintering with the laser. This paper will cover a complimentary approach of actively controlling laser fluence on the powder surface based on infrared temperature measurements. By controlling the amount of energy input by the laser, a high level of control over the final part temperature can be achieved and uniformity can be improved. This paper will cover development of the feed-forward control system and will present results showing that for constant cross-section specimens, a 45% improvement in ultimate flexural strength standard deviation was achieved.

A Study on Topology of Lateral Surface of Components Manufactured by Selective Laser Sintering

This work presents the results of a study carried out to determine the topology of lateral surface and its effect on the process parameters of components manufactured by selective laser sintering (SLS). Using Taguchi’s experimental technique, an orthogonal array of L4 had been developed. Surface roughness was measured along built direction and analysis of variance (ANOVA) technique was used to investigate the effect of process parameters and to identify main process parameter that influences surface roughness on SLS components. It has been found that slice thickness and scan spacing have more significant influence than the laser power. Microstructure of the sintered specimen along the build direction was studied using Scanning Electron Microscope (SEM). It was observed that variations in slice thickness affect surface topology of SLS components.

Study on the Effect of Process Parameters on Reciprocating Wear Behavior of Components Produced by Selective Laser Sintering (SLS)

This work presents the results of a study carried out to determine the reciprocating wear behavior and its effect on the process parameters of components manufactured by selective laser sintering (SLS). A standard procedure and specimen had been used in the present study to find the wear behavior. Using Taguchi’s experimental technique, an orthogonal array of modified L9 had been developed. Reciprocating wear testing was carried out and analysis of variance (ANOVA) technique was used to investigate the effect of process parameters and to identify the main process parameter that influences the properties of wear behavior on the SLS components. It has been found that laser power had more influence on wear as compared to other selected process parameters. Micro-structural analysis was also carried out using scanning electron microscope on the wear testing sample.

Study on the Effect of Process Parameters on Sliding Wear Behavior of Components Produced by Selective Laser Sintering (SLS)

This work presents the results of a study carried out to determine the sliding wear behavior and its effect on the process parameters of components manufactured by selective laser sintering (SLS). A standard procedure and specimen had been used in the present study to find the wear behavior. Using Taguchi’s experimental technique, an orthogonal array of L4 had been developed. Sliding wear testing using pin-on-disk machine was carried out and analysis of variance (ANOVA) technique was used to investigate the effect of process parameters and to identify the main process parameter that influences the properties of wear behavior on the SLS components. It has been found that scan spacing had more influence on wear as compared to other selected process parameters, slice thickness and infiltration.

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.

Densification of Porous Stainless-Steel SLS Components During Cold Isostatic Pressing

The process that combines selective laser sintering (SLS) and cold isostatic pressing (CIP) can manufacture nearly fully dense metal components with complex geometries. However, the SLS component will shrink to a significant extent during the CIP process. The modified cam-clay model was used to describe the constitutive equation of porous stainless-steel SLS components. The densification process of SLS porous components was simulated using the finite element method. The visual distributions of shape change, displacement, density, and stress were obtained, which showed that SLS components shrank with the same shape as the original design over the CIP process. In addition, a relative uniform density distribution appeared in cold isostatic pressed components. The experiment measurements displayed that the shrinkage rate of SLS components during the CIP process in height direction was a little higher than that on the forming plane due to the layer-by-layer manufacturing process of SLS. On the forming plane, the dimensional errors between simulations and experiments for the cuboid and the gear components are lower than 1% and 3%, respectively. However, the errors in height direction of the two components increase to the range of 6% and 9%.

Material properties and fabrication parameters in selective laser sintering process

As part of a manufacturing system, rapid prototyping (RP) should be integrated with other manufacturing technologies. To ensure that this integration is successful and intelligent, it is necessary to understand and incorporate the properties of RP components. Selective laser sintering (SLS) is an important RP method because of its wide range of materials which can be used. The properties of different SLS powders influence the fabrication parameters in the process and these fabrication parameters in turn affect the mechanical properties of the resultant component. SLS components generally require post‐processing which can also affect the mechanical properties. To obtain optimum quality output, knowledge of the effects of sintering and post‐processing must be incorporated into design and process planning.