PA12 Parts Research Articles

Laser Beam Polishing of PA12 Parts Manufactured by Powder Bed Fusion

PurposeMulti Jet Fusion™ (MJF) is a powder bed fusion technology that fuses material locally with infrared radiation. Fabricated parts show high mechanical strength, low porosity and good dimensional accuracy, even for challenging geometries. They do, however, have a distinctive grainy surface with a roughness of Ra > 5 μm limiting possible applications. A fairly recent technology for the smoothing and polishing of polymer surfaces is the surface re-melting by laser beam polishing (LBP). The objective of this study is to characterize the LBP-process of MJF-manufactured Nylon PA12 parts and evaluate it in relation to state-of-the-art finishing methods.MethodsPA12 samples produced using the Multi Jet Fusion™ process are laser beam polished with a 30 W CO2-laser system. A numerical model is applied in order to estimate the effects of different processing parameters and laser scanning strategies. Calculated temperature progressions are validated experimentally with thermographic measurements. The laser beam polished surfaces are subsequently characterised by surface topography, tensile strength, surface energy and hardness.ResultsA re-melting and concurrent smoothing of PA12 surfaces was demonstrated for a number of different processing strategies. The use of a line-focus resulted in the best combination of processing speed, flexibility and surface quality with a reduction in roughness of up to 91%.ConclusionLaser beam polishing is applicable to parts manufactured by Multi Jet Fusion™. Depending on the case of application, it can be preferable to conventional post-processing strategies for fusing residual powder and improving tribological properties.

Influence of processing parameters on tensile properties of PA12 parts manufactured by selective laser sintering

Influence of processing parameters on tensile properties of PA12 parts manufactured by selective laser sintering

Effects of Laser Power and Hatch Orientation on Final Properties of PA12 Parts Produced by Selective Laser Sintering.

Poly(dodecano-12-lactam) (commercially known as polyamide “PA12”) is one of the most resourceful materials used in the selective laser sintering (SLS) process due to its chemical and physical properties. The present work examined the influence of two SLS parameters, namely, laser power and hatch orientation, on the tensile, structural, thermal, and morphological properties of the fabricated PA12 parts. The main objective was to evaluate the suitable laser power and hatching orientation with respect to obtaining better final properties. PA12 powders and SLS-printed parts were assessed through their particle size distributions, X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), a scanning electron microscope (SEM), and their tensile properties. The results showed that the significant impact of the laser power while hatching is almost unnoticeable when using a high laser power. A more significant condition of the mechanical properties is the uniformity of the powder bed temperature. Optimum factor levels were achieved at 95% laser power and parallel/perpendicular hatching. Parts produced with the optimized SLS parameters were then subjected to an annealing treatment to induce a relaxation of the residual stress and to enhance the crystallinity. The results showed that annealing the SLS parts at 170 °C for 6 h significantly improved the thermal, structural, and tensile properties of 3D-printed PA12 parts.

An investigation on mechanical properties of PA12 parts produced by a SLS 3D printer: An experimental approach

Additive manufacturing methods such as Selective Laser Sintering (SLS) have attracted numerous scientists and different companies to print 3D parts. However, the mechanical properties of printed parts have been always the research area of many scientists. In this paper, the effects of SLS setting variables (laser power, scan speed, and hatch spacing) and scan length were investigated experimentally on key mechanical properties (strength, apparent modulus of elasticity, and elongation) of polyamide-12 printed parts using the response surface methodology. The results showed that the hatch spacing is the most effective variable on mechanical properties; the laser power and the scan speed are also important. By increasing the laser power and decreasing the hatch spacing and the scan speed, a higher strength part with a higher apparent modulus of elasticity and elongation can be printed. However, since a bigger hatch spacing and a faster scan speed are more desirable to have a more economical production, a challenging decision must be made for setting these variables to print parts with good mechanical behavior economically. If the hatch spacing, the laser power, and the scan speed are selected so that the laser energy density is too high, powders will burn and the printing process will fail. The scan length has a slight effect on the apparent modulus of elasticity and no significant effect on the strength and elongation. • Input variables: laser power, scan speed, hatch spacing, and scan length. • Mechanical properties: strength, modulus of elasticity, and elongation. • Effects of input variables on mechanical properties in the SLS process. • Determining effective inputs by experimental study and response surface methodology. • Predicting mechanical properties based on effective inputs and laser energy density.

Micromechanical characterization of the material response in a PA12-SLS fabricated lattice structure and its correlation with bulk behavior

Selective laser sintering (SLS) of polymers has made possible the introduction of lattice-based cells as building blocks of polymer parts, allowing to obtain optimal specific properties. The actual mechanical performance of an SLS part is strongly dependent on the printing direction and part shape. Nevertheless, macroscopic testing is not usually possible due to size restrictions of the fabricated part, as it happens, for example, in lattice-based materials. In this case, microscopic tests performed directly on the lattice surface become fundamental. In this work, the mechanical behavior of SLS PA12 under a wide range of strain rates from 10−3 to 103 s−1 and different printing directions is characterized using macroscopic tests on bulk samples and compared with nanoindentation performed directly on the lattice material surface. An excellent correlation was found between the rate-dependent mechanical behavior obtained at the two scales, validating microscopic techniques for characterizing the mechanical response of SLS fabricated PA12 parts.

Effects of build positions on the thermal history, crystallization, and mechanical properties of polyamide 12 parts printed by Multi Jet Fusion

ABSTRACT Multi Jet Fusion (MJF) has gradually been utilised for the commercial fabrication of final products. In particular, the mechanical properties of MJF-printed polyamide 12 (MJF PA12) parts have been widely investigated by manipulating the process parameters such as the printing orientation and the cooling rate. In this work, the effects of build positions on the thermal history, crystallization, and mechanical properties of MJF PA12 parts were investigated. The thermal history of printed parts was obtained using the MJF Thermal Prediction Engine software developed by Hewlett-Packard HP Labs (HP Inc.). As compared to the parts printed at the boundaries, those in the centre region experienced a slower cooling rate, which was favourable for crystal growth. Both the crystallite size and crystallinity of the parts in the centre region were larger than those of the parts at the boundaries. The parts printed in the centre region had slightly higher tensile modulus and significantly smaller elongation at break and strain energy density than those printed at the boundaries. The tensile strength of the parts at different locations was comparable. This work serves as a guide to selecting the build position of MJF-printed parts to achieve desirable mechanical properties.

Relationships between porosity and mechanical properties of polyamide 12 parts produced using the laser sintering and multi-jet fusion powder bed fusion processes

Laser powder bed fusion (L-PBF, or Laser Sintering) and Multi-Jet Fusion (MJF) are two commercial powder bed fusion (PBF) additive manufacturing (AM) processes for polymers. While the strength of parts produced with polymer PBF processes is typically good, the toughness of AM parts is significantly reduced compared to traditional processes, such as Injection Molding (IM). This study evaluates the impact of residual porosity on the strength and ductility of polyamide-12 (PA-12) parts produced by powder bed fusion. Hot isostatic pressure (HIP) treatment is used to eliminate virtually all porosity from treated L-PBF and MJF parts. The relationship between porosity and mechanical properties (ultimate tensile strength, elongation at break, toughness) is evaluated for groups of parts with and without HIP treatment. For untreated parts, the thickness of the part was found to have a significant impact on mechanical properties, with 5 mm parts having more than 25% higher UTS, 39% higher maximum strains, and 21% higher Young's Moduli than 1 mm parts produced using the same process. In L-PBF parts, the HIP treatment greatly reduced porosity and increased ultimate tensile strengths by an average of 12% compared to parts that were not subjected to HIP, but they also exhibited reduced max strains. While HIP eliminated porosity in MJF parts, MJF parts did not exhibit any statistically significant improvements in mechanical properties from HIP. Though it was not possible to correlate the strength of an untreated part with density, a correlation does exist between density and some mechanical properties (UTS, Young's Modulus) as a result of a density change in L-PBF parts due to a post-processing HIP treatment. • No direct correlation between density and mechanical properties for L-PBF or MJF. • Hot isostatic pressure (HIP) treatment eliminated porosity in PA12 parts. • HIP increased tensile strength but reduced strain at failure. • Pore elimination did not improve ductility in PA12 AM parts.

The effect of UV-C radiation on the durability of 3D printed plastic parts in disinfectant devices

The usage of far or hard ultraviolet radiation in wavelength 200 – 280 nm or shortly UV-C disinfectors are becoming more and more popular due to their universal ability to fight against bacteria and viruses. It is well known that according to DIN 5031-7, both UV-A and UV-B radiation from sunlight have clear influence on the mechanical and visual properties of plastic parts, but the influence of intensive artificial UV-C is not so widely investigated. As the UV-C is in the shorter end of the UV radiation wavelength spectrum and is completely absorbed by the ozone layer and atmosphere, it is not possible to see the influence of it in everyday life. But in the equipment where the artificial UV-C radiation wavelength is used as a disinfectant, and probably in the open space, the influence of UV-C could be remarkable. Recently, there has been increasing interest in the food industry to avoid contamination in the food packing process. The global COVID-19 coronavirus pandemic has amplified this interest and has forced authors to run a set of tests with printed plastic parts. This paper analyses the outcome of those tests including two different printing directions and two different surface paints. The study shows that there is considerable influence of UV-C radiation on mechanical and aesthetic properties of 3D SLS printed PA12 parts. However, the influence can be diminished by use of appropriate paints.

Parametric Optimization on Impact Strength of Selective Inhibition Sintering Fabricated PA-12 Parts Based on Evolutionary Optimization Algorithms

Selective inhibition sintering (SIS) is one of the novel additive manufacturing techniques to fabricate complex three-dimensional (3D) functional parts in short span. The quality of SIS processed parts can be achieved through appropriate selection of various SIS process variables such as infrared (IR) sintering temperature, part bed temperature, IR heater scanning distance, IR heater feed rate and layer thickness. The higher impact resistance is always preferred so that the materials absorb more energy during the collision. However, additively manufactured parts have experienced low impact strength. The effect of SIS process variables on the impact strength characteristics of SIS-processed parts has not yet studied. Hence, the present investigation emphasizes on the optimization of these variables on enhancing the impact strength of polyamide parts through using metaheuristic techniques, namely genetic and simulated annealing algorithms. The SIS experiments were planned and performed based on three-level five-factor Box-Behnken design (BBD). An empirical model was developed to correlate the impact strength and input process variables. The cogency of the developed model was validated using analysis of variance (ANOVA) at 95% confidence levels. The optimization results show that the genetic algorithm provides optimal SIS parameters with minimized computational efforts compared to that of simulated annealing algorithm. The maximum impact strength of 44.26 J/m was found with optimal IR heater temperature of 240 °C, sintering bed temperature of 176 °C, IR heater feed rate of 3.46 mm/s, IR heater scanning distance of 10 mm and layer thickness of 0.6 mm. Further, the validation experiments were conducted based on the attained optimal SIS process variables for evaluating the effectiveness of both the optimization methods.

SIS Parameters Optimization and Reliable Analysis to Achieve Reduced roughness of PA12 Parts

Selective inhibition sintering (SIS) results in easy, flexible, fast and cost-efficient fabrication of functional parts by using powder material for various applications. The functional part is important for operational examination by fabricating the part unswervingly from CAD data. However, poor surface quality is the major disadvantage in SIS procedure. Selection procedure of optimal operating parameters plays a major role in the fabrication of end products. The present study discusses the effect of key contributing operating parameters on the surface quality of the Polyamide parts fabricated by the SIS process. The parameters like heater power (HP), layer thickness (LT), heater feed rate (HFR), machine feed rate (MFR) and bed temperature (BT) were considered in this study. Face-Centered Central (FCC) design was employed as a statistical technique to set the optimal inhibition sintering parameters. Different mathematical models had also been generated in order to develop a relationship between influencing parameters. Further, adequacies of generated models were validated by analysis of variance (ANOVA) approach. Moreover, to decide the survival rate of the SIS parts for industrial applications, the surface roughness reliability with higher error ([Formula: see text]%) was tested by using Weibull statistics. It was observed that HP, LT and HFR are contributing more to increase surface roughness.

Influence of Surface Milling in Mechanical Property of PA12 Parts Built by Laser Sintering

Influence of Surface Milling in Mechanical Property of PA12 Parts Built by Laser Sintering

Influence of energy density on selective laser sintering of carbon fiber-reinforced PA12

This work provides an in-depth investigation of the influence of laser energy density on the mechanical, surface, and dimensional properties of carbon fiber-reinforced PA12 parts manufactured by selective laser sintering (SLS). A space-filling design of experiments (DOE) was used to conduct the experimental trials to cover a wide range of laser sintering parameters. The consolidation mechanism was evaluated by microstructural and crystallization evolution of the samples produced at different energy densities, supported by mechanical testing, scanning electron microscopy (SEM), X-ray diffraction (XRD), and infrared spectroscopy (FTIR). Surface morphology was evaluated by profile measurements and SEM images. Laser sintering parameters had a significant influence on physical and mechanical properties, exhibiting complex and nonlinear behavior. Low energy density resulted in better dimensional accuracy, whereas intermediate laser energy resulted in the best mechanical properties. A trade-off could be seen when mechanical or dimensional properties were desired, and optimum energy values were strongly dependent on the criteria desired. All samples exhibited a brittle fracture behavior, with little plastic deformation present. Fracture mechanism occurred in the interlayer region or interface between carbon fiber and PA12, depending on the energy density applied. XRD analysis revealed a decrease in crystal fraction with increasing energy density. FTIR measurement suggested that polymer degradation at high energy densities could be present by both polymer chain scission and oxygen functional group decomposition and gas release upon laser heating of carbon fiber, resulting in lower mechanical properties.

Selective laser sintering of carbon fiber–reinforced PA12: Gaussian process modeling and stochastic optimization of process variables

This work presents an in-depth investigation of the influence of the individual laser sintering parameters on density, mechanical, and dimensional properties of carbon fiber–reinforced PA12 parts manufactured by selective laser sintering (SLS) . A space-filling design of experiments method was used to plan the experiments and SLS trials were conducted to manufacture test samples that were characterized in terms of dimensional accuracy, density, and mechanical properties. Gaussian process–supervised learning was used to model the interaction between laser sintering parameters and quality properties. Stochastic optimization via evolutionary algorithm was employed to obtain trade-off solutions for several multi-objective optimization tasks. The Gaussian process presented excellent model quality for the majority of response variables evaluated. Laser sintering parameters had a significant influence on physical and mechanical properties, exhibiting complex and non-linear behavior. Multi-objective optimization showed a wide range of optimized laser sintering parameters available, depending on the trade-off objective desired.

An Investigation into Thermal History and Its Correlation with Mechanical Properties of PA12 Parts Produced by Selective Laser Sintering Process

Thermal history is a key factor affecting mechanical properties of polymeric parts made by the selective laser sintering (SLS) process. In this research, the effect of thermal history on the mechanical properties of PA12 parts produced by the SLS process has been investigated. It is hypothesized that different cool-down methods (normal to very slow cooling) and built orientations, resulted from flat and edgewise layouts fabrication, could be influencing factors on the thermal history during the SLS process. The temperature changes at different points inside the powder bed were recorded during the fabrication of specimens. Afterward, the morphology of fabricated samples was examined using scanning electron microscopy. In addition, the degree of crystallinity and melting point of the parts were studied by differential scanning calorimetry analysis. It was found that the built orientation was more effective than the cooling methods on ultimate tensile strength (UTS) and elongation at break (EaB), so that UTS and EaB of the edgewise parts were 10%, 50% greater than the flat parts. On the other hand, the variation of crystallinity with cooling methods has been found to be much less than might be expected from the implemented various fabrication conditions. However, the applied slowest cool-down method slightly increased the edgewise parts crystallinity to 23%, compared to 19.2% for the normal cooled down samples, leading to greater UTS than the normal cooled specimens. The morphology observation of specimens fracture surfaces suggests that better mechanical performance of the edgewise samples is likely connected to fewer defects such as pores and un-melted powder particles remained in their cross sections due to experiencing higher temperature during fabrication. The work is relevant to attempts to build high mechanical performance parts by selective laser sintering.

Inverse Interval Field Quantification via Digital Image Correlation

This paper presents the application of a new method for the identification and quantification of interval valued spatial uncertainty under scarce data.Specifically, full-field strain measurements, obtained via Digital Image Correlation, are applied in conjunction with a quasi-static finite element model.To apply these high-dimensional but scarce data, extensions to the novel method are introduced.A case study, investigating spatial uncertainty in Young's modulus of PA-12 parts, produced via Laser Sintering, shows that an accurate quantification of the constituting uncertainty is possible, albeit being somewhat conservative with respect to deterministic values reported in literature.

Hybrid spatial uncertainty analysis for the estimation of imprecise failure probabilities in Laser Sintered PA-12 parts

This paper presents the application of non-deterministic modelling techniques for the quantification of imprecise failure probabilities in PA-12 parts produced via Laser Sintering (LS). Specifically, a modelling approach consisting of a combination of interval and random fields is applied, and the effect hereof on the resulting polymorphic uncertainty in the mechanical performance of the LS parts is studied. A link with the underlying process physics is given, relating the spatial porosity distributions that are inherently present in LS PA12 parts to a spatial distribution in the apparent Young’s modulus. Furthermore, uncertainty on the final dimensions of other parts that are constructed in the same build envelope as the designed part is linked to uncertainty in the cross-sectional area of the designed part.The effect of these sources of uncertainty is studied in three case studies, illustrating the need for a well-thought production process planning given the influence on the resulting mechanical performance of the designed structure. Especially the effect of epistemic uncertainty on the design process is shown to be significant.

Impact of extended sintering times on mechanical properties in PA-12 parts produced by powderbed fusion processes

Additive Manufacturing provides many advantages in reduced lead times and increased geometric freedom compared to traditional manufacturing methods, but material properties are often reduced. This paper considers powder bed fusion of polyamide 12 (PA12, Nylon 12) produced by three different processes: laser sintering (LS), multijet fusion (MJF)/high speed sintering (HSS), and large area projection sintering (LAPS). While all utilize similar PA12 materials, they are found to differ significantly in mechanical properties especially in elongation to break. The slower heating methods (MJF/HSS and LAPS) produce large elongation at break with the LAPS process showing 10x elongation and MJF/HSS exhibiting 2.5x the elongation when compared to commercial LS samples. While there are small differences in crystallinity between these samples, the difference may be attributed to changes in the heating and cooling rates of the LAPS samples.

Tribological anisotropy of selective laser sintered PA12 parts

Additive manufacturing techniques like selective laser sintering (SLS) of polymers are on the verge from a pure prototyping technique to producing small lot sizes, as it enables the production of highly complex components without a mould. The parts are build layerwise and therefore the resulting components exhibit specific characteristics like anisotropic mechanical behavior, porosity and a high surface roughness. As SLS enables the production of whole assembly groups in one building step without the need of assembly, a missing factor is the tribological interaction of these parts. The scope of this paper therefore is to identify the influence of the building orientation on the tribological properties. The resulting anisotropic behavior is presented under different loads and in comparison to specimens produced in a pvT-device to point out the influence of the inner structure and surface of the parts during the different stages of a tribological interaction.

Investigating the influence of X-ray CT parameters on porosity measurement of laser sintered PA12 parts using a design-of-experiment approach

Polymeric parts produced by Laser Sintering (LS) present a consistent amount of pores with a wide pore size distribution. The knowledge about the porosity value and its distribution within the part allows to perform a quality control of the LS process, and gives insights in how to improve it. In this work the influence of the sample size on the porosity measurement is discussed, as well as its representativeness of the LS process itself. The reliability of porosity measurement of those parts using X-ray Computed Tomography (CT) is assessed taking into account the influence of the CT scanning parameters, the reconstruction and noise reduction algorithms using a design-of-experiment approach. The quality of the CT datasets obtained is assessed by calculating Contrast-to-Noise Ratio (CNR) and Signal-to-Noise Ratio (SNR) on representative reconstructed images. Repeatability of the measurements is also assessed along the entire workflow: CT acquisition, reconstruction and porosity measurement using commercial software packages.

Bonding quality and fracture analysis of polyamide 12 parts fabricated by fused deposition modeling

PurposeThis work aims to evaluate the influence of rheological properties of building materials on the bonding quality and ultimate tensile strength in the fused deposition modeling (FDM) process, through the investigation of parts printed by semi-crystalline and amorphous resins. Little information is currently available about the influence of the crystalline nature on FDM-printed part quality.Design/methodology/approachSemi-crystalline polyamide 12 and amorphous acrylonitrile butadiene styrene (ABS) were used to assess the influence of rheological properties on bonding quality and the tensile strength, by varying three important process parameters: materials, liquefier temperature and raster orientation. A fractography of both tensile and freeze-fractured samples was also investigated.FindingsThe rheological properties, mainly the melt viscosity, were found to have a significant influence on the bonding quality of fused filaments. Better bonding quality and higher tensile strength of FDM parts printed with semi-crystalline PA12, as compared with amorphous ABS, are suggested to be a result of higher initial sintering rates owing to the lower melt viscosity of PA12 at low shear rates. Near-full dense PA12 parts were obtained by FDM.Originality/valueThis project provides a variety of data and insight regarding the effect of materials properties on the mechanical performance of FDM-printed parts. The results showed that FDM technique allows the production of PA12 parts with adequate mechanical performance, overcoming the greatest limitation of a dependence on amorphous thermoplastics as a feedstock for the production of prototypes.