scholarly journals Powder Surface Roughness as Proxy for Bed Density in Powder Bed Fusion of Polymers

Polymers ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 81
Author(s):  
Francesco Sillani ◽  
Ramis Schiegg ◽  
Manfred Schmid ◽  
Eric MacDonald ◽  
Konrad Wegener
Keyword(s):  
Manufacturing Industry ◽  
Thermoplastic Elastomer ◽  
Powder Bed Fusion ◽  
Polyamide 11 ◽  
Powder Bed ◽  
Polyamide 12 ◽  
End Use ◽  
High Standards ◽  
Laser Line Scan ◽  
Part Density

Powder bed fusion of polymers is becoming increasingly adopted by a variety of industries to tailor the strength, weight and functionality of end-use products. To meet the high standards of the modern manufacturing industry, parts built with powder bed fusion require consistent properties and to be free of defects, which is intrinsically connected to the quality of the powder bed prior to melting. The hypothesis of this work is that the roughness of the top surface of an unmelted powder bed can serve as a proxy for the powder bed density, which is known to correlate with final part density. In this study, a laser line scan profilometer is integrated onto the recoater arm of a custom powder test bench, which is able to automatically create layers of powder. A diverse group of polymers was investigated including polyamide 12 (PA12), polyamide 11 (PA11), polypropylene (PP), and a thermoplastic elastomer (TPU) under different recoating speed in order to increase the variance of the dataset. Data analytics were employed to compare roughness to measured powder bed density and a statically significant correlation was established between them.

scholarly journals Setting the Optimal Laser Power for Sustainable Powder Bed Fusion Processing of Elastomeric Polyesters: A Combined Experimental and Theoretical Study

Materials ◽  
2022 ◽  
Vol 15 (1) ◽  
pp. 385
Author(s):  
Ruben Vande Ryse ◽  
Mariya Edeleva ◽  
Ortwijn Van Stichel ◽  
Dagmar R. D’hooge ◽  
Frederik Pille ◽  
...  
Keyword(s):  
Laser Power ◽  
Theoretical Study ◽  
Selective Laser Sintering ◽  
Polymeric Materials ◽  
Thermoplastic Elastomer ◽  
Processing Parameters ◽  
Operating Conditions ◽  
Powder Bed Fusion ◽  
Powder Bed ◽  
Bed Temperature

Additive manufacturing (AM) of polymeric materials offers many benefits, from rapid prototyping to the production of end-use material parts. Powder bed fusion (PBF), more specifically selective laser sintering (SLS), is a very promising AM technology. However, up until now, most SLS research has been directed toward polyamide powders. In addition, only basic models have been put forward that are less directed to the identification of the most suited operating conditions in a sustainable production context. In the present combined experimental and theoretical study, the impacts of several SLS processing parameters (e.g., laser power, part bed temperature, and layer thickness) are investigated for a thermoplastic elastomer polyester by means of colorimetric, morphological, physical, and mechanical analysis of the printed parts. It is shown that an optimal SLS processing window exists in which the printed polyester material presents a higher density and better mechanical properties as well as a low yellowing index, specifically upon using a laser power of 17–20 W. It is further highlighted that the current models are not accurate enough at predicting the laser power at which thermal degradation occurs. Updated and more fundamental equations are therefore proposed, and guidelines are formulated to better assess the laser power for degradation and the maximal temperature achieved during sintering. This is performed by employing the reflection and absorbance of the laser light and taking into account the particle size distribution of the powder material.

scholarly journals Controlling the porosity of 316L stainless steel parts manufactured via the powder bed fusion process

2019 ◽  
Vol 25 (1) ◽  
pp. 162-175 ◽  
Author(s):  
Abdullah AlFaify ◽  
James Hughes ◽  
Keith Ridgway
Keyword(s):  
Stainless Steel ◽  
Layer Thickness ◽  
Exposure Time ◽  
Process Parameters ◽  
Pulsed Laser ◽  
Powder Bed Fusion ◽  
Content Type ◽  
Powder Bed ◽  
Point Distance ◽  
Part Density

Purpose The pulsed-laser powder bed fusion (PBF) process is an additive manufacturing technology that uses a laser with pulsed beam to melt metal powder. In this case, stainless steel SS316L alloy is used to produce complex components. To produce components with acceptable mechanical performance requires a comprehensive understanding of process parameters and their interactions. This study aims to understand the influence of process parameters on reducing porosity and increasing part density. Design/methodology/approach The response surface method (RSM) is used to investigate the impact of changing critical parameters on the density of parts manufactured. Parameters considered include: point distance, exposure time, hatching distance and layer thickness. Part density was used to identify the most statistically significant parameters, before each parameter was analysed individually. Findings A clear correlation between the number and shape of pores and the process parameters was identified. Point distance, exposure time and layer thickness were found to significantly affect part density. The interaction between these parameters also critically affected the development of porosity. Finally, a regression model was developed and verified experimentally and used to accurately predict part density. Research limitations/implications The study considered a range of selected parameters relevant to the SS316L alloy. These parameters need to be modified for other alloys according to their physical properties. Originality/value This study is believed to be the first systematic attempt to use RSM for the design of experiments (DOE) to investigate the effect of process parameters of the pulsed-laser PBF process on the density of the SS316L alloy components.

Powder characterization and part density for powder bed fusion of 17-4 PH stainless steel

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Sean Daniel Dobson ◽  
Thomas Louis Starr
Keyword(s):  
Particle Size ◽  
Stainless Steel ◽  
Flow Behavior ◽  
Full Density ◽  
Powder Bed Fusion ◽  
Metal Powders ◽  
Production Environment ◽  
Content Type ◽  
Powder Bed ◽  
Part Density

Purpose Characteristics of the metal powder are a key factor in the success of powder bed fusion (PBF) additive manufacturing. Powders for PBF from different manufacturers may have a different particle size and/or bulk packing and flow behavior. Powder properties change as the powder is reused for multiple builds. This study seeks to measure the variability of commercial 17-4 PH stainless steel powders to determine the effect of powder variability on part density and demonstrate characterization methods that ensure part quality. Design/methodology/approach Commercial atomized metal powders from four different vendors were produced with two different atomizing gases (N2 and argon). Powder was characterized in both new and extensively reused conditions. All powders were characterized for flow and packing behavior, particle size and internal porosity. Coupons were manufactured using the laser PBF process with optimized scan strategy and exposure parameters. The quality of fabricated parts was measured using bulk density measurement. Findings Despite differences in powder flowability and particle size, fully dense parts (>99 per cent) were produced using all powders, except one. Residual porosity in these parts appeared to result from gas trapped in the powder particles. The powder with extensive reuse (400+ h in machine fabrication environment) exhibited reduced flowability and increased fraction of fine particles, but still produced full density parts. Originality/value This study demonstrates that full density parts can be fabricated using powders with a range of flowability and packing behavior. This suggests that a single flowability measurement may be sufficient for quality assurance in a production environment.

scholarly journals Experimental, numerical and analytical investigation of the polyamide 12 powder bed fusion with the aim of building dimensionless characteristic numbers

2021 ◽  
Vol 201 ◽  
pp. 109470
Author(s):  
Moritz Grünewald ◽  
Kevin Popp ◽  
Johannes Rudloff ◽  
Marieluise Lang ◽  
Alexander Sommereyns ◽  
...  
Keyword(s):  
Analytical Investigation ◽  
Powder Bed Fusion ◽  
Powder Bed ◽  
Polyamide 12 ◽  
Characteristic Numbers

scholarly journals Fatigue assessment of additively manufactured AlSi10Mg structures using effective stress concepts based on the critical distance approach

2021 ◽  
Author(s):  
Kai Schnabel ◽  
Jörg Baumgartner ◽  
Benjamin Möller ◽  
Matilde Scurria
Keyword(s):  
Critical Distance ◽  
Powder Bed Fusion ◽  
Powder Bed ◽  
Linear Elastic ◽  
Notched Specimens ◽  
Different Types ◽  
Reliable Design ◽  
End Use ◽  
Metallic Parts ◽  
Distance Approach

AbstractIn the last decade, Additive Manufacturing (AM) technologies have been considered by both the automotive and aerospace industries for the production of end-use metallic parts, with a main focus on Powder Bed Fusion – Laser Beam / metallic (PBF-LB/M) technologies. However, AM parts present features that are deleterious to their cyclic properties. For a reliable design in terms of fatigue strength, existing influencing variables must be identified and transferred to a numerical model. In particular, different types of defects, as well as their distribution, should be taken into account. In addition to the identification of relevant parameters based on literature data, an AlSi10Mg component-like structure is assessed based on results from notched specimens and a linear-elastic assessment concept using effective stresses.

scholarly journals Automatic Quality Assessments of Laser Powder Bed Fusion Builds from Photodiode Sensor Measurements

2020 ◽  
Author(s):  
Sarini Jayasinghe ◽  
Paolo Paoletti ◽  
Chris Sutcliffe ◽  
John Dardis ◽  
Nick Jones ◽  
...  
Keyword(s):  
Machine Learning ◽  
Gaussian Process ◽  
Learning Algorithms ◽  
Gaussian Process Regression ◽  
Machine Learning Algorithms ◽  
Sensor Data ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Part Density

This study evaluates whether a combination of photodiode sensor measurements, taken during laser powder bed fusion (L-PBF) builds, can be used to predict the resulting build quality via a purely data-based approach. We analyse the relationship between build density and features that are extracted from sensor data collected from three different photodiodes. The study uses a Singular Value Decomposition to extract lower-dimensional features from photodiode measurements, which are then fed into machine learning algorithms. Several unsupervised learning methods are then employed to classify low density (< 99% part density) and high density (≥ 99% part density) specimens. Subsequently, a supervised learning method (Gaussian Process regression) is used to directly predict build density. Using the unsupervised clustering approaches, applied to features extracted from both photodiode sensor data as well as observations relating to the energy transferred to the material, build density was predicted with up to 93.54% accuracy. With regard to the supervised regression approach, a Gaussian Process algorithm was capable of predicting the build density with a RMS error of 3.65%. The study shows, therefore, that there is potential for machine learning algorithms to predict indicators of L-PBF build quality from photodiode build-measurements. Moreover, the work herein describes approaches that are predominantly probabilistic, thus facilitating uncertainty quantification in machine-learnt predictions of L-PBF build quality.

On the effect of irradiance on dimensional accuracy in multijet fusion additive manufacturing

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Mattia Mele ◽  
Giampaolo Campana ◽  
Gian Luca Monti
Keyword(s):  
Additive Manufacturing ◽  
Dimensional Accuracy ◽  
Crystallinity Degree ◽  
Content Type ◽  
Powder Bed ◽  
Polyamide 12 ◽  
Part Density ◽  
The Relationship ◽  
Am Processes

Purpose The amount of radiated energy is known to be a crucial parameter in powder-bed additive manufacturing (AM) processes. The role of irradiance in the multijet fusion (MJF) process has not been addressed by any previous research, despite the key role of this process in the AM industry. The aim of this paper is to explore the relationship between irradiance and dimensional accuracy in MJF. Design/methodology/approach An experimental activity was carried out to map the relationship between irradiance and dimensional accuracy in the MJF transformation of polyamide 12. Two specimens were used to measure the dimensional accuracy on medium and small sizes. The experiment was run using six different levels of irradiance. For each, the crystallinity degree and part density were measured. Findings Irradiance was found to be directly proportional to part density and inversely proportional to crystallinity degree. Higher irradiance leads to an increase in the measured dimensions of parts. This highlights a predominant role of the crystallisation degree and uncontrolled peripherical sintering, in line with the previous literature on other powder-bed AM processes. The results demonstrate that different trends can be observed according to the range of sizes.

AMB2018-04: Benchmark Physical Property Measurements for Powder Bed Fusion Additive Manufacturing of Polyamide 12

2019 ◽  
Vol 8 (3) ◽  
pp. 335-361 ◽  
Author(s):  
Erich D. Bain ◽  
Edward J. Garboczi ◽  
Jonathan E. Seppala ◽  
Thomas C. Parker ◽  
Kalman B. Migler
Keyword(s):  
Additive Manufacturing ◽  
Physical Property ◽  
Powder Bed Fusion ◽  
Powder Bed ◽  
Polyamide 12

scholarly journals The Influence of Particle Shape, Powder Flowability, and Powder Layer Density on Part Density in Laser Powder Bed Fusion

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 418
Author(s):  
Lukas Haferkamp ◽  
Livia Haudenschild ◽  
Adriaan Spierings ◽  
Konrad Wegener ◽  
Kirstin Riener ◽  
...  
Keyword(s):  
Particle Shape ◽  
Final Part ◽  
Powder Layer ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Layer Density ◽  
Hausner Ratio ◽  
Powder Flowability ◽  
Part Density

The particle shape influences the part properties in laser powder bed fusion, and powder flowability and powder layer density (PLD) are considered the link between the powder and part properties. Therefore, this study investigates the relationship between these properties and their influence on final part density for six 1.4404 (316L) powders and eight AlSi10Mg powders. The results show a correlation of the powder properties with a Pearson correlation coefficient (PCC) of −0.89 for the PLD and the Hausner ratio, a PCC of −0.67 for the Hausner ratio and circularity, and a PCC of 0.72 for circularity and PLD. Furthermore, the results show that beyond a threshold, improvement of circularity, PLD, or Hausner ratio have no positive influence on the final part density. While the water-atomized, least-spherical powder yielded parts with high porosity, no improvement of part density was achieved by feedstock with higher circularities than gas-atomized powder.

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