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Optimising Additive Manufacturing via comprehensive powder flow testing

In recent years, our technology has been increasingly used to test powders for Additive Manufacturing (AM) or 3D Printing applications. AM is a transformative technique which is becoming widely adopted across a broad range of industries and sectors.

​​​​​​​Image Credit: Freeman Technology 

Below is a selection of studies where the FT4 Powder Rheometer® has been successfully employed:

“Screening Pharmaceutical Excipient Powders for use in Commercial 3D Binder Jetting Printers”

A. Antic, J. Zhang, N. Amini, D.A.V. Morton, K.P. Hapgood | School of Engineering at Deakin University

Advanced Powder Technology | 26 May 2021

Abstract

Binder jetting is an additive manufacturing technique that creates three-dimensional constructs from a powder feedstock. It is used by several industries, including pharmaceuticals. This additive approach to manufacture provides several functional benefits that are not easily achievable using conventional manufacturing methods. There is currently only limited publicly available knowledge that details the requirements of an effective binder jetting powder. Specifically, in the pharmaceutical industry, since the 2015 release of Spritam®, a binder-jetted tablet containing levetiracetam, no new pharmaceutical tablets have been produced using such methods.

There appears to be gap in powder technology expertise and the development of 3D printing processes. Our goal is to enhance our knowledge in terms of powder flow, powder wetting and powder binding to link particles with process and build the capability to create a greater range of powders suitable to be binder-jetted into new products. After initially screening several standard pharmaceutical excipient powders for their relevant properties, two candidates showed best fit potential for use in binder jetting, specifically microcrystalline cellulose (Pharmacel 101 and 102) and lactose (Lactohale 200). Using simple formulations of these pharmaceutical excipient powders as a model, we analysed for printability and powder performance using a range of quantitative parameters including dimensional accuracy, construct hardness, friability, porosity and surface finish. In general, formulations of these powders showed good printability, but some powder blends produced constructs with more obvious manufacturing imperfections. Several routes to improve the printability of these pharmaceutical powders are proposed for future works. Ultimately, this work provides a fundamental basis to start to quantitatively assess the potential of standard pharmaceutical excipient powders in binder jetting printers using powder characterisation techniques and print quality outcomes.

https://www.sciencedirect.com/science/article/abs/pii/S0921883121002387

“Powder Characterization for Additive Manufacturing Processes”

Lisa Markusson | Luleå University of Technology, Department of Engineering Sciences and Mathematics

2017

Abstract

The aim of this master thesis project was to statistically correlate various powder characteristics to the quality of additively manufactured parts. An additional goal of this project was to find a potential second source supplier of powder for GKN Aerospace Sweden in Trollhättan. Five Inconel® alloy 718 powders from four individual powder suppliers have been analyzed in this project regarding powder characteristics such as: morphology, porosity, size distribution, flowability and bulk properties. One powder out of the five, Powder C, is currently used in production at GKN and functions as a reference. The five powders were additively manufactured by the process of laser metal deposition according to a preprogrammed model utilized at GKN Aerospace Sweden in Trollhättan. Five plates were produced per powder and each cut to obtain three area sections to analyze, giving a total of fifteen area sections per powder. The quality of deposited parts was assessed by means of their porosity content, powder efficiency, geometry and microstructure. The final step was to statistically evaluate the results through the analysis methods of Analysis of Variance (ANOVA) and simple linear regression with the software Minitab.

The method of ANOVA found a statistical significant difference between the five powders regarding their experimental results. This made it possible to compare the five powders against each other. Statistical correlations by simple linear regression analysis were found between various powder characteristics and quality of deposited part. This led to the conclusion that GKN should consider additions to current powder material specification by powder characteristics such as: particle morphology, powder porosity and flowability measurements by a rheometer.

One powder was found to have the potential of becoming a second source supplier to GKN, namely Powder A. Powder A had overall good powder properties such as smooth and spherical particles, high particle density at 99,94% and good flowability. The deposited parts with Powder A also showed the lowest amount of pores compared to Powder C, a total of 78 in all five plates, and sufficient powder efficiency at 81,6%.

https://www.diva-portal.org/smash/get/diva2:1084670/FULLTEXT01.pdf​​​​​​​

“Production of Spherical Polymeric Composite Powder for Selective Laser Sintering via Plasma Assisted Solid State Shear Milling: From Theory to Piezoelectric Application”

Shiping Song, Yijun Li, Shibing Bai, Qi Wang | State Key Laboratory of Polymer Materials Engineering, Polymer Research Institute, Sichuan University

Chemical Engineering Journal | 19 February 2021

Abstract

With the advent of digital industry, intelligent manufacturing is becoming a pillar industry guiding the rapid development of modern industry and daily life of human kind. Nevertheless, the lack of advanced functional materials severely restricts the technological updates and product upgrades. Herein, we developed a facile method to fabricate polyvinylidene fluoride (PVDF)/barium titanate (BaTiO3) spherical piezoelectric powder for SLS processing by combining solid state shear milling (S3M) and plasma technology. With assistance of simulation of heat transfers and molecular dynamics, the transformation of irregular powder to spherical one was successfully clarified by melt surface tension. As a proof-of-concept, the as-prepared spherical powder endowed SLS parts with advanced mechanical properties and piezoelectric properties derived from the excellent accumulation characteristics. The improved piezoelectric properties could reach an open-circuit voltage of 4.7 V and a short-circuit current of 106.5 nA, which exhibited better output performance than those of most reported piezoelectric 3D parts. This work not only contributed a high quality piezoelectric material for SLS processing, but also provided a new route for efficient and clean preparation of polymer-based spherical powder for all chemical engineering fields.

https://www.sciencedirect.com/science/article/abs/pii/S1385894721006276​​​​​​​

“Adapting L-PBF Process for Fine Powders: A Case Study in 420 Stainless Steel”

Subrata Deb Nath, Alfred Okello, Rajendra Kelkar, Gautam Gupta, Martin Kearns & Sundar V. Are | Materials Innovation Guild, University of Louisville, Louisville, Kentucky, USA; GE Additive, West Chester, Ohio, USA; Dept. Of Chemical Engineering, University of Louisville, Louisville, Kentucky, USA; Sandvik Osprey Ltd., Neath, UK

Materials & Manufacturing Processes | 26 January 2021

Abstract

The laser-powder bed fusion (L-PBF), also known as selective laser melting (SLM), is widely processed to a narrow powder size of 15 (D10) to 45 (D90) μm. However, expanding the particle size distribution (PSD) that can be processed by L-PBF can have important technical and economic benefits. Using 420 stainless steel as a case study, the current investigation successfully shows that finer particles can also be successfully processed by L-PBF to achieve comparable tensile strength, corrosion resistance, microstructure and density. The results of the study determined that agglomeration of fine powders was the critical barrier that previously limited successful processing. Further, the study clearly showed that a simple and scalable vibratory sieving process was sufficient to deagglomerate the fine powder to improve flowability and achieve consistent printability of engineering parts.

https://www.tandfonline.com/doi/abs/10.1080/10426914.2021.1885707?journalCode=lmmp20

“Spreadability Testing of Powder for Additive Manufacturing”

Christopher Neil Hulme-Smith, Vignesh Hari & Pelle Mellin | Department of Materials Science and Engineering, KTH Royal Institute of Technology, Stockholm, Sweden & Swerim AB, Kista, Stockholm, Sweden

Berg Huettenmaenn Monatsh | 14 January 2021

Abstract

The spreading of powders into thin layers is a critical step in powder bed additive manufacturing, but there is no accepted technique to test it. There is not even a metric that can be used to describe spreading behaviour. A robust, image-based measurement procedure has been developed and can be implemented at modest cost and with minimal training. The analysis is automated to derive quantitative information about the characteristics of the spread layer. The technique has been demonstrated for three powders to quantify their spreading behaviour as a function of layer thickness and spreading speed.

https://link.springer.com/article/10.1007/s00501-020-01069-9

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