Linking Aluminum powder flowability and processability in AM manufacturing processes

Linking aluminum powder flowability and processability in additive manufacturing processes

Introduction

A set of five Aluminum powders coming from different producers has been analyzed with the GranuDrum and GranuPack instruments.

According to the information shared by the producers, the grain shape and size are roughly identical from one sample to the other.

The different samples are corresponding to different grain surface treatments and possibly to the addition of flow aid agents.

In parallel, we have tested the processability of these powders in 3D printers.
The aim of this study is to show the link between GranuTools instruments flowability indexes and the processability in powder bed based additive manufacturing processes.

These powders do not flow in a Hall flowmeter (ASTM B213) without strong vibrations.

Thus, this classical method does not help in the present case.

The powders are made of polydisperse spherical aluminium grains with an average size of 40 um.
They are named P1, P2, …, P5.

You can also find a summary of the obtained results with the whole set of powders at the end of the document.

First, we will focus on P1 and P2 having respectively a very bad processability and a fairly good processability.

P1

P2

photography of the powder P1 made of polydisperse spherical aluminium grains with an average size of 40 um with a very bad processabilityphotography of the powder P2 made of polydisperse spherical aluminium grains with an average size of 40 um with a fairly good processability

GranuDrum

Then the next plots are showing the main GranuDrum parameters (flowing angle and cohesive index) as a function of the rotating speed.

graph that shows the main GranuDrum parameters flowing angle as a function of the rotating speed for P1 and P2

graph that shows the main GranuDrum parameters cohesive index as a function of the rotating speed for P1 and P2


As you can see, both powders have a slight shear-thickening behavior.
The powder having a bad processability has a higher flowing angle and a higher cohesive index.

GranuPack

The GranuPack measures automatically the evolution of the powder density during a tapping procedure to obtain a compaction curve.

The next plot show the compaction curves obtained with samples P1 and P2.

graph that shows the compaction curves obtained with samples P1 and P2 with the GranuPack combining the density (in g/ml) and the tap number

Also, the measurement has been repeated three times with each sample.
It shows that the curves for the same sample are very similar showing the high reproducibility of GranuPack measurement.

Conclusion

As you know, the last page of the document presents a summary of the indexes measured with the GranuDrum and the GranuPack for the whole set of powders.

So it clearly shows that a powder with a good processability in AM application is characterized by:

– A low flowing angle, cohesive index and Hausner Ratio;
– A high bulk density.

Summary of the main flowability indexes compared with the processability

graph that shows the 3D printer processability (in %) compared to flowability index for P1 to P5

Graph that shows the GranuDrum flowing angle compared with the processability for P1 to P5

Graph that shows the GranuDrum cohesive index compared with the processability for P1 to P5

Graph that shows the GranuPack Hausner Ratio compared with the processability for P1 to P5

Graph that shows the GranuPack Bulk density compared with the processability for P1 to P5