Why particle size and shape is critical for additive manufacturing powders

The growing success of powder metallurgy and additive manufacturing is tied to their ability to lower costs and craft specific parts that cannot be (easily) produced using conventional subtractive techniques such as machining. So, instead of smelting a block of metal alloy and removing material to create a part, for instance, these techniques allow near-net shape parts to be made from metal power feedstock with minimal post-processing.

However, successful manufacture is directly dependent on the quality of the metal powders used, particularly for additive manufacturing with particle size and shape critical to performance. Learning how to produce high-quality powders as cost-efficiently as possible, and manage them during processing, is crucial to further improve the economics of PM and AM processes and extend their application.

The ideal particle size for metal powders

Particle size defines process performance by affected powder packing behavior, flowability, response to heat, and surface finish. Larger particles pack less efficiently than small particles, which melt more readily. However, a range of particle sizes is often preferable, as the smaller particles fill the voids left by larger particles, and larger particle powders typically have better flowability. Although too wide a distribution can lead to segregation. The preferred particle size distribution very much depends on the application as shown below.

Consequently, it is important to control the powder manufacturing process so that you get a higher yield of powder with the expected particle size distribution, and to classify powders according to their application. As additive manufacturing processes such as powder-bed fusion may employ <20% of the powder in a single build – then powder re-use is important from both an economic and sustainability perspective, which means checking it is still within specification.

Why laser diffraction is an effective solution for metal powder analysis

There are several challenges for effective particle sizing in metal powder manufacturing:

• The analysis must be done rapidly and with a high throughput to allow necessary process changes to be implemented quickly and avoid becoming a bottleneck.
• The analytical method employed should provide a representative analysis of the full particle size distribution within a batch – so small and large particles.
• The analysis must be straightforward so that operators on the production floor or the laboratory can achieve reliable results with minimal training and effort.

To overcome these challenges, many researchers and manufacturers use laser diffraction, which is highly flexible and very well adapted to this context. Compared to traditional methods, laser diffraction provides considerably faster and more reliable particle size measurements. Laser diffraction measures the angular variation in light intensity as a laser beam passes through a particulate sample, using the Mie theory of light scattering to calculate particle sizes. Unlike sieving, it measures the entire distribution of particle sizes, so giving a more representative size distribution for a batch of material.

Offline, laboratory-based particle sizing techniques like laser diffraction provide faster measurement times. Yet, there are still time delays – between production and sampling, sampling and measurement, and measurement and receipt of results. The most modern solution is to use in-line particle sizing technology, where metal powder components pass through the instrument without leaving the process line.

Insitec, the in-line laser diffraction solution

Insitec leverages the strengths of laser diffraction, which can handle high throughputs and for which sample preparation, measurements, and analysis can all be automated. As a result, Insitec can be integrated into a production process for real-time analysis and adaptive control.

This includes at various points within an atomization process, or even as part of a sieving or classification operation, to ensure the collected material meets specification.

Delve into the details of in-line metal powder screening!

In-line instruments like Insitec therefore make it easier to make highly consistent products even with a tight particle size specification. If you’d like more detail regarding Insitec’s effectiveness in various metal powder applications, such as high-value powder reuse, read our recent whitepaper!