Machine augments Archimedes’ principle with automation for use in production environments.
As additive manufacturing becomes more prevalent, new approaches to measurement are necessary to ensure the efficient production of high-quality parts and products. Although 3D printing has several advantages over conventional subtractive manufacturing processes—such as milling and turning—one of its major challenges is part density.
Subtractive processes start with billets of material that have been forged or cast, enabling them to yield parts with 100% density consistently. Achieving the same density with additive manufacturing is more difficult due to porosity: the presence of cavities between build layers.
Density and Porosity in 3D-Printed Parts
In metal additive manufacturing, porosity is typically caused by issues with the printing process, e.g., inconsistency in the powder particle size or applying the incorrect sintering temperature. If the powder is not fully melted before moving to the next layer as a result of these variables, porosity is the result.
Porosity can negatively affect the mechanical strength and stability of a part, reducing its durability and making it more susceptible to failure under stress. It can also impact a part’s thermal and electrical properties, making it less resistant to corrosion, high temperatures and other environmental factors. Additionally, porosity can affect an additive part’s ability to retain liquids or gases, which may be crucial to its performance in certain applications, such as fuel nozzles.
In short: porosity is a problem for additive manufacturing. If you want to ensure your 3D-printed part has a density comparable to one made via conventional machining, you’ll need some way to calculate it.
How Archimedes Calculated Density
Born over 2,000 years ago, Archimedes was one of the first engineers in history. He paved the way for countless generations after him, creating tools—like the Archimedes screw—that are still in widespread use today. He’s best known for discovering a method of calculating the volume of objects by submersing them in liquid, based on a law of physics known as Archimedes’ principle.
This principle is often conflated with the apocryphal story of Archimedes realizing that he could calculate the volume of an irregularly shaped object by immersing it in water and measuring the resulting displacement. In actuality, Archimedes’ principle states that the buoyant force exerted on a body immersed in a fluid is equal to the weight of the fluid the body displaces.
Nevertheless, we can use Archimedes’ principle to calculate density by comparing the weight of a body in the air with its weight when submersed in a liquid with a known density. While Archimedes’ principle is a foundational part of fluid mechanics, its usefulness in manufacturing has grown more limited as the needs for greater accuracy and precision have increased.
4 Ways to Calculate Density in 3D-Printed Parts
As indicated above, the simplest way to calculate the density of a part made with modern manufacturing is via Archimedes’ principle: weigh a sample in air and in a liquid with a known density, then calculate the part’s density using the difference between the two measurements. While this approach can be highly accurate, it can also suffer from a lack of precision due to human influence.
A greater level of precision can be found in micrograph analysis, where a sample is segmented and the segments’ surfaces are examined for pores under a microscope. The downside is that the preparation of samples for microscopic analysis tends to be time-consuming.
Using computed tomography (CT) to analyze parts via x-rays also takes a fair amount of time—though in this case the waiting comes after the scan due to the need for post-processing images to eliminate artefacts.
Optical density determination uses an optical scanner to measure all of an object’s dimensions in order to determine its volume. The object is then weighed and these two pieces of information are used to determine its density. However, parts with complex geometries are difficult to assess with this approach.
Whatever method we choose, we seem forced to make a sacrifice: either precision (Archimedes), speed (micrograph analysis and CT scans), or accuracy (optical density determination). Enter a German testing- and measurement-technology company that claims to have solved this problem by augmenting Archimedes with automation.
Automated Density Determination
Dimensionics Density designed its new density determination machine with additive manufacturing in mind. According to the company, the imprecision in the Archimedes method is due to variable positioning on the scale, which is where automation comes in.
“To counteract this problem and to ensure the repeatability of the measurements, Dimensionics Density offers a universal carrier that can transport most parts, and which can be easily adapted if necessary for more complex geometries,” said the company’s head of sales, Philiipp Pruesse, in a recent release.
The carrier system is designed to accommodate parts up to 80 mm by 80 mm by 50 mm in size and up to 5 kg in weight. (The company told engineering.com that although it can create custom carriers for larger parts, the machine’s accuracy will suffer beyond these specifications.) Dimensionics Density claims the machine is highly precise, with a repeatability of 0.001 g/cm3.
Dimensionics Density has also stated that automation makes the machine’s density determinations faster. “With a cycle time of less than two minutes per component and the possibility of inspecting up to 18 components simultaneously in one inspection process as standard,” said Pruesse, “the Dimensionics Density solution supports the optimisation and efficiency of manufacturing processes.”
In addition to being designed for parts built with additive manufacturing technologies, such as selective laser melting (SLM), selective laser sintering (SLS), electron-beam melting (EBM) and binder jetting, Dimensionics Density told engineering.com that the new machine is also useful for parts made via powder metallurgy and ceramic processes that produce parts via sintering.
The machine’s base price is €75,000, with a higher price for better accuracy, cycle time, throughput, etc. Dimensionics Density can also customize, automate and integrate additional quality checks, as well as integrate the machine into existing processes, with prices varying further based on individual customer requirements.
Whether automated density determination using Archimedes will become the standard for 3D-printed parts remains to be seen, but it’s incredible to think that a 2,000-year-old method can be brought into the modern age with a little automation.
