Introduction
Porosity is an important concept when discussing any kind of media or material and particularly when looking at additive manufacturing processes. Porosity is the measure of the internal structure of a material, which can vary by material type and processing procedure. It is expressed as a fraction and refers to the volume of flaws or voids in the material relative to its total volume. Porosity can be expressed in terms of permeability, which measures the ability of a material to let fluids or air pass through it. The overall porosity of a material has a direct impact on its mechanical properties, such as strength and ductility, as well as its flow characteristics.
The most common method of measuring porosity is the gas saturation method. This method involves submerging a sample of the material into an inert gas and measuring the amount of gas trapped in the sample. The trapped gas is then expressed as a proportion of the total sample volume. Gas saturation is a good method for obtaining an overall indication of porosity, but it can be inaccurate due to sample variations or non-uniform distribution of the gas through the material.
Dynamic Gas Porosity
Dynamic gas porosity (DGP) is a method of measuring porosity that is more accurate than traditional gas saturation. It involves the application of a static pressure to a sample in order to measure the diffusion rate of a known volume of gas through the sample. The sample is then placed in a gas containing chamber, and the pressure is increased until the sample has popped and the gas has filled the volume of the sample. The resulting rate of diffusion of the gas can then be used to calculate the porosity of the sample.
The advantages of DGP over traditional gas saturation are numerous. It is more accurate and reproducible, can measure porosity in samples of varying sizes, and can be more sensitive to changes in porosity. Additionally, it can be used to measure both permeability (i.e. the speed at which gas can pass through the material) and permeate rate (i.e. the amount of material that can be corrected by a specific pressure). The most important use of DGP is in determining the media fill rate of a material or process.
Media Fill Rate
Media fill rate is an important consideration for any type of manufacturing process, especially when it involves the use of an additive manufacturing process. It refers to the rate at which a material can be filled with an additive or media, such as a resin or powder, to produce a three-dimensional object. The media fill rate of a process can be affected by numerous factors, such as material properties and process parameters.
The most accurate way to determine the media fill rate is to use the DGP technique. By measuring the diffusion rate of a known volume of gas, the media fill rate can be accurately calculated. This allows manufacturers to better understand the behavior of the material under various process conditions, allowing them to optimize the process parameters in order to achieve the desired level of accuracy and quality.
Conclusion
In conclusion, porosity is an important concept in the field of materials science and additive manufacturing. Traditional methods, such as gas saturation, provide an overall measure of porosity but can be inaccurate. DGP provides an accurate and reproducible method for determining porosity and can be used to measure other important characteristics, such as permeability and media fill rate. It is the most reliable way to determine media fill rate, an important parameter in the additive manufacturing process.
