When 3D printing was first developed in the 1980’s, it was primarily used for a product’s proof of concept or initial prototypes. The limits of the technology and material did not allow one to use the process for field testing, or production. The past decade has seen a surge in 3D printing use. The rapid developments in 3D printing technology and materials has accelerated areas like product development, offer customized product, and eliminate design restrictions.
3D printing has streamlined the product development cycle in industries like die casting. The process is commonly used to test a working model for fit and function prior to die casting production. The technology helps die casters bypass costly and time-consuming aspects of creating and testing dies.
However, parts created through the process are susceptible to the same porosity that plagues those created through more traditional processes. The porosity is inherent to the properties of the material and technology. And, although it may not be fully eliminated within the 3D print process itself, it can be effectively sealed through vacuum impregnation.
This blog will discuss common materials, applications, and misconceptions related to impregnating 3D printed parts.
Common 3D Materials Vacuum Impregnation Seals
The two primary materials that vacuum impregnation seals are plastic and sintered metal.
Acrylonitrile butadiene styrene (ABS) and Nylon are the most commonly used plastic materials. ABS is ideal for low-cost prototyping, developing mechanical parts. Nylon is ideal for functional parts, complex models with intricate design, and assemblies.
Sintered metals are ideal for functional prototypes, and end-use parts. The material is also used for complex designs that cannot be machined by traditional machining methods.
Common Applications for Sealing 3D Printed Materials
The two common reasons why vacuum impregnation is used in 3D printing is to seal leak paths, and improve part integrity.
Seal Leak Paths
The laser, or nozzle, of the 3D printing machine creates a part by melting or fusing material, layer by layer. While a finished part is 98 – 99 percent dense, the process can leave a small number of micro-cavities within the part. This porosity is an almost unavoidable effect of the 3D printing process.
Certain applications require the part to be pressure tight, with 100 percent density. In order for parts to be pressure tight, the porosity needs to be sealed. If the porosity in 3D printed parts is not sealed, then fluids or gasses will leak. Vacuum impregnation seals the porosity within the part, allowing it to be pressure tight.
Improve Part Integrity
A 3D printed part is not as dense — and thus not as strong — as a part made from traditional manufacturing processes. Vacuum impregnation can be used to strengthen the material. As the vacuum impregnation sealant cures within the perforations, it creates a bond between the part layers (Figure 1). This strengthens the part by increasing the density.
Figure 1: The vacuum impregnation sealant will cure within the perforations, and strengthen the part by increasing the density.
Eliminate the Risk of Blooming
A common problem of 3D printed parts is blooming. The part features bloom, or swell as the layers absorb fluids. This risk of blooming is eliminated with vacuum impregnation. As previously written, the vacuum impregnation sealant cures within the perforations. After vacuum impregnation, fluids cannot be absorbed within the part's walls.
Misconceptions for Sealing 3D Printed Parts
The three most common misconceptions of applying vacuum impregnation to 3D printing are:
1. "Does vacuum impregnation remove build lines?"
Vacuum impregnation does not remove build lines (Figure 2). Build lines are a concern if the part is used for cosmetic purposes. Vacuum impregnation does not remove the build lines, because the process is done within the part’s walls and not above the surface.
Figure 2: Vacuum impregnation will not remove these build lines.
2. "Does vacuum impregnation seal surface defects?"
Vacuum impregnation only seals micro-porosity only within the part, and not visual defects on the part's surface (Figure 3). If applied to visual defects, then the sealant will not cure because there is little material for the sealant to adhere. Only the impregnation sealant that has been drawn into the walls by the force of the vacuum and pressure remains in the part.
Figure 3: Vacuum impregnation will not fill in these visual defects.
3. "Does vacuum impregnation increase part thickness?"
Because the process occurs subsurface, it does not add any thickness to the overall part dimensions. Impregnation allows engineers, designers and parts manufacturers complete freedom to design and make parts to their actual net shapes with no dimensional allowance to add or incorporate the impregnation process.
3D printing is being used for more rigorous prototyping and even in certain production applications. This enables manufacturers to streamline the production process. Vacuum impregnation helps make this possible by making the 3D printed part pressure tight and improving its integrity.