Quality Management Guide to Sealing Additive Manufacturing Porosity
Parts made by the additive manufacturing process are as susceptible to porosity as components made by conventional methods. This article will discuss common materials, applications, and misconceptions related to impregnating additive manufacturing parts.
When additive manufacturing was first developed in the 1980s, 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 additive manufacturing use. The rapid developments in technology and materials have accelerated areas like product development, offer customized products, and eliminate design restrictions.
Additive manufacturing has streamlined the product development cycle. However, parts created through the process are susceptible to the same porosity that plagues those created through more traditional methods. The porosity is inherent to the properties of the material and technology. And, although it may not be fully eliminated within the process itself, any leak paths created by interconnected porosity can be sealed through vacuum impregnation.
Common Additive Manufacturing 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 intricate designs that cannot be machined by traditional machining methods.
Common Application for Sealing Additive Manufacturing Materials
The main reason why vacuum impregnation is used in additive manufacturing is to seal leak paths.
Seal Leak Paths: The laser, or nozzle, of the machine, creates a part by melting or fusing material, layer by layer. During the manufacturing process, any formed porosity may be interconnected and breach the part’s wall. Specific applications require the part to be pressure tight. For parts to be pressure tight, the leak path needs to be sealed. If not sealed, then fluids or gasses will leak. Vacuum impregnation seals the leak path within the part, allowing it to be pressure tight.
Improve Part Integrity: An additive manufacturing 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’s internal layers (Figure 1). This strengthens the part by increasing the density.
Misconceptions for Sealing 3D Printed Parts
The three most common misconceptions of applying vacuum impregnation to additive manufacturing are:
1. Does vacuum impregnation remove build lines or surface flaws?During the impregnation cycle, the sealant is drawn deep into the leak path by pressure. After the impregnation cycle, water emulsifies the part, and the sealant washed from all surfaces, machine features, blind holes, and taps.
Only the sealant drawn into the leak path by the force of the vacuum and pressure remains in the part. The part will exhibit the same build lines and surface flaws after the process. However, the leak path below the surface will be sealed.
2. Does vacuum impregnation seal cracks?
Additive manufacturing cracks typically occur as a result of mishandling. If attempting to seal a crack, then it may start sealed, but it can propagate since it is a structural failure. During assembly and use, the torque or the applied pressure may cause the cracks to expand. The cured sealant will remain static as the crack expands. As a result, any fluids or gases may seep out of the newly created leak path.
3. Does vacuum impregnation increase part thickness?
Vacuum impregnation does not change the part's dimensions, thus allowing engineers the freedom to design and make parts to the net shapes. Since the vacuum impregnation process occurs subsurface, an engineer does not need to incorporate dimensional allowance.
Additive manufacturing is being used for more rigorous prototyping and even in specific production applications. This enables manufacturers to streamline the production process. Vacuum impregnation helps make this possible by making the part pressure tight and improving its integrity.