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How to Seal 3D-Printed Parts: Ultimate Guide to Eliminating Porosity

When 3D printing was first developed in the 1980s, it was primarily used for proof-of-concept models or initial prototypes. Early limitations in technology and materials meant that 3D-printed parts were rarely suitable for field testing or production. However, the past decade has brought rapid advancements in additive manufacturing. These advancements have allowed for more sophisticated materials, faster product development, customization, and greater design freedom.

Modern-day 3D printing has streamlined product development cycles and design iterations. In sectors like die casting, 3D printing is often used to test working models for fit and function before full-scale production begins. The technology helps die casters bypass the costly and time-consuming aspects of creating and testing dies.

However, parts created through 3D printing are susceptible to the same porosity that plagues those created through more traditional processes. Porosity is inherent in the properties of the material and technology. These tiny voids or imperfections can weaken parts and lead to leaks. Although porosity may not be fully eliminated within the 3D print process itself, it can be effectively sealed through vacuum impregnation.

This guide will discuss how vacuum impregnation solves porosity issues in 3D-printed parts, reveal common applications for vacuum impregnation, and clarify misconceptions about the process.

What Causes Porosity in 3D-Printed Parts?

Porosity refers to microscopic voids or defects that form during the 3D printing process. These occur due to incomplete fusion between material layers or trapped gases during melting and solidification. In metal additive manufacturing, such as laser powder bed fusion (LPBF), porosity can seriously compromise mechanical integrity.

There are two primary types of porosity:

• Lack-of-fusion porosity (LoFP). Caused by inadequate melting between layers, LoFP leads to gaps or discontinuities in the material structure.
• Gas-entrapped pores (GeP). Resulting from gas bubbles trapped during the melting process, GeP remain embedded in the final part.

In addition to reducing the durability of 3D-printed parts, these voids can make components unsuitable for pressure-sensitive or high-performance applications. Porosity can also affect surface finish and dimensional accuracy.

In applications that require pressure-tight parts, even microscopic leak paths can cause catastrophic failure in the field. Moreover, certain industries, such as aerospace and medical devices, maintain strict quality control standards that do not accept hidden defects. In these industries, knowing how to seal 3D-printed parts effectively is critical.

How Vacuum Impregnation Seals and Strengthens 3D-Printed Parts

Vacuum impregnation is a proven solution for sealing porosity within 3D-printed components. The process involves placing the part in a vacuum chamber and introducing a liquid resin or sealant that fills micro-voids inside the material. As the sealant cures, it bonds within the part’s internal structure. The process of vacuum impregnation has been shown to significantly improve multiple aspects of 3D prints, including the following:

• Leak resistance
• Mechanical strength
• Chemical resistance
• Dimensional stability
• Surface integrity

All of these benefits are what make vacuum impregnation ideal for functional prototypes, end-use parts, and any other application where consistent performance is critical. Proper resin selection, vacuum pressure control, and curing time are essential for ensuring full impregnation and maximizing part performance.

Two common material types that benefit from vacuum impregnation include:

• Plastics. Nylon and acrylonitrile butadiene styrene (ABS) are frequently used in 3D-printed projects. ABS is cost-effective and suitable for mechanical parts, while nylon offers durability for more complex, functional components.
• Sintered metals. These small components are often used in applications that require high strength and complexity, especially when traditional machining is not feasible.

In addition to increasing strength in 3D-printed parts, vacuum impregnation contributes to sustainability. By sealing internal defects, manufacturers can reduce scrap rates and extend the useful life of parts, which minimizes material waste and energy consumption during production. This makes vacuum impregnation an environmentally responsible post-processing method that aligns with green manufacturing principles.

Common Applications for Sealing 3D-Printed Materials

Here are the main reasons for sealing 3D-printed parts via vacuum impregnation.

Seal Leak Paths

Even highly optimized 3D-printed parts typically achieve a density of about 98-99%. That remaining 1-2% of micro-voids is enough to cause fluid or gas leaks. For applications requiring airtight or watertight performance, such as aerospace components, cooling channels, or sensor housings, sealing this porosity is essential.

Improve Part Integrity

Because 3D-printed parts aren’t as dense as machined parts, they often lack comparable strength. Vacuum impregnation reinforces these parts by bonding internal layers and increasing structural density. As the sealant cures, it enhances layer adhesion and contributes to a more robust part.

Eliminate the Risk of Blooming

Blooming is a condition where the 3D-printed part swells as layers absorb fluids. This not only affects visual appearance but can degrade performance. Vacuum impregnation eliminates this risk by filling the voids where fluid would otherwise accumulate.

In addition to improving performance, vacuum impregnation can increase confidence in the manufacturing process. Engineers can validate prototype designs knowing that material limitations, such as porosity, can be managed effectively. This shortens the timeline between prototyping and production, saving development time and costs.

Misconceptions About Sealing 3D-Printed Parts

Several misconceptions persist about vacuum impregnation in 3D printing. Let’s go through them.

1. Does Vacuum Impregnation Remove Build Lines?

No. Build lines result from the layer-by-layer deposition of material and are part of the surface texture. Build lines are only a concern if the part is intended for cosmetic applications. Vacuum impregnation addresses subsurface porosity, not surface appearance.

2. Does Vacuum Impregnation Seal Surface Defects?

No. Surface cracks or cosmetic flaws aren’t sealed because vacuum impregnation works within the material structure. Only the impregnation sealant that has been drawn into the walls by the force of the vacuum and pressure remains in the part. For visual defects, other post-processing methods like sanding or coating are more suitable.

3. Does Vacuum Impregnation Increase Part Thickness?

No. The process occurs below the surface and does not affect the part’s external dimensions. This makes it suitable for precision applications where tight tolerances are required. Vacuum impregnation is designed to integrate seamlessly into existing workflows. The process is non-destructive and can be automated for high-volume production, making it ideal for industries looking to scale 3D printing without compromising quality.

Why Godfrey & Wing Is the Trusted Name in Sealing 3D-Printed Parts

Established in 1948, Godfrey & Wing is the world’s longest-serving and largest provider of vacuum impregnation services, equipment, and sealants. With a legacy of innovation and precision, we help manufacturers across industries enhance the performance and reliability of their components, 3D-printed and otherwise.

We work closely with engineers and manufacturers to develop tailored solutions for their applications. Whether your priority is sealing micro-porosity in functional prototypes or reinforcing structural integrity in final-use parts, our team can help you implement vacuum impregnation with minimal operational disruption and maximum results.

Whether you’re prototyping a new part or preparing for scaled production, sealing with vacuum impregnation ensures your parts meet the highest standards of strength and reliability. To learn more about our process or to get started on your solution, contact us today.

What’s the Difference in Gas and Shrinkage Porosity?

Porosity is any void or hole in, or on, a casting and is caused by gas formation or solidification shrinkage that occurs while the metal solidifies. If the casting needs to be pressure tight, porosity can allow gas and fluids to seep from the part. In this blog, we will discuss the difference between gas and shrink porosity and the best solution to seal porosity.

What Is Gas Porosity?

One of the most prevalent types of die casting defects is gas porosity, which occurs when rounded air pockets or voids form within or on the surface of the casting. While minor levels of porosity may be allowable for non-critical parts, gas entrapment can ultimately compromise the quality and integrity of critical parts for high-strength applications. Because of this, manufacturers must detect and address porosity promptly in adherence with industry standards.

Types of Gas Porosity Defects

There are several different types of gas porosity defects. These include:

• Blisters. Raised defects that form on the surface of the casting.
• Blowholes. Larger round-shaped gas bubbles that form inside the casting and can be difficult to detect without specialized equipment.
• Open holes. A variant of blowholes that form on the surface of the casting.
• Scars. Shallow open hole defects that are typically non-centric.
• Pin holes. Tiny subsurface holes that form in groups in the casting.
• Sand blows. These are large voids that tend to form in the upper portion of the casting.

What is Shrinkage Porosity?

Shrinkage porosity defects are cavities that form when a casting solidifies inside the tool, but there isn’t enough liquid metal to fill the newly formed voids. These have angular surfaces and are different from air entrapment holes, which have rounded shapes.

Shrinkage porosity can cause material weakening. If on the surface, this porosity can lead to lower corrosion resistance as well as a worsened aesthetic appearance. Identifying the size, shape, and position of cavities is essential to determine which defect is occurring and what is causing it to occur.

Types of Shrinkage Porosity Defects

There are several different types of shrinkage porosity defects, including:

• Closed shrinkage. These defects form within the casting and typically occur at the top of hot spots.
• Open shrinkage. These defects are visible on the surface of the casting and either have caved surfaces or “pipes” that extend into the casting itself.
• Sponge shrinkage. These thin defects are typically found in the casting’s mid-section.
• Filamentary shrinkage. These form a network of cracks or lines within thick sections of material.
• Dendritic shrinkage. These are narrow, random cavities or fractures. Unlike filamentary shrinkage, these are often unconnected.

Problems of Porosity in Castings

As the amount of porosity increases in an aluminum or iron casting, it can become interconnected and create a leak path. The porosity makes the casting unusable for holding pressure in applications like pumps, compressors, transmissions, and plumbing fixtures.

How to Stop Casting Porosity

The most economical and successful approach to stop casting porosity is through vacuum impregnation. Vacuum impregnation is a method that seals the casting. To complete this process, the impregnating sealant is introduced into the voids within the wall thickness of the casting through vacuum and/or pressure methods.

This method is a cost-effective and permanent solution to casting porosity. Additionally, there is no limit to the size of castings that can be impregnated. Since the impregnation process occurs within the part, it will not distort, discolor, or affect the casting.

Why Godfrey & Wing Is the Solution to Casting Porosity

With first-time-through (FTT) recovery rates of over 99%, Godfrey & Wing’s vacuum impregnation equipment provides an effective and economical solution for stopping casting porosity. We build our systems around OEM’s parts sealing requirements to ensure leak-free and pressure-tight casting.