Welding vs Brazing: Choosing the Right Joining Method for Critical Metal Assemblies

For manufacturers who produce critical metal assemblies, a major consideration of the engineering process is how metal components will be joined. Some of the most commonly used metal assembly joining methods are welding, conventional brazing, and vacuum brazing. 

One method isn’t inherently “better” or “worse” than another, but depending on the nature of your project, some methods are more suitable than others.

Making the right choice involves understanding the core service requirements of the component or piece, the materials being used, and the assembly requirements.

Getting this choice right early on is key to your process. The choice of metal joining methods directly impacts performance, reliability, and dimensional accuracy. 

Understanding How the Three Primary Metal Joining Methods Work

Each of these three metal joining methods has different strengths and weaknesses. Choosing the right one will depend on your specific project.

Welding

Welding is one of the most commonly used techniques for joining metals. It works by melting two base materials together, often combined with a third filler material. 

The process is so ubiquitous because it creates strong structural joints quickly, and often at lower cost than many of the other metal joining methods. It’s also excellent for simple geometries and large pieces of metal, such as frames. There’s also an abundance of welders available.

There are also numerous types of welding, including MIG, TIG, arc and laser welding, all of which have different applications. 

Of course there are limitations. Because the process melts the parent materials, it can create warping, distortion, and dimensional variations that make the process less suited for applications that require precision metal joining.

Dissimilar metals can be difficult to join with welding, though not impossible. The technique generally works better when joining similar metals like aluminum-to-aluminum, or steel-to-steel. It can also be difficult to weld together thick and thin sections of metal, because the heat required to melt the thick section runs the risk of damaging or burning through the thinner metal.

Conventional Brazing

Brazing works fundamentally differently than welding. Instead of melting the parent materials themselves, conventional brazing techniques melt a filler material between them. 

Because the filler has a lower melting point than the two parent materials, they will not melt. Capillary action draws the molten filler material into the gap, forming an extremely durable joint.

In conventional brazing methods like torch brazing or induction brazing, a flux is used to remove oxides and protect the joint from oxidation. It also improves wetting of the filler material and transfers heat.

When comparing welding vs brazing, conventional brazing uses lower temperatures than welding. It also has a lower chance of distorting the parent materials and can also be used to join some dissimilar metals. Joints can also be visually inspected after the brazing process.

However, one of the main limitations of conventional brazing techniques is that they often leave behind flux residue. This can usually be cleaned, but in highly controlled applications, any residue at all can be unacceptable. More complex assemblies also increase the chance of contamination, which leaves conventional brazing best suited for simple metal fabrications, like copper plumbing, HVAC components, and fittings.

Vacuum Brazing

Vacuum brazing is a more advanced form of brazing. It eliminates the need for a flux by using a vacuum furnace to remove oxygen, moisture, and other contaminants from the atmosphere. The temperature in the furnace can be gradually raised, heating the assembly evenly and melting the filler metals so that it cleanly flows through the joints. 

This offers a major advantage in cleanliness, vital for precision metal joining in applications like medical devices, semiconductor equipment, and aerospace components. 

Assemblies that use vacuum brazing also benefit from the process’s ability to heat parts uniformly. This significantly reduces the chances of warping and distortion when compared to welding and even conventional brazing. 

Vacuum brazing is also capable of producing leak-tight, hermetic seals, which is essential when pressure or liquid containment is a requirement.

It’s also possible to join dissimilar materials through vacuum brazing that would be difficult or even impossible to join using welding techniques. Many joints can also be created during a single furnace cycle, which is very useful when creating heat exchangers and high-performance thermal management systems. 

Vacuum brazing isn’t without its limitations. Brazing limits depend on furnace sizes, but they often top out at assemblies around 20” x 20” x 20”, making it impractical for large assemblies. The processing costs are also higher than welding, which is comparatively fast and cheap. Vacuum brazing requires long cycle times.

The best applications of the process are in precision metal joining, such as heat exchangers, aerospace components, and medical devices. For applications where the benefits of precision vacuum brazing services aren’t a requirement, it can be overkill.

Key Factors to Consider When Choosing Between Metal Joining Methods

Understanding the differences between metal joining methods is just the beginning. To choose the right method, you have to understand the core requirements of the materials being joined.

Parent Materials

Material compatibility is one of the first deciding factors. All three metal joining methods we’ve discussed work very well when joining similar metals, but welding is often the default choice due to its low cost and accessibility. 

However, when dissimilar types of metals are being joined, brazing can make it easier to join material combinations that would prove extremely difficult with welding. 

That’s because material differences in melting temperatures and thermal expansion rates make it challenging to produce a reliable welded joint. Brazing allows the parent materials to stay solid, while a filler metal creates the actual bond between the metals.

Performance Conditions

The conditions under which a finished assembly is intended to perform play a large role in determining the right type of joining method to use. 

Industrial metal joining applications that must support large structural loads often benefit from welding, while critical metal assemblies like heat exchangers favor vacuum brazing. Environmental exposure as well as repeated stress cycles all need to be taken into consideration when choosing the right metal assembly joining method. Thermal loads are particularly important, as the repeated heating and cooling cycles create expansion and contraction stresses that affect the joint over time.

Precision & Dimensional Requirements

The complexity of an assembly’s dimensional requirements can also influence the choice of joining method. Welding is ideal when these requirements are simple, however critical metal assemblies with tight tolerances and complex geometries often benefit most from precision brazing services. 

When there are highly demanding positional accuracy requirements, precision vacuum brazing services are often needed.

Assembly Size

The overall size of the assembly must also be considered. For very large assemblies, welding is often used simply because the components cannot fit within the confines of a vacuum furnace. Vacuum brazing is often preferred for small to medium-sized high-performance components, where precision, cleanliness, and dimensional stability are required.

Hermetic Sealing

Whether a joint requires a leak-tight seal is a major decision point. While welding can produce leak-tight joints, brazing is often preferred for creating hermetically sealed joints while minimizing distortion. Vacuum brazing is preferred for assemblies where gases cannot enter or escape the system, such as heat exchangers, semiconductor equipment, electronic sensor packages, and aerospace components. 

Inspection Requirements

When designing a joint, inspection requirements should also be considered. Some joining methods can be quickly visually inspected, while others require leak testing or other means to verify joint quality. Knowing how the finished assembly will be inspected helps manufacturers select the most appropriate joining method from the beginning.

When Vacuum Brazing Offers the Greatest Advantages

Both welding and brazing are capable metal assembly joining methods. However, there are certain applications where vacuum brazing is the clear choice. 

One of the best use cases for vacuum brazing is the production of critical metal assemblies with strict dimensional controls. Because vacuum brazing generally heats assemblies more uniformly, while only melting the filler metal, it typically produces less distortion and greater dimensional stability than welding.

The vacuum brazing process is commonly used to create leak-tight hermetic seals, which are often a requirement in aerospace, semiconductor, and thermal management applications. 

Vacuum brazing is often preferred when two dissimilar metals need to be joined. Different metals have different melting points and thermal expansion characteristics, which can make welding certain metal combinations difficult. Vacuum brazing only requires the braze filler material to be melted, creating a wider range of metals that can be joined together, while minimizing distortion.

Conventional brazing uses a flux to reduce oxide formation, however it can leave behind residue which can be unacceptable in ultra-clean applications like semiconductor manufacturing. When even trace amounts of oxygen, nitrogen, carbon, or other contaminants could cause problems, a specialized form of brazing called high vacuum brazing is often used. High vacuum brazing is typically reserved for applications where contamination control is critical, such as semiconductor equipment, advanced ceramic assemblies, and certain aerospace components.

In truth, many assemblies will use both metal joining methods. For example, heat exchangers or radiators may use vacuum brazing to create a solid core piece, which then has manifolds welded into place. 

VPE: Precision Vacuum Brazing Services

Choosing between welding vs brazing isn’t a matter of “which is better”, as much as it is “which is better for this application”. 

Welding is a highly versatile choice for joining similar metals. It excels at producing strong bonds quickly and cost effectively, and is ideal for larger assemblies. 

When precision and cleanliness are needed, brazing and vacuum brazing in particular, are often better suited. 

Ultimately, the project’s performance and materials requirements will dictate which metal joining methods to use, and in many cases, multiple metal joining methods will be used together. 

For companies in need of precision vacuum brazing services, Vacuum Process Engineering (VPE) brings over 50 years of experience with advanced metal joining techniques. Our facilities feature extensive vacuum brazing capabilities, including furnaces designed specifically for aluminum vacuum brazing. 

To learn more about how VPE can meet your needs for precision brazing services, contact our team today.

FAQs

Should I use welding or brazing for critical metal assemblies?

The answer depends on the materials and performance requirements of the assembly. Welding works well for larger assemblies and those with simple geometries. Critical metal assemblies that require tight tolerances, hermetic sealing, minimal distortion, or joining dissimilar metals benefit from vacuum brazing. In some applications, both welding and brazing are used. 

How do I choose the right metal joining process?

Decision making starts by understanding the parent materials and the operating conditions of the final assembly. Structural and thermal loads, as well as environmental exposure and dimensional requirements, can all impact the final choice. Working with an experienced industrial metal joining partner can guide you in the right direction.

When should vacuum brazing be used?

For applications that require cleanliness, dimensional stability, or hermetic sealing, vacuum brazing is preferred. Because the vacuum brazing furnace eliminates the need for a flux, the process produces extremely clean joints with minimal distortion or contamination. The vacuum brazing process is commonly used for creating heat exchangers, aerospace components, semiconductor equipment, and medical devices.

What is the best joining method for dissimilar metals?

Both welding and brazing can be used to join dissimilar metals, however brazing is often preferred because it does not require melting the parent materials, as welding does. Metals have different melting points, which can make welding certain dissimilar metal combinations difficult or impractical. Brazing makes it possible to join a wider variety of metals together because only the braze filler is melted. The best method will depend on the specific metals involved and the overall design of the assembly.