February 02, 2023 by SME When it comes to processes used to develop products for aerospace, “Which is better for metal-to-metal bonding?” is a common question for manufacturers. There are several different processes for bonding different metals together. In the aerospace industry, combining different metals to get the benefits of both materials is a common practice. Aircraft are exposed to many different environmental conditions, and products that use dissimilar metals often perform better than single alloy products. Some examples of joined metals include titanium with stainless steel, titanium with iron-nickel, and aluminum with other metals. There are several different processes to bond these metals, but which one is better is up for debate. Diffusion Bonding Diffusion bonding involves placing dissimilar metals into a hot press. Inside the press, high pressure and temperature combine to mold the metals together. This bonding method is useful when creating a product that requires good structural integrity. Hot press diffusion bonding has several benefits, including consistent results. The precision and accuracy of this metal-to-metal bonding method make it a good choice for many aerospace applications. Despite this, diffusion bonding is not as commonly used as other methods because it requires an understanding of the effects a hot press will have on the metals being bonded, and knowledge of the best design for a component made through metal-to-metal bonding. Many manufacturers do not have this in-depth technical knowledge of the diffusion bonding process, which has led to slow adoption within the aerospace industry. However, diffusion bonding is used for certain aerospace applications, such as fabricating aircraft structural components, and creating gas and other fluid flow devices. Explosion Bonding Also known as explosion welding, explosion bonding bonds dissimilar metals at an atomic level. It requires two plates — each made of a different metal — and an explosive charge. The two plates lay flat and are pressed against each other, leaving a small gap in between for an explosive charge that detonates at the edge of the plates — molding the plates together in the process. Explosion bonding can be used to bond copper, nickel, stainless steel, and titanium. This type of metal-to-metal bonding is useful for metals that aren’t usually compatible, such as aluminum and stainless steel. Use of this process also depends on the end use of the aerospace component being created. Because explosion-bonded metals usually require another metal layer between the two primary metals, the third layer’s properties must be taken into consideration for the final product. Adhesive Bonding Aerospace adhesives, usually a paste or film, are often applied on aircraft to bond metal as well as components. Adhesives can be used on the interior, exterior, or engine compartment of an aircraft. Using adhesives in place of other options, such as fasteners, makes the craft lighter, improves performance, and is better for stress distribution. Despite being a lightweight option, adhesives still offer corrosion protection and resistance in extreme conditions. Adhesives that are commonly used in the aerospace industry include anaerobics, cyanoacrylates, epoxies, and structural acrylics. These different adhesives have several uses and benefits. Anaerobics are most commonly used in engine compartments, but can also be used throughout the whole aircraft, as they’re good at preventing components from loosening. Cyanoacrylates are a quick fix — they hold metal parts together while other, slower adhesives are working to bond. Epoxies are a light but durable adhesive commonly used in aircraft, while structural acrylics are used for bonding magnets to motors and attaching harness clips. What Type of Aerospace Metal-to-Metal Bonding Is Best? Though not commonly used, diffusion bonding is one of the best metal-to-metal bonding processes due to its consistent results and structural durability. Plus, the resulting part has beneficial properties from each metal used in its creation. Explosion bonding is also a good metal-to-metal bonding process, but manufacturers have to consider how each metal affects the resulting aerospace component. You can also use adhesive bonding for metal-to-metal bonding, but it does not intermingle the metals in the same way as the other two methods. The metals are bonded, but they aren’t combined and don’t share any properties. To learn more about which is a better process for metal-to-metal bonding in the aerospace industry, attend AeroDef — a manufacturing technology show focused entirely on the aerospace and defense industries.
