Finishing aluminum parts with bead blasting is a convenient, effective way of ensuring your components get your desired finish, are more protected against fatigue damage like cracking, and are prepared for any secondary finishes that may be required.
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To put it simply, bead blasting works by firing small beads of media, made of materials like glass or steel, against the surface of parts at high pressure, resulting in a uniform finish. The bead blasting process strengthens aluminum components and improves their overall longevity.
The size and material of the media used to bead blast aluminum will affect the components differently, so the all-important first step is to determine what the required end result will be.
For example, smaller media can produce brighter finishes with satin textures, while using larger media will result in rougher, if still uniform, finishes. Glass media will not affect the color of the substrate, which can help retain a higher polish, while steel and other materials may darken the color slightly, especially when using larger sized media.
After the size and type of media are selected, the components are put into a durable blast cabinet and the operator uses a blaster gun that propels the media at high pressure against the surface of the components. This process can take time on larger surface areas or for rust removal, but the precision provided by bead blasting is excellent for consistent, reliable results.
A wide range of aluminum components can benefit from bead blasting, and the process is used in various industries. It’s particularly useful for aluminum due to its ability to clean or create a surface finish without removing significant material or altering the dimensions of the part.
Any aluminum parts that require cleaning, deburring, peening or a uniform, professional-looking finish are great candidates for Eaglemaster’s bead blasting service.
Bead blasting can also be used for preparing aluminum components for various post-finishes, including powder-coating and painting, allowing for an even wider range of applications.
When deciding whether bead blasting is the ideal finishing process for your aluminum components, it’s worth taking the time to understand the broad benefits and potential downsides.
Benefits of bead blasting aluminum include:
Considerations to keep in mind:
Steel shot is another type of media that can be used. It is made by casting small steel beads according to SAE standard sizes ranging from S-70 (~0.125mm screen size) to S930 (~3mm screen size). There are also multiple hardness ranges, which go from a hardness of 40 Rc up to 62 Rc. The hardness and density of steel shot make it highly durable and in many cases enable it to be re-used for hundreds of cycles! The most common uses for this type of media are cleaning, de-rusting, stripping, and shot peening applications. Metal surfaces can be stress-relieved and hardened to prevent metal fatigue when shot peened using steel shot media.
Steel shot is best used for heavy-duty applications and materials such as steel and cast iron; it is not generally suitable for softer metals or plastics.
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Aluminum Oxide is a tough and abrasive grit media with an angular shape and is often used as a substitute in the sand blasting process. Due to its hardness and angular shape, it is effective at quickly cutting into and etching even the hardest materials. It is often used to prepare surfaces for paint, round sharp edges, and provide a consistent-looking finish. The roughness of the finish will generally correlate to the grit size used. Larger-sized grit will etch the surface more quickly and leave a rougher finish, while finer grits will leave a smoother finish with longer processing times.
Surfaces blasted with aluminum oxide will attain a consistent matte finish with a dull appearance. Aluminum oxide is generally brown in color and can cause some discoloration. Aluminum oxide can be used prior to anodizing to produce uniformly matte anodized parts. It is not suitable for applying finishes to plastic parts.
While there are multiple types of plastic blasting media, the most common and widely used is called Urea. It is made of angular-shaped grains of recycled plastic materials. Being plastic, it is much more gentle than most other abrasives, highly re-usable, and lightweight. This makes it ideal for use on delicate parts or materials without causing damage. Blasting equipment can accelerate the lightweight plastic particles to high velocities, making it effective at quickly stripping light coatings. Plastic blast media is also helpful for de-flashing and deburring operations for molded parts.
While plastic media such as Urea is excellent for cleaning and stripping applications, it is not a good option for achieving cosmetic finishes since the media does not dimple the surface like other types of media.
From the wide selection of available media to the applied pressure and technique, many variables can influence the appearance of your bead blast finished parts. Suppose you are looking to achieve a particular finish. In that case, it is essential to provide specifications to control some of these variables to guide the intended result. When striving for consistent results across production runs or multiple batches, specifications are critical.
When ordering bead blasted parts through Xometry's Instant Quoting Engine, if no further instructions are provided, we will defer to using glass bead media and sufficient pressure to remove tool marks and smooth the surface without damaging the part. The sections below go over tips and best practices you can incorporate to achieve greater control of the process and more predictable and consistent bead blast finishes.
The type of media or abrasive used will significantly influence the look and feel of your finish. For instance, fine glass beads will produce a consistent, satin-like finish, whereas aluminum oxide will yield a uniform but duller appearance. It may take some experimentation to determine what media works best for your project, but you will want to include that information in your order or part drawings notes section once you do. In addition to the type of media, be sure to specify its shape if there are multiple options to choose from.
Another variable that plays a role in how your finish comes out is the particle size of your chosen media. Suppliers often refer to the abrasion grade or grit. The grit is very similar to what you would find when shopping for sandpaper at your local hardware store. The lower the grit, the larger and more coarse the particles are. On the other hand, higher grits will be of finer particles. Mesh size is often referred to as well. The easiest way to understand mesh size is if you were to observe a 1"x1" screen made up of equally sized holes. With a mesh size of 20, there would be 20 holes in the screen, and particles smaller than those holes will pass through, while larger ones will be blocked. With a mesh size of 200, there would be 200 holes in the same 1"x1" area, and thus would be much smaller and only allow finer particles to pass through.
Media size is typically broken down into coarse, medium, fine, and very fine grades. Calling out a grade will simplify your notes and prevent being overly specific, which can limit a manufacturer's options.
By the nature of the blasting process, the part's surface roughness will be directly impacted. It can be challenging for shops to maintain tight surface roughness requirements while also applying a media blasted finish. When these requirements mix, it is often the case that a shop will want to pause the project and get clarification on what the expectations are.
We recommend limiting surface roughness to no lower than 32 µin Ra when you need a smooth bead blasted part. We do not recommend blasting surfaces that must be lower than 32 µin Ra and instead call out for masking on just those surfaces. Take note that masking requirements can significantly increase labor time and thus cost.
A boundary sample can be invaluable for manufacturers when producing a finish that meets expectations. If your project has strict finishing criteria or detailed notes, a boundary sample can help resolve concerns and provide clarity. Manufacturers can use their knowledge and expertise to produce an output that matches provided examples, reducing the need for detailed notes. If a physical sample is not available, the next best thing would be high-resolution photos taken at various angles. Xometry's engineers and case managers can help you make such arrangements with our manufacturers after placing your order.
Lastly, we recommend including masking notes if your part has any critical features or surfaces that should be guarded against abrasion. Examples of these features are sealing surfaces and o-ring grooves. Although most shops already do this per shop practice, we recommend adding masking requirements for threaded features, especially for small or fine pitch threads.
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