Aluminum and stainless steel are commonly used materials across a wide range of fabrication and manufacturing applications. It’s easy to see why they are frequently chosen as they deliver several key benefits such as corrosion resistance and durability.
However, working with either material isn’t without challenges. Many factors – including operator experience and work environment – can impact the results when grinding and finishing these materials, so choosing the right abrasive products for the job is the first step in achieving success. Pairing the proper products with some common best practices helps get the job done faster, reduces costs and time spent on rework, and produces the best possible results.
Challenges posed
Both aluminum and stainless steel have characteristics that can make them more difficult to work with and make it harder to achieve the desired results. It’s important to be aware of some key factors about these materials to be prepared to work on them.
Prone to contaminants: Stainless steel and aluminum are more susceptible to heat and contamination compared to other materials like carbon steel. They can be contaminated if there is product crossover with carbon steel workpieces or if the brush being used has carbon steel wire or the abrasive contains iron. Be sure to use abrasives marked as contaminant-free that are designed for aluminum and stainless.
Softer materials: Stainless steel is a softer material, so it gouges much easier than carbon steel. Take extra precautions when finishing it to avoid removing too much material, which can later weaken the weld. Stainless steel is also highly sensitive to heat, so using too much pressure during grinding or finishing can discolor the material, leading to a secondary process to remove it.
Aluminum is also a softer material with a lower melting point than other materials. As a result, it can gum up or load the abrasive or wire brush during cutting, grinding and finishing. When heat and friction build up during these processes, it can melt the aluminum, causing it to stick and accumulate on the product’s surface (known as loading) and make it less effective.
More expensive materials: Aluminum and stainless steel are more expensive than many other commonly used materials, so replacement and repair costs can be much higher if parts and workpieces become damaged. Mistakes or rework are costly both in labor time and scrap material loss. This makes it even more critical to carefully preserve the material’s appearance and finish when cutting and grinding it.
Aluminum can form an oxide layer: Aluminum that is exposed to the atmosphere contains an oxide layer. If this isn’t removed before welding aluminum, it can cause imperfections such as inclusions or porosity. Remove this layer with a dedicated stainless steel wire brush before welding aluminum.
Abrasive meets the challenge
The basic styles of abrasive products used to clean, cut, grind and finish aluminum and stainless steel are the same as those used on carbon steel. But there are several differences in the composition of these abrasives that make them easier to use and more productive.
For aluminum, many cutting and grinding products are available, each with advantages and disadvantages. Consider these four categories when choosing a product for aluminum.
Coated abrasives: Flap discs and resin fiber discs fall under this category. Coated abrasives are well-suited to removing the oxide layer and are more aggressive than non-woven abrasive products. The best discs are pre-treated or coated with a topcoat that helps reduce heat buildup while grinding. This prevents the disc from loading and offers higher cut rates along with longer product life.
Non-woven abrasives: Products in this category include surface conditioning and coarse stripping discs, and they tend to be used for light to medium finishing work or when a fine surface finish is required. The natural makeup of non-woven abrasives is helpful in reducing loading on aluminum.
Power brushes: Wire brushes are good for prepping and cleaning the black discoloration around aluminum welds. Power brushes can be used to clean without removing any base material or changing the dimension of the workpiece. For aluminum, choose a brush with the smallest diameter wire that will still do the job. This helps prevent loading or buildup. Also, use a stainless steel wire brush to avoid contaminating the aluminum workpiece.
Cutting and grinding wheels: Grinding wheels are often used in structural aluminum applications and when there is a need to remove a lot of base material. Cutting wheels are used everywhere, often for dimensional reasons or creating openings. Grinding wheels tend to be less popular than coated abrasives for grinding general purpose aluminum as the operator typically has less control with a grinding wheel, increasing the risk of gouging the base material.
When working with stainless steel, it’s important to choose wheels that are labeled as contaminant-free or Inox to ensure that they contain less than 0.1 percent of certain elements including iron, sulfur and chlorine. This preserves the stainless steel’s corrosion-resistant properties. Whether or not a contaminant-free product is needed depends on the final requirements of the application.
Coated abrasives designed for stainless steel typically also feature a topcoat that helps reduce heat buildup during the grinding and finishing processes. Certain wheels, like Weiler Abrasives Tiger Inox 2.0 wheels, are engineered to minimize heat buildup to prevent discoloration and maintain the integrity of the stainless steel.
Best practices to follow
Tip 1: Avoid contamination. Optimizing results when cutting, grinding or finishing stainless steel and aluminum starts with choosing a product designed for those materials. This designation is typically marked on the label, although be aware that just because a product is labeled for use with carbon steel or stainless steel doesn’t mean it’s contaminant-free. Bonded abrasive products labeled Inox are contaminant-free. It’s also important to avoid using a product on aluminum or stainless steel after it’s been used on carbon steel, which can introduce contaminants from ferrous material.
Tip 2: Focus on technique. Because aluminum and stainless steel are softer materials that can be easily damaged, always start with a pull-back motion and maintain a constant, fluid motion while grinding (especially with hard wheels). Don’t linger too long in one spot, which can damage the workpiece and cause heat discoloration. When using a wire brush, focus on using the tips of the wires and not applying too much pressure. Keep the product moving, since dwelling in one area too long can build up heat that can damage the base material and result in added time and rework.
Tip 3: Don’t use too much pressure. When using abrasive products, pressure equals heat and heat buildup can more easily damage aluminum and stainless steel. Control the heat when grinding or finishing by minimizing pressure and letting the abrasive work as it was designed. Maintain a moderate and consistent amount of pressure.
Tip 4: Finishing stainless steel is a process. There is no shortcut when it comes to finishing stainless steel to meet specific aesthetic and functional requirements. It’s a multistep process that often requires several products. No one product does it all. For example, it’s common to start with a bonded abrasive for heavy stock removal, move to a flap disc to blend, then use a resin fiber disc to blend the parent material to the weld before finally ending with a polishing or buffing disc.
The abrasives market has changed a lot over the past decade or so. New products designed specifically for aluminum and stainless steel can help improve productivity and finish quality when working with these materials. Because they are softer and more prone to contamination than some other materials, it’s critical to pay close attention when cutting, grinding and finishing them. Choosing the right product and then following key best practices can help operations achieve the best results and reduce the time and money spent on rework and scrap.
