From household items to automotive and aerospace applications, aluminum is widely used across many industries. This versatile material offers many benefits, including being lightweight, strong, malleable, flexible and corrosion resistant. But it is a difficult material to work with when grinding or finishing. Choosing the right product, and following some common best practices, can help make the process go easier to get the job done faster and still produce the best possible results.
“Resisting loading is the main objective when it comes to working with aluminum,” says Joe O’Mera, CEO, Weldcote.
Because it’s a softer material with a low melting point, the heat and friction that builds up during a grinding or finishing process can quickly melt the aluminum and make it gummy. The aluminum material that is being removed adheres to the abrasive and “loads” it up, causing the surface of the abrasive to become smooth and unusable. The abrasive will load until it is unable to cut or finish, making it completely useless.
In addition to loading, another common challenge when working with aluminum in welding applications is the potential for porosity and oxide inclusions. If the aluminum oxide layer is not removed properly prior to welding, it can cause these imperfections.
Contamination is also prevalent with when working with aluminum if there is product crossover with steel or if the abrasive contains iron. Abrasives marked as contaminant-free are designed for use with aluminum to avoid cross contamination of aluminum surfaces.
Aluminum is also a challenge because the soft material can be easily damaged with overly aggressive processes. Aluminum is more expensive than other materials, so replacement and repair costs can be high should it be damaged.
Special safety precautions need to be taken when grinding and finishing aluminum. It should be performed in a separate area away from any steel grinding. Even if pure, non-ferrous aluminum is used, sparks can occur when a grinder is used on ferric material (e.g., steel) prior to being used on the aluminum material and vice versa. The reaction, similar to a fireworks explosion, can create 4,500-degree F sparks.
This type of sparking and associated fire hazard may be eliminated by restricting the use of a grinder to only one type of material. In the absence of that safeguard, if grinding under these circumstances creates sparks, it is considered hot work and a fire watch would be required under any of the circumstances described in OHSA standard 1915.504(b).
To combat these issues, many tools and products are available for grinding and finishing aluminum, each with advantages and disadvantages. Understandably, making the right choice for the application can provide better quality, productivity and safety while also reducing downtime and labor costs. Here are some insights on how to choose the right wheel or disc for the job.
“Early on, the same abrasives were used for all materials whether it was steel, carbon, stainless or aluminum because specific products for aluminum were not known or available,” O’Mera says. “But more and more products continue to be added for specific and targeted applications. In the past few years, manufacturers have been developing abrasives with grinding aids that provide better performance on aluminum than traditional abrasives. Users will find that they save a lot of time and labor costs by not having to frequently change out abrasives that have loaded.”
In general, depressed-center grinding wheels, resin fiber discs and flap discs are all appropriate for grinding and finishing aluminum. Each, when used for its specific purpose, can provide the required results.
Depressed-center wheels: These abrasives are best-suited for deburring and grinding applications, such as weld preparation and weld removal. They offer the best wheel life because they have a more resilient and much harder backing than the fiber and flap discs. With that in mind, depressed-center wheels are not recommended for finishing applications.
As an example, Weldcote’s Alu-Prime depressed-center grinding wheel is well-suited for aluminum. The wheel’s combination of silicon carbide and aluminum oxide along with its special bond offer fast stock removal and long life.
The open characteristics of the abrasive are critical for successful aluminum grinding and finishing. During the manufacturing process, the abrasive grains and resin materials are bonded
together at a high temperature to form the wheel. More space is left between the grains, which allows the grains to come out of the aluminum material more readily than if they were spaced tightly together, which promotes the material packing between the grits. The more openness in the grains, the more room there is to release the aluminum material after it is cut.
Resin fiber discs: These abrasives are a good option for grinding, blending and finishing. They have a firm rubber backing pad that offers flat, consistent contact with the material, which makes them easier to control on large, flat or curved surfaces. For non-loading, the best discs are treated with a top coat that prevents the disc from loading and offers higher cut rates, along with a longer product life. Weldcote’s C-Prime ceramic resin fiber discs with a heavy top coat work well. Other products that are used in the grain mixture to resist loading may include paraffin or other inhibitors.
Flap discs: These abrasives combine the best attributes of depressed-center grinding wheels and fiber discs and allow for grinding and finishing in one step. Flap discs are pliable and require higher operator skill to achieve the desired surface finish. Again, the best flap discs are treated with a top coat that prevents the disc from loading.
Weldcote’s Alu-Prime flap discs feature a unique calcium stearate top coat that serves as an effective non-loading agent for aluminum applications, allowing the aluminum material to release from the abrasive. The calcium stearate coating has been found to be highly successful at combating loading and offering a quality finish on aluminum.
The company’s surface conditioning flap discs are an option for aluminum, as well. While these non-woven discs do load slightly, they offer good control for welds and for finishing.
After choosing the type of product that is best for the specific aluminum application, the next challenge is to use it properly.
“With any of these solutions, light pressure and a slow, steady movement is needed to effectively work on soft material such as aluminum,” O’Mera says. “Medium to light pressure is always suggested for aluminum. The biggest mistake operators make is to work too quickly and apply too much pressure. Aluminum is so soft it can be easy to remove too much material.”
Weldcote aluminum flap discs and surface conditioning flap discs are specifically made with a slight angle that allows the operator to use the grinder on an angle to allow for flatter grinding.
When working with aluminum, it is best to use a grinder with adjustable speed, so the operator has the option to reduce the speed. More control can be achieved while working at a slower speed.
Operators sometimes apply their own non-loading agent in the form of some type of lubrication, such as a paraffin or silicone stick. These types of non-loading agents can be effective in adding life to the abrasive because they resist loading. However, the negative is that these products are messy and the operator must clean the material afterward. As a rule, this type of practice is not recommended, according to O’Mera.
Overall, using a product designed for use on aluminum always produces the best results in grinding and finishing applications. These products cut cleanly and smoothly to get the job done quickly and efficiently.
“Ultimately, the key to effective aluminum grinding and finishing is using an abrasive that is constructed to release the aluminum material during the process,” O’Mera says. “If you’re not using an abrasive that has been specifically designed for aluminum, the only alternative is to constantly change wheels or discs with new ones. Discarding abrasives that have been loaded and are no longer effective can become quite expensive.”