Can you grind aluminum workpieces? What are the risks involved and what safety measures should you follow?
Grinding aluminum can be challenging as aluminum melts easily. This molten aluminum can get deposited over the abrasive surface of the grinding wheel covering the grit, and rendering the surface incapable of grinding. Therefore, it is important to take precautions and use appropriate cutting fluid to minimize heat generation.
This article discusses the processes and challenges associated with aluminum grinding.
It also discusses the risks associated with aluminum grinding and how those risks can be eliminated to safely grind aluminum.
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Grinding Aluminum- Is it Safe?
Aluminum is one of the most popularly used metals in manufacturing industries, but grinding aluminum can be challenging as it tends to melt under the heat generated during the grinding operation.
The primary reason for overheating of the workpiece is the use of an improper grinding wheel and lack of coolant.
Grinding aluminum also produces aluminum dust that suspends in the air and can be dangerous if inhaled by the operator.
Apart from that, aluminum dust is highly combustible as it undergoes an explosive aluminothermic reaction when subjected to heat in the presence of metal oxide.
Therefore, it is important to use the right tools and maintain good process control to grind aluminum with a perfect finish.
Factors to Consider When Grinding Aluminum
Selecting the right tool for your application determines the material removal rate and quality of the surface finish.
There are many distinct types of abrasive tools available for grinding operations. A variety of grain types are available in a range of sizes and with different bonding agents.
Type of Grinding Wheel
|Bond Type||Rigid grade bond to prevent dislodging of grains and maximize tool life|
|Abrasive material||Blend of aluminum oxide and silicon carbide|
Material properties help determine the correct grain type to be used.
Hard metals require comparatively greater cutting force when grinding, but their low ductility facilitates easy chip clearance.
For example, grinding stainless steel produces short chips that take away the heat from the grinding area and eliminate the risk of plowing.
In contrast, grinding ductile metals like aluminum produces long chips and requires durable grains that can withstand high temperatures and don’t break down prematurely.
A rigid-grade bond prevents premature wheel wear, thereby maximizing wheel life.
Generally, a grinding wheel with aluminum oxide and silicon carbide abrasives is preferred for grinding non-ferrous metals like aluminum and copper.
The absence of ferrous metals from these wheels eliminates the risk of contamination, ensuring a high-quality grinding finish.
Cutting Force Required for Material Removal
The amount of material to be removed is also an essential factor to consider, as it can help in determining the grain type and grit size.
For operations involving high cutting forces, durable grains are used, as they can withstand these forces without premature failure.
Aluminum grinding requires a comparatively lower cutting force, and mild grains with finer grits can be used to get a clean surface with minimum heat generation.
|Abrasive Type||Use Case|
|Fine Grains||Finishing aluminum|
|Coarse Grains||Roughing with high material removal rate|
Depending on the requirement for higher stock removal or a fine surface finish, you can select the grain size of the abrasive that is best suited for your application.
Fine grits are used for achieving a better surface finish, while coarse grits can provide high material removal rates with a comparatively poor surface finish.
However, using a fine-grain wheel to remove a high volume of material is not recommended as it increases the machining time and the corresponding heat generation.
It is advised to use coarse grain to perform rough grinding and remove the material, followed by a finish grinding by using a fine-grain wheel.
Contact Area Between the Workpiece and the Wheel
Aluminum grinding typically involves a fine-grit wheel, which provides a higher number of abrasive points, leading to a smaller area of contact per grain.
As the contact area per grain decreases, the pressure at the point of contact increases.
Therefore, grinding wheels with hard-grade bonds are recommended to minimize premature wheel wear.
|Wheel Speed||4500-5000 SFPM|
It must be noted that for every 1000 SFPM increase or decrease in the wheel speed, the abrasive acts 1 grade harder or softer respectively.
Therefore, a grinding wheel with a rigid grade bond is recommended for grinding aluminum at high speeds, as it minimizes premature abrasive wear even under high cutting force.
The use of coolant affects the grinding wheel differently based on the type of bonding agent used.
In the presence of a coolant, vitrified bonded wheels act softer due to lubrication, and organic resin bonded wheels act harder because of the lower heat.
Therefore, based on your application, a vitrified bonded wheel can be used for low material removal and an organic resin bonded wheel can be used for high material removal from aluminum workpieces.
The power required to grind the workpiece depends upon its machinability and hardness.
Aluminum is a ductile material that does not require strong cutting forces for grinding.
Therefore, a moderately powerful grinding machine is suitable for grinding aluminum workpieces with a smooth surface finish.
Grinding Tools Used for Aluminum Grinding
|Grinding Tool||Optimal configuration for aluminum grinding|
|Grinding Wheels||Depressed center wheel with aluminum oxide and silicon carbide abrasives|
|Resin Fiber Disc||Zirconia fiber disc|
|Sanding Drums||Interleaf flap wheels|
|Wires and Brushes||Stainless steel or Brass brushes to minimize ferrous contamination|
Although there are various abrasives available, selecting an aluminum-specific grinding tool is critical for safety and quality concerns.
It is also essential to account for the cost-effectiveness, efficiency, material removal rate, tool life, etc., especially for commercial applications where multiple workpieces are to be ground every day.
Grinding wheels or discs contain abrasive grains and fiberglass for reinforcement, bonded together in a circular shape. They are used for deburring and have a longer wheel life due to a more rigid backing.
A depressed center wheel, or Type 27, is recommended for aluminum grinding applications such as pre and post-weld operations.
An aluminum-specific grinding wheel generates less friction and self-sharpens through micro fractures. These wheels generally have a mix of aluminum oxide and silicon carbide grains.
Using non-specific wheels can damage the workpiece and cause severe injuries to the operator by accidents such as exploding of the grinding wheel from overheating.
Resin Fiber Discs
Resin fiber discs are abrasive discs that can perform operations ranging from stock removal to surface preparation. Abrasive grains are bonded onto a vulcanized fiber backing using resins.
These discs provide cool cutting action and are more versatile in their operation but have a shorter life span than grinding wheels or flap discs.
Zirconia grains are recommended for aluminum grinding as they have a longer service life and provide consistent cutting action due to their ability to microfracture, resulting in sharp cutting points.
Flap discs are a combination of grinding discs and fiber discs to perform deburring and finishing operations simultaneously.
It consists of overlapping flaps having an abrasive coating glued to a backing plate. The layered abrasive cloth of a flap disc provides a cushioned surface that helps to achieve an excellent surface finish.
A flap disc that provides load-resistant properties and maintains a low temperature during operation is recommended for aluminum grinding, as it prevents the risk of melting the aluminum workpiece.
Apart from that, selecting a contaminant-free flap disc is vital to avoid impurities from embedding the surface.
Sanding drums are best suited for sanding large areas of aluminum. They help to grind large surfaces quickly.
Interleaf flap wheels are less prone to heat generation during operation due to their design and are capable of performing deburring, sanding, and finishing operations.
Wire Wheels and Brushes
Wire abrasives are used to remove rust, paint or weld spatter, but it doesn't provide a smooth surface finish.
It leaves marks on the surface, which requires further finishing operations to be performed.
Stainless steel or brass brushes are recommended over other materials, like carbon fiber wheels, as they may lead to after-rust.
Risks Involved in Aluminum Grinding
Agency for Toxic Substances and Disease Registry (ASDR) states that usually aluminum dust is not harmful in smaller quantities.
However, grinding aluminum on a regular basis can lead to lung problems, nervous system-related issues, and metal fume fever.
The Occupational Safety and Health Administration (OSHA) has set a limit of 15 mg/m3 of total dust and 5 mg/m3 of the respirable fraction of aluminum dust.
As a result, it is strongly recommended to wear respiratory protection (mask) when grinding aluminum workpieces.
Aluminum dust is highly combustible in the presence of a heat source.
Apart from that, it can undergo an explosive aluminothermic reaction when comes in contact with metal oxides.
This type of reaction can occur if the grinder is used on different materials, as it can create sparks and lead to fire hazards from the accumulated aluminum dust.
Even the suspended aluminum dust in the air at higher concentrations can be combustible or even explosive.
Therefore, proper housekeeping practices, ventilation, dust collection systems, and filters can help minimize such risks.
Using an unsuitable grinding wheel to machine aluminum can overheat the contact area, resulting in the melting of aluminum.
The molten aluminum deposits onto the abrasive surface, resulting in metal-to-metal contact and raising the working temperature.
Therefore, if the right tools are not used for aluminum grinding, it can cause severe injury as the tool may break or explode from overheating.
Furthermore, aluminum is highly susceptible to contaminants as compared with other metals, making it important to select a contaminant-free abrasive to prevent surface contamination.
Aluminum is a soft metal with a low melting point that has an increased risk of gouging, heat discoloration, excess material removal, and other surface defects when machined with improper techniques and tools.
Using improper grinding techniques can result in the melting of the workpiece or cause discoloration under extreme frictional heat.
Hence, it is important to use a cutting fluid/coolant and ensure process control to prevent physical or aesthetic damage to the workpiece.
Factors to Consider to Improve Aluminum Grinding
Selecting the right tools for the job is essential to achieve desired results, but operator skill and experience also go a long way in improving the overall product quality.
Using the right products with the recommended practices can help you achieve better results with reduced costs and a better finish.
While grinding, initiate the process with a pullback motion and maintain a steady to-and-fro motion. Avoid lingering in one spot for extended periods to avoid heat buildup and discoloration.
Using constant moderate pressure and an increased number of spark-out passes can result in a high-quality finish.
Pushing harder to achieve a faster cut rate generates more heat and can be counterintuitive.
Glazing and loading are the most common reasons for the termination of the useful life of an abrasive. Lubricants are vital in producing a better finish and increased tool life.
Adequate lubrication will minimize metal loading on the surface while keeping the temperatures down, leading to a faster cut rate and longevity.
Lubricant should be applied before starting the grinding operation to achieve maximum benefits.
Continuous or flood lubrication should be used wherever the operations permit. Dry lubricants such as grease and wax sticks can be used where wet lubricants are inconvenient.
In smaller projects where efficiency, longevity, etc., are not the primary concerns, grinding can be done using sandpaper.
To grind the workpiece with sandpaper, start with a smaller grit size for heavy sanding and high material removal, followed by finer sandpaper based on the type of surface finish required.
Applications of Aluminum Grinding
Grinding of aluminum workpieces is performed to prepare them and remove contaminants such as the oxide layer, oil, paint, grease, etc., from the surface to attain perfect weld quality.
This is done because, welding without preparing the surface can lead to low weld strength and poor fatigue resistance.
Aluminum grinding is also performed for post-weld blending and leveling to clean the weld and the surrounding metal, removing slag, weld spatter, and other welding defects.
Furthermore, grinding aluminum is also performed to enhance the surface finish of the workpiece, and is known as finishing.
It is a multiple-step process, where finer abrasives are used progressively until the desired surface finish is achieved.
Grinding aluminum is a complicated process and requires the user to consider various factors to achieve optimal results.
There are also various health and safety concerns associated with the process. If proper procedures and precautions are not followed, it can lead to significant accidents.
Using aluminum-specific grinding tools and techniques make the process completely safe and effective.
However, it is essential to wear proper personal protective equipment to minimize other risks associated with it.
Frequently Asked Questions (FAQ)
What type of grinding tool is suitable for aluminum?
The most commonly used grinding tools for working with aluminum are grinding wheels, resin fiber discs, and flap discs. Each tool has its specific application and considerations. Proper use and selection of these products can help you achieve desired results.
Is it safe to grind aluminum?
Yes, it is safe to grind aluminum, provided that you use the right tools and follow the safety protocols. Its low melting point and exothermic reactions with metal oxides are the concerns that you need to look out for when grinding aluminum.
Can you use an angle grinder for aluminum?
Yes, an angle grinder can be used on aluminum workpieces for various operations such as sanding, polishing, and cutting. However, using an aluminum specific abrasive is mandatory for safe and effective operation.