Rolling aluminum plates can be a challenging endeavor, especially when dealing with relatively thick nonferrous materials like 1/8-inch aluminum plates.
Understanding Aluminum’s Behavior
One of the initial concerns when working with aluminum is its susceptibility to cracking when exposed to heat. It’s a common misconception that aluminum will invariably crack when heated. However, this typically occurs when the bend angle exceeds 80 degrees complementary, especially in aluminum grades like T4 and T6. These grades can be softened through annealing, making them more malleable, similar to mild carbon steel.
Mitigating Cracking and Breakage
To avoid cracking or complete breaking, it’s crucial to consider the material’s grain direction during bending. Bending across the grain, rather than with it, is less likely to result in damage. Additionally, the risk of cracking can be exacerbated by corrosion, which manifests as “white rust.” Corrosion weakens the material’s surface, making it more prone to cracking under sustained stress.
The Role of Passive Oxide Film
During the cooling process of aluminum alloy plates, a thin, smooth, transparent, passive oxide film naturally forms on the surface. This film, typically between 0.001 and 0.0025 inches thick, is not detrimental to the material; in fact, it acts as a protective barrier against corrosive elements. However, when heating aluminum for bending, it’s essential to be aware that this oxide film forms a hard outer shell as the material cools. Excessive heating, especially with an acetylene torch, can lead to “blowouts” or “burn-throughs,” as the film melts at a higher temperature than the base aluminum.
Selecting the Right Equipment
When it comes to bending thick aluminum plates, selecting the appropriate equipment is crucial. While some may consider purchasing inexpensive slip rolls for hobby or home use, these tools may not meet the quality standards required for production. Aligning and maintaining the accuracy of such rolls can be a labor-intensive process. Alternatively, constructing a homemade slip roll can be even more challenging, as slip rolls are complex machines. For consistent and efficient results, investing in a used power roller or reviewing various types of slip rolls, such as 2-roll, 3-roll pyramid, and 4-roll variable machines, is recommended.
Consider Material Condition
The choice of aluminum material condition is also a critical factor. To minimize the risk of cracking and breaking, consider using aluminum in the “O” condition, where the material is soft and easily bent or rolled. After forming the pieces, they can be sent for tempering to achieve the desired hardness state. However, it’s essential to anticipate dimensional variations caused by tempering, such as changes in radius, and make necessary adjustments during subsequent processing.
Subcontracting for Efficiency
Expanding your shop’s equipment repertoire should be a carefully considered decision. If the job doesn’t justify the investment in new equipment, subcontracting to professionals with the necessary expertise and equipment can be a financially prudent choice. This is particularly true for rolling, as it often takes time for operators to master the art of producing consistent workpieces, especially with complex machinery. Subcontracting can offer a cost-effective solution and allow you to focus on your core strengths.
Conclusion
Rolling aluminum plates, especially when dealing with thickness and potential cracking, demands careful consideration of techniques, equipment, material condition, and the value of subcontracting. By understanding the material’s behavior and employing the right tools and methods, you can successfully overcome challenges in aluminum plate rolling while achieving the desired results.