When working with heavy metal and bending processes, the thickness of the material determines the rules of bending the piece of material from metal sheets, steel, and aluminum. With innovation and technology over the years, working with a heavy-duty metal bender requires accurate bending force pre-calculations. The calculations include the thickness and strength of the material before working with it; additionally, the chemical composition will help identify where to place and bend the material.
Ultimately, you need to understand that the outer surface will take on some expansion in the bending process, and the inside is compressed. Depending on the thickness of your material or pipe, this will determine how far you can bend it without breaking the edge or making it fragile before use. Materials like soft aluminum and mild steel are more flexible than hard and robust metals; therefore, they can be bent more to sharper edges. Generally, these materials come with recommended bend radius by the manufacturer and should be followed to avoid failure.
Grain Direction
Running parallel to the rolling position, grain direction is essential when forming a bend, especially when working with the plate. Whether you create a vertical or longitudinal shape along the grain direction, not much bending force is required. When the material is stretched on the outer surface during the bending process, the grain spreads and cracks may begin to open.
A more effective bend radius is required to prevent this from happening or mitigate the damages; this will retain the tonnage while giving allowance for a tighter radius bend without cracking the outer surface.
A Rule of Thumb
To determine the minimum bend radius of steel, the rule of thumb is to divide the material’s specific tensile, given by the manufacturer, by 50. This trick and value usually work with aluminum and varies by grade. However, this is not set-in stone; when working with aluminum plate or steel, more research is required to determine the actual minimum bend radius. The answers are pretty much there at your disposal; the manufacturer will offer data on how to bend with or against the grain and how to apply each technique.
Localized Stress
The forming outcome of the material is highly influenced by localized stress, limiting how compressed the bend radius can be. Laser cutting and thermal processes are more likely to harden the surfaces and create tension constraints on the material. You may need to sharpen corners and remove surface gouging along sheared edges to help remove or reduce microfractures in essential areas. Between 200- and 300-degrees F, preheating the material in uniform is vital to achieving a tight bend radius, especially on thick and heavy material.
Spring Back
All materials experience spring back upon being released from the bending forces, including plastics, aluminum, and heavy steels. The material strength determines the direct yield of spring back, which is the elastic strain released in the process. High-yield-strength materials like aluminum and steel require a greater bend angle to achieve the desired angle. Always remember the spring back increases in direct proportion as the bend radius increase. Excessive spring back can be compensated with the right die angle and width.
Hot Forming Steel
When steel is heated between 1600 and 1700 degrees F, hot forming occurs. The benefits of hot forming steel reduce and eliminates distortion of the grain structure, cracking of the radius, and strain to harden. As a result of the high temperature, the plate’s molecule structure is changed and causes it to be recrystallized. Should you want the plate in its original form again, you may need to reprocess it.
Hot forming is the better option compared to cold forming; it offers a higher degree of formability and eradicates the need for tonnage. Like anything, hot forming has its cons, like causing oxidation, decarburization as a defect, and steel losing valuable carbon content.
Hot Forming Aluminum
Any aluminum material harder than 5054 may require annealing and heating along the bend line during the bending process to avoid cracks or breaking while forming. Unlike steel, aluminum needs about 865 to 1240 degrees F to melt. Although aluminum heats, recrystallizes and bends like steel, it may not respond the same way; aluminum has more spring back in many cases.
Before aluminum melts down, it goes into a malleable process, gets brittle, and melts down. Avoid heating aluminum to its melting point because if you try bending it in that state, you stand a chance of cracking and breaking the workpiece.
