In bending sheet metal using a press brake, choosing the right bend radius is essential. One type of mistake related to bend radius called a sharp bend occurs often in press brake bending and has the potential to skew calculations and affect your product's final quality.
Let's take a look at what a sharp bend is and what custom metal fabricators like APX York Sheet Metal do to avoid it.
What Is a Sharp Bend?
In metal fabrication, a sharp bend is defined as the smallest bend radius you can apply to a material during air-bending without actually stamping it. It may differ from a material's minimum bend radius, which is the smallest possible inside radius you can physically produce.
In a sharp bend, the small bend radius allows the upper die in your press brake to push into the surface of the material. Instead of bending the sheet metal evenly, a crease forms down the center, exaggerating inconsistencies in bend angle between workpieces — after all, it's very difficult to get material to crease the same way every time. Sharp bends can cause even small variations in thickness, yield, grain direction and other metrics to balloon into larger, more noticeable problems. When manufacturing custom parts, slight bend angle inconsistencies turn into big problems in dimension.
Sharp bends can also render parts unusable in some industries. Aircraft components, for example, must generally be free of creases and other imperfections and have a one-to-one ratio of bend radius to material thickness to be considered viable.
What Causes a Sharp Bend in Sheet Metal?
A sharp bend occurs when the bend radius used is too small for the type of material you're bending. Because the bend radius relies on the punch radius, the tonnage applied and the tensile strength of the material, all of these factors influence the formation of a sharp bend. As a result, changes in punch radius, forming tonnage or material could create a sharp bend.
Sharp bends occur in metal fabrication for several common reasons, which relate back to the variables that produce bend radius:
You're using a punch radius that's too small for the material.
You're using a tonnage less than the material's yield strength.
You're using a punch radius smaller than the material's minimum bend radius.
How Can You Avoid Creating a Sharp Bend?
The best way to avoid creating a sharp bend is to account for it in your calculations. You can do so by choosing a punch radius and tonnage appropriate for the material. One rule of thumb to avoid a sharp bend is to use a punch radius larger than 63 percent of the material thickness. For a more precise estimate, multiply this amount by a factor that describes the strength of the material in relation to cold-rolled steel.
Contact the Metal Bending Experts at APX York Sheet Metal
Creating custom parts using press brake bending requires great attention to detail. By choosing the right punch radius, tonnage and material for the application, you can avoid sharp bends and increase part consistency.
At APX York Sheet Metal, we have 71 years of experience in custom metal fabrication. We specialize in bending and tackle each step in-house to ensure that every detail of your fabrication project is handled correctly. Contact us for a free quote to learn how we can create custom parts that meet your specifications.