Curling sheet metal is the process of adding a hollow, circular roll to the edge of the sheet. The curled edge provides strength to the edge and makes it safe for handling. Curling is different than a tear drop hem because in a curl the edge finishes inside itself, where a hem leaves the initial edge exposed. Sheet Metal Hems are formed using very different methods, though produces features with similar uses and functionality. Curls are most often used to remove a sharp untreated edge and make it safe for handling.
Curls come in two basic forms, off center and on center rolls. Off center rolls have the center of the roll above the original plane of the sheet metal. On center rolls will have the center of the roll in line with the plane of the sheet metal.
The type of curl you produced is a matter of design intent and the machinery available. As we will discuss below the process of forming a curl is different for each type of fabrication machine. Because of this certain machines will lend themselves towards one style or another.
Forming A Sheet Metal Curl
How a curl is formed depends entirely on the type of machinery you wish to use. Curls can be fabricated through roll forming, stamping, leaf bending, and on a traditional press brake. Each machine will have its own set of tooling for achieving the curl. Here we will be discussing the fabrication and tooling methods for forming on a leaf bender and press brake.
Forming a Curl on a Panel Bender
Curling on a panel or leaf bender is often limited to off center curls because most panel benders do not have tooling profiles which can create the necessary down bend to put the curl on center. Off center rolls however are very easily formed on this type of machine. The desired radius is created by Step Bending a progressively larger radius into the sheet, beginning with the desired curl radius minus the material thickness, and ending with the desired curl radius. The smaller radius is formed first to allow the material to finish inside itself. The process of step bending involves producing very small bends in very close to each other, and while the finished bend is technically a polygon, it’s often impossible to detect the steps if they are formed correctly. For lighter gauges a hand operated panel bender can be the most affordable method for creating a curl.
Forming a Curl on a Brake Press
To curl sheet metal on a Brake Press specialized tooling is required. Most curls are formed in three stages and some setups require two tooling setups with specialized tooling for each stage. The first 2 stages form the curves required to form the curl, and the third stage closes the curl. A locating notch is typical for this type of tooling to ensure that the first and second stages are bent in the correct location. Below is a typical two setup, three stage tooling.
Because of this the tooling is typically unbalanced, meaning the tonnage isn’t evenly distributed front to back, so stabilizing features are sometimes incorporated. When a stabilizing bar is used it allows for the two stages to be combined into one set of tooling. Below is an example of a one setup , three stage tooling.