Sheet metal bending for manufacturing and ductwork applications developed gradually during the Industrial Revolution and the first half of the 20th century. During the past 50 years, computerization has improved the process even further. Metal bending has never been in better shape, but the great variety of available techniques presents a fresh challenge — choosing the best solution.
Metal bending allows fabricators to manufacture their target designs, such as V-shapes, U-shapes and channel shapes, using machine tools called press brakes. These are available in a range of sizes (commonly 20-200 tons) designed to fit a wide variety of sheet metal gauges and useful for an array of applications. A press brake contains one tool called the punch and another called the die, between which the sheet metal is located.
Depending on the amount of force needed to create the shapes and other factors, different press brake versions are used: mechanical, pneumatic, hydraulic, and servo-electric. Until the 1950s, mechanical brakes dominated the world market. Today, better hydraulics and computer controls have made hydraulic machines the most popular. Pneumatic and servo-electric machines are typically used in lower tonnage applications.
The Bending Basics (and then some)
Let’s take a look at the choices. To start with, there are three basic types of bending on a press brake: Air Bending, Bottoming and Coining.
This metal bending method involves pressing a punch (also called the upper or top die) into the metal, forcing it into a V-die. A wide range of angles can be obtained. The flexibility of air bending and its relatively low tonnage help to make it a popular choice.
In bottoming, the metal sheet is forced against the V opening in the bottom tool. U-shaped openings can’t be used. Advantages include greater accuracy and less springback. A disadvantage is that a different tool set is needed for each bend angle, sheet thickness, and material.
This technique delivers a more powerful force than air bending, causing permanent deformation through the sheet. There is little, if any, springback. While coining can attain high precision, higher costs mean that it is not often used.
But there are more methods to consider than the three basics:
A relatively new process that uses a die with an adjustable-height bottom tool, moved by a servo motor. Bend angles with 0.25 degree precision can be achieved. Three-point bending costs are high and use is mostly confined to high-value niche markets.
Large sheets can be handled with this process, and the operation is easily automated. Clamping beams hold the longer side of the sheet which can be moved up or down, permitting the fabricating of parts with positive and negative bend angles. There is little risk of surface damage to the sheet.
In wiping, the longest end of the sheet is clamped, then the tool moves up and down, bending the sheet around the bend profile. Though faster than folding, wiping has a higher risk of producing scratches or otherwise damaging the sheet.
Similar to wiping, but the top die is made from a freely rotating cylinder with the final formed shape cut into it with a matching bottom die. Can produce angles greater than 90° in a single hit. Considered mostly suitable for pre-painted or easily marred surfaces.
Roto-Die hydraulic benders and other products like beaders, roll formers, or notchers are either versatile enough to handle various bending jobs, or specialized to take on repeated actions at a high volume. We still know that every now and then, you have to be creative and try a few methods to get your bend just right. How have you had to get innovative with your fabrication process? Tell us in the comments!