Press brakes (or brake presses) are some of the most common machines used by sheet metal fabricators and have been the go-to bending machines for many years. Press brakes are powerful machines that are capable of forming both simple and complex parts.
While there are dozens of different press brakes in various sizes and each with unique characteristics and capabilities, we will only discuss the three main types of press brakes along with the three main types of press brake forming.
How it Works
Press brakes perform bends on metal sheets through the use of a punch that forces the metal into a die. Punches and dies can come in different shapes and angles depending on the desired bend, and the tooling used in the machine may need to be switched out between bends to achieve different results. The amount of force (or tonnage) and the shape of the die determine the angle of the bend. Sometimes a workpiece requires multiple repetitions of a punch to achieve the desired bend angle. Press brakes are typically very long and shallow machines to allow wide metal pieces to be bent. The width of the machine determines the maximum bend length of a workpiece.
Types of Press Brakes
There are three main kinds of press brakes on the market today.
Mechanical press brakes operate through a motor that turns a flywheel at high speeds. The operator uses a clutch to control the wheel and move the rest of the parts to make the bend. It’s the oldest type of press brake and fairly simple to operate. However, adjusting bend angles frequently can be time consuming, so a mechanical press brake is best for easy, repetitive jobs. Also, the ram must complete a full cycle without the possibility of interruption, so if a mistake is made it cannot be prematurely canceled.
Hydraulic press brakes use hydraulic arms to force the ram down. They offer a higher level of control and accuracy than mechanical brakes, as well as multiple ram speeds and faster set up.
Electric press brakes are the newest iteration but tend to be sturdier and more accurate. They are specially designed for more precise and intricate bends. They have a slower approach speed than hydraulic presses, but have faster ram acceleration and deceleration into position. Therefore, they are faster overall in output and bending speed.
Types of Press Brake Forming
There are three major methods of bending: air bending, bottom bending (or bottoming), and coining.
This is the most common method of bending and requires the least amount of force. The metal sheet comes in contact with the top “shoulders” of the V-shaped die and is pressed down just enough to achieve the bend, never touching the bottom of the die. The space between the sheet and the bottom of the die is open, hence the name “air bending.” As mentioned before, this method requires the least amount of force; another major benefit is that the punch radius and the die radius do not need to be the same, and the die can be any size equal to or larger than the desired bend angle. This saves time and money because less die size variations are required to achieve a range of angles and the dies have to be changed out less frequently.
When bending a sheet there is always the potential for “springback,” or the bend angle relaxing and widening out slightly after the bend. Different types and grades of metal respond to forming differently, so the level of springback varies depending on the material. Air bending is most susceptible to springback because it uses the least amount of force of any method. To combat this issue, press brake operators may need to sharpen the programmed bend angle slightly in order to achieve desired results. For example, achieving a 90-degree angle on the finished product may require programming an 88-degree bend on the machine. Overall, air bending is fast and efficient but not as accurate as some other methods.
In this method, more force is applied by the punch so that the sheet makes full contact with the die. “The punch nose presses the sheet metal until it “bottoms” at the bottom of the die, stamping the punch nose radius into the bend and forcing the sheet metal against the die angle” (The Fabricator). The sheet touches the bottom of the die, hence the name “bottom bending.” Because more force is used, the potential for springback is reduced (but not eliminated) and a more precise angle can be achieved. However, the die must match the desired angle exactly, requiring a larger range of tooling sizes on hand and the additional time to change them. A separate tool set is required for every bend angle and material thickness.
This method requires the largest amount of force, but is also the most accurate. As a coin would be punched to achieve a highly repeatable inscription, so in the “coining” method, the sheet is punched with enough force to ensure permanent shaping. The punch forces the sheet to the bottom of the die, applying excess pressure at least 5-10 times stronger than air or bottom bending. The punch tip actually penetrates into the workpiece, relieving internal stress which reduces springback to virtually zero and results in a precise, highly repeatable bend. The penetrative force means the bend radius is always equal to the punch tip radius. Coining can be achieved without sophisticated CNC machines; however, the force required for coining puts greater wear and tear onto the machines than air bending or bottom bending.
How to Determine Which Type of Bending to Use for Your Project
Understanding your material’s ductility and springback is a key step in figuring out which method to use. A less ductile metal will require more forceful bending than a more ductile, malleable metal will. If you need a highly accurate bend, coining may be the way to go. If you have more room for variance, air bending is a quick and efficient option. Your fabrication partner will be able to help you determine the best press brakes and bending techniques for your project.
Estes Press Brakes
Since 1976, Estes has invested in the best people and the latest equipment to produce high-quality precision sheet metal parts and products. We utilize 11 different press brakes with various capacities to fit all of our customers’ needs, including our Amada HG 1003 with automatic tool changing capabilities. A previous blog on the Amada press brake reports that “punches and dies are automatically loaded and unloaded with four tool manipulators….The result is an expected reduction in setup time from 40 minutes to less than 10 minutes. Reduced setup times translate into lower costs and increased throughput, which shortens lead-times.” We also have a press brake specifically for our Estes Accelerator program, dedicated to meeting prototype needs with speed and efficiency.
Whatever capabilities you may need, Estes is ready to work with you. Contact us today to see how we can help you on your next sheet metal fabrication project!