Today, we’re talking about press brake metal forming basics. But before we dive right in, I’m sure many of you are wondering about the history behind the name of the press brake.
In the 15th-century, the brake was defined as “an instrument for crushing or pounding.” This term changed slightly over the years. But, ultimately, “brake” became synonymous with “machine.” So in the term’s simplest form, a “pressing machine” and a “press brake” are the same.
With the development of technology, the press brake machine evolved from manual press brake to mechanical press brake, hydro-mechanical press brake, hydraulic press brake, and the electro press brake. No matter what it’s called, though, the “press brake” still refers to the machine used for “bending.”
What Is Press Brake Forming?
Press brake metal forming is one of the oldest mechanical metal deformation processes. During this process, a piece of metal is “formed” along a straight axis.
This “forming” is accomplished by a punch and die set. The set can be “V”- shaped, “U”-shaped, or channel-shaped.
Although press brake metal forming appears a simple concept, maintaining accuracy can often be quite tricky.
The equation for precision bending involves the press, the tooling, and the workpiece material. Metal properties such as yield strength, ductility, hardness, and the material condition all affect the amount of spring-back of the material.
Characteristics of the press brake metal forming process include:
- The ability to form ductile materials.
- The press’s use in both low- and medium production run applications.
- The need for minimal tooling.
- Its suitability for producing smaller parts.
- The output of long workpieces using a “V,” “U,” channel, or other impressive punch and dies.
What Metals Can Be Formed In A Press Brake?
Metals commonly used in the brake forming process include:
- Cold-rolled carbon steel
- Hot-rolled carbon steel
- Sheet metal
- Stainless steel
Press brake metal forming can commonly form metals up to 10″ thick. Some press brakes will include pieces as long as 20 feet.
Types Of Press Brake Forming
The three types of press forming most often employed by metal fabricators include air bending, bottom bending, and coining.
Air bending is the most common industrial press braking process. Air bending relies upon three-point bending. The bend’s angle is decided by how far the punch tip penetrates the “V” cavity. The greater the penetration of the punch tip, the greater the rise achieved.
Air bending’s main benefit is that it uses much less force than other methods to achieve a 90° bend. This is due to the leverage effect.
With air bending, the metal makes even less contact than with bottom bending. The tooling only touches the material at three points: the punch, tip, and the die shoulders.
The factor that determines the bend’s angle is how far the punch descends into the die. The further in the force descends, the more acute the resulting angle.
Because the depth of the stroke (and not the tooling itself) determines the bend angle, one can get a wide range of bend angles from one set of tooling.
Since force doesn’t produce the bend in air bending, you don’t need as much power as you do with coining. Like bottom bending, there will be a certain amount of spring back expected with air bending. That said, you will likely need to bend to a slightly more acute angle to get the final bend you want.
In bottom bending or “bottoming,” punch and die are brought together so the metal contacts with the punch tip and the sidewalls.
Bottom bending differs from coining in that the punch and die don’t make full contact with the metal. Also, there isn’t enough tonnage used to imprint or thin the metal.
Because bottom bending uses less force than coining, the material doesn’t entirely conform to the tooling’s bend angle. In fact, with bottoming, the metal experiences a “spring back,” which happens when it relaxes to a broader angle after being bent. So, with bottom bending, to get a certain angle, you need to use tooling that has a slightly sharper angle to account for the spring back that will naturally occur once the sheet metal is released. Different thicknesses and different materials result in different amounts of spring back.
The term “coining” comes from coin making. To put Lincoln’s face on a penny, machines using too high force compress a disc with enough power to make it conform to his image inscribed on the die set.
In that same vein, “coining” with a press brake involves using enough force to conform to the punch’s precise angle and die used.
During the process of coining, the metal is more than bent. It is thinned by the punch and die’s impact, as it is compressed between them and along the bending surfaces.
The theory behind coining is: with enough force, your metal will bend to the precise angle of your tooling. Therefore, your tooling should be an identical match to the grade you want.
Hiring A Metal Press Brake Forming Pro
Metal forming on a press brake used to be pretty straightforward. Pick a V-Die at the angle you desire. Run the punch into the material, forcing it down to the bottom of the die. Then push it just a little more, 10% of the material thickness or so.
Fast forward to today….
We have introduced Computer Numerical Controls (CNC) and much more accurate control of the ram depth. As the CNC technology developed, manufacturers begin to incorporate more and more “logic” into them, thus simplifying the layout and setup process.
Today’s press brake metal forming is faster, more accurate, and much more reliable.