Press brakes are used for bending sheets of metal to a certain angle using tooling known as dies and punches. Although that sounds rather straightforward, choosing the right press brake is not a simple process. To make a wise and informed decision it requires researching series of different factors to determine which press brake options best meet your needs.
Components of a Press Brake
Brake presses usually have an upper and lower section. The upper section holds a piece of tooling such as a punch that normally has a V shape. The lower section holds a matching shape referred to as the die. When the two sections of the press brake are moved together it forces the metal sheet in between to bend.
Background
It is important to identify the nature of the job the press brake will be doing because over 40 different types of forming, cutting and drawing operations can be performed on a press brake. Some operations must be done alone and other operations can be done in combination.
Failing to consider the characteristics of the press brake can be an expensive mistake. It is also important to know what tooling will be needed and if special dies will need to be made or sourced.
The type of metal is also critical to know in order to ensure the press brake has capabilities adequate for the job. General industry press brake ratings are based on mild steel with a tensile strength of approximately 60 ksi (415 MPa).
Metals with higher tensile strengths require proportionately greater tonnage and will have different working characteristics. Some high-strength metals work best when pre-heated prior to bending because they are more brittle than mild steel.
One must also consider the raw material tolerances because there are variations in piece to piece milling metals that can run as much as 50% in hardness and 10% in thickness. Foreign metals often vary even more. These variations make it important to plan for reserve tonnage in order to prevent overloads of machine stalls.
Tonnage
Press brake tonnage refers to the maximum bending pressure or bending capacity of a press brake. It is expressed as the force in tons exerted by the press against a workpiece.
The tonnage the press can exert is a function of the torque it develops as well as the strength and size of its parts. Just as important as tonnage is the energy requirements of the press.
Press Brake Tonnage Chart
(Click to enlarge)
Click here to access a press brake tonnage calculator
All brake presses should have an energy rating as well as the maximum tonnage rating. Every job that is completed needs tonnage and that tonnage must be pushed through a specific distance. When one multiplies the tonnage by the distance the result is the energy in inch-tons that is required to do the work
The first factor to consider in purchasing a press brake is the bending force or tonnage required. In order to calculate that number, you can use formulas or refer to manufacturer tonnage charts. The tonnage required depends on the thickness and length of the plates you will use as well as the metal that will be bent.
Bend Length
The second factor to consider is how long the bend will be. You cannot bend anything longer than the maximum capacity of the brake you choose. For example, if the press brake you want to buy has a maximum bend length capacity of 2 feet then you cannot create a bend longer than 2 feet.
It is crucial to verify that the press brake you choose can handle all parts or sheets from the smallest to the biggest required bending lengths.
Back Gauge
Finally, the back gauge is one of the most critical parts of the brake press. It positions the metal part before bending. It is important to make sure that the back gauge can be easily and quickly changed. A lot of time and productivity can be lost when it takes too long to change or readjust the back gauge.
Pneumatic, Hydraulic or Mechanical?
Another consideration is whether the brake press will be pneumatic or hydraulic. Pneumatic presses use air pressure to create tonnage on the ram and they are designed for smaller jobs that do not require a lot of tonnage. Hydraulic presses have two or more synchronized hydraulic cylinders on the C frames that move the upper and the lower tooling.
In a hydraulic press servo-electric brakes utilize a servomotor to drive a ball screw or belt drive to create tonnage on the ram. Hydraulic presses can move up or down at any point in their operation and can even be tilted by putting different tonnages on each cylinder.
This allows more complicated crowning control. These presses are superior for heavy-duty machinery and bigger jobs because they offer greater accuracy, safety and control. Mechanical presses are no longer manufactured due to safety concerns although used mechanical presses are still available on the market.
In a mechanical press an electric motor is used to add energy to a flywheel. When an operator starts the machines a clutch connects the flywheel to a crank mechanism that moves the ram vertically. Mechanical presses are not very accurate nor can the speed of the ram be controlled.
Mechanical presses are not a good choice for high-end fabrication applications. They can be used successfully in shops that do not need accuracy or control.
The best way to determine the best press brake for your situation is to consult a manufacturer’s tonnage chart. Begin by narrowing down your choice of manufacturer and then begin to study their press brake materials.
It is very helpful to speak directly with the manufacturer to discuss your specific needs because they are very familiar with their press brake products and what applications each machine is best able to handle based on all of the factors discussed in this article and the complexity of a specific client process or application.