In press brake work, the die size that a person select for a given job will have an impact upon the force that must be used, the geometry of that die, and upon the way in which the metal respond to that force. If a person chooses the wrong tooling for the job, then the wrong tooling may lead to the metal cracking at the edge of the part, or the wrong tooling may overload the press brake machine itself. The upper punch will determine the type of bend that a person are able to make with the press brake, and the upper punch will also determine how the part will clear the tooling that the press brake has created during the next operations performed on that part.
For example, straight punch are used for creating 90-degree bends in metal parts, but goosenecks punches are used for allowing for clearance of other metal components, such as those require for creating box shapes. Additionally, acute punches are used for creating metal parts with relatively sharp angle, radius punches are used for allowing those parts to include softer curves, and offset punches are used for creating steps within the metal part. The lower die opening will impact the tonnage that is required to bend the metal part, as well as the radius of the bend that is created by the metal part.
How to Choose the Right Die Size for Bending Metal
Narrow die openings will require more pressure to bend the metal, and may even crack the outer surface of that metal part. In contrast, wide die openings will lower the tonnage that is required to bend that metal part, and the wide die openings will create a larger inside radius of the bent metal part. A person can use the reference grid to determine that the die opening should be roughly six to eight times the thick of the material that is to be bent.
For stainless and aluminum metal parts, however, a person should use a narrower die opening for those metals, respectively. Springback is another factor to consider in the decision of the size of the die opening that is to be used in the press brake. Mild steel will springback two or three degree after the punch that bent the metal part is removed from the metal part.
Stainless steel, however, will springback more than mild steel due to the higher strength of that metal. Aluminum metal will springback even more than stainless steel. To account for springback, a person can overbend the metal part by the amount that is expected the part will springback.
The only way to know for sure, however, the amount of springback that will occur is to create a test part made of the same metal as the parts that are to be created. Tonnage is another calculation that a person must perform before starting the press brake machine. A formula is used to calculate the tonnage that will be required to bend the metal.
Additionally, if a person sets the press brake machine to run near its upper limit of tonnage, the bed and the frame of the press brake may deflect under the metal part. Therefore, a person should operate the press brake machine well under its tonnage limit. The punch tip that is used to bend the metal part and the opening of the die opening will create the inside bend radius.
The radius of that bend will be roughly one-sixth of the V-opening of the press brake die opening. This dimension will remain one-sixth of that V-opening, regardless of the type of punch tip that is to be use. Thus, a person cannot create a radius that is smaller than this value by the use of a different punch tip.
Many mistake are made in the operation of a press brake machine. For example, one of the most common mistake is to use a die opening that is too narrow for the thickness of the metal parts that are to be made. Such use will overload the tooling and the machine itself.
Additionally, if the springback of the metal part is not accounted for, the part may not meet the order of the angle of the part. If the punch and die opening are not properly aligned, the part may become twisted. Finally, if the punch tips has worn with use, the radii of the bends may not be consistent.
The direction of the grains of the metal sheet is another factor to consider before bending the metal. If the metal part is to be bent in a direction that is parallel to the rolling direction of the metal sheet, the part may crack on the outside of the metal part. In contrast, if the part is to be oriented in a direction that is perpendicular to the metal sheet’s grain, the part will have a better chance of not developing a crack.
The reference grid includes information regarding the recommended die openins, minimum lengths of the flange of the part, springback information, and tonnage per meter for metal parts made of mild steel. These dimensions are guidelines for the worker, and are not absolute rules that must be followed. A person can use the reference grid to determine if the setup that is to be create for the metal part is within the normal parameters for that metal part, and to avoid having to calculate each of these values for each metal part that is to be manufactured.
Thus, getting the die size right for a given metal part means that a person must match the tooling to the metal part and to the requirements of the finished part.
