Last article,we send a brief introduction of press brake,from manual press brake to hydraulic press brake,and then on to cnc press brake,many choice when we shop for a new brake for our job shop or production floor.This is not the trivial matter because once you made the wrong decision, your production cost will surge and your cost recovering gonna be an impossibility.
so we make a guide of buying press brake for our customers.Use this guide to know what you’re looking for before you begin shopping for your next press brake.
Important factors to consider when purchasing your next press brake include the material you wish to bend, the flanges and other bends you wish to make, your operator experience and braking knowledge, operating costs, speed, and how much you are able to invest in your new machine.
Here we summary 7 factors which will help you to make the right choice when you purchasing the press brake
The first one you need to know is What size press brake should I buy?
The most important factors when purchasing a press brake are the tonnage and bending length. These specifications are determined by the size and thickness of the material you will bend.
Knowing your application in advance and planning accordingly will help you to make the best decision.
The point is you need to purchase one press brake which can help you finish the processing task,moreover this press brake have the shortest worktable and and the minimum tonnage.
The press brake’s bending force, known as tonnage, determines how much pressure can be applied by the punch during a bend. Higher tonnage allows for bending thicker and harder metals, and lower tonnage is most appropriate for thinner metals.
The bending length of a press brake is the maximum possible length of a metal sheet which can be bent.
If you have a very small press brake with 4ft bending length, you won’t be able to bend a 6ft piece of sheet metal because it would be too long. You want to get a press brake with a bending length that is slightly larger than the length of sheets you will be bending.
Check the sheet metal types as well as maximum thickness and length,if most of your processing is the low carbon steel metal with max 16 gauge thickness and 10ft length, then the free bending force has no need to exceed 50 ton.
However, if you need to process hollowing block at the bottom, probably you should consider purchasing one press brake with about 160-ton force.
If the sheet metal is 1/4 inches thickness,10ft length with free bending,then you should purchase 200-ton press brake. and if hollowing block at the bottom, probably you should consider purchasing one 600-ton cnc press brake,If the sheet metal is 5ft length or shorter,the tonnage should be half.small smart cnc press brake is the best choice.the length of the work piece is one of key factors in your choice for the suitable press brake.
pls refer to this how-to-calculate-bending-force
Why are the tonnage and length so important?
These factors are important because every press brake has a concentrated load limit which is calculated in tons per inch, in the center of the press. Using the wrong tonnage can damage the press ram, the die or the working part, and in the worst case, could ruin the machine.
During the bending process, especially bending those long work piece, the CNC press brake must have deflection. The longer of the work piece, the larger deflection of the press brake.
Under the same load, the deflection of those press brake which processing 10ft sheet metal is four times than those processing 5ft sheet. the shorter press brake with less gasket adjustment make qualified products. Reducing the adjustment of gasket also help short preparing time.also the types of sheet material is a key factor.compare with the low carbon steel,the loading of the stainless will Increase by about 50%.and most of the aluminum sheet loading will reduce by 50%.The good thing is, most CNC hydraulic press brakes have already added hydraulic deflection compensation function during the manufacturing process, which is helpful for reducing operator’ S adjustment of machines. Meanwhile, it improved the accuracy of bending as well as production efficiency.
Hydraulic deflection compensation function is controlled by the CNC system.
Hydraulic oil enters into compensation oil cylinder via a magnetic servo valve, and push the worktable upward. At the same time, the deflection compensation force increased with the bending force of the press brake, which plays the function of deflection compensation
Bending radius of the workpiece
During the bending process, the bending angle radius of the workpiece should also be taken into consideration.The bending radius is 0.156 times compared to the V groove opening dimension.During the free bending process, the dimension of V groove opening should be 8 times larger than the thickness of the metal sheet.For example, if use press brake with 1/2inch V groove opening to bend 16 gauge low carbon sheet metal, the bending radius should be 0.078inch. If the bending radius close to the thickness of the metal sheet , then bottom hollowing mold should be used. However, the pressure will be four times larger than free bending.For free bending, please pay attention to the clearance between the punch and die at the bottom of the stroke, and the resilience of when bending sheet metal with 90°.If the bending radius less than the thickness of the metal sheet,it should use bending radius convex larger than thickness of sheet.by embossing bending method. This requires 10 times the pressure of free bending
Generally, the free bending mold will generate less than 2 degrees’ resilience angle on the new press brake. And the bending radius equals to 0.156 times of down mold opening distance.
Thus, for common free up and down bending processing, the mold angle will be 86° -90°.
At the bottom of the stroke, there should have one clearance which is slightly larger than the thickness of sheet metal.
Bending accuracy requirement is one serious factor
It is just the factor that determines you choose CNC press brake or common NC press brake. If the accuracy requirement is +0.5 degree and can’t be changed, then you should put your eye on CNC press brake. The repositioning accuracy of the ram can be controlled at t0.01mm. So for those highly precise finished products, you have to choose such press brake with high accuracy and good performance.
However, the ram’s repositioning accuracy of NC press brake is about +0.5mm. Under the proper condition of the punch, it still will cause +2~3 degree deviation.
Besides, CNC press brake always equipped with CNC controller for quick punch installation and clamping. If you need to process many small parts, then this factor has to be your first consideration.
The reason why the angle of punch improved is that larger bending tonnage of hollowing block dies been used (4 times bigger than free bending mold).
This is helpful for reducing resilience force within the scope of bending radius.
Bottom bending is the same as air bending.The only difference is the front end of the punch been turned into the bending radius which
gonna be needed.Meanwhile, the resilience force is avoided because the clearance between the punch and die at the bottom of the stroke is less than the thickness of sheet metal, plus enough pressure force (10 times than free bending), the front end of the punch will contact with the sheet metal.
In order to choose the press brake with the lowest tonnage, you better choose the one with bending radius larger than the thickness of sheet metal. And choose free bending because large bending radius will not affect the quality of finished products and will ensure the long service life of the press brake.