How to choose a press brake: 7 factors you should consider
CNC press brake and other CNC equipment are different in aspect to processing field and technology, so as the manufacturers, you have to take full consideration (including the application, deflection, bending radius of parts, etc) before you made the decision to buy it. As the decision maker, you gonna have the responsibility to understand the performance, processing range, function, precision of press brake.
This is not trivial matter, because once you made the wrong decision, your production cost will surge and your cost recovering gonna be impossibility. Therefore, you should take below 7 factors which will help you make right choice before purchasing into consideration:
The point is you need to purchase one press brake which can help you finish the processing task, rather than the one with shortest worktable and the minimum tonnage.Check the types of steel sheet as well as the max thickness and length. If it’s low carbon sheet metal with max 3mm thickness and 2500mm length, then the free bending force have no need to exceed 80 ton.However, if you need to process hollowing block at the bottom, probably you should consider to purchase one press brake with about 150 ton force.If the sheet metal is low carbon steel with 6mm thickness and 2500mm length, then you should purchase 100 tonpress brake.
If you need to bending sheet metal with hollowing block at the bottom (levelling bending), then you gonna need large CNC press brake.If the sheet metal is about 1250mm or shorter, then smaller CNC press brake should be choosing, even half above size.In this way, your purchase cost will decrease a lot.You should memorize that the length of sheet metal is one of the key factors for you to choose suitable press brake.
During bending process especially bending those long work piece, the CNC press brake must have deflection. The longer of work piece, the larger deflection of press brake.Under the same load, the deflection of those press brake which processing 2500mm sheet metal is four times than those processing 1250mm sheet. That is to say, the shorter press brake with less gasket adjustment will make qualified products. Reducing the adjustment of gasket also help short preparing time.
The good thing is, most CNC hydraulic press brakes have already added hydraulic deflection compensation function during 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 CNC system. Hydraulic oil enters into compensation oil cylinder via magnetic servo valve, and push the worktable upward. At the same time, the deflection compensation force increased with bending force of press brake, which play the function of deflection compensation.
Compared with low carbon steel, the load need to increase about 50% for stainless steel. But for soft aluminum sheet metal, the load will decrease 50%. You can get the standard bending pressure parameters from CNC press brake manufacturers. The data sheet shows the bending force which will be needed for 1000mm sheet metal with different thickness and materials.
During bending process, the bending angle radius of work piece should also be taken into consideration. The bending radius is 0.156 times compared to V groove opening dimension.During free bending process, the dimension of V groove opening should be 8 times larger than the thickness of metal sheet.For example, if use press brake with 12mm V groove opening to bend 1.5mm low carbon sheet metal, the bending radius should be 1.9mm. If the bending radius close to the thickness of metal sheet or less than it, 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 upper mold and down mold at the bottom of stroke as well as 90 degrees bending of sheet metal to compensate resilience.
Generally, the free bending mold will generate less than 2 degrees’ resilience angle on new CNC press brake. And the bending radius equals to 0.156 times of down mold opening distance. Thus, for common free up and down mold bending processing, the mold angle will be 86-90 degree. At the bottom of stroke, there should exist one clearance which is slightly larger than the thickness of sheet metal.
The reason why molding angle improved is that larger bending tonnage of hollowing block mold been used (4 times than free bending). This is helpful for reducing resilience force within the scope of bending radius. Emboss bending is same as bottom hollowing block bending. The only difference is the front end of upper mold been turned into the bending radius which gonna be needed. Meanwhile, resilience force is avoided because the clearance between upper mold and down mold at the bottom of stroke is less than the thickness of sheet metal, plus enough pressure force (10 times than free bending), the upper mold front end contact sheet metal.
In order to choose lowest tonnage press brake, the better choose the one which bending radius larger than the thickness of sheet metal. And adopt free bending way as possible because large bending radius will not affect the quality of finished products and ensures the long service life of press brake.
It is just this factor determines you should 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 re-positioning accuracy of slider can be controlled at ±0.01mm. So for those highly precise finished products, you have to choose such press brake with high accuracy and good performance.
However, the slider’s re-positioning accuracy of NC press brake is about ±0.5mm. Under the condition of proper mold, it will still cause ±2-3 degree deviation.Besides, CNC press brake always equipped with fast mold filling CNC system and mold clamping. If you need to process many small parts, then this factor have to be your first consideration.
The mold of press brake has direct influence on the accuracy of bending process. Therefore, the mold should be checked carefully.How to check the mold of press brake? It easy. To check the length from front end of upper mold to worktable shoulder and the distance between down mold worktable shoulder. For regular mold, the deviation should in the range of ±0.1mm per 10mm, and the total length deviation should less than ±0.15mm.
As for accurate grinding mold, the deviation should in the range of ±0.005mm per 100mm, and the total length deviation should less than ±0.05mm. The accurate grinding mold better been used on CNC press brake and regular mold been used on NC press brake.
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