by Steve Brown
When left to their own devices, press brake operators come up with all sorts of creative ways to curb deflection, aka the “canoe effect” when bending longer parts in the press brake. Often, there are so many scraps of paper or cardboard left behind from repeated efforts to shim the die to achieve a consistent angle that their shop looks like an elementary school craft project went awry.
The reason for this is that any time you are bending a part over four feet long on a press brake that part is susceptible to deflection. A result of uneven downward pressure combined with slight nuances built into the machine itself, deflection occurs when more tonnage is applied to the ends of the beams than in the centre. This causes the angle of the bend to be tighter on the left and right and less so in the middle, creating a bow in the bend angle.
A common method for countering the “canoe effect” is to manually shim press brake dies using folded paper or cardboard in order to offset the deflection. However, doing so requires a significant amount of trial and error resulting in costly downtime. And once a solution is found, it’s not easily repeatable the next time you need to perform the same bend, which means you’ll waste even more time tinkering to find the same solution over and over again.
Fortunately today, press brake crowning systems are available from the machine OEM and aftermarket suppliers that take the guesswork out of correcting sheet metal bowing. Crowning systems are installed in the lower beam of the press brake to offer precise crowning and micro tuning of the die. Crowning adjusts the beam up to 3.5 mm (.137 in.), depending on length, with available micro adjustment at points every 200 mm (7.87 in.) on the beam for fine-tuning up to 5 mm (.020 in.)
Not only are crowning systems faster to set up and more precise than manual shimming, the results can be repeated setup after setup with no tinkering required.
Crowning systems generally have two key features: a method to hold the die and a way to control deflection. Die holding can be accomplished with set screws every inch along the beam for manual tightening or with hydraulic actuation.
Deflection is controlled using either a manually adjustable hand crank for overall height control and digital display to measure movement. Or crowning can be adjusted via the machine control using a CNC controlled electric motor.
Producing consistently straight bends in long parts shouldn’t be a game of guess and check, where the operator with the most creative solution wins one round, with the answer for the next round being anyone’s guess.
Instead, installing a crowning system will eliminate the guessing game and improve your press brake profitability by significantly reducing unnecessary downtime and producing consistently higher quality bends. SMT
Steve Brown is bending product manager, Wilson Tool International.
