Bending is one of the most common operations in the manufacture of sheet metal. This method, also known as press-bending, hemming, die-bending, folding and piping, is used to give the material an angular shape.
This is done by applying force to the workpiece. To achieve plastic deformation, the force must exceed the yield strength of the material. Only then will you achieve lasting results with magnificent forms.Bend method
There are many bending methods available. Each has its own benefits. There is usually a dilemma between striving for precision or simplicity, with the latter being used more frequently. Simple methods are more flexible and, most importantly, require fewer different tools to get results.
V-bending is the most common bending method using punches and dies. It is divided into three subgroups - Lower, Bending and Stamping. Air bending and bottoming account for approximately 90% of all bending jobs.
The table below helps to determine the minimum flange length b (mm) and the inner radius IR depending on the thickness of the material (mm) t ( mm). You can also see the V (mm) mold width required for such specifications. Each operation requires a certain tonnage per meter. This is also shown in the table. You can see that thicker material and smaller internal radii require more force or tonnage. The highlighted parameters are the recommended metal bending parameters.
Bending force diagram
Let's say I have a sheet of paper that is 2mm thick and I want to fold it. For simplicity, I also use an inner radius of 2mm. I now see that the minimum flange length for this bend is 8.5mm, so it must be designed with that in mind. The required die width is 12 mm and the density per meter is 22. The smallest total table capacity is about 100 tons. My workpiece has a fold line of 3 m, so the total force required is 3 * 22 = 66 tons. So even a simple bench with enough space to bend 3m will do the job.
However, please keep one thing in mind. The table refers to structural steels with a yield strength of about 400 MPa. If you want to bend aluminum, the tonnage value can be divided by 2 as it requires less force. With stainless steel, the opposite is true - the required force is 1.7 times higher than indicated in this table.
Bending with air
Partial bending, or air bending, gets its name from the fact that the workpiece does not actually fully touch the tool part. With partial bending, the workpiece stops at 2 points, and the punch pushes through the bend. This can usually still be done with a press brake, but the side dies are not really needed.
Bending in air provides more flexibility. Let's say you have a matrix with a 90° angle. Using this method, you can get results ranging from 90 to 180 degrees. Although not as precise as priming or stamping, this simplicity is a strength of the method. If the load is removed and the springback of the material causes the wrong angle, it can be easily adjusted by simply applying more force.
Of course, this is the result of less precision than the primer. In this case, the biggest advantage of local bending is that there is no need to reset the mold for bending at different angles.
In principle, a U-bend is very similar to a V-bend. There is a die and a punch, and this time they are both U-shaped, resulting in the same bend. For example, this is a very simple way to bend steel U-profiles, but it is rare because other, more flexible methods for making such profiles are available.
Basically, staggered curves are repeated V-shaped curves. This method, also known as impact bending, uses many V-bends in a row to produce large workpiece radii. The final quality depends on the number of bends and the steps between them. The more of them, the smoother the result.
Ribbed curves are used in many cases. Some examples include cone funnels and snow plows. Large radius bends are possible with conventional tools. A simple set-up keeps the price down, especially in small batches.
Roll bending is used to make pipes or cones of various shapes. Can also be used to make large radius bends if desired. Depending on the power of the machine and the number of rolls, one or more bends can be performed simultaneously.
This process uses two drive rollers and a third adjustable roller. This one is propelled by friction. Additional operations will be required if the part needs to be bent at both ends and in the middle. This is done using hydraulic presses or bending machines. Otherwise, the edges of the parts will be smoothed out.
Edge folds, or hem folds, are another method of bending the edges of sheet metal. It is important to make sure that the paper is correctly pushed onto the napkin matrix. As a result, wiping the die also determines the inside radius of the knee. The gap between the trowel and the punch plays an important role in achieving good results.
Rotate and bend
Another way to bend an edge is to rotate it. It has a big advantage over wipes or V-bends - it doesn't scratch the surface of the material. In fact, special resin tools can be used to avoid any tool marks, not to mention scratches. The rotary pipe bender can also bend sharp corners in excess of 90 degrees. With public angles like this, it helps a lot, as recoil is no longer an issue.
The most common method is 2 rolls, but there are also 1 roll options. This method is also more flexible than other methods and is therefore also suitable for making U-ducts with adjacent flanges.