The definition of sheet metal bending
Steel structures fabrication as an industry has many different operations that it can perform with sheet metal. These operations are used in combination with each other to make the sheet metal piece into a desired shape. Some examples of steel fabrication operations are cutting, drilling, punching, forging, drawing, extrusion, and so on.
This list also includes one particular operation type called bending. Bending seems like a very simple process by definition – changing the shape of the material by applying enough force. However, it is slightly different in the metal fabrication industry, and there are several nuances about this process.
Bending itself dates b ack to the late 16th century, and its original concept was sketched an entire century earlier by none other than Leonardo Da Vinci. The first iteration of metal bending used two heavy cylinders to alter the original material’s shape or thickness. This particular method is now called rolling and is much more accurate than before – and it is not the only bending method that exists right now, either.
Methods of sheet metal bending
Roll bending, or rolling, is one of the oldest bending methods so far, even though it has been modified quite a lot since its introduction. Roll bending uses a set of rollers that spin around and bend the metal piece into the desired angle. Some of the more common results of roll bending are tubes, cones, rolls and several other curved shapes of the metal. It can be used to create longer sheet metal parts with none more than 20 inches and possible thickness ranging from 0.125 inches to 0.004 inches – such as tracks, panels and multi-purpose shelving (roofing, HVAC, lighting, etc.).
The very nature of rotary draw bending makes it similar to the aforementioned roll bending – but the process itself is very different. Rotary draw bending uses a rotating die that the sheet metal is clamped to, and this same sheet metal is then drawn around the die to achieve the necessary bend radius. It is fairly common for rotary draw bending to cause wrinkling during the bending process, which is why an internal supporting mandrel is often recommended, if not necessary.
Wipe bending uses a similar idea of firmly holding the sheet metal piece in place, but uses a combination of a wipe die and a pressure pad to hold it in one place horizontally – with the edge of the sheet that needs to be bent being extended beyond both the pressure pad and the wipe die. After the sheet metal piece is confirmed to be firmly held in one place, the punch of a specific shape is then forced against the edge of the sheet metal piece, bending it to a specific angle.
Since this process is more mechanical, it allows for less force to be applied during the bending process. However, it is also not particularly suitable for something more complicated than simple bending processes due to the requirement of a more complex equipment piece to create obtuse bend angles.
Air bending is one of the more common sheet metal bending methods that uses a combination of a punch with a desired angle (some variation of the V-letter shape) and the die with the groove that is nearly identical to the shape of a die. The sheet metal piece is placed on a die above the groove, and the punch then applies pressure to the sheet metal piece to force it to change shape.
This particular bending method does not force the punch all the way down to the die’s groove, allowing for a lot of control over the necessary bend angle. This approach is far more liberating in terms of the bending angle since it allows for the punch to be stopped at any point of the bending process, allowing for the creation of pretty much any angle from 180 degrees down to the degree of the punch. However, the springback is an important nuance here – a nuance that we are going to go over a bit later.
V-bending is a process similar to air bending in a lot of ways – it uses the same idea of a die with a groove and a sharp punch of a specific angle. However, V-bending implies that the punch is fully pressed to the die, creating the exact same angle as the angle of the punch. While this method might not seem as flexible as the aforementioned air bending, it is more or less the most popular bending method for sheet metal due to its speed and ease of use. This particular method also has a notable issue with springback that is going to be explained further into the article.
Bottoming (bottom bending) is a variation of V-bending, making it nearly identical to that particular method – using the combination of the punch and the die and creating the desired angle via pressing the punch fully into the die’s groove. The main difference between the two is that bottoming uses far more power to make this angle to eliminate the issue of a springback.
Springback is the detail that can be applied to a number of different bending methods, and it concerns the nature of the metal during the bending process. The springback itself is the natural effect of the metal that changes its shape in a small way after being bent with one of the aforementioned methods.
This particular change appears due to the way the V-bending and other methods work – by applying pressure to a specific point of the metal. In this specific point (and around it) the metal itself is deforming in two different ways – pulling and compression. The compression happens on the inside of the now-bent metal piece, while the pulling is on the outer side of it.
Each metal’s capability to be pulled and compressed tends to vary quite a lot, but it is natural for most materials to have their compressive strength to be that much higher than the tensile strength. This little difference in the angle is capable of making the entire metal piece unusable for its intended purpose.
As such, the springback effect needs to be taken into account when performing V-bending or air bending, and this is why bottoming does not have any springback effect – because the amount of force applied is high enough to surpass both the tensile and the compressive strength of the metal piece.
There are also other methods of bending that are not as widespread or intended for very specific purposes, such as:
- Three-point bending;
- Rotary bending.
For example, three-point bending is relatively new, while coining has a high cost for its precision. U-bending is the variation of V-bending with a U-shaped punch for specific metal shapes, and rotary bending is more fit for sharper angles thanks to its usage of a saddle with a rotary die that has a groove with the appropriate angle inside of it.
Tips for sheet metal bending
While springback is an important factor to consider when it comes to sheet metal bending, it is not the only important topic that you have to remember before performing the bending process.
For example, it is recommended to use process position holes on sheet metal whenever possible, since process position holes can be used to ensure accuracy of the bending process when it comes to multiple identical metal parts. These same holes also keep the metal piece from moving during the bending process, as well, improving the end result accuracy even more.
Another possible option of keeping the metal sheet plate in place is to use a press brake of some sort (in a similar fashion to the pressure pad in wipe bending). The usage of a press brake makes it easier for the bending process to be perfect, or at least as close to perfect as possible.
Malleability is also important for the overall bending process. Malleability represents the angle that the current material can bend at without cracking or distorting itself. Different material types offer different levels of malleability, and this parameter is crucial if you want to calculate all of your bending parameters with as much accuracy as possible.
If the metal part in question also has some variation of slots or holes, it is recommended to perform the bending operation as far away from these holes as possible so that they are not deformed in some way by the bending process.
Manual sheet metal bending
That’s not to say that sheet metal bending can only be performed with industry-level tools. In fact, it is possible to bend relatively small sheet metal parts with just your vise and a hammer (and possibly a blowtorch).
However, this method requires a lot of preparation compared with using some sort of machinery – you would have to cut the sheet metal piece by hand to fit the vise, calculate bend allowance by hand (compared with bend allowance on the industrial level that can be calculated in CAD) to mark it on your sheet metal piece, and you also have to have a form or forms made of wood that you would be using to bend your sheet metal piece with.
The bending process itself is also somewhat more complicated, since you have to place the form in the vise first, clamp your sheet metal piece in place, and only then can you start bending the metal piece with the help of your mallet. There are several nuances about this particular process, including the possibility of an error in your calculations about bend allowance, as well as the necessary amount of pressure for you to apply with your vise.
If the bending process is particularly hard, you can try to apply heat to the bending location to make it easier to bend. However, this process is extremely difficult since you can damage the metal piece itself while heating it up too much or incorrectly.
There is no definitive way to determine one sheet bending method that can be objectively above the rest of the methods. Each and every method on the list serves its own purpose and can be above the rest in a specific set of circumstances – including the type of metal, the necessary angle of the workpiece, the overall shape of the metal piece, and so on. There can also be quite a lot of difference in how hard or how easy one sheet metal type can bend, with one metal being extremely soft, and the others requiring external force to be bent in the first place.
Despite its own nuances and difficulties, sheet metal bending remains one of the easier processes in the metal fabrication industry. However, it is still a part of the massively complicated industry as a whole, so it has its own nuances and things to keep track of. This article’s goal was to provide basic information about the topic of sheet metal bending, its types and different tips.