Tag: bending

Let’s Get Bendy

In the metal fabrication industry, metal bending is one of the most common metal forming processes. Metal bending, also known as press braking, flanging, and folding, is used to deform a metallic workpiece into an angular shape by use of extreme force. In order for the deformation to take place, the force exerted onto the workpiece must exceed the piece’s strength.

With metal bending, there are quite a few different methods a fabricator could take. In addition, there are various materials other than steel in which a fabricator can transform with a press brake. These materials can range from plastic to wood and iron to alloys, for example.

To get started, let’s break down a few of the more common metal bending methods and the advantages they offer.

V-bending

V-bending is the most common form of metal bending with a punch and V-shaped die. There are three subgroups to V-bending: air bending, coining, and bottoming, with air bending and bottoming taking up 90% of all bending jobs. The V-bending process takes place when a V-shaped punch forces the work into the V-shaped die, ultimately bending it.

Air Bending

Air bending is a subgroup of V-bending that does not require a sided die. The term air bending, also known as partial bending, is when a metallic workpiece is reshaped without actually touching the die cavity. The workpiece is, instead, rested on two points and the punch pushes down on the bend. If a fabricator makes the decision to use air bending, they will be offered much more flexibility, but less accuracy than coining or bottoming.

One of the advantages that comes with opting for air bending is that it allows the bending of thicker materials and varies the depth of the punch stroke in order to successfully bend at different angles. With this kind of flexibility and adaptability, the fabricator can invest less on tooling and won’t need to change their tools as often. In addition, since air bending does not require as much tonnage, this means that there will be less wear and tear on your machines, ultimately making them last much longer.

Unfortunately, air bending does have its disadvantages as well. While this method offers more flexibility with forming different angles, the bending angle can be heavily influenced by the sheet metal’s spring-back. Spring-back is when the metal relaxes after bending. Depending on the type of metal, the spring-back can also vary and cause the metal to bend at angles that were not initially intended or desired. In order to counteract the spring-back, it’s often suggested that sheet metals with constant thickness and resistance be used.

Coining

Prior to modern machinery, coining used to be the preferred method of metal bending as it once offered the most accuracy. The term coining comes from actual metal currency coins because coins need to be made identical to one another in order to keep them distinguishable enough to spot counterfeit coins. However, with modern technology and equipment, it is now not as commonly used.

Contrary to air bending, coining deforms the workpiece to fit the die’s exact shape by applying an extreme amount of tonnage. Fortunately, since this method allows the fabricator to deform the workpiece to the die’s exact shape, there is no spring-back to worry about. This is due to the fact that when the die deforms the workpiece, it’s using extreme force to penetrate the workpiece, ensuring a very small radius for the bend, which ultimately guarantees high precision.

While coining seems to be a more accurate method, due to the extreme amount of tonnage needed to deform the workpiece, it requires four to five times more high bending force than air bending. In addition, it requires more tools for each angle and shape. For some fabricators, this isn’t an issue. It’s all up to preference and what the project is!

Bottoming

The last form of V-bending is bottoming, also known as bottom pressing or bottom striking. Bottoming is when the punch pushes the workpiece onto the die surface, ultimately deforming the piece. What makes this method different from the others is that the inner radius of the angled sheet is completely dependent on the die’s radius.

As the inner line becomes more compressed and deformed, the more force is needed to fully deform it. Fortunately, the final bend angle is preset based on the die’s radius, making the exertion possible. In addition, the more force that is used, the chances of experiencing spring-back decreases. Unfortunately, like coining, bottoming requires a different tool set for each bend angle, sheet thickness, and material.

At MFI, we use a 225-ton press brake for all of our metal bending needs. This powerhouse of a machine is capable of bending sheet metal up to 12 feet long and 3/4” thick, making it easy to craft large and small projects. With a team that is committed to delivering high quality projects and decades’ worth of experience in the fabricator industry, we hope you think of us for all of your metal fabrication needs.

To get a better look at our metal forming and bending capabilities, check out our video below.

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Understanding Bend Tests & Radius

Welding procedures require bend tests for many parts such as tubes or pipes. It’s important to know the properties of the part to be worked on. The inside bend radius (sometimes called the intrados), the outside bend radius (extrados), and the centerline radius (or neutral line) where neither compression nor stretching occurs are all critical variables when bend testing.

The distance between bends (DBB) is the distance between two tangent points where a straight section begins to curve and the bend finishes. Similar to press brake forming, tubes and other parts experience a springback after being bent, which can produce radial growth in the tube. Depending on the metal of course, outcomes will vary. For example, stainless steel will have more radial growth post-bend than copper. The quality of the metal, size, and consistency of weld seam are all integral parts of the finished bend. If two edges of a joint aren’t aligned correctly, or the weld bead (deposited melted filler metal) isn’t the right size, it could end up affecting the shape of the tube negatively and the “perfect bend” won’t be achieved. “Elongation” is the term coined for when the outside radius stretches causing wall thinning. This causes the outside of the surface of the bend to cave in, resulting in an oval type shape much distorted from the original desired round shape. Most tubes are bent by ram-type bending, roll bending, compression bending, or rotary draw bending.

Ram-type bending uses a hydraulically driven ram that forces a tube against rollers or pivot blocks and can achieve three to four times the original diameter of the workpiece. These types of benders can be found in any muffler shop. This particular method is popular in square tubing applications. It is the least expensive way to bend tubes or pipes; however, it is not as controllable as some of the other methods. If one is in need of certain aesthetics or cosmetics to the workpiece, or need tight bending tolerances, the ram-type method may not be the most suitable.

Roll bending is generally used for large workpieces in construction. The material is formed by applying force from two to four rollers within a CNC machine. There is a narrow gap between the two middle rolls through which the metal sheet is fed. In this setting, a metal sheet panel would pass through the machine without being bent. After the CNC machine is set to roll bending, the middle rolls down in relation to the two side rolls to create the bend. The deeper these rolls are set, the smaller the bending radius. The smallest bending radius is equal to the upper roll diameter. The metal is not cut or removed. Roll bending is generally used when a metal sheet is to be given a large smooth radius, or to produce spirals.


Compression bending uses a roller as well or a compression die to bend the workpiece but instead compresses it around a stationary bend die. It clamps the workpiece from behind and compresses the tube against the stationary bend die. This is a good method for those creating symmetrical workpieces. Identical bends can be achieved with this use in one go with the machine creating two bends on each side. This method is mostly used to produce household items and commercial products. An example of compression bending that can be seen in the daily world would be a towel bar with two identical bends on each side hanging on the wall of a bathroom.

Rotary draw bending is ideal for tube bending involving tight radii. This method gives the utmost control regarding wall thinning and risks of ovality that ram-type bending may fall victim to. Rotary draw bending supports the metal being bent used a mandrel inside the tube while utilizing precision tooling on the outside. A rotary draw bend entails a pressure die holding the straight section of the tube, a clamp die rotating the workpiece around a curved rounded bend die, a mandrel with a series of balls on the tail end to support the interior of the tube around the bend, and a wiper die that wipes the workpieces tangent point of the inside radius to prevent against any wrinkles that could potentially be formed in the process. The pressure die also supports the outside radius of the tube during a bend. More common today, hydraulics are being used by pushing against the pressure die to minimize wall thinning further. Each element involved in rotary draw bending allows for total control of the inner and outer diameter throughout bending. It’s important to practice attentiveness with what metals and tools you’re working with when rotary bending. It’s important to have a combination of hard and soft materials. When using a hard work piece, a soft mandrel is optimum. If mandrel is too hard it could get stuck inside of the tube. Respectfully, a soft workpiece would in turn require a harder mandrel.

There is always a level unpredictability involved with any trade; however, with the advancements of modern technology, bending will only become more precise every time. Whether working with pipes or tubes, whichever method of bending utilized is always relative to the quality of the material, machines, tools, and lubrications involved. Also, knowing the proper bends is just as important as the quality of material being used. Due to different levels of spring back from different metals, it’s crucial to know what’s best for the desired outcome. Here at MFI, we utilize the ideal bends for our end user’s desired project requirements and can assure that our expert fabricators will produce the highest quality products.