Sheet metal rolling is another method of bending steel, but in this case the goal of manufacturing is to achieve a rounded circular bend, under specific radius, rather than a V-shaped angular form. Some of the main purposes of this metal-processing method is to manufacture pipes, ducts and cones, which have non-standard diameters and are needed for custom-designed industrial installations.

Of course, the rounded shapes, under which a sheet metal can be bent, are quite diverse, so rolling does not always refer to pipes and cones only. Rectangular shapes with rounded corners like the one on pic.1 are often and object of sheet metal rolling.

Bending preparation: cutting the correct unfolding.

Whenever we speak about sheet metal rolling or bending, the 1^st thing which MUST come in mind is to prepare the correct sheet unfolding. In order to achieve a pipe with a certain diameter, we must correctly calculate the rectangular unfolding or the sheet, which we will roll (pic.2).

As we can see on pic.3, in order to calculate the correct unfolding, we need the outer diameter, which we want to achieve and the plate thickness. 

Having this in mind we cans imply apply the formula for circle length:

Unfolding = (OD – Thk.) x π

Where:
OD – outer diameter
Thk – Plate thickness
π – 3,1415

So for a pipe OD 720 with 10mm thickness we can calculate the unfolding:

 (720 – 10 )x 3,1415 = 2 230,47 mm.

Note:
Often manufacturers prefer to cut the unfolding of thick materials a bit shorter, since the lower edges collide earlier after rolling – pic.4.  

Furthermore, cutting the unfolding 3-10mm short, provides 1-3mm clearance for welding seam.

When we roll a cone or branch cone, we have different unfolding, which are not so easy to calculate. Normally designers use multiple types of software, many of which are free-to-use, but for professional purposes they often differ.

At My Euro Steel, we always recommend our customers to upload unfolding and other designs, made with legit CAD software, so that the end result would actually match the expectations. In cases, when customers don’t have access to this type of software, our engineers can create one, just for the purpose of the order.

Unfolding a cone for rolling could be tricky, especially when it depends on the CAD program which is unfolding the part.

Conical shapes can also vary in many ways, like their eccentricity, orientation and branches.

Pic.7 – Eccentric Cone

Pic.8 – Eccentric Cone, cut left.

Next on list of possibilities, when rolling sheet metal, is the segment bend (pic.9).

Creating a duct elbow with non-standard diameter, radius and angle is quite expensive, rare and complicated for manufacturing, so engineers often create angular pipe connections via segment bended elbows. These segments are then unfolded, where the length of the unfolding is again calculated by the circle length formula, but the shape is not rectangular, but rather belt-like (pic.10)

In practice there are many more round and conical shapes for ducts and pipes, which are always engineered to suit specific installation or equipment. This is why sheet metal rolling finds many applications in the industry.

Types of rolling machines:

3-roll machines are very popular with sheet metal manufacturers, since they are quite accessible and provide lower cost for production.

The main roll in the middle moves down and presses the work piece, while the two down rolls push up, before rolling. After roll setup the main roll begins to move and shape the work piece. Nowadays there are many CNC-controlled 3-roll machines, which offer shaping of pipes with just 1 cycle.

On the downsides of 3-roll machines is the lack of pre-bending, which results in partial non-bend area. This result can be avoided in two ways:

               1^st: pre-bending by a press-brake.

               2^nd: cutting a longer unfolding and after rolling, manually cutout the unnecessary material.

4-roll machines use an additional lower roll in the, which in the beginning of the rolling solves the problem with the pre-bending. The middle roll presses the work piece to the main roll, bends the sheet via the 1^st lower roll and then proceeds with the rolling sequence (pic.13)  

My Euro Steel operates a secure network of certified manufacturers, which is why we can provide our clients with quality sheet metal rolling services. Our partners are capable of rolling custom-sized pipes and cones, but also other circular shapes, depending on the engineering requirements.