Both roll forming and tube and pipe forming involve bending steel with roll tools, and each pair of rollers gradually processes the steel strip until a desired shape is obtained. The difference between roll forming is that it is very suitable for pre-punching, middle and post-punching in all pipelines, and sweeping before cutting.
Application examples include impact bars, chassis sections, and window guides in automobiles, which can be pre-punched in continuous operation, roll forming, medium punching, more roll forming, then welding, cleaning and cutting. Some of these parts are butt welded, such as a tube or pipes, while others can be seam welded or lap welded.
Although the process is similar and some equipment may be the same, there are differences in the design of roll-formed profiles and the tools and machine layout and settings required.
Let's look at the production of 2 inch diameter tubes on a 2 inch shaft tube mill. The rolling mill may have three fault passes, the idler is between one and two, two and three, there are two pairs of idlers between the fault pass and the three fin passes. Between each fin bead is an idler bead, which may also be the seam guide before the welding station. Weld 0.02 inches extra large on 2 inches. The diameter tube increases the diameter to 2.030 inches. Therefore, welding needs to reduce the diameter.
The welding station is usually followed by a blanking table with or without corresponding ironing channels, then an elliptical guide or similar device to guide the tube to the first through three driven channels and idlers in a certain diameter channel. After sizing, use single or double Turk’s head braces for straightening.
In this example, the total number of drive passes before the welding station is six, and the sizing after welding is three. Each driven sizing pass and idler pass reduce the diameter of the tube until it reaches the desired size. During the shaping process, the tube is elongated and the wall of the tube becomes thicker, which usually cannot guarantee the position of the weld.
Now, let's roll form the same 2 inch diameter tube by pre-punching. This process requires 10 passes before the welding station, because a typical roll forming machine does not have an idler frame. The steel pipe plant uses idlers between almost every process to help form rounded corners. These idlers help to form the strip, feed the steel to the next pass, and stabilize the profile as it passes through the rolling mill. Most roll forming does not require an idler, but usually more passes are used to make the tube. Similarly, a tube mill may need to run hundreds of feet per minute, but roll mills, especially those with pre-punching, can never reach these speeds. With few exceptions, most roll forming machines, especially those with pre-punched steel, run much slower than tube mills.
In addition, during the rolling process, the strip width is calculated differently. On the tube rolling mill, the fin allowance and welding allowance are calculated and added to the strip width. If you are drilling holes, the pressure in the fins will distort the holes.
It is best to form the roller into a progressive edge form with a high oval shape without rollers. On the first pass of approximately 15 degrees, the over-shaped radius is used to form a strip from the outside. The second pass forms the next 15 degrees, allowing the first pass to relax, and then continue to use this type of forming method to keep the high ellipse on the side. Roll forming only provides pressure in the vertical plane, so this must be kept in mind when designing the rolling tools.
Like tube and pipe mills, roll forming works with all metals, both ferrous and nonferrous. Stainless steels, martensitic steels, high-strength low-alloy steels, and aluminum coils can be roll formed. Steel and aluminum coils sometimes are embossed with wood grain finishes, such as for garage doors. When embossing, the depth of the embossment must be considered so that the roller dies do not roll the embossment back out.
Pre-painted or even vinyl-laminated steel can be rolled, but not welded. Tubes from prefabricated materials are usually formed with lock seams. The lock seam needs to knurl the edge of the strip on a flat surface or other places during the forming process, then make opposite hooks and form a tube, and then wrap the tube around the mandrel to lock the hook and then cut it.
Roll forming is a universal process that allows for design innovation. Setting up a rolling line requires the expertise of skilled rolling machine designers and the cooperation of sellers and manufacturers in developing successful products. But with the right preparation, the transition can be easy. Choose the appropriate equipment carefully, design the products and tools proficiently, train the operators properly and maintain the production line adequately to make roll forming easier.
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