Pipe rolling is a manufacturing process that produces arc and curve shaped metal pipes. Some of the equipment used in this process include brake presses, box and pan brakes among other specialized machinery. Metal pipes created by this process are used to make rectangular ductwork and electrical enclosures.
The Process
In pipe rolling, a sheet of metal is positioned over a die block, which presses the sheet to form certain shapes. The sheet should be able to withstand tensile and compressive stresses. When sheets of metal are bent, they will spring back to their original positions. This means they should be bent at a certain angle to achieve the desired bend. The metal spring back is determined by the material and type of forming. Bending stretches the length of sheet metals to achieve a specific bend radius. The dies used as well as material thickness and properties determine this radius.
Types of Pipe Rolling Processes
There are three common pipe rolling processes each defined by the material thickness and end tool position. The three processes include bottoming, air bending and coining. Tools used in these processes are configured in a nearly identical pattern.
The tools include a die with a radiused tip to locate the inside profile of the metal bend. The tip of the die is called a punch. The punch is normally attached to the ram of a machine by clamps, which will produce the bending force. The dies are located under the material on the machine bed.
Air Bending
This pipe rolling method forms materials by pressing a punch into a metal sheet forming a V-die. The distance between the punch and side wall of the V-die is greater than the thickness of the material. Air bending uses smaller equipment than other pipe rolling methods because it requires less bend force.
The shape formed in the bottom die may either be V-shaped or have a square opening. Sets of top and bottom dies are made for each product produced in the press. Some of the tools used in major manufacturing processes are adjustable. This allows manufacturers to use different press-stroke depths to produce varying product profiles. Air bending is a flexible pipe rolling process because it allows different materials to be bent in varying angles.
The downside to air bending is that it is not as precise as other pipe rolling methods because the sheet does not come into full contact with the die. This is a significant factor because stroke depth must be accurate to avoid defects on parts produced.
Bottoming
In this process, metal sheets are forced against the bottom tool’s V opening. This process does not use U-shaped openings. Space is created between the sheet and V opening. This pipe rolling technique has various advantages, including greater accuracy and less spring back. But the disadvantage of this pipe rolling technique is that it requires different sets of tools for each bend angle, material and sheet thickness. However, this is the preferred pipe rolling method for many manufacturers.
Coining
In this process, the top tool forces the metal sheet into a bottom die with 5-30 times the force used in air bending. This force causes permanent deformation of the metal sheet eliminating spring back. Coining is a highly accurate, but sometimes expensive, pipe rolling technique.
Other pipe rolling processes include three point bending, folding, rotary bending, roll bending and wiping. Common materials used with these pipe-rolling processes include new plastic materials, aluminum and mild steel.
