The pipe or tube bending It is a cold forming process that produces a permanent bend according to the shape of a die, while preserving the cross-sectional shape of the pipe, be it round, square, rectangular or extruded.
The process is not as simple as the bending or bending of sheets and requires greater care than this, since the pipe or tube is a hollow element that can easily deform. However, precisely the characteristic of being hollow differentiates them from solid pieces, which are more expensive and require more complex machinery. With the appropriate devices to prevent deformation and change of mechanical properties, the tube bending machines they can complete the operation in a few minutes with excellent performance.
Currently there are tube bending machines ranging from small bench or tripod sizes, manually or foot operated, to sophisticated fully automated industrial machinery featuring CNC control.
Beyond the complexity of any tube bending machine, they all have a series of main components that we can outline in the following figure.
pipe bender tubes parts and components
- bending die
- Anchor Matrix
- pressure matrix
- slip matrix
Bending or bending die
It constitutes the main element of the bending process, since it molds the tube with a certain radius of curvature. It is made up of two parts that have a central groove, the depth of which is generally half the diameter of the tube. Those parts are:
- a curved portion, the length of which depends on the degree of bending required and includes an excess to compensate for the elastic recovery that occurs after bending.
- a straight portion, designed to hold the part of the tube immediately after bending.
Holding or anchoring matrix
As its name indicates, this matrix fulfills the function of holding the tube and is used together with the bending die. Its length coincides with the clamping part of the bending die and supports the tube during bending. The size of the clamping die depends on the size of the tube and the radius of bend, while its surface can be treated with alloys or it can incorporate a knurled pattern to improve the clamping of the tube.
Pressure or tracking matrix
It functions as a holding tool during bending and its length depends on the degree of bending and the radius of the midline. It provides constant pressure on the tube and follows it throughout the bending process, achieving two benefits:
- The narrowing of the tube wall can be reduced.
- Tears and marks on the tube can be minimized by decreasing drag.
The two elements that follow are not present in all tube benders, particularly the older ones, the smaller ones or the manually operated ones, but it is clear that the machines that incorporate them achieve much better precision and quality of the finished product.
It is the element that provides support inside the tube. Its shape and the material with which it is constructed depend on the outer diameter and the wall thickness of the tube, so there are several variants. The main function of the mandrel is to prevent the tube from being deformed or wrinkled.
This piece works together with the chuck and it consists of a semi-cylinder of variable length, with one of its ends machined in the shape of the bending die, so that both dies fit perfectly, as well as a central groove whose depth is half the diameter of the tube. The main function of the slip die is to prevent the appearance of wrinkles in the tube during the bending process and it becomes necessary when the resistance of the tube to compression is very high. Like the mandrel, this piece is in a state of constant friction with the tube, so its lubrication is essential.
Types of tube bending machines
Although the pipe bending It is done in various ways, there are at least four main types whose use depends on the material and the precision required, and which originate the corresponding types of machines. As we can see in the following figure, the most common ways of bending tubes are:
types of pipe bends
- Rotary drag bending
- compression bending
- press bending
- Bending by 3 roller system
Let’s briefly see what each method is about, with the help of a video in each case.
Rotary drag bending machines
It is the most precise and versatile bending method. The tube is clamped between the bending die and the anchoring or clamping matrix. The rotation of both tools around the bending axis bends the tube to the radius of the bending die. The pressure matrix It serves the purpose of receiving the radial tension that is generated during the forming process and supports the straight tube end from the outside. If you also apply a chuck and one slip matrix, particularly in copper and nickel tube bending, a high quality part can be obtained even with thin-walled tubes and very small bending radii. The applications of rotary bending machines They include the bending of non-ferrous materials in small radii and low production, copper elbows, heat exchangers, heating coils, copper forks, radiator circuits and refrigeration equipment.
It is very similar to the previous case, only that the method is carried out with a pressure matrix and one fixed bending die, between which the tube is clamped. The pressure die, which rotates around the bending die, bends the tube to the radius of the bending die. This method finds wide application in the refrigeration industry, diesel injection and auto parts in general. The two videos that follow show a manual and an automatic machine.
This method differs from the previous ones in that it is more like a sheet metal press brake with a piston or punch die operated manually or by hydraulic force. They can be vertical presses or, in the smaller models, horizontal. The punch die has the bending radius and with its movement towards the tube pushes the tube down against two opposing tube-shaped dies, which pivot upwards, forcing the tube to bend around the punch die. Since the part cannot be clamped from the inside with a chuck, this method is suitable for thick-walled tubes and large bend radii only. Applications for press brakes include construction sites, boilers, distilleries, gas and oil pipelines, and the shipbuilding industry.
Bending by 3 roller system
This method is also used to produce parts with large radii of curvature. The method is similar to the method of folded in press, except that the driving matrix and the two opposite stationary matrices rotate forming the curve. This system is useful for the construction of ships, appliances and pipelines.
Depending on the material used, modern machines incorporating a mandrel can bend almost any type of cold-formable tube to radii of curvature from approximately 1xD to 5xD (where D is the external diameter of the tube) safely and with the desired accuracy.
Today, the main differences in rotary drag bending machines are the maximum external diameter of the tube that can be worked with and the degree of automation of the various functions. On less sophisticated machines, only the bending function is automatic; feeding and rotation of the tube between two bends are carried out manually.
However, for the user tube bending machines With CNC or fully automatic control, all functions are available quickly and easily, and can be complemented with automatic feeding and unloading systems for the efficient and trouble-free production of large series of tubes of all types of profiles.