A bending machine is used to bend tubes, bars, and profiles to produce angle sections, T-sections, U-sections, and similar metal parts. These machines are widely used in metalworking.
The rolls are the most important part of the machine. They apply combined force to the profile and create deformation perpendicular to its length.
How to Choose a Bending Machine
To choose the right bending machine, first determine whether it will be used for tubes, bars, or profiles.
Next, consider the size of the part to be bent, such as the tube diameter and wall thickness, or the height and width of the bar.
These factors determine the correct roll size, the distance between rolls, and the required machine size.
You also need to know the minimum bending radius and the bending angle you want to achieve. In general, the minimum bending radius for a tube is 2.5 times its outside diameter, while the minimum bending radius for a bar is three times its cross-section.
The bending angle also affects machine selection. For example, a roll bending machine usually needs several passes to achieve a bending angle greater than 90°.
Material properties, such as tensile strength and elongation, must also be considered.
Cold Bending and Hot Bending
Most bending machines are designed for cold bending. Some machines can process bars, tubes, and profiles in a heated state, mainly in ironworking and metalworking.
Another hot bending method is induction bending, often used for large stainless steel tubes.
Cold bending preserves the mechanical properties of the metal. Hot bending allows greater deformation flexibility and smaller bending radii.
When to Choose a Manual Bending Machine
A manual bending machine is suitable for one-off use or small-batch production where high precision is not required.
Its bending accuracy and repeatability depend on the operator’s experience, but the investment is much lower than that of an industrial bending machine.
Manual bending machines can be mechanical or hydraulic.
Mechanical bending machines are generally used for small-diameter tubes. A crank drives the rolls, which move the tube, bar, or profile.
Hydraulic bending machines are used for larger-diameter tubes. They use a hydraulic cylinder to apply steady force to the bending roll.
How to Choose an Automatic Bending Machine
When choosing an automatic bending machine, select a model that meets your requirements for speed, performance, and precision.
Automatic hydraulic bending machines offer high bending quality and precision, but they are relatively slow compared with electric bending machines.
Electric bending machines are faster.
CNC bending machines are programmable, with high repeatability and precision, but they require a larger investment.
How Many Rolls Are Needed?
Most bending machines use three rolls. Depending on the model, two or all three rolls may be motorized. Four-roll bending machines are also used for specific jobs.
Machines with two motorized rolls are the least expensive. They are mainly used for small-batch production where surface finish is less important, as grooved rolls may leave marks on the part.
Machines with three motorized rolls are faster and provide better processing quality, but they cost more.
Four-roll bending machines make it easier to bend both large- and small-diameter tubes and offer the highest efficiency.
Rolls and drive systems affect processing quality and durability. Hardened and ground rolls improve service life.
For gear drives, gears with induction-hardened teeth are the most durable. For shaft-drive systems, a plastic part may be designed to break under excessive load, protecting the machine and simplifying maintenance.
Other Selection Criteria
Bending machines can be pyramid-type or asymmetrical.
In a pyramid-type bending machine, only the top central roll moves. The distance between the two lower rolls is fixed. This larger roll spacing allows large-diameter tubes and relatively large bending radii.
In an asymmetrical bending machine, the central roll is fixed, while the lower rolls move along an arc. This allows different jobs to be completed with less deformation and smaller bending radii.
Depending on the workplace, bending machines can be vertical or horizontal.
Vertical bending machines require little floor space, but the ceiling height must be sufficient.
Horizontal bending machines need more working area and may require guide rails to support the bent workpiece.
Some bending machines are equipped with a mandrel, which supports the inside shape of the profile and helps prevent external collapse.