Relationship between tonnage and pressure gauge reading (MPa) in a bending machine: "Megapascal (MPa)" is the unit of pressure. The pressure exerted on one square meter of area is equivalent to one pascal (1Pa) when a force of one newton is applied [1Pa = 1N/(m×m)]. 1 megapascal equals 1,000,000 pascals. On the other hand, kilogram-force is the unit of force: 1 kilogram-force is equal to 9.8 newtons.
These are two different physical quantities and cannot be directly converted by saying "1 megapascal equals how many kilogram-force."
However, they have a certain relationship: To generate a pressure of "1 megapascal," a pressure of approximately 10 kilograms needs to be applied on an area of 1 square centimeter.
Bending machines are categorized into manual bending machines, hydraulic bending machines, and CNC bending machines.
Hydraulic bending machines can be further divided into torsion bar synchronization, mechanical-hydraulic synchronization, and electro-hydraulic synchronization. This is the classification of bending machines.
Manual bending machines can be further divided into mechanical manual bending machines and electric manual bending machines. Hydraulic bending machines can be categorized based on synchronization methods: torsion bar synchronization, mechanical-hydraulic synchronization, and electro-hydraulic synchronization.
Hydraulic bending machines can be further classified based on the motion type: upward motion and downward motion.
A bending machine consists of a frame, a workbench, and a clamping plate. The workbench is placed on the frame and consists of a base and a pressure plate. The base is connected to the clamping plate through a belt. The base is composed of a seat shell, a coil, and a cover plate, with the coil placed in the recess of the seat shell and the top of the recess covered by the cover plate.
Electromagnetic force clamping allows the pressure plate to accommodate various workpiece requirements and enables processing of workpieces with sidewalls. The main features of a bending machine are:
1. Large low-frequency torque with stable output.
2. High-performance vector control.
3. Fast torque dynamic response and high-speed accuracy.
4. Quick deceleration and stopping speed.
5. Strong anti-interference capability.
When correctly selecting a bending machine, most of the work involves low-carbon steel with a thickness of 16 gauge and a maximum length of 10 feet (3.048 meters).
When bending parts with a free bending radius, the bending radius is 0.156 times the opening distance of the die. During free bending, the opening distance of the die should be 8 times the thickness of the metal material.
If the bending radius is smaller than the material thickness, a convex die with a front-end radius smaller than the material thickness should be used, along with the assistance of the embossing bending method. This requires 10 times the pressure compared to free bending. For free bending, the convex and concave dies are processed at 85° or less (slightly smaller is better). When using this set of dies, pay attention to the gap between the convex and concave dies at the bottom of the stroke, as well as enough compensation for springback to maintain an approximately 90° bend in the material. Typically, the springback angle generated by the free bending die on a new bending machine is ≤2°, and the bending radius is equal to 0.156 times the opening distance of the concave die.
For bottom-die bending, the die angle is generally between 86° and 90°. At the bottom of the stroke, there should be a gap slightly larger than the material thickness between the convex and concave dies. The forming angle is improved because bottom-die bending requires higher tonnage (about 4 times that of free bending), reducing the range of bending radii that typically cause stress-induced springback.
Embossing bending is similar to bottom-die bending, except that the front end of the convex die is processed to the desired bending radius, and the gap between the convex and concave dies at the bottom of the stroke is smaller than the material thickness. By applying sufficient pressure (approximately 10 times that of free bending) to force the front end of the convex die to contact the material, springback is essentially avoided.
