I. Ordinary Knife Bending Arc
1. Select a 0.2R upper die for ordinary bending and choose the lower die based on the selected die standard. Calculate the arc length and determine the number of bends required based on the arc length and material thickness. Calculate the bending angle for each bend based on the arc angle and the number of bends. Then proceed with the bending process. However, since the formation of the arc is achieved through several bends, even dozens of bends, by the CNC bending machine, the size range of the bent arc is limited by the tooling.
Typical processing ranges are as follows:
1) Forming a 90-degree arc: Forming arcs with a radius larger than R12.
2) Forming arcs greater than 120 degrees: Capable of processing all R arcs larger than the tooling limit.
2. Processing Considerations
When selecting CNC bending machine tools, the selection of V-groove width should be based on the feed rate.
II. R Die Bending Arc (Round Bar and Arc Knife Bending Arc)
Form the arc with the inherent R angle of the tool. When selecting the die, if the formed arc is smaller than R12, the upper and lower dies of the corresponding size can be selected for one-time forming. Since the R die is a standard die with limited R specifications, the size of the processed arc is restricted.
Existing standard die specifications include:
1) Ordinary knife with R angle: R3.0.
2) Round bar specifications include: R3.0, R4.0, R5.0, R6.0, R8.0, R10, R12. If the required R is not within the standard die specifications, additional material can be added to the outer periphery of the R die to increase the R. If the formed arc is larger than R12, it also needs to be formed in multiple bends, following the same processing conditions as ordinary knife bending arcs.
R die bending arcs have the advantage of compensating for the shortcomings of ordinary knife bending arcs. They provide a smooth bending appearance and excellent results, making them suitable for processing products with strict aesthetic requirements.
III. Processing Considerations
1) When bending arcs with the R die, it is important to select the die according to the die selection standard. However, when processing a 90-degree arc, due to the rebound of the sheet metal during CNC bending, the desired 90-degree arc cannot be achieved when the lower die is set at 90 degrees. Therefore, manual pushing is required during the bending process to ensure the desired angle. Therefore, when there is an 88-degree lower die available, it should be preferred when bending a 90-degree arc.
2) During arc bending, the use of inspection fixtures is required to ensure the dimensional appearance of the processed workpiece.
3) When processing arcs with large process angles, it is generally done using easily moldable tools or manual methods.
4) Using R die (round bar and arc knife), the standard V-groove width for selecting the lower die in CNC bending is as follows:
(1) For bending a 90-degree arc, the V-groove width of the lower die should be: V > 2(R + T).
(2) For bending a 135-degree arc, the V-groove width of the lower die should be: V > 1.5(R + T).
IV. Types of Bending Arcs
1) 1/4 circular bend forming: The workpiece arc R = bending tool R + shim.
2) When the workpiece has a large R angle, it is processed in multiple bends to achieve the desired arc angle.
3) 2/4 circular arc processing: bending tool R + shim + 30-degree lower die + forming = workpiece processed R; round bar + shim = workpiece processed R.
4) 3/4 circular arc processing:
(1) For long workpieces, it is processed with the bending tool one bend at a time (suitable for larger R angles).
(2) For narrow workpieces, ear tooling is used (suitable for larger R angles).
(3) Special methods can be used, such as roll bending.
