Common Issues with Sheet Metal Bending Dies

Common Questions and Answers on Sheet Metal Bending Dies:
Anyone familiar with sheet metal fabrication engineering knows that bending is one of the more difficult and skill-intensive processes in the field.
(1) What is sheet metal bending?
Sheet metal bending is the process of using pressure equipment and specially designed dies to transform a flat metal sheet into a three-dimensional shape.
Due to variations in material, thickness, length, and width of the sheets, as well as the different shapes and angles required, bending machines of various tonnages and sizes are used, paired with upper and lower dies of different heights, shapes, and V-opening widths, along with specially shaped dies for specific applications.
(2) What are the types of bending processes?
Bending processes are classified into three types: partial bending, coining bending, and stamping bending.
① Partial bending uses an upper die with an angle below 88° and a lower die with V=12t (V denotes the groove width, t denotes the material thickness) to achieve right-angle and obtuse-angle bends.
② Coining bending uses a 90° upper die to achieve right-angle and obtuse-angle bends. The lower die for coining bending is selected with V=6~12t.
③ Stamping bending uses a 90° upper die to achieve right-angle bends (a standard right-angle bend). The lower die for stamping bending is selected with V=5~6t.
(3) How to use a press brake?
Currently, there are many types of press brakes used in sheet metal processing. By drive method, they can be classified into mechanical (servo motor) and hydraulic types. By control system, they can be classified into simple manual press brakes, ordinary domestic digitally positioned press brakes, and fully functional digitally controlled process press brakes. By axis configuration, they can be classified into 4-axis, 8-axis, 12-axis, etc.
① Before using the press brake, check that the power is on, the air pressure is sufficient, the hydraulic oil is adequate, the machine is clean, and there are no obstructions on the slide rails. Only after confirming these can you proceed with subsequent operations.
② Turn on the machine's main power switch, start the hydraulic pump, and align the home positions of the L-axis, D-axis, CC-axis, and Z-axis to complete the startup process.
③ For tooling installation: After selecting the appropriate dies, set the machine's mode switch to the "Jog" position. Install the base, lower die, and upper die. Then set the switch to "Inching" or "Single Stroke" mode. Use the foot pedal to raise the ram, and use the up/down handwheel or knob to bring the upper and lower dies together, applying pressure to set the D-axis zero point. Lock the lower die to complete the tooling setup.
④ Read the drawings to understand the bending sequence and dimensions, then begin programming the press brake. There are two input methods for programming: angle input and depth input. We commonly use the depth input method. First, put the controller into memory mode and input values such as bending dimension L, D value, Z value, speed, time, and cycle count. Then review and confirm the program. Once correct, switch the controller to run mode. Use scrap material to test bend and adjust the program to achieve the optimal angle and dimensions. Then perform a trial bend with an actual product. After inspecting the trial piece and confirming it is correct, you can proceed with mass production.
⑤ During bending, if you need to increase speed, you can set the mode switch to "Single Stroke" or "Continuous" operation. However, for safety, it is generally recommended to use only "Single Stroke." When bending long workpieces, the angle in the middle often becomes too large. You can adjust the CC-axis to correct the middle angle to match the angles on the left and right sides. Also, pay attention to the principle of center bending during the process, which is crucial for ensuring bending accuracy. Never bend at one end of the machine; this not only results in poor angles but can also damage the machine.
⑥ For short breaks, do not turn off the main power; simply turn off the hydraulic pump. This saves electricity and avoids the need to re-home the axes when you return, saving time and improving machine utilization.
⑦ When finishing a batch or at the end of the shift, lower the lower die to its lowest position, then turn off the hydraulic pump, and finally turn off the main power. If the batch is complete, remove the dies and return them to the die rack, and reset the control panel.
⑧ It is strictly forbidden to operate the press brake improperly, as this may cause personal injury or damage to the machine and tooling. Always maintain cleanliness and perform regular maintenance on the machine, and develop good habits of caring for the equipment and dies.
(4) How to Use Bending Dies?
Bending dies come in several types for different bends, such as L-shape, R-shape, U-shape, and Z-shape. The upper dies mainly have angles of 90°, 88°, 45°, 30°, 20°, and 15°. The lower dies have single- and double-V grooves with widths ranging from 4V to 18V, as well as R lower dies, acute-angle lower dies, and flattening dies. The upper and lower dies are available in segmented and one-piece versions: segmented upper dies are typically 300mm, 200mm, 100mm, 100mm, 50mm, 40mm, 20mm, 15mm, and 10mm, while the one-piece upper die is 835mm. Lower dies are generally available in 400mm, 200mm, 100mm, 50mm, 40mm, 20mm, 15mm, and 10mm segments, with the one-piece version being 835mm.
① Bending dies are made from high-quality steel and undergo special heat treatment, giving them high hardness, wear resistance, and the ability to withstand significant pressure. However, each die set has its maximum pressure limit, expressed in tons per meter. Therefore, when using dies, it is essential to select the correct die length and calculate the pressure per meter, ensuring it never exceeds the rated pressure indicated on the die.
② To prevent damage to the dies, we have established that when performing the home position (origin) setting, you must use upper and lower dies with a length of at least 300mm. After the origin is correctly set, you may then use upper and lower dies of the same height. It is strictly forbidden to use small segmented dies for the origin setting, and the origin setting must always be based on the machine's internal origin pressure as specified by AMADA.
③ When using dies, note that different dies have different heights. Therefore, on a single machine, you may only use dies of the same height; mixing dies of different heights is not allowed.
④ When selecting dies, choose the appropriate upper and lower dies based on the hardness, thickness, and length of the metal sheet. Generally, use a lower die with a V-groove width of 5 to 6 times the material thickness, and the die length should be slightly longer than the sheet. For harder or thicker materials, use a lower die with a wider V-groove.
⑤ When bending acute angles or hemming (dead bends), use a 30° upper die: first bend the acute angle, then flatten the hem. For bending R angles, use R-shaped upper and lower dies.
⑥ When bending longer workpieces, it is best to avoid segmented dies to reduce tool marks from multiple hits. Also, prefer a single-V lower die, as the outer corners of the V-groove have a larger R, which helps prevent bending marks.
⑦ When selecting the upper die, you should be familiar with the specifications of all available dies and then decide which upper die to use based on the desired product shape.
⑧ When bending extremely hard or very thick materials, it is not permitted to use the dies to bend rebar or other cylindrical products.
⑨ When using the die, keep a clear mind. After the machine has completed its home position setting, lock the upper and lower dies to prevent them from falling and causing injury to personnel or damage to the die. During operation, apply pressure with caution—do not increase pressure too quickly at once, and pay attention to the data changes displayed on the screen.
⑩ After using the die, return it to the die rack promptly and place it according to the labels. Regularly clean dust off the die and apply anti-rust oil to prevent corrosion, which could reduce the die's precision.