Principles and Calculation Methods of Sheet Metal Unfolding
The competition in the sheet metal processing industry has become increasingly fierce. To establish a strong position, companies must continuously improve their processing techniques. In applications such as precision stainless steel, aluminum alloy, aerospace parts, and copper sheet bending, customers no longer settle for functional products but also have higher requirements for craftsmanship and aesthetics. Traditional bending processes can easily damage the surface of the workpiece, leaving visible indentations or scratches from contact with the die. These marks cannot be removed and result in scrapped parts. Therefore, the demand for seamless bending is growing stronger. This article provides a detailed introduction to five methods for reducing indentation marks: die parameters (V-opening size, shoulder radius R), mark-free membrane pressing, non-metallic material V-groove, rotary die, and roller-type Multi-V die, offering solutions for seamless bending.
Impact of Die Parameters on Bending Indentation
Influence of V-opening Size
When bending different thicknesses of metal sheets, the choice of V-opening size for the lower die varies. Under the same plate thickness and with the same upper die, a larger V-opening size results in less pressure between the metal sheet and the shoulder of the V-opening, reducing frictional force and naturally decreasing the depth of the indentation. Therefore, it is recommended to use a slightly larger V-opening for the lower die.
Influence of Shoulder Radius R
Different shoulder radius R values of the V-opening result in different frictional forces on the metal sheet during the bending process. The larger the shoulder radius R of the V-opening, the lower the pressure between the metal sheet and the shoulder, resulting in lighter indentations, and vice versa. Test diagrams of indentations on the same metal sheet with different R values (Ra < Rb) clearly show that Ra has significantly more bending indentations than Rb. Therefore, it is recommended to use a lower die with a slightly larger shoulder radius.
Mark-Free Membrane Pressing
From the perspective of the friction pair, seamless bending can be achieved by avoiding direct contact between the upper and lower dies and the metal sheet and using a mark-free membrane to separate them. There are three types of mark-free membranes: K-003, K-004, and K-005, with their relevant parameters listed. The mark-free membrane mainly acts as a buffer between the workpiece and the shoulder of the lower die, reducing the friction coefficient and offsetting the pressure between the die and the metal sheet, thereby preventing indentation marks during bending.
Mark-free membranes have the advantages of low cost and easy use. Simply place the mark-free membrane on the lower die during operation. Bending tests with mark-free membranes have shown that they effectively prevent bending indentations.
Non-Metallic Material V-Groove
From the perspective of the friction pair, it is possible to consider using non-metallic materials that are softer than the metal sheet for the shoulder of the V-groove while ensuring the desired extrusion effect. Materials such as polyurethane and nylon can be used. Currently, the K-001/5 V-groove with polyurethane elastomer can be used in conjunction with the standard die OZU-016/327. The unique INZU series V-groove, made of high-strength nylon material, is used in combination with an extended die and is typically used for bending aluminum sheets with a thickness of 0.4-0.5mm, yielding good results.
Rotary Die
The rotary die deviates from the traditional fixed lower die V-opening structure by incorporating a flip mechanism on the inclined surfaces on both sides of the V-opening. During the process of the upper die pressing the sheet, the flip mechanism on the lower die is flipped inward by the pressure from the upper die, allowing the sheet to be bent into shape. The rotary die comes in three models and can bend sheets with a thickness ≤5mm.
Thanks to the strict tolerance requirements, CNC depth hardening technology on the contact surface, and the ability to rotate the V-opening, the rotary die allows for easy production of parts with shorter flange edges and minimizes surface indentation during bending. The advantages of the rotary die include:
(1) Manufacturing holes and grooves without deformation in the area near the bending centerline.
(2) Reducing surface indentation during part bending.
(3) Achieving very small inner bending radii.
(4) The rotary mechanism and contact surface undergo hardening treatment, ensuring a longer lifespan and accuracy.
(5) Easy disassembly and maintenance of the rotary die.
(6) Strict tolerance requirements during die processing ensure maximum precision during bending operations.
(7) Compact die dimensions ensure maximum bending flexibility.
(8) The same die can bend various thicknesses of sheets.
(9) Can be combined with certain customized lower dies for 90° bending.
The rotary die, equipped with a tension spring and flip plate structure, can achieve bending of parts with shorter flange edges and oblique edges by using a replaceable rotating V-opening. A comparison test was conducted using the rotary die OZU-WRB-301 and the lower die OZU-051 for bending. A 1mm-thick mild steel sheet and the same BIU-021 upper die were used. The test results showed that the rotary die was more effective in avoiding bending indentation compared to the conventional lower die OZU-051.
Multi-V Die with Roller-Type Adjustable V-opening
Similarly, based on the principle of reducing the friction coefficient between the sheet and the shoulder of the lower die V-opening, the sliding friction pair between the sheet and the shoulder can be transformed into a rolling friction pair, significantly reducing the friction force on the sheet and effectively avoiding bending indentation. This technique has been widely used in the die industry, and the solution includes a roller-type adjustable Multi-V lower die. The die is equipped with hardened rollers with low friction coefficients, greatly reducing external creases on bent parts and reducing bending force by approximately 10% to 30% compared to traditional lower dies.
In summary, different seamless bending solutions can be provided based on customer requirements. Technical support and actual seamless bending results (bending tests) can be provided anytime and anywhere. In the fiercely competitive sheet metal industry, efforts are being made to provide more efficient and higher return on investment bending products for the domestic sheet metal industry.
The competition in the sheet metal processing industry has become increasingly fierce. To establish a strong position, companies must continuously improve their processing techniques. In applications such as precision stainless steel, aluminum alloy, aerospace parts, and copper sheet bending, customers no longer settle for functional products but also have higher requirements for craftsmanship and aesthetics. Traditional bending processes can easily damage the surface of the workpiece, leaving visible indentations or scratches from contact with the die. These marks cannot be removed and result in scrapped parts. Therefore, the demand for seamless bending is growing stronger. This article provides a detailed introduction to five methods for reducing indentation marks: die parameters (V-opening size, shoulder radius R), mark-free membrane pressing, non-metallic material V-groove, rotary die, and roller-type Multi-V die, offering solutions for seamless bending.
Impact of Die Parameters on Bending Indentation
Influence of V-opening Size
When bending different thicknesses of metal sheets, the choice of V-opening size for the lower die varies. Under the same plate thickness and with the same upper die, a larger V-opening size results in less pressure between the metal sheet and the shoulder of the V-opening, reducing frictional force and naturally decreasing the depth of the indentation. Therefore, it is recommended to use a slightly larger V-opening for the lower die.
Influence of Shoulder Radius R
Different shoulder radius R values of the V-opening result in different frictional forces on the metal sheet during the bending process. The larger the shoulder radius R of the V-opening, the lower the pressure between the metal sheet and the shoulder, resulting in lighter indentations, and vice versa. Test diagrams of indentations on the same metal sheet with different R values (Ra < Rb) clearly show that Ra has significantly more bending indentations than Rb. Therefore, it is recommended to use a lower die with a slightly larger shoulder radius.
Mark-Free Membrane Pressing
From the perspective of the friction pair, seamless bending can be achieved by avoiding direct contact between the upper and lower dies and the metal sheet and using a mark-free membrane to separate them. There are three types of mark-free membranes: K-003, K-004, and K-005, with their relevant parameters listed. The mark-free membrane mainly acts as a buffer between the workpiece and the shoulder of the lower die, reducing the friction coefficient and offsetting the pressure between the die and the metal sheet, thereby preventing indentation marks during bending.
Mark-free membranes have the advantages of low cost and easy use. Simply place the mark-free membrane on the lower die during operation. Bending tests with mark-free membranes have shown that they effectively prevent bending indentations.
Non-Metallic Material V-Groove
From the perspective of the friction pair, it is possible to consider using non-metallic materials that are softer than the metal sheet for the shoulder of the V-groove while ensuring the desired extrusion effect. Materials such as polyurethane and nylon can be used. Currently, the K-001/5 V-groove with polyurethane elastomer can be used in conjunction with the standard die OZU-016/327. The unique INZU series V-groove, made of high-strength nylon material, is used in combination with an extended die and is typically used for bending aluminum sheets with a thickness of 0.4-0.5mm, yielding good results.
Rotary Die
The rotary die deviates from the traditional fixed lower die V-opening structure by incorporating a flip mechanism on the inclined surfaces on both sides of the V-opening. During the process of the upper die pressing the sheet, the flip mechanism on the lower die is flipped inward by the pressure from the upper die, allowing the sheet to be bent into shape. The rotary die comes in three models and can bend sheets with a thickness ≤5mm.
Thanks to the strict tolerance requirements, CNC depth hardening technology on the contact surface, and the ability to rotate the V-opening, the rotary die allows for easy production of parts with shorter flange edges and minimizes surface indentation during bending. The advantages of the rotary die include:
(1) Manufacturing holes and grooves without deformation in the area near the bending centerline.
(2) Reducing surface indentation during part bending.
(3) Achieving very small inner bending radii.
(4) The rotary mechanism and contact surface undergo hardening treatment, ensuring a longer lifespan and accuracy.
(5) Easy disassembly and maintenance of the rotary die.
(6) Strict tolerance requirements during die processing ensure maximum precision during bending operations.
(7) Compact die dimensions ensure maximum bending flexibility.
(8) The same die can bend various thicknesses of sheets.
(9) Can be combined with certain customized lower dies for 90° bending.
The rotary die, equipped with a tension spring and flip plate structure, can achieve bending of parts with shorter flange edges and oblique edges by using a replaceable rotating V-opening. A comparison test was conducted using the rotary die OZU-WRB-301 and the lower die OZU-051 for bending. A 1mm-thick mild steel sheet and the same BIU-021 upper die were used. The test results showed that the rotary die was more effective in avoiding bending indentation compared to the conventional lower die OZU-051.
Multi-V Die with Roller-Type Adjustable V-opening
Similarly, based on the principle of reducing the friction coefficient between the sheet and the shoulder of the lower die V-opening, the sliding friction pair between the sheet and the shoulder can be transformed into a rolling friction pair, significantly reducing the friction force on the sheet and effectively avoiding bending indentation. This technique has been widely used in the die industry, and the solution includes a roller-type adjustable Multi-V lower die. The die is equipped with hardened rollers with low friction coefficients, greatly reducing external creases on bent parts and reducing bending force by approximately 10% to 30% compared to traditional lower dies.
In summary, different seamless bending solutions can be provided based on customer requirements. Technical support and actual seamless bending results (bending tests) can be provided anytime and anywhere. In the fiercely competitive sheet metal industry, efforts are being made to provide more efficient and higher return on investment bending products for the domestic sheet metal industry.
