4 Solutions to Achieve Seamless Bending

The competition in the sheet metal processing industry is becoming more and more fierce. If companies want to remain invincible, they must continuously improve their processing technology. In some bending applications such as precision stainless steel, aluminum alloy, aerospace parts, and copper plates, users are no longer satisfied with the functionality of the product and have higher requirements for its manufacturability and aesthetics. The traditional bending process is more likely to cause damage to the surface of the workpiece, and an obvious indentation or scratch will be formed on the surface in contact with the mold, which cannot be removed, resulting in scrapped parts. Therefore, the user's demand for seamless bending is becoming stronger and stronger.

The Influence of Lower Mold Parameters on Bending Indentation:

1. V influence of Opening Size：

From the perspective of the friction pair, it can be considered to change the V-groove shoulder to a non-metallic material that is softer than the plate, such as polyurethane, nylon, etc., while ensuring the originally required extrusion effect. High-strength nylon material is used in conjunction with an extended mold. It is usually used for the bending of aluminum plates with a thickness of 0.4~0.5mm under specific occasions, and the effect is better.

2. The Influence of The R-value of The Shoulder Fillet：

The R-value of the rounded corner of the V opening shoulder is different, and the friction caused to the plate during the bending and forming of the plate is different. The larger the R angle of the shoulder of the V opening, the smaller the pressure between the sheet and the shoulder of the V opening, and the lighter the indentation, and vice versa. The figure below is the indentation test chart of WILA on the same plate with different R values (Ra<Rb). Obviously, the bending indentation of Ra is obviously more than that of Rb. Therefore, it is recommended to choose a lower mold with a slightly larger shoulder fillet.

Solutions For Non-marking Bending:

1. Non-marking Film:

From the perspective of the friction pair, by avoiding the direct contact between the upper and lower molds and the plate, the non-marking film can be used to separate the upper and the non-marking film mainly to buffer between the workpiece and the shoulder of the lower mold. It functions and reduces the coefficient of friction, offsets the pressure between the mold and the plate, thereby preventing the workpiece from producing indentation during bending. The non-marking film has the advantages of low cost and convenient use. When using, only the non-marking film is placed on the lower mold. The picture below shows that the non-marking indentation film is being used for the bending test. The test results show that the use of the non-marking indentation film can effectively avoid bending and indentation.

2. Non-metallic Material V Groove:

From the perspective of the friction pair, it can be considered to change the V-groove shoulder to a non-metallic material that is softer than the plate, such as polyurethane, nylon, etc., while ensuring the originally required extrusion effect. High-strength nylon material is used in conjunction with an extended mold. It is usually used for the bending of aluminum plates with a thickness of 0.4~0.5mm under specific occasions, and the effect is better.

3. Rotor Mold：

The rotary-wing mold changes the V-opening structure of the traditional setting lower mold. The inclined surfaces on both sides of the V-opening are set as a reversible mechanism. When the upper mold presses down the plate, the upper mold presses the turning mechanism on both sides of the lower mold from the upper mold. The vertices of the mold are turned inward, thereby bending the sheet into shape, as shown in the figure below.

Thanks to the most stringent tolerance standards, the CNC deep hardening technology of the contact surface, and the rotatable V-port, it is easy to use the rotor mold to produce parts with shorter flanges and minimize part folding. The indentation on the surface during bending. The advantages of the rotor mold are:

● Holes and grooves are made without deformation in the area close to the bending centerline.

● Reduce the indentation on the surface when the part is bent.

● A very small bend fillet can be obtained.

● The rotor and the contact surface have been hardened to ensure a long service life and accuracy.

● The rotor is easy to disassemble and assemble, which is easy to clean and maintain.

● Strict tolerance requirements during mold processing ensure the ultimate accuracy during bending operations.

● The compact die size design ensures the greatest bending freedom.

● The same mold can bend plates of various thicknesses.

● It can be used in combination with some customized lower molds for 90° bending.

The rotor mold is equipped with tension spring and a flap structure and can be bent with a short flange side and a beveled side part through the built-in replaceable rotating V port.

A comparison test of bending was carried out. The results of the test showed that the use of a rotary-wing mold can more effectively avoid bending indentation than a conventional lower mold.

4. Roller Type Adjustable V Port

Also based on the principle of reducing the friction coefficient of the friction pair between the plate and the lower mold V opening, the sliding friction pair between the plate and the lower mold V opening shoulder can be transformed into a rolling friction pair, thereby greatly reducing the friction force on the plate and effectively avoiding the occurrence bending creasing.

At present, this process has been widely used in the mold industry. The mold is equipped with hardened rollers with a low coefficient of friction, which can greatly reduce the external creases of the bending parts, and at the same time, can reduce the bending force by about 10% to 30% compared with the traditional lower mold.