Sheet Metal Bending Parameters Guide
Sheet Metal Bending
Refers to the process of changing the angle of sheet metal or plate parts, such as bending sheets into V-shape, U-shape, etc. Generally, there are two methods for sheet metal bending: one method is die bending, which is used for structurally complex, small volume, and mass-produced sheet metal structures; the other is bending machine bending, which is used for processing larger structural sizes or lower volume sheet metal structures. These two bending methods have their own principles, characteristics, and applicability.
Die Bending:
For annual processing volumes of over 5,000 pieces and part sizes that are not too large (generally 300X300), manufacturers usually consider die stamping for processing.
Step Processing Method
For some sheet metal Z-shaped step bends with low height, manufacturers often use simple dies on stamping presses or hydraulic presses for processing. For small batches, they can also be processed on a bending machine with a segment difference die, as shown in the figure below. However, its height H should not be too high, generally it should be within (0～1.0)t. If the height is (1.0～4.0)t, the use of a die with a loading and unloading structure should be considered according to the actual situation.
The height of this die step can be adjusted by adding shims, so the height H is adjustable. However, there is a disadvantage: the length L dimension is not easy to ensure, and the verticality of the vertical edge is not easy to guarantee. If the height H dimension is large, it is necessary to consider bending on a bending machine.
Bending machines come in two types: conventional bending machines and CNC bending machines. Due to high precision requirements and irregular bending shapes, sheet metal bending for communication equipment is generally done on CNC bending machines. The basic principle is to use the bending machine's bending knife (upper die) and V-groove (lower die) to bend and form the sheet metal parts.
Advantages: Easy to clamp, accurate positioning, fast processing speed.
Disadvantages: Low pressure, can only process simple shapes, low efficiency.
Bending Knife (Upper Die)
The forms of bending knives are shown in the figure below. During processing, they are mainly selected according to the shape requirements of the workpiece. Manufacturers usually have a variety of bending knife shapes, especially those with a high degree of specialization, who order many shapes and specifications of bending knives to process various complex bends.
The lower die generally uses a V=6t (t is the material thickness) die.
There are many factors affecting bending processing, mainly including the upper die fillet radius, material, material thickness, lower die strength, lower die mouth size, etc. To meet the needs of the product, while ensuring the safe use of the bending machine, manufacturers have standardized the bending knife dies. We need to have a general understanding of the existing bending knife dies during the structural design process. See the figure below, the left is the upper die, and the right is the lower die.
Basic Principles of Bending Processing Order:
(1) Bend from the inside out;
(2) Bend from small to large;
(3) Bend special shapes first, then general shapes;
(4) The previous process should not affect or interfere with subsequent processes after forming.
Bending Radius
When sheet metal is bent, there must be a bending radius at the bend. The bending radius should not be too large or too small and should be appropriately selected. A bending radius that is too small can easily cause cracking at the bend, and a bending radius that is too large makes the bend prone to rebound.
For ordinary low-carbon steel plates, anti-rust aluminum plates, brass plates, copper plates, etc., an inner fillet of 0.2 is no problem, but for some high-carbon steel, hard aluminum, super-hard aluminum, this bending fillet will cause bending fractures or outer fillet cracking.
Bending Springback
Springback angle Δα=b-a
In the formula, b-the actual angle of the workpiece after springback;
a-the angle of the die.
Factors affecting springback and measures to reduce springback
(1) The mechanical properties of the material: The size of the springback angle is proportional to the yield point of the material and inversely proportional to the elastic modulus E. For sheet metal parts with high precision requirements, to reduce springback, materials should be chosen as low-carbon steel as much as possible, and high-carbon steel and stainless steel should not be chosen.
(2) The relative bending radius r/t: The larger it is, the smaller the degree of deformation, and the larger the springback angle Δα. This is a relatively important concept. The fillet of sheet metal bending should be as small as possible within the limits of material properties to improve precision. Special attention should be paid to avoiding the design of large radii, as shown in the figure below. Such large radii pose greater difficulties for production and quality control.
