# Structural design of metal presses and bent parts

Guidelines: When bending, the designed structure must follow the law of bending deformation. Minimum radius of curvature, amount of springback, minimum bending length, bending holes or grooves, hole margins, bending, bending dimensions and bending accuracy, etc. You may need to calculate things such as a blank estimator.

Bending process:

Stamping is the bending of plates, special-shaped materials, pipes and other components into parts with a certain curvature and a specific shape, which is called bending.

It is usually bent on a press, bent on a folding machine, wound on a coiler, bent or bent manually. The use of hemming and bending to increase the moment of inertia, and the use of cross-section modulus to increase the stiffness are good ways to reduce the design weight.

When bending the composition of a part, you need to pay attention to how the part is placed in the mold.

Especially for hard materials, it is difficult to deform 180 degrees over the total length of the bend. Therefore, a small opening must be left at the corner before bending.

When bending U-shaped parts. The long side is too small to choose.

The bending radius should be selected according to the material grade and thickness of the hardness tester. For thinner materials, it is easy to bend, and the bending radius can be fixed and small. Because of its less elasticity, it is more robust.
When bending, the rough surface of the workpiece should face the bending direction as much as possible to avoid pulling and tearing the burr.

For symmetrical parts, symmetrical positioning holes can be set in advance to prevent error-proofing positions during bending.
For U-shaped workpieces, the two curved sides should be as long as possible to avoid moving to one side during bending. If not allowed, we can provide a craft hole for positioning.

Hemming is a special kind of bending. The inner diameter of the coil hole is determined by the thickness of the material to be crimped. The inner diameter of the winding hole must be capitalized. Generally speaking, the inner diameter D (>1.5t) is sufficient. There is no need to set the center line of the crimping edge to the center of the metal plate. If the plane of the metal plate is tangent to the cylinder, it is economical to manufacture.

Part piping

Bending deformation characteristics:

The sheet is bent, and the bending deformation zone is usually thin.

When the steel bar is bent, when r≥1.5d, the bending section is basically unchanged. When r <1.5d, the bending deformation zone will be distorted and the neutral layer coefficient x will change. (See related manuals for specific parameters)

Since the outer wall is thin and the inner wall is thick, the tube is curved and usually changes from a circular shape to an oval shape.
The fillet radius of the bent part must be greater than the minimum bending radius of the material.

In order to obtain a smaller bending radius, a bending method or a multiple bending method can be used after the inner groove is bent.

Curved holes or slots:

If the bending line of the bent part overlaps the outer edge, a hole or groove needs to be drilled first to avoid corner deformation or cracking. The processing hole d≥t (d is the processing hole diameter, t is the plate thickness); the groove depth is A>R (bending radius), B>t (plate thickness).

Punching process hole or slot

Hole margin: curved holes should avoid bending deformation zone. If you need to get close, add a craft hole and then bend it.

The holes in the bent part are punched before bending, and bent before punching. Bending holes are divided into first punching, back bending, first bending and punching. Some corners are not good after the corner.

The holes in the bent part are punched before bending, and bent before punching. Some bends are not punched well. Do not be too close to the edge of the hole that is first punched and then bent to avoid deformation of the hole. If possible, if holes or grooves are added during processing, or the edge of the hole is far away from the bending center, then s≥t, t will be very large, and s will be correspondingly larger.

Hole edge processing standard

Shape design of bending parts:

The shape suitable for bending is easy to understand. This is a good process, but not necessarily low cost. As shown in Figure a below, three molds are required for blanking, bending, and re-cutting. It is more economical to cut into strips. As shown in Figure b, the bending direction has been changed to uniform, and the mold structure is simple and easy to manufacture. Certification analysis, unchanged storage materials, blanking dies, small bending dies, more bending is required, but two operations are required.
Part blanking mold

When bending parts of different widths, you need to pay attention to the position of the bending line. Otherwise, protrusions and cracks will appear on the wide side. The bend line can move a certain distance or enter the process gap.

The height of the straight edge of the curved part should be more than twice the thickness of the material. If the straight side of the curved part needs to be straight, the height H of the straight side (excluding the bending radius) must be greater than twice the thickness of the material, preferably H>3t. If it is less than 2T, the groove must be pressed in advance.

size:
As shown in Figure a, the hole position and size are processed by blanking and punching, which is easy but low in accuracy. As shown in Figures b and c, this process is stamping, bending or simultaneous stamping. The mold is complicated, but the precision is high. Therefore, the size is related to the process, precision and cost, and it is worthy of consideration by the designer.

Parts bending accuracy

Bending accuracy:

The accuracy of the bending part is not high, and the dimensional accuracy is IT12 to IT16 due to various influences such as plate thickness deviation and repulsive force.

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