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There are 20 taboos in mold design process. How many do you know?

Twenty taboos in die design process, what do you know?

The reasonable process analysis is needed to avoid design defects and die scrap. There are short boards in the design without practical operation. How to avoid process defects?

Taboo of bending process

1、 Bend fillet radius should not be too large

When the workpiece is bent, besides plastic deformation, it also has elastic deformation and springback phenomenon. Therefore, the fillet of the bending part should not be too large. Otherwise, the bending angle cannot be guaranteed to be stable.

2、 The radius of the bend fillet should not be too small

Too small bending angle R can lead to tensile cracking of outer fiber. For low carbon steel, the minimum bending fillet is about 1.0T; The minimum bending fillet of brass and aluminum is about 0.6T; For medium carbon steel, the minimum bend fillet is about 1.5T.

3、 Bending straight edge should not be too small

In order to ensure the bending quality of the workpiece, the straight edge height h of the bending product should not be too small, and it must be greater than or equal to the minimum bending height Hmin.

h≥hmin= +2t

Where:

R - curved fillet

T - thickness of bending plate

4、 The distance between the bending edge and the hole should not be too small

When bending the blank with holes, the hole margin should not be too small. If the hole position is too close to the bend edge, the shape of the hole changes when bending. The distance L from the hole edge to the bending edge shall conform to the following formula:

When T < 2, l ≥ R + T

When t ≥ 2, l ≥ r+2t

Where:

R - curved fillet;

T - thickness of bending plate.

5、 The symmetry between bending shape and size should not be too different

In order to prevent deformation, the height difference of bending parts should not be too large. The shape and size of the bending parts shall be symmetrical as far as possible, otherwise, abnormal distortion will occur at the small end. If such results are difficult to improve at design time, it is necessary to ensure that:

h>r+2t

Where:

H - height of small side;

R - curved fillet;

T - thickness of bending plate.

6、 The punching and unloading hole groove should not be ignored at the local bending edge

When bending a certain part of the edge locally, in order to make the tear at the junction due to stress concentration, it is not necessary to ignore the first punching and unloading hole, cutting groove, or displacement of bending curve for a certain distance.

picture

7、 The process cut should not be ignored in narrow edge bending

When the narrow edge is bent, the shape of the section in the deformation area will be distorted, that is, the width of the inner surface becomes wider and the width of the outer surface becomes narrower. When the width of the plate is B < 3T (t is the thickness of the plate), it is especially obvious.

If the accuracy of width b of bending part is high and bulge is not allowed, the process cut should not be ignored in advance on the bending line.

8、 Springback cannot be ignored in bending process

The plastic deformation and elastic deformation exist simultaneously in bending. When the external load is removed, the elastic deformation disappears and springback is produced. The rebound value is related to the material properties, relative bending radius r/t, bending angle and other factors.

Yield point of material σ The higher s, the smaller the elastic modulus E, the smaller r/t and the larger the bending angle, the greater the rebound. In order to ensure the accuracy of the workpiece, springback can not be ignored when bending.

The method of mold repairing, different rebound direction of different parts, and local increase of triangle rib can be used to reduce springback, and the concave die structure of swinging block can be used to reduce springback.

9、 The ordinary bending method cannot be used for workpieces with large bending radius

For parts with large bending radius, the common bending method cannot be used. Otherwise, due to its large elastic deformation, the required shape and size cannot be obtained, so the method of pulling and bending can be used.

Before bending, an axial tension is added, and the data make the stress in the blank section slightly greater than the yield point of the material, and then bend at the same time as the tensile force.

10、 Bending of complex shape parts cannot be in place at one time

For the bending parts with complex shape, it is not allowed to bend at once, but it needs to be bent for many times. The principle of process arrangement is to bend the outer corner first. The latter bending can not affect the deformation of the previous bending part. The number of bends can be twice, three, or even more.

11、 No notch is allowed at the edge of bending part

If the edge part has a notch, if the gap is punched out in the blank, the fork will appear during bending, and it will not be formed in case of serious. This is to leave a connecting strip at the notch and then cut the joint strip after bending.

12、 The structure of bending die cannot ignore the blank offset

In bending process, offset is an important factor affecting the accuracy of workpiece. Therefore, before bending, the blank should be fixed on a part of the mold reliably to prevent the offset during bending.

The holes in the parts shall be used as much as possible to locate. If there are no available holes on the part, process hole positioning can be considered.

13、 Bending die structure shall not make the material thin and scratched locally in the closing die

Bending die should pay attention to bending only in the bending curve position determined by the part during the die closing process. The blank should not produce large local thinning and scratch.

When bending with the structure shown in the left figure, the position of the bending curve at the outer corner C changes during the bending process. It is at point B and finally to point C, so the shape of the outer corner of the part is not correct and the straight arm part becomes thinner.

14、 The die structure shall not prevent and prevent the turning and moving of blank during the die closing process

The structure of bending die should consider the turning space of blank during bending, which can not prevent and prevent the blank from moving and turning, otherwise, it will affect the shape and size of workpiece. This is particularly important for the complex shape of multi angle bending.

15、 Bending workpiece should not be made of materials with small elastic modulus

The bending rebound is proportional to the elastic modulus of the material. The elastic recovery of the material with small elastic modulus is large after deformation, so it is not suitable for bending process.

The elastic recovery of the materials with large elastic modulus is small when the materials are at the same yield point. Annealed mild steel is more suitable for bending work than soft manganese brass.

16、 Bending workpiece should not be made of materials with high yield point

The bending rebound is proportional to the yield limit of the material. The material with high yield point has a large elastic recovery after deformation, and it is not suitable for bending process. That is, the material with the same elastic modulus and the material with high yield point has a large elastic recovery. Therefore, cold working hardening steel is not suitable for bending process.

17、 For bending parts with large bending radius and arc angle, it is not suitable to use the common bending method

Bending parts with large bending radius and arc angle should be rolled (rolling plate), rather than ordinary bending method. Rolling bending is to place the slab in 2-4 rollers to pass through, and with the rotation of the roller, the slab is bent to form. In addition, because the position of the roller can be changed relative to the slab, it can also be made into quadrilateral, elliptical and other non-circular section cylinder parts.

18、 The bending method of long strip material should not be ordinary

The bending of long strip material around the longitudinal axis should be formed by rolling instead of ordinary bending method. Rolling forming is to place the strip in the front and back straight array forming roller.

With the rotation of the roller, the belt material is sent forward, and then the axial bending is carried out in a sequential manner. Rolling forming can produce the complex section shape parts. The manufacturing of the roller is simple, the cost is low and the life is longer.

19、 The general rolling forming method is not suitable for parts with variable cross section

In order to reduce investment, rolling forming can be used for the small and medium-sized production of variable section groove parts. At this time, the forming roller needs to move horizontally in addition to the longitudinal relative movement of slab.

20、 The bending method of pipe and profile should not be ordinary

Although the bending of pipe and profile is the same as that of sheet metal, the process and difficulty are different from each other. The bending of pipe and profile must prevent the shape distortion of blank section in the bending deformation area.

In production, the bending methods of pipe and profile are drawing bending, rolling bending, pushing bending and bending. It should be noted that the working surface of the convex die, roll roll, push bending and bending fixed die shall be made into grooves consistent with the shape of the blank section to prevent the rotation of the section and the distortion of the shape. If necessary, the corresponding mandrel shall be added to the pipe.