Sheet metal part and structural design knowledge-Sheet metal process analysis
Sheet metal part and structural design knowledge-Sheet metal process analysis
Sheet metal parts (sheet metal model) manufacturability refers to the parts in the punching, bending, stretching processing of the degree of difficulty.Good technology should ensure less material consumption, fewer working procedures, simple mold structure, high service life, stable product quality.In general, the biggest influence on sheet metal parts process is the material performance, parts of the geometric shape, size and precision requirements
1. Features of Sheet metal parts Sheet metal parts can generally be divided into three categories:
Sheet metal parts (sheet metal model) manufacturability refers to the parts in the punching, bending, stretching processing of the degree of difficulty.Good technology should ensure less material consumption, fewer working procedures, simple mold structure, high service life, stable product quality.In general, the biggest influence on sheet metal parts process is the material performance, parts of the geometric shape, size and precision requirements
1. Features of Sheet metal parts Sheet metal parts can generally be divided into three categories:
（1）Flat plate refers to general flat blanking parts.(2) Bending type is composed of bending or bending plus simple forming parts.(3) Forming type regular surface type or free-form surface type parts processed by drawing and other forming methods.These parts are by the plate blank by punching and deformation and other stamping methods, and they are very different from the general machining way processing parts.In the stamping process, bending deformation is the main processing method that causes the complex spatial position relation of sheet metal parts.Other processing methods generally only produce bumps or depressions and notches, holes and edges on the plate.This feature must be paid attention to when building sheet metal parts modeling system.
（2）In the process of mold design, the shape of sheet metal parts is the main basis of mold design, which determines the overall structure and shape of the mold.The dimension tolerance of sheet metal parts affects the dimension and tolerance of mold working part (such as convex and concave die).In addition, the material, shape and position tolerance and technical requirements of sheet metal parts have a great impact on the working parts of the die.Therefore, in addition to the shape information, the sheet metal part model must also include the dimensional tolerance, precision, material and technical requirements of the parts, so as to ensure the accuracy of the die design results.The model of sheet metal parts is the carrier of all kinds of information required by the following mold design application program, which requires the model of parts to reflect the characteristics of sheet metal parts, specifically to reflect the engineering semantics of sheet metal parts, so that the mold design application program can understand and easily extract the required information.
（3）Sheet metal parts generally have complex spatial position relations. Only by constructing according to the shape characteristics of sheet metal parts can user operation be simplified.
（4）Design knowledge of sheet metal structure :(minimum bending radius of the plate) when the plate is bent, if the rounded corners at the bending point are too small, the outer surface is prone to crack.If the bending corner is too large, due to the impact of springback, the precision of bending is not easy to ensure.The minimum bending radius is determined for this purpose.As follows:
The straight edge height of bending should not be too small, otherwise it is not easy to form enough bending moment, it is difficult to get the shape of accurate parts.Its value h≥R+2t only.As shown in figure:
The distance L between the edge of the hole and the center of the bending radius R should not be too small when punching the hole, so as to avoid deformation of the hole after bending.Its value L≥2tonly.As shown in figure:
When A < R, after bending, there is still a residual arc on side B near A. In order to avoid the residual arc, a must be ≥R.As shown in figure:
In the U-bend, the two bending sides should be the same length to avoid the displacement to one side during bending.If not allowed, a process positioning hole may be provided.As shown in figure:
Prevents side (trapezoid) bending from cracking or deformity.The grooves should be reserved, or the root should be changed into echelon form.Slot width K≥2t, slot depth L≥ T +R+K/2.As shown in figure:
To prevent the corner from creasing after extrusion under compression when bending, a reserved notch should be designed.Such as outdoor side plate (upper end, lower end) round corner incision form.As shown in figure:
To prevent bending, the two sides of the right Angle plane fold, should be designed to reserve the incision.As shown in figure：:
After preventing bending, a spring back cut form is created.As shown in figure:
Prevent perforation after bending to produce cracks in the cut form.As shown in figure:
To prevent bending, one side shrinks inward.Can design process positioning hole, or both sides bend at the same time, can also increase the width of the way to solve the shrinkage problem.As shown in figure:
A lap joint bent at right angles.As shown in figure:
The bending of the convex part, if the bending line is consistent with the step line as shown in Figure A, will sometimes crack and deform at the root.Therefore, make the bending line out of the step line as shown in Figure B, or design the incisions like C and D.
When bending is prevented, the hole on the bending surface will deform after being stressed, and the hole edge distance (to the bottom root) A≥4 can only be used.As shown in figure:
（2）In the process of mold design, the shape of sheet metal parts is the main basis of mold design, which determines the overall structure and shape of the mold.The dimension tolerance of sheet metal parts affects the dimension and tolerance of mold working part (such as convex and concave die).In addition, the material, shape and position tolerance and technical requirements of sheet metal parts have a great impact on the working parts of the die.Therefore, in addition to the shape information, the sheet metal part model must also include the dimensional tolerance, precision, material and technical requirements of the parts, so as to ensure the accuracy of the die design results.The model of sheet metal parts is the carrier of all kinds of information required by the following mold design application program, which requires the model of parts to reflect the characteristics of sheet metal parts, specifically to reflect the engineering semantics of sheet metal parts, so that the mold design application program can understand and easily extract the required information.
（3）Sheet metal parts generally have complex spatial position relations. Only by constructing according to the shape characteristics of sheet metal parts can user operation be simplified.
（4）Design knowledge of sheet metal structure :(minimum bending radius of the plate) when the plate is bent, if the rounded corners at the bending point are too small, the outer surface is prone to crack.If the bending corner is too large, due to the impact of springback, the precision of bending is not easy to ensure.The minimum bending radius is determined for this purpose.As follows:
| Material | Minimum bending radius (R) |
| Cold rolled sheet, galvanized sheet, galvanized sheet | R≥2t |
| Brass plate | R≥ lt |
| Aluminium alloy plate | R ≥1.2t |
The straight edge height of bending should not be too small, otherwise it is not easy to form enough bending moment, it is difficult to get the shape of accurate parts.Its value h≥R+2t only.As shown in figure:
The distance L between the edge of the hole and the center of the bending radius R should not be too small when punching the hole, so as to avoid deformation of the hole after bending.Its value L≥2tonly.As shown in figure:
When A < R, after bending, there is still a residual arc on side B near A. In order to avoid the residual arc, a must be ≥R.As shown in figure:
In the U-bend, the two bending sides should be the same length to avoid the displacement to one side during bending.If not allowed, a process positioning hole may be provided.As shown in figure:
Prevents side (trapezoid) bending from cracking or deformity.The grooves should be reserved, or the root should be changed into echelon form.Slot width K≥2t, slot depth L≥ T +R+K/2.As shown in figure:
To prevent the corner from creasing after extrusion under compression when bending, a reserved notch should be designed.Such as outdoor side plate (upper end, lower end) round corner incision form.As shown in figure:
To prevent bending, the two sides of the right Angle plane fold, should be designed to reserve the incision.As shown in figure：:
After preventing bending, a spring back cut form is created.As shown in figure:
Prevent perforation after bending to produce cracks in the cut form.As shown in figure:
To prevent bending, one side shrinks inward.Can design process positioning hole, or both sides bend at the same time, can also increase the width of the way to solve the shrinkage problem.As shown in figure:
A lap joint bent at right angles.As shown in figure:
The bending of the convex part, if the bending line is consistent with the step line as shown in Figure A, will sometimes crack and deform at the root.Therefore, make the bending line out of the step line as shown in Figure B, or design the incisions like C and D.
When bending is prevented, the hole on the bending surface will deform after being stressed, and the hole edge distance (to the bottom root) A≥4 can only be used.As shown in figure:
