Sheet Metal Bending Flattening
In flatten state of sheet metal bending, the factors affecting the calculation on accuracy of the unfolding length are: bending inner radius r, width of lower mold (V-shaped groove), actual thickness of sheet material t, and bending angle a. When calculating the unfolding length of the bending sheet material, there is no explicit formula to calculate the bending allowance, and only the bending allowance of the different bending inner radius can be found.But the inner radius is related to actual processing. Different V-groove widths of the lower die will lead to the difference of inner radius, which makes impossible to determine the accuracy of the bending allowance. The bending allowance is generally determined empirically.
In sheet metal bending, we commonly use L, N, and Z bend. We will discuss about three different bending ways following:
L Bending
L fold: 90 degree fold and non 90 degree fold.
●Some conclusion of 90 degree fold in Form 1:
L=A+B-Bend Allowance
L=A+B+0.25(2*Π*r){0.25(2*Π*r) size of neutral layer}
● Non 90 degree fold:
L=A+B+Compensation ★only for reference
T=0.8 R=0.5, 120°≤q≤160°, Compensation is 0.1
160°＜q≤180° Can be negligible
T=1.0 R=0.5
120°≤q≤145°, Compensation is 0.2
145°＜q≤170°, Compensation is 0.1
170°＜q≤180°, Can be negligible
T=1.2 R=0.5, Compensation is same as T=1.0
T=1.5 R=0.5, 120°≤q≤130°, Compensation is 0.3
130°＜q≤150°, Compensation is 0.2
150°＜q≤170°, Compensation is 0.1
170°＜q≤180°, Can be negligible
180°-qq
L=A+B+ ------(2*Π*r)
360°
N Bending
N fold (Return fold):
L=A+B-C
Not completely return fold (unfold by using neutral layer)
L=A+B+C, C=0.5 (2*Π*R)
Z Bending
Z fold conclusion:
L=A+K
Note: following attached bend allowance for Z fold (Form 2)
* Coressponding K value to H height not listed on Form 2 can be calculated according to what we have.
For example: T=1.2, H=1.4;
Due to H value (1.3) is between 1.0 to 1.5, so K=(0.25-0.13)/5*3+0.13, K=0.2
Note:
1. When H value (H-T)＜V/2+1.5 (one level smaller V groove according to material thickness), we will form by differential bending die.
2. When H value (H-T)≥V/2+1.5 (one level smaller V groove according to material thickness), we will bend front side first then back side.
3. When L value ＜V/2+1.5 (one level smaller V groove according to material thickness), we will form by differential bending die.
4.When L value ＞V/2+1.5, we will bend front side first and then back side of sheets.
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