Bending Part Development Size Calculation

In the metal stamping industry, accurately calculating the development size of bending parts is crucial for producing high-quality, precision components. As a professional manufacturer and factory in China specializing in metal stamping and deep drawing, China Custom Stamping leverages advanced techniques and empirical data to ensure optimal material usage and dimensional accuracy. This article provides a detailed overview of bending part development size calculation, covering key principles, formulas, and practical applications.

1. Determining the Strain-Neutral Layer Position

During the bending process, the strain-neutral layer shifts depending on the degree of deformation. The strain-neutral layer’s curvature radius ρₑ can be derived using the volume consistency principle:

$ρ_{e} = (t r + 2 η) η βt$

In practice, the empirical formula is often used for simplicity:

$ρ_{e} = r + x t$

Here, x is the neutral layer coefficient, which varies with the r/t ratio:

Table 5-8: Neutral Layer Coefficient x Values

r/t	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	1.0	1.2
x	0.21	0.22	0.23	0.24	0.25	0.26	0.28	0.30	0.32	0.33

r/t	1.3	1.5	2.0	2.5	3.0	4.0	5.0	6.0	7.0	≥8
x	0.34	0.36	0.38	0.39	0.40	0.42	0.44	0.46	0.48	0.50

2. Blank Length Calculation for Bending Parts

A. r > 0.5t Bending Parts

Table 5-9: Development Size Calculation Formulas (r > 0.5t)

Bending Characteristic	Diagram	Calculation Formula
Single Right-Angle Bend		$L = a + b + 2 π (r + x t)$
Double Right-Angle Bend		$L = a + b + c + π (r + x t)$
Four Right-Angle Bend		$L = 2 a + 2 b + c + π (r_{1} + x_{1} t) + π (r_{2} + x_{2} t)$
Circular Tube Bending		L=πD=π(d+2t)

B. r < 0.5t Bending Parts

Table 5-10: Blank Length Calculation for r < 0.5t Bending Parts

No.	Bending Feature	Calculation Formula
1	Single-Angle Bend	$L = a + b + 0.4 t$
2	Double-Angle Simultaneous Bend	$L = a + b + c + 0.6 t$
3	Triple-Angle Simultaneous Bend	$L = a + b + c + d + 0.75 t$
4	Two Angles First, Then Third Angle	$L = a + b + c + d + t$
5	Four-Angle Simultaneous Bend	$L = a + 2 b + 2 c + t$
6	Four Angles in Two Steps	$L = a + 2 b + 2 c + 1.2 t$

General formula for no-radius bending:

$L = l_{1} + l_{2} + \dots + l_{n} + n K t$

Where K values are:

r = 0.05t: K = 0.38–0.40
r = 0.1t: K = 0.45–0.48
Single-angle bend: K = 0.5
Multi-angle bend: K = 0.25
High ductility materials: K = 0.125

C. Coiled Parts Calculation

Table 5-13: Neutral Layer Coefficient K for Coiled Parts

r/t	>0.3–0.6	>0.6–0.8	>0.8–1	>1–1.2	>1.2–1.5	>1.5–1.8	>1.8–2	>2–2.2	>2.2
K	0.76	0.73	0.70	0.67	0.64	0.61	0.58	0.54	0.50

Table 5-12: Coiled Parts Development Length Calculation

Coil Form	Diagram	Calculation Formula
Hook Type I		$L = L_{1} + L_{2} + (180 ^{\circ} π R α)$
Hook Type II		$L = L_{1} + L_{2} + L_{3} + 4.71 R$
Hinge Type		$L = L_{1} + (180 ^{\circ} π R α)$

Where $R = r + K t$

3. Large Radius Bending (r ≥ 8t)

For large radii where neutral layer coefficient approaches 0.5, development size is calculated based on material thickness center layer.

Table 5-11: Different Bending Shapes Development Calculation

No.	Reciprocal Curve Shape	Calculation Formula
1		$A = l R ^{1} sin β = R π α 360 s i n α sin β$
2		$A = 2 B (R^{1} + R^{2}) - B^{2}$ $cos β = R ^{1} + R ^{2} R ^{1} + R ^{2} - B$
3		$A = B cot β + (R_{1} + R_{2}) tan 2 β$ $y = s i n β B - (R_{1} + R_{2}) tan 2 β$
4		First coil bending radius: $R_{2} = (β 180 ^{\circ} - 1) R_{1}$

4. Practical Applications at China Custom Stamping

At China Custom Stamping, we implement these calculations with precision:

Material Analysis: Selecting appropriate K and x coefficients based on material properties
Trial Verification: Conducting test bends to validate theoretical calculations
Process Optimization: Adjusting parameters for complex geometries
Quality Assurance: Ensuring dimensional accuracy through systematic calculation methods

Our expertise covers all bending scenarios:

Small radius bends (r < 0.5t) using empirical correction factors
Medium radius bends (0.5t < r < 8t) using neutral layer principles
Large radius bends (r ≥ 8t) using center layer calculations
Coiled components using specialized K coefficient tables

5. Conclusion

Accurate development size calculation is essential for efficient metal stamping production. The comprehensive tables and formulas presented here provide a systematic approach for different bending scenarios. As a leading metal stamping and deep drawing manufacturer in China, China Custom Stamping combines theoretical knowledge with practical experience to deliver precision components with optimal material utilization.

By mastering these calculation methods and applying the appropriate coefficients from the provided tables, manufacturers can significantly improve product quality, reduce material waste, and enhance production efficiency.

China Custom Stamping – Your trusted partner for precision metal stamping and deep drawing solutions in China.

Bending Part Development Size Calculation