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Flanging and Hole Flanging

Flanging and Hole Flanging

Flanging and Hole Flanging – Complete Technical Guide for Custom Metal Stamping

Basic Definition of Flanging & Hole Flanging

Flanging and Hole Flanging

As a professional metal stamping and deep drawing maker in China, China Custom Stamping relies on flanging and hole flanging as core secondary sheet metal forming processes for all custom stamped metal components, including automotive hardware, electronic enclosures, appliance brackets and precision deep drawing parts exported worldwide.
Sheet metal forming refers to reshaping blank metal via localized plastic deformation. Standard forming processes cover flanging, hole flanging, bulging, necking, expanding, embossing, leveling and sizing. Among all forming technologies, edge flanging and hole flanging are the most commonly used post-blanking and post-piercing operations.

1.1 Two Classifications of Edge Flanging

Two types of sheet metal flanging

Edge flanging (outer edge flanging) bends vertical short flanges along the outer curved contour of workpieces, split into two deformation modes as shown in Figure 7-1:
  1. Inward Concave Flanging (Stretching Flanging)The deformation zone material bears tangential tensile stress, causing the vertical flange wall to thin drastically at the top edge. Exceeding the material’s allowable deformation limit will lead to edge cracking.Deformation degree formula for concave flanging:

E凹=b/(R-b)*100%(7-1）

Where:

E凹= inward concave flanging deformation degree (%)

b = vertical flange wall height (mm)

R = inner concave curve radius (mm)

  1. Outward Convex Flanging (Compression Flanging)Material inside the deformation zone bears tangential compressive stress. Flange edges thicken instead of thinning; cracking rarely occurs, while wrinkling becomes the primary defect to control.

1.2 Definition & Deformation Principle of Hole Flanging

Hole flanging (inner hole flanging) forms vertical cylindrical flanges around pre-pierced inner holes on flat or deep drawn blanks. It is widely used to create tapping thread bosses, assembly connecting flanges and integrated bushing structures without welding.
The core deformation feature is uniaxial tensile stretching of the material surrounding the prefabricated hole. The blank stretches along the punch axis, expanding the hole diameter and continuously reducing wall thickness from the flange base to the top edge. Excessive stretching will create cracks at the flange top.

2. Core Calculation Formulas + Complete Material Limit Flanging Coefficient Tables

Flat blank hole flanging dimension

All calculation parameters rely on standardized material flanging coefficient tables, which are fully listed below for direct engineering reference, eliminating reader confusion about Table 7-1, 7-2 and 7-3.

2.1 Hole Flanging Coefficient K & Table 7-1 (Limit Flanging Coefficients by Forming Method)

The hole flanging coefficient K =d0/D  (Formula 7-4) is the core index to judge forming feasibility. Smaller K means larger deformation risk of cracking.

Table 7-1: Limit Flanging Coefficients of Common Industrial Metals (Rigid Die Forming vs Rubber Flexible Die Forming)

Material Grade Material State Limit Coefficient (Rigid Metal Die Forming) Limit Coefficient (Rubber Flexible Die Forming)
1050 Aluminum Alloy Soft (O temper) 0.30 0.25
3A21 Aluminum Alloy Soft 0.30 0.23
5A02 Aluminum Alloy Soft 0.35 0.25
H62 Brass Soft 0.45 0.35
H62 Brass Half-Hard 0.40 0.33
1Cr18Ni9 Stainless Steel Soft Annealed 0.58 0.40
H68 Brass Soft 0.45 0.38

2.2 Table 7-2: Limit Hole Flanging Coefficients for Low Carbon Steel by Relative Thickness d₀/t

Low carbon steel is the most widely used stamping material; its limit flanging coefficient changes with the ratio of pre-hole diameter to raw material thickness.

Table 7-2: Low Carbon Steel Limit Hole Flanging Coefficient

| Relative Thickness d₀/t | 0.2 | 0.3 | 0.5 | 1.0 | 1.5 | 2.0 | 3.0 | 5.0 | 10 |

| —- | —- | —- | —- | —- | —- | —- | —- | —- |

| Limit K Value | 0.47 | 0.48 | 0.50 | 0.53 | 0.55 | 0.58 | 0.65 | 0.70 | 0.75 |

2.3 Table 7-3: Min & Max Hole Flanging Coefficients for Annealed Blank Materials

This table is used for rapid prefabricated hole size calculation in engineering design, covering galvanized sheet, aluminum, brass, carbon steel and titanium alloy.

Table 7-3: Minimum & Maximum Hole Flanging Coefficient mₘᵢₙ / m₀

Blank Material Material Thickness t (mm) mₘᵢₙ (Minimum Flanging Coefficient) m₀ (Standard Limit Coefficient)
Galvanized Steel Sheet (White Tin Plate) 0.70 0.61 0.65
Brass H62 t=0.25~2.0 0.62 0.68
Aluminum Alloy (Soft Temper) t=0.5~5.0 0.55 0.70
Hard Aluminum Alloy t=0.5~6.0 0.40 0.64
Titanium Alloy (Cold Temper) t=0.40~0.50 0.65 0.85
Titanium Alloy (Heated 300~400℃) t=0.40~0.50 0.75 0.90

2.4 Maximum Theoretical Flanging Height Calculation (Flat Blank Hole Flanging)

Figure 7-3 shows the dimensional relationship for single-step flat blank hole flanging.
Formula for maximum allowable flanging height H:

H=(D-d0)/2+0.43r+0.72t=D/2(1-K)+0.43r+0.72t (7-6)

Where:

H = theoretical maximum vertical flange height (mm)

D = outer diameter of finished flanged hole (mm)

d0= prefabricated piercing hole diameter (mm)

r = punch fillet radius (mm)

t = original blank material thickness (mm)

If the target finished flange height exceeds calculated H, one-step flanging cannot complete forming. The alternative two-process flow is shown in Figure 7-4: deep drawing to form a boss first, then piercing and secondary hole flanging.

2.5 Hole Flanging Force Calculation

Flanging force determines stamping press tonnage and die structural strength. Approximate force formula (7-7):

F=1.1πtσₛ(D−d₀) (7-7)

Where:

F = hole flanging forming force (N)

σₛ= sheet metal yield strength (MPa)

1.1 = safety correction factor for stamping impact load

For integrated piercing-flanging punches without prefabricated holes, the required forming force is 1.3~1.7 times the calculated value to account for piercing shear force consumption.

2.6 Thinning Hole Flanging Calculation & Step Punch Diagram

Thinning flanging creates ultra-high vertical flanges by controlled wall thickness reduction. The thinning deformation coefficient k is defined in Formula (7-8):

k=t₁/t (7-8)

Where:

t₁ = flange wall thickness after thinning flanging (mm)

t = original blank thickness (mm)

In mass production, k can reach 0.4~0.5, meaning the finished wall thickness is only half the raw material thickness. Step-shaped cylindrical punches are the standard die structure for thinning flanging, shown in Figure 7-6.
All formulas and material tables can be directly applied to engineering design when you order our custom sheet metal stamping service for automotive, electronics and home appliance components.

3. Standard Hole Flanging Punch & Die Structure Design (Table 7-5 Full Description + Diagram)

Die structure directly controls dimensional accuracy, surface quality and production stability of flanged parts. Table 7-5 summarizes six mainstream hole flanging punch designs with application scenarios, paired with the structural comparison diagram:
  1. Flat-Top Cylindrical Punch
    Flat-Top Cylindrical Punch

    Simplest low-cost structure, only for large-diameter flanging workpieces with loose surface quality requirements. Limitation: tensile stress concentrates on hole edges, low limit flanging coefficient and easy cracking.

  2. Parabolic Punch
    Parabolic Punch

    Universal preferred punch for precision custom stamping. Smooth curved transition gradually expands the pre-hole, evenly disperses tensile stress across the deformation zone and eliminates edge cracking. China Custom Stamping prioritizes parabolic punches for aluminum, brass and stainless steel thin-plate mass production.

  3. Piercing-Flanging Integrated Punch (No Prefabricated Hole)
    Piercing-Flanging Integrated Punch

    Combines piercing and flanging in one stamping stroke, simplifying die stations. Punch front end uses a 60° conical piercing tip with a material retaining shoulder on the die to control flange height. Suitable for small-batch low-complexity flanging components.

  4. Guided Straight Section Punch
    Guided Straight Section Punch

    Adds a cylindrical guiding segment at the punch front. The guide enters the pre-hole first to lock punch-blank concentricity, achieving ultra-high dimensional tolerance precision. Ideal for electronic precision connector hardware with strict coaxiality requirements.

  5. Punch with Post-Flanging Sizing Shoulder
    Punch with Post-Flanging Sizing Shoulder

    The rear punch section features a sizing shoulder. At stroke bottom dead center, the shoulder compresses the flange arc to eliminate springback, completing dimensional sizing without secondary shaping processes. Perfect for automotive thread flanging holes with tight thread tolerance standards.

  6. Die Inlet Fillet Optimization Design
    Die Inlet Fillet Optimization Design

    Die inlet fillet radius r is critical for flanging surface quality, with design rules matched to blank thickness t:

  • t ≤ 2mm: fillet radius r = (2~4)t
  • t > 2mm: fillet radius r = (1~2)t
Too small fillets scratch blanks and cause shear cracking; oversized fillets lead to uncontrollable flange dimensional accuracy.

3.1 Punch-Die Single-Side Clearance Selection Table (Table 7-4)

For conventional equal-thickness hole flanging without thinning, the single-side clearance between punch and die is selected based on raw material thickness t:

Table 7-4: Single-Side Clearance Between Flanging Punch & Die (Unit: mm)

| Blank Material Thickness t | 0.3 | 0.5 | 0.6 | 0.7 | 0.8 | 1.0 | 1.2 | 1.5 | 2.0 |

| —- | —- | —- | —- | —- | —- | —- | —- | —- |

| Single-Side Clearance | 0.25 | 0.45 | 0.60 | 0.60 | 0.70 | 0.85 | 0.90 | 1.3 | 1.7 |

4. Special Flanging Processes

4.1 Special-Shaped Irregular Hole Flanging

Circular hole flanging is standard, while irregular special-shaped flanged holes are widely used for automotive lock plates and appliance support brackets. Special-shaped flanged holes consist of three contour segments with distinct stress states: convex arc, concave arc and straight line, shown in Figure 7-7.
Segmented unfolding calculation rules for special-shaped flanging:
  1. Convex arc segments: treated as deep drawing compression deformation zones
  2. Concave arc segments: treated as stretching flanging deformation zones
  3. Straight line segments: calculated by linear unfolding length without extra deformation correction
The theoretical pre-hole contour from unfolding calculation needs secondary correction based on curvature radius differences. Small-radius concave arcs bear larger tangential tensile stress and crack easily, so pre-hole sizes at these positions reserve material compensation. The comprehensive correction coefficient K’ for special-shaped hole flanging is generally:

K’=(0.85~0.9)×K

Where K = standard circular hole flanging coefficient of the same material.

4.2 Mass Production Advantages of Thinning Hole Flanging

Thinning flanging is an optimized high-efficiency process for workpieces requiring ultra-high vertical flanges, with three core production benefits:
  1. Raw material cost savings: Ultra-high flanges can be formed on thin raw blanks without purchasing thicker sheet metal, reducing single-part material consumption.
  2. Simplified production flow: Avoid multi-step deep drawing + flanging combined processes; complete high-wall flanging in one stamping stroke to boost production line efficiency.
  3. Stable dimensional consistency: Step-shaped punches control uniform wall thickness reduction; finished flanges maintain consistent inner and outer diameters without uneven deformation defects.

5. Custom Flanging & Hole Flanging Stamping Service from China Custom Stamping

As a professional custom metal stamping manufacturer and deep drawing maker in China, China Custom Stamping provides one-stop custom sheet metal forming solutions integrating flanging, hole flanging, blanking, deep drawing, bending and welding for global industrial clients.
Our core flanging & hole flanging service advantages:
  1. Full-process engineering technical support: Our internal engineering team completes all calculation work including flanging deformation degree, flanging height, flanging force and prefabricated hole size according to client 2D/3D drawings, provides DFM design for manufacturability reports to eliminate forming defects in the early design stage;
  2. Customized mold development: Develop dedicated flanging dies, parabolic hole flanging punches, step thinning flanging punches and special-shaped hole flanging molds according to workpiece batch volume and precision requirements, supporting single-piece prototype trial production and million-piece mass manufacturing;
  3. Wide material processing coverage: Process all mainstream industrial metal raw materials for flanging and hole flanging, including 1050/3003/5052 aluminum alloy, H62/H65 brass, SPCC/DC01 low carbon steel, 304/316 stainless steel, galvanized steel sheet and titanium alloy;
  4. Strict quality control system: Conduct full dimensional inspection of flanged hole coaxiality, wall thickness uniformity, vertical wall height and edge crack defect detection after stamping, provide material certification, dimensional inspection reports and surface finish test data for export customs clearance and client incoming inspection.
Our custom metal stamping products with flanging & hole flanging forming are widely exported to automotive new energy, consumer electronics, household appliances, communication equipment, medical hardware and industrial machinery markets across the United States, Canada, Germany, France, Italy, Spain, Vietnam, Thailand, Malaysia and other regions. We accept customized drawings and samples, provide flexible MOQ solutions for small-batch prototype orders and large-volume mass production clients.

6. Summary

Flanging and hole flanging are irreplaceable localized sheet metal forming processes in custom metal stamping manufacturing. Mastering core technical points including flanging deformation degree calculation, complete material limit flanging coefficient tables, maximum flanging height theoretical calculation, flanging force tonnage design and punch-die structural design is the foundation to eliminate cracking, wrinkling, springback and dimensional out-of-tolerance defects during mass stamping production.
China Custom Stamping, a professional metal stamping and deep drawing maker in China, relies on mature flanging & hole flanging process technology, independent mold development capacity and strict quality control standards to deliver high-precision, cost-effective custom sheet metal stamping parts for global industrial buyers. If you have custom stamping parts requiring flanging, hole flanging or deep drawing forming, send your 2D/3D technical drawings to our engineering team for free DFM analysis and customized quotation.
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