Manufacturing Process
Hole Flanging
翻孔 / 冲孔翻边
Forming a collar around a punched hole to add strength for thread rolling, self-tapping screws or tube connections.
Process Steps
- Pilot hole punched
- Flange die forms collar
- Collar height and ID checked
- Thread or assembly test
What is hole flanging?
Direct answer: hole flanging forms a collar around a pierced hole by pulling material upward (or downward) with a punch. The flange adds threaded length, provides a bearing surface, or stiffens the hole — all without adding a weld nut or a thicker sheet.
Why it is used
- Thread engagement in thin sheet. A flanged hole gives a tap enough material to hold torque, which is otherwise impossible below about 0.8 mm.
- Bearing surface. The flange presents a cylindrical face for a shaft, pin or bushing.
- Stiffness. A flange acts like a short boss and stiffens the surrounding area against bending.
- Assembly location. The flange centres a mating part during assembly.
What the design has to get right
| Parameter | Practical limit |
|---|---|
| Flange height | Roughly 0.5–0.75× the hole diameter, less for thin material |
| Wall thickness at the flange edge | Not less than about 60 % of the original thickness |
| Pre-pierce hole diameter | Set by the flange OD and height, not by the final hole |
| Edge condition | A generous radius on the punch reduces cracking |
The wall thins as it is stretched over the punch, and the flange height is limited by how much the material can stretch before it cracks. For most steels that is where the practical limits above come from; softer materials go further, harder ones less far.
How it is made
- The hole is pierced undersize — the pierced hole becomes the top of the flange.
- A flanging punch with a suitable radius pushes the material into a die cavity, forming the collar.
- The flange is often formed in the same stamping tool, in a station after the pierce.
- If the hole is to be threaded, it is tapped afterwards, in-die or as a secondary operation.
Alternatives, and when they win
- Direct tapping when the material is thick enough to hold the thread.
- Weld nut or clinch fastener where the thread needs to take repeated loading or a large diameter.
- Extruded and tapped hole (a flanged hole with a deep collar) where the thread needs several pitches of engagement.
- Thicker sheet where the flange would require a stretch the material cannot take.
Frequently asked
What is hole flanging used for?
Adding thread length or a bearing surface to a thin sheet part without adding a separate fastener or increasing the material thickness.
How tall can a hole flange be?
Rule of thumb: about 0.5–0.75× the hole diameter, limited by the material's ability to stretch. Aluminium and mild steel go further than high-strength or heavily work-hardened stock.
Will the flange crack?
Only if it is asked to stretch beyond what the material can take, or if the punch radius is too tight. Both are avoidable at design stage: a larger pre-pierce hole and a radiused punch solve most cases.
Does flanging change the hole diameter?
The hole you finish with is set by the punch. The pre-pierce hole is smaller and is calculated from the finished height and diameter, so the drawing should give the final dimensions.
Related: piercing · tapping · countersinking · blanking · deep drawing