Manufacturing Process
Blanking
下料 / 落料
Cutting a flat blank from coil or sheet metal before forming, using a dedicated blanking die on a stamping press.
Process Steps
- Material coil loaded
- Blanking die cuts blank
- Blank edges inspected
- Blank transferred to next operation
What is blanking?
Direct answer: blanking shears a flat part out of coil or sheet metal with a punch and die on a press. The piece that falls through the die is the part. Piercing uses the same tooling and the same physics, but there the strip is the part and the hole is the feature.
Blanking is usually the first operation in a stamping route and the last one for a flat part. A washer, a shim, a lamination, a bracket blank and the circular blank that is about to be deep drawn all come off a blanking die.
Blanking, piercing and fine blanking — what is the difference?
| Operation | What comes out | Edge you get | Typical tolerance |
|---|---|---|---|
| Blanking | The cut-out is the part | Sheared: rollover, burnish band, fracture zone, small burr | ±0.05–0.25 mm |
| Piercing | The strip is the part; the hole is the feature | Same sheared profile, mirrored | ±0.05–0.12 mm |
| Fine blanking | The cut-out is the part | Smooth, near-vertical shear over 80–95 % of the thickness | ±0.01–0.03 mm, flatness better than 0.02 mm |
If the drawing shows a functional edge with no burr and a tolerance under ±0.05 mm, the answer is usually fine blanking or a shaved edge, not a tighter ordinary blanking die.
What decides the blanking tolerance and the burr
| Factor | What it does |
|---|---|
| Die clearance | Typically 5–10 % of material thickness per side, tuned to the material. Too little clearance raises the burr and wears the die; too much pulls a rougher fracture zone. |
| Material | Mild steel blanks cleanly; stainless work-hardens and needs more clearance; aluminium tears more easily but smears and marks. |
| Punch and die condition | Burr height grows through the die's life. A punch kept sharp holds a burr under about 5 % of thickness; a worn punch does not. |
| Strip utilisation | The layout decides how much of the coil becomes part and how much becomes scrap. On a blank with an awkward outline, the layout can move the piece price more than the press does. |
| Press and feed | Feed pitch accuracy and press parallelism set the position tolerance between features cut in different stations. |
Common problems and how they are avoided
- Burr above specification. Caused by worn punches, wrong clearance, or a material that work-hardens. Fixed by re-grinding, correcting clearance, or moving to fine blanking.
- Slug pulling. The cut slug rides back up with the punch and marks the strip. Fixed by shear on the punch face, a slug-ejector pin, or slightly different clearance.
- Edge cracking on hard or thick material. Fixed by annealing, a larger corner radius on the part, or a shaved/ground edge.
- Dimensional drift over a long run. Fixed by in-process gauging on the critical feature rather than a single first-article check.
Frequently asked
What is blanking in metal stamping?
It is the operation that cuts a flat part out of sheet or coil with a punch and die. It is normally the first step of a stamping route, and for a flat part it is also the last.
What tolerance can blanking hold?
For a well-maintained die, roughly ±0.05–0.25 mm on the blank outline and ±0.05–0.12 mm on a pierced hole. Tighter than that means shaving, fine blanking or a secondary machining operation.
What is the difference between blanking and fine blanking?
Fine blanking adds a V-ring impingement and a counter-punch that clamp the material in three directions, so the part shears with a smooth edge instead of a fractured one. It costs a more expensive tool but removes a later shaving or grinding operation.
Which materials can be blanked?
Low-carbon and mild steels, stainless steels, electrical steels, aluminium, brass and copper, plus coated and plated stock. Thickness normally runs from 0.2 mm to about 6 mm on our presses.
Does the blank have to be flat?
The blank itself is flat, but the same die can form it in the following station — a drawn housing, a bent bracket or a coined face often starts life as a blank cut one station earlier.
Related: piercing · fine blanking · trimming · deep drawing · precision metal stamping · progressive die stamping