The three words describe the same cutting action - a punch shears the material against a die - and differ only in what the cut is for. That difference matters, because it decides which piece is the part, which piece is scrap, and which one the customer measures.
What is the difference between blanking, piercing and notching?
All three cut sheet metal by shearing it between a punch and a die, and the difference is which side of the cut is the part. In blanking, the piece that falls through the die is the part and the sheet around it becomes scrap. In piercing, the piece that falls through is scrap and the sheet stays as the part - that is how holes and slots are made. Notching removes material from the edge of a strip or a part, usually to shape the outline or to let a progressive strip index correctly, so it produces neither a part nor a finished hole. Because they are the same action, the mechanics are shared: clearance per side, punch and die condition, and the point at which the top and bottom cracks meet all decide the sheared band, the fracture zone and the burr.
Which one you are doing, and why it matters
- Blanking. The blank is the product. Its edge quality is the part's edge quality, so burr height and the sheared-to-fracture ratio are specification items rather than process trivia.
- Piercing. The hole is the feature and the slug is scrap. Hole diameter, position and burr direction matter, and the slug has to be cleared reliably or it comes back through the die.
- Notching. The cut shapes an edge or a corner. It is often a strip-layout device rather than a functional feature, and it is the operation most likely to be specified loosely because nobody measures it.
- Fine blanking is a different machine and tool concept altogether - it uses a counterforce and an impingement ring to produce a near-full sheared edge, and it is chosen when the edge itself is the function.
What to put on the drawing
Name the direction of the burr if the edge is functional, because it is a process decision rather than an inspection detail. State hole diameter and position with their tolerances, and say which edge is cosmetic if any. Where the edge carries fatigue or sealing duty, say so - that is the requirement that decides whether the edge is blanked conventionally or needs shaving or fine blanking, and it is much cheaper to state before the tool is cut.
Key point
Blanking, piercing and notching are one shearing action used three ways: the blank is the part, the pierced slug is scrap, and the notch shapes an edge. The mechanics are shared; what changes is which surface the customer measures - so that is what belongs on the drawing.
Balford runs blanking, piercing and notching on presses from 25 t to 350 t, with the dies designed and built in its own tool room.
Frequently asked questions
What is the difference between blanking and piercing?
Both shear the material between a punch and a die. In blanking the piece that falls through the die is the finished part; in piercing the piece that falls through is scrap and the remaining sheet is the part. The tooling mechanics are otherwise the same.
What is notching used for?
Removing material from an edge or corner, usually to shape the outline of a part or to let a progressive strip index correctly. It produces neither a finished part nor a finished hole, which is why its tolerances are often specified more loosely.
Do blanking, piercing and notching need different clearances?
No, they use the same clearance logic per side, because the action is identical. What differs is the consequence of the cut: on a blank the edge is the part's edge, on a pierce the hole is the feature, and on a notch nothing functional is usually created.
When is fine blanking used instead?
When the sheared edge itself carries the function and a conventional cut's fracture zone is unacceptable. Fine blanking uses a counterforce and an impingement ring to produce a near-full sheared edge, and it is a different machine and tool concept rather than a tighter clearance.