The short version
Drawing is the general operation of pulling material into a die. Deep drawing is the case where the depth is large relative to the diameter, so the material has to flow a long way and a blank holder becomes necessary. Redrawing reduces the diameter again in a second or third stroke. Ironing deliberately thins the wall. Spinning and hydroforming are different processes that are often confused with drawing because the finished part looks similar.
1. Why this vocabulary is confusing
Two collisions cause most of the confusion.
The first is between a drawing and drawing. In engineering, a drawing is a document — the dimensioned print of a part. In metalforming, drawing is an operation. So a search for sheet metal drawing mixes people looking for a CAD drawing template with people looking for a forming process. Both are legitimate, and they are not the same question.
The second is between shallow and deep drawing. Both pull material into a die. The difference is how much material has to move, and that decides whether you need a blank holder, how many strokes the part takes, and what the tooling will cost.
2. The operations, side by side
| Term | What happens to the material | Wall thickness | Typical parts |
|---|---|---|---|
| Drawing (shallow) | Blank is pulled into a die; depth is small relative to diameter | Largely unchanged | Shallow trays, caps, covers |
| Deep drawing | Blank flows a long distance into the die; depth more than roughly half the diameter | Wall stays close to blank thickness; bottom and radius vary | Cups, housings, shells, sleeves |
| Redrawing | A second or third stroke reduces the diameter further | Unchanged in principle; work hardening accumulates | Long, narrow drawn parts |
| Ironing | The cup is pushed through a die with reduced clearance, thinning the wall on purpose | Deliberately reduced, often controlled to a tolerance | Beverage cans, solenoid valve housings |
| Metal spinning | A rotating disc is formed over a mandrel with rollers | Thins where the roller works the metal | Large, low-volume round shapes |
| Hydroforming | Fluid pressure forms the blank instead of a solid punch | Generally unchanged; very uniform strain | Complex tubular and panel shapes |
3. The depth-to-diameter rule
The practical dividing line used on the shop floor is the ratio of depth to diameter.
| Depth ÷ diameter | What it usually means |
|---|---|
| Under about 0.5 | Shallow forming; often done in a single stroke, blank holder may not be required |
| About 0.5 – 1.0 | Classic deep drawing; blank holder required, usually one stroke for steel and aluminium |
| About 1.0 – 2.0 | Multiple draws, possibly with intermediate annealing |
| Over about 2.0 | Several draws plus annealing; the process route and tooling cost change materially |
The ratio is a rule of thumb, not a limit. The actual limit is the material: its r-value, its work-hardening exponent and its current condition decide how far it can be drawn before it tears.
4. Deep drawing and ironing are not the same
This is the distinction that changes part cost most often. Deep drawing moves material and keeps the wall close to the original thickness. Ironing deliberately thins the wall by forcing the drawn cup through a die with less clearance than the wall thickness.
That matters commercially. A part whose drawing specifies inner diameter, outer diameter and wall thickness tolerances — a solenoid valve housing, for example — can often be produced by drawing plus ironing instead of by cold extrusion followed by turning. Ironing holds both diameters and the surface finish without a machining operation.
Go deeper: the complete deep drawing guide — draw ratio, blank size, draw force and die clearance, with the defects and their remedies.
5. Where the terms came from
The industrial vocabulary grew out of 19th-century metal packaging. Drawn metal containers for food preservation were among the first mass applications, and the demand for cheap, seamless containers drove both the presses and the die practice. The beverage can industry later pushed ironing to an industrial standard, because a can wall has to be thinner than the base it is drawn from.
In the 20th century the automotive industry industrialised sheet metal drawing at a different scale: body panels, housings and structural parts, often on transfer and progressive lines rather than single-station presses.
Since the 1990s, finite element simulation has moved tool design away from pure trial and error. Draw ratios, blank shape and springback are now calculated before a die is cut, which is why a modern drawing review can predict a split or a wrinkle before tryout rather than after it.
6. Glossary
- Blank — the flat piece of sheet cut to size before drawing.
- Draw ratio — blank diameter divided by punch diameter for one stroke.
- Limiting drawing ratio (LDR) — the largest ratio a material survives in one stroke without tearing.
- Blank holder (hold-down) — the ring that restrains the flange so it does not wrinkle.
- Draw bead — a ridge in the die that controls how much material flows in.
- Ironing — wall thinning by pushing the cup through a reduced clearance.
- Springback — elastic recovery after the punch is released; larger for aluminium and high-strength steels.
- Annealing (intermediate) — softening the work-hardened part between draws.
- Earing — a wavy top edge caused by planar anisotropy in the sheet.
7. Frequently asked questions
Is deep drawing the same as drawing?
No. Drawing is the general term; deep drawing describes the case where depth is large relative to diameter, so the material flows a long distance and a blank holder is needed.
What is the difference between deep drawing and ironing?
Deep drawing moves material and keeps the wall close to the original sheet thickness. Ironing thins the wall on purpose by forcing the cup through a die with reduced clearance. Many housings use both: draw first, then iron to hit the diameter and wall tolerances.
Is sheet metal spinning the same as deep drawing?
No. Spinning forms a rotating disc over a mandrel with rollers and needs no drawing die. It suits large, low-volume round parts; deep drawing suits higher volumes where a die can be amortised.
At what depth does forming become deep drawing?
The usual rule of thumb is a depth greater than about half the diameter, which is also the point where the flange starts to wrinkle and a blank holder becomes necessary.
Related pages
- Deep Drawing: The Complete Technical Guide — the full engineering reference
- What is deep drawing? — definition, limits and the depth-to-diameter table
- Ironing in deep drawn stamping — how wall thinning replaces a machining operation
- Deep drawing vs press forming — which process the geometry actually needs
- Deep draw force calculator — draw force, draw ratio and press tonnage
- Deep drawn metal parts — what Balford manufactures
References and further reading
- Deep drawing — en.wikipedia.org, general definition and process description
- Drawing — AHSS Guidelines — forming modes and material behaviour in advanced high-strength steels
- Deep drawing: key design principles — The Fabricator, practical design rules
- Balford's own engineering reference: the complete deep drawing guide and the draw force calculator