Deep Drawing
Deep drawing pushes a sheet metal blank through a die with a punch so the metal flows into a seamless cup or box deeper than its own diameter.
- Part
- Forming
- Revised
- 2026-08-11
At a glance
- Family
- Metal
- Typical tolerances
- Roughly ±0.010 in (±0.25 mm) on drawn diameters and depth; ironed walls hold tighter, near ±0.002 in (±0.05 mm). Wall thickness varies 10–25% from the blank gauge by design
- Surface finish
- Reflects the incoming coil finish, typically 16–63 µin Ra (0.4–1.6 µm), with draw lines possible on the wall
- Typical volumes
- 25,000–10,000,000+ parts; below about 5,000 a single-sided process is usually cheaper
- Lead time
- 8–16 weeks for a multi-station draw die; 1–3 weeks per production run thereafter
- Materials
- Metal
What it is
Deep drawing pushes a sheet metal blank into a die cavity with a punch, so the flange material flows radially inward and becomes the wall of a seamless cup, can, shell, or box. The defining test is depth relative to diameter: a part drawn deeper than its own diameter is deep drawn, while shallower forming is stretch forming or simple stamping.
It is the process behind beverage cans, cartridge cases, kitchen sinks, oil filter shells, and automotive fuel tanks. Materials must be ductile and have good through-thickness anisotropy — drawing-quality low-carbon steel, 304 stainless, 1100/3003/5052 aluminum, and cartridge brass are the workhorses.
A well-designed first draw reduces blank diameter to roughly half, giving a limiting draw ratio of about 2.0; deeper cups need redraws, each taking a further 20–25% off the diameter. Walls thin by roughly 10–25% during the draw, so a drawn part is not a constant-thickness part.
How it works
- Blank. A circular or profiled blank is cut from coil, sized by surface-area development plus a trim allowance. Blank diameter versus punch diameter sets the draw ratio, which is the single most important number in the design.
- Load and clamp. The blank sits on the draw ring, and a blank holder (binder) presses it down. Blank holder force is the process's balance point: too little and the flange buckles into wrinkles as it is compressed circumferentially, too much and the wall tears because the flange cannot feed inward.
- Draw. The punch descends and the flange metal flows over the die radius into the cavity. Punch-to-die clearance is set at roughly 1.1–1.3× the sheet thickness per side so the wall is not ironed unintentionally.
- Redraws. A cup deeper than roughly 75% of its diameter usually cannot be made in one hit. Each redraw pulls the cup through a smaller die, taking off another 20–25% of diameter. Work hardening accumulates; interstage annealing is required for stainless and heavily worked aluminum.
- Ironing (optional). A pass with clearance deliberately less than the wall thickness thins and lengthens the wall to a controlled dimension. This is how a beverage can gets a wall far thinner than its base.
- Trim and pierce. Earing — the scalloped top edge caused by planar anisotropy in the rolled sheet — is trimmed off, and holes are pierced after drawing rather than before.
Material selection is metallurgy, not just strength. The plastic strain ratio r measures a sheet's willingness to thin from the width rather than the thickness; drawing-quality steels reach r values around 1.4–2.0, which is why they outdraw aluminum, whose r is typically below 1. The strain hardening exponent n governs how much stretch the part can take before necking.
Design guidelines
Depth-to-diameter and the draw ratio
Aim for a first draw that reduces blank diameter by no more than about half — a limiting draw ratio near 2.0 for a good drawing steel, less for aluminum and stainless. In practice a cup up to about 75% as deep as it is wide is a single-operation part. Anything deeper is a multi-station tool, and each station is tooling money.
Die and punch radii
Die profile radius should be about 4–8× sheet thickness. Too small and the sheet tears as it bends over the entry; too large and the flange is unsupported and wrinkles. Punch nose radius should be at least 3× thickness — a sharp punch nose concentrates strain at the cup bottom, which is where fractures start.
Punch-to-die clearance
Use roughly 1.1–1.3× material thickness per side for a plain draw. Clearance below material thickness irons the wall, which is a deliberate operation with its own force and lubrication requirements, not something to fall into by accident.
Corner radii on rectangular draws
Corners of a box draw are effectively small-diameter deep draws and are always the failure site. Keep corner radius at a minimum of 4–6× material thickness, and larger is much better. The bottom radius at the corner should be at least as generous as the side radius.
Expect thinning, not uniform wall
The wall thins 10–25% relative to the blank, most severely just above the punch nose radius, while the flange actually thickens. Do not dimension a drawn wall as though it were the original gauge, and do not put a sealing or bearing surface at the thinnest region.
Blank development and material
Blank diameter comes from surface-area equivalence plus 10–15% trim allowance for earing. Specify a drawing-quality grade explicitly — DDQ or EDDQ steel, 3003-O or 5052-O aluminum, 304 with a controlled ferrite level. A structural grade with the same nominal strength will not draw. Start from the sheet metal gauge chart when choosing blank thickness, and the bend radius and K-factor chart when developing flat patterns for any flanges added after the draw.
Pierce after drawing
Holes punched in the blank distort into ovals as the metal flows. Pierce after the final draw unless the hole is in the flat bottom and well away from the punch radius.
| Feature | Recommended | Limit | Why |
|---|---|---|---|
| First draw ratio (blank ÷ punch dia) | 1.6–1.8 | ≈2.0 in drawing-quality steel | Above the limit the wall tears before the flange feeds |
| Cup depth, one operation | ≤ 0.75× diameter | Deeper needs redraws | Single-hit strain limit for most ductile sheet |
| Reduction per redraw | 20% | 25% | Work hardening reduces remaining ductility each pass |
| Die profile radius | 6× thickness | 4× thickness | Small radii tear the sheet at the die entry |
| Punch nose radius | 4–6× thickness | 3× thickness | Sharp noses concentrate strain at the cup bottom |
| Punch-to-die clearance | 1.1–1.2× thickness/side | 1.3× thickness/side | Less than 1× thickness becomes an ironing operation |
| Box corner radius | ≥ 6× thickness | 4× thickness | Corners are the highest-strain region of the draw |
| Wall thinning | Design for 10–20% | 25% | Metal comes from the wall as the flange feeds in |
Cost drivers
Cost is dominated by the die set and the number of stations in it. A single-draw tool is a modest investment; a five-station transfer or progressive tool that draws, redraws, irons, trims, and pierces is a major one, and each added station multiplies both tooling cost and press requirements. Press time per part is short — a progressive draw line runs continuously — so at volume the material and the amortized tool dominate, not machine hours.
Volume breakpoints: below roughly 5,000 parts, metal spinning or hydroforming with a single-sided tool almost always beats a matched draw die. From 25,000 to a few hundred thousand, a conventional draw die pays back. Above a million, transfer presses with progressive tooling and optimized blank nesting take over, and blank utilization becomes the biggest single lever on cost.
- Cut a station. Relaxing depth or opening a corner radius so the part draws in two hits instead of three removes a whole tool section.
- Nest the blank. Round blanks waste 10–20% of the strip even when nested well. A profiled or squared blank, where the part allows, recovers much of it.
- Specify drawing-quality material. Scrap from tearing dwarfs the price premium on a proper DDQ or EDDQ grade.
- Avoid interstage annealing. Every anneal is a furnace pass and a handling cycle. Splitting the reduction across more stations is often cheaper than annealing.
- Let the wall thickness float. Holding a drawn wall to a tight thickness forces an ironing station and much higher press tonnage.
Questions
6 questionsHow deep can you deep draw in one operation?
About 75% of the cup diameter for a good drawing-quality steel, corresponding to a limiting draw ratio near 2.0 between blank and punch diameter. Deeper cups need redraws, each removing a further 20–25% of the diameter, and each redraw adds a die station.
What punch and die radii should a draw tool use?
Die profile radius of roughly 4–8× sheet thickness and punch nose radius of at least 3× thickness. A die radius that is too small tears the sheet at the entry; one that is too large leaves the flange unsupported and it wrinkles.
How much does the wall thin during deep drawing?
Typically 10–25% relative to the blank thickness, with the thinnest point just above the punch nose radius. The flange, in contrast, thickens. Never place a sealing or bearing surface at the thinnest region, and do not dimension the wall as though it were the original gauge.
What causes wrinkles in a deep drawn part?
Insufficient blank holder force. As the flange is pulled inward its circumference must shrink, putting it in compression; without enough hold-down it buckles. Too much blank holder force causes the opposite failure — the flange cannot feed and the wall tears.
What is the best material for deep drawing?
Drawing-quality low-carbon steel (DDQ or EDDQ), which reaches plastic strain ratios of roughly 1.4–2.0, plus annealed 3003 and 5052 aluminum, 304 stainless, and cartridge brass. The r-value matters more than tensile strength — it measures whether the sheet thins from its width or its thickness.
Deep drawing or metal spinning?
Spinning needs only a mandrel, so it wins below roughly 5,000 pieces and for large diameters. Deep drawing wins at volume — cycle times are seconds rather than minutes — and it can produce non-round shapes such as rectangular pans, which spinning cannot.