Deep Drawing
Also: deep draw stamping, drawn parts, cup drawing, draw forming, deep drawn metal, redrawing, ironing, deep draw
Deep drawing pushes a flat blank into a die with a punch to form seamless cups, cans, shells and housings, with depth approaching or exceeding the diameter.
50 shops tagged Deep draw among 1,023 metal stamping companies in the Noramark directory
A blank is clamped between the die and a blankholder, and a punch pushes its center into the die cavity; the flange flows inward and becomes the wall. The blankholder pressure is the balance point: too little and the flange wrinkles, too much and the wall tears at the punch radius. A single draw reduces the diameter by about half (a limiting draw ratio of 2.0-2.2 for drawing-quality steel), so deeper parts are redrawn in stages of 20-30% each, with an anneal between draws for work-hardening materials such as 304 stainless.
The walls of a drawn part are seamless, work hardened and, in a well-designed draw, thinner near the bottom radius and thicker toward the rim. Ironing, a pass through a die slightly smaller than the wall, thins and evens the wall to ±0.025 mm (±0.001") and gives a bright burnished finish; beverage cans are the extreme case. Bottom features, side holes, flanges, beads and threads are added in later stations or by machining.
Tooling is a hardened, polished punch, die and blankholder per stage, on hydraulic or transfer presses, so the process suits volumes from a few thousand to millions of parts: battery cans, sensor housings, EMI shields, cookware, sinks, filter bowls, pressure-vessel heads. For a handful of parts the same shape is spun, machined from bar or fabricated from tube.
At a glance
| Typical tolerances | Diameter ±0.05-0.13 mm (±0.002-0.005") standard, ±0.025 mm (±0.001") with care on ironed walls. Height ±0.5 mm (±0.020") as drawn, ±0.13 mm (±0.005") after trimming. Wall thickness varies by design, thinning 10-25% at the punch radius and thickening at the rim, unless the wall is ironed, which holds it to ±0.025 mm (±0.001"). Concentricity of bottom to wall about 0.13 mm (0.005"). |
|---|---|
| Size limits | Diameters from about 2 mm (0.08") to 600 mm (24"); depths up to five or six times the diameter with multiple redraws. Thickness 0.1-6 mm (0.004-0.25"), most work in 0.2-3 mm (0.008-0.125"). Presses of 50-1,500 tons; transfer presses for multi-stage parts. Rectangular boxes need corner radii of several times the thickness and draw shallower than round cups. |
| Surface finish | The wall is burnished by the die and often better than the incoming sheet, about 0.4-0.8 µm Ra (16-32 µin); ironed walls are bright. Lubricant residue, faint draw lines and a witness at the trim edge are normal. Stainless can gall if the lubricant and die material are wrong. Parts are washed, and then passivated, electropolished, plated or painted as needed. |
| Lead time | Tooling 6-14 weeks depending on the number of stages; samples 1-2 weeks after. Prototypes by spinning, soft tooling or machining in 2-4 weeks. Production runs in days once tooled. |
Typical of U.S. job shops; confirm with the shop for your part.
Materials
Drawing-quality low-carbon steel (A1008 DS, DDS and EDDQ, not 1018) is the reference material. 304 stainless draws deep but work hardens fast and needs interstage annealing; 316 and drawing-quality 304 DDQ ease that. Aluminum 1100, 3003, 5052-O and 6061-O draw well; 5xxx-H tempers less so. Copper C110 and cartridge brass C260, named for the deep-drawn case, are the classic drawing alloys. Grade 2 titanium, Monel 400 and Inconel 625 are drawn for aerospace and chemical housings with heavy presses and careful lubrication. High-strength and spring-temper stock does not draw.
What drives the cost
- Number of draw stages, each with its own punch, die and press hit
- Interstage annealing for stainless, nickel alloys and aluminum
- Tooling: hardened, polished die sets and, for multi-stage parts, a transfer press
- Material: stainless and nickel alloys draw slowly and need more stages than steel
- Trimming, piercing and forming of the bottom and flange
- Wall thickness tolerance and ironing
- Volume and blank utilization
When to use it
- Seamless cups, cans, shells and housings in thousands to millions
- Battery cans, sensor and connector housings, EMI shields, filter bowls, cookware, sinks, tank heads
- Parts that must be leak-tight without a weld seam
- Thin walls with good surface finish that would be expensive to machine
When not to
- Under a few thousand pieces: spin, machine from bar, or fabricate from tube and plate
- Sharp inside corners on the bottom or the walls; deep drawing needs radii
- Tall rectangular boxes with small corner radii
- Walls that must be a uniform thickness without ironing
- Thick-walled parts, or diameters and depths beyond the press
Design tips
- Round cups draw deeper and cheaper than rectangular ones; if the part must be rectangular, give the corners a radius of at least 4-6t.
- Give the bottom corner (punch radius) at least 3t and let the shop choose the die radius, typically 4-8t.
- Keep the depth to diameter ratio under 0.75 for a single draw and expect a redraw stage for every further 20-30% reduction.
- Allow for a trim: the rim of a drawn part is uneven (earing) and is cut to height afterwards.
- Do not tolerance the wall thickness unless the wall is ironed; tolerance the inside or outside diameter, whichever mates.
- Specify drawing-quality material by spec (A1008 DS or DDS, 304 DDQ, 3003-O) rather than a machining grade.
- Add side holes, flanges, beads and threads as later operations and say which surfaces are cosmetic.
- Send a model with the wall thickness as drawn and the blank material thickness noted; the shop develops the blank.
Frequently asked questions
- What is the maximum depth for deep drawing?
- A single draw reaches a depth of roughly half to three quarters of the diameter in drawing-quality steel. Redraws add 20-30% each, so depths of two to three times the diameter are routine with three or four stages, and five or six times the diameter is possible with more stages and interstage annealing. Rectangular parts draw shallower.
- What is the draw ratio in deep drawing?
- The blank diameter divided by the punch diameter. The limiting draw ratio for one stage is about 2.0-2.2 for drawing-quality steel, a little less for aluminum, and lower for hard tempers; going past it tears the wall at the punch radius. Deeper parts are drawn in stages, each with a smaller ratio.
- Can stainless steel be deep drawn?
- Yes. 304 and 316 draw very well, but they work harden quickly, so multi-stage parts are annealed between draws, and the tooling and lubricant must be chosen to prevent galling. Expect more stages and a higher part cost than in mild steel; 304 DDQ (drawing quality) helps.
- What causes wrinkling and tearing in deep drawing?
- Wrinkles form when the flange is not clamped hard enough and the compressed metal buckles; tears happen when the wall is pulled harder than it can carry, usually because the draw ratio is too high, the radii are too small, the blankholder is too tight or the lubricant failed. The tool designer balances these with the blankholder force, the radii and the stage plan.
- Deep drawing vs metal spinning?
- Spinning forms a round part over a mandrel with a roller and needs only a mandrel, so it wins for prototypes and small runs of round shapes; deep drawing needs a die per stage but makes parts in seconds, so it wins from a few thousand pieces. Spun parts have visible roller marks and looser tolerances.
