Lesson 4.2DeformChapter 4 · Sheet and tube forming

Stamping and deep drawing

Matched dies cut and press sheet into shape, often in a second

Stamping shapes sheet metal between matched dies in a press, one part per stroke. Deep drawing is the stamping operation that pulls a flat blank into a die to make a seamless hollow part. Drink cans, kitchen sinks, battery cans and car body panels are all drawn this way.

Photo: Pressteck S.p.A, CC BY-SA 2.0, via Wikimedia Commons

deep drawing of a cup · 3 stagesThe three panels cut through the middle of a round cup as it is drawn; circled numbers match the steps below.

Stamping and deep drawing in a minute, by MecMade

How it works

Load the blank. A flat blank (a piece cut from sheet, here a disc) is placed on the die, a block with a hole whose edge is rounded. That rounded edge is called the die radius.
Clamp the rim. The blank holder, a ring around the punch, presses the rim with a controlled force. Too little force and the rim wrinkles; too much and the wall tears.
Draw. The punch pushes the center down into the hole. The rim slides inward under the holder and bends over the die radius to become the wall.
Eject and trim. The punch and holder lift, an ejector pushes the cup out, and the uneven rim is trimmed. Deeper parts are drawn again in later stages (redraws), each narrower and deeper.

In high-volume stamping, a progressive die does several operations at stations along a coil strip: cutting, piercing (punching holes), bending and drawing. The strip moves one station per stroke, so a finished part drops out every stroke.

Key facts

Materials: Ductile sheet: low-carbon and stainless steel, aluminum, copper, brass; typically about 0.2 to 6 mm thick
Typical parts: Cans, cups, sinks, cookware, fuel tanks, car body panels, battery cans, brackets
Part size: From shells a few millimeters across to car body side panels a few meters long
Precision: About ±0.1 mm on small parts; looser on large panels
Surface finish: Smooth, close to the sheet's own finish; good enough for painted car panels
Batch size it suits: High volume: thousands to millions of parts, because the dies only pay off at scale
Tooling and machine cost: Dies from about $10,000 for small simple parts to over $1 million for a set of car body dies; presses from about $100,000 to many millions for a car-panel line
Speed: One part per stroke: large car panels about 10 to 15 per minute; small parts in progressive dies tens to hundreds per minute

Strengths and limits

Strengths

Very fast and cheap per part at high volume
Seamless, leak-tight hollow parts with no welds
Strong, light parts; the metal hardens as it is worked
Very repeatable from part to part

Limits

Dies are expensive and take weeks to months to build and tune
Depth per stage is limited: the blank can be only about twice the punch diameter
Defects to control: wrinkles in the rim, tears near the punch corner, a wavy rim
A design change means new or reworked dies

Where it's used

AutomotiveDoors, hoods, roofs, fenders, fuel tanks, oil pans
PackagingDrink and food cans, aerosol cans, bottle caps
Kitchen and appliancesSinks, pots, pans, appliance housings
Electronics and batteriesCylindrical battery cans, connector shells, shielding cans
DefenseCartridge cases

How to recognize it

Seamless hollow shapes, such as cans, cups and sinks, with no weld line.
Rounded inside and outside corners at the bottom, copied from the punch and die radii.
A clean, trimmed rim at the opening, often rolled or folded over.
Faint vertical scratch lines on the outer wall, where the metal slid over the die.

Compare with

Sheet metal bending4.1cheap tools but straight folds only; stamping forms a full 3D shape in one stroke.Metal spinning4.3makes similar round hollow parts with cheap tooling, suited to small batches but slower per part.Hydroforming4.5fluid pressure replaces one solid tool, allowing complex shapes in fewer stages.

Watch it

Toledo Metal Spinning · A beginner overview of deep draw stamping

Hubert Stüken GmbH & Co. KG · How a part is drawn in several stages, explained by a manufacturer

Gut Metallumformung AG · Real deep drawing of a cup in a press

ANDRITZ Schuler · A car body press line with robots moving panels between dies

See real photos

Wikipedia: Deep drawing — process diagrams and a deep-draw line
Wikipedia: Stamping (metalworking) — overview of stamping operations
Wikimedia Commons photo search

Remember

Matched dies shape sheet in one press stroke; deep drawing pulls a flat blank into a seamless cup.
The blank holder stops the rim from wrinkling as it slides inward.
Dies are costly, so stamping pays off at high volume.