Key takeaways
- Stamping is a cold forming process where a press forces a die into sheet or coil.
- Blanking, piercing, bending, forming and drawing are the core operations, often combined in one tool.
- Stamping suits thin, flat parts at volume, not thick blocks or deep three-dimensional shapes.
- The die decides the cost, the tolerance and the strip layout, so the drawing should be written for the tool.
What sheet metal stamping is
Sheet metal stamping is a cold forming process. A flat sheet or coil is fed into a press, and a die cuts, bends or stretches the material into a finished part. The press supplies force and stroke. The die supplies the shape, the clearance and the sequence of operations. Neither is useful without the other, which is why a stamped part is really a tooling project with a part attached.
The process covers a wide range. A shim can be 0.1 mm thick and a chassis bracket can be 6 mm thick, and both can be stamped. Volume matters as much as size: a mechanical press may run from 60 to over 1,000 strokes a minute depending on stroke length, feed, part weight and the type of die. Most of the cost sits in the die and the material, not in direct labour.
The operations inside a stamping die
Almost every stamped part is built from a small set of operations. A single die can perform several of them in one stroke, or a progressive die can spread them across a line of stations. The names below are the ones a toolmaker will use on a die drawing.
- 01
Shearing and blanking
Shearing cuts the sheet along a line. Blanking cuts a closed outline so the cut piece is the part. The punch and die clearance sets the edge quality and the burr direction.
- 02
Piercing
Piercing cuts holes, slots or windows without removing the part from the strip. Hole size, edge distance and punch strength set the practical limit.
- 03
Bending
A punch pushes the sheet into a die opening and forms a bend. The inside radius, the bend allowance and springback decide the final angle and leg length.
- 04
Forming
Forming adds a shallow three-dimensional shape without deliberately thinning the wall. Ribs, embosses, dimples and small offsets are typical forming features.
- 05
Drawing
Drawing pulls material into a cavity and thins or stretches the wall to make a cup or a shell. It needs a blank holder, lubrication and a draw ratio the material can survive.
- 06
Trimming and coining
Trimming removes the carrier or excess flange after forming. Coining presses the material into a fine detail, such as a contact profile or a coined edge, in a single closing stroke.
Press types and what they change
The press sets the force, the speed and the accuracy of the stroke. A mechanical press stores energy in a flywheel and delivers a fixed stroke, which makes it fast and repeatable for blanking and progressive work. A hydraulic press gives a programmable force and dwell, which suits drawing and forming where the material needs time to flow.
A servo press drives the ram with a motor and can control the speed through the stroke. That allows a slow contact for drawing, a fast return and a short dwell at the bottom. High-speed presses are built around small parts and fine blanking, with tight guidance and low vibration. The choice is usually made by the toolmaker, but the buyer should know which press the die is designed for, because it limits the supplier list and the available tonnage.
| Press type | Force profile | Typical use |
|---|---|---|
| Mechanical | Fixed stroke, flywheel energy | Blanking, piercing, progressive dies |
| Hydraulic | Programmable force and dwell | Drawing, forming, thick material |
| Servo | Programmable ram speed and position | Draw and form in one tool, fragile parts |
| High-speed | Short stroke, high rate | Small terminals, contacts, laminations |
The press tonnage must cover the cutting force plus the stripping force plus a margin. A die that is run in a press that is too small will flex and wear.
Parts that stamping makes well
Stamping is strongest when the part is flat or shallow, has a constant thickness and needs a lot of identical pieces. Electrical and electronic assemblies are the classic market because terminals, contacts and shields are thin, conductive and produced in large numbers.
The list below is not exhaustive, but it covers the shapes that quote well and run reliably in a progressive or compound die.
- Terminals, tabs and male or female contacts
- Brackets, clamps and mounting plates
- Laminations for motors and transformers
- Heat sink fins, base plates and clips
- Washers, shims and spacers
- Screens, covers and EMI shields
- Busbar links and small current-carrying parts
Materials and thickness
Mild steel, usually a drawing grade such as DC01 or CR4, is the default for brackets and structural parts. Stainless steel 301 and 304 add corrosion resistance but work-harden quickly, which raises the punch force and the wear on the die. Copper C11000 and brass CW614N are common for electrical parts because they combine conductivity with formability. Aluminium 1050 and 5052 are light and conductive, but they gall easily and need the right lubricant and die finish.
Thickness tolerance is part of the design, not a mill detail. A coil that runs 0.05 mm heavy changes the bend allowance, the springback and the hole clearance. For a part with a critical bend, state the thickness range on the drawing and ask for the mill certificate. The same applies to temper: half-hard material springs back more than annealed material and may need a different bend radius.
Pre-plated coil is a separate decision. A tin or nickel coating applied before stamping removes a post-plating step, but the coating has to survive the shear and the bend. Tin can crack at a tight radius, and the die contact can rub it through. If the part needs a coating on one face only, or a thicker coating on a contact area, post-plating with masking may be the better route. Either way, state the coating on the drawing and test the adhesion on the first article.
Where stamping stops
Stamping cannot make a true undercut in a single direction without a side action, and side actions add cost and maintenance. It cannot produce a thick boss or a solid section, because the starting material is thin. It cannot hold a sharp internal corner at the bottom of a deep pocket, because the punch needs a radius to survive.
Volume is the other limit. A die has a fixed cost, and that cost has to be spread across the parts. At 200 pieces, laser cutting or machining is usually cheaper. At 20,000 pieces, the die is often paid back before the first year ends. The crossover is specific to the part, so ask for both routes priced at the same annual volume rather than comparing a prototype price with a production price.
Some features are better added after stamping. A tapped hole, a welded stud, a thread-forming boss or a machined face is usually a secondary operation. A shallow emboss or a coined contact can be made in the die. The drawing should separate the features made in the tool from the features added later, because they carry different tolerances and different inspection points.
A stamped part is designed around a strip
Every part needs a carrier to travel through the die. If the outline leaves no room for a carrier, the tool needs a different layout or the part needs a redesign. Ask to see the strip layout before the die is cut.
What to put on a stamping drawing
A stamping drawing should give the toolmaker everything needed to build the die and the inspector everything needed to prove the part. That means the material grade and thickness range, the finish, the burr direction, the critical dimensions and the datum scheme. A general tolerance such as ISO 2768-m can cover the rest.
It also helps to say how the part is used. A terminal that carries current needs a contact area and a spring force called out. A bracket that carries a load needs the fixing holes and the load path toleranced. A cover that is only cosmetic needs far less. The drawing should reflect that difference instead of tightening every dimension to the same value.
A first article is not the same as a production sample. The first article proves the die can make the drawing; a production sample proves the process is stable. Ask for both, and ask for the dimension report to identify the station or operation that made each critical feature. That record is what the quality team will use when a shipment is challenged.
- Material grade, temper and thickness range
- Finish and any masked or contact areas
- Critical dimensions, datums and the general tolerance class
- Burr direction and the acceptable burr height
- Flatness or bend angle where the assembly needs it
- Annual volume, release size and inspection level
Frequently asked questions
Is stamping the same as pressing?
In everyday use the terms overlap. Stamping usually means cutting and forming sheet in a die, while pressing can include forging, coining and other press operations. In a sheet metal context, stamping is the more specific word.
What is the difference between blanking and piercing?
Blanking cuts the outer outline so the cut piece is the part. Piercing cuts holes or windows inside the part and the removed material is scrap. Both use a punch and a die, but the clearance and the slug handling are different.
What thickness can be stamped?
Most sheet metal stamping runs from about 0.1 mm to 6 mm. The practical limit depends on the press tonnage, the die strength and the feature size. Very thin material needs careful strip handling, and very thick material may need a different process.
Can stamping produce a part with no burr?
No sheared edge is completely free of burr. The aim is to control the burr height and put the burr on the non-critical side. If the edge must be clean, fine blanking, shaving or a secondary deburring step is needed.
Sources and further reading
- ISO 2768-1:1989, General tolerances, linear and angular dimensions
- DIN 6935, Cold bending of flat steel products
- Qumek DFM reviews for progressive-die and compound-die stampings
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