Designing Small Deep Drawn Parts: 8 Considerations

Why Small Parts Deserve a Different Design Lens

Deep drawing small parts — say under 20 mm in diameter — follows the same physics as large shells, but the tolerances on those physics get unforgiving. A 0.2 mm wall that is trivial on a 100 mm can becomes a structural decision on a 10 mm one. Ejector clearance, material springback, and press repeatability all scale against the part, so a design that draws beautifully at scale may crack or stick when shrunk.

This guide collects the eight considerations that most often decide whether a small deep drawn part runs cleanly or turns into a scrap problem. Pair it with our geometry difficulty classification to place your part on the simple-to-difficult spectrum.

1. Wall Thickness and Minimum Drawable Gauges

Thin stock is the first temptation on small parts, but there is a floor. Below roughly 0.15–0.2 mm, the blank tears at the punch radius and the press cannot hold a consistent feed. Start from the thinnest wall that survives the draw, then add margin for the application rather than designing to the absolute minimum. A deep drawn parts supplier can confirm the practical minimum for your alloy.

2. Corner and Bottom Radii

Radius scales with wall thickness, not with part size. A small part still needs a punch and die radius several times the material thickness to avoid cracking. Designers used to CNC fillets often spec radii that look fine in CAD but fail in the press. Keep radii generous relative to gauge; a slightly larger bottom radius rarely hurts function but prevents most small-part failures.

3. Aspect Ratio Limits

Depth divided by diameter is the aspect ratio, and it caps how deep you can go before redraws multiply. Small parts tolerate high ratios better than people expect — long thin pins and sleeves are common — but each added draw adds an anneal and a station. Confirm the ratio against a limiting draw ratio reference before committing to a deep, narrow form.

4. Material Choice for Small Parts

Small parts magnify material behavior. Stainless steel springs back more than aluminum, so a tight small bore may need a slight over-form to land in tolerance. Brass and copper draw smoothly but work-harden slowly, which helps thin walls. Match the alloy to the dominant requirement — corrosion, conductivity, or strength — rather than defaulting to stainless steel. Our SS304 vs SS316 guide covers the common sensor-housing case.

5. Tolerances and Springback

Tight diameters on small parts are hard because springback is a larger fraction of the feature size. Hold critical dimensions on the outside where the die controls them, and relax inside diameters unless function demands otherwise. If you need a precise small bore, plan for a light sizing or ironing pass rather than expecting the raw draw to hold it.

6. Ejector and Stripper Clearance

Small parts stick. The contact area between the drawn shell and the punch is large relative to the part’s mass, so vacuum or friction can hold it on the punch. Design adequate draft, vent holes where allowed, and confirm the ejector scheme with the toolmaker. A part that will not release costs you more in downtime than any design saving.

7. Surface Finish and Burrs

On a small part, a 0.05 mm burr is a large fraction of a 0.3 mm wall. Specify edge condition and finish explicitly, and decide early whether the trim edge needs deburring or tumbling. Deep drawing itself leaves a clean drawn surface, but the trim and any pierced holes are where small-part burrs appear.

8. Secondary Operations and Assembly

Small parts are often handled in bulk, so design for it. Avoid fragile protrusions that bend in a feeder, and place any threads or press-fits where automated inline operations can reach them. Where a feature can be coined in the draw rather than added later, do it — handling a tiny part twice costs more than handling it once. The advantages of deep drawn manufacturing extend straight to small-part economics when features are combined upstream.

A Quick Design Checklist

• Wall at or above the practical minimum for the alloy.
• Radii several times the material thickness.
• Aspect ratio confirmed against the draw-ratio limit.
• Material chosen for the dominant requirement, not by habit.
• Critical dimensions on surfaces the die controls.
• Ejection and venting designed in from the start.
• Edge finish and burr spec stated explicitly.
• Secondary features combined into the draw where possible.

Run this list before the quote and most small-part surprises disappear. For the full process picture, our Deep Drawing: Process, Materials & Design Guide explains each stage from blank to finished shell.

Small Parts We Run Every Day

Under about 20 mm, deep drawing shifts from “forming a shape” to “holding a tolerance on a tiny feature”. The parts that run cleanly at this size tend to be simple round forms with one closed end and no undercut. Three examples from our own lines:

• Micro tubes. Our stainless steel micro tubes with closed and open ends show how small a drawn tube can go while still holding a consistent wall.
• Needle pins. The stainless steel precision needle pins are drawn and then ground where the tip geometry is critical.
• Hollow rivets. Our stainless steel semi-tubular hollow rivets are a classic small drawn part where the closed end and the shank diameter are the only controlled dimensions.

Handling and Packaging Small Parts

Small drawn parts are far more likely to be damaged after forming than during it. Three decisions prevent most complaints:

• Decide the counting method early. Weight-counting is cheap but needs a consistent part weight; tray or tape counting costs more but removes disputes.
• Specify separation. Loose small parts in a carton scuff and nest; layered trays or partitioned bags cost a little and save the whole batch.
• Protect the trim edge. A burr that is invisible on a large shell is a real edge defect on a 6 mm part.

When a Small Part Should Not Be Drawn

Very thin walls below practical gauge, features that need deep undercuts, or tolerances tighter than the draw can hold all argue for a different route — typically machining from bar, or a drawn blank followed by a machining finish. The honest answer is usually a hybrid: draw the shell to get the shape cheaply, then machine only the surfaces that matter. See deep drawn vs machined vs welded housings for the comparison.

Inspecting Small Drawn Parts

Measurement is where small parts most often surprise buyers. A dimension that is easy to check on a 60 mm shell may need a fixture on a 6 mm one, and the cost of that fixture belongs in the quotation rather than in a dispute later.

• Plan for gauges, not calipers. Small diameters and wall thicknesses usually need go/no-go gauges or optical measurement.
• Sample size matters more than precision. Because variation between pieces is the risk, agree an inspection level up front.
• State the datum. On a tiny part, arguing about which surface the dimension is measured from wastes more time than measuring it.

Our material selection guide covers how alloy choice affects dimensional stability, and the draw ratio reference explains the wall-thinning behaviour behind those tolerances.

Lead Times for Small Parts

Small drawn parts are often assumed to be quick, but the tooling can take as long as it does for a large part. The die still has to be designed, machined and tried out, and small features usually demand finer work than large ones. What is genuinely faster is the run: once the tool is proven, high volumes of small parts come off the press quickly.

Plan the tooling lead time, not the piece rate, when you set your schedule — and where the programme allows, confirm the sample before releasing the full order.

Frequently Asked Questions

What is the smallest wall thickness you can deep draw?

Practically, around 0.15–0.2 mm depending on alloy and part size. Below that the blank tears at the punch radius and feed becomes inconsistent, so designs should add margin above the absolute minimum.

Why do small deep drawn parts stick to the punch?

The drawn shell has large surface contact relative to its tiny mass, so vacuum or friction holds it on the punch. Adequate draft, vent holes where the design allows, and a confirmed ejector scheme prevent sticking and downtime.

Is stainless steel a good choice for small parts?

Stainless steel draws well but springs back more than aluminum or brass, so tight small bores may need over-forming or a sizing pass. Use it where corrosion or strength demands it rather than by default.

How tight can tolerances be on a small drawn part?

Hold critical dimensions on outside surfaces the die controls, and expect a light sizing or ironing pass for precise small bores. Inside diameters and very tight small features are harder because springback is a larger fraction of the size.

Should small parts combine features in the draw?

Yes where possible. Combining necks, steps, or coined details into the draw avoids handling a tiny part multiple times, which is where small-part cost and defect risk accumulate.