Hinged Military Case
Hinged Military Case
Zinc-plated DC04 rectangular draw with a formed hinge flange.
| Material | DC04 steel |
|---|---|
| Draw depth | 90 mm |
| Wall thickness | 1.2 mm |
| Tolerance | ±0.05 mm |
| Forming route | Rectangular draw + restrike |
| Measured LDR | 2.1–2.2 |
The challenge
A non-round case is harder than a cup: the corners thin out, the flat walls bow, and the flange that carries the lid seal has to stay flat. If the flange warps, the lid will not seat and the case fails its seal test.
DC04 is picked because its draw ratio of 2.1–2.2 lets the rectangular shell form in fewer stages than a higher-strength grade, which means fewer restrike steps and less accumulated corner thinning. The trade-off is that DC04 is soft, so flatness has to be set by the restrike, not assumed from the draw.
Downstream, the case is closed with a lid and a hinge, so the flange and the pierced hinge ears have to be located to the lid geometry. A shell that is square on a CMM but off on the flange will not seal in the field.
How AUNOV draws it
Rectangular draws throw most of the deformation into the corners, so we watch corner thickness as the control point and size the blank so the corners do not run out of material before the walls are fully formed.
- DC04 chosen for its high draw ratio (2.1–2.2) so the rectangular shell can be drawn in fewer stages
- Rectangular draw, then a restrike to correct corner thinning and wall bow
- Flange flattened and pierced for the hinge and lid
- Flatness and dimensional check on the seal face
Process control and inspection
Corner thickness is the control point on a rectangular draw, so we measure it directly and watch it through the run; the flat walls follow once the corners are fed enough material.
Flange flatness is checked on the seal face before zinc plating, because the coating will not hide a warp and a warped flange fails the lid seal test at incoming inspection.
What this means for your part
If your case is a non-round steel shell with a sealing flange, the draw-plus-restrike route above is what keeps the flange flat. Send the seal requirement and we size the restrike.
Zinc plating is applied after forming so the drawn surface is sealed evenly; we check the seal face flatness before plating so the coating does not mask a warp that would later break the lid seal.
- Send the lid and hinge geometry; the flange and pierce positions are set from them.
- A restrike is cheaper than a welded box when the seal must stay flat, so prefer draw-plus-restrike for non-round shells.
- Tell us the seal standard; we size the restrike and flatness check to it.
Frequently asked questions
Can a rectangular case be deep drawn instead of welded?
Direct answer: Yes. A rectangular shell can be deep drawn from DC04 in a draw plus restrike, which avoids the weld seam of a fabricated box. The restrike is what corrects corner thinning and keeps the sealing flange flat.
What keeps the lid flange flat on a drawn case?
Direct answer: AUNOV flattens and restrikes the flange after the main draw, then checks flatness on the seal face. Drawing alone tends to bow the flange, so the restrike and flatness check are what make the lid seat.
Why choose DC04 over a stronger steel for a military case?
Direct answer: DC04’s high draw ratio (2.1–2.2) lets the rectangular shell form in fewer stages, which cuts corner thinning and restrike steps. The case is then zinc-plated for corrosion resistance, so we get the shape first and the protection after.
Have a similar part?
Send the drawing and material — AUNOV returns a DFM review and a quote within 24 hours.
Request a quoteReferences & Further Reading
The specifications and process steps in these examples follow the test methods and classifications published by the bodies below. Every example is drawn from a real production run, not a catalogue figure.
- ASTM E517 — Standard Test Method for Plastic Strain Ratio (r) of Sheet Metal. The r-value predicts earing in drawn cups.
- ASTM E646 — Standard Test Method for Tensile Strain-Hardening Exponents (n) of Metallic Sheet Materials. The n-value sets how much a wall can thin before necking.
- DIN 8584 — Manufacturing processes, forming: classification of deep drawing operations and their subgroups.
- ISO 20482 — Metallic materials: Erichsen cupping test, a formability measure complementary to LDR.
- Wikipedia: Metal forming — the broader process family these limits sit within.