Thin Wall Large Section Aluminum Profile - Die Opening

Thin wall and large section are two separate difficulties. Put them in the same profile and they multiply. A 0.8 mm wall is achievable inside a 60 mm section. A 750 mm wide section is achievable at 3 mm wall. A 750 mm wide section with 0.8 mm walls is a different problem, and it is the one this page is about.

We open dies for wide thin-wall profiles, multi-cavity thin-wall sections, sections with large wall thickness differences, and special-shaped thin-wall parts, up to a 750 mm class width with walls down to 0.8 mm, in 6061-T6, 6063-T5, 6005-T6 and 6082-T6. Below is what actually decides whether the part comes out right.

Extrusion ratio: the number that governs everything

Extrusion ratio is the billet area divided by the profile area. A thin wall over a large width produces a low profile area, which produces a high extrusion ratio — often above 60 on a flat die, and above 40 on a split die. High ratio is normally good: more deformation, finer grain, better properties.

It is also harder. High ratio means high extrusion pressure, and pressure is what deflects the die, wears the bearing, and breaks mandrels. That is the core trade in thin-wall large-section work: the geometry that gives you good metallurgy is the geometry that pushes the tooling to its limit.

Parameter	Reference limit	What happens beyond it
Extrusion ratio, flat die	about 60	Die face deflection becomes significant; wall thickness varies across the width
Extrusion ratio, split combination die	about 40	Welding chamber pressure loss; seam quality drops before ratio becomes critical
Minimum wall	0.8 mm	Bearing length control becomes binary: too long and it tears, too short and it runs
Maximum width	about 750 mm class	Press and die size limit
Maximum mass per metre	up to about 100 kg/m	Handling and thermal mass, not the die

Why a split die loses about a third of its ratio

A hollow section needs a split die: metal flows through portholes, around a mandrel, and re-joins in a welding chamber. The welding chamber is necessary — it builds the pressure that closes the seam — and it also costs pressure. That pressure loss is why a split die tops out around a ratio of 40 while a flat die manages 60 on the same press.

The practical consequence for thin-wall hollow sections: if you need a cavity, you are working with roughly two-thirds of the pressure budget you would have on an open section. That is the reason a 0.8 mm wall is realistic on an open profile and optimistic on a multi-cavity one.

Two design responses that work:

• Open the section where you can. A C-channel or a hat section with a separate closure is far easier to extrude thin than a closed box of the same envelope. If the function allows a two-part assembly, the extrusion gets cheaper and the wall gets thinner.
• Reduce cavity count before reducing wall. Going from three cavities to two raises the pressure budget enough to make a thin wall viable. That is usually a better trade than specifying 0.8 mm on a three-cavity section and living with the scrap rate.

Die deflection: why the middle comes out thin

A wide flat die behaves like a plate supported at its edges and loaded on one face. Under extrusion pressure it bows, and the bow is largest at the centre. Metal flows fastest where the gap is largest, so the wall at the centre of the die comes out thicker or thinner than the edges depending on how the bearing was cut.

The die shop compensates by varying bearing length across the width — longer bearing where metal runs fast, shorter where flow is starved. This works, but the correction is empirical and it is specific to one press, one billet temperature and one alloy. Change the alloy and the balance shifts.

This is why thin-wall wide sections are hard to transfer between suppliers even with the same drawing: the die carries a correction that only makes sense in the press it was tuned on.

Wall thickness difference: the harder problem

A section with a 5 mm wall on one side and a 0.8 mm wall on the other is more difficult than a uniformly thin one, for a reason that is easy to picture: metal flows faster through the thin gap and slower through the thick one, because the thick section has more bearing contact area per unit volume.

The result is that the thin wall is pulled along by the thick wall's slower exit, and it stretches. It comes out thinner than designed, and the thinner it gets, the faster it wants to run — so the section is unstable rather than merely out of tolerance.

Three fixes, in order of effectiveness:

Balance the wall. If the 5 mm wall can become 2 × 2.5 mm with a rib, the flow evens out and the part becomes manufacturable. This is a design change and it is almost always the right one.

Change the bearing. A longer bearing on the thick side slows it down; that is exactly what the die shop does in trial correction. It works, but it narrows the process window.

Accept and machine. Extrude the thin side with stock and machine it to final thickness. This converts a flow problem into a machining cost, which is predictable.

Cooling distortion: thin walls cool first

A thin wall loses heat far faster than a thick one. In a section with a mixed wall the thin side contracts first, while the thick side is still hot and soft, so the section bows toward the thick side. When the thick side finally cools and contracts, some of that bow is locked in.

This is separate from flow distortion and it needs a separate correction. Options are a controlled cooling ramp after the quench, pre-bending the run-out, or mechanical straightening — and the last one introduces stress that may release later during machining.

For a thin-wall part that will be machined, the sequence matters: straighten, then stress relieve, then machine. Straightening a quenched thin-wall section and machining it straight away is how a part ends up 0.3 mm out after the final cut.

Specifications

Item	Reference value
Section types	Wide thin-wall, multi-cavity thin-wall, mixed wall thickness, special-shaped thin-wall
Maximum width	about 750 mm class
Circumscribed circle	φ5 mm to φ750 mm
Minimum wall	0.8 mm
Maximum mass per metre	up to about 100 kg/m
Dimensional tolerance	Reference ±0.02 to ±0.04 mm
CNC machining accuracy	Reference ±0.005 to ±0.01 mm
Maximum machined length	6,500 mm
Alloys	6061-T6, 6063-T5, 6005-T6, 6082-T6
Extrusion press	600 T to 12,000 T
Standard	GB/T 6892-2023 high precision
Surface treatment	Anodising, hard anodising, powder coating
Die lead time	10–15 days to sample for conventional structures
Batch lead time	12–18 days after sample approval
Minimum batch	50 kg for R&D builds

The section types, and what each one costs you

Type	Structural character	Manufacturing cost driver
Wide thin-wall open section	Large envelope, low mass, low stiffness in torsion	Die deflection and bearing correction; easiest of the four
Multi-cavity thin-wall	Closed cavities give torsional stiffness with low mass	Mandrel support, welding chamber pressure, seam quality
Mixed wall thickness	Function-driven: thick where load is, thin where it is not	Flow imbalance; the hardest to hold tolerance on
Special-shaped thin-wall	Non-symmetric, often aesthetic plus functional	Distortion control; straightening is difficult without marking

Where it does not fit

• You need a 0.8 mm wall in a multi-cavity section at full width. Each constraint is achievable; the combination is not reliable. We will quote it with an honest scrap allowance, or propose an open section plus a closure instead.
• The part is structural and torsionally loaded. Thin-wall open sections are poor in torsion. If the load path is torsional, a closed box or a different process is the right answer — no die design fixes a section property.
• The wall difference is more than about 4:1. Flow balance becomes unstable and the thin side runs away. Redesign the wall or accept machining on the thin side.
• You need a mirror surface on a wide thin section. Anodising a large thin-wall part is a distortion risk, not just a finish step. Powder coating or a lower-grade finish may be the practical choice.
• Your volume is small and the section is at the limit. At the edge of the process window, scrap rate is high and a small order carries all of it. Better to run a larger batch or relax one constraint.
• The design is still moving. A die at this complexity level is expensive to correct. Freeze the envelope and the wall distribution first.

What to send for a quote

Send the section drawing with every wall thickness dimensioned, the alloy and temper, the length, the application and the load case if the part is structural. Tell us which walls are functional minimums and which are nominal — that distinction changes the die approach. If you have a weight per metre target, send it: it is the fastest way to see whether the section is inside the press window.

We will reply with the extrusion ratio on the proposed die type, the wall thicknesses we consider reliable, the flow and distortion risks, and a written statement of the tolerances we can confirm. Where a wall is below what the section can hold, we will say so and propose either a thicker wall or a different section type.

FAQ

What is a thin-wall large-section profile?

A section where the wall is thin relative to the overall envelope — typically 0.8–2.0 mm wall on a section 300–750 mm across. The difficulty is not the thin wall alone or the size alone, but the extrusion ratio and the flow balance that the combination produces.

What is the thinnest wall you can hold?

Reference minimum is 0.8 mm, and it is achievable on open sections of moderate width. On a closed multi-cavity section at full width, 1.2–1.5 mm is a more honest number. The value on your order is set by your drawing and we confirm in writing what we can hold — including telling you when a wall is too thin for the section type you have drawn.

What tolerance is possible on a wide thin section?

Reference ±0.02 to ±0.04 mm on critical positions and ±0.005 to ±0.01 mm after CNC finishing. On the as-extruded thin wall, expect the tolerance to be stated on wall thickness specifically, because that is where flow variation shows. We confirm the achievable value per dimension before quotation.

Why do wide thin sections cost more per kilo?

Because of scrap and die correction. A section at the edge of the process window produces more trial material, needs more bearing correction passes, and has a lower yield per billet. The metal cost is the same; the process cost is not. A price that ignores this is a price that will be renegotiated after the first failed lot.

Can you bend or weld a thin-wall large section afterwards?

With care. Thin walls buckle in bending and distort in welding, and a large section concentrates both problems over a long length. If the finished part needs bending, tell us at die design stage — the section, the radius and the alloy interact, and a bend-friendly wall is different from an extrusion-friendly one.

What alloys work best?

6063-T5 extrudes most easily and gives the best surface, which matters on a wide visible part. 6061-T6 gives strength but is harder to run thin at width. 6005-T6 sits between them and is a good compromise for structural thin-wall. 6082-T6 for higher strength where the wall can be a little thicker.

What is the lead time?

Reference 10–15 days to first sample for a conventional structure, 12–18 days for the batch after you approve the sample. At the edge of the process window, plan for at least one correction pass — it is normal, and it is better scheduled than discovered.

Send your drawing

Email the section drawing with all wall thicknesses, the alloy, the length and the load case to linjunbing@truetrustlv.com, or send it on WhatsApp at +86 136 6644 0600. You will get an extrusion ratio assessment, a wall thickness opinion and a written tolerance statement before you commit.