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Casing panels, access doors and filter frames formed flat enough to seal — and a note up front on the one thing we do not supply: rectangular duct lines.
An air handling unit is a sealed box assembled from folded panels, and its performance is measured by how well that box holds air. Casing panels, access doors, blank-off plates and filter frames are typically 0.6 to 1.2 mm galvanised or stainless sheet, and their flatness and edge geometry determine the casing air leakage class far more than the gasket specification does.
The equipment set follows from that. A flexible edge folding machine produces the dead edges, offsets and returns that give a panel its rigidity and its sealing face. A CNC turret punch press produces filter fixing patterns, fan and coil access cut-outs, acoustic perforation for inner skins and stiffening ribs in one clamping. A panel bender handles deeper four-sided panels and access doors. What none of these produce is rectangular ductwork — duct lines with integral TDF flange forming are a separate machine category that STON CNC does not supply, and we say so before quoting rather than after.
STON CNC (Qingdao Ston Mechanical Technology Co., Ltd.) is a Chinese original manufacturer of CNC panel benders and turret punch presses, founded in 2006 in Qingdao, China. All equipment described here is built inside STON CNC's own 20,000㎡ factory, from casting and heat treatment through machining, assembly and inspection. Machines carry ISO 9001 quality certification and CE marking under Machinery Directive 2006/42/EC, and are exported to more than 80 countries. View certifications and patents →
AHU and purification equipment concentrate their sheet metal in flat panels whose edges have to seal against each other. Edge geometry, not panel size, is the manufacturing problem.
A casing panel that bows will not seal against its neighbour, and the leakage test fails whatever gasket is specified. Straightness of roughly 0.2 mm per metre and angle accuracy of roughly ±0.5° per metre across the panel are what make even gasket compression possible along the whole joint.
Casing panels commonly require a hemmed dead edge, an offset for the inner skin, or a return that closes onto the insulation. These are the three special processes a flexible edge folding machine performs directly, with a minimum folded height of 4 mm, and which a press brake produces only with multiple setups.
An attenuator inner skin can carry thousands of holes. A laser pierces each one, so cycle time scales with hole count and the acoustic panel becomes the constraint. A turret punch multi-hits and nibbles the pattern with standard tooling and adds rib forming in the same clamping.
Size the folding capacity against your largest casing panel and the punching capacity against your acoustic products. Those two parts set the machine list.
The duct row is the important one on this page. Everything else about AHU casing panels sits comfortably inside the forming window.
| Parameter | Flexible edge folding machine | Panel bender | Notes |
|---|---|---|---|
| Typical casing gauge | 0.6–1.2 mm | 0.6–1.2 mm | Well inside capacity |
| Galvanised / cold-rolled max | 0.5–2.0 mm | ≤2.0 mm cast / ≤1.5 mm welded | At full bending length |
| Stainless steel max | — | ≤1.2 mm cast / ≤1.0 mm welded | For pharmaceutical and food AHUs |
| Max forming size | 1200 × 1200 to 2000 × 1500 mm | up to 2800 × 1500 mm | By model |
| Minimum bending height | 4 mm | 5 mm | Casing returns live here |
| Maximum bending height | 100 mm | 170 / 300 / 400 mm | Panel depth check |
| Special processes | Arc, dead edge, offset | Positive and negative, 0–180° | Double-skin edges use dead edge |
| Straightness | approx. 0.2 mm/m — decides casing leakage performance | — | |
| Rectangular duct with TDF flange | Not possible — separate machine category, not supplied | Different supplier | |
| Utilities | Three-phase 380 V, 0.6 MPa air | Configured to destination voltage | |
Flat casing panels, access doors, filter frames and cleanroom panels in 0.6–1.2 mm with hemmed, offset or returned edges, plus acoustic perforation. This is the core of AHU and purification sheet metal.
Rectangular duct production lines with integral flange forming, spiral round duct machines, circular flange rolling, and extruded or roll-formed casing frame profiles. All separate machine categories that STON does not supply.
Structural base frames, heavy lifting brackets, damper shafts and thicker mounting plates. One press brake alongside the panel cell covers all of it.
Risk assessment follows EN ISO 12100; safety-related control functions such as light-curtain interruption and emergency stop are specified to EN ISO 13849-1. Hydraulic press brakes supplied into the EU are built against EN 12622. Machines placed on the EU market carry CE marking under Machinery Directive 2006/42/EC with the accompanying technical file. Quality management is certified to ISO 9001, and machined structural tolerances follow ISO 2768. For the finished unit, EN 1886 defines casing strength, air leakage, filter bypass leakage and thermal performance classes, and ISO 14644-1 applies to cleanroom classification. These test your assembled unit rather than the machine — what the equipment contributes is the panel flatness and edge consistency those classes depend on.
On the machines this means fully enclosed rear fencing, protective covers on all protruding moving parts, laser guarding that halts motion when the protected zone is broken, over-tonnage protection on turret punch presses, and grating-ruler offset-load detection on panel benders.
Most AHU factories need the folding machine first. The choice between the three is decided by edge geometry and panel depth, not by panel size.
| Flexible edge folding machine | CNC panel bender | CNC press brake | |
|---|---|---|---|
| Dead edge and offset returns | Direct process | Limited | Multiple setups |
| Four-sided access doors | Good | Single clamping | 4 rotations |
| Maximum folded height | 100 mm | 170 / 300 / 400 mm | Tool dependent |
| Minimum folded height | 4 mm | 5 mm | Tool dependent |
| Maximum panel length | 2000 mm | 2800 mm | 4100 mm |
| Base frames and heavy brackets | No | No | Yes |
| Operators | 1, or 0 with automatic loading | 1, or 0 with automatic loading | 1–2 |
| Does STON supply it? | Yes | Yes | Yes |
If your business is primarily ductwork rather than unit casings, this page is not the right solution. Duct lines with integral flange forming come from specialist duct machinery suppliers, and we will tell you that on the first call rather than after an order.
Figures below describe the direction and mechanism of the change. Actual results depend on your part mix, batch size and shift pattern — we model them against your own drawings before quoting.
| Item | Press brakes only | Folding machine and punch cell |
|---|---|---|
| Double-skin edge return | Multiple setups per panel | Single dead-edge operation |
| Casing panel straightness | Crowning and operator dependent | approx. 0.2 mm/m |
| Leakage test failures | Common at panel joints | Reduced by consistent edge geometry |
| Acoustic perforation | Laser, scales with hole count | Punch, largely independent of hole count |
| Stiffening ribs | Separate operation | Same clamping as the holes |
| Operators per large panel | 2 | 1, or unattended with loading |
| Changeover between unit sizes | Tool change and gauge reset | Program recall |
Payback logic we use with customers: (annual labour released + reduction in rework and scrap + additional saleable output) ÷ installed equipment cost. We build this with your real numbers rather than publishing a headline figure that would not match your plant.
Dead edge, arc and offset bending with a 4 mm minimum folded height — the processes that produce double-skin casing returns. Up to 25 concurrent servo axes, 42CrMo forged blank holder, fully enclosed rear fencing.
View folding machine →
Filter fixing patterns, fan and coil access cut-outs, acoustic perforation and stiffening ribs in one clamping. ±0.1 mm accuracy, turret speed to 40 rpm, brush and steel-ball composite table for galvanised sheet.
View SF series →
Access doors and deeper four-sided panels beyond the folding machine's 100 mm height. Full-electric servo closed-loop control, rapid compensation adjustment, cast or welded frames to 2800 mm.
View press arm type →
Exchange-table fiber laser for casing blanks, coil access apertures and unit-specific specials. Burr-free edges on galvanised and stainless sheet, with the next sheet loading while the current one cuts.
View laser unit →
Acoustic perforation and access cut-outs on the same panel in one clamping, in roughly 40% less floor space than two machines, with no secondary alignment between the pattern and the aperture.
View SFL series →
Base frames, lifting brackets, damper components and thicker mounting plates outside the panel window. Direct-drive servo, mechanical crowning compensation, multi-axis CNC back gauge.
View PBE series →Founded in 2006 and headquartered in Qingdao, one hour from major export ports and the airport. Casting, heat treatment, machining, welding, assembly and inspection all happen inside our own 20,000㎡ factory. That is why a configuration change for an AHU casing line does not become a six-month subcontracting problem.
AHU projects run to building services programmes with fixed commissioning dates. A unit that fails a leakage test on site is remade, not adjusted, so panel consistency and support response belong in the same conversation.
Specifications on this page verified against STON engineering documentation on 4 August 2026. Forming limits are confirmed against your own drawings before quotation. Published on 4 August 2026 · Last updated 4 August 2026 · Reviewed by Vicky Xu, Head of Overseas Sales.
The edge detail decides the machine. Send a section through your double-skin casing edge plus an acoustic panel with its real perforation pattern, and we return a configuration within 24 hours.
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