A precision sheet metal enclosure moves through nine controlled operations — design review, cutting, bending, forming, welding, deburring, hardware insertion, finishing and inspection. Each step sets a limit that the next inherits, so a shortcut at step two surfaces as a fit problem at step nine. Here is what each step does, the capability it carries, and where your drawing has the most influence on cost and lead time.
Key takeaways
- The nine steps are cumulative: cutting sets the accuracy floor, bending sets the fit, and finishing protects what the earlier steps built.
- DFM review happens before any metal is cut, and it is where most cost is decided — bend reliefs and hole-to-bend distances cost nothing to change on screen.
- Capability is a band, not a number: ±0.1 mm class cutting and about ±0.5° bend angles are realistic production figures.
- Deburring and surface preparation are not cosmetic — edge condition decides coating adhesion, handling safety and whether a gasket seals.
- Standard parts ship in 7–15 working days, complex custom builds in 20–30 days; sample lead time is quoted per project, because it scales with the work involved.
What are the nine steps in a sheet metal fabrication process?
In order: design and DFM review, laser cutting, CNC bending, forming, welding, grinding and deburring, hardware insertion, powder coating, then assembly and quality control. The order is not arbitrary — separation comes before shaping, shaping before joining, and finishing assumes the geometry is final. What differs between suppliers is not the list of steps but how tightly each one is controlled, and how much is measured rather than assumed.
What does each step actually do, and what capability does it carry?
The capability figures below are production bands for common enclosure work, not laboratory limits — confirm them against your own drawing before specifying tighter.
| Step | Operation | Typical capability | What it controls |
|---|---|---|---|
| 1. Design & DFM | CAD review, tolerance stack-up, bend relief and hole-to-bend checks. | Drawing released as production-ready. | Rework, scrap and how many quotes you need. |
| 2. Laser cutting | Fiber laser cutting of the programmed flat pattern. | ±0.1 mm class on common gauges; 0.5–6.0 mm everyday band. | Profile and hole positions — the floor for every later step. |
| 3. CNC bending | Press brake forming along programmed bend lines. | Angles held to about ±0.5°; minimum inside radius near material thickness. | Panel fit, squareness, whether the door closes. |
| 4. Forming | Louvres, stiffening ribs, countersinks and drawn features. | Feature depth and position held by dedicated tooling. | Stiffness without paying for a thicker gauge. |
| 5. Welding | TIG, MIG or laser welding, usually jigged. | Seam continuity and distortion control. | Structural integrity and whether the enclosure seals. |
| 6. Grinding & deburring | Weld grinding, edge break and burr removal. | Edge condition specified, not assumed. | Coating adhesion, handling safety, gasket sealing. |
| 7. Hardware insertion | Studs, standoffs, clinch fasteners and hinges pressed in. | Insertion height and torque-out resistance. | Serviceability and field mounting. |
| 8. Powder coating | Pre-treatment, electrostatic application, oven cure. | Film build measured; adhesion set by pre-treatment, not the powder. | Corrosion life and appearance. |
| 9. Assembly & QC | Fit, dimensional inspection and functional checks. | Measured against the released drawing. | Whether the unit ships. |
Why does design and DFM review come before any metal is cut?
Because it is the only step where a change is free. On screen a bend relief can be widened, a hole moved away from a bend line, or a tolerance relaxed in seconds. Once the sheet is cut, the same change is scrap plus a new setup. Our DFM review looks for the geometry that costs money later: holes too close to a bend, flanges shorter than the tooling can form, ribs a punch cannot reach, and tolerances tighter than the process holds.
The step also settles material and finish, because both constrain everything after them — gauge sets the minimum bend radius, and finish adds thickness that close-fitting hardware has to allow for. Our material selection guide covers that choice in detail.
The same freeze-first logic holds one level up: if the enclosure could be molded as cheaply as fabricated, the review has to happen before the tool is cut rather than after — when the part is better molded than fabricated.
How does cutting set the accuracy floor for every step after it?
Every later dimension is measured from an edge or hole the laser produced. If the flat pattern is out, no amount of care at the press brake recovers it, because bending multiplies error rather than correcting it. That is why the flat pattern is treated as the reference for the whole build and checked before the blank leaves the cutting table.
Cutting also sets the edge condition that welding and coating inherit. A laser edge carries a narrow heat-affected zone, and heavier plate can carry dross — both cheap to fix at step six, expensive to discover at step eight. Whether the profile is cut by laser or blanked in a die is a separate decision with its own economics; our laser cutting vs stamping comparison works through it.
What determines bend quality, and why does springback matter?
Two things: tooling and compensation. Every alloy springs back differently after the punch releases, so bend compensation is set for the specific material and gauge and then verified on a first part — a program tuned on mild steel will not hold on stainless. The design rules are just as binding: minimum inside radius follows the material, holes must sit far enough from the bend line not to be pulled oval, and flanges must be long enough for the tooling to grip. Those are set out in our bending guide.
When is welding needed, and what does it add to the schedule?
Welding is needed when the enclosure must be structural, sealed, or both — a frame that carries load, a seam that has to hold an IP rating, a corner that cannot be fastened. TIG, MIG and laser welding suit different materials, seam lengths and appearance requirements, and the choice is covered in our welding guide.
What welding adds is a jig and a distortion risk. Heat moves thin sheet, so assemblies are fixtured and sequenced to keep corners square, and seams are ground before finishing. A design that can be folded and fastened instead of welded usually builds faster and holds dimension more easily — worth asking at DFM stage.
Why are deburring, hardware and surface preparation separate steps?
Because they solve different problems and are easy to under-specify. Deburring removes the burr and breaks the edge so the part is safe to handle and coating has something to grip — a sharp edge coated over tends to rust first, because film build pulls away from a corner. Our edge break and deburring guide covers what to specify.
Hardware insertion is positional. Studs, standoffs and clinch fasteners go in before coating so the finish does not have to be machined off afterwards, and their height has to allow for coating build. It is also what makes the enclosure serviceable in the field — a panel that can be removed and refitted without losing threads is worth more than one that was cheaper to assemble.
What does finishing actually protect against?
Corrosion — and it does that mostly through pre-treatment rather than the powder. A multi-stage clean and conversion coating is what decides whether the film still adheres at a scribed edge; the powder is the visible part of the system, not the part doing the protecting. There is a dimensional consequence too: coating adds thickness, so threads, press-fit hardware and close-fitting assemblies must be dimensioned on the finished size, not the raw gauge. Our surface finishing guide sets out the options.
How is quality verified, and how long does the whole flow take?
Dimensional inspection against the released drawing, functional checks where the assembly does something, and visual inspection of the finish. On repeat orders the first article carries the full inspection and the run is sampled, which keeps a production run consistent without inspecting every part twice.
On timing: standard parts ship in 7–15 working days and complex custom builds in 20–30 days. Sample lead time is quoted per project rather than as one number, because it scales with how much forming, welding, finishing and assembly the part needs. SanJun runs the flow across a 5,000㎡ facility certified to ISO 9001 and ISO 14001 with RoHS and REACH compliance; we do not hold CE marking, so raise it at enquiry stage if your market requires it. Our custom enclosure manufacturing overview covers how we stage programs.
Punching carries its own constraints inside that flow — die clearance, minimum web width, turret tonnage and burr direction. They are covered step by step in our sheet metal punching and turret press guide.
A rack chassis concentrates the whole process chain into a small part — drawing review and DFM through cutting, forming, welding and finishing to first-article measurement. How that sequence applies to a 2U unit is set out in 2U rack chassis design and fabrication.
Frequently Asked Questions
Do I need to supply a 3D model, or is a 2D drawing enough?
Either works. A 3D model speeds up flat-pattern development; a dimensioned 2D drawing with material, gauge and finish is enough to quote and build from. What slows things down is a drawing that leaves material or finish to be guessed.
Which step most often delays a first article?
Design release. When a first article slips, it is usually because the drawing was still moving when cutting started, or because a tolerance assumed a capability the process does not hold. Both are prevented at DFM review, which is why we do it before quoting rather than after.
Can steps be skipped to save cost?
A few can be combined, but the ones people want to skip are usually the ones that matter. Skipping deburring saves a little and costs coating adhesion; skipping pre-treatment saves more and costs the corrosion life of the unit. Forming can genuinely save money — a stiffening rib is cheaper than a thicker gauge, as our rib design guide explains.
How is springback handled in production?
By compensation, verified on the first part. The bend program over-bends by the amount the material is expected to spring back, then the first article is measured and the compensation corrected if needed. It is a material-and-gauge setting, not a one-time machine setting.
Does powder coating change part dimensions?
Yes, and this catches people out. The cured film adds thickness to every surface, so threaded features, press-fit hardware and close-fitting assemblies have to be dimensioned on the finished size. It is one of the checks a DFM pass should catch.
What does quality control actually measure?
Critical dimensions against the released drawing, fit and function of the assembly, and the finish — film build, adhesion and appearance. On repeat orders the first article gets the full inspection and the run is sampled.
How long does the whole process take?
Standard parts ship in 7–15 working days and complex custom builds in 20–30 days. Sample lead time is quoted per project rather than as one number, because it scales with how much forming, welding, finishing and assembly the part needs. Tooling, if the part needs it, is quoted separately.
Which step should I ask a supplier about first?
Ask what their DFM review covers, and whether it happens before or after quoting. A supplier who reviews geometry first will tell you what drives your cost; one that quotes first and reviews later discovers it on your first article. Tolerance specification is the other useful probe — see the tolerance guide.
Want a second opinion on a drawing? Send it with material, gauge and quantity — we will run a free CAD and DFM review and quote within 24 hours.
What a laser cut edge condition actually specifies — kerf width, dross, angular tolerance, roughness and heat-affected zone — is a drawing question, and it belongs in step one rather than step six.
Every step in this sequence has its own limits and its own drawing callouts; all of them are collected in the sheet metal process and DFM cluster.