Digital Fabrication
Chế tạo sẵn / Fabrication
Extract data directly from the BIM model to drive CNC/plasma machines producing steel, precast, or MEP modules off-site in the factory — reducing field labor.
Common tools
Tekla Structures, Advance Steel, Autodesk Inventor
Value delivered
Applied on Vietnamese supertall towers for complex transfer-floor steelwork and precast components
Adoption in Vietnam
Common among Vietnamese steel contractors (PEB Steel, Zamil) and large precast projects.
Level of Information Need (LOIN)
G = Geometry · A = Alphanumeric · D = Documentation (ISO 7817-1:2024 method). A blank cell means this use sets no specific requirement for that discipline/stage.
| Discipline | Concept | Schematic | Developed | Technical | As-built / Operation |
|---|---|---|---|---|---|
| Architecture | — | — | — | G4·A2·D1 | — |
| Structure | — | — | — | G4·A2·D2 | — |
| Mechanical | — | — | — | G4·A2·D1 | — |
| Electrical | — | — | — | G4·A2·D1 | — |
| Plumbing | — | — | — | G4·A2·D1 | — |
Critical stages: Technical
Rationale: G4 (fabrication / CNC-ready, LOD400) is the defining requirement across all disciplines — shop drawings, spool sheets, precast/prefab modules are driven directly from model geometry. A2 carries manufacturer / material / connection specifications. STRU reaches D2 for mill certs / test certificates on structural steel or precast. This sets the G-ceiling at ST4.
What it really is
Digital Fabrication is the process of raising a BIM model from a design-intent Level of Information Need to a fabrication-level LOIN (per ISO 7817-1:2024), breaking it into individually tagged components (piece marks), then exporting control data directly to CNC/plasma steel-cutting machines, rebar-bending lines, or ductwork and sheet-metal forming lines in a factory — instead of workers reading paper drawings and measuring by hand. Unlike a design model, which only needs to be right in position and overall size, a fabrication model must be right down to every bolt hole, weld, fabrication tolerance and erection tolerance — a single millimetre of error here can mean a component does not fit on site. The workflow runs both ways: downstream, an approved design model flows to the shop as fabrication data; upstream, deviations measured during fabrication and erection must feed back into the model to update the as-built record, rather than stopping at a one-off file export. In Vietnam, the two areas with genuinely wide uptake are prefabricated structural steel (industrial sheds, high-rise steel frames) and prefabricated MEP (ductwork modules, pipe clusters); precast concrete fabrication and other complex-geometry fabrication remain limited, mostly confined to the small number of factories that have invested in automated lines.
When to use
Worth investing in when a project has enough structural steel or prefabricated MEP scope to offset the cost of building a fabrication model and setting up CNC data — industrial sheds, steel-framed high-rises, or projects with a high density of mechanical and electrical equipment. Start only once the design model has passed basic clash coordination and the main connection details are approved — sending an insufficiently detailed model to the shop is the most common reason a project has to redo the work.
Prerequisites
- •A design model through basic clash coordination with the main connection details approved — depends directly on Design Authoring and 3D Coordination
- •A shop or specialty subcontractor with compatible CNC equipment and software able to read model-exported data (NC1/DSTV for steel, DXF for sheet metal and ductwork)
- •A BEP or fabrication contract stating who is responsible for raising the LOIN to fabrication level — usually the specialty subcontractor, not the original design consultant (Art. 8(2))
- •Erection tolerances and the construction method already agreed among the designer, the fabrication shop and the erection crew before material is cut
- •A shop QA/QC procedure and an as-fabricated measurement plan defined before batch production starts
Inputs
Design task team · .rvt / IFC
Appointing party · lead appointed party · .pdf / .docx
Structural engineer · .pdf / .rvt
Design consultant · appointing party · .pdf
Construction contractor · .pdf / .xlsx
Lead appointed party · .pdf
Outputs
Fabrication model broken into components with piece marks
mô hình Advance Steel/gốc + IFC → Fabrication shop
Accepted when: Every component has a unique piece mark, matches the approved connection design, no orphaned components remain
CNC control data (NC1/DSTV, nested DXF)
.nc1 / .dxf → Fabrication shop
Accepted when: Loads directly into the CNC machine, no manual re-entry of dimensions
Shop and erection drawings
.pdf / .dwg → Fabrication shop · erection contractor
Accepted when: Complete dimensions, tolerances, weld/bolt symbols, consistent with the fabrication model
Fabrication cutting list / bill of materials
.xlsx → Fabrication shop · procurement
Accepted when: Matches model quantities, no double counting, traceable to individual components
Fabrication and erection tolerance report
.pdf / .xlsx → Lead appointed party · appointing party
Accepted when: States measured deviation against the model, the acceptance threshold, and what must be updated back into the model
General workflow
Freeze the design model before handover to fabrication
Verify the model has passed basic clash coordination, objects are the correct types, and the main connection details are approved. A design model and a fabrication model sit at two different LOIN levels — handing the design model straight to the shop without an enrichment step is the most common starting mistake.
BIM Coordinator · Revit · Navisworks Manage → Frozen design model ready for handover to the shop
Enrich the fabrication model
The shop or fabrication team rebuilds objects to bolt/weld connection detail, assigns a unique piece mark to each component, and defines the fabrication method per section type. This is the step that raises the design LOIN to a fabrication LOIN — skip it and the exported CNC data is wrong from the start.
Shop fabrication engineer (fabrication task team) · Autodesk Advance Steel (Tekla Structures is also common in the industry for the same role) → Fabrication model with piece marks
Check fabricability, transport and erection feasibility
Simulate the erection sequence, check transport size and weight limits along the real route, crane working radius, and add erection tolerance allowances into the fabrication model before material is cut.
BIM Coordinator · construction crew · Navisworks Manage → Approved fabricability and transport report
Export CNC control data
Export NC1/DSTV data for steel cutting/drilling, or nested DXF for sheet metal and ductwork, directly from the fabrication model. Never re-enter dimensions into the machine by hand — this is the most common source of error when the model and the shop remain disconnected.
Shop fabrication engineer · Autodesk Advance Steel (NC1/DSTV export) → CNC control files
Fabricate in the shop and run quality control
The CNC line cuts, drills and welds per the exported data. Each component is measured against the defined fabrication tolerance before packing — anything out of tolerance is held and reworked in the shop, never allowed to reach site.
Fabrication shop · In-house CNC line and QC inspection procedure → QC-passed fabricated components
Pack, transport and erect
Pack in the sequence simulated for erection, transport and erect on site per the erection drawings. Measure the as-erected position with an electronic total station to confirm the agreed erection tolerance is met.
Erection contractor · Electronic total station and erection drawings → Erected components with as-measured coordinates
Feed tolerance data back into the model
Compare as-measured data against the fabrication model, log the deviation, and update the model when it exceeds the agreed threshold. This is the step most often skipped, leaving the later as-built model out of step with what is actually installed on site.
BIM Coordinator · Navisworks Manage · Revit → Model updated to as-fabricated state, data handed to Record Modelling
Diagram
↺ Site measurement data must feed back to the shop and the model — this is not a one-way flow from model to shop
Common pitfalls
The shop rejects the model for lacking connection detail to fabricate from
Cause: The design-LOIN model was sent straight to the shop, mistaken for a fabrication-LOIN model
Fix: Require a separate fabrication-model enrichment step and assign responsibility clearly in the BEP before signing the fabrication contract
Components match the drawings but do not fit on site
Cause: Erection tolerance was not accounted for, so deviation accumulates across a chain of connected components
Fix: Build erection tolerance into the fabrication model and simulate erection before exporting CNC data
The design changes after handover to the shop but components are still fabricated to the old version
Cause: The fabrication model and data were fully disconnected from the source model, with no shared version control
Fix: Keep the fabrication model linked to the design model through the CDE and require production to stop on any unconfirmed change
Fabricated components cannot be transported to site
Cause: Transport size and weight limits were not checked before splitting components into modules
Fix: Check vehicle and route transport limits while building the fabrication model, before CNC data is exported
Field-measured deviations never make it back to the shop or the model
Cause: The workflow only runs one way from model to shop, with no mandatory feedback step
Fix: Make the as-fabricated survey and tolerance feedback to the model a mandatory part of the acceptance process
Measuring effectiveness
Components erected correctly to tolerance on the first attempt divided by total components erected in the batch
Benchmark: no independent benchmark — set an internal target
Count RFIs concerning the model or fabrication data raised after the CNC export milestone
Benchmark: no independent benchmark — set an internal target
Working days from the design-freeze milestone to the NC1/DSTV export
Benchmark: no independent benchmark — set an internal target
Legal basis
There is NO specific requirement for digital fabrication in Decree 217/2026/NĐ-CP — this use falls under Article 8 generally. Art. 8(1)(a) makes BIM mandatory for new-build works Grade II and above; Art. 8(2) assigns scope, content and information requirements to the contract — the sole basis for bringing the fabrication LOIN, fabrication-model responsibility and tolerance thresholds into the EIR/BEP; Art. 8(6) requires BIM data to be managed under intellectual-property law, which matters in practice because a fabrication model (piece marks, connection detail) is often copyrighted by the specialty subcontractor and its usage rights need to be agreed at handover. The practical consequence: like 4D and 5D, digital fabrication is a CONTRACTUAL obligation — if a fabrication model at the right LOIN is wanted, it must be written into the EIR and BEP; the law does not mandate it automatically.
Sources
Only official sources (legislation, standards) and peer-reviewed academic work are cited. No vendor marketing figures or press sources. Reference only — does not replace legal advice.