Forming
- Processes
- 60
- Families
- 6
- Column
- Tolerances
Metal22
- Centrifugal CastingOutside diameter, cast against a metal die, holds substantially tighter than the bore, which is uncontrolled and always machined; wall thickness is set by pour volume and carries the loosest tolerance of the three
- CNC Wire BendingRoughly ±0.020 in (±0.5 mm) on leg lengths and ±1–2° on bend angles, tightening to about ±0.010 in and ±1° with first-article correction; tolerances accumulate along multi-bend parts
- Deep DrawingRoughly ±0.010 in (±0.25 mm) on drawn diameters and depth; ironed walls hold tighter, near ±0.002 in (±0.05 mm). Wall thickness varies 10–25% from the blank gauge by design
- Die Casting±0.010 in (±0.25 mm) on the first inch, then ±0.002 in per additional inch (NADCA standard linear tolerance, aluminum); dimensions crossing the parting line need added allowance
- ElectroformingThe mandrel-contacting surface replicates the mandrel closely, so its accuracy is the mandrel's accuracy; wall thickness typically varies ±10–25% across a part unless shields and current thieves are used
- ForgingCommercial impression-die forgings hold roughly ±0.030 in (±0.8 mm) on small parts, widening with size, plus separate allowances for die wear, mismatch, and die closure; machine anything needing better than about ±0.010 in
- Heat Treatment
- HydroformingRoughly ±0.010–0.030 in (±0.25–0.75 mm) on formed features; sections calibrated hard against the die hold better than regions that are only partly expanded
- Investment CastingAbout ±0.005 in (±0.13 mm) on the first inch plus roughly ±0.003 in per additional inch; flatness and straightness are usually the limiting characteristics on long or thin parts
- Metal ExtrusionStandard mill tolerances per published aluminum extrusion practice — roughly ±0.010 in (±0.25 mm) on small cross-section dimensions, wall thickness held as a percentage, plus separate straightness, twist, and flatness allowances
- Metal Injection MoldingAbout ±0.3% of the dimension as standard (roughly ±0.003 in on a 1 in feature), with ±0.1–0.2% achievable on controlled features or after sizing; machine anything tighter
- Metal SpinningRoughly ±0.010–0.030 in (±0.25–0.75 mm) on diameters, tighter on CNC machines with hard mandrels; wall thickness varies through the part in conventional spinning and follows the sine law in shear spinning
- Metal Stamping±0.005 in (±0.13 mm) typical on blanked and pierced features; ±0.001–0.002 in (±0.025–0.05 mm) achievable in precision dies. Formed dimensions spanning several stations hold looser than single-station features
- Panel Beating
- Powder Metallurgy (Press and Sinter)Roughly ±0.001–0.002 in per inch on dimensions perpendicular to the pressing direction, controlled by die and core rod steel; dimensions along the pressing axis hold considerably looser unless the part is sized after sintering
- Press Braking±0.010 in (±0.25 mm) on a single bend dimension, accumulating roughly ±0.010 in per additional bend; bend angle ±1°, or ±0.5° with in-process angle measurement
- Roll Forming±0.010–0.030 in (±0.25–0.75 mm) on cross-section dimensions and about ±1° on formed angles; cut-length tolerance depends on whether cutoff is flying or stationary
- Sand CastingAbout ±0.030 in (±0.8 mm) on the first inch plus roughly ±0.003 in per additional inch in green sand; no-bake and shell molds hold tighter. Allow up to 0.030 in (0.8 mm) mismatch across the parting line
- Sheet Metal Fabrication±0.005 in (±0.13 mm) on laser-cut features; about ±0.010 in (±0.25 mm) per bend, accumulating across bends; welded assemblies are substantially looser unless fixtured or machined after welding
- Superforming
- SwagingRoughly ±0.002–0.005 in (±0.05–0.13 mm) on swaged outside diameter; inside diameter holds a comparable tolerance only when a mandrel is used
- Tube and Section BendingRoughly ±1° on bend angle and plane of bend, and about ±0.030 in (±0.75 mm) on leg lengths; tolerances accumulate along a multi-bend part, so dimension from a single datum end
Additive Manufacturing12
- Binder JettingRoughly ±0.5% of dimension on sintered metal (about ±0.008 in on a 1.5 in feature), with ±0.3% achievable on well-characterized geometry. Binder-jetted foundry sand molds hold approximately ±0.012 in (±0.3 mm).
- Direct Metal Laser Sintering (DMLS)About ±0.004 in (±0.1 mm) on features up to 1 in (25 mm), then roughly ±0.2% of nominal. Suppliers commonly quote ±0.003 in (±0.076 mm) plus ±0.001 in/in for well-controlled geometry; machined features are far tighter.
- Directed Energy Deposition (DED)As-deposited surfaces are held to roughly ±0.02–0.04 in (±0.5–1.0 mm) at best, and large WAAM structures to considerably less. Final tolerances come from the machining operation that follows, not from the deposition.
- Electron Beam Melting (EBM)About ±0.012–0.016 in (±0.3–0.4 mm), looser than laser powder bed fusion because of the thicker layers and coarser powder. Machined interfaces hold normal machining tolerances.
- Fused Deposition Modeling (FDM)±0.020 in (±0.5 mm) or ±0.5% of nominal, whichever is greater, on desktop-class machines. Industrial systems hold ±0.008 in (±0.2 mm) or ±0.002 in/in. Drilled and reamed features are far tighter.
- Masked Stereolithography (MSLA / DLP)About ±0.004–0.008 in (±0.1–0.2 mm) on general geometry; ±0.002 in (±0.05 mm) is achievable on small parts with fine-pitch panels and a compensated first article.
- Material Jetting (PolyJet)About ±0.004 in (±0.1 mm) on parts up to 4 in (100 mm), and roughly ±0.008 in (±0.2 mm) or ±0.1% of nominal on larger geometry.
- Multi Jet Fusion (MJF)±0.008 in (±0.2 mm) or ±0.3% of nominal, whichever is greater. Tighter features are machined or reamed after the build.
- Rapid PrototypingProcess-dependent: ±0.004 in (±0.1 mm) for SLA, MSLA, PolyJet, and metal powder bed fusion; ±0.008–0.012 in (±0.2–0.3 mm) for MJF and SLS; ±0.020 in (±0.5 mm) for desktop FDM. Machined features are tighter than any of these.
- Selective Laser Melting (SLM)About ±0.004 in (±0.1 mm) up to 1 in (25 mm), then roughly ±0.2% of nominal. Machined features hold normal machining tolerances.
- Selective Laser Sintering (SLS)±0.012 in (±0.3 mm) up to about 4 in (100 mm), then ±0.3% of nominal. Critical bores are normally reamed after the build.
- Stereolithography (SLA)±0.006 in (±0.15 mm) over the first inch, then about ±0.001 in/in (±0.1% of nominal); ±0.004 in (±0.1 mm) on small, well-supported features. Vendors quote between ±0.1% and ±0.2% of dimension.
Plastics and Rubber12
- Blow Molding±0.020 in (±0.5 mm), roughly ±1%, on blown body dimensions; injection-molded neck finishes hold about ±0.005 in (±0.13 mm). Wall thickness is not directly controllable and commonly varies 30% or more across a part.
- Compression MoldingAbout ±0.005 in (±0.13 mm) on features contained within one mold half; ±0.010 in (±0.25 mm) or more on dimensions spanning the parting line, since flash thickness varies with charge weight. Rubber tolerance classes follow ISO 3302-1.
- Dip MoldingInside diameter follows the former closely, about ±0.005 in (±0.13 mm); wall thickness is much looser at roughly ±0.010–0.030 in (±0.25–0.75 mm) and varies along the dip axis.
- Injection Molding±0.005 in (±0.127 mm) commercial on features under 1 in; ±0.002 in (±0.05 mm) precision; ±0.1–0.2% of dimension on larger parts. Add tolerance for anything spanning the parting line or a side action.
- Insert MoldingMolded features hold normal injection molding tolerances, about ±0.005 in (±0.127 mm). Insert position relative to molded features is looser and depends on how positively the insert is located — budget the insert's own tolerance plus the locating clearance.
- Liquid Silicone Rubber (LSR) MoldingAbout ±0.002–0.004 in (±0.05–0.10 mm) on small precision features; ISO 3302-1 class M1 is achievable on tightly controlled dimensions. Larger dimensions scale with the 2–3.5% shrinkage allowance.
- OvermoldingSubstrate features hold normal injection molding tolerances, about ±0.005 in (±0.127 mm). Dimensions taken over the elastomer are looser and compressible; in insert-transfer overmolding, add the substrate loading clearance to the position tolerance of the second shot.
- Plastic Extrusion±0.005 in (±0.13 mm) on small dimensions held against a calibrator; ±0.020–0.060 in (±0.5–1.5 mm) on free-extruded surfaces of large profiles; angles ±1–2°. Bow and twist are specified separately per unit length.
- Reaction Injection MoldingAbout ±0.020 in (±0.5 mm) on features under 12 in; on large panels expect roughly ±0.1–0.2% of the dimension. Thermal expansion of polyurethane is high, so specify the inspection temperature.
- Rotation MoldingAbout ±1–2% of the dimension on mold-formed features; wall thickness commonly varies ±10–20% around nominal. Polyethylene shrinkage of 3.0–3.5% must be built into the tool.
- Thermoforming±0.030 in (±0.75 mm) on vacuum-formed tool-side features; ±0.015 in (±0.4 mm) pressure formed and on CNC-trimmed edges. Non-tool-side dimensions carry all sheet thickness variation.
- Vacuum Casting (Urethane Casting)±0.3% of the nominal dimension, with a minimum of about ±0.010 in (±0.25 mm). Accuracy depends on the master pattern and drifts slightly as the silicone mold ages.
Glass and Ceramics6
- Ceramic Injection Molding (CIM)±0.3–0.5% of dimension as fired (about ±0.006–0.010 in on a 2 in feature); diamond-ground features hold ±0.0002 in (±0.005 mm) or better.
- Ceramic Slip CastingRoughly ±1–2% of dimension on the fired part, dominated by variation in drying and firing shrinkage rather than by the mold.
- Clay Throwing
- Glassblowing
- Lampworking
- Press Molding CeramicsRoughly ±0.5–1% of dimension for dry-pressed parts and ±1–2% for plastic-formed jiggered and ram-pressed ware. Ceramic tile dimensional classes are defined in ISO 13006 and ANSI A137.1.
Composites5
- 3D Thermal LaminatingSet by the machined substrate; the laminate itself adds roughly 0.008–0.024 in (0.2–0.6 mm) per laminated face depending on foil or veneer thickness.
- Composite Laminating±0.010 in (±0.25 mm) on tool-side surfaces. Laminate thickness varies ±10–20% on open (bag-side) surfaces; matched tooling or RTM is required to control both faces.
- DMC and SMC MoldingAbout ±0.1–0.3% of dimension, roughly ±0.005 in/in, thanks to the near-zero mold shrinkage of low-profile compounds. Tighter than most thermoplastic molding, and dimensionally stable with temperature.
- Filament WindingInside diameter ±0.005–0.010 in (±0.13–0.25 mm), set by the mandrel. Wall thickness and outside diameter carry roughly ±0.5–1% because thickness builds in whole layers.
- PultrusionGoverned by ASTM D3917 for glass-reinforced pultruded shapes (EN 13706 in Europe). Wall thickness is held closest; overall width, straightness, and twist carry progressively looser bands. Do not assume machining-class tolerances on any pultruded dimension.
Wood3
- Paper Pulp Molding±0.020–0.060 in (±0.5–1.5 mm) for thick-wall and transfer molded parts; ±0.010–0.020 in (±0.25–0.5 mm) for thermoformed precision pulp.
- Steam Bending
- Wood LaminatingSpringback is typically 1–3% of the bend curvature with a rigid adhesive, against 5–10% for a steamed bend. Forms are made slightly overbent and calibrated on the first assembly.
About forming
Forming processes shape material without removing it. Molten, softened or solid stock is pushed into the geometry of a mold, a die or a tool, and the part emerges at or near net shape.
This is where tooling cost and part cost diverge most sharply: a forming process usually demands an expensive tool up front and then produces parts for pennies, which is why volume is the first question to ask of any forming route.