Rapid Prototyping Industry Glossary: Key Manufacturing Terms Explained

Rapid prototyping is a set of manufacturing techniques used to quickly produce physical models and functional parts for design validation, fit checks, and early performance testing. It spans additive manufacturing (AM) processes like FDM, SLA, SLS, and MJF; subtractive approaches such as CNC rapid prototyping; and bridge methods like vacuum casting for low-volume production. This glossary provides clear, standards-aligned definitions, why each term matters to engineering outcomes, and typical application contexts—using SI units with inch equivalents and presenting values as typical references, not guarantees.

Rapid Prototyping Overview

Rapid prototyping accelerates the product development cycle by compressing the iteration loop between CAD and physical parts. It enables early detection of design issues, material suitability checks, and manufacturability reviews before committing to production tooling.

Relationship with CNC prototyping: Subtractive machining of metals and plastics delivers tight tolerances and isotropic properties, making CNC a go-to for precision prototypes and mating components.
Relationship with additive manufacturing: AM offers speed, design freedom, complex internal geometries, and consolidated assemblies. Properties, accuracy, and surface finish vary by process and material.
Relationship with low-volume production: Techniques like vacuum casting and rapid tooling bridge prototypes to short-run production when injection molding is not yet economical.

For readers exploring capabilities and process selection, see the rapid prototyping capability overview for a structured summary of methods and materials: rapid prototyping capability overview.

Rapid Prototyping Process Terminology

Each process entry includes a definition, why it matters, and typical application context, along with indicative ranges for layer thickness, tolerances, and surface finishes. Values are typical engineering references (not contractual specifications).

FDM (Fused Deposition Modeling)

Definition: An extrusion-based AM process that deposits thermoplastic filament layer by layer to build parts.

Why it matters: Thermal bonding and visible layer lines produce anisotropy (weaker Z-direction) and stair-stepping on angled surfaces. It’s widely accessible and cost-effective for fixtures and conceptual models.

Typical ranges:

Layer height: 0.1–0.3 mm (≈0.004–0.012 in)
Typical tolerance: ±0.3 mm or ±0.5% (whichever is greater)
Surface roughness: Ra ~6.3–12.5 µm (≈250–500 µin)

Application context: Jigs and fixtures, simple housings, snap-fit tests with generous tolerances, and iterative design models.

Reference: Practical ranges aligned with industry guidance; for process principles and equipment capabilities.

SLA (Stereolithography)

Definition: A vat photopolymerization process that cures liquid resin with a laser or projector to form solid parts.

Why it matters: SLA yields high detail and smooth surfaces with near-isotropic properties; support placement affects cosmetic areas more than bulk strength.

Typical ranges:

Layer thickness: 0.05–0.15 mm (≈0.002–0.006 in)
Typical tolerance: ±0.1 mm or ±0.2% (whichever is greater)
Surface roughness: Ra ~1.6–3.2 µm (≈63–126 µin)

Application context: Appearance models, small complex features, casting masters, and components requiring fine detail or smooth finishes.

Reference: Typical design specifications and tolerance behavior are documented by OEMs.

SLS (Selective Laser Sintering)

Definition: A powder bed fusion process that uses a laser to sinter polymer powder (commonly PA12) layer by layer.

Why it matters: SLS parts are close to isotropic, require no support structures, and have a characteristic grainy surface that can be improved via post-processing.

Typical ranges:

Layer thickness: ~0.10–0.15 mm (≈0.004–0.006 in)
Typical tolerance: ±0.2–0.3 mm (≈±0.008–0.012 in)
Surface finish: As-printed grainy texture; Ra often in the 6.3–10 µm range (≈250–400 µin), improvable by bead blasting or vapor smoothing

Application context: Functional nylon parts, enclosures, living hinges (material-dependent), integrated assemblies, and parts needing moderate accuracy without supports.

MJF (Multi Jet Fusion)

Definition: A powder bed fusion process where inkjet-deposited fusing and detailing agents are activated by infrared energy to solidify polymer powder.

Why it matters: MJF delivers consistent dimensional accuracy, fine features, and near-isotropic properties, often at competitive build speeds.

Typical ranges:

Layer thickness: ~0.08–0.12 mm (≈0.003–0.005 in)
Typical tolerance: ±0.2–0.3 mm (≈±0.008–0.012 in), scaling to ±0.2% for larger dimensions
Surface finish: Matte; improvable via blasting or chemical smoothing

Application context: Functional PA12 parts, housings, clips, brackets, and production-intent prototypes where repeatability is important.

Reference: Dimensional capability details are published by HP.

CNC Rapid Prototyping

Definition: Subtractive machining (milling, turning, EDM) of metals and plastics to produce prototypes with high accuracy and surface finish control.

Why it matters: CNC parts exhibit isotropic properties of wrought stock and support tight tolerances and fine finishes. It’s ideal for precision mating components and performance-critical prototypes.

Typical ranges:

General tolerance reference: ISO 2768-m when drawings do not specify (classes f/m/c per feature size)
Typical prototype tolerance: Around ±0.13 mm (≈±0.005 in) for many features, depending on geometry and setup
Surface roughness: Standard machining ~Ra 3.2 µm (≈126 µin); fine machining ~Ra 1.6 µm (≈63 µin)

Application context: Precision housings, shafts, brackets, and assemblies requiring accurate interfaces, material properties, and repeatable performance.

Contextual navigation: For process selection and capabilities, review CNC machining capabilities.

Vacuum Casting

Definition: Urethane casting in silicone molds under vacuum, typically using an SLA master to create the mold cavity.

Why it matters: Provides injection-mold–like aesthetics and mechanical behavior for short runs without hard tooling. Excellent for appearance models and low-volume functional housings.

Typical ranges:

Typical accuracy: ±0.25 mm (≈±0.010 in) or ±0.3% (varies by resin and part size)
Shrinkage consideration: Commonly ~0.15–0.30% depending on urethane formulation and mold conditions
Surface finish: Replicates master; smooth when using polished SLA masters; paint and texture compatible

Application context: Pilot runs of enclosures, elastomeric parts, color/finish trials, and design validation before investing in injection tooling.

Reference: Workflow and typical capabilities are well documented by OEMs and service guides.

Material Terminology in Rapid Prototyping

Materials determine mechanical performance, accuracy, and surface quality. The following are commonly used in prototype manufacturing.

Prototype Plastics

ABS: An engineering thermoplastic with good toughness and dimensional stability. Frequently used for functional prototypes, housings, and master patterns for molding.
Nylon (PA12): Offers balanced stiffness and chemical resistance. Powder-bed fusion (SLS/MJF) produces accurate, durable parts suitable for enclosures, clips, and brackets.
PC (Polycarbonate): High impact resistance and elevated heat deflection compared to ABS. Selected for functional components that must resist deformation under load and temperature.
PEEK: A high-performance thermoplastic suitable for demanding environments (aerospace, medical). Often machined for prototypes requiring high temperature resistance and strength-to-weight.

Prototype Metals

Aluminum: Widely used in CNC prototyping due to machinability and favorable strength-to-weight ratio. Supports anodizing and varied finishes; suited to structural components and heat sinks.
Stainless steel: Selected for corrosion resistance and strength. Commonly used for shafts, fasteners, and enclosures where durability and hygiene matter; polishing and passivation are typical post-processes.

Accuracy, Tolerance, and Surface Finish Terms

Dimensional tolerance: Allowable variation from nominal size on drawings. When unspecified, industry often references ISO 2768 classes; for prototypes, many features fall around ±0.13 mm (±0.005 in) depending on geometry and process.
Layer thickness: Vertical resolution of AM builds. Typical references: FDM 0.1–0.3 mm; SLA 0.05–0.15 mm; SLS ~0.10–0.15 mm; MJF ~0.08–0.12 mm. Layer selection affects surface smoothness and build time.
Surface roughness (Ra): Arithmetic mean height of the roughness profile, indicated and measured per ISO 4287/ISO 21920. Representative ranges: SLA ~Ra 1.6–3.2 µm; FDM ~Ra 6.3–12.5 µm; SLS/MJF matte/grainy improvable; CNC standard ~Ra 3.2 µm, fine ~Ra 1.6 µm.
Isotropic vs anisotropic strength: Isotropic materials exhibit uniform properties in all directions; anisotropic parts vary with build orientation. FDM often shows weaker Z-direction bonding; SLA and powder-bed polymers (MJF/SLS) are closer to isotropic.

Design for Rapid Prototyping (DFM Terminology)

Design for Manufacturability (DFM): Engineering practices that adapt designs to process constraints, enabling reliable, cost-effective production. Examples include appropriate tolerances, draft angles for molded parts, and minimizing support scarring on cosmetic surfaces.
Wall thickness: Minimums depend on process and material. Typical references: SLA often ≥0.6–1.0 mm; FDM minimums scale with nozzle/layer height (e.g., ≥4× layer height for stable walls); powder-bed polymers sustain thin features but benefit from ≥1.0 mm for robustness.
Draft angle: Applied to casted or molded parts to aid demolding—commonly 1–3° for plastics, increasing for textured surfaces.
Support structures: Required for overhangs in FDM/SLA; avoided on cosmetic faces when possible. SLS/MJF do not require supports due to surrounding powder.

Cost, Lead Time, and Production Terms

Prototype vs production parts: Prototypes validate form/fit/function and manufacturability; production parts meet full quality and compliance requirements, often with tighter tolerances, validated material certifications, and process controls.
Low-volume manufacturing: Short-run production using CNC, vacuum casting, rapid tooling, or robust AM (MJF/SLS). Appropriate when demand is limited or when bridging to full-scale molding.
Tooling cost: Capital associated with hard tooling for injection molding or forming. Rapid tooling reduces lead time and cost for early runs but still requires DFM considerations and draft.
Lead time considerations: Influenced by setup complexity, part geometry, material availability, and finishing. AM is often fastest for complex shapes; CNC offers accuracy for critical interfaces; vacuum casting is efficient for small batches with cosmetic requirements.

Post-Processing Terms

Bead blasting: Abrasive blasting that produces a uniform matte finish and hides print/tool marks; may slightly increase Ra while improving visual consistency.
Polishing: Mechanical or chemical refinement to reduce Ra and enhance aesthetics or hygiene; metals and some resins can be polished to smoother finishes.
Vapor smoothing: Chemical smoothing (e.g., for PA12) that reduces surface roughness substantially and improves liquid resistance; note potential dimensional changes and property implications.

Industry Application Context

Automotive product development: MJF/SLS for ducts and brackets; CNC aluminum for precision mating parts; vacuum casting for appearance panels and trim trials.
Medical device prototyping: SLA for detailed housings and surgical models; MJF/SLS for robust functional components; CNC stainless/aluminum for mechanical prototypes under regulatory scrutiny.
Aerospace R&D: CNC metals for strength-critical parts; high-performance polymers (PEEK/PAEK) for thermal/chemical resistance; powder-bed polymers for lightweight assemblies.
Consumer electronics: SLA for cosmetic prototypes; MJF/SLS for enclosures and snaps; CNC aluminum for structural frames; vacuum casting for low-volume housing runs.

Quick-Reference Table

Process	Layer Thickness (mm)	Typical Tolerance	Typical Surface Finish (Ra)
FDM	0.10–0.30	±0.3 mm or ±0.5%	6.3–12.5 µm
SLA	0.05–0.15	±0.1 mm or ±0.2%	1.6–3.2 µm
SLS	0.10–0.15	±0.2–0.3 mm	6.3–10 µm
MJF	0.08–0.12	±0.2–0.3 mm	Matte, improvable
CNC (reference)	N/A	ISO 2768-m; ~±0.13 mm	3.2 µm (std), 1.6 µm (fine)

Values are indicative references, not guarantees. Use SI units; inch equivalents: 0.05 mm ≈ 0.002 in; 0.10 mm ≈ 0.004 in; 1.6 µm ≈ 63 µin; 3.2 µm ≈ 126 µin.

Conclusion and Call to Action

A clear understanding of rapid prototyping terminology helps teams choose the right process, set realistic tolerances, and plan finishes that match functional and cosmetic needs. If you’re evaluating feasibility or preparing a quote, submit CAD files for a manufacturability review and process/material recommendation through the appropriate internal enquiry channel—start with the rapid prototyping capability overview and, for precision machined parts, see CNC machining capabilities.