By the end of this topic, you should be able to...
respond to emerging technologies and describe the advantages and disadvantages of why designers use rapid prototyping techniques, such as: stereolithography (SLA), fused deposition modelling (FDM) and selective laser sintering (SLS).
Guiding Question
How do designers understand the relationship between users, the product and the environment?
Did you know?
Before rapid prototyping existed, making one physical prototype of a plastic component took a skilled model maker several days and cost hundreds of pounds. In 1984, Chuck Hull invented stereolithography — a process that could build a plastic part overnight, directly from a computer file, with no mode lmaker required. That single invention changed how designers test ideas.
Why This Topic Matters
Rapid prototyping has fundamentally changed the speed and cost of design development. By converting CAD data directly into physical objects — no tooling, no moulds, no specialist machinists — designers can iterate faster, test earlier, and fail cheaply.
Rapid prototyping is a group of manufacturing techniques used to manufacture a physical object quickly for testing aspects of a product. All three techniques share a common workflow — a CAD model is sliced into layers by software, and the physical object is built layer by layer from that digital data.
Rapid Prototyping Technologies
Fused Deposition Modelling (FDM)
FDM is a 3D rapid prototyping printing methodology that deposits melted layers of material on a bed to build up a 3D model.
An FDM machine works by feeding a continuous filament of thermoplastic material — most commonly PLA (polylactic acid), ABS (acrylonitrile butadiene styrene), or PETG — into a heated extruder nozzle that melts the material and deposits it in a precise pattern on a build platform. The nozzle traces the cross-sectional geometry of the part layer by layer, building the three-dimensional form from the bottom upward. Each deposited layer fuses to the layer below as it cools and solidifies.
Characteristics of FDM:
Low cost — FDM machines range from desktop consumer printers costing a few hundred pounds to industrial systems
Wide material range — engineering thermoplastics, flexible materials, composites
Visible layer lines — surface finish is rougher than SLA or SLS without post-processing
Best suited to low-fidelity and functional prototypes where surface finish is less critical
Anisotropic mechanical properties — strength varies with print orientation
Excellent for structural testing of geometry and mechanism testing
Design Technology application: FDM is the most widely accessible rapid prototyping technology in school and university design environments. It enables design students to translate CAD solid models directly into physical test objects for ergonomic evaluation, assembly testing, and mechanism prototyping.
Advantages | Disadvantages |
Lowest cost of all three techniques | Visible layer lines — poor surface finish without post-processing |
Wide range of thermoplastic materials available | Weakest in the Z-axis — parts can delaminate under load |
Widely accessible — desktop machines available to schools and individuals | Lower resolution than SLA or SLS |
Good for early low-fidelity prototypes | Overhanging geometry requires support structures that must be removed |
Best used for: Early-stage concept models, low-fidelity prototypes, functional testing of basic mechanisms.
Stereolithography (SLA)
SLA is an additive manufacturing technique that creates 3D physical prototypes layer by layer by hardening molecules of a photosensitive liquid polymer using a laser beam.
An SLA machine builds parts in a tank of liquid photopolymer resin. A UV laser traces the cross-section of each layer on the surface of the resin, curing (hardening) the polymer where it strikes. The build platform descends incrementally after each layer, exposing a fresh layer of liquid resin to the laser. The process is continued layer by layer until the full part is built.
Characteristics of SLA:
Very high surface finish and dimensional accuracy — layer resolution typically 25–100 microns
Capable of very fine geometric detail
Best suited to aesthetic prototypes and high-fidelity prototypes where surface quality is critical
More expensive than FDM
Post-processing required — parts must be washed and UV-post-cured after printing
Limited material range compared to FDM — primarily engineering resins, some flexible and rigid options
Design Technology application: SLA is widely used in the consumer products industry for producing appearance models for client presentations, design reviews, and marketing photography. A well-finished SLA model, painted and surface-treated by a skilled model maker, is visually indistinguishable from a production component.
Advantages | Disadvantages |
No support structures required — powder bed supports the part | Most expensive of the three techniques |
Produces strong, durable parts with good mechanical properties | Rough, granular surface finish — post-processing often required |
Can produce highly complex geometries in a single build | Slow cooling time — long total build cycle |
Suitable for functional prototypes and performance testing | Machines are large and specialist — not widely accessible |
Best used for: Functional prototypes, complex assemblies, performance testing, parts requiring real mechanical strength.
Selective Laser Sintering (SLS)
SLS is an additive manufacturing technique that uses a laser to fuse small particles of material into a mass that has a desired 3D rapid prototyping shape.
An SLS machine builds parts by spreading a thin layer of powdered material — typically nylon (PA12), glass-filled nylon, or metal powders for DMLS (Direct Metal Laser Sintering) — across a build platform. A high-power laser then scans the cross-section of the part, fusing the powder particles together by sintering (partial melting and bonding). The platform lowers by one layer thickness, fresh powder is spread, and the process repeats.
Characteristics of SLS:
No support structures required — unfused powder supports the part during building
Good mechanical properties — sintered nylon parts approach injection-moulded nylon in strength
Capable of complex internal geometries — undercuts, channels, interlocking components — that would require support structures with FDM or SLA
Surface finish rougher than SLA but smoother than FDM
Higher cost than FDM; requires industrial equipment
Excellent for functional prototypes of complex assemblies and end-use parts
Design Technology application: SLS is extensively used in aerospace, automotive, and medical device prototyping for producing fully functional structural components. It is also used for small-batch production of complex end-use parts where injection moulding tooling is not cost-effective.
Advantages | Disadvantages |
|---|---|
Highest surface resolution of all three techniques | Photopolymer resin is brittle — poor impact resistance |
Smooth surface finish — ideal for aesthetic prototypes | Degrades under UV light — not suitable for outdoor performance testing |
Fine detail capture — suitable for complex geometries | Requires post-processing — washing and UV curing |
Direct from CAD data — no tooling required | More expensive per part than FDM |
Best used for: Aesthetic prototypes, presentation models, fine-detail components.
Comparative Summary
Technique | Surface Quality | Strength | Cost | Best Application |
|---|---|---|---|---|
SLA | ⭐⭐⭐ High | ⭐ Low | $$ | Aesthetic prototypes |
FDM | ⭐ Low | ⭐⭐ Medium | $ | Low-fidelity prototypes |
SLS | ⭐⭐ Medium | ⭐⭐⭐ High | $$$ | Functional prototypes |
Why Designers Use Rapid Prototyping
Advantages
Speed — physical objects produced in hours, not weeks
No tooling — eliminates expensive moulds and jigs for prototype quantities
Direct from CAD — design data flows directly to manufacture with no translation errors
Design iteration — multiple design variants can be tested simultaneously at low cost
Complexity is free — geometries impossible with conventional machining are achievable (Gibson et al., 2015)
Disadvantages
Material limitations — prototype materials rarely match the mechanical properties of final production materials
Surface finish — all three techniques produce layer artefacts requiring post-processing
Scale limitations — build volumes restrict maximum part size
Not suitable for mass production — unit cost does not reduce with volume (Redwood et al., 2017)
CASE STUDY
McLaren Formula 1 — Rapid Prototyping at Race Speed
McLaren Racing has publicly documented its use of rapid prototyping across all three techniques as part of its aerodynamic development process (McLaren, 2022).
Formula 1 teams operate on a development cycle where aerodynamic components must be designed, tested, and fitted to the car within days.
FDM is used to produce early low-fidelity prototypes of bracket geometries and duct routing concepts — cheap, fast, and sufficient to check spatial fit within the car's chassis before any precision work is committed.
SLA produces high-resolution wind tunnel models of aerodynamic surfaces — bodywork, front wing endplates, diffuser elements — where surface accuracy directly affects the quality of aerodynamic data collected. The smooth surface finish of SLA is essential; FDM layer lines would introduce aerodynamic noise into test results.
SLS produces functional prototypes of structural brackets and load-bearing components in nylon composites — parts that must survive real mechanical loads during wind tunnel testing and initial track validation.
In this environment, choosing the wrong rapid prototyping technique produces bad data. Choosing the right one means the difference between a competitive upgrade and a wasted development token.
Key Vocabulary
Term | Definition |
|---|---|
Rapid prototyping | A group of manufacturing techniques used to manufacture a physical object quickly for testing aspects of a product; typically, 3D CAD models are used |
Stereolithography (SLA) | An additive manufacturing technique that creates 3D physical prototypes layer by layer by hardening molecules of a photosensitive liquid polymer using a laser beam |
Fused deposition modelling (FDM) | A 3D rapid prototyping printing methodology that deposits melted layers of material on a bed to build up a 3D model |
Selective laser sintering (SLS) | An additive manufacturing technique that uses a laser to fuse small particles of material into a mass that has a desired 3D rapid prototyping shape |
Physical prototype | The creation of a full-size, smaller or larger tangible version of an object that can be physically interacted with |
Functional prototype | Also referred to as a "physical working prototype"; works in the same way as a final product and simulates real-world functionality |
Aesthetic prototype | A physical model developed to look and feel like the final product but that does not function |
Low-fidelity prototype | A simplified physical or virtual prototype typically created to test a few aspects of a design idea in the early stages of a design process |
High-fidelity prototype | A physical or virtual model that is highly functional and interactive, aesthetically similar to the final product, and typically full scale |
Computer-aided design (CAD) | The use of computer software to aid the design process |
Prototyping techniques | The methods used to create prototypes at different levels of fidelity, from sketching through to functional prototypes |
Practice Questions
Question 1. Describe two advantages and two disadvantages of using SLS compared to FDM for producing a functional prototype. [4]
Question 2. A designer is developing a new pair of wireless earbuds. Describe how SLA and FDM could each be used at different stages of the design development process. [6]
Question 3. Explain why rapid prototyping techniques have become an emerging technology in product design, with reference to CAD and the design development process. [4]
Sources
"Design Technology Teacher Support Material." International Baccalaureate Organization, 2024. Topic-specific glossary of terms, A2.2 Prototyping techniques, pp. 70–71.
EOS GmbH. "SLS 3D Printing Technology." EOS, 2022, www.eos.info/en/additive-manufacturing/3d-printing-plastic/sls-technology.
Formlabs. "SLA 3D Printing Technology." Formlabs, 2023, formlabs.com/blog/ultimate-guide-to-stereolithography-sla-3d-printing.
Gibson, Ian, David Rosen, and Brent Stucker. Additive Manufacturing Technologies: 3D Printing, Rapid Prototyping, and Direct Digital Manufacturing. 2nd ed., Springer, 2015.
McLaren Racing. "How McLaren Uses 3D Printing." McLaren, 2022, www.mclaren.com/racing/formula-1/3d-printing.
Nike News. "Nike Flyprint: The First 3D-Printed Performance Upper." Nike, 2018, news.nike.com/news/nike-flyprint.
Redwood, Ben, Filemon Schöffer, and Brian Garret. The 3D Printing Handbook. 3D Hubs, 2017.
Stratasys. "FDM Technology." Stratasys, 2023, www.stratasys.com/en/guide-to-3d-printing/technologies-and-materials/fdm-technology.
Wohlers Associates. Wohlers Report 2023: 3D Printing and Additive Manufacturing Global State of the Industry. Wohlers Associates, 2023.
Hubs. "3D Printing Technologies Compared: FDM vs SLA vs SLS." Hubs, 2023, www.hubs.com/knowledge-base/fdm-vs-sla-vs-sls-3d-printing-technologies-compared.
Linking Questions
What ergonomic aspects should be considered when selecting prototyping techniques? (A1.1)
How are concept models used to generate user feedback in a user-centred design (UCD) approach? (B1.1)
Why are different prototyping techniques used as part of the design process? (B2.1)
How does a good understanding of prototyping techniques help designers approach modelling and prototyping of their potential design solutions? (B2.2)
How can prototyping techniques be used to evaluate the appropriateness of material selection? (B3.1)
To what extent can virtual prototypes and simulations model real-world situations involving structural, mechanical and electronic systems? (B3.2, B3.3, B3.4)