Lesson 28 · Unit 4

Rapid Prototyping &
CAD Overview

Turn CAD geometry into fast physical feedback using additive processes—and understand the trade-offs among common techniques.

80 minutesA2.2.6 + B2.2.5SLA · FDM · SLS

Guiding question: Why do designers rapid-prototype, and how do different processes change what can be tested?01

Today’s destination

By the end of class, you should be able to…

Explain rapid prototyping

Describe why fast physical prototypes accelerate design development.

Compare SLA/FDM/SLS

Describe advantages and disadvantages of three common rapid-prototyping techniques.

Connect CAD to manufacture

Explain why CAD geometry must be suitable for the chosen process.

Choose a process

Select a technique based on form, fidelity, material/process limits and testing needs.

Success check: explain the concept accurately, then use it to make a justified design decision.

Know it → use it → explain the evidence.02

A2.2.6

CAD → physical prototype → feedback → revised CAD.

CAD

Create / revise geometry

→

Rapid prototype

Build a physical version quickly

→

Feedback

Users + team test and refine

Emerging technologies: rapid-prototyping processes continue to evolve. Designers should respond by evaluating new processes against the evidence they need—speed, detail, material behaviour, cost, safety and test validity—rather than assuming newer is automatically better.

Speed matters because it increases the number of useful iterations.03

Fused deposition modelling

FDM builds parts by depositing molten filament layer by layer.

Material extrusion

Common desktop route to fast, affordable prototypes.

Advantages: accessible, low relative cost, many thermoplastic filaments, good for iterative form/fit models.

Disadvantages: visible layers, support/overhang issues, anisotropic strength and lower surface fidelity than some alternatives.

FDM is often ideal when speed and accessibility matter more than surface perfection.04

Stereolithography

SLA cures liquid photopolymer resin with light.

Photopolymerization

Thin cured layers can produce fine detail and smooth surfaces.

Advantages: high detail, smooth surface, useful for small features and presentation-quality prototypes.

Disadvantages: resin handling/post-processing, supports, material behaviour may not match final production material, higher consumable complexity.

Choose SLA when detail and surface fidelity are important.05

Selective laser sintering

SLS fuses powder selectively to create each layer.

POWDER

Powder-bed process

Unfused powder can support complex geometry during the build.

Advantages: complex geometry, nested parts, often no separate support structures, useful functional polymer prototypes.

Disadvantages: higher equipment/process cost, powder handling, rougher/grainier surfaces and post-processing requirements.

SLS is powerful for complex geometry that would be awkward to support in other processes.06

Process selection

No process is universally “best.”

	FDM	SLA	SLS
Typical strength	Accessible + fast	Fine detail + smooth finish	Complex functional geometry
Support issue	Often needs supports	Often needs supports	Powder self-supports much geometry
Surface	Layer lines visible	Usually smooth	Often grainier
Classroom accessibility	Often highest	Moderate / handling considerations	Usually specialized

Match the process to the evidence you need.07

Apply it

Choose the process

A team needs a small ergonomic control prototype with fine tactile ridges and smooth curved surfaces for user evaluation. Structural load is low.

Which process is the strongest fit from the three?

Choose before you reveal the feedback.08

B2.2.5

A beautiful CAD model can still fail as a rapid prototype.

Thickness

Too thin?

Features may break or fail to form.

Overhang

Needs support?

Orientation affects support and finish.

Tolerance

Parts fit?

Clearance must account for process accuracy.

Geometry

Closed / valid?

Models need suitable solid geometry for reliable slicing/build preparation.

B2.2.5: students must be able to construct and interpret CAD models suitable for rapid prototyping.09

Why speed matters

More cycles can improve the evidence base.

Fit test

Discover interference / reach problem.

User handling

Adjust radius, grip, control location.

Integrated test

Check final geometry against multiple specifications.

Rapid prototyping is valuable because it supports repeated evidence-driven revision.10

15 minutes

Choose FDM, SLA or SLS for each brief.

Brief A

Large quick enclosure

Low cost, next-day form/fit check.

Brief B

Miniature detailed knob

Fine texture and smooth curves for appearance/handling.

Brief C

Complex nested duct

Internal geometry difficult to support conventionally.

Your task: choose the process, then justify with one advantage and one trade-off.

Good answers connect process characteristics to the testing goal.11

Vocabulary lab

Rapid prototyping vocabulary

Retrieve first. Then check.

TermRapid prototypingClick to reveal

MeaningCreating physical prototypes quickly from digital models so teams/users can interact, test and provide feedback.

TermStereolithography (SLA)Click to reveal

MeaningAn additive process that cures liquid photopolymer resin layer by layer using light.

TermFused deposition modelling (FDM)Click to reveal

MeaningAn additive process that deposits molten filament layer by layer.

TermSelective laser sintering (SLS)Click to reveal

MeaningAn additive process that fuses powder selectively, layer by layer.

TermSupport structureClick to reveal

MeaningTemporary geometry used to hold overhangs/features during some additive builds.

TermToleranceClick to reveal

MeaningAllowed dimensional variation or clearance needed for reliable fit/function.

TermBuild orientationClick to reveal

MeaningHow a part is positioned during additive manufacture, affecting support, strength, surface and time.

TermSlicingClick to reveal

MeaningPreparing a 3D model as build layers/toolpaths for additive manufacture.

Say the meaning before you flip the card.12

Knowledge check

Can you retrieve it without looking back?

1. Why do designers use rapid prototyping?

To create physical prototypes quickly so users/teams can interact with them and provide feedback that drives development.

2. Name the three techniques explicitly listed in A2.2.6.

SLA, FDM and SLS.

3. Give one advantage of FDM.

Accessibility, speed, lower relative cost or range of common thermoplastic filaments.

4. Give one advantage of SLA.

Fine detail and smooth surface.

5. Give one advantage of SLS.

Complex geometry and reduced need for separate support structures.

6. What does B2.2.5 add beyond knowing the process names?

Students must be able to construct and interpret CAD models suitable for rapid prototyping.

Say the answer first. Then reveal it.13

Exit ticket

Before you leave…

1. Choose one RP process and state its strongest advantage.

2. State one process limitation that could influence a CAD design.

3. Identify one IA feature you might prototype rapidly and what you would test.

Next lesson

IA Day 8 — Generate Full Range of Redesign Ideas

Keep the evidence chain moving: user → research → decision → test.

Curriculum alignment
A2.2.6 SLA/FDM/SLS advantages and disadvantages · B2.2.5 CAD models suitable for rapid prototyping.

Lesson complete14 slides

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IB Design Technology SL · Lesson 2814

Rapid Prototyping &CAD Overview