---
title: "Rapid prototyping and additive manufacturing"
subject: "Computer Aided Design"
chapter: 6
key: "semester_4/computer_aided_design:rapid-prototyping-additive-manufacturing"
source: https://www.bctengineer.com/q/semester_4/computer_aided_design/rapid-prototyping-additive-manufacturing
site: BCT Engineering
---

# Rapid prototyping and additive manufacturing

Computer Aided Design · Chapter 6: CAM and Recent Technology

- Asked in: year not given, 5 marks
- Video: [Rapid Prototyping Additive Manufacturing | ENGINEERING STUDY MATERIALS](https://www.youtube.com/watch?v=FSOV9nPG6To) — Engineering Study Materials
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/computer_aided_design/rapid-prototyping-additive-manufacturing
- Whole chapter: https://www.bctengineer.com/md/semester_4/computer_aided_design/chapter-6

## Question

Explain rapid prototyping (additive manufacturing). Describe its general process chain from CAD model to part and briefly describe any two processes. State its advantages and limitations.

## Short answer

The process chain involves CAD modeling, STL conversion, slicing, layer-wise building, and post-processing. Common methods: FDM deposits melted thermoplastic; SLA cures photopolymer resin with a laser. Advantages: complex geometries without tooling, fast prototypes, low material waste. Limitations: stair-step finish, anisotropic strength, slow for high volumes.

## Answer

**Rapid prototyping (RP)**, now called **additive manufacturing (AM)** or 3D printing, builds a part directly from the CAD model by adding material layer by layer, instead of removing it (machining) or forming it.

#### Process chain
```text
 CAD solid -> STL file -> slicing into layers
      -> build (layer by layer) -> post-processing -> part
```
1. Create the 3D solid model in CAD.
2. Convert it to **STL** (triangulated surface).
3. Choose the orientation and add supports; **slice** into thin layers (0.05 to 0.3 mm), generating the machine code.
4. Build the layers on the machine.
5. Post-processing: remove supports, clean, cure, sand, infiltrate or heat treat.

#### Two common processes
- **Fused deposition modelling (FDM):** a thermoplastic filament (PLA, ABS) is melted in a heated nozzle and deposited along the layer path; the layer solidifies and the platform moves down. Low cost, good for prototypes.
- **Stereolithography (SLA):** a UV laser traces the cross-section on a bath of photopolymer resin, curing it layer by layer; high accuracy and surface finish.

(Others: selective laser sintering (SLS) of powder, laminated object manufacturing (LOM), and binder jetting.)

#### Advantages
- Very complex shapes (internal channels, lattices) with no tooling.
- Fast models for design review and fit checks; lower cost for one-offs.
- Direct link from CAD, with little human work; low waste.

#### Limitations
- Stair-step surface finish; STL approximation errors.
- Limited materials and strength; anisotropic properties.
- Slow and costly for large production runs; size limits.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How does rapid prototyping (additive manufacturing) build a part?
   A. By removing material from a block
   B. By adding material layer by layer directly from the CAD model
   C. By casting in a mould
   D. By forging
   Answer: B. AM adds material in layers, unlike machining or forming. (Key point: RP principle)

2. Which is the correct process chain?
   A. STL, CAD, build, slice
   B. CAD solid, STL conversion, orientation/supports and slicing, layer build, post-processing
   C. Build, CAD, STL, slice
   D. Slice, build, CAD, post-processing
   Answer: B. The solid is converted to STL, sliced into 0.05 to 0.3 mm layers, built, then post-processed. (Key point: Process chain)

3. How do FDM and SLA differ?
   A. FDM melts thermoplastic filament through a nozzle; SLA cures photopolymer resin with a UV laser
   B. FDM uses UV laser on resin; SLA melts filament
   C. Both sinter powder
   D. Both cut sheets of paper
   Answer: A. FDM is low cost; SLA gives high accuracy and surface finish. (Key point: FDM vs SLA)

## Related in Computer Aided Design

- [CAD software modules: part, assembly, drafting](https://www.bctengineer.com/question.md?key=semester_4%2Fcomputer_aided_design%3Acad-software-modules) — Computer Aided Design, chapter 1
- [Define CAD, CAM and CAE](https://www.bctengineer.com/question.md?key=semester_4%2Fcomputer_aided_design%3Acad-cam-cae-definitions) — Computer Aided Design, chapter 1

## Related in other subjects

- [Classification of manufacturing processes; evolution](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Aclassify-manufacturing-processes-evolution) — Manufacturing and Production Processes, chapter 1
- [Prototyping model of software](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aprototype-model) — Instrumentation II, chapter 9, asked 3×
- [Test: mean weights of two processes](https://www.bctengineer.com/question.md?key=semester_5%2Fprobability_and_statistics%3Abulbs-factory-two-processes-weights) — Probability and Statistics, chapter 6
- [Manufacturing process of bricks](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Amanufacturing-process-of-bricks) — Civil Engineering Materials, chapter 3, asked 4×