IB Design Technology Topic B2.2 Modelling and…

CAD: A Model You Can Test Before You Build

Definition

Computer Aided Design (CAD)

CAD (Computer Aided Design) refers to the use of computer software to create, modify, and communicate design ideas with precision.

Types of CAD Models

Surface models
Solid models
Virtual models

Surface Models

Definition

Surface CAD Models

Digital 3D models that represent only the external surfaces of an object, without defining its internal structure or volume.

Characteristics:
1. Lightweight: Surface models require less computational power.
2. Flexible: Ideal for complex curves and organic shapes.
Applications:
1. Automotive and aerospace design: Analysing aerodynamics.
2. Consumer products: Focusing on aesthetic appeal.

Note

Surface models are not suitable for structural analysis or manufacturing as they lack internal volume and material properties.

Solid Models

Definition

Solid CAD Models

Digital 3D models that provide a complete representation of an object, including its external form, internal structure, and material properties.

Characteristics:
1. Comprehensive: Includes volume, mass, and material data.
2. Accurate: Suitable for engineering analysis and manufacturing.
Applications:
1. Mechanical engineering: Designing functional components.
2. Architecture: Creating detailed building models.

Tip

When working with solid models, consider factors like material properties and manufacturing constraints to ensure the design is feasible.

Virtual Models

Definition

Virtual Models

Digital representations of a product that go beyond physical form to include simulations, animations, and interactive elements for testing and visualisation.

Characteristics:
1. Dynamic: Can simulate real-world conditions.
2. Interactive: Allows for user interaction and testing.
Applications:
1. Virtual reality (VR): Immersive design reviews.
2. Augmented reality (AR): Overlaying designs onto real-world environments.

Example

In architecture, virtual models can simulate lighting conditions and structural behavior, providing valuable insights before construction begins.

The Role of CAD in Design Development

Precision: Accurate dimensions and tolerances
Flexibility: Easily edited and adapted
Analysis: Simulate motion, test stresses, explore materials
Communication: Share visuals or technical drawings with stakeholders
Prototyping Ready: Can be exported for 3D printing, CNC machining or laser cutting

Analogy

Think of CAD as a digital workshop where designers can build, test, and refine their ideas without the constraints of physical materials.

Example

In automotive industry:

Surface Models: Used for aerodynamic analysis and aesthetic design.
Solid Models: Essential for engine components and structural parts.
Virtual Models: Simulate crash tests and performance scenarios.

Surface, Solid or Virtual: Which One and Why

The three types are not interchangeable, and choosing the wrong one wastes the work.
A surface model is a hollow skin. It has no thickness and no interior, so it cannot tell you mass, volume or strength. It is for styling complex curves.
A solid model knows it is made of material. That is why it can calculate mass, take a material property, run an FEA and be sent to a 3D printer.
A virtual model adds interaction and environment, letting a user walk through a building or handle a product in VR before it exists.

Common Mistake

A surface model cannot be used for engineering analysis or 3D printing.
It is an infinitely thin shell, so the software does not know what is inside it, and FEA needs to know exactly that.
If a question asks for a model that will be analysed or manufactured, the answer is a solid model.

Example question

A team is designing an electric kettle. They first model the sculpted outer body to explore its styling, then later need to calculate its mass and check that the handle will not snap when the kettle is full.

(a) Identify the type of CAD model appropriate to each of these two stages. (2 marks)

(b) Explain why the model used for the styling stage could not be used to check the handle. (3 marks)

Solution

(a) Award [1] for each correct model type, up to [2 max].

Styling the sculpted body: a surface model, which handles complex flowing curves easily. [1]
Calculating mass and checking the handle: a solid model. [1]

(b) Award [1] for each linked point, up to [3 max].

A surface model defines only the outer skin. It has no thickness and no defined interior. [1]
Mass and stress both depend on how much material there is and where it sits, so the software cannot compute either from a surface. [1]
A solid model can be assigned a material and its density, which is what lets it return a mass and run an FEA on the handle. [1]

Active recall

Name the three types of CAD model on the syllabus.
What is the key difference between a surface model and a solid model?
Why can a solid model calculate mass when a surface model cannot?
What does a virtual model add that neither of the others provides?
Give two advantages of CAD over hand drawing in design development.

CAD: A Model You Can Test Before You Build

Definition

Computer Aided Design (CAD)

CAD (Computer Aided Design) refers to the use of computer software to create, modify, and communicate design ideas with precision.

Types of CAD Models

Surface models
Solid models
Virtual models

Surface Models

Definition

Surface CAD Models

Digital 3D models that represent only the external surfaces of an object, without defining its internal structure or volume.

Characteristics:
1. Lightweight: Surface models require less computational power.
2. Flexible: Ideal for complex curves and organic shapes.
Applications:
1. Automotive and aerospace design: Analysing aerodynamics.
2. Consumer products: Focusing on aesthetic appeal.

Note

Surface models are not suitable for structural analysis or manufacturing as they lack internal volume and material properties.

Solid Models

Definition

Solid CAD Models

Digital 3D models that provide a complete representation of an object, including its external form, internal structure, and material properties.

Characteristics:
1. Comprehensive: Includes volume, mass, and material data.
2. Accurate: Suitable for engineering analysis and manufacturing.
Applications:
1. Mechanical engineering: Designing functional components.
2. Architecture: Creating detailed building models.

Tip

When working with solid models, consider factors like material properties and manufacturing constraints to ensure the design is feasible.

Virtual Models

Definition

Virtual Models

Digital representations of a product that go beyond physical form to include simulations, animations, and interactive elements for testing and visualisation.

Characteristics:
1. Dynamic: Can simulate real-world conditions.
2. Interactive: Allows for user interaction and testing.
Applications:
1. Virtual reality (VR): Immersive design reviews.
2. Augmented reality (AR): Overlaying designs onto real-world environments.

Example

In architecture, virtual models can simulate lighting conditions and structural behavior, providing valuable insights before construction begins.

The Role of CAD in Design Development

Precision: Accurate dimensions and tolerances
Flexibility: Easily edited and adapted
Analysis: Simulate motion, test stresses, explore materials
Communication: Share visuals or technical drawings with stakeholders
Prototyping Ready: Can be exported for 3D printing, CNC machining or laser cutting

Analogy

Think of CAD as a digital workshop where designers can build, test, and refine their ideas without the constraints of physical materials.

Example

In automotive industry:

Surface Models: Used for aerodynamic analysis and aesthetic design.
Solid Models: Essential for engine components and structural parts.
Virtual Models: Simulate crash tests and performance scenarios.

Surface, Solid or Virtual: Which One and Why

The three types are not interchangeable, and choosing the wrong one wastes the work.
A surface model is a hollow skin. It has no thickness and no interior, so it cannot tell you mass, volume or strength. It is for styling complex curves.
A solid model knows it is made of material. That is why it can calculate mass, take a material property, run an FEA and be sent to a 3D printer.
A virtual model adds interaction and environment, letting a user walk through a building or handle a product in VR before it exists.

Common Mistake

A surface model cannot be used for engineering analysis or 3D printing.
It is an infinitely thin shell, so the software does not know what is inside it, and FEA needs to know exactly that.
If a question asks for a model that will be analysed or manufactured, the answer is a solid model.

Example question

(a) Identify the type of CAD model appropriate to each of these two stages. (2 marks)

(b) Explain why the model used for the styling stage could not be used to check the handle. (3 marks)

Solution

(a) Award [1] for each correct model type, up to [2 max].

Styling the sculpted body: a surface model, which handles complex flowing curves easily. [1]
Calculating mass and checking the handle: a solid model. [1]

(b) Award [1] for each linked point, up to [3 max].

A surface model defines only the outer skin. It has no thickness and no defined interior. [1]
Mass and stress both depend on how much material there is and where it sits, so the software cannot compute either from a surface. [1]
A solid model can be assigned a material and its density, which is what lets it return a mass and run an FEA on the handle. [1]

Active recall

Name the three types of CAD model on the syllabus.
What is the key difference between a surface model and a solid model?
Why can a solid model calculate mass when a surface model cannot?
What does a virtual model add that neither of the others provides?
Give two advantages of CAD over hand drawing in design development.

B2.2C CAD modelling and design development

B2.2C CAD modelling and design development

Subtopics and learning objectives

B2.2.3 CAD modelling and design development

CAD: A Model You Can Test Before You Build

Types of CAD Models

Surface Models

Solid Models

Virtual Models

The Role of CAD in Design Development

In automotive industry:

Surface, Solid or Virtual: Which One and Why

CAD: A Model You Can Test Before You Build

Types of CAD Models

Surface Models

Solid Models

Virtual Models

The Role of CAD in Design Development

In automotive industry:

Surface, Solid or Virtual: Which One and Why

A. Design in theory

B. Design in practice

C. Design in context

A. Design in theory

B. Design in practice

C. Design in context

B2.2C CAD modelling and design development

B2.2C CAD modelling and design development

Subtopics and learning objectives

B2.2.3 CAD modelling and design development

B2.2.3 CAD modelling and design development

CAD: A Model You Can Test Before You Build

Types of CAD Models

Surface Models

Solid Models

Virtual Models

The Role of CAD in Design Development

In automotive industry:

Surface, Solid or Virtual: Which One and Why

CAD: A Model You Can Test Before You Build

Types of CAD Models

Surface Models

Solid Models

Virtual Models

The Role of CAD in Design Development

In automotive industry:

Surface, Solid or Virtual: Which One and Why