Sub-assembly creation in Solidworks - Deep Dive

Overview - Sub-assembly creation

What is it?

Sub-assembly creation is the process of grouping multiple parts or components into a smaller, manageable unit within a larger assembly in SolidWorks. It helps organize complex designs by breaking them into logical sections. Each sub-assembly behaves like a single part but contains multiple parts inside it.

Why it matters

Without sub-assemblies, large designs become hard to manage, slow to update, and difficult to understand. Sub-assemblies simplify design changes, improve performance, and allow teams to work on different sections independently. This leads to faster product development and fewer errors.

Where it fits

Before learning sub-assembly creation, you should understand basic part modeling and simple assembly creation in SolidWorks. After mastering sub-assemblies, you can explore advanced assembly techniques like top-down design, assembly configurations, and motion studies.

Mental Model

Core Idea

A sub-assembly is like a mini-assembly inside a bigger assembly that groups related parts to simplify design and management.

Think of it like...

Think of a sub-assembly like a LEGO module: you build a small LEGO structure first, then use it as a single block to build a bigger LEGO model.

Main Assembly
┌─────────────────────┐
│                     │
│  ┌───────────────┐  │
│  │ Sub-assembly  │  │
│  │  ┌───────┐    │  │
│  │  │ Parts │    │  │
│  │  └───────┘    │  │
│  └───────────────┘  │
│                     │
└─────────────────────┘

Build-Up - 7 Steps

1

Foundation

Understanding Basic Assemblies

Concept: Learn what an assembly is and how parts fit together in SolidWorks.

An assembly in SolidWorks is a file that combines multiple parts. You insert parts and position them using mates, which define how parts connect or move relative to each other. This is the foundation for creating more complex structures.

Result

You can create a simple assembly by inserting parts and applying mates to fix their positions.

Understanding assemblies is essential because sub-assemblies are just assemblies nested inside bigger assemblies.

2

Foundation

Creating and Saving Parts

Concept: Know how to create individual parts that will be used in assemblies.

Parts are the building blocks. You create parts by sketching shapes and adding features like extrudes or cuts. Each part is saved as its own file, which you later insert into assemblies or sub-assemblies.

Result

You have multiple part files ready to be combined into assemblies.

Good part creation habits make assembly and sub-assembly work smoother and more reliable.

3

Intermediate

Making a Sub-assembly from Parts

🤔Before reading on: do you think a sub-assembly is created by grouping parts in the main assembly or by creating a separate assembly file? Commit to your answer.

Concept: Learn to create a sub-assembly by combining parts into a separate assembly file.

Instead of inserting all parts directly into the main assembly, create a new assembly file and insert related parts there. Apply mates to position them. Save this as a sub-assembly file. Then insert this sub-assembly into the main assembly like a single part.

Result

You have a sub-assembly file that acts as one unit inside the main assembly.

Knowing that sub-assemblies are separate assembly files helps manage complexity and reuse groups of parts easily.

4

Intermediate

Using Sub-assemblies to Simplify Main Assembly

🤔Before reading on: do you think sub-assemblies improve performance or just organization? Commit to your answer.

Concept: Understand how sub-assemblies reduce clutter and improve assembly performance.

By inserting sub-assemblies instead of many individual parts, the main assembly becomes cleaner and faster to open or update. You can hide or suppress sub-assemblies to focus on specific areas. This also helps teams work on different sub-assemblies separately.

Result

Main assembly is easier to navigate and faster to work with.

Recognizing performance benefits motivates using sub-assemblies beyond just organization.

5

Intermediate

Editing Parts within Sub-assemblies

Concept: Learn how changes in sub-assemblies affect the main assembly.

When you edit a part inside a sub-assembly, the changes automatically update in the main assembly. You can open the sub-assembly file directly or edit it from the main assembly. This keeps designs consistent and reduces errors.

Result

Changes propagate smoothly from sub-assemblies to the main assembly.

Understanding this link prevents confusion about why changes in one place affect others.

6

Advanced

Top-down Design with Sub-assemblies

🤔Before reading on: do you think sub-assemblies can contain references to the main assembly or only internal parts? Commit to your answer.

Concept: Explore how sub-assemblies can be designed with references to the main assembly for coordinated updates.

In top-down design, you create parts and sub-assemblies that reference geometry or parameters from the main assembly. This allows changes in the main assembly to drive updates in sub-assemblies, enabling complex, coordinated designs.

Result

Sub-assemblies dynamically update based on main assembly changes.

Knowing this advanced technique unlocks powerful design workflows for complex products.

7

Expert

Managing Large Assemblies with Sub-assembly Strategies

🤔Before reading on: do you think all sub-assemblies should be fully detailed or can some be simplified? Commit to your answer.

Concept: Learn expert strategies like lightweight sub-assemblies, simplified configurations, and modular design to handle very large assemblies.

Experts use lightweight mode to load sub-assemblies faster, create simplified versions to reduce detail, and design modular sub-assemblies that can be reused across projects. These techniques improve performance and collaboration in large-scale designs.

Result

Large assemblies become manageable, faster, and easier to collaborate on.

Understanding these strategies prevents common bottlenecks and supports scalable design practices.

Under the Hood

A sub-assembly is stored as a separate assembly file that contains references to part files. When inserted into a main assembly, SolidWorks treats it as a single component but maintains links to all internal parts and mates. This hierarchical structure allows independent editing and efficient data management.

Why designed this way?

This design allows modularity and reuse. Instead of duplicating parts, sub-assemblies encapsulate complexity and enable parallel work. Alternatives like flat assemblies would be harder to manage and slower to update, especially for large projects.

Main Assembly
┌─────────────────────────────┐
│                             │
│  Sub-assembly 1             │
│  ┌───────────────┐          │
│  │ Part A        │          │
│  │ Part B        │          │
│  └───────────────┘          │
│                             │
│  Sub-assembly 2             │
│  ┌───────────────┐          │
│  │ Part C        │          │
│  │ Part D        │          │
│  └───────────────┘          │
└─────────────────────────────┘

Myth Busters - 4 Common Misconceptions

Quick: Do you think sub-assemblies increase file size significantly? Commit yes or no.

Common Belief: Sub-assemblies always make the main assembly file much larger and slower.

Reality: Sub-assemblies are separate files and only references are stored in the main assembly, so they often reduce file size and improve performance.

Why it matters: Believing this can discourage using sub-assemblies, leading to cluttered and slow main assemblies.

Quick: Can you edit parts inside a sub-assembly only by opening the sub-assembly file? Commit yes or no.

Common Belief: You must open the sub-assembly file separately to edit its parts; you cannot edit them from the main assembly.

Reality: SolidWorks allows editing sub-assembly parts directly from the main assembly, keeping workflows smooth.

Why it matters: Not knowing this slows down design changes and causes unnecessary file switching.

Quick: Do you think sub-assemblies always behave exactly like parts in the main assembly? Commit yes or no.

Common Belief: Sub-assemblies behave exactly like single parts with no differences.

Reality: Sub-assemblies can have their own mates and motion, which parts do not have, making them more complex than simple parts.

Why it matters: Assuming they are identical can cause confusion when applying mates or analyzing assembly behavior.

Quick: Do you think sub-assemblies cannot reference geometry outside themselves? Commit yes or no.

Common Belief: Sub-assemblies are isolated and cannot reference or depend on the main assembly geometry.

Reality: With advanced techniques like top-down design, sub-assemblies can reference main assembly geometry for coordinated updates.

Why it matters: Ignoring this limits design flexibility and prevents powerful parametric relationships.

Expert Zone

1

Sub-assemblies can be configured with different versions or states, allowing multiple design options within one file.

2

Lightweight loading of sub-assemblies improves performance by loading only essential data until full detail is needed.

3

Using sub-assemblies enables parallel work by multiple designers, reducing conflicts and speeding up development.

When NOT to use

Avoid sub-assemblies for very simple designs where overhead adds complexity. For extremely large assemblies, consider using assembly visualization tools or breaking designs into separate projects instead.

Production Patterns

In production, sub-assemblies are used to represent functional modules like engines or chassis in automotive design. Teams work on these modules independently and integrate them into the final product assembly.

Connections

Modular Programming

Sub-assemblies in CAD are like modules in programming that group related code for reuse and clarity.

Understanding modular programming helps grasp why breaking designs into sub-assemblies improves manageability and collaboration.

Project Management Work Breakdown Structure (WBS)

Sub-assemblies correspond to WBS elements that break a project into smaller, manageable tasks.

Seeing sub-assemblies as design tasks clarifies how complex projects are organized and tracked.

Biological Cell Organization

Sub-assemblies are like organelles inside a cell, each performing specific functions but working together.

This analogy shows how complex systems rely on smaller functional units to maintain order and efficiency.

Common Pitfalls

#1 Inserting all parts directly into the main assembly without sub-assemblies.

Wrong approach:

Insert PartA.sldprt
Insert PartB.sldprt
Insert PartC.sldprt
... (all parts individually)

Correct approach:

Create SubAssembly1.sldasm with PartA and PartB
Insert SubAssembly1.sldasm
Insert PartC.sldprt

Root cause:

Not understanding the benefits of grouping parts into sub-assemblies leads to cluttered and slow assemblies.

#2 Editing parts in sub-assemblies by opening only the main assembly and expecting changes to save automatically.

Wrong approach:

Edit part geometry in main assembly context but forget to save sub-assembly file.

Correct approach:

Open sub-assembly or edit part from main assembly, then save the sub-assembly file explicitly.

Root cause:

Misunderstanding file relationships causes lost changes and confusion.

#3 Assuming sub-assemblies cannot have mates inside them.

Wrong approach:

Try to mate parts only in the main assembly, ignoring sub-assembly mates.

Correct approach:

Apply mates inside sub-assembly to define part relationships before inserting into main assembly.

Root cause:

Not realizing sub-assemblies are full assemblies with their own internal constraints.

Key Takeaways

Sub-assemblies group related parts into manageable units inside larger assemblies, simplifying design and collaboration.

They are separate assembly files that behave like single components but maintain internal structure and mates.

Using sub-assemblies improves performance, organization, and allows parallel work on complex designs.

Advanced techniques let sub-assemblies reference main assembly geometry for coordinated updates.

Avoid skipping sub-assemblies in complex projects to prevent clutter, slowdowns, and errors.

Practice

1.

What is the main purpose of creating a sub-assembly in SolidWorks?

easy

A. To group related parts for easier management

B. To create a new part from scratch

C. To export the assembly as a 2D drawing

D. To change the color of parts automatically

Solution

1. Step 1: Understand sub-assembly concept

   Sub-assemblies group related parts to manage them easily within a larger assembly.

2. Step 2: Compare options

   Options A, B, and D describe unrelated tasks, not the main purpose of sub-assemblies.

3. Final Answer:

   To group related parts for easier management -> Option A

4. Quick Check:

   Sub-assembly = Group parts [OK]

Hint: Remember: sub-assemblies simplify complex assemblies [OK]

Common Mistakes:

• Confusing sub-assembly with part creation
• Thinking sub-assembly changes part colors
• Assuming sub-assembly exports drawings

2.

Which of the following is the correct way to create a sub-assembly in SolidWorks?

1. Insert parts into a new assembly document
2. Save the assembly with a clear name
3. Use the sub-assembly inside a larger assembly

easy

A. Create a new part, then save as sub-assembly

B. Export parts as separate files and link them

C. Open a drawing and add parts as sub-assembly

D. Insert parts into a new assembly, save it, then use it inside a larger assembly

Solution

1. Step 1: Identify correct sub-assembly creation steps

   Insert parts into a new assembly document, save it clearly, then use it inside a bigger assembly.

2. Step 2: Eliminate incorrect options

   Create a new part, then save as sub-assembly creates a part, not a sub-assembly. Open a drawing and add parts as sub-assembly uses drawings incorrectly. Export parts as separate files and link them exports parts separately, not sub-assembly.

3. Final Answer:

   Insert parts into a new assembly, save it, then use it inside a larger assembly -> Option D

4. Quick Check:

   Sub-assembly steps = Insert + Save + Use [OK]

Hint: Think: assemble parts first, then save as sub-assembly [OK]

Common Mistakes:

• Saving a part as sub-assembly
• Trying to create sub-assembly inside a drawing
• Not saving the assembly before using it

3.

Given a main assembly with two sub-assemblies, each containing 3 parts, how many total parts will the main assembly show?

medium

A. 2

B. 3

C. 6

D. 9

Solution

1. Step 1: Calculate parts in each sub-assembly

   Each sub-assembly has 3 parts, so 2 sub-assemblies have 3 x 2 = 6 parts.

2. Step 2: Add parts from sub-assemblies to main assembly

   Main assembly includes all parts from sub-assemblies, so total parts = 6.

3. Step 3: Check if main assembly has extra parts

   Since main assembly contains 2 sub-assemblies only, total parts = 6 parts inside sub-assemblies plus 0 extra parts = 6.

4. Final Answer:

   6 -> Option C

5. Quick Check:

   2 sub-assemblies x 3 parts = 6 parts [OK]

Hint: Multiply sub-assemblies by parts inside each [OK]

Common Mistakes:

• Counting sub-assemblies as parts
• Adding sub-assemblies and parts incorrectly
• Ignoring parts inside sub-assemblies

4.

What is wrong with this sub-assembly creation process?

1. Insert parts into assembly
2. Save assembly as a part file (.sldprt)
3. Use it inside main assembly

medium

A. Inserting parts before saving is wrong

B. Saving assembly as a part file is incorrect

C. Using sub-assembly inside main assembly is not allowed

D. Parts should be inserted after saving

Solution

1. Step 1: Identify file type error

   Assemblies must be saved as assembly files (.sldasm), not part files (.sldprt).

2. Step 2: Confirm correct workflow

   Insert parts, save as assembly file, then use inside main assembly.

3. Final Answer:

   Saving assembly as a part file is incorrect -> Option B

4. Quick Check:

   Assembly file extension = .sldasm [OK]

Hint: Save assemblies as .sldasm, not .sldprt [OK]

Common Mistakes:

• Saving assemblies as part files
• Confusing file extensions
• Thinking parts insert order matters

5.

You have a complex assembly with 50 parts. To improve performance, you want to create sub-assemblies. Which approach is best?

hard

A. Group related parts into sub-assemblies and save them separately

B. Keep all parts in one assembly without sub-assemblies

C. Create sub-assemblies but do not save them separately

D. Convert all parts into drawings before assembly

Solution

1. Step 1: Understand performance benefits

   Grouping related parts into sub-assemblies reduces complexity and improves performance.

2. Step 2: Importance of saving sub-assemblies

   Saving sub-assemblies separately allows reuse and better management.

3. Step 3: Evaluate other options

   Keeping all parts together slows performance; not saving sub-assemblies loses benefits; converting parts to drawings is unrelated.

4. Final Answer:

   Group related parts into sub-assemblies and save them separately -> Option A

5. Quick Check:

   Sub-assemblies + save separately = better performance [OK]

Hint: Save sub-assemblies separately to improve performance [OK]

Common Mistakes:

• Not saving sub-assemblies separately
• Keeping all parts in one big assembly
• Confusing drawings with assemblies