112.4.1 - CAD/DFM

Symmetry, Patterns, & Constraints

What is "Symmetry"?

Symmetry = Something being the same as another thing / An object being dividable into two or more identical pieces, arranged in an organized fashion
- Symmetry - in some form or another - is present in almost all designs of man & nature
  - If you can recognize & understand different forms of symmetry, you can utilize that understanding to make designs more efficiently
Types of Symmetry include:
- Bilateral/Reflectional/Mirror Symmetry
- Radial/Rotational Symmetry
- Translational Symmetry
- Helical Symmetry
- Scaling Symmetry

Bilateral/Reflectional/Mirror Symmetry

2D = Line means line geometry can be mirror across a line
3D = Plane
Bilateral Symmetry is the most common example found in Nature, as evidenced below:

Radial/Rotational Symmetry

Rotational Axis = Line or Arc
- Examples:
  - Polygons & Stars
  - Starfish
  - Bolt Hole Circles (BHC's)

Translational Symmetry

Defined by distance in one or more axial directions away from the parent object
- Examples:
  - Bee Honeycomb
  - Brickwork
  - Tiling

Helical Symmetry

Translated & Rotated
- Examples:
  - Threads/Screws
  - DNA
  - Viruses

Scaling Symmetry

All features of an object maintain the same relative relationships to one another, regardless of the overall size of the object
- Examples:
  - Scale Models
  - Items that shrink during processing (Heat-shrink tubing, Sintered 3D-Printed parts, Shrinky Dink)

What are "Patterns"?

Patterns can be used to improve the structural integrity, stability, aerodynamics, weight reduction, interchangeability, and safety of a product.
1. Additionally, patterns such as repetition and modularity can be used to simplify the manufacturing process and reduce the cost of production.
2. Design patterns can include patterns related to the shape and structure of a product, such as the use of symmetrical shapes and patterns to improve the structural integrity and stability of a product.
Symmetry and patterns go hand in hand in engineering and manufacturing, as symmetry is one of the design patterns that can be applied to improve the performance and manufacturability of a product.
1. Symmetry & patterns are commonly used in the design of products for several reasons related to engineering and manufacturing:
  1. Structural Integrity: Symmetry and patterns can be used to create a sense of balance and stability in a design. This can help to distribute stress and load more evenly throughout the structure, which can improve the overall structural integrity of the product.
  2. Manufacturing: Symmetry and patterns can be used to make a product more easily mass-produced, which can reduce the cost of production. By using repetitive patterns, manufacturers can easily create identical parts, which simplifies the manufacturing process and reduces the risk of errors.
  3. Aerodynamics: In the case of planes and cars, symmetry and patterns can be used to improve the aerodynamics of the design. This can help to reduce drag and improve the overall performance of the product.
  4. Weight Reduction: Symmetry and patterns can be used to optimize the weight distribution of the product, which can help to reduce the overall weight of the product without compromising its structural integrity.
  5. Cost-Efficiency: Symmetry and patterns can make a product more cost-effective by reducing the need for custom tooling and allowing for more efficient mass production.
  6. Interchangeability: Symmetry and patterns can improve the interchangeability of parts. For example, using a standard pattern in the design of a part can make it easier to replace a damaged part with a new one.
  7. Safety: Symmetry and patterns can be used to improve the safety of a product. For example, a symmetrical design can make it easier to identify a failure in a structure and repair it before it becomes a critical issue.
Overall, symmetry and patterns can be used to create a sense of balance, stability, and structural integrity, making a product more reliable and cost-effective. Additionally, in the context of engineering and manufacturing, symmetry and patterns can be used to improve aerodynamics, weight reduction, interchangeability, and safety.

Using Symmetry/Patterns in CAD

The most common use of symmetry in CAD is with Mirroring & Revolving
- Mirror
  - Utilizes Bilateral/Reflectional/Mirror Symmetry
- Revolve
  - Utilizes Radial/Rotational Symmetry
    - Revolve geometry/features around an axis line
The most obvious form of using pattern recognition is by patterning 2D/3D features
- The types of patterning we can utilize in Fusion 360 include:
  - Rectangular Pattern
    - Duplicates a certain amount of geometry/features in rows and columns, with consistent spacing
      - Both the amount and spacing are adjustable
    - Can pattern at any diagonal angle; not limited to just horizontal/vertical
  - Circular Pattern
    - Duplicates a certain amount of geometry/features around and axis, arc, or curved surface
  - Pattern Along Path
    - Duplicates a certain amount of geometry/features along a a path, with consistent spacing
      - This path can be nonlinear and nonplanar
  - Geometric Pattern
    - Creates a pattern with size and distribution gradients (gradually increasing/decreasing)
- When patterning in Fusion 360, it is highly recommended to PATTERN FEATURES, NOT SKETCH GEOMETRY
  - The reason for this is that while Features are captured & editable in the Design Timeline, patterns of sketch geometry are not as easily editable
  - Therefore, sketch as little 2D geometry as necessary to locate the beginning of a pattern, then create the 3D feature(s) from the 2D sketch geometry, then pattern the feature(s)
Aside from 2D/3D features, there can also be patterns of relationships between sketch geometry and features
- Rather than assigning individual relationships over and over that are essentially the same, if you pattern a geometry/feature that already has those relationships, the relationships will pattern as well
  - This can be done with either Constraints or Parameter linking, or both!

Constraints in CAD

In order to fully-constrain/define geometry in CAD, there are two requirements that must be fulfilled:
- Dimensionally Constrained
  - Applying length/width/height/diameter/radius dimensions to a line or other 2D geometry adds a Dimensional Constraint to that geometry, and it will not change unless you directly change that constraint
- Positionally Constrained
  - Applying location to 2D geometry adds a Positional Constraint to that geometry, which will stay the same until changed
    - Since sketches (typically) are 2-Dimensional, in order to fully constrain the position of 2D geometry, it must be defined in both dimensions/axes within the 2-Dimensional Plane
      1. For example, the location of a circle in a sketch must be defined by its distance from a reference position (oftentimes the origin point) not just horizontally, but also vertically. If the location is defined diagonally, it must also be defined rotationally
Pro-Tip: One of the easiest ways to determine how a sketch geometry needs to be further constrained is by clicking-and-dragging the geometry and seeing how it changes. Some examples:
- If it changes in dimension/size, it needs to be dimensionally constrained
- For positional constraints:
  - If it moves vertically, it needs to be vertically constrained
  - If it moves horizontally, it needs to be horizontally constrained
  - If it moves diagonally, it needs to be diagonally constrained
  - If it rotates, it needs to be rotationally constrained
You can use Constraints to your advantage to maintain relationships between multiple sketch lines/objects
- If you are drawing a square and want to ensure it stays a square at all times, you can apply equal/parallel/perpendicular Constraints to all the lines, and they will maintain those relationships with one another, regardless of where you relocate the square or what dimensions/scaling you apply to the square
- If you link all your 2D geometry together with constraints, you can reduce the total number of individual dimensions needed, as apply one dimension can translate to all associated, constrained features
- If you create constraints on a "parent" geometry (something that other geometry is based/copied from, AKA "children"),
Fusion 360 can oftentimes add constraints by default when you create 2D geometry
- The most common way this happens is when you Model About the Origin point - a good best-practice for most CAD applications
- Sometimes this can help you, but other times it can hinder you from being able to adjust things as desired
- You can tell if/when a constraint will be added by default in Fusion 360 when symbols pop up around your cursor
  - The most common Constraints applied by default are Coincident, Midpoint, & Horizontal/Vertical, but others can also be applied automatically

Types of Constraints

Over-Constrained/Driven Geometry

If you are attempting to apply additional constraints within CAD and are confronted with an error along the lines of "Adding the dimension will over constrain the sketch...", it is because the geometry is already fully constrained/defined.
- The reason for this is entirely logical - something cannot exist in two different states of being simultaneously
  - In CAD, for example; a circle cannot at the same time be two different dimensions/sizes (ex: a dimensions cannot equal 6" and 12" simultaneously)
The dimensional and positional constraints that define and control geometry within CAD are known as Driving constraints
- You can, however, reference dimensions that are indirectly defined by these constraints - AKA Driven constraints
It can be incredibly useful to use driven constraints to define other geometry, which is possible through the use of parameters (more on these later!)

4.1✔ CHECKPOINT

Lego Brick CAD Model

Create a CAD Model of a 2x2 Lego Brick:
- Research the dimensions of a standard LEGO bricks, then model the LEGO Brick accordingly
  - Instead of "LEGO" on each stud, put your initials (ex: John Alex Smith = "JAS")
  - Utilize the functions shown in this module - symmetry, patterns, & constraints to ensure your LEGO Brick is fully-defined
- 3D-Print two (2) of your Lego Bricks and test-fit them, both:
  - To themselves, and...
  - To a standard, Lego brick (available in the lab)
Once done, create a "LEGO Brick" Project page on your portfolio website, and upload documentation of your progress (text/pictures/gifs/videos/etc.), including:
- Embedded link to the CAD file of your LEGO brick
- Different views of your LEGO brick showing all design features
- Descriptions/summaries of what you did/learned

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