Page 478 - 02. Subyek Computer Aided Design - Beginner’s Guide to SOLIDWORKS 2019- Level 1 by Alejandro Reyes

Assembly Modeling

Chapter 5: Assembly Modeling

The next step in our design after making the parts and drawings is to get all

the parts together into an assembly. The process of designing the parts first and

then assembling them is known as "Bottom-Up Design." Think of it as buying a

bicycle: when you open the box, you get all the pieces needed ready for assembly

and some parts pre-assembled. A different approach known as "Top-Down

Design" is where the parts are designed while working in the assembly; this is a

very powerful tool that allows us to match parts to each other, changing a part if

another component is modified. In this book we'll cover the Bottom-Up Design

technique, since it is easier to understand and is also the basis for the advanced

Top-Down Design, which is covered in the Beginner's Guide to SOLIDWORKS

Level II book.

In general, it's a good idea to design the parts, make the assembly to make

sure everything fits and works as expected (Form, Fit and Function), and then

make the drawings of the parts and assemblies; this way the drawings are done at

the end, when you are sure everything works correctly. In our case, we chose to

make the drawings before the assembly to show how changes in the assembly are

propagated to the part, and then to the drawing.

So far, we've been working on parts, single components that are the

building blocks of an assembly. In an assembly we have multiple components,

either parts or other assemblies (called sub-assemblies). The way we tell

SOLIDWORKS how to relate components (parts and/or sub-assemblies) together

is by using Mates (or relations) between them. Mates in the assembly are similar

to the geometric relations in the sketch, but in the assembly, we use faces, planes,

edges, axes, vertices and even sketch geometry from the component's features in

order to mate them to each other.

To make an assembly we add components one at a time until we complete

the design. In an assembly, every component has six degrees of freedom,

meaning that they can move and rotate six different ways: three translations along

the X, Y and Z axes, and three rotations about the X, Y, and Z axes. By mating

components to each other we are essentially restricting how they move in relation

to one another based on which degrees of freedom are constrained. This is the

basis for assembly motion and simulation. Based on this, the first component we

add to the assembly has all six degrees of freedom fixed by default. Therefore, it's

a good idea to make sure the first component added to the assembly is one that

will be a reference for the rest of the components. For example, if we make a

bicycle assembly, the first component added to the assembly would be the frame.

For the gear box we are designing, the first component added to the assembly will

be the 'Housing', since the rest of the components will be attached to it.

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