One of the tricky things about mechanical design is that requirements might change over the design stage of the project (more about that here). Therefore, it is important that a team of designers should be able to cope with sudden changes and deal with them quickly and efficiently.
Getting your CAD data into a coherent state is one way you can maximize your efficiency!
To get straight to the point, the way a CAD model tree is organised makes a huge difference. If this is done smartly it will save an enormous amount of time in the future when modifications are required. The way a part is modeled is also important: For example, it can take considerably more time to modify the a hole drafted within the primary 2D sketch, than to just modify the diameter if it were a feature added to the primary shape.
Here are some tips for good CAD tree housekeeping that will make modifications, especially within a workgroup, a swift task:
1) Define the primary shape
The primary shape is the basic block you create as a basis to model the part from. It should be as simple as possible. It’s easy to overcomplicate this. Let’s take a gear for example: You could either extrude a 2D sketch that represents the whole shape, or you can make a more basic form that you will elaborate on afterwards by adding features (I.E. the teeth)
The first option can be less efficient: if ANY feature is adjusted then the entire model needs to be rebuilt completely.In the second option, the primary shape isn’t linked to the teeth, and therefore it will be easier to modify the gear. In fact, knowing a gear answers to a set of defined equations depending on its shape, the designer can even make a parametric CAD model that will enable creation of other gears of different geometries that are driven by an equation.
2) Separate construction elements from the model
Datum planes, lines, curves, even 3D shapes are often used to create the final 3D model. Such elements should be kept in separate geometric sets and disposable body parts within the tree structure. This not only makes hiding them better, but the designer can differentiate between construction geometry and the model itself. It is also the main indicator to others of how the modeling was conducted.
3) Use automated options when possible
CAD software has advanced so much that sketching every single feature in detail is no longer necessary. The more sketches you have the harder a model can be to manipulate. Most CAD packages can now semi-automate the creation of holes, parametric ribs, chamfers, fillets etc. with minimal 2D data input. Another advantage of this is when it comes to FEA: designers have always needed to simplify the shape of the part, so using “disposable” features is easier than remodeling the 3D model.
4) Make special surfaces a different colour
If you have a specific requirement for a surface, or the design of that area is not complete, why not think of changing the colour of the surface and keeping track of their meaning? I remember a customer who wanted low roughness of a specific surface, but would not accept polishing. We had to determine critical surfaces and colour them depending on the roughness level we thought was adequate. During the development process the colour coding helped enormously when communicating with the customer and manufacturer.
5) Name critical parts of your design
Identify features in the model tree by giving them proper names. This might take some time at first, but it saves a huge amount when you will be looking for a specific plane that holds a specific surface that was located somewhere within the innards of your design!
6) Put yourself in someone else’s shoes
Whenever you complete a crucial part of your work, take a step back and and just look at it. Is it understandable? Will others make sense of your thought process? Is your model tree logical? Even if somebody else isn’t going to work with your model, make sure you leave behind work that you can still comprehend months or years after doing it.