What is SOLID MODELLING?
What is solid modelling? It is the process of digitally creating a 3d design using CAD software. There are 2 primary forms of 3d modelling, solid and surface.
Surface usually for visual purposes and solid for real world fabrication and computer simulations. First lets start with the basics, The difference between 2d & 3d CAD.
2d its just a flat drawing which include the x,y axis. 3d is a solid three-dimensional object which includes the x,y & z axis.
2d drawings can communicate a design sufficiently to a human, however if you wanted to produce the CAD design using computer controlled production machinery then it would more then likely need to be 3d. Here you can see a 2d CAD model vs a 3d CAD model (built using solid modelling method). Now lets look at the definition of a solid model.
Solid model definition
A solid model is a more complete representation of a surface (or wireframe model). A solid model communicates both geometric and topological information, this represents a solid unambiguously. Geometric information addresses shapes, sizes and positioning in a 3d environment or coordinate system.
Topology deals with what people call ‘relationship information’, its non graphical, no scalar data.
This square shows 2 parts of information, topological and geometric. Geometric is the 100mm length of the squares side and topological is the perpendicular relationship of the vertical and horizontal sides joining at a 90 degree angle.
lets look at how solid models are made up of primitive shapes and primitive shapes made up of 2d sketches….
Solid models are made up of primitive shapes like cubes, spheres or cylinders. Primitive shapes are made of 2d sketches. For example a solid cube is made up of 6 flat squares surfaces that join together.
With any 3d solid model, however complex, it can be broken down into sub shapes. The subshapes are formed with 1 or more 2d sketches. think about the design below, that design is made from a number of cylinders, square and triangles
FULL SOLID MODEL
2d has no Z axis is made up of edges and vertices, its the oldest form of 3d modelling. You cannot represent complex surfaces and it does not show interior details.
Three Dimensionsal Drawing
3d includes all x,y & axis or in other words all 3 dimensions. a 3d model contains edges and vertices as with 2d however these edges are filled in with surfaces and interior detailing.
WHAT CAN I DO WITH A 2D DRAWING?
typically architects would express a building with a large variety of 2d drawings but in modern day manufacture 3d drawings are always required. What you can do with a 2d drawing depends, if its a pencil drawing on paper, nothing really. If it’s a 2d drawing modelled with 2d CAD software you can cut sheet flat sheet material with a cnc cutter. You can map out a floor plan or have a 3D CAD guy build the model in 3D. Other then that, not much.
WHAT CAN I DO WITH A 3D DRAWING?
You can send to a 3d printer to make a physical prototype, or simulate forces acting on the design. You can use to make artwork for all marketing or for communication purposes with anyone anywhere instantly. If you want to mass produce you’ll usually make a mold or production tool. these both require 3d cad files. You can preform motion studies to explore how mechanical parts or systems function. The list goes on and on.
2D shapes are used with the primary feature forming operations
As mentioned earlier nearly all 3d forms are made up of, or start as a 2d shape. With most parametric solid modelling softwares 3d forms are built from 2d sketches using the 6 primary forming operations as shown below.
Extruding is the primary forming operation. It involves taking a flat 2d sketch and extruding it up so it has a thickness
Cut extrude is the opposite of boss extrude, it involves using a flat sketch to cut material from a thickened shape
Revolve boss allows us to take a flat sketch and rotate it around a center to create a solid shape
Sweep boss takes a flat sketch and extrudes it along a path. Can include guide curves to manipulate the uniformity
Loft emboss takes 2 separate flat sketches and joins them together with a often curved and unique surface.
Boundary boss is very similar to loft boss however it can join open open paths as well as closed flat shapes.
Take the image below for example, this form was modelled using all 6 operations.
join the 2d circle
and square base
using a single
2d sketch and
sweeps it along
spiral path to
create solid bar
takes a sketch split
vertically down the
center. the 2d sketch
is revolved around
the center axis to
create solid shape
a solid body joins
the 3 separate 2d sketches in the stem of the design
Added guide curves
can manipulate the
outer surface profile
for a more freeform
This is the inverse operation of boss extrude. Cut extrude is cutting material away to create a circular array of holes the base platform of the model
A powerful operation that isn’t included in the 6 primary operations is BOOLEAN. Boolean is a example of Constructive Sold Geometry, or CSG
CSG constructs solid models by combining shapes. The boolean operation come in 3 forms:
- Union (unite) – this simply joins 2 shapes together into one single solid body
- Difference (cut) – Subtracts the volume of one shape from another shape.
- Intersection – Keeps the volume when 2 shapes intersect.
So these 7 shape forming operations can build almost any design you could ever imagine…. For more in depth example watch our video below.
Now you have a concept of how models are actually built in 3d CAD software lets talk about a slightly more advanced solid modelling concept called PARAMETRIC MODELLING
What is PARAMETRIC MODELLING?
Parametric is a word used to describe a designers ability to change a measurement in a 3d model which changes the shape or size of a models geometry. In other words measurements control the model.
Design intent is how a model reacts when a measurement values are changed.
Take for example changing the diameter of screw holes in a table design. That table is made up of forming operations like 6 mentioned above. In this context the screw holes were made using the cut operations.
This cut operation was made from a 2d sketch of a circle which had a measurement value assigned to it. These screw sizes were later changed for some reason, now the designer can easily open the model and change the diameter value at any time which updates screw holes. This is the value of parametric modelling. If its modelled with the correct design intent, it should be easy to change design details retrospectively. Contact microworkshops on 0203 0341 334 to speak with one of our parametric modellers. Or check out our CAD design services for further information
Advantages of 3d model
Easy to interpret with multiview perspectives
Simulate real life conditions like stress or force loading
Cheaper and faster than building a physical model
Can be used for visuals when presenting or selling
Directly used for CAM manufacture like 3d printing or CNC
allows mass and volumetric analysis. For example weight, center of mass, volume and inertia.
Can be exported into large variety of file formats depending on its purpose
Solid modelling is usually parametric meaning it size and detail changes can be made easily retrospectively, extremely useful for flexible design iteration