Introduction to Parametric Modeling

Parametric modeling tools give you a degree of flexibility which is not possible with conventional 3D tools. Parametric modeling allows complex elements to be edited easily without the need to be manually rebuilt. For example, the parameters used to create an object may be changed afterward to achieve a different result without manually rebuilding the element. Modifications to elements can be made by selecting and using handles to make changes interactively, or by changing the object's parameters in the element's Properties dialog.

The general procedure for parametric modeling includes creating a profile by using 2D drafting tools and extruding or revolving the profile into a solid or surface using the 3D creation tools. Various other steps can be added to achieve an intricate design. For example. applying features to the 3D element will let you design complex machine parts. To simplify the workflow, constraints can be applied to the 2D profiles and also to the 3D parametric elements. This workflow captures the design logic, and provides reusability to generated parametric component which can be placed as a Parametric Cell. So, the overall workflow would include the following stages:

Create a 2D parametric sketch (profile)
Apply constraints to the 2D parametric profile
Create a 3D parametric element using the 2D profile
Modify the 3D element using handles or changing the parameters
Apply constraints to the 3D parametric elements
Apply variable-driven features to create complex design components
Reuse the complete component by placing it in another design as parametric Cell

Parametric elements keep a record of how objects are built. When you change parameters in the element, the element is updated automatically. MicroStation re-executes the operations used to create the object using the new inputs to generate a new result.

Parametric modeling has multiple benefits:

Design alternatives - Try and test various sizes or parameters to determine which is the best by simply adjusting the model parameters getting a new result every time.
Accommodating changes - Save time by editing a part without having to recreate it.
Managing complexity - Create intricate, variable-driven parts with relationships that would be too complex to maintain manually.

Parametric elements are generated by adding or removing material. When adding, 3D parts are generated using profile based features such as Extrude and Revolve. While removing, volume of solid is reduced by applying features such as Fillet, Chamfer and Hole.

2D profile extruded into a 3D solid

2D profile revolved into a 3D solid

A Cut is created in a solid using a 2D profile

In parametric modeling, designs are driven by their inputs - property values, profiles, and operand objects used to create them - the inputs stay connected to the outputs. It is not necessary to get the perfect result on the first try, but it is easy to change specific values later. An object needs only to be the approximate size and shape of the intended element being created, as dimensions can be adjusted or constraints can be added later to change the shape of the geometry to get the desired shape.

For example, when you move a parametric entity, such as a hole, to another location on a solid, the hole correctly re-orients itself relative to the solid it cuts. On completion of the move the solid regenerates automatically to reflect the change.

Left: Select the hole | Center and Right: As it is moved, the hole orientates itself to the surface nearest the viewer (shown in heavy line weight for emphasis).

Note: It is important to analyze and plan every part before modeling to determine the most efficient sequence for creating a complex element. Poor modeling strategies will result in parts that take longer to create and that are difficult to edit. Finished elements should be created to allow for maximum part flexibility and variation. Rather than perceiving the finished entity as a large element, it needs to be viewed as a composition or parts that are likely to be modified.