Bottom-up and Top-down Assembly Design

Overview

Assembly modeling represents the structure of a designed product and consists of using components to group geometric entities in hierarchies. Assembly modeling is commonly used in Mechanical Computer-Aided Design (MCAD) applications, it simplifies the design of complex products containing thousands or millions of geometric entities.

The following terms are used in this guide:
  • An assembly is a component that contains inserts of other components
  • A subassembly is a separate assembly that is inserted into another assembly
  • A part is a component that does not contain inserts of another component.

An assembly with inserted components (which in turn can be assembled with other inserted components) forms a tree that is called a mechanical structure of the 3D model. This tree is displayed in the Mechanical Browser.

There are 2 main ways to design mechanical products: top-down and bottom-up approaches. You can also add mechanical structure to existing geometry, designed in BricsCAD or imported from another source.

Use the BMNEW command to create a new document for a new mechanical component.

Use the BMMECH command to convert existing blocks and external references to components. Use the BMUNMECH command to do the opposite.

Bottom-Up Design

With bottom-up approach, you can start to design a product by detailing its low-level component. These components are then grouped into higher-level components. The process is continued until the very top component is corresponding to the product itself.

The main command for bottom-up design is BMINSERT. Use this command to insert an existing component into the current drawing.

Top-Down Design

With top-down approach, you can start to design a product by defining, but not detailing, its first-level components. Each component is then refined in more detail by defining its subcomponents. The process is continued till all low-level components are defined and detailed.

Use the BMFORM command to create a new subcomponent for an existing component.

Adding Mechanical Structure to Existing Geometry

You can add component hierarchy to any existing drawing, created in BricsCAD, or imported from a different CAD format.

Use the BMFORM command to convert a selected set of geometric entities to a subcomponent of the current drawing.

Changing Mechanical Structure

During the design process, you can realize that a particular component must be moved up or down in the component hierarchy.

Use the BMFORM command to form a new subcomponent for the current drawing that will contain a selected set of a component.

Use the BMDISSOLVE command to delete a component and move all its subcomponents to the level of the dissolved component.

Using Standard Components

A few standard components are:
  • screws
  • nuts
  • washers
  • bearings
  • holes.

BricsCAD provides a huge library of standard components, more than 30,000 details in a variety of sizes. You can significantly increase design performance by using standard parts.

Use the Library panel to insert standard components into your parts and assemblies.

Assembly Constraints

Assembly constraints are ordinary 3D Constraints, that link faces and edges of bodies to represent the components of an assembly. You can link 3D Constraints at the top-level and at the subcomponents level.

Component Visibility

A component within a complex assembly may seem invisible due to other components surrounding it.

Example: a piston is invisible inside a cylinder block. To make such a component visible, you may need to hide the other components surrounding it.

You can hide any subcomponent inserted into the current drawing or any subcomponents, on any level of nesting.

You can also make a component transparent and/or visualize it as a wireframe model.

Use the BMHIDE command to hide a particular subcomponent.

Use the BMSHOW command to make a hidden subcomponent visible.