Bottom-up and Top-down Assembly Design

Overview

Assembly modeling represents the structure of a designed product and consists of using mechanical blocks 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 with inserted mechanical blocks (which in turn can be assembled with other inserted mechanical blocks) forms a tree that is called a mechanical structure of the 3D model. This tree is displayed in the Mechanical Browser panel.

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 block.

Use the BMMECH command to convert existing blocks and external references to mechanical blocks. 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 mechanical block. These mechanical blocks are then grouped into higher-level mechanical blocks. The process is continued until the very top mechanical block is corresponding to the product itself.

The main command for bottom-up design is BMINSERT. Use this command to insert an existing mechanical block 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 mechanical blocks. Each mechanical block is then refined in more detail by defining its sub-mechanical blocks. The process is continued till all low-level mechanical blocks are defined and detailed.

Use the BMFORM command to create a new sub-mechanical block for an existing mechanical block.

Adding Mechanical Structure to Existing Geometry

You can add mechanical block 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 sub-mechanical block of the current drawing.

Changing Mechanical Structure

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

Use the BMFORM command to form a new sub-mechanical block for the current drawing that will contain a selected set of a mechanical block.

Use the BMDISSOLVE command to delete a mechanical block and move all its sub-mechanical blocks to the level of the dissolved mechanical block.

Using Standard Parts

A few standard parts are:

BricsCAD® provides a huge library of standard parts, 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 parts into your parts and assemblies.

Assembly Constraints

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

Mechanical block Visibility

A mechanical block within a complex assembly may seem invisible due to other mechanical blocks surrounding it.

You can hide any sub-mechanical block inserted into the current drawing or any sub-mechanical blocks, on any level of nesting.

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

Use the BMHIDE command to hide a particular sub-mechanical block.

Use the BMSHOW command to make a hidden sub-mechanical block visible.