Bottom-up and Top-down Assembly Design

Assembly modeling represent 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 across this topic:

• An assembly is a component that contains inserts of other components and a subassembly is 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 assemblies 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 two 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.

BmNew command is called to create a new document for a new mechanical component.

BmMech command can be used to convert existing blocks and external references to components, while BmUnmech does the opposite.

Bottom-Up Design

With bottom-up approach users 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, which is used to insert an existing component into the current drawing.

Top-Down Design

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

BmForm command creates a new subcomponent for an existing component.

Adding Mechanical Structure to Existing Geometry

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

BmForm converts a selected set of geometric entities to a subcomponent of the current drawing.

Changing Mechanical Structure

During design process users may realize that a particular component should be moved up or down in the component hierarchy.

BmForm command forms a new subcomponent for the current drawing that will contain a selected set of a component.

BmDissolve deletes a component and moves all its subcomponents to the level of the dissolved component.

Using Standard Components

Some of the standard components are: screws, nuts, washers, bearings and holes.

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

Use the Components 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. For example, a piston is invisible inside a cylinder block. To make such a component visible user may need to hide the other components surrounding it.

Users 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.

BmHide hides a particular subcomponent.

BmShow unhides a hidden subcomponent.