CATIA Assembly Design Workbench: Flexible vs. Rigid Sub-Assembly

By Ray Olson

 

When adding an existing product using Existing Component command or creating a new product using New Product command, it is added to the main product (assembly)  with the default state of Rigid. The Rigid state is for sub-assemblies made up of components or parts where the position of the components within the sub-assembly will not change each time the sub-assembly is instanced into the main or top level product. An example of a sub-assemble that the state should be Rigid is the Ball_Mount sub-assembly from the Hitch assembly pictured below.

 

Set the sub-assembly state to Flexible for sub-assemblies made up of components or parts were the position of the components within the sub-assembly will change each time the sub-assembly is instanced into the main or top level product. In the Flexible state the position of the components within the sub-assembly  are managed at the top level of the main assembly. This way the position of the components within the sub-assembly are stored or saved with main assembly and not at the sub-assembly product file level. Two examples of a sub-assemblies that the state should be Flexible are pictured below.

In the example of the hydraulic cylinder, the distance the piston will be extended from the cylinder may change each time it is instanced in the main or top level assembly. In the example of the vise, the distance from the fixed jaw and the movable jaw may change each time it is instanced also.

 

In the example below the command Define Multi Instantiation (Ctrl +E) is used to add 3 additional instances of the Vise Sub-Assembly to the Vise-Setup product.

 

Now in one of the Vise Sub-Assemblies changing the distance between the vise jaws causes all four instances to change. Using Save Management after this change shows both the Vise-Setup product and Vise-Standard Sub-Assembly product have been modified. This is because the Vise-Standard Sub-Assembly products state is Rigid. Cancel Save Management and Undo (Ctrl + Z) to before changing distance between the vise jaws.

 

After pre-selecting all Vise-Standard products, with the Flexible/Rigid Sub-Assembly command the state is changed to Flexible.

 

Now with the Vise-Standard Sub-Assembly products state set to Flexible, the distance between the vise jaws can be managed independently for each instances of the Vise-Standard Sub-Assembly. Using Save Management after this change shows only the Vise-Setup product has been modified. Now that the Vise-Standard Sub-Assembly products state is Flexible, the position of the components within the sub-assembly  are managed and saved with the top level Vise-Setup product file. No change was made to the Vise-Standard Sub-Assembly product file, the state in Save Management is open and does not need to be saved.

 

In the example below of the Excavator Arm Assembly, needs two instances of the hydraulic cylinder sub-assembly. Because each instance of the hydraulic cylinder sub-assembly state is Flexible, the distance the piston will be extended from the cylinder can be managed independently for each instance. This will allow moving the components to different positions by changing offset constrain distance of the hydraulic cylinder piston sub-assemblies. Which can be saved using the Enhanced Scene command in the Assembly Design Workbench.

 

Machining Process files and Flexible vs Rigid Sub-Assembly

In the example below the sub-assemblies are inside a machining Process file. Product files default state in a Process file is Flexible when added to this file for machine setup. It is recommended to manage the position of the sub-assemblies components from inside the machining Process file. This is done by double clicking top level product  branch in the specification tree which will active the Assembly Design Workbench. After completion of position task double click Process branch or Part Operation to return to machining workbench. Using Save Management after this change shows only the Vise-Cut1-Setup.CATProcess file has been modified. This is because the position of the components within the sub-assembly are managed and saved with the top level Vise-Cut1-Setup.CATProcess file. No change was made to the Vise-Setup-33 product and Vise-Standard Sub-Assembly product file, the state in Save Management is open and does not need to be saved.

 

Another option for a machining Process file is to change product file state to Rigid. In the Rigid state the position of the components within the sub-assemblies are managed and saved with the top level Vise-Setup.CATProduct file. This will allow you to work with only the product file in a new window. After saving the product file the changes made to the position of components will be displayed in the process file. Below is a example of changing a product file to Rigid from inside a process file.

 

 

This shows the products specification tree with the Vise-Setup.CATProduct file opened in a new window. After changing the process file to Rigid state. Note that the state of the Sub-Assemblies is Flexible.

 

Below shows using Save Management, after this change shows only the Vise-Cut1-Setup.CATProcess and Vise-Setup.CATProduct files have been modified. This is because the position of the components within the sub-assemblies are managed and saved with the top level Vise-Setup.CATProduct file now. No change was made to the Vise-Standard Sub-Assembly product file, the state in Save Management is open and does not need to be saved.

 

 

This topic is one of many covered in the CATIA: Advanced Assembly Design & Management class.