What is an assembly?
An assembly or a product, in general, refers to the collection of different parts and assemblies, that together perform a required function. For example, an engine that comprises of piston, crankshaft, camshaft etc. is an example of an assembly. In Catia, an assembly is basically a document with .CATProduct extension that stores information about the collection of different components (parts, assemblies etc.) that the assembly constitutes, and all these parts are held in position / assembled together at their respective working positions. So wherever you open this assembly document, it displays all parts and assemblies that the document constitutes.
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| Assembly shown with specification tree |
So, the assembly design workbench is used to assemble the individual parts by applying suitable parametric assembly constraints. These constraints help restrict the degree of freedom according to their working positions.
The approach to assembly may be either top-down or bottom-up. The bottom-up approach refers to the method of simply assembling the parts that have been made already in the part design workbench, so it’s just a matter of calling these parts in the workbench and assembling them by applying appropriate constraints. The bottom-up approach is used for products that are already validated and perhaps you are re-making them for the purpose of documentation in the new software. We have already studied one part of this, since so far we have been making parts (.CATPart) in the part designed workbench. So, it's now a matter of creating an assembly file with .CATProduct extension in the same folder and calling these parts in the assembly file and applying constraints to them.
The top-down approach method on the other hand refers to the method that is commonly used for new product development. In this case, we first create an assembly file i.e with .CATProduct extension, and the part files (with .CATPart extension) are created and designed from within the assembly design workbench itself, with reference to other parts in the assembly. There may be back and forth in the design of the parts, since reference of other parts is required and is dependent on other parts. You may also use top-down with bottom-up too, where some parts are newly created in the Assembly design workbench, while others are already pre-made and you assemble both.
What’s common between top-down and bottom-up approaches?
A thing that’s common in case of assembly design regardless of whether you assemble parts top-down or bottom-up is the constraints that you apply. In assembly design, parts are constrained with respect to each other, keeping in mind how they will interface with each other in the final product and reducing the degree of freedom to a level that they do not move inadvertently, so generally we aim of zero degree of freedom.
Is there any other use of the assembly design workbench?
Besides, doing an assembly, we specifically check for clash between parts in an assembly design workbench. This is particularly useful in case of mechanisms, engines or any assembly that may have moving parts.
How to create an assembly document and work in Assembly design workbench?
You can create a new .CATProduct file using the shortcut
Ctrl+N and using the option “Product”. Or you can create a new file using the option
File > New. By default, the last workbench used for .CATProduct will be opened up and new file will be created.
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| Ways you can open / navigate to Assembly design workbench |
If the workbench opened is not the Assembly design workbench, you can open it by using the path
Start > Mechanical > Assembly design.
How to change product properties?
Product properties can be easily changed. To do this, select the Product document in the specification tree and right click on the product, subsequently select the properties option.
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| Product properties displayed using right-click in the specification tree |
Using the dialogue box that opens up, you can modify Part number, revision number etc.
Some terms worth remembering
Assembly / Product - The term is used for the document with extension .CATProduct. So, it is essentially a file that contains details about all components that make up the assembly.
Component - It's a generic term is used for all parts, assemblies or sub-assemblies that are added to the product.
Part number - This is used to identify the file used in the assembly. A part number is generally same as file name.
Instances - A component may be used many times in an assembly. Each component is represented in the specification tree as separate using the instance number. Instances refers to the quantity of a component is used in an assembly. All instance will have a unique instance number in an assembly and can be seen in the specification tree.
Active item - You can edit any item in the specification tree by double clicking on the item. Double clicking on the item will make it active and it will be highlighted as soon as you double click.
