1MAE 455 Computer-Aided Design and DraftingAssembly ModelingMAE 455 Computer-Aided Design and Drafting2Assembly models• An assembly is modeled as a collection of components (parts and sub-assemblies) arranged in a specific way.• Assembly models are useful for:E.g., Widget assembly has components: A, B, C.CBA2MAE 455 Computer-Aided Design and Drafting3Assembly Part Info.• In early Assembly Modelers, all the information for each component was put in the file. This was very inefficient when the same part was used multiple times. E.g., A and C are the same. Information for A and C was included twice.• Now CAD systems keep references to the part or sub-assembly information. I.e., an assembly only keeps track of which file has the part information for each component.CBAWidget Assembly End_part Middle_partMAE 455 Computer-Aided Design and Drafting4Assembly Positioning• Since the details of each component come from a separate part file, it is also necessary to keep track of the location of each component. • The location of each component is given by:– the position of the origin of the part’s coordinate system– the directions of the x, y, and z axes of the part’s coordinate system.BAWidget Assembly End_part Middle_partxyxyxyCxyxyxy3MAE 455 Computer-Aided Design and Drafting5Assembly Constraints• Components can be positioned with respect to each other using positioning commands.• However, modern CAD systems use constraints(or mating conditions) to automatically position components. • Assembly constraints allow components to be automatically re-positioned when the size of a part changes (e.g., if Middle_part becomes wider, component Cautomatically moves right.)• SolidWorks assembly constraints are:MAE 455 Computer-Aided Design and Drafting6Assembly Information• For each component, an assembly keeps track of:–––––––––4MAE 455 Computer-Aided Design and Drafting7Bottom-Up vs. Top-Down Design• Bottom-up: component parts are designed and edited apart from their usage in a higher assembly.1. Create part solid models.2. Combine parts into sub-assemblies.3. Combine sub-assemblies into assemblies.• Top-down: the hierarchy of assemblies and sub-assemblies is designed first, then part solid models are designed in place.1. Create highest level assembly.2. Add empty sub-assemblies and parts to assemblies.3. Create solid models in empty part files.MAE 455 Computer-Aided Design and Drafting8Bottom-Up vs. Top-Down DesignBottom Up Top Down1.2.3. 1.2.3.5MAE 455 Computer-Aided Design and Drafting9• Also known as “Design in Context.”• Solid Models are created such that the part and assembly coordinate systems line up in the assembly.• Neighboring part can be used as reference. Design in PlaceNot Designed in Place Designed in Place