The Assembly Drawing

By Ted Visaya 6/7/2011 (this webpage is CURRENTLY under contruction)

Once all fabrication drawings have been completed or near completion the assembly drawing should be next in line to finish off the design project.

When creating an assembly drawing the designer simply needs to take the fully assembled conceptual layout and place it on a drawing format. The key is to be able to identify as many parts on the drawing with the least amount of views. I found this easier to accomplish with isometric views.

The Assembly Drawing

Assembly drawings show how an assembly of different parts come together. These parts are identified by numbered ballon callouts. These numbers correspond to an item number on the parts list, also referred to as a BOM, Bill Of Materials.

Assembly drawings may or may not have dimensions on the drawing views. If views have dimensions on them it's there for reference only in parenthesis. Drawing views may be isometric exploded views, orthographic views, sectioned views, detailed assembly views, or a combination of all. The main objective is to identify and locate all parts, sub-assemblies, and special features unique to the assembly.

On smaller assembly drawings the PL, Parts List, may be on the face of the drawing for easy reference. On larger assemblies the PL may be a seperate document in the form of a BOM. This is easier to maintain the documentation of the drawing.

The BOM (Bill Of Materials)

The BOM is a simple list of parts extracted from an assembly printed out from a database managed by the designers and engineers. There are document database management programs that they use to create BOMs from data collected from their CAD assemblies drawings.

Since I have more experience using Solidworks I've been exposed to SolidWorks PDM for drawing data management. SolidWorks Enterprise PDM is a full-featured data management program to manage drawing files and BOMs for any size engineering department.

What I love about these kind of programs is that they can extract data from the Solidworks geometry and enter the data into a bill of materials format. The video to the right shows how the program is used.

In the engineering department there usually is one engineer dedicated to managing the drawings and BOMs. This person is responsible for checking the completeness of the design before handing the full drawing package over to the Document Control Center for production release. The design package is usually released Through an ECO. (back to top)

The Sub Assembly

In the order of assembly heiarchy the Top Assembly may have several sub-assemblies reporting to the BOM as a single item.

Sub-assemblies can be separated by specific functions of the Top Assembly and/or a distinct area of the Top Assembly. As an example an electronic control box in a robotic arm assembly is a function of the Robot Assembly. An Arm Assembly that includes the electronic box is a section of the Robot Assembly. There could also be sub-assemblies inside of a sub-assembly. An Assembly and sub-assembly can be as few as 2 parts.

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Other Assembly Functions

There are other ways you can use an assembly drawing for example I had the opportunity of creating the Pneumatics Panel Assembly to the right which displays components on the panel in reference to the Wiring Chart that shows in order how the components are hooked up and determines flow of the pneumatics throughout the assembly. This is a creative way of using the drawing as a flow diagram. Although there is a seperate logic flow diagram with proper pnuematic diagram symbols on a schematic. The assembly drawing I created made it easier for someone to use the logic flow diagram and assembly drawing together.