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As designers what are we really doing with assemblies?
I thought it would be interesting to look at what tasks around real assemblies and subassemblies we need to accomplish without worrying about the mechanics of the CAD tool.
In talking about mates, @bill ended his post with "...it's about creating a tool I can use." This is the bottom line for me.
My grandfather taught me to really treat tools with respect. I remember very clearly him tearing into me the first time I grabbed a crescent wrench, the nearest thing with heft, to bash a lever into place. "Damnit! Use the right tool for the job and get up off your ass to get the right one if it's not handy".
However, a good toolmaker becomes intimately familiar with the context his tools are used in. He knows that we have work to do and a good tool enables that work as transparently as possible.
I'm sure Onshape has done their homework in developing the requirements for their assembly models. Nevertheless I think it would be interesting to lay out what assembly related tasks we need to accomplish. Here are the things that jump to mind. I'm really curious what you guys are dealing with; please add your own items to the list or put your perspective on the things below.
- We manage BOMs
For BOMs I need to group parts and subassemblies into assemblies. I need to be able to associate information with parts and assemblies and be able to run automation (scripts) tools on the whole thing. Some information needs to be extracted from the model (mass properties, part counts, material) and some information the model needs to extract (descriptions for drawings, ...). For myself, manipulating this info in a common format with common tools (JSON/YAML, Python) is preferred to database api's and proprietary tools.
- We manage documentation for fabrication and assembly.
As an assembler, I want to understand the parts, tools/jigs and consumables I need to put the assembly together. Sequence of steps, exploded views, key assembly specs (bolt torque) and checks all help. An entirely 3D interaction could be nice however my experience has been that over-the-shoulder snapshots, a manual of standard techniques, and a few assembly specific notes is the quickest way to document low volume stuff.
- We check the assemble-ability of parts within the assembly as a whole as we design them.
For checking the assemble-ability of parts ("can the parts be assembled together"), I need to start accurately defining their position relative to each other. At minimum I need to lock groups of parts together and move the different groups relative to each other. Theoretically, this could be done automatically with a path planner. Tools and fixtures have to be verified.
- We design the mechanical interface between parts.
Checking the mechanical interface features... Do holes line up? Does the assembly still work when you stack up manufacturing variations? Here we need LMC and MMC configurations of the parts and mates to the surfaces rather than some datum as the surfaces are what changes.
- We use motion studies to verify kinematics and dynamics during the design.
Rigid body analysis is the norm here. I have to admit that I'm not up to speed with the latest tools here. I usually extract mass properties from the model and run them through my custom tools. The ability to export the kinematic chains and loops would be helpful. In the past motion study tools integrated with cad were too simplistic. I have not checked this in a while.
- We generate materials for marketing and design review
Maybe we generate animations using the motion study tools. Maybe we export the model in a format that graphic designers can import. I have been blissfully uninvolved with marketing in my career.
- We evolve the design as it progresses
No project is static. Changes are being made often, and with every change we need to make sure we are not breaking something. I hinted in previous posts how I have used the mate solver as a tool to detect issues.
What else? I know I'm missing things...