Mechanology

Design Automation

It’s worth covering the requirements and the history for this topic.

In a previous role, Mechanology were involved in design of a product that leant itself to parametric design. Its stated here, that despite the engineers’ best intentions, the products usually develop a life of their own and may have their basics in parametric design, but the reality makes the products become something else.

As an engineer involved in this with a 7,000+ hours of design automation experience, the lessons learnt are here to be passed on.

But first some questions for the user tempted to venture down this road.

  • Does the product lend itself to parametric design?
  • Are there lots of variants on the same thing?
  • Are there rules which can be coded into the model or a driving spreadsheet?
  • Is the main push for the design office to have “drawings out by Friday”?
    • If the answer to this is “yes” it is highly unlikely that anyone will have the headroom in time to enable design automation.
  • Does the CAD operator know how to model cleanly and create stable models?
    • Previous models are usually useless, and a great deal of “design intent” has to be introduced into the model. Sadly, most CAD training does not teach this mind set, as there is usually so much for the new CAD engineer take in picking up all the functionality of the CAD system.

The advantages

  1. A new model is defined with few parametric inputs.
  2. The design standards for the model are kept in the model and hard coded in.
  3. Creative people spend their time on creative tasks, not generating yet another adaptor/ bracket/ connector/ flange etc…
  4. Drawing checking time is drastically reduced as all that’s required as checks- are the input parameters. Experience indicates that approximate reductions of 85-90% are easily accomplished.
  5. Modelling time isn’t just reduced but slashed. Previous experience indicates that it’s possible to reduce the time from 13 hours to 11 minutes. A 98% reduction in time/cost.
  6. If the feature, note, tolerance, geometric tolerance, surface finish etc… can be hard coded into the model, as long as the calculations supporting it are stable, then model features don’t need checking to see if they are there or correct. They have to be! – they were hard coded in. It also means that the drawing creator only has to ensure that all the parametric features are displayed on the appropriate view in a suitable matter, not check whether they are correct or not.

 

The disadvantages

  1. Some CAD systems don’t lend themselves to this work easily. Oh dear!
  2. A large chunk of time/resource from the design office is put to one side for the CAD engineer(s) to program the rules in.
  3. The work must have the full support of the relevant senior management. It isn’t a cheap exercise.
  4. It is NOT an IT assignment. It must be done by an experienced CAD engineer.
  5. This is skilled work, and in reality, is only done successfully by those who can:

 

  • Apply themselves.
  • Can model cleanly and in a stable manner.
  • Must understand the product and many (if not all) of its nuances.
  • Understand the basics of writing code.
  • The code in the model is usually simple, and doesn’t allow any links to external libraries. This means some models can have 100’s of lines of code within the model that only the design automation engineer should be modifying. Previous models of the author’s had over 17,000 lines of code to ensure the maths always worked for the models.
  • An appreciation that much of the design office skill is concentrated in maybe a single or 2 individuals with all the risk that entails if they leave.

 

An example

The B16.3 pipe flange.

Although this product is well defined in the standards already, its used here as a tutorial to explain how it all happens. It’s a product all reading this can probably relate to.

The key is to assume that there is no ASME standard defining it already and we have to design a new range for our own purposes.

What would be our main design criteria?

  • Size of pipe
  • Schedule of pipe (wall thickness)
  • Material used
  • Pressure rating
  • Gaskets used
  • Pressure code applied
  • Weld preparation expected
  • Standard tooling sizes used

 

And so on, and so forth

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