Basic CAD data management

Introduction

Since it has been a while since I wrote a whitepaper I thought I'd write a short paper on basic CAD data management. I will start with some definitions about document management and also some caveats and assumptions.
CAD is always the most controversial part of PLM implementations and people are much more passionate about CAD than any other system/tool that is in general use inside engineering.

Document management overview - what is it?

Structured Documents

There is an oversimplification that abounds about document management. When I refer to document management I mean rich content documents which are made up of multiple types of data. For example a book might be made up of several word documents (one for each chapter), there could be pictures/illustrations etc and possibly other content.
Document management is the process of managing the versions of each of the items that makes up the “document” and insuring that a version of the document has all the correct versions of sub documents.
This definition also covers CAD, an assembly is made of parts and (usually) in a CAD tool there is a part file (or some other file type) for each part. The situation is usually complicated further by other types of file such as drawings which are also related to parts and assemblies
So a document/assembly (CAD or otherwise) is a structure of documents. In and engineering scenario the structure can be thought of as the bill of materials.

Iterations/Check-in/Check-out

Along with structured documents and CAD most PLM tools allow you to track changes to individual parts and assemblies. As the design progresses you can save the design and the tool will keep track of these iterations. If you find you have made a fundamental mistake somewhere you can backtrack to an earlier iteration and not have to start from scratch. Many PLM tools have a preference for how many iterations to save – typically I’ve seen the default as three. Once a design is finalised these iterations can be deleted (or purged).
Also while editing PLM tools have the concept of check in and out so that you can insure that only one person is editing data at once.

Caveats/Assumptions

In this paper I will try to be a generic as I can be since each CAD tools I’ve ever worked with had multiple file types e.g. PTC’s Pro/E/Creo has assembly and part files and others whereas Siemens’ NX has part files that can also be assembly files too! I’m sure that the situation is different again in AutoCAD and also CATIA.
This paper is only intended to cover some general concepts of CAD data management and will not cover details.

Keep it simple

When working on an approach to CAD data management keeping it simple is a good approach. CAD data/designs are complicated enough without adding too much with the PLM tools etc. I always try to work with the PLM tool as much as possible. Explore out of the box (OOTB) approaches and try to use these along with changes to your company’s design approaches instead of forcing existing techniques into the new tools.

Design approaches

When designing “things” there are two main approaches. Hopefully you are aware of these but here is a quick summary.

Top down

In top down you begin with an overall design and then break it down into sub systems and design these finally ending up working on the components.
I have also seen people design an entire product in one CAD part and then begin extracting the components of the product into smaller component parts.
Top down tends to be a more structured approach to design.

Bottom up

In a bottom up approach you may have a number of components already and build these into a product. It is a more experimental way of working. You could start by designing some of the components and then work on how they fit together. I’ve heard bottom up is a more experimental way of working and could be thought a bit like working on a jigsaw.

Which design approach is best for PLM?

The answer here is both! PLM tools will help you whichever approach you take.

Design driving PLM

One great benefit of utilising a CAD tool within PLM is the “free” benefits you get. For example some PLM tools allow you to define the CAD structure and automatically create the BOM from this; others allow you to build the product the product structure from a set of CAD parts and then open the CAD tool and orientate the CAD models. There are many other examples but these can streamline the process of design.
Having said this the configuration management teams (or whoever owns the bill of materials) will have the final say in how the BOM is structured. So there are process changes and discussions that will need to be ironed out before the full benefits of the “free” BOM are realised!

Part centric or drawing centric

Traditionally companies relied on drawings to be the definition of their products. Many companies still rely on drawings but a richer 3D model of a product can replace the drawing. There are ramifications to this approach and changes of tools on the shop floor are often needed to accommodate this. 3D data on the shop floor can help with assembly/disassembly instructions and quality assurance if tools are available. This approach can reduce errors but incurs training/retooling costs on the shop floor since new technology is needed and some shop floors can be hard on new technology!
Drawings can still play a part in the design of course and a company needs to define what is the single source of truth for their products.

Free Visualization!

Using CAD in the context of a PLM tool opens up the use of 3D visualization tools. Most PLM tools will automatically generate lightweight 3d representations of the parts. These can be configured to be generate each time the part is saved or on release.
Visualization allows others in your company to view the 3d data (and structure) of you product without expensive CAD tools.