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Step One: Choose Your Model Management Scheme

At Lunar, we primarily use the Master Merge and Skeleton Model management schemes, depending on the nature of the product design and the client’s preferences. Review all four choices to determine which is best for your project and work style.

Regardless of which option you choose, you begin by creating a Master Model as a single part that comprises most or all of the complex surfaces in the design. The Master Model enables you to visualize the complete ID before you create (or “break out”) parts, especially if you merge all surfaces.

Option A
The Basic Master Model

With this approach, you make multiple copies of the completed Basic Master Model and turn each copy into a unique part by deleting any unnecessary geometry. You then merge the remaining surfaces and turn each part into a solid model. To make ID changes, you modify surfaces in each part separately. Although the Master Merge and Skeleton Model functionality in Pro/ENGINEER has superseded this approach, it is worth mentioning as a historical precedent to these newer and more reliable functions.

Each part in the Basic Master Model is completely independent from other parts or assemblies and contains only its own relevant complex surfaces, allowing different people to make ID changes simultaneously. Nevertheless, making dimensional changes and redefining geometry part by part can be time-consuming and error-prone, especially for complex assemblies. To make this option successful, excellent team communication is essential to ensure that ID changes made to one part are duplicated in all others.

This approach also involves making multiple copies of the Master Model, and turning each copy into a unique part by deleting any unnecessary geometry. You assemble the Master Model and all the parts into a top-level enclosure assembly using coordinate systems. You then write assembly relations that tie all identical geometry in each part to the Master Model.

To make design changes, you simply modify the Master Model and regenerate all parts in the assembly. Each part will update based on the assembly relations. While a step ahead of the Basic Master Model method, this approach still lacks the numerous model management benefits of the Master Merge and Skeleton Model techniques.

Like the first option, each part contains only its own relevant complex surfaces, so different people can work on different parts and make changes simultaneously. In this case, though, the Master Model now controls all ID geometry, saving time and reducing errors during the revision process.

The downside is that setting up assembly relations can be tedious. Moreover, the parts update only when regenerated in the assembly. This means you can make design changes in a part and unwittingly fail to update the Master Model. The next time someone regenerates all parts in the assembly, the assembly relations will drive the geometry back to the last state dictated by the Master Model. What’s more, design changes that involve redefining portions of the cosmetic geometry not only require part-by-part updates, but also the rewriting of assembly relations.

Option C
The Master Merge.

With the Master Merge option, you again start with a complete or nearly complete Master Model, but assemble it into a blank “dummy” assembly via coordinate systems. You create a new part by assembling a default/start part into the assembly using the same coordinate system, and then merging (using Adv Util, Merge) a copy of the Master Model into the part.

Once you complete the first part, you can actually discard the original dummy assembly. Create additional parts by making as many copies of the first part as you need, and then simply rename each part. To make changes, modify the Master Model and regenerate the parts with or without the assembly. The merged features in each part update automatically.

The Master Merge option has all the benefits of the Master Model with Assembly Relations in that it saves time and reduces errors during ID changes. It further enforces centralized ID control because changes now require a conscious effort by the user to open up the Master Model. Meanwhile, parts remain completely independent of any assemblies, updating automatically as long as the Master Model is stored in RAM.

You can even execute multiple or nested Master Merges in a part—for example, one merge that controls overall cosmetic geometry and one that defines subassemblies in greater detail. A laptop computer, for instance, could have a primary Master Model that describes shared features such as mating surfaces, hinge axes, and latch positions, as well as secondary masters for the top and bottom clamshell subassemblies.

The drawback is that each part contains all of the complex surfaces and hence the extent of the entire assembly as defined in the Master Model. This means small parts can be bogged down with excessive geometry. In addition, parts will not regenerate successfully after modifications, even on features unrelated to ID, unless you keep the Master Model stored in RAM or you set the merge to Read-Only.

Option D
The Skeleton Model.

As in the other three approaches, this option involves assembling the Master Model into a top-level enclosure assembly via coordinate systems. But before proceeding, you designate the Master Model as your Skeleton. You again assemble a default/start part using the same coordinate system, but unlike the Master Merge, you use the Copy Geom command to transfer the applicable geometry to each part. You create additional parts by repeating this process, rather than by making copies of the first part. To make changes, you modify the Master Model and regenerate the parts with the assembly in session, updating the copied geometry features of each part automatically. You cannot, however, delete the top-level assembly without dire consequences.

Like the Master Merge approach, the Skeleton Model saves time and reduces errors during ID changes. In addition, each part contains only its own relevant complex surfaces and has a relatively “light” geometry (compared with the Master Merge option). Features created using Copy Geom are frozen when the assembly is not in RAM, letting you modify other features and regenerate parts without failure.

On the downside, your Skeleton assembly must reside in RAM in order for changes to your Master Model to carry over to all parts. In addition, initial setup of individual parts can be time-consuming because each is likely to need a unique set of Copy Geom features. Subsequent part modifications can require redefinition, addition, or deletion of pertinent Copy Geom features. Moreover, you are limited to one Skeleton per part.