Simplified representations or subassemblies: which method is best for defining weldments in Pro/ENGINEER Expert Framework?
Today’s CAD technology is not only powerful, but it’s flexible enough to meet the needs of many different types of users. Doing things the right way first time will cut the time it takes you on a project and improve accuracy. Pro/ENGINEER Expert Framework provides two very effective ways to define weldments. Here’s a quick primer on how to select the best one for your project.
Structural design challenges. First let’s review how Pro/ENGINEER Expert Framework can improve the structural design process. In the conventional approach, you define each of the elements in the structure one entity at a time. Entities with complex profiles typically are designed by first defining the profile cross-section then extruding the member. In most cases it is necessary to machine a complex contour, called a cut, into one of each pair of adjacent members so it matches up to its partner.
It takes considerable time to produce the initial design using the conventional method, but design changes are even more tedious. Even a small change, such as increasing the length of the structure, usually changes many elements and cuts. The cross-sections of the structural members may also change and this again requires every cut — involving a changed member — be recalculated.
Pro/ENGINEER Expert Framework improves this process by taking care of the details of creating profiles and cuts so you can focus on proactive design tasks. Structural changes can be made at the same high level at which the structure was created. You can change the dimensions of the structure, move beams, swap one beam size for another or change the beam profile completely. The software will then parametrically update the design — including other beams — and connect and calculate all the new cuts.
Simplified representation. The simplified representation method in Pro/ENGINEER Expert Framework lets you freely structure the assembly into weldments. Then you create drawings of the weldment groups along with the associated bill of materials (BOM). Follow these steps:
Select EFX5.0 > Weld Groups and the weld groups dialog will open
Use the dialog to define a new weldment, add and remove components from existing weldments and re-use existing weldments
Once a weldment has been defined a tree structure is presented in a new window showing its contents
Select the appropriate simplified representation and use Pro/TABLE functionality to create a drawing and BOM
“A key advantage of the simplified representation method is that it allows you to concentrate on creating the design rather than having to be concerned with the structure of the assembly,” says Jim Barrett-Smith, PTC Product Manager.
“Weldments may be defined whenever you prefer. It is often easier to design the entire structure then go back and make decisions on how to subdivide members into weldments. Components can easily be moved into and out of weldment groups and from one weldment group to another at any point in the design process.”
Simplified representation, however, has its limitations. The structure of the weldments is different than the model tree structure. The weldment groups are not handled as separate objects in the product data management (PDM) system.
Copying of complete units, such as structural members with endplates, is harder to achieve with this method. That’s where subassembly comes in.
Subassembly method. The subassembly method offers another approach for creating weldment groups. To use this method, you simply define each component as part of a subassembly when it is created.
Create a subassembly and give it a name
Whenever you open a placement dialog you will have the option to select a subassembly
From that point on, any entity you create will be assigned to the subassembly
One advantage of this method is that the model tree structure matches the weldment structure. The weldment structure is also reflected in the PDM structure which makes it possible to generate BOMs from the PDM system.
Subassembly functionality allows you to open just the subassembly rather than the entire design. This can save a considerable amount of time when working with larger designs. Subassembly also provides the opportunity to duplicate subassemblies throughout the design. This saves time in the initial design as well as when making design changes.
But using the subassembly functionality will mean that you need to plan out how the weldments will be structured in the very early stages of the design. Changing the weldment structure can only be accomplished by deleting and re-creating components. It also takes more time to move parts between subassemblies.
“Both the simplified representation and subassembly methods offer advantages in different types of applications,” Barrett-Smith says. “Choose the method that best fits your project. Understanding the advantages and limitations of each method will help you take full advantage of the capabilities of Pro/ENGINEER Expert Framework."
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