|SolidWorks Featured Author Blog - December 2012|
Multibody vs. Assembly Techniques
Let’s explore some questions that may help you answer the bigger question; “Should I create a model in a single part, assembly, or combination of the two?” The goal is not to tell you to create your models using multibodies or assemblies. Rather it is to compare and contrast some of the aspects of these methods so that you can make an informed choice for each of your projects.
Your actual deliverables may have the most influence your decision on which technique to utilize. What is the end use of the project? Is there a meeting in 2 hours, and you need to show three different concepts for a proposal? Will the parts be quickly 3D printed, painted, and displayed to show a concept before further development? Or is this a revision of a more mature design where you are tasked to provide parts, assemblies, and drawings for a high volume production run.
Will there be drawings created, and what types of drawings. Do you need to document each individual component in a separate revision maintained file? PDM Vaults can handle the additional references, but how does the company part numbering scheme handle the idea of a multibody “master part”? Can you take advantage the “master part” as an Envelope in an assembly file? Do you anticipate any type of animation or motion studies? How about renderings?
Who will you share the files with? Are you working globally with others to complete the design or create a mold or fixtures to manufacture the components? Are the others you are working with familiar with more advanced techniques such as “master part” or in-context relationships? This may be a reason to rethink and simplify your modeling techniques or at least rethink what types of files you will be delivering. Otherwise you may want to plan to train or explain the techniques as part of the hand off, so they can continue to utilize the same efficient modeling techniques.
What types of files will be needed to manufacture the components? Will there be any analysis done on the parts and/or assembled components? Are there subassemblies or portions of individual part files that need to be analyzed? What types of mesh will be used for the analysis? Will you rely on the Hole Alignment tool for checking your hole patterns for alignment? Keep in mind Hole Alignment does not recognize holes in derived or imported bodies.
Design intent is defined as the design specifications of the model itself, and how you will fold the design information such as shape and variations into the sketches, features, and components that make up your project. The complexity of the product and the interdependency of the component parts to one another is one factor that will help you determine which method or combination of methods to use.
Other considerations would be how to handle materials, mass properties, components that need to move and rotate, bill of materials, exploded views, and fastening components including insert nuts / threaded inserts. Will it be to your advantage to insert a part into another part file or just create an assembly? Will you be using any fastening features such as Lip /Groove, Mounting Boss, or Snap Hooks? Any of these tasks can be accomplished utilizing both multibody and assembly techniques. You may need to think ahead and make sure the results meet your deliverable requirements.
The two methods (multibody verses assembly techniques) may also need further thought as to how you will proceed:
For example, creating a multibody part can be done using what is commonly referred to as “master part” technique, or just be a collection of separate bodies tied together by shared sketches. As you add features, you can choose to merge with previous adjacent bodies, or create a new body with the feature. There are several methods for dividing up bodies into more bodies such as Split or the new for 2013 Intersect tools.
If you are creating the individual in-context parts in an assembly, it may be more difficult to blend complex shapes between components, but you can easily share some shapes and profiles of parts within the same assembly using such tools as offset surface, convert/offset edges, and derived sketch.
So as you can see, the answer to the question; “Should I create a model in a single part, assembly, or combination of the two?” is “yes”.
Phil Sluder, mechanical engineer, owner of TriAxial Design and Analysis (http://www.triaxialdesign.com/), Certified SolidWorks Instructor, Certified SolidWorks Professional, a longtime member of the SWUGN committee, and leader of the San Diego SolidWorks User Group. He can be reached at firstname.lastname@example.org