Before getting to Tribrid Modeling, let’s spend some time on hybrid modeling. In Part 1 of this series I briefly explained the difference between solid modeling and surface modeling. I also mentioned that solid modeling is good for designing prismatic parts, whereas surface modeling is the preferred method when designing parts with sexy curvy surfaces. Its not that one method cannot be used to do both things. Just that it sometimes gets difficult. Its more a question of choosing to use the right tool for the job.
To design any modern real world part, one often finds the need for using both these methods. This has led to CAD software developers mixing these two modeling methods into the same software. Basically, solid modelers are beginning to add surface modeling capabilities and vice versa. This mixing has led to the term Hybrid Modeling which is basically the combination of solid and surface modeling.
While designing the Lego block in the previous parts of this series, I used only solid modeling. I really didn’t mess with surfaces at all. Let’s change that in this part. Lets assume that for manufacturing purposes the base block of our Lego block should remain hollow but the pins should be solid. One quick way to achieve this would be to delete the last hollow feature and extrude cut a rectangle into the bottom face of the base block. But let’s not do that, and here is why. Lets assume that the Lego block was designed by someone else in another CAD system and I was handed only a STEP file of the model. In that event, the model would not have any feature information which I could use and hence could not simply delete the hollow feature.
I used PowerSHAPE’s surface modeling features to solidify the pins of the Lego block. I exploded the solid body into its individual surfaces using Edit > Convert > Solids to Surfaces. Then I deleted the inner bottom face of the base block as well as the inner faces of the pins.
The red faces you see in the image above are the back faces of the outer skin of the model which have now been exposed. So now we have a surface model that does not describe a closed volume. PowerSHAPE has a brilliant surfacing tool called Automatic Surfacing.
In fact, I could write an entire series just on this tool. I used Object > Surface > Automatic Surfacing to fill the rectangular hole that was created after I deleted the inner faces of the base block and pins.
Although the model looks closed, it is still an open surface model. I knitted the individual surfaces into a closed watertight solid using Object > Feature > Addition. Finally I used Dynamic Sectioning to inspect the solid model. As you can see the base block is hollow but now the pins are solid.
This is all very basic stuff. I am no expert at flying PowerSHAPE 2010. I just started using it yesterday. Like I said before, my point here is to get a hang of the software and see how easy or difficult it is to use. As it stands I have managed to design a cute little Lego block without going through hours of tutorials. I believe that’s good enough to get people who downloaded the software to decide to spend a little more time evaluating the software.
In the next part I hope to actually get to Tribrid Modeling.