MCAD Modeling Methods-Virtual Prototyping31 Jul, 2005 By: IDSA ,Mike Hudspeth
TWENTY SHORT YEARS AGO, if you wanted to present a design for a new product, you had two options: rendered sketches or expensive semi- or nonfunctional mock-ups. With the sketch route, you ended up with a static representation of the product revision current at the time the drawing was done.
The mock-up route offered two options, both of which required skilled craftsmen.
- 1. You could run up a fast foam or wooden model that you could turn over in your hand and view from all sides.
- 2. You could have a machine shop make your model. Most companies had their own shops with various levels of capability. (The downside of in-house shops was always scheduling: Everyone wanted a piece of the shop's time.) The advantage of a machined part: You ended up with a fairly accurate representation of your product. Sometimes you could even do some testing with it. To go this route, though, you needed a healthy budget.
Once you had buy-off on your design, you had to test it, and test it, and test it. If testing revealed necessary changes, you had to rebuild the test models all over again. Companies could opt to alter the physical models, but that was often harder than starting over. Often, products took years to get to market. But they worked, most of the time.
Nowadays, we have it so-o-o much better. If things can't really go at light speed, it's very near. When we have a design we need to sell to upper management, we can build a virtual prototype and run it through its paces before anybody even sees it. It boggles the mind what real power we have available right on our desktops.
The process of design hasn't changed all that much throughout history. You think of something, capture it in whatever media you have at hand, and get it built. Today, we have ever more powerful computer tools. I'll leave most of the hardware to the real tech geeks, but I will discuss one of the neatest design tools to pass through my hands in years: the Tablet PC (see figure 1). For making fast sketches, there's nothing like it. Many companies make them.
Figure 1. With a Tablet PC you can sketch right on the screen—anywhere. Because its a computer, you can save and manipulate your sketches, e-mail them and even build models based on them.
Wacom has a similar device, the Cintiq tablet (figure 2), that is wired to your computer. With both, you draw directly on the LCD screen. Many applications take advantage of these devices. Alias StudioTools springs to mind (see my review in Cadalyst April 2005, http://manufacturing.cadalyst.com/0405alias). Together, the hardware and software enable you to draw naturally as you would on a napkin. The difference is that you can take that fast hand sketch and turn it into a 3D model. Alias (and other 3D modelers like SolidWorks, Unigraphics, and so on) lets you import sketches onto planes where you can create geometry by tracing right on the images (figure 3). It's really a great way to capture the exact shape you sketched in your weekly design meeting. You can construct your product in 3D space down to the last detail. But what then?
Figure 2. Like a Tablet PC, the Wacom Cintiq tablet lets you sketch right on the screen. What the Tablet PC offers in portability, the Cintiq matches in sheer size. The Cintiq comes in 17” and 21” displays.
Once construction is complete, you can assemble your product digitally and simulate its function. By setting up appropriate mating conditions, you can put the model through its complete range of motion. By pushing and pulling on the digital model, you can see if the parts interfere. Many 3D modelers offer collision detection capability and will stop the free movement of the assembly at the place where the parts hit. That can eliminate costly mistakes. You can also make some pretty neat animations of the working assembly that you can show to others.
Figure 3. Using software like Alias StudioTools, you can start a design simply by sketching, then trace the sketch to create a 3D model.
The real advantage to virtual prototyping is iteration. By having the entire product modeled down to the bolt, you can perform infinite what-if scenarios. It can be liberating to use the Save As command and then whack away at a model. Once you get something you like, go back and rebuild it parametrically.
A picture is worth a thousand words, but a rapid prototype is worth a thousand pictures. I know, this is about virtual prototypes, but if you are concerned with the heft of your device, or how it feels in your hand, nothing can replace actual hardware. Rapid prototypes are called that because they're generated quickly from your computer models. Imagine designing a hand tool and sending it off to the RP machine and in a few hours you have a part in your hand. We'll look at this exciting technology in more detail next time.
Once your parts are built to your satisfaction, you'll want to test them. You don't have to send them out to an expensive model shop anymore. You can test them right on your PC. FEA (finite-element analysis) can tell if your part will fail and where. You import your data into the analysis environment, assign materials, and define the forces acting on the part and where they act. The software tests your part and shows you the stresses graphically. Mold flow software (figure 4,) can save hours of guessing when it comes to injection-molded parts. You tell the software what the part is made of and where the injection gate is, and the software generates a report that shows how the part will fill. It predicts the confidence of fill, where the knit lines will be and even where air will be trapped without vents.
Figure 4. Analysis software, like this plastic injection molding application from MoldFlow, can identify areas of concern in your designs. Once you see the problems, it's easy to fix them.
Another great thing about a virtual prototype is that once you have something you like, you can cut tools directly from the 3D model. You don't have to worry about whether the shop has measured things correctly or if it's forgotten something entirely. If the numbers are right in the computer file, they'll be right on the cutters, in the tools and in the final parts. You'll know what you're getting. What's not to like?
Most of the time, even with rapid prototypes, you'll want a method to present your design to others. An artist is still handy to have around, but many times what you need is readily available on your desktop. Most 3D modeling packages today come with some level of photorealistic rendering capability. And most of them are more than adequate for in-house presentations to your design team. You just find the view you're interested in and render it. The computer handles the lighting and the textures (once you've told it what you want). You can even place your product in a virtual showroom. Programs like Illustrator and CorelDraw are wonderful for annotating images output from your models. You can add all kinds of callouts and flags to point out different features of your product. You can also send these pictures to marketing or sales. One downside to great images is that when customers see them, frequently they assume the product is farther along the development pipeline than it is. They might ask for parts tomorrow. I'll leave it to you whether that is a good thing.
As does any technology, virtual prototyping incurs costs. Obviously you'll need a good computer. You'll want a large monitor (the biggest you can afford—trust me on this one). If you don't have one already, you'll want a 3D controller like those produced by 3DConnexion (but that's another article). You'll generate a lot of bytes, so you might want to look at storage options, including online storage space. A company called Panasas (www.panasas.com) makes storage hardware (ActiveScale storage clusters) for companies that require large amounts of storage, helping them avoid performance bottlenecks in their data stream. Also, because we're talking wish-list stuff, several companies make rapid prototyping machines for around $30,000. That may sound like a lot, but considering the effect of dropping a physical model into your CEO's hand, it's reasonable.
A word of caution: As helpful as virtual prototyping is, it should not totally replace physical testing. It may one day, but for now you'll want to have results that are real world. Besides, most regulatory agencies require empirical data. That said, building and using virtual prototypes will help your company go farther faster, and for less. Go virtual, and you'll never look back.
Mike Hudspeth, IDSA, is an industrial designer, artist, and author based in St. Louis, Missouri.