MCAD Modeling Methods-Trends in Design Analysis1 May, 2006 By: IDSA ,Mike Hudspeth
Analysis tools make product design faster and more accurate.
More people are using design analysis than ever before, which is a good thing. If you haven't started yet, you should consider it seriously. Why? Well, you care about the products you make, don't you? You want them to behave in predictable ways. You want to know what to expect. You want the assurance that you've done everything you can to design and verify that your product meets its highest quality standards. Design analysis can give you that.
The Long and Winding Road
The path to market is never straight. Turns and potholes crop up every step of the way. Navigating this road can be a full-time job in itself, never mind keeping your sanity. Design issues, regulatory hurdles, customer misconceptions and management (don't even get started on management!) problems all contribute. It's all a designer can do to develop a new product. Does it really need to be perfect, too?
In the old days, you had to be smart (not that you don't nowadays) and work really, really hard. Long hours, bad coffee, cigarettes and junk food were part of the process. Products got out, but you had to perform many empirical tests. First, you came up with your design and then got drawings made. Your model shop would take days or even weeks to cobble together a one-off version so you could do some testing. Heaven help you if something went wrong.
Figure 1. How light will play over and through your designs can easily make or break a project.
Nowadays, things are much easier. The hours are still long, but the coffee is much better. Product development happens practically overnight. Schedules are tight, but the job gets done because you have tools that let you do what no one ever dreamed could be done. Part of what makes it worth your while to build exacting 3D computer models is what you can do with them. They're not just pretty pictures anymore.
Tools of the Trade
After you've modeled your product—be it a new cell phone or a condominium—you really have the world around your finger. The tools at your disposal can tell you so many things—things that only a few years ago you needed an expert to point out. Let's look at a few of these tools.
I'll grant you that shadow studies aren't something a cell phone designer generally worries about, but those in the architectural trade do. Whether it's a single building or a whole complex, the way shadows play makes a big difference between a successful design and an eyesore. We all know that the sun moves across the sky and casts shadows differently at different times. (Okay, okay, I know it's the Earth's movement. Just humor me.) Products such as SketchUp from @Last Software/Google enable you to build a model and position it as it would be on a building site. You also can simulate how sunlight will enter a room and what the shadows cast will be like (figure 1).
Something product designers deal with is the smoothness of surfaces. How a surface transitions from one side of a model to another can make it flow gracefully or tumble suddenly, disrupting your whole design. Many tools can help with this problem. In the automotive business, they used to (and probably still do) have a room with a grid on all six faces. Designers would park a new car in the room and then just look at how the reflections of the grid flowed around the car. Nowadays, we can do the same thing inside our 3D modeling software. It's called surface analysis, and it comes in handy. You can apply zebra stripes or environment maps; in fact, you can wrap any bit-map image you want onto your model (for an example, see figure 2 in the KeyCreator 5).
Figure 2. Knowing where a part might break helps you to design it so it won t break. FEA can show you how.
For those who don't know what all the hubbub with FEA (finite-element analysis) is about, it's a way to approximate the behavior of your model when given forces are applied to it (figure 2). It could show you where something might break. Most of us already know that. But a lesser-known fact is that an increasing number of 3D modeling programs come with simplified versions of FEA programs in their product bundle. This trend definitely is to our advantage. Although we may not have all of FEA's capabilities at our disposal, we can get a pretty good ballpark idea of how our designs will perform. Obviously, the idea behind offering all this capability for free is that we will get hooked on running the analysis and want more, and then we'll eventually upgrade to the full analysis package.
In This Article
One analysis package included with some modeling packages today is Moldflow. With it, you can glean all sorts of information about how a plastic part will turn out. You import your part into it, usually as an STL (stereolithography) file, and tell Moldflow the gate locations. Then specify what the part is made of. The software has a list of manufacturers and the materials they offer. It's not an exhaustive list, so the software lets you set up custom materials by filling out a form. Depending on the complexity of your model, processing could take a little while, but I've never had it take longer than an hour or so.
If you have a large number of blended edges on your model, Moldflow may warn you your model will take a long time. Sometimes, if you have thin walls in your model, Moldflow may tell you your part isn't going to be a good candidate for processing. It allows you to continue anyway, but with a warning that your results might not be very accurate.
Figure 3. By adjusting the number of injection gates and their locations, you can optimize how plastic fills your mold.
You can pick and choose what information Moldflow includes in the report it generates. It will show how your part will fill (figure 3) and even generate an animation of the fill. The report also reveals what your plastic flow front will look like, what the pressure drop-off will be like, what kind of confidence of fill you can expect, where the weld lines will be and where sink marks might appear (figure 4).
Figure 4. When a plastic part has heavy-duty wall thicknesses, it runs the risk of sink marks. Sinks occur because the thinner plastic cools faster than the thicker plastic. The plastic will shrink and pull away from the intended shape.
Users can derive a huge amount of information. If you upgrade to the full package, you can get modules that do all sorts of tasks. One computes how your model will warp—not only that, but where and how much. These modules aren't cheap—some cost thousands of dollars. But if you want that kind of capability, you can get it.
Analysis on the Rise
Design analysis is an important tool for all kinds of designers. Now that simple packages are increasingly included with 3D modeling software, more people are beginning to experience what they can do with it. The more they see, the more they get comfortable with it. The more comfortable they are, the more they'll use it. And the more they use it, the better the quality of the products manufacturers produce. And that's a good thing for everybody.
Mike Hudspeth, IDSA, is an industrial designer, artist and author based in St. Louis, Missouri.
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