Posted by Robert Kiser on Fri, Jan 30, 2009 @ 12:16 PM
There are two basic factors taken into account which define overall "build speed" of rapid prototype systems and 3D printers. One factor is "Total Build Time" and the other is "Post Processing Time". These two totalled together = Total part production time.
Total Build Time is an important consideration when studying the many rapid prototype systems on the market today. Many lay claim to being "the fastest", but you have to consider not only physical build speed that occurs on the machinery platform, but also post processing time (processes involved after the 3D model has finished building). If it takes 4 total hours to build a 3D model on a platform from one manufacturer, and 6 more hours after completion for cleanup, post curing, and other processes prior to shipment, the total build time is 10 hours. If the same 3D model takes 5 hours to build on another manufacturer's platform, but only takes 3 hours for post processing, the total build time is 8 hours. So overall, the rapid prototype system that gets the final 3D model into the shipping box sooner is overall faster and should be a strong consideration of yours.
A general rule of thumb is that a system that builds faster normally has poorer surface resolution than a slower building machine. This is because a faster rapid prototype system is building in thicker layers in the Z-axis (height), while slower systems generally build in thinner layers which allow a tighter compaction and finer surface quality. Slower, higher surface resolution rapid prototype systems make up for the tighter layering process by speeding an array of other processes that occur inside the system during build. Hence, a higher surface resolution system may only lag slightly behind a lower surface resolution system and advancements in technology now have these higher resolution systems building faster. But if post processing time of the faster system is greater than the post processing time of the slower system, end product completion is actually faster using the slower system.
I read a white paper once that listed build comparisons of rapid prototype technologies. I was amazed to find that technologies I knew were slower than others were listed as faster. The test had each rapid prototype system build the same part at the same layer thickness (in this case .012" thickness), started at the same time, then a winner was picked. Problem I found is the fact that all rapid prototype systems don't build at the same layer thicknesses. So of course, the results were skewed. Also, average post processing times were not taken into account. I then did my own notes and found that systems that actually built slower, but had a faster post processing time associated with them, produced the end product faster, much faster in many instances.
So when you look at purchasing a rapid prototype system, ask for fair comparisons of technologies against others. Ask in detail about the post processing procedures. Ask yourself if you can sacrifice surface quality to gain speed. Every person who I have spoken with that purchased a low resolution rapid prototype system has said: "if I had to do it all over again, I would spend the money on a high surface resolution machine".
Posted by Robert Kiser on Sun, Jan 25, 2009 @ 11:55 AM
Yes, and let me explain why.
When most people think of a printer, the image that comes to mind is a device you print a computer generated document to. I asked some very bright associates of mine what came to mind when I asked them what a 3D Printer is. They all stated it was a device that printed blueprints from 2-Dimensional drawings. I told them they were very warm.
All rapid prototyping systems use a concept to place a 2-Dimensional image on top of another. These processes differ in method per system manufacturer, but the end result is the same. This is an additive process to "grow" a shape that takes up more and more space. It is a physical process that requires that each 2-Dimensional image be somehow "fused" together to create the final solid shape. You might then think that this 2-Dimensional image really isn't 2-D after all, because if you could held it in your hand, it would actually be a 3-Dimensional solid mass. The 2-Dimensional images that rapid prototype systems use to create 3D models are in fact a large (or small) series of 2-Dimensional images, like the images you see on a computer screen. The are referred to as "bitmap" images, and their appearance to the naked eye is controlled by what is termed "resolution". The higher the resolution, the easier it is to see the image. There are software programs in existence that can design an image that is 3-Dimensional in appearance on a computer monitor. This 3-Dimensional image is what is called a "Solid Model". This is where the rapid prototyping process begins.
Once the 3-Dimensional image is complete and ready to be created into a hand held object, some neat things occur. The 3-Dimensional image is saved as a Stereolithography file which is a big series of triangular shapes put together to form the image. This file is then imported into the rapid prototype system's application software and maneuvered around for fastest creation time. When ready, the operator starts the process and the 3-Dimensional image file is sliced up into many of those 2-Dimensional bitmap images I mentioned. So now, our software is acting like a printer at this point. How do we take these images and "fuse" them together into a 3-Dimensional physical objet we can hold in our hand? This is where the rapid prototype system comes in.
The PolyJet is a true 3-Dimensional printer. Think of the PolyJet rapid prototype technology as an overgrown inkjet printer. It holds a liquid inside the jetting heads and jets out each individual 2-D bitmap image, on on top of another. Each 2-D bitmap image is jetted out at a certain mechanical thickness, fused together via ultraviolet light, then machined down to a certain height. This is the point at which a 2-Dimensional bitmap image becomes a 3-Dimensional physical objet.
So, are 3D printers and 3D printing technology rapid prototype systems? Yes, indeed, and the classification is called the "PolyJet" technology and is part of the rapid prototype technologies that exist today.