Repeatability of 3D Printer rapid prototype systems
Posted by Robert Kiser on Fri, Jan 16, 2009 @ 03:15 PM
Rapid prototype system manufacturers normally state one specific tolerance the part measurements should never exceed across the surface of a 3D model. From experience, a critical dimension on a part may measure +/- .002" off dimension on one side of part, while on the other side, a dimension may measure +/-.003", .001", or .000" etc. The overall reason for this is what is termed "repeatability".
System repeatability speaks to the mechanics and software programs of automated manufacturing equipment and critical subsystems within whole systems. Some manufacturing systems have better critical dimensional accuracy capabilities than others. For example, I'll use a laser traveling across a build area of one foot in the X plane (left to right, or right to left). That laser energy beam looks nice and smooth as seen by the human eye as it draws a bitmap image of a certain depth (layer height in the Z axis) into the medium (powder in this case). What we can't see is that the laser is not actually traveling smoothly, but it is most likely traveling within acceptable parameters specified by the manufacturer and meets the manufacturer's definition for repeatability. It stops and starts (shutters) a little in it's travel and deviates off a straight line a little here and there. The key to good quality of 3D models being produced on a rapid prototype system is to have performance of critical subsystems meeting repeatable performance standards throughout production.
There are deviations in all axes on all manufacturing systems, some systems with better repeatability than others, even though the system may be the same model and manufacturer. For this reason, it is CRITICAL to have good and knowledgeable Field Support Engineers supporting your systems. In the Field, I have never seen a PolyJet part measure more than .005" off actual dimensions in all axes and normally measures no more than +/-.001" to .0025". A maximum dimensional tolerance number is issued by manufacturers as a baseline tool for Field Engineering and Applications of what to expect and target. State of the art software applications have increased repeatability excellently over the last 10 years in Rapid Prototyping and other manufacturing systems. In reality, a manufacturer states a maximum tolerance value average that is normally very high and all systems can be tuned to degrees of calibration for tolerance values of normally +/- .005" and less. Again, it is a baseline number. But in general, the PolyJet 3D printer system produces impressive dimensional accuracy and is the most "repeatable" rapid prototype system I have encountered because it is a 3D printer system.
