Derek Ellis of Computer Aided Technology LLC discusses the Polyjet method of 3D printing.Photo: Keith Norbury
When it comes to the actual 3D printing itself, Computer Aided Technology LLC employs one of two methods, says Derek Ellis, a senior applications engineer with the company.
Polyjet uses a liquid coated polymer resin that is cured with an ultraviolet lamp to thermal set the plastic. Fuse deposition modeling, or FDM, uses thermal plastics than be melted down and reshaped over and over again.
“Once that UV lamp cures that resin, that’s bonded, that’s it,” Ellis said during a presentation at the 2017 Work Truck Show in Indianapolis. “With thermal plastics, you technically can take that chocolate bar, melt it down, pour it back into a different mold and reshape it. (With) thermal sets, you can’t print a part and get it back to grain and wheat.”
By and large, Polyjet is designed for design intent and verification as well as light prototyping. FDM is more suited to manufacturing. However, Ellis noted that there is some overlap, such as for jigs and fixtures, marketing applications, and moderate-duty functional prototyping.
Polyjet has the advantages of fine feature details and materials that can be rubber-like or transparent. FDM materials are more durable, stable, and repeatable.
BMW is now using FDM to create tools to affix the badges on its vehicles in place of machined aluminum tools that would often scratch the paint, Ellis said.
Asked if there’s a rule of thumb of when to employ 3D printing instead of more traditional methods like machining and casting, Ellis said the cut off would be if the job takes three days.
“And the reason I say three-day builds is because if you print one, the next morning you’ve made your mold and the third day you’re casting,” Ellis said. “And now you can just do casting.”
A similar rules applies to a related technology called laser sintering, he said.
Another alternative to 3D printing parts is to 3D print a mold out of silicone and then pour material into it to create a prototype or perform short manufacturing runs. Such molds can be made using Polyjet or FDM. Polyjet is best for occasions where a smooth surface is required while FDM is more suitable for larger patterns.
Similarly, injection molds can be 3D printed for runs of 10 to 100 parts.
“Your objective in the prototype stage is to get a model for 1,400 bucks in a couple of days and start producing,” Ellis said.