3D Printing and Injection Molding: Charting the Best of Both Worlds
How do you choose between 3D printing and injection molding?
According to Plastics Today:
The acquisition of Collider and its Orchid printer technology by industrial 3D-printing company Essentium, and University of North Florida (UNF) professor Steve Stagon’s patent for a 3D-printed mold raise the bar in the quest to reduce or eliminate costly tooling while producing optimally performing parts in greater volumes.
In acquiring Collider’s technology — which prints a thin, dissolvable photopolymer shell and fills it with a traditional thermosetting polymer, all in the same build chamber — Essentium is firmly committing to programmable tooling through digital light processing (DLP).
“We believe programmable tooling, and other parts from our Orchid Platform, will help drive the revolution into polymer-based Additive 2.0,” said Graham Bredemeyer, Director of Photopolymer at Essentium, based in Pflugerville, TX. The technology produces “parts that mimic the strength and surface quality of legacy technologies such as injection molding and CNC machining — but in a fraction of the time.”
Technology accelerates development and production timelines
In terms of production goals, Essentium prefers “to think of the activity in groups of machines needed to produce 50 to 1,000 parts per day and higher,” Bredemeyer added. “We see this as accelerating our customer’s development and volume production timelines by months, if not years, especially in the medical, military, and transportation sectors.”
This best-of-both-worlds approach leverages the core advantages of 3D printing and molding, Bredemeyer explained.
“The DLP direct-print process produces parts as good as the resin utilized. Today, photo resins are not as robust as off-the-shelf materials used for injection molding or CNC machined parts. The Collider technology uses the broader class of thermoset polymers as the base for the finished parts and, therefore, doesn’t suffer these limitations.”
Process overcomes challenges of 3D-printing plastic molds
Meanwhile, Stagon’s patent for a printed injection mold with optimized coatings and cooling channels takes aim at an idea “quite a few groups have looked into,” he said — producing a polymer mold whose performance matches metal molds as much as possible to save time and money.
Stagon’s molds target small to medium batch sizes, and part families with slightly varied geometries, the Jacksonville professor said. “In this area, traditional molds aren’t cost effective — too much capital investment for small batches.” But attempts at printed polymer molds have suffered from several issues:
- Molds hot tear and lose edges and surface features quickly. “You can only get a handful of parts out on each mold, eating into margin in changing out tooling and prepping new printed tools,” explained Stagon.
- Poor cooling means cycle times are 10 to 100 times longer, and solidification and uniformity can become issues. “Full polymer printed molds behave very differently because of the heat transfer differences, and our partners were spending too much time tuning in the processes — cutting into margin, again.”
The UNF professor’s solution? Create a process that preserves surface features “past more than a handful of parts and improves the thermal conductivity closer to a point so tuning injection parameters is decreased. In high-run production, metal molds are still, and always will be, king. Our work pushes the small batch a little closer to aluminum molds and makes the workflow faster with less tuning in.”
For his mold’s coatings, Stagon has borrowed technology from traditional molds.
“We combine electroless and vapor deposition, or ‘sputtering,’ to first ‘strike’ the mold surface to make it conductive. We then plate on 1 to 50 microns of eNi, NiP, or CoP. This gives us a very strong layer that conducts heat really well. On top of this we put classical mold coatings like PTFE Ni and electroless Ni-boron. By making the surface slippery and having good lubricity and release, we are able to preserve the thick structural coating for longer and take some stress off the adhesion between the polymer and plating.”
Meanwhile, 3D printing lets Stagon put cooling channels close to features and position them relative to interior mold features. “With the strength of the metal coatings on the surface, we are able to cut the thickness down to a centimeter or less, in some cases, when the injection pressures are kept low. We are working on getting good temperature profile data for this, but we have seen cooling times decrease by a factor of two in our early prototypes.”