Ireland's Mcor Technologies has always stood out from the pack in the additive manufacturing (AM) industry as the inventor of a novel paper 3D printing process that produces vibrant, full-color parts. As beautiful as those prints may be, paper 3D printing doesn’t necessarily have the same industrial appeal as other AM technologies.
However, the Honda Corporation recently demonstrated some impressive industrial applications for 3D printing with paper that may previously not have been considered: producing carbon fiber–reinforced plastic (CFRP) parts. To learn how this was possible, ENGINEERING.com spoke with Mcor CEO Conor MacCormack.
How Paper 3D Printing Works
Mcor's technology is known as selective deposition lamination (SDL) and works as follows:
- A digital 3D model is broken down into individual slices that will make up the layers of the final printed object.
- Paper is fed into the print chamber before an adhesive is selectively deposited into the shape of those slices.
- Another layer of paper is loaded, and a heated plate applies pressure, causing the adhesive to bind the two layers together.
- A tungsten carbide blade slices around the printed layers.
- This process is repeated until the object is complete.
In the case of color printing, each layer is printed on with water-based ink using modified 2D color inkjet printing. The Mcor IRIS system relies on standard sheets of A4 paper, which are printed on using a separate inkjet printer, making it possible to reuse papers lying around the office.
In contrast, the more affordable McorARKe uses a spool of paper and a built-in inkjet head. While it’s not possible to grab paper from the recycling bin for use with the ARKe, MacCormack explained that the paper spool gets around the differences in standard paper sizes worldwide and ensures a smoother printing process.
A large number of clients use SDL for the ability to 3D print realistic and colorful models, according to MacCormack, but some, including Honda, are finding new uses for the technology that may not have been previously considered.
3D Printing Molds for CFRP Parts
There is an increasing number of 3D printing companies looking to enter the carbon fiber space, particularly because traditional methods for laying carbon fiber are labor intensive and costly. 3D printing could offer an automated way for producing short-run fiber-reinforced parts with complex geometries and on demand.
Outside of the Markforged systems, there are, so far, no other carbon fiber 3D printing systems actually on the market. Through Honda, Mcor has found a unique method for leveraging existing paper 3D printing technology for producing CFRP parts.
Typically for short-run manufacturing of CFRP parts, a company might use a CNC machine to cut a mold out of metal. This mold then has CFRP material laid on top of it before entering an autoclave. The turnaround time and cost for such a process can be lengthy and expensive. After coming across SDL 3D printing, Honda has begun experimenting with laying traditional CFRP over 3D-printed paper molds, which are then placed together in an autoclave for final curing.
“We've been working with Honda for 12 months now, and they've been using our SDL technology to see how could it be used in various segments within the Honda corporation,” MacCormack said. “The one that we were most excited about was using it for making carbon fiber parts. The reason they used it is because paper is extremely strong under compression.”
MacCormack pointed out that, when bundled together and compressed, paper exhibits different characteristics than in the form of individual sheets—properties that are more similar to blocks of wood. Because paper doesn't melt, as plastic does, it can withstand prolonged exposure to heat and being under pressure without deformation. And because the tungsten carbide blade cuts have great precision during the initial printing process, the end part has high dimensional accuracy that can translate to the final CFRP part.
“The 3D-printed die can be put into an autoclave running at 135°C with a pressure of one-half of a megapascal for a couple of hours,” MacCormack explained. “That enables Honda to get to a sufficient temperature and pressure to get the carbon fiber to form over the molds. Because of the way that the paper is constructed, the dimensional accuracy (100 microns) doesn’t lose any strength at those elevated temperatures. So, you have a very accurate carbon fiber mold.”
Though it may not always be necessary, it's possible to reuse the 3D-printed part repeatedly, depending on the geometry. This is because the properties of the paper component change very little after consecutive firings. The mold is coated in a release agent, such as a Teflon spray, that makes it easy to pry the CFRP part off of the mold once it leaves the autoclave. As long as this removal does no damage to the paper part, MacCormack said, it should be possible to reuse the paper part many more times.
Altogether, it was estimated that producing CFRP molds with this process would be about 10 times less expensive than traditional CNC molds.
Other Uses for Paper
MacCormack explained that this was not the only industrial application for which paper 3D printing was being used. It's also possible to create molds for sand casting, which involves using a 3D-printed part to make a sand-based negative, into which liquid metal can be poured to create the final part.
“There are automotive companies that are experimenting with our technology for making sand-cast parts,” MacCormack said.“Normally, sand cast objects are large, so you can print multiple parts on paper, place them together, sand cast to make the negative and then pour in the liquid metal.”
He also said that some clients have been using the technology for investment casting or lost wax casting. Traditionally, in this process, a mold is coated in a ceramic shell, which is then placed in an autoclave, burning out the mold and leaving only the shell with which to cast metal objects.
“What's really intriguing about doing that for last wax or investment casting is that when you put the whole part and the ceramic shell into the autoclave, the paper has a much lower thermal expansion rate than plastic or other materials. The tendency with some of the other things that we do with investment casting is that when you put it into higher temperatures, plastic will expand and actually crack the ceramic. Paper doesn't expand as much, so they can actually create some really nice, complex objects.”
Additionally, Honda is able to perform traditional rapid prototyping with Mcor's technology, such as a full-scale wing mirror prototype for wind testing, as well as a scale model of an aerodynamic race car body spoiler for GT Aero. So far, this work has been performed with previous Mcor machines, as the company has not yet gotten its hands on the new McorARKe, which is $17,995. If it really is possible to produce CFRP parts, as well as full-color prototypes with the machine, that may be a low price for those capabilities.