We are on the cusp of a new era in experimental aviation like we have never seen before. We often hear doom and gloom from those who have been in the general aviation market and who have seen the downturn in the number of active pilots and airplanes coming off the factory floor. The overused cliché “it’s always darkest just before the dawn” is really apropos in this circumstance. We are here to tell you that the future of aviation looks very bright. There are several paradigm shifting technologies that are changing the world of aviation equivalent to that the Wright brothers first flight, the dawn of the jet age, and Burt Rutan’s contributions to composite aircraft. Some of the most exciting of these new technologies which we have embraced, include, electric propulsion, 3-D solid modeling software, and 3-D printing. Over the next couple of months, we will be writing articles exploring, in-depth, some of these new technologies which are rapidly becoming tangible for the average aircraft builder. In this article, we’re going to take a closer look at the possibilities of using 3-D printing in experimental aircraft.
With today’s proliferation of 3-D solid modeling software available to the average experimental aircraft builder, we are now starting to see the leveraging of this technology into the average builder’s toolbox. We have been using 3-D modeling software for the past 30 years, and “Solidworks” extensively for the last 15 years. We have become so dependent upon it, that we feel it is one of the most valuable tools that we use on a daily basis. With the ability to 3-D model components virtually on your desktop, the cost of design has plummeted dramatically. It allows us to import the 3-D models into other software and export g-code (computer numerical control (CNC) programming language) for manufacturing of components on different CNC machinery. Seeing this potential, we purchased our first CNC machine some 15 years ago. Since then, we have continued to exploit the advantages of this technology and we now operate 6 different CNC machines. The latest of these “machines” if you can call it that, is a 3-D printer.
In the early days of 3-D printing the capabilities of the low-cost 3-D printers were relegated to the hobbyist and much more limited than they are today. Many of the 3-D printers that were capable of building parts for aircraft quality applications were just too expensive. These were hard to justify even for many small aircraft manufacturers, let alone the average experimental aircraft builder. And the quality and capability of the hobby printers just didn’t meet up to expectations. However, the exponential growth in the 3-D printing market has significantly closed the gap between the hobbyists type 3-D printer and the high-end manufacturing 3-D printers. Over the last year or so, we started to see more and more 3-D printers with high enough quality and low enough pricing that the temptation to purchase became overwhelming. One of the tricks that Brian uses to justify the purchase of a new piece of equipment, when in fact it doesn’t really make sense from a business standpoint, is to throw it into the category of a birthday present. The possibility of using the 3-D printer for this article, combined with the birthday present fuzzy math, and the obvious inevitability of needing a 3-D printer to compete in the current business environment, finally met the threshold to justify the purchase of a 3-D printer for “work”.
Having closely followed the 3-D printing evolution for the last several years, when it came time to purchase, we already had a pretty good idea of which 3-D printer we wanted. We elected to purchase the Zortrax M-200 Pro 3-D printer. (Figure: 1) Similar to purchasing an aircraft, there are a lot of different criteria which goes into the decision-making process for any piece of equipment. Being able to produce end-use products of aircraft quality was first on the list. The price point had to be reasonable enough to see the possibility of the machine paying for itself over time.
There are many different types of 3-D printers. The Zortrax M 200 is called an FDM (Fused Deposition Modeling) or LPD (Layered Plastic Deposition) printer. This is a process of fusing together layers of melted plastic. The FDM printers are the most popular printers in the under $2000 price range. The 3-D printing process is really quite simple. Like most CNC machines, the printer uses drive motors in the X, and Y, axes to drive the print-head and another drive motor to control the build platform in the Z axis. It also uses a 4th axis drive motor to control the feed of the plastic into the heated print-head. The plastic print media on the Zortrax M 200 is .069 inch diameter plastic rod and comes on coiled spools. The plastic media is fed into the drive gears on the print-head which controls the feed rate into the heated extruder. The heated extruder is simply a small reservoir in the print-head which can be heated to over 700°F. This melts the incoming plastic media prior to being forced through an extruder nozzle. After the .069 inch plastic media is forced through the extruding nozzle and exits as a .015 inch diameter bead. This bead of melted plastic is now applied to the model on the heated build plate in z-axis resolutions as fine as .0035 inch layers. This allows this new generation of 3-D FDM printers to produce extremely high resolution components.
The selection of materials used in these type of printers is growing on a daily basis. The most popular types of material are ABS (acrylonitrile butadiene styrene) , and PLA (polylactic acid) plastics. ABS plastic is very useful for end use products and is very cost-effective at about $30 per roll. The PLA and other plastics run about $50 per roll. Each roll contains about 1.75 pounds of plastic material. It’s surprising how many parts you can make from a single role of plastic material. The Zortrax M 200 currently has the option for 5 different types of plastic depending on your printing requirements. The company is also currently developing several other exotic media for printing. Many other printer manufacturers have a myriad of printing media including carbon fiber and Kevlar reinforced plastics for high-strength applications. Silicone and rubber media, wood look-alike materials, simulated metals, and the list goes on. Some of the more interesting applications involve using a metal conducting material to print 3-D electronic circuit boards. And, of course we’ve all seen the news headlines, doctors using living cells to 3-D print functional organs for transplant into the human body.
Let’s look at the sequence of events taking place in the process of making a useful 3-D printed part for your aircraft. The first process in creating a 3-D printing part is to create your part in a 3-D modeling software program. (Figure: 2) 3-D modeling software has been around for many years and is now available in many different formats from relatively basic software which can be used for free, to sophisticated modeling programs like Solid Works which can cost several thousands of dollars per year to maintain your subscription. Keep in mind though, even if you are not a 3-D modeling expert there are literally hundreds of thousands of 3-D models available for free download online. For example, we provide all of the 3-D printed part STL (Stereo-lithography) files for the EMG-6 Electric Motor Glider on our website for free.
After you have created your 3-D model, you will need to export the file into and STL file format. Unlike standard CAD file formats, the STL file describes only the surface geometry of a three-dimensional object through triangulated surfaces. These are created using the cartesian coordinate system. Every point of each of the triangles uses an X, Y, and Z coordinate to define their location. Most CAD programs, including the free programs, have the ability to export into the STL file format. (Figure: 3). Next drag-and-drop, literally, the STL file into the Z-Suite software that comes with the Zortrax printer. Working with the software default parameters allows a beginner to press the “print” button and the software creates a raft, support structure, and part layout automatically. (Figure: 4). The Z-suite software is basically a slicing program that converts the STL file into individual layers that will be printed. Within the software, you can scroll through the individual layers to see how the part will be constructed one layer at a time. (Figure: 5) When you are satisfied that your part will print in the orientation that you wish, simply press the “Save To Print” button and save the file on an SD (Secure Digital) memory card. This file contains the “G code” necessary to run the 3-D printer. This is the equivalent of a post processor file and is specific to each type of printer. In the case of the Zortrax printer the file extension is a “.Z-code” file. You can now transfer the data from the SD card to the printer using a simple single button menu-driven interface. Select “model”, select “filename”, and press enter. At this point you can simply walk away from the machine and leave it to its own devices. One of the characteristics of a 3-D printer is that they are relatively slow. A simple part like, the jury strut fairing, which we are using in this article as our example, can take up to 2 hours to print.
The machine will heat the build platform to a maximum temperature of 230°F. and it will then preheat the extruder upwards of 700°F before the printing will begin. Starting with the machine in the cold configuration this can take up to 15 minutes before the printing process begins. The Z-suite software also provides you with information about the length of time required to print the part as well as how much material will be used and the total weight of the completed part, raft, and support material. For this small jury strut fairing, which we are using for an example, we will expect the part to take 1 hour and 49 minutes to complete. We will use 4.58 meters of Z-Ultrat plastic. And the final weight will be 11 grams. If you happen to be in the vicinity of the 3-D printer when it finishes, the printer will give a beep indicating that the process is finished. If you rush in to extract your part from the build platform, you will find that the platform is very hot. Extracting the part from the build platform initially seems rather difficult, but once you’ve developed the technique using a scraper, you soon find it to be a rather painless process. After extracting the part from the build platform, you are left with your part which is still attached to the support structure and the raft. The software designs a raft, which is a platform from the same plastic material as your part is manufactured from. The raft plastic is extruded into the holes located on the heated build a platform. This builds a rigid structure which adheres exceptionally well to the build platform during the printing process. This raft and support structure material is designed and printed in such a fashion that it very lightly attaches itself to the final product. With a few simple tools you can separate the part away from the raft and support structure. (Figure: 6)
Many of the plastic materials are UV resistant and can be placed directly into service without any other processing. The quality of the parts are really quite amazing in their off-the-printer configuration. (Figure: 7).
However, if you’re still not satisfied with the finish quality of the final part, there are many post processing procedures that can be employed to improve the surface finish. We use acetone with many of the plastics to repair cracks or glue pieces together. Acetone can also be used to melt the surface and provide for a more contiguous and smooth surface. The parts can be sanded very easily making them as smooth as any composite part, and many of the plastics are very compatible with painting. Prior to 3-D printers the possibility of making a part like this would be out of the realm of practicality. The cost to develop a mold and produce a plastic injection molded part would require that you produce thousands of parts to even make it worthwhile. With 3-D printing we can design and produce as many prototypes as needed to finally perfect the part, as well as produce functional parts on an on-demand basis. The Z-suite software even contains a cost calculation function as well. Plug in the price per roll of the material that you’re using and the software will tell you the exact cost for the material. By the way, the jury strut fairing that we have used for our example only used $.62 of material. This simply changes everything. The lightweight nature of plastics lend themselves very well to aircraft components. There are many other advantages that we’ve not been able to leverage until now. The ability to build a lattice or honeycomb structure inside of an existing part would be a highly complex process. With 3-D printing, we can simply program a lattice structure into the part to both save weight as well as significantly influenced the structural characteristics. (Figure: 8). The possibilities for 3-D printing in experimental aircraft is almost unimaginable at this point. We are sure to be amazed at the new ideas and products that will be developed by the talented individuals within the EAA community in the next couple of years. At the time of this article, we are brainstorming the best method to provide a file sharing site for all of the EAA members to share their 3-D modeling files for 3-D printing.
3-D printing has become so prolific that there are an unlimited number of companies that will offer 3-D printing services, so you can take advantage of the 3-D printing revolution without having to purchase your own printer. Many businesses like Staples and the UPS store now offer 3-D printing services. Or, possibly, a group of aircraft builders might pool their resources to purchase a 3-D printer for joint use.
Looking to the future, we can see that a 3-D printer will be as commonplace as the desktop printer in your home office. Capt. Kirk would probably be annoyed at the slow speed of printing, but the reality is, the Star Trek replicator exists today.