By Scott Orlosky, Contributing writer
Most people don’t realize that 3-D printing has been around for over 25 years. As the concept has taken hold and a lot of manufacturers have gotten into the game, the types of products available have proliferated. Just as a quick tutorial, the concept behind 3D printing is simple. The designer takes a digital model of the part they want to produce and slices it into a series of parallel planes (layers). The thickness of those planes depends on the printing technology being used. Then the 3D printer lays down the contents of layer #1 to match that portion of the finished part. Often the balance of that layer is filled with some other material that provides some temporary support, but which will ultimately be dissolved and washed away as the final step. As subsequent layers are laid down the finished part is eventually built up, supporting material is dissolved away and the completed part is revealed.
Some of the first machines used FDM (fused deposition modeling) involving a thermoplastic filament that was fed and melted at a controlled rate. This allowed the material to quickly fuse to the layers below the extrusion head to build up the various layers. A variety of plastics could be used depending on the accuracy and finish required of the final part. Practical materials include ABS, TPU and Peek to name a few.
A notable variation for plastic and even ceramic materials is stereolithography (SLA), where a fluid is selectively “activated” via light causing it to rapidly harden locally. This is similar to UV light-cured epoxies. By using different formulations of the fluid, variations in color and physical properties can be produced. Usually, the liquid is custom formulated for the application.
Of course, certain applications require metal parts, which led to the development of selective laser sintering (SLS). In this process, a bed of metal powder is selectively fused (sintered), often with a laser, in order to build up the layers that make the finished part. The powder is leveled-up in between each pass with the laser to help maintain the geometry. Common materials include titanium and nickel alloys.
Let’s have a look into the lab, shall we?
This is more or less where the mainstream part of the market sits today. But innovation never sleeps and inspired by the 3D revolution, manufacturers have been busy adapting 3D printing techniques and ideas to other useful materials. Take, for example, the fiber composites of Impossible Objects. Their web site has a short video detailing the process. Mats of random-oriented long fiber (carbon or glass) have an image drawn on them with a specialized fluid that traps fine polymer particles. Each mat creates a “slice” through the designed part. These mats get stacked together, compressed and heated to fuse the plastic and fiber together. Waste fiber is then removed leaving the finished part behind. This is a fast process, similar to injection molding in timing and produces strong lightweight parts. Perfect for certain aerospace applications, some consumer products, or places where strength and low inertia would be important.
If you could imagine a plastic injection molding process was crossed with an office copier and combined with a layering process on a hot iron, that would roughly describe the Evolve printer. Based on the same principle as a copier/printer with up to five toner stations, the Evolve printer can do some pretty extraordinary things. Most impressive is that each individual voxel (3D pixel) can be printed with any one of the preloaded material selections. You could print a layer or a row of ABS plastic for example that includes an embedded feature made of TPU, to act as a bumper, or maybe even a gasket. This printer uses electrostatic drums as printing plates to transfer the 22µ particles of the working material. Each slice of the part, once it has been transferred to the final drum, is carefully aligned on the fly (part templates have built-in fiducials that ensure tight alignment) and then fused under pressure and heat to the layer below. This machine is designed to manufacture parts in production volumes, and with the ability to produce parts containing multiple materials, parts can be optimized in terms of performance and weight for specific applications. Look for interest in the consumer goods, automotive industries and the military.
The two above-mentioned technologies are at the commercialization stage. However, if we look slightly upstream into the material labs of the world there are some interesting developments involving industrial diamonds. To be fair, it is not possible to just layer molten diamond on to a substrate to create parts as you would do with plastic. In order to 3-D print a diamond, it needs to be part of a matrix that can fit in with an existing additive manufacturing process. For the scientists at Sandvik, they hit on a stereolithographic process that uses a diamond/polymer slurry to create the original structure. Then, in order to achieve the finished part and to preserve the valuable physical properties of diamond required the development of a proprietary post-printing process. The final product has the hardness, high thermal conductivity, low thermal expansion and superior corrosion resistance associated with diamond. This could have significant possibilities for tooling, heat sinks, bearings and high temperature/high wear applications such as rock drilling and mining.
To really bring home the notion that 3D printing is transforming industries in unexpected ways, you don’t have to look any further than your feet. Adidas is already selling shoes whose soles are made using a proprietary formulation and a stereolithography technique, which they have branded as “4D Shoes”. Adidas can print the soles of shoes that are designed to precisely support your feet depending on your planned activity. From walking to running marathons, they have engineered the sole for precise foot alignment, comfort and performance using inputs from thousands of wearers. You could even imagine a time in the future where you walk into a store and step on a mat that creates a dimensional and pressure map of your feet. While you shop, your matched soles are printed onto a pair of shoes and you leave the store with your custom shoes in hand.
To infinity . . . . .
It’s a brave new 3D world full of exciting developments. Parts as complex as rocket nozzles are already being manufactured using these technologies. One of the fastest growing areas of use are the medical industries: joint replacements and dental bridges to name a few. There may even be a time in the future when you order a replacement part for your home or kitchen and instead of mailing it, the manufacturer just sends a file to your home 3D printer and in 30 minutes or so the complete part has been fabricated in your workshop. I can already hear the old timers lamenting, “In my day we had to wait 24 hours for a package to arrive.” I guess some things will never change.