It is time to shift our discussion of the extrusion system to the component that I see is the most important one in the entire process, even though it's not a part of the machine itself, the 3D printing filming. The substance that your final parts will be constructed from. This art and highly specialized material whose unique chemical properties make this miracle of fabrication possible. Desktop 3D printers don't print just any plastics. They print specific classes of polymers and co-polymers that had been prepared to match the mechanical and chemical properties compatible with a 3D printers themselves. It is thanks to their fairly unusual characteristics that it is even possible to produce such a diverse range of printed parts from machines that I hope you're coming to understand are fairly simple and straightforward. The most important thing to remember for the discussion that follows is this even if you remember nothing else. The nature of the material to be extruded and process followed by the machine to deliver this material into the build volume is tuned in such a way to make it possible to predict successfully how this material will behave. When a specific amount of energy, that's temperature and force driving forward and back are applied to the system. Remember that you are designing for a process and not casting entire parts at one shot in the material that you are selecting. Because of this it is important that before the printer even begins worrying into motion, that the 3D slicer in the control software must successfully plan the paths for how to process those materials, and build the part shell by shell and layer by layer for the entire sequence without the opportunity to monitor and make adjustments along the way. You might see this as preparing for a space mission where you need to launch your project on a rocket and you might not have an opportunity to put your hands on it again until the end of the mission. At the end of the day, if your job instructions for the machine can't be trusted and material is not being deposited at the right flow rate to the right places, or isn't sticking down to the build plate, nothing else about the machine really matters. We're going to discuss the properties that make this planning possible and why it tends to work out even though it's certainly won't with most of the regular substances out there in the world. Before we jump to the discussion of the common types of materials, stuff that may be familiar to those who have dabbled in desktop 3D printing previously, I want to briefly crack open an organic chemistry textbook and share more context for why a number of the popular polymers we are using in this field are perfectly matched to additive manufacturing. For all the discussion online about what can be done with a desktop 3D printer, I think we spend far too little time deeply exploring the nature of the acentric polymers that are themselves the 3D stuff your dreams are made of. All plastics, polymers are large molecules or macromolecules that are created in long strings via the polymerization process. The chemical chaining together of monomers, tiny simple molecules. These long bizarre molecule chains are what is responsible for the range of mechanical properties, stretchy, squishy, bindy, fluid-like behaviors. This specific class of polymers that are most useful to 3D printing of the FFF variety are what are called thermoplastics. Thermosoftening plastics. Thermoplastics are long organic molecules that are joined to each other by a weak intermolecular bonds, bonds that are less sturdy than solid intramolecular bonds. As a result of this disparity between the bonds to keep the long molecular chains intact, and the weaker attractions each polymer chain has with its neighbors allows for secondary melting point called the glass transition where those weaker bonds break apart. But without causing a deep chemical change in the substances as a whole as might happen in a more standard phase transition, when a material is subjected to enough heat to pass it's true melting point and transition more permanently. The result of all this is that these materials can become goopy, malleable, and behave more like liquids without inherently changing. The process of causing the material to melt when reaching that lower glass transition temperature, and then solidify when the temperature drops low enough again, can be repeated again and again without fully degrading the material. What's more breaking and reforming those weak bond intermolecular structures doesn't produce the more dangerous byproducts like gases, soots, and small reactive mono molecules that are the reason that most serious chemistry really needs to be done in a chemistry lab and not in your bedroom. So here we have a magic material science trick that allows us to have most of what we need from melting and reforming without all of the nastiness of a true transformation. Thank you chemistry. So this process can happen in your bedroom without requiring [inaudible] that chemical shields though I don't advise this. Again, nanoplastics are like these. This is a special category. The main two classes of plastics are the thermoplastics that we have been discussing before and thermosets. Thermosets can have a broader range of types of molecular chain links and bonding properties such that when you heat them up or subject them to chemicals they can crosslink and combine them. They come together in ways where you can't use heat and chemicals to separate them again. If you think of two-part epoxies, for example, you'll know what I mean. Once the two component elements react together, you can't unmix them to separate out the original substances. These materials on the whole are not useful for FFF style 3D printing. There is also another small subset of plastics called thermoplastic elastomer materials. These materials can be processed like thermoplastics, but exhibit some of the mechanical properties of rubbers. These are materials used to create flexible materials such as TPUs and TPEs. So let's close the organic chemistry textbook for now and look at what filament is and how we use it. To keep the story simple and clear for now, we are using materials that become running with the addition of heat, and then cool back into a firm solid at room temperature. Because this material is not truly experiencing a phase change, they would permanently change its behavior after this process. It can instead be heated and cooled many times behaving the same every time. As a result, it is not only possible to predict how to build with material that dribbles out of the nozzle, but knowing these properties you can gain these processes to use the filament strand itself as the tool for delivering the running material. As with the hot glue stick, you're able to apply physical force to advance a solid part of the filament forward or retract it back, and as it goes forward it heats up, swells, and become something like a piston in the thermal chamber capable of translating that force in a solid part of the filament into pressure forward on the molten material at the front of the thermal chamber. By continuing to drive the filament forward or pulling it back, the force forward or section back control the behavior of the material as it exits or doesn't exit the nozzle. If this sounds like a bit of a hack, it is, but it is a clever hack. By reducing the number of moving parts down to the fewest possible, you're granted enough control over the rate by which it will be dispensed into the build on flow. That is how you are able to plan these paths with thousands and thousands of moves in every printed object successfully so far at advanced. This is why you're limited to extrudable materials that are compatible with responding with as linear and proportional a manner as possible to the forces applied. One of the properties that makes this possible is called shear thinning, which I've mentioned before means that if you push on the material, it squishes around instead of compressing. Most normal materials compress so you would need a feedback loop to determine what the result is of every change in pressure to properly plan how to reform the material. But by using a predictable material it is possible to know with a fine degree of accuracy just how much material will be extruded when you want to extrude, and how much of retraction reversal the filament feeder will be necessary to prevent material from being extruded at other times. So what is 3D printing filament? As spool of filament is itself a 3D printed object. This coil of material is extruded into this shape at a filament factory where the base polymer is combined with additives such as colorants. There are many materials you can process through a desktop 3D printer these days, and a number of 3D printer models engineered specifically to better handle a broad range of material types, properties, and temperature ranges. So let's take for instance PLA, polylactic acid. A corn starch based thermoplastic that is frequently used for food containers, recyclable, cutlery, that sort of thing. The natural color of this material is translucent to clear. But when you add a dense magenta pink colorant, you get PLA material that looks like this but still behaves much like other PLA. There are colorants added to this and lots of filler materials to help it as it cool, so it doesn't work and also other compatibility strategies to make sure that each new filament behaves the way your machine expects any other material of the same type to behave despite vastly different colorant additives. Having the filament material itself is only half of what you need. You also need a material profile to match it. Now, you can create these yourself via testing and research into resources such as the technical data sheet for the materials, but in practice this work is best done by those with a more intimate knowledge of how the materials were produced and the chemistry you need to the specific formulation you will be printing. Filament manufacturers collaborate with a 3D slicer and 3D printer manufacturers to help reduce printing profiles that account for as many of the unique tweaks to temperature, retraction, flow rate, and similar that need to be accounted for in order to make it possible to plan how to print in this material to match, how the machine will process the material. Automakers have an open filament system meaning that you're not restricted to printing only 3D filament sold by automakers as official materials. In fact, you can see these machines practically any FFF printing material that is at a 2.85 millimeter diameter if you want to. As a result, these machines are often used as a research platform to see new material combinations that are possible. It is both a good thing and a challenge that not all printable materials behave the same way, and exhibit the same mechanical and chemical properties. Even within the narrow band of plastics available for 3D printing at this time, there can be a range of temperature and retraction settings, better adhesion strategies, warping, and layer adhesion properties to consider. So consider a bit of a warning that this topic is vast in our challenge to introduce even just a highlights of this subject to you is compounded by the fact that there are more and more options for what types of materials you can print in a 3D printer every day. With all the startling new composite materials alone, how can we predict what engineering properties will be available to you in the future? As manufacturers and enterprise engineering firms explore the role of desktop 3D printers in a factory and production role, there has been an uptick in efforts on the part of filament manufacturers to offer a wider variety of easily printable formulations. Not just refining the expected materials, but expanding the options for base polymers, fillers, and additives to produce a broader range of manufacturing appropriate materials. Nylons, co-polyesters, TPEs, TPUs, metal filled, and carbon filament reinforced materials. Now, any desktop 3D printer operator can obtain special formulations of PLA, ABS, and co polyester suitable for high temperature, high impact resistance, and chemical resistance applications. Other popular areas to explore medical and food safe related materials for use in hospitals and for production of edible and food safe products. Conductive, anti-static, and insulating materials for the electronics industry are also interesting as well as material engineered specifically for the ease of integrating with secondary mold making and casting processes. Here are a few of these materials now available and why you might consider using them along with resources to help you print, slice, and post-process them. The last thing we'd like to include in this materials introduction is that there are a number of filament options that are using their thermoplastics as a delivery mechanism, but are counting on a secondary material or set of materials suspended in the thermoplastic to provide the intended engineering property. For example, carbon filled, bronze filled, wood filled filaments. They might have as much as 60 percent of their mass made up of this target material with the rest as a combination of thermoplastic and compatibility materials that suits this delivery method to the 3D printer used to process them. As a result, you can see things such as a copper filled filament that has enough copper in it that the surface oxidizes the way you might expect, but it is a lot cheaper than working with that much pure copper. Just make sure to check out the intended composite material you intend to use to make sure your nozzle or core can process it without abrasion damage. There are abrasion resistant nozzles and course as we have discussed. We could spend an entire week on this topic alone, but given the speed of evolution in this field, I'd readily this topic here for now with the basics. With so many of the leading experts in polymer production now trying their hands at producing specialty materials for desktop 3D printing, I suspect that the critical areas of focus in this field will no doubt switch many more times in the coming years. While no single provider offers the full range of a pantomime classic chipset right in the store, checking between a number of providers you're likely to find something pretty close to what you need. Still not finding the color or material property you need, say a color distinct to a brand or context, and have a need for a lot of that material? A handful of filament manufacturers can work with you to deliver a precise colorant mix specific to your needs as a special order. Don't forget that the color you need might be closer than you think, prime your part and paint it.
