If your company has not already made the leap into additive manufacturing (AM) to solve production challenges, market predictions indicate you soon might. However, although prices have dropped as the technology has matured, any investment in 3D printing is still significant and needs to be thoroughly considered.
Different 3D printing processes have been developed to print with different materials—polymers, metals, ceramics, hybrids and others—in forms including but not limited to liquid droplets, wire and powder.
ASTM International identifies seven classifications of AM technology, ranging from different types of fusion to extrusion and vat polymerization. That simple categorization, however, belies an underlying complexity, according to Todd Grimm, an AM industry consultant for nearly two decades who also has written extensively on the topic.
“Under each one of those categories there can be one, two, three or even four major interpretations of what that process classification means,” he says. “And then, under that you can have one to 100 or more companies with their own machines and their own interpretations on that. So, like a tree, the industry branches out very quickly.”
Taking the right approach
Although AM may provide an elegant solution to any number of challenges, there are more parameters to consider in selecting the right approach. Beyond the variety of processes and equipment being offered, there is also the question of material selection.
A successful AM implementation begins by first determining the performance criteria for the product, then selecting a material and process that will produce those results. Building prototypes for wind tunnel testing is one example. Plenty of materials would be suitable for modeling an automotive part to see how it behaves in a 65 mile-per-hour wind, but modeling an airplane part to be tested at a wind speed of Mach 1 likely would require a much stronger, stiffer material that may involve a different production process.
For example, consider acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA), which are both thermoplastics frequently used with fusion deposition modeling (FDM) technology—and theoretically might be used with the same printer. However, they are very different materials. PLA is made from organic materials, like cornstarch and sugarcane, whereas ABS is a non-biodegradable petroleum-based plastic.
Parts printed using PLA tend to be smoother and shinier than those printed out of ABS, but ABS provides far greater strength and resilience. Also, because ABS has a higher glass transition temperature, it may have to be printed on a heated surface (which PLA printing does not require) to avoid warping as the part undergoes differential cooling. This latter point, in conjunction with other factors, means that PLA can be faster and easier to 3D print.
A potential 3D printing vendor might say, “You want to use ABS? Great, but let's just do some PLA prototypes to show you the kind of quality and speed we can get.” If you allow this substitution, you may not get an accurate assessment of the technology. For any AM machine, time, cost and quality, as well as other process-related factors, will be different for every material. That difference may be insignificant, but you run the risk of making an incorrect assessment.
The benefits of metal
Although its low barriers to entry and relative simplicity have made plastic the most common medium today for 3D printing, technologies for printing with metal, composites, and other materials present their own benefits. Direct metal laser sintering (DMLS), for example, which is in the powder bed fusion (PBF) family of processes, is a popular AM technology for metals. In DMLS, a laser fuses particles of metal powder to build a part layer by layer. One advantage of such an approach is that because it is additive rather than subtractive, voids can be built into an object that would be difficult or impossible to produce through machining techniques.
“There are a lot of processes to choose from, and each one has different materials and strengths, so it becomes a question of how you blend your needs into what can be done with the process,” says Carl Dekker, president of Met-L-Flo Inc., and AMUG. “You can design the product to take advantage of the material, which typically is where you have the most success. The other option is to accept that you're going to have a material that will not match your production process, which is the case in a lot of prototyping applications.”
Designers also must take into account the material properties that will result from the 3D printing process; for example, to determine whether a secondary process will be required to finish the product. “In any type of additive manufacturing, you’re dealing with the manufacturing of a product and the material at the same time,” Dekker says. “Building in layers will only produce a representation of the CAD file so all secondary processes should be considered in the design phase. Doing this will dramatically help increase the success of you’re additively manufactured products.”
Thoroughly investigating the options is critical before committing to any system, whether for production or prototyping.
“The bottom line on this is you've got to educate yourself on all the tools available in the marketplace that could possibly meet your needs,” Grimm says. “Then, talk with the company supplying the system you’re considering. Ask the tough questions and demand answers. But also talk to the user community that already has it; this is where you’ll get answers to the questions you didn't know to ask.”
Prior to any purchase, experts recommend buying a representative number of parts from a service organization that are produced on the machine under consideration. “And, always evaluate the machine you plan to buy in combination with the material you plan to use,” Grimm says. “By thoroughly testing the platform you want with the material or materials you plan to use, you'll have a much higher possibility of understanding its pros and cons.”
Even when you bring production in-house, it is wise to maintain the relationships you have built with your parts providers. Such arrangements can offer support for growing demand and potentially provide access to additional technologies, allowing you to grow your capabilities safely.