Greg Morris doesn’t spend much time wondering about the factory of the future. He already runs it.
His company, Morris Technologies, specializes in tough-to-manufacture metal components for aerospace, medical and industrial applications. At first glance, Morris seems to operate a conventional machine shop full of high-end CNC machines. Next to the machine tools, though, Morris quietly runs a bank of EOSdirect metal laser-sintering (DMLS) machines, which build up parts from successive layers of fused metal powder.
With six machines, Morris has the world’s highest concentration of DMLS capacity. And he has been using those machines not just to make prototypes but also to turn out production parts. It’s a practice that goes by many names — including rapid manufacturing, direct digital manufacturing, solid freeform fabrication and low-volume-layered manufacturing. All of the names refer to the use of additive fabrication technologies, which were initially intended for prototyping, to make finished goods, instead. Morris believes additive fabrication systems will soon occupy an increasingly prominent space on our shop floors. “We’re on the verge of a revolution in how things are made,” he says.
He’s not the only one on the front lines of that revolution. Boeing, for example, has made extensive use of rapid prototyping machines to produce parts, tooling and manufacturing aids for the F18 and other military aircraft. “We’ve just touched the tip of the digital manufacturing iceberg,” says Jeff DeGrange, an engineering manager with Boeing's Phantom Works. Direct digital manufacturing has also become standard practice in the hearing aid industry. “Literally millions of hearing aid shells have been produced on our stereolithography systems,” says Abe Reichental, CEO of 3D Systems.
Other less prominent users have jumped on the digital manufacturing bandwagon, too. Terry Wohlers, an analyst who publishes an annual report on the state of the rapid prototyping industry, estimates nearly 12 percent of the additive fabrication users now derive some of their revenue from manufacturing. In 2003, that figure was just 3.7 percent. “Rapid manufacturing is a hot topic right now,” he says.
It may soon get a lot hotter. A handful of additive fabrication technologies are already poised to make the jump from prototyping and one-off jobs to full-fledged manufacturing. But before the additive technologies can gain wide acceptance in manufacturing environments — and win over design engineers — they will have to overcome significant technical barriers.
The biggest barrier in the coming years relates to materials. Conventional wisdom holds that the additive parts simply don’t measure up to their molded, machined and cast counterparts when it comes to tensile and other mechanical properties.
And in the case of additive plastics systems, there’s some truth to that wisdom. “The difference in properties varies with the type of machine, the specific material and even the orientation of the part on the build platform,” says Tim Gornet, manager of operations for the University of Louisville's Rapid Prototyping Center. In general, though, he believes the laser-cured photopolymers used on SLA machines have tensile and impact properties best suited to no-load or light-load applications. Thermoplastic additive materials, such as those used by Stratasys' fused deposition modeling or 3D Systems’ selective laser sintering systems, close the gap with molded plastic properties to some degree. But a gap in properties typically remains. “We never tell anyone that our materials are a one-to-one replacement for molded plastics. We do say we get close,” says Fred Fischer, product manager for Stratasys’ fused deposition modeling systems, which build up parts from layers of extruded thermoplastics. With ABS, for example, Fischer says the FDM part is typically within 70 to 80 percent of the molded properties. Other data shows a wider properties gap. With additive metals processes, by contrast, there’s growing evidence properties don’t really suffer compared to casting. Morris says his aerospace and medical customers have spent hundreds of thousands of dollars on mechanical property testing as part of their efforts to qualify the DMLS process for their applications. The results are confidential, but Morris does report that the process’ tensile properties — ultimate tensile strength, yield strength and elongation — are very similar to wrought properties and “better than casting in many cases.” The same goes for fatigue properties, he says.
Another material issue involves freedom of choice. With additive technologies, engineers currently have to settle for a limited materials line-up. As Morris puts it, “There are hundreds if not thousands of alloys for casting and machining. DMLS currently has four.” That lineup consists of cobalt chrome, 17-4 stainless, a bronze alloy and a new maraging tool steel. EOS users have also been beta testing a titanium alloy that should be ready to go in a few months. Arcam, makers of a powder-metal system that uses an electron beam to melt the build material, likewise has a limited materials line-up that currently consists of two titanium alloys and cobalt chrome.
Or consider there are tens of thousands of commercial thermoplastic grades available today, but only a few dozen grades of thermoplastics and photopolymers are available for additive plastic systems. The material choice limitations won’t necessarily cause any difficulties in applications that rely on common plastics. Additive machines, for example, are capable of running variants of nylon, ABS, polypropylene and other common thermoplastics. “Where you start to notice the difference is in the speciality materials,” Gornet says, citing the lack of flame-retardant, conductive, impact-modified, glass-filled and high-temperature grades in the additive fabrication world. “We’ll need a much broader menu of materials for these machines to become more widely adopted,” he says.
Design Data Needed
A persistent lack of design data presents another barrier to the adoption of direct digital manufacturing. As Gornet explains, it’s not so much that current prototyping materials have some shortcomings as the fact engineers have no way of knowing exactly what those shortcomings are. “There’s burning need for design allowables,” Gornet says. He and other prototyping experts cite a lack of long-term creep and environmental data for additive plastic parts and fatigue data for metals as the most glaring examples of this data deficiency.
Ronald L. Hollis, president and CEO of Quickparts, believes the lack of design data makes it easy to overlook the fact additive fabrication systems already can and do turn out parts whose properties are good enough for many applications — even if they don’t exactly match the properties of a conventional manufacturing method. “It all depends on how you want to use the part,” he says. Even though the print may specify an ABS, an SLA photopolymer or selective laser sintered (SLS) nylon may still do the trick. “A prototyping material may very well satisfy the application requirements, but engineers will need access to more data to know whether that’s the case,” Hollis says.
Rapid manufacturing observers expect more and more data will become available as direct digital manufacturing becomes more popular. In the meantime, large OEMs with stringent manufacturing requirements have worked to develop their own property data. Morris says his larger customers have started this process. Boeing has likewise conducted extensive mechanical testing to support its work with direct digital manufacturing, according to Brian Hastings, a materials and process engineer responsible for the aerospace company’s SLS machines.
Stratasys will, in the next few months, make its mechanical property data, accuracy specs and testing protocols public on its website. According to Fischer, inconsistencies in how different companies test their additive parts create “an enormous range” in properties. “We want to take a leadership position in standardizing how some of this data is developed,” he says.
Prototyping Isn’t Production
Using prototyping machines to produce finished goods in some ways represents business as usual for additive fabrication. “Engineers have always done it when they run into trouble with a deadline or need just a few parts and don’t want to bother with tooling,” Hollis says. Making good production parts every day, however, ups the ante on process repeatability, quality control, throughput and reliability. “Today’s additive fabrication systems aren’t completely ready for prime time. They’re still primarily prototyping machines that you can coax into working as manufacturing systems,” Morris says.
Suppliers of high-end additive fabrication machines have been addressing all these manufacturing capability issues, even to the point of developing new machines specifically for direct digital manufacturing. Arcam, for instance, recently came out with a new machine that enables 75 percent larger builds, and consequently greater throughput, than its previous electron beam system.
And Stratasys will, later this month, roll out a new system with a variety of features that target rapid manufacturing. Among them are a larger build volume as well as accuracy enhancements thanks to improvements in the machine’s x-y table, encoders and controls. Fischer says the new machine will also run recently improved materials that close the strength gap with molded plastic properties. And in another nod to manufacturing needs, Stratasys has also developed production control software that can manage builds on one or more machines. Fischer describes the software as a tool for optimizing capacity utilization. For example, it can distribute jobs across multiple machines depending on where they physically fit best.
Even with more capable additive machines, a typical prototyping house would have lots of work to do before it could satisfy the manufacturing needs of a large OEM. According to Boeing’s Hastings, making production aerospace parts requires the adoption of statistically rigorous process control, quality assurance and testing capabilities. He likewise emphasizes that poor repeatability would be a deal breaker. “You have to be able to run the same process over and over again,” he says. That may not be so easy for prototyping shops used to making one-off parts. “It will be very tough for prototyping houses to switch to production,” Morris says. “If they want to do it, they’ll have to adjust to a whole new reality.”
Morris goes on to make a case that today’s direct digital systems aren’t even suitable for standalone use. Even the best direct digital manufacturing systems cannot yet meet his tightest tolerance and surface finish requirements without secondary machining, bench work and polishing. “We still have to leverage our machining capability to achieve our critical tolerances and I don’t see that changing anytime soon,” he says. “I can’t imagine doing what we’re doing without a real machine shop behind us.”
Users of plastic-based systems similarly predict additive systems will coexist with conventional plastics manufacturing methods. “I think you’ll start to see hybrid factories that combine layered manufacturing with conventional manufacturing methods like injection molding,” says Hollis. As with metal machines, the additive plastic machines don’t yet match the tightest injection molding or plastic machining tolerances. And without secondary operations, they lack the surface finish required by cosmetic plastic parts. They also can’t currently approach the production volumes possible with the high-volume injection molding. (See “What Engineers Should Know about Direct Digital Manufacturing” for more information.)
Ready for Prime Time?
With all these factors weighing against direct digital manufacturing, you might wonder, why bother? But, these additive systems already offer design benefits that can offset their manufacturing limitations.
For one, additive machines can produce complex part geometries without regard to conventional manufacturing limitations. Additive fabrication methods based on powder metal beds, for example, can enable parts with interior cavities and features that could not be machined or cast — at least not in an economical one-piece part. “The more complex the geometry, the more that direct metal starts to look like a good option,” Morris says.
The plastic-based processes can likewise enable part geometries that would be impossible or costly to mold. Consider a sphere, for instance, whose exterior is a thin skin and whose interior is an intricate support lattice. “There’s a lot of interest in creating optimized structures whose geometries couldn’t be molded,” Gornet says. Additive processes can also skirt design for moldability rules — including those related to draft angles, avoidance of severe wall thickness transitions and the placement of through holes and undercuts in line with the mold pull. “Until now, engineers designed with an eye on the limitations in their manufacturing processes. Or at least they should have,” Gornet says. “Additive fabrication allows them to design new parts with only their functional requirements in mind. Additive machines don’t care about design for manufacturability rules.”
The upshot of all this design freedom, and the benefit most cited by advocates of direct digital manufacturing, is parts consolidation. “There’s a big opportunity to simplify your BOM and drive down costs when you can consolidate parts in creative ways,” says Hollis.
How long will it take for engineers to recognize the design benefits associated with additive processes? Todd Grimm, a consultant to the rapid prototyping industry, thinks it could take 10 or even 20 more years given the current lack of familiarity with additive machines and the technical barriers associated with the machines themselves. “It’s going to take a long time for direct digital manufacturing to be considered commonplace. We really are talking about the factory of the future here,” he says.
For a handful of applications, though, the future is now. The best known and highest volume direct digital manufacturing niche has, so far, involved applications where mass customization plays a role. 3D Systems’ Reichental points to the hearing aids as one example and also says SLA machines have seen use in the production of casting tools for Invisalign braces. And as the additive machines in general become more capable, Gornet believes they’ll play a stronger role in other kinds of customized medical and dental devices whose geometry is tailored to the requirements of individual patients.
Another attractive application in the here and now involves the use of additive fabrication to produce manufacturing aids such as jigs, fixtures and assembly guides. “These applications make a lot of sense,” says Grimm. In these cases, additive fabrication can provide lead time, cost and design advantages over conventional toolmaking methods. “These applications are very low risk and accessible today,” he says.
And he’s not the only one to say so. BMW has been using FDM parts to create ergonomic assembly and testing tools — including one that helps workers install nameplates on the M3. DeGrange likewise says Boeing has used its digital manufacturing systems not just to make finished parts, but to produce composite tooling and other kinds of manufacturing aids. His vision for the technology also includes its use as a way to support products over long lifecycles — by growing spare parts or tools to make spare parts. “Our products tend to be in service for 20 or 30 years. So this is pretty important for us,” he says.
Morris Technologies, meanwhile, continues to ramp up its direct digital operations and has launched a spin-off called Rapid Quality Manufacturing, which is dedicated solely to making production parts. The company’s largest rapid manufacturing project to date involves the ongoing production of four different turbo engine components in cobalt chrome. Morris says the volumes for this will reach about 450 parts over the course of a year. In 2008, he expects to begin another engine-related project that has similar production volumes but represents a breakthrough for direct digital. “What’s special about the new job is that the part is the first one we’ve had that’s been designed for additive manufacturing from the beginning. You wouldn’t be able to make it any other way,” he says.