This automotive assembly jig includes curves and other features that would have been difficult or even impossible to create using conventional fabrication techniques. Photo courtesy Stratasys Inc.
Take the case of rapid prototyping. Or should that be rapid manufacturing? How about direct digital manufacturing? Additive fabrication? How about…well, you get the idea. The salient point here is that none of these terms includes the word “assembly.”
In fact, when it comes to direct digital manufacturing (or DDM-the preferred term according of the Society of Manufacturing Engineers), assemblers might assume this kind of “prototyping” and “fabrication” technology doesn’t really concern them. However, in doing so they risk overlooking one of the most important aspects of any assembly process: jigs and fixtures.
Not only are these pieces of equipment often very expensive, they can be time consuming and frustratingly difficult to produce and replace. Lead times for new tooling is often measured in weeks. If the final product turns out to be not quite what you wanted, well, that’s just too bad-management wants to get that new equipment up and running!
Along these same lines, in the event a piece of tooling should ever break, replacing it can be a nightmare. In many cases, a less-than-perfect jury rig may be necessary to tide you over until you can get a replacement. This, in turn, can result in quality problems and increased scrap. All too often, jury rigs become permanent.
Now imagine what it would be like to be able to fabricate even the most highly complex fixturing and jigs at will, without any kind of outside help. No more having to worry about your company’s tooling department or an outside vendor misinterpreting your drawings. No more having to coordinate with somebody else’s work schedule.
Better still, imagine being able to create tooling in a matter of hours, as opposed to days or weeks. Sound too good to be true? In fact, it is very much within the realm of possibility, thanks to today’s DDM technology.
By using an FDM machine, engineers were able to dramatically reduce the number of parts making up this test fixture for oxygen valves. Photo courtesy RedEye RPM
How It Works
A modern rapid prototyping system works by taking a CAD file of the component to be produced and slicing it up into thousands of digital “layers,” ranging from 0.0005- to 0.01-inch thick. The machine then fabricates the actual part by depositing thousands of correspondingly thin layers of metal or plastic, via any one of a number of different technologies, including stereolithography, laser sintering and fused deposition modeling.In stereolithography (SLA), a platform is placed in a vat of UV-curable resin and a laser traces out the contours of each layer, curing the plastic. After the pattern for one slice has been cured, the platform is lowered the distance of a single layer thickness, and the laser traces out the next slice-which cures onto the one immediately beneath it. This process continues until the machine has created a completed 3D object.
Similarly, with laser sintering (LS), a laser beam traces out the pattern of each component section over the surface of a tightly compacted layer of photosensitive powder. The heat of the laser then sinters, or bonds, the powder to create the physical object.
By contrast, with fused deposition modeling (FDM), the machine builds up each additive layer via a heated nozzle, which extrudes a thin bead of plastic that immediately bonds itself to the layer below. A plastic filament unwinding from a coil provides material flow to the nozzle.
In practice, all three technologies can be used to fabricate an almost limitless array of complex shapes. However, the resulting components tend to differ in terms of their physical properties, so it’s important to select the correct technology for a particular application.
For example, SLA can be used to fabricate objects from a wide variety of materials, ranging from softer plastics to rigid, high-temperature ceramic-filled resins. As a result, it is employed to produce everything from design prototypes to master patterns for molding tooling.
Similarly, LS can be used to fabricate parts out of such sturdy, functional materials as glass-filled nylon and even stainless. However, cycle times tend to be longer because the parts require a longer cool-down period before they can be handled.
Although FDM does not provide quite the same finish and detail as LS and SLA, it does allow for the use of robust production-grade thermoplastics, such as ABS, polyphenylsulfone and polycarbonate. For this reason, it is often the technology of choice when it comes to fixturing and jig applications.
Rapid prototyping machines allow engineers to create highly complex components completely in-house. Photo courtesy 3D Systems Corp.
DDM in Action
In terms of specific applications, it is still very much early days. However, automated teller machine manufacturer Diebold Inc. (North Canton, OH) provides an excellent example of the potential of this kind of technology.Initially, the company purchased an FDM Titan machine from Stratasys Inc. (Eden Prairie, MN) to fabricate actual product components and subassemblies. However, it didn’t take long before the company was also using the equipment to product low-cost tooling to be used in actual assembly. Specific examples include a fixture for assembling each ATM machine’s keypad and privacy shield.
“Producing the fixtures using conventional machining methods could easily take a week…. FDM enables us to produce assembly and machining fixtures in one quarter the time and at one half the cost,” says Diebold senior mechanical engineer Rich Lute. “The fixtures can be produced to an accuracy of 0.005 inch, which is more than enough for this application.”
Another facility using an FDM machine from Stratasys is the BMW plant in Regensburg, Germany. According to BMW engineer Gunter Schmid, the DDM process not only provides faster turnaround times, it allows him to create balanced, curvaceous, ergonomically friendly tooling that might not otherwise be possible. Among the specific jigs BMW has produced are those used for installing model badges and bumper components. The latter, in particular, have benefited from the use of DDM technology.
“The tool designs we create often cannot be matched by machined or molded parts,” Schmid says, citing the example of a jig in which his department was able to reduce total weight by about nearly 3 pounds, or 72 percent. “This may not seem like much, but when a worker uses the tool hundreds of times in a shift, it makes a big difference.”
Terry Wohlers, president of the rapid product development consulting firm Wohlers Associates Inc. (Fort Collins, CO), says the aerospace industry-which often employs rapid manufacturing to produce complex components like air ducts for jets-is also increasingly using rapid manufacturing equipment to fabricate items such as custom drill guides, jigs and fixtures.
A Streamlined Process
Complementing this design flexibility is an increase in overall process flexibility, which allows engineers to focus their attention on the fixture itself, as opposed to overcoming fabrication restraints. Building even a simple fixture the old-fashioned way often requires multiple meetings to iron out things like design, scheduling, prototyping, and final inspection and acceptance.However, as Todd Grimm, president of the rapid-prototyping consulting firm T.A. Grimm & Associates Inc. (Edgewood, KY), explains, many of these steps simply disappear when producing tooling with the help of a rapid prototyping machine.
“Direct digital manufacturing is not only fast, it’s efficient,” Grimm says. “If provided direct access to a company’s rapid prototyping machines, a manufacturing engineer can design and produce new fixtures independently. The ‘self serve’ nature of this process eliminates all dependencies on others’ schedules, queues and priorities.”
Same goes for repairs and maintenance: In Grimm’s words, “The moment a problem is discovered, companies can devise a fixturing solution that can be implemented in as little as a day. All that is required is 3D CAD data, machine capacity and materials.”
The end result of all this independence and efficiency is not only shorter lead times and less downtime, but better tooling. Because it is easier to produce, manufacturing engineers have the option of creating more than one version to maximize performance on the assembly line.
Along these same lines, manufacturers no longer need to stock replacement tooling in anticipation of a possible problem down the road. Because new jigs and fixtures can be fabricated from scratch in a matter of hours, all that is necessary is that a CAD file be available to create the new part when needed.
“The manufacturing engineer now has the opportunity to prototype and evaluate multiple iterations of a fixture’s design,” Grimm says. “In the time it takes to receive a quote for a conventional process, direct digital manufacturing delivers fixtures that keep manufacturing rolling.”
Of course, for many companies, the idea of purchasing what is often a very expensive piece of equipment-rapid prototyping machines can cost anywhere from $15,000 to several hundred thousand dollars-for the sake of producing fixtures doesn’t make sense economically. However, these same companies can still benefit from the speed of rapid manufacturing by outsourcing the work to one of any number of rapid prototyping job shops.
Granted, you can’t simply plug in your CAD file, turn out the lights and have a brand-new fixture waiting for you the next morning, the way you could if you owned your own machine. But, you can still expect much faster times than when working with a conventional machine shop. For years now, designers have been experiencing turnaround times of as little as 48 hours when ordering prototypes from firms like RedEye RPM (Eden Prairie, MN). There’s no reason manufacturers shouldn’t expect the same kind of service when ordering fixtures.
As an added benefit, this kind of outsourcing allows a company and its manufacturing engineers to get some good real-world experience with the strengths and weaknesses of the different kinds of rapid prototyping technologies out there, without having to make any kind of major investment.
In the event it does make sense for a company to invest in its own rapid prototyping machine, engineers can then be confident they are choosing the best system for their particular needs. “Outsourcing is a great way to test the waters,” Wohlers says.
