CompositesWorld
Issue link: https://cw.epubxp.com/i/532917
23 CompositesWorld.com NEWS N E W S N S N E W S E N W S W 3D-Printed Tooling project engineer Dan Cottrell at Aurora Flight Sciences (Manassas, VA, US). But the key is that AM now enables its users to circum- vent much of the lead time — much of it, simply wait time — and eliminate many of the multiple toolmaking steps that stand between the molder and the beginning of his frst part production- and-assembly cycle. "Metal tools take months," Cottrell points out. "AM tools take days … or hours." Challenges, and benefts Te focus here is on polymeric tooling (3D printing of metal tooling is a growing trend as well), and the sources interviewed for this article use fused deposition modeling (FDM) processes for 3D-printed tooling applications, at least at present. FDM is currently the most mature and widely used AM method. Given those parameters, the use of AM for aerospace tooling can be broken down into three broad areas: 1) Rapidly-produced master models, from which a part splash or reverse is made with more traditional composite materials. 2) Actual layup tools used to produce composite parts, either for autoclave or out-of-autoclave processes. 3) Washout mandrels for trapped tooling. A fourth category — ancillary holding fxtures, jigs, trim tools, or metal forming dies — is expanding as well, and is the subject of "3D-printed fxtures and jigs," on p. 26. AM for tooling still presents some challenges. For one, printer working size is limited, but sources agree that envelope restric- tions do not limit tool size because a large tool or jig can be printed in segments and joined using thermal welding or struc- tural adhesive bonding methods (that said, large-format AM tech- nology is emerging; see "Learn More"). Another challenge: Te use of 3D printing is what Mike Vander Wel, head of equipment and tool engineering for Boeing Commer- cial Airplanes (Seattle, WA, US), refers to as "application depen- dent." Low-temperature, short-run tools for prototyping that won't see high temperatures, for example, are commonly 3D-printed and well within AM's scope. But tools that must withstand the heat of a cure cycle in an autoclave? Tese, he says, are more formidable. "But our application envelope is expanding," he adds, because new materials could expand that space. Heat is problematic, in part, because AM materials are (usually) unreinforced plastic polymers. Tey expand if heated, and it can be difcult to maintain dimensional stability as mold size increases, explains Tim Schniepp, a project manager and additive manufacturing research engineer with extensive aerospace expe- rience at Stratasys (Eden Prairie, MN, US). "Coefcient of thermal expansion [CTE] is certainly a challenge, but there are ways to address or compensate for that," he says. Schniepp and Stratasys application engineer David Dahl recommend recently introduced Ultem 1010, a polyetherimide (PEI) polymer from SABIC (Pitts- feld, MA, US) with a CTE about twice that of aluminum. Of all the materials available, to date, for FDM 3D printing, Ultem 1010 reportedly has the lowest CTE, and a T g of 217°C. Another way for dealing with CTE is to avoid female tool designs, if possible, which can lock the part in the mold, and instead opt for mandrel, or male, approaches, where higher CTE can be used to advantage to provide consolidation pressure. Challenges also include surface fnish and tool porosity. "Te way FDM works and lays down layers, yes, it creates some roughness on the surface, and there is going to be porosity," says Schniepp. Again, he and Dahl say it is not insurmountable. With some hand sanding — they point out that sanding is normally done in any case to fnish tools made with composites — an acceptably smooth surface fnish can be achieved. To deal with AM tool porosity, Schniepp recommends "envelope" vacuum FIG. 2: Aircraft wingskin tools The Boeing Co.'s (Chicago, IL, US) John Melillo reports that low-cost AM tooling reduced development cost for Boeing's Phantom Eye UAV. Many of its parts were made on 3D-printed tooling, including the huge wingskins for its 46m wingspan. Source | The Boeing Co. FIG. 1: Multi-piece male mandrel This CAD drawing from Aurora Flight Sciences (Manassas, VA, US) shows a multi-piece printed male mandrel for an aircraft belly fairing, as assembled for layup of the part. A male tool design can help to mitigate issues with tool growth when heated. For a large part such as this, the use of multiple tool pieces mitigates the current limitations of 3D printers in terms of part size. Source | Aurora Flight Sciences