Left: Pod construction in female tool infused from the male plug machined in the Posidon, (right) Pod plug machined in the CMS Poseidon www.engineeringnews.co.nz 33 has been used extensively to produce large composite tooling and components for Oracle Team USA’s AC72 America’s Cup racing yacht. Typical composite parts combine reinforcing fibers of Kevlar or carbon with thermoset resins like epoxy and vinyl ester. CBC cures the constituents in an autoclave to produce monolithic single-skin laminates. Often the skins are bonded on either side of a low-density core material to form sandwich panels, dramatically increasing the stiffness-to-weight ratio of the part. CBC constructs the tools (molds) used to build up the composite parts. The tools are fabricated from composites to assure that when they are heated in the autoclave their behavior will match that of the part being formed. “We produce a tool and it doesn’t stop there,” says Tim Smyth. “We’ll build a portion of the part in the tool and then we’ll introduce it back into the CNC machine. After machining operations, it returns for more building and then we’ll come back to into the CNC machine again.” A critical group parts is the daggerboards or appendages or that enable a boat to take advantage of a hydrodynamic phenomenon called foiling. When foiling, a sailing vessel at speed is supported by appendages (also called hydrofoils) that suspend it above the water, balancing lift and drag and maximizing speed. The most advanced appendages are formed in complex ‘L’ shapes that generate both vertical lift and horizontal force. Justin Capitao, CNC composites and metal machinist says, “There is one appendage or daggerboard on each side of the boat, and they work in a relationship with the rudders located at the back of the boat. So you’ve got a boat that weighs perhaps seven tons traveling on a footprint of about a meter long by 400 mm wide. “It’s pretty amazing to think that you can lift that whole boat on a surface area so small.” Manufacture of appendages is “something that we’ve had to perfect as sailing has gone into foiling”, Smyth says. “Foiling imparts a tremendous amount of load on the appendages and makes them a very crucial part to build. We’re a little bit unique here in building appendages from only one tool surface.” Traditionally, rudders, keels, and daggerboards are built in two halves then joined together along the vertical axis. CBC found the parts are more reliable when built from one side up, beginning in the negative female mold. Although that approach necessitates more machining, surface development and programming, “It results in a much more accurate and strong part,” Smyth said. Part designs originate with Oracle Team USA and are sent to CBC. According to Capitao, “We get the CAD files sent over from the states to our little group of designers here and they manipulate them. Basically the files get reverse engineered so we can construct the tools for building the parts.” CAM software is the bridge between the CAD file of a part and the CNC machine, directing the machine and cutting tool movements necessary to produce a part. Capitao has experience in programming in a variety of CAM packages, and said Mastercam (CNC Software, Inc., Tolland, CT USA) suits CBC’s machining needs in a variety of ways. For machining the tools, “Mastercam programming is so easy compared to what I used before,” Capitao says. “The range of tool paths that are available in Mastercam have made my life so much easier,” he adds. “I’m actually physically machining parts probably at least 30 percent faster than with my old CAM system.” One source of the improvement is reduced times for toolpath calculation and error recognition. “In my old CAM system I would have to create copious amounts of wire frame, extra surfaces,” Capitao says. “Then sometimes the software would calculate for an hour and suddenly just stop, with no message to say why it failed. Whereas, if Mastercam got thorough calculating and would encounter a problem, it would stop and say, ‘this is your problem’. If I know where my problem is I can just go back and rectify it and I’m away again. That is where I’ve saved so much time.” When the tools are complete, building up the composite part starts in the negative female half of the tool. “The bottom mould face is where we build the inside skin of the daggerboard,” Capitao said. The skin is machined after being cured, and then the components of the core are added. Machining occurs at each step, and “When the mould with the half-built tool comes in and out of the CNC machine, it needs to be located again,” Capitao says, “The software is great; I can just grab that CAD file and drop it straight into Mastercam, automatically positioned based on a new work board that I’ve chosen, and it just comes back, bang on, every single time.” Accuracy is crucial. A daggerboard can be up to 4m long and because they must smoothly slide on a system of bearings when in use at sea, machining tolerances are between 0.05mm and 0.1 mm. The large size of the daggerboards and other parts results in long machining cycles. “We can run between eight and 15 hour cycle times,” Capitao says. “Lots of times I’ll see the tool path running at 4 o’clock in the afternoon and I’ll come back at 7 o’clock the next morning and the machine’s still running on the same tool path.” Capitao says the tool paths generated by Mastercam are smoother “and that makes my big machine run smoother”. He notes that the software has features that accommodate part design as well as machining. “Now that there is Mastercam for Solidworks you can design a part and write the tool path within Solidworks. This part building system is included in Mastercam, and there are no extra fees to pay. It’s such a powerful package and such value for money. If I were to ever open my own business and needed a CAM package, that’s where I’d go.” In addition to its comprehensive composite manufacturing capabilities, CBC also has a dedicated metal machining shop with two Mazak CNC machining centres, a Mazak CNC lathe, and a Haas UMC-750. The machines are capable of producing complex parts up to 2m x 0.6m x 0.6m out of any metal or industrial plastic, to a dimensional accuracy of 0.01mm. CBC makes its 5-axis CNC large envelope machining capabilities available to the wider composites industry, including the civil infrastructure, architecture, aviation, energy and entertainment sectors. Recent projects include tooling for helicopter blades, a light sport aircraft, the mining industry, and an architectural roof for a historic site, as well as industrial wastewater manhole covers and even a 1.2m diameter disco ball (which required 5-axis machining of a perfect sphere to a surface tolerance of 0.2 mm). The variety of projects demonstrates CBC’s combination of technical skill, responsiveness, and creativity.
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