Adapting Machining Centers
A few suppliers of machining centers offer models that are suitable for composites, either by themselves or after modification. One such is Haas Automation Inc. (Oxnard, CA). Though the company doesn’t sell machines specifically for composites, a representative says that its distributors and on-staff application engineers will modify a machining center for the materials.
VMC 6535 HTX machining center from MAG Fadal cuts hard metals like titanium. Photo courtesy of MAG Fadal.
One requirement is installation of a dust-extraction system, according to John Nelson, North American Business Manager. “This is mandatory to keep the abrasive dust and debris produced during cutting from getting under the way covers and onto the ball screws where they will cause premature wear.” Haas supplies a dust-collection option for its VF-1 through VF-4 range of vertical machining centers (VMC), and after-market systems are available through distributors.
The company can equip a machining center with options for composites like high-speed spindles and finer-pitch ball screws for greater accuracy. “Composite materials generally need to be cut with high spindle speeds and fast feed rates,” says Nelson.
One recent offering is the GR-408 Bridge Router, which is designed to cut fiber (along with foam and wood). The unit has a 10,000-rpm spindle, 50 X 98-inch traveling table with 1,000-lb. capacity, and high-pitch ball screws. A high-speed machining option yields fast contour speeds without distortion of the program path.
Fadal Machining Centers (Chatsworth, CA) supplies models for hard metals like titanium and invar. While these aren’t for composites, they nevertheless meet another machining need that moldmakers can tap for business: fabricating high-tech metal components.
Stadco uses invar tubing to fabricate tool substructures. The tubing improves autoclave heating and cooling cycles and reduces tool weight. Photo courtesy of Stadco.
Ron Bruno, Global Marketing Director, says the latest offering is the VMC 6535 HTX, a high-powered unit designed for fast finishing, high-precision cutting and rapid material removal. The machine covers a 65 X 35 X 31-inch area in X, Y and Z axes, has a cutting-feedrate of 600 ipm, and travel rates of 900 ipm in the X and Y axes and 700 ipm in the Z axis. The 50-taper, high-torque spindle generates 6,000 rpm. Fadal claims axis-positioning accuracy of ±0.002 inches, and axis repeatability of ±0.001 inch.
Advances in Cutting Tools
A key factor affecting machining efficiency is cutting-tool design. Conventional cutters that work on metal usually create problems with composites, due to the comparatively soft nature of the material and its multilayer structure.
Suppliers find that 3-D cutting edges with tips of polycrystalline diamond (PCD) provide the most effective performance. “It’s a technological leap forward in productivity and tool life, which means lots of dollars are saved,” says Matt Collier, Product Manager for MegaDiamond Inc. (Provo, UT), a manufacturer of cutting tools.
Collier notes that it’s crucial to maintain a sharp edge as long as possible. “To do that you need a material that is abrasion-resistant to the fiber-reinforced composite.” That, he adds, is PCD. But applying PCD to a straight cutting edge will not by itself improve cutting.
“You must form a 3-D cutting edge to properly shear the fibers as the tool cuts material.” Otherwise, the cutting tool will cause delamination and quality problems. “Straight cutting edges and flutes won’t cut composites properly.”
MegaDiamond’s V-tec cutting tools have helically shaped edges for maximum efficiency. To achieve abrasion resistance, grooves are formed in the solid carbide rods and packed with PCD powder. The tool is then sintered in a high-temperature, high-pressure process that forms a covalent bond between the PCD and the rod.
Emuge Corp. (West Boylston, MA) takes a similar design approach with its end mills, which were originally developed to machine glass fiber-reinforced plastics, says Stephen Jean, Milling Products Manager. “The technology works well.”
PCD end mill from Emuge has specially designed cutting edges that provide a clean and accurate trim to composite parts. Photo courtesy of Emuge.
Jean says the tools, which Emuge describes as “solid carbide end mills for fiber-reinforced synthetics,” have two cutting edges: one side angles up and the other angles down. When the tool revolves the cutting direction alternates, creating a scissors-like action that leaves a clean and even cutting surface, with no damage to the composite. The tools can also be used with aluminum castings and hard metals, and come with PCD coatings optional.
The importance of effective cutting tools was demonstrated by the NCDMM. Two years ago, Lockheed Martin was having difficulty machining the composite wing skin of the F-35 Lightning II, an advanced warplane. The cutting tools were only effective for about 9 linear feet of machining and produced rough surfaces, which caused delamination. Due to a tight production schedule, Lockheed Martin didn’t have time to develop an alternative tool. It funded a project at NCDMM to design an improved cutter.
Slusarcyk says the group tapped the expertise of industry partners—Aramco Tool Co., Diamond Tool Coating, Kennametal Inc., McCullough Machine and RNDT Inc.—and in nine months validated a design that maintained its cutting edge over 57 linear feet of wing, improving finishing speed and reducing scrap and quality problems.
The design also reduced the cutting tools necessary for machining the wing to two per plane from 24. Lockheed Martin as a result saves $80,000 in tool costs per aircraft, which equates to $222.6 million over the proposed 2,783-unit order for the F-35—not a bad return for its $105,000 investment in the project.
Manufacturers work under tight delivery schedules and do not have time to shut down production to evaluate new techno-
logy,” Slusarcyk says. “The NCDMM and its partners assist manufacturers in implementing technologies without disrup-tion to the shop floor. It’s not a matter of knowing all the technology—it is about knowing where to get that technology.”
EDO technicians fabricate an aircraft component with tape lay-up. Demand for composites is creating opportunities for machining parts to final spec. Photo courtesy of EDO Corp.
Software Broadens Capabilities
Complementing machining systems and cutting tools are upgraded software programs. Some developments stem from work that suppliers did for tape-laying and other fiber-placement processes. CGTech, for example, was contacted by Boeing, which had purchased its Vericut metal-machining software, to develop a program for fiber placement for the 787.
The result, says Hasenjaeger, is Vericut Composite Simulation (VCS). An add-on to Vericut version 6.2, VCS gives a conventional moldmaker the ability to move into composite fabrication with features like fiber-placement simulation and trimming. In beta testing is a water-jet cutting feature developed for Lockheed Martin, which will be commercially available.
Delcam developed software with features for composites fabrication and finishing. PowerMill is designed for five-axis machining of tooling and parts. Capabilities include fast production of large patterns, engraving of scribe lines to define component boundaries on lay-up tools, part trimming and drilling.
The software’s PowerMill program, meanwhile, generates 2-D prepreg patterns from 3-D component models, and provides nesting simulations that optimize material use to reduce waste and lower fabrication cost.
SolidWorks Corp. (Concord, MA) has added a curve continuous (C2) boundary and freeform surfaces program to its Office Premium software, along with the functionality necessary to analyze and validate designs.
Craig Therrien, Product Manager, says many composite parts need C2 boundary and freeform surface capabilities due to the complex nature of their designs. The software lets users develop the surface design, mechanical design, tooling design and lay-up process. It evaluates load-bearing areas of a part, identifies points of stress and deflection, and analyzes the direction, strength and number of fiber layers necessary for a structurally sound part.
Emerging Business Opportunity
Composites are an emerging opportunity for moldmakers, whose skills in shaping complex metal molds and working with automated processes will serve them well in this market.
The continuing strength of the aerospace and defense industries is increasing demand for efficient and economical techniques of composite fabrication and finishing. Moldmakers are well positioned to meet this need and thereby gain access to new sources of revenue.
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