CompositesWorld
Issue link: https://cw.epubxp.com/i/882089
OCTOBER 2017 46 CompositesWorld FOCUS ON DESIGN located. In terms of labor and processing steps, Bolfing contends, "It's a lot easier to build a composite CNC machine than a steel CNC machine." But applying composites to a CNC machine, which had not been done before, says Bolfing, would require substantial design, investment and time. So, the idea simmered in his head until 2015, when he began an earnest effort to apply carbon fiber compos- ites in a CNC machine. e product that resulted — introduced in 2016 — is Autoscale's carbon fiber-intensive Monster cgr-series machine (see photo, p. 44), designed to process composites, foams, clays and lightweight metals. The mettle to replace metal As he designed the cgr-series, Bolfing decided early on to apply composites only where their greatest advantage, weight reduc- tion, would increase speed — the y-axis gantry, the z-axis carrier and the z-axis arm. Other parts, namely the x-axis columns and beams, would be welded steel. "Everything that doesn't move is steel," he explains. "All the moving mass is carbon." Bolfing says he knew that speed would come naturally from the reduced weight of the composite y and z axes. e challenge would be the design and construction of a composite structure stiff enough to maintain the rigidity required in high-precision machining operations. "All three axes have to have equal support," Bolfing says. "at was what I worked on first." Bolfing, who was the cgr-series' sole designer, began in Solid- Works (Dassault Systèmes, Waltham, MA, US) and Rhino (Robert McNeel & Assoc., Seattle, WA, US), but confesses his virtual work on the composite structures eventually had to move to a more difficult shake down in the physical world: "ere is only so much you can do, drawing in CAD. You eventually have to start building things." He focused first on the gantry and fabricated several 8- to 10-ft-long (2.4m to 3m) process panels, using multiple material combinations (UD and woven laminates) to test their weight- bearing capability and stiffness. Bolfing hung from the center of these test panels a variety of weights, measuring deflection with each, and using the results to guide further material combination refinements. en, says Bolfing, "I over-engineered it by about 10% ." Why? As is often the case with composites, massive weight savings convey to designers a margin that allows for use of additional material, with minimal penalty. A steel gantry, Bolfing notes, would weigh about 3,500 lb (1,588 kg). e carbon fiber gantry he designed to replace it weighs only 350 lb/159 kg, "so even if it's 50% overbuilt, it's still incredibly light." e resulting design consists of two parallel 8-by-8-inch (203 by 203 mm) box beams 14.5 ft/4.72m long, featuring aramid honey- comb, aluminum honeycomb and Divinycell (Diab Americas, DeSoto, TX, US) foam core overwrapped on three sides with dry unidirectional (UD) carbon fiber, topped by an outer ply of woven carbon fiber twill. e fourth side of each beam is covered with a carbon fiber composite lattice structure, to provide access to wiring that must pass through the beam. All carbon Replacing extruded steel with a sandwich composite The cgr-series gantry features two infused box beams, comprising a honeycomb-and-foam core over- wrapped with UD and woven carbon fiber. The machine's z-axis carrier rides rails atop the beams as it moves back and forth along the gantry's length.