CompositesWorld
Issue link: https://cw.epubxp.com/i/866813
NEWS 79 CompositesWorld.com Automated Preforming, Part 2 Savings through simulation Composites consulting company CIKONI (Stuttgart, Germany) has applied its expertise in composites design, finite element (FE) analysis and advanced simulation to offer solutions for automated preforming. "Typically, preforming is thought of as a passive process, where you apply pressure and produce a preform," says CIKONI co-founder Dr. Farbod Nezami. "But with our approach," he contends, "you can act upon the preform to dramatically improve its quality and also the weight reduction and performance of the finished part." One part of CIKONI's approach is called active interlayers. ese are metal sheets placed between the plies at a preform's outer edge, which are then stimulated with piezo actuators to reduce friction. When combined with tailored clamping of discrete plies, the active interlayers can reduce or eliminate wrinkles and other defects in preforms with complex geometries. e active interlayers are not part of the finished preform, but instead are removed and reused. "is approach is not appropriate for every situation," Nezami advises. "You need to have a certain degree of design complexity and a need for high quality." Although the interlayers are not expensive — just laser-cut sheet metal and very low-cost actua- tors — using them is a multi-stage process that relies on computer aided engineering (CAE). Nezami explains, "We use FE-based draping simulation to produce a forming limit diagram which helps us to identify and assess areas of risk for wrinkles and/ or fiber waviness." CIKONI then tailors the arrangement and forces imposed by the active interlayers to remediate only these areas. A recent case history is CIKONI's work with Mercedes-Benz (Sindelfingen, Germany) on an E-coupe model decklid. e woven carbon fabric preform, surrounded by active interlayers, can be seen in Fig. 1 (above). CIKONI performed a draping simulation that identi- fied the need for dart cut-outs in both the 0°/90° and ±45° NCF layers (Figs. 1a & b). e subsequent forming limit diagram was then used to design the active interlayers, which were clamped in different areas (green funnels and hashed boxes in Fig. 1b). "ese clamping areas were tested via iterative simulations and then optimized experimentally," explains Nezami. "We were able to remove the initial fiber waviness completely and reduced the size of wrinkles from 11 mm to 3 mm, so that they remained only outside of the main load-carrying and visible areas." Although Nezami argues that active interlayers are only one possible solution, for Mercedes- Benz, CIKONI developed it into a low-cost automated preforming system for mid-range part volumes with a 3-minute cycle time, including automated cutting and handling. 3D preforming vs. 2D and 2.5D orsten Groene, managing director of the preforming technology company Cevotec (Taufkirchen/Munich, Germany), contends that most automated preforming processes output a 2D preform that still requires a forming step to achieve a 3D composite part. "It is difficult to achieve different thicknesses within the preform with FIG. 1 Active wrinkle/defect prevention Active interlayers are metal sheets — placed between plies at the outer molded edge during preforming — which are stimu- lated with piezo actuators to reduce friction (above). Active interlayers can reduce or eliminate wrinkles and other defects in complex geometry preforms when combined with tailored clamping of discrete plies (shown above left). Based on a draping simulation and subsequent forming limit diagram, active interlayers were developed to achieve wrinkle- free preforms for a Mercedes-Benz E-coupe model decklid, applying diagonal force to 0°-90° NCF layers and 0°-90° force to ±45° NCF layers (a and b, bottom left). CIKONI (Stuttgart, Germany) developed it into a low-cost automated preforming system for mid-range part volumes with a 3-minute cycle time, including automated cutting and handling. Source | CIKONI GmbH