Long pursued as a superior option to traditional materials, thermoplastic composites offer dramatic strength-to-weight benefits along with highly desirable physical and chemical properties. Continuous-fiber thermoplastic composites (like those used by Automated Dynamics) produce lighter, stronger, less brittle parts with greater fatigue properties and chemical resistances than traditional materials and many other composites. But perhaps the most impactful benefit is thermoplastics’ enabling of out-of-autoclave manufacturing.
Recent industry focus has intensified as efficient production methods are pursued to take advantage of these materials. Automated Dynamics, now part of Trelleborg Group, has worked with Composites World to profile some of this work, shining a light on developments Automated Dynamics has achieved during it’s history.
The goal of this work is one-step consolidation of composite materials in place, otherwise known as in-situ consolidation. “The key is the use of thermoplastic rather than thermoset matrices. Thermoplastic materials are liquid when heated to melt temperature and solidify when cooled, but do not need to crosslink like thermosets. Consolidation of a thermoplastic composite (TPC), then, can be accomplished by quickly heating the impregnated reinforcement to the melt temperature of the thermoplastic polymer matrix and then applying pressure as the tape or tows are placed onto a tool and/or a previously placed laminate. True in-situ consolidation (ISC) is a one-step process — no further heating or pressure steps are required after fiber placement or tape laying is completed.” (Compositesworld.com)
Consolidating Thermoplastic Composite Aerostructures in Place, Part 1
Consolidating Thermoplastic Composite Aerostructures in Place, Part 2
Building on this, consideration must now be given to processing speeds. Challengers will cite the slower processing speeds of in-situ consolidation as rendering the benefit of eliminating consolidation steps, such as curing in an autoclave, moot. However, Robert Langone, General Manager at Automated Dynamics, stands behind the in-situ process. “‘In many cases, you bump up against secondary speed issues like managing crystallinity, inertia of the AFP tool and acceleration and deceleration of the robot system.’ He notes that actual part production speeds are not simply based on maximum machine speed. ‘You also have to deal with the complexity of the part, fiber orientations, ply build-ups and drop-offs and stopping and restarting in order to produce near-net shapes and reduce waste,’ he explains. And these issues slow production regardless of whether the material is thermoset or thermoplastic.
Further, Langone contends that the real advantage is found in the extent of the benefits of eliminating the second step: ‘A second consolidation step hurts the economics of the parts overall,’ he says. ‘We use the standard process of prefabricating stringers, ribs and bulkheads, placing these into a tool/mandrel and then fiber placing on top. The resulting in-situ-consolidated, integrated structure is one of Trelleborg’s key capabilities, because you can produce structures without adhesive or fasteners.’ Although welding also eliminates adhesives and fasteners, it is a third step compared to ISC. These extra steps must be factored into the production cost for a true comparison of one- vs. two-step TPC processes.”(Compositesworld.com)
By opening the door for fully consolidated cobonded parts, ISC allows for more complex construction while limiting process steps. Add to this the introduction of laser heating systems as a method for faster production, and the future looks bright for in-situ manufacturing to continue to strengthen its position.
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