Tape Laying, Fiber Replacement and the CNC

The composite manufacture of aircraft parts requires an integrated, tailored process chain. This is the main reason many of the supply system partners in the aerospace industry prefer to rely on CNC machine automation solutions. The CNC functionality of the Sinumerik 840D guarantees controlled, stable processes.

The aerospace industry increasingly uses carbon fiber-based composite materials for wings, tail assemblies and fuselage segments. Tape laying and fiber placement have now become key technologies in aircraft construction. In the case of tape laying, 70 mm to 200 mm wide tapes made from carbon fibers and composite resin are placed layer-by-layer on a flat support and are then cut off parallel to the edges of the workpiece. Where edges are complex, pre-cut tape segments are used, which requires the tape to be positioned very precisely.

The fiber orientation of the tape must, where possible, conform exactly to the direction of the point tension that will occur in the material during flight. For this reason, the tape must be applied without any tension or folds and with precisely defined pressure. As a result, instead of wider tapes, components with complex curved surfaces such as the segments of the aircraft fuselage, have several very narrow tows placed on the mandrel of fiber placement machines.

To achieve the maximum strength and load capacity of the aircraft component, the tape layers must be applied to each other so that they adhere across the whole surface, without any air or dust entering. Therefore, the quality requirements for placement are uncompromisingly high. To prove out the quality and safety, each composite component is subjected to an extensive, area-wide and nondestructive material test.

If delamination is detected during this test, the entire part is normally rejected, which means a considerable amount of time and material is lost, especially on large-scale aircraft components. The economic and timely manufacture of wings and fuselage parts made from composite materials requires the reliable control of tape laying and fiber placement quality, as well as new solutions for drilling, cutting and trimming operations.

HIGH PERFORMANCE CNC REQUIREMENTS . . .
Different requirements are placed on the CNC for the building processes of tape laying and fiber placement, compared with conventional cutting applications. To coordinate cutting control and motion control in the best possible way for fiber placement, the Sinumerik 840D from Siemens offers synchronizing functions controlled according to actual positions, which synchronize the switch actions of the user or parts program with the motion control and position control. As a result, all the cuts “sit” precisely in their target positions, even at high laying speeds, which produces very clean laying edges.

High-performance transformation functions are also integrated in the Sinumerik 840D, which makes it possible for workpiece coordinates to be programmed. This makes the part programs, in principle, independent from the machine kinematics and also improves clarity and the maintainability of the part programs. Even if an accurate axis-parallel mounting of the mold is not possible, due to the size and weight of the mandrel, high-performance transformation functions guarantee the synchronous programming of the laying head movements and of the mandrel, as well as the appropriate alignment of the laying roller. It is necessary that these structures be designed for genuine five-axis operation or, as is the case with fiber placement, for at least six or seven synchronous axes of motion.

. . . AND CYCLES FOR HIGH QUALITY
In addition, the advanced CNC on these and other production machines must support composite material prep with special cycles for composite drilling and other lightweight construction materials for laser and waterjet cutting and for many other operations. High-performance open interfaces enable seamless logging of the actual values for all the process-relevant parameters and machine data for quality assessment. Here again, programming the workpiece coordinates is a key factor, in order to utilize the results of an automated material test with very little effort, or even automatically for process optimization.

REALISTIC PROCESS SIMULATION
In order to precisely simulate the time-consuming production of large and complex aircraft components, not just geometrically, but also technologically – including all process-relevant machine properties – the Sinumerik 840D CNC has a virtual NC kernel (VNCK) onboard. The real-time control software can be run on a Windows platform without any CNC hardware and enables a realistic simulation of all the CNC functions as a plug-in to conventional simulation systems. The production machine’s data are also applied here. This means that the use of the simulation is no longer restricted only to the pure test of the part programs generated in the CAD/CAM system, but also enables an optimization of both the part program and the major process parameters.

Controlled, stable processes, which lead to optimum results, are an essential prerequisite in economic aircraft construction with a high proportion of composite components. This is the main reason many of the supply system partners in the aerospace industry prefer to rely on CNC machine automation solutions.

Siemens Industry, Inc., Aerospace Center of Competence, 390 Kent Avenue, Elk Grove Village, IL 60007, 847-640-1595, Fax: 847-437-0784, SiemensMTBUMarCom.sea@siemens.com, www.usa.siemens.com/cnc.