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To accomplish the complex manufacturing problems of machining and drilling Boeing 787 floor beams to the requisite tolerances and to meet the required production rates, Hitco turned to Bertsche to develop a complex 5-axis profile beam milling machine for the purpose.
Hitco Carbon Composites was selected as one of the suppliers to Boeing 787 program for floor beams manufactured from CFRP. The cured floor beam profiles are sawed, edge routed, cut to length and drilled. They are manufactured as ship sets in a demand driven on-off manufacturing environment, each ship set corresponding to an airplane order.
Floor beams in an airplane are those structural members that run crosswise down the length of the airplane. The length of the beam (the width of the airplane) varies as the airplane widens in width going from front to centre of the airplane and then narrows again moving to the rear of the aircraft. While having a similar cross section the each beam is manufactured for different length and has a different hole drilling pattern dependant on the attaching connecting structural elements. In an effort to keep floor beam weight to an absolute minimum, the design of a floor beam is further complicated by gauge (or in this case layup thickness) reduction from end to centre of the floor beam. The floor beam also has a recess section in the centre third section which serves to route wiring and plumbing in the airplane form fore to aft.
Bertsche’s 5 axis machine features automated part setup, part program control of all work holding fixtures, a wave milling feature and 100% part inspection. The work holding fixtures can clamp beams of varying web width, varying flange length and programmable web thickness datum surfaces. The fixtures themselves are repositionable so that they can be prepositioned as part of an automated CNC setup program as well as moved out the way during machining operations to provide better access to certain areas of the floor beam for cutting and drilling operations. The fixtures are individually controlled but also operate as coordinated groups that open and close, lift and retract and reposition in synchronous fashion for part loading sequences, when machining or when measuring parts.
Parts are machined dry. Dry machining is the preferred method of manufacture by the airplane manufacturers to avoid composite material swelling due to coolant absorption by material exposed from cutting. Coolants, especially oil base coolants can interact with the composite material causing the material to swell and the formation of residue that then must be cleaned after part machining. Dry machining also has an advantage because dust containment and removal is an easier problem to solve than preventing dust sludge buildup when the plastic material and cutting fluids forms a sludge that adheres to every crevice and nook in the machine.
For dust containment all machining is done in a fully enclosed machining compartment with integral dust collection hoods that capture air borne dust, directing it out of the machine into a dust filtration system. Composite slugs, chards and similar material are swept into a debris collection chute with a debris pusher device as part of an automatic cleanup cycle. A set of large HEPA filters cleans the air to a safe level and a dust collection drum makes for easy machine cleanup and dust disposal.
Now in full production, the machine drills, mills and saws complete floor beams on all sides in a single setup. The finish machined product is inspected using a full function metrology software package integral to the HMI front end PC. Parts are inspected for dimensional accuracy and statistical data are collected with complete tracking history created for each manufactured part.
While current production rates are already four times faster than by previous methods, continued program optimization and process improvements are being implemented by Hitco with the expectation that floor beam manufacturing times will be reduced by at least another 50%, in the future.
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