When Hitco Carbon Composites was selected as one of the suppliers to Boeing’s 787 program for floor beams manufactured from carbon fiber reinforced plastic (CFRP), it turned to Bertsche Engineering to develop a complex 5-axis profile beam milling machine to help Hitco meet tolerance and production specifications.
Bertsche incorporated several features into one automatic machining system. The resultant full 5-axis machine features automated part setup, part program control of all work holding fixtures, a wave milling feature, and 100% part inspection. The complex work holding fixtures can clamp beams of varying web width, varying flange length, and programmable web thickness datum surfaces. The fixtures can be prepositioned and repositioned as part of an automated CNC setup program. They can also be moved out of 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 measuring parts.
The work holding fixtures are designed to hold U, H, or J cross-sectional beams from 3.0-in. to 12.0-in. widths and can adjust for gage reduction (web ply thinning for weight reduction). The fixtures automatically adjust to varying web and flange thicknesses.
Parts are machined dry, which is the preferred method of manufacture by the airplane industry to avoid composite material swelling due to coolant absorption by material exposed from cutting. Coolants can interact with the composite material causing it 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.
For dust containment all machining is done in an enclosed compartment with dust collection hoods. Composite slugs, chards, and similar materials are swept into a debris collection chute for automatic cleanup. HEPA filters clean the air to a safe level and a dust collection drum makes for easy machine cleanup and dust disposal.
To verify that parts are machined to tolerance and the end user’s desire to measure the parts for dimensional accuracy in the same state in which they were machined, parts are 100% feature inspected in the machine. The inspection probe is used to verify the position of fixtures, datum surfaces of the fixture, and dimensional inspection data for all drilled and milled features. The machine is also equipped with a calibration sphere that allows the machine to quickly check itself for any position deviation and the inspection probe calibration software is used to insure 100% reliability of collected inspection data.
The machine drills, mills, and saws complete floor beams on all sides in a single setup. The finish machined product is inspected using metrology software that is 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.
The floor beam machining system is housed in a specially built facility that is temperature regulated. Engineering and manufacturing offices surround the machine, giving manufacturing engineers constant oversight of operations and allowing them to stay involved at all times with the manufacturing process.
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.
Hitco Carbon Composites
Bertsche Engineering Corp.
Filed Under: Aerospace + defense, Machine tool industry + subtractive manufacturing, Materials • advanced, Mechanical