Thin Wall Machining

 

THIN WALL MACHINING

New Heights in Aerospace Realized Through Advanced High-Speed Machining Process
 

The manufacturing demands faced by the aerospace industry are quite clear,with experts forecasting 13,000 new aircraft required over the next 20 years.To realize a suitable return on investment to manufacture these aircraft,manufacturers must eliminate approximately 30 percent in costs.

And while it may seem impossible to meet these demands, some leading aerospace manufacturers are doing just that. By changing their machining processes, and in some instances redefining them, aircraft structural components are being manufactured with fewer parts and with fewer manufacturing and assembly operations required to make them. In some instances, industry leaders have reduced part cycle times as much as 75 percent.

These dramatic results are achieved by implementing advanced high-speed machining processes such as thin wall machining. Thin wall machining of structural components, or monolithic parts, allows for higher quality, more precise parts in less time than ever before. These efficiencies, in turn,impact business issues including inventory and Just-In-Time (JIT)manufacturing.

Eliminating The Parts Puzzle

Thin wall machining aggressively collapses part cycle time by creating one piece flow of monolithic parts. Now certain parts can be machined from one piece of metal, eliminating the need to manufacture multiple pieces for assembly into one final part. Even intricate thin walled parts can be machined as one piece. In one instance, a structural part previously made up of 125 pieces is now machined as one piece using thin wall techniques. Using this advanced process, there is no need for expensive, time-intensive multiple-part manufacturing, including laborious setup on different machine sand the riveting of pieces together into a finished part.

Thin wall machining techniques also provide extensive improvements in part accuracy and quality. The dramatic difference in consistency between a riveted part and a machined part cannot be argued. In fact, thin wall machining techniques can machine 777 deflection control ribs within "jig bore" tolerance from one part to the next. This accuracy makes it possible to more efficiently machine parts with straight, thin and flat walls to exacting customer tolerances — even at high rpm. Similarly, intricate component surface finishes, such as convex or concave Keller surfaces and contoured surfaces, can also be machined within tight tolerances.

Flexible Machining Centers Eliminate Steps, Increase Throughput

To achieve these complex part geometries, new monolithic part design relies on advanced high-speed machining centers supported by sophisticated tooling and software control. The most obvious benefit of these machining centers is the flexibility to perform various steps on one machine. In fact, one machining center can now create the same amount of parts that previously needed three or four machines.

In the past, a part might require a specific operation performed on the forward side of a machining center and another operation in another machine.This would require multiple setups and fixturing of the part which, in addition to lengthening cycle time, can create inaccuracies from part to part. From milling to drilling and reaming — hog, finish and bore — most steps in the machining of individual parts can now be performed on one machiningcenter. And with multi-sided fixtures and automated tool changers and pallet changers, several setups can be eliminated and a variety of parts can be machined.

For example, a typical honeycomb part with thin wall and contour surface finishing can be machined four to five times faster utilizing higher metal removal rates and 5th-axis programming — which can eliminate kellering on the part. Different axes will be required depending on the part, however, certain machining centers can accommodate up to five-axes with optimum overshoot control. This is achieved by making real-time adjustments based on machine dynamics to compensate for servo lag, inertia and friction. This allows the machining center’s tooling to maintain the exact tool path and the fastest feedrates possible for all lengths of movement while maintaining high accuracy and greater spindle access to the part.

Using five cutting tools at up to 10,000 rpm with up to 300 ipm (7,620 mm/min)feedrates, the honeycomb part is quickly machined out of 6061-T6 aluminum with wall and floor surface thickness of 0.030" (0.76 mm). These fast material removal rates are achieved with either HSK or CAT50 taper spindles with powerful integrated drive motors. Utilizing an internally cooled spindle limits thermal growth during metal removal and is positioned horizontally for better chip evacuation and more flexible spindle orientation. Additionally, a high-speed automatic tool changer (2.0 second tool-to-tool) reduces out-of-cut time and increases throughput rates, increasing spindle utilization to as high as 95 percent.And with advanced servo technology, machining of thin wall parts with a single spindle can occur four to five times faster than when using three spindle gantry mills.

These advanced technologies are guided by the software. Several of the more advanced software packages track multiple operations and part numbers and, by interfacing with CAD/CAM and CIM software systems, also facilitate job priority scheduling, multiple processes per workpiece, multi-programs per pallet, pallet routing, tool life management and presetter interface.

Results Impact Entire Shop Floor

Efficiencies realized through thin wall machining impact the entire part manufacturing process. Take part inspection, for example. Hours are eliminated off the first inspection as well as each time the job is repeated.This benefit is further leveraged when the machining center is configured with a rapid pallet changer. This system automatically manages work flow and stores numerous qualified fixtures in queue for simplified setup and maximum productivity. Now parts can be inspected while parts are being machined.With a rapid pallet changer, part setup and unloading is conducted outside the enclosure while another part is in a machining cycle — set up "dead time" is eliminated and the operator merely loads and unloads the pallet.

On a larger scale, these shortened cycle times provide the flexibility to support JIT manufacturing. In the past, a lengthy lead time was necessary before parts could be produced. Heavy investments were required in a forging die for a test part. Once it was created, even minor design changes meant almost investment. With a monolithic part being thin wall machined, the part merely needs to be remachined depending on the design changes and the part.Casting and forging to test a part’s design is no longer a lengthy process,making design changes and rapid prototyping easily achievable. Manufacturer scan respond JIT to orders by merely buying materials off the shelf without tying up resources and incurring capital expenditures. This elevates a manufacturer’s flexibility and, more importantly, makes them more competitive allowing them to meet small quantity demands for specialty and replacement parts.

Answering An Industry’s Demands

Industry-leading companies are already experiencing the benefits of high-speed machining techniques such as thin wall machining. These benefits become hard to ignore with Makino aerospace customers reporting up to 200 percent increases in productivity. Thin wall machining’s dramatic cost reductions impact everything from the part, the process and the bottom line.As leading manufacturers rush to meet the exacting demands that have been leveled on the aerospace industry, these advanced manufacturing technique swill undoubtedly be used on a more widespread basis.