Tip-entry machining of blisks can be practical for shorter blades. Machining blades in a single operation improves efficiency and reduces head movements and chance of collisions.
Software for aerospace machining
Aerospace structural components are often characterized by complex pockets separated by thin walls for high strength and low weight. Producing these parts tends to involve substantial material removal and machining flats, thin sections, and flanges.
To address these requirements, Delcam's PowerMill 6 CAM system includes a wide range of new functions for two, three, and five-axis machining. According to company officials, the software improves three-axis machining of flat areas, in particular to aid machining aerostructures. One feature includes setting levels for roughing flats. This minimizes machining operations and avoids situations where thin slices of material must be removed after roughing. And a dedicated strategy for finishing flats gives a smoother surface finish.
New plunge-milling strategies produce deep pockets. Plunge milling is not new, but it also has not enjoyed widespread success, says Delcam's Peter Dickin. The process plunges a tool downward much like a series of overlapping drilling operations, instead of cutting across a part, he explains. It is particularly useful for older machines that are incapable of high-speed machining methods.
"Many systems start on one side and perform a series of drilling operations across a part. It is easy to program and gives relatively consistent material removal," says Dickin. "However, when generating that first narrow slot, there is high tool loading as well as difficulties clearing material out of the slot."
Dickin says Delcam has developed a technique that guides the tool through a series of arcs as it progressively moves down a path. Tool pressure and material removal are more consistent, making machining more efficient.
Each plunge is calculated from a stock model that is updated after every cutting operation. The new plunge center optimizes the cutting area and removes the most possible material without risking tool damage. Calculations also ensure that small up-stands of material do not remain because these may crush under the plunging tool and cause damage.
A default-thickness command in PowerMill 6 helps the cutting tool avoid clamps and fixtures, and leaves extra material on thin walls to avoid bending during rough machining. Setting an offset distance applies it to all subsequent toolpaths. Previously, the offset was manually applied to each calculation.
For all machining operations, the stock model can be shaded or displayed as a wire frame. This makes it easier to visualize the amount of material to be removed when undertaking a series of operations with progressively smaller cutters.
Among five-axis improvements are new options for swarf machining, which involves cutting with the side of the tool, rather than the tip. This includes support for tapered tools, especially useful when machining undercut areas that would otherwise require long, thin tools for finishing. In addition, tapered tools remove more material than tipped cutters, with less risk of rubbing or gouging adjacent surfaces. Better accessibility can also reduce the number of fixtures required.
It can create swarf toolpaths from wire-frame profiles as well as surfaces. This approach is needed for poor-quality data with small discrepancies that would prevent generating satisfactory toolpaths directly from the surfaces.
An automatic collision-avoidance feature changes the tool axis when collisions might occur. The software tilts the cutter away from obstacles by a specified tolerance and then returns to the previous cutting angle once it has been cleared.
A special technique for five-axis plunge finishing mills along a surface rather than across it. This efficiently removes metal and can produce cusps parallel to gas flow in engine ports and similar applications.