CNC Machining

Aerospace CNC machining is typically programmed offline with a CAD CAM package, using a CAD parts description as input. The package reads in a CAD file and eventually outputs the brand-specific G-code that programs toolcutter paths or workpiece motions.

Material Removal and Roughing

Increasingly methods are being found, with CNC machining automatic lathes, to combine processes, for example turning, spline hobbing and serration rolling to produce a serrated shaft. The principles of CNC machining, however, remain the same.

When machining a curved surface component, for example, a wing section, roughing is the first stage of machining where the object is to quickly remove the bulk of the waste material, normally with the aid of a ripper cutter, this gives the coarse stepped product. Roughing begins with the introduction of the raw stock, or billet, which is cut into the approximate shape of the final product. 

Semi Roughing

This stage of CNC machining generally uses a smaller cutter than roughing, typically an end mill, although the aim is still to remove the bulk of the waste material.

Semi Finishing

The next stage, using a relatively large ball nosed cutter, is to start to form the final profile of the workpiece, removing the steps generated in the two above procedures. Semi-Finishing employs raster passes, constant step-over passes, waterline passes, or pencil milling techniques to hone the material closer to its final shape.

Finishing

The final stage, and the longest process of all, is the final cut to the desired size. A small ball nosed cutter traversing across the surface produces the finished shape.

Finishing initiates a faster spindle rotation speed and a decreased material feed rate. This step produces a finer finish to the piece and although this is the final machining stage, there is still much work to do in the form of polishing and finishing before the article is complete. Aerospace contour Milling is usually done on hardware with five or more axes. During contouring with contour milling cutters, the work piece is rotated to allow the cutting tool to finish the part with higher dimensional accuracy. Contour milled components can have greatly improved surface finish.

Aerospace cutting tools and types of cutter

A - Ripper Cutter

Used for the rapid removal of large amounts of metal, the serations along the cutting edge literally rip the material away. This cutter is designed to cut along it's sides only.

B - End Mill

Similar to a ripper only without the serrations, used for removing the bulk of the material. The cutting edges, like the ripper, are down the sides of the tool.

C - Slot Drill

Typically this cutter has less cutting surfaces than the two above, and unlike the end mill and ripper can be used to plunge directly into the workpiece. As a result of the reduction in cutting surfaces there is better swarf removal meaning the tool can be used in enclosed pockets and slots.

D - Ball Nosed Slot Drill

This cutter, as its name suggests, has a semi-circular cutting face, with the aid of computer software it is possible to cut tangentially to the work piece enabling curved surfaces to be machined.