FandMmag.com |

The aerospace industry constantly searches for new technology that allows them to produce their parts faster, with greater accuracies and reliability. The expanding varieties of alloys being machined for aircraft manufacturing, and the high raw material prices associated with these materials, all add to this challenge.

Such a demanding combination of requirements (faster productivity in hard-to-machine, expensive exotic materials) has prompted a full assessment of the complete machining process by engineers at the world's leading aircraft manufacturers.

Aerospace engineers usually study a great number of factors in order to find the best solution for their machining process. The first element they typically review in the machining process is the machine tool selection for the particular machining application, followed by an investigation into the fixturing of the workpiece. Once this baseline setup is established, the engineers then look closely at the cutting tool technologies available.

Cutting performance plays an important role in a plant's production. Special materials (such as aluminium, titanium, and composites) and part geometries always present difficulties in aircraft machining processes.

For example, one specialty in the aerospace industry involves cutting large structure components which, in most cases, show a high number of cavities. These work pieces are cut from the solid, with often 90 percent of the original material being machined.

Other challenges include titanium machining, where the cutters move quite slowly but aggressively chip away at the material. For these reasons, a number of extremely specific carbide grades and coatings are available for use with specific geometries to provide the best machining process possible for efficient cutting.

Finally, the method of holding the cutting tool is examined. The tool holding technique is crucial in the overall machining process. In fact, all of these processes must execute in top quality and precision: not only the machine tool, but the cutting tool and its tool holder are all responsible for providing a properly machined workpiece.

With competition forcing the aerospace industry to maintain high productivity, high performance cutting (HPC) — which uses the driving power to full capacity to cut into the material with a high feed — is very popular, especially since special cutting tools on the market can support this kind of machining. These cutters resist the conditions of high torques, feed and tensile forces without breaking.

However, the danger of pulling the cutter out of the chuck with this force increases in the case of tool holders that offer precise clamping with high run-out accuracy, such as shrink fit chucks, milling chucks, hydraulic chucks or press fit chucks that use friction to clamp the tool. Their clamping force is limited and sometimes insufficient for HPC (in this case, the cutting tools are very expensive).

As an alternative, many applications use conventional set-screw endmill holders to grip the tool via a clamping screw that locks down on a flat. This technique can generally transmit any desired torque until the cutter finally breaks. Set-screw endmill holders, however, carry disadvantages with imprecise run-out (which causes poor clamping because the shank in the chuck needs a little clearance) and a short cutting tool life, which are very expensive in this case.

No further alternatives existed until a patented solution was developed that combines a shrink fit chuck or another high-precision chuck with locking elements. Its principle follows that helical grooves are ground on the cutter's shank for form-closed drivers. The helical form of the groove protects the tool against overturning and pulling out. The drivers, which can be balls or rods, are integrated in the chuck. This unifies the high accuracy advantages of clamping with the advantages of positive locking.

With the helical form of the grooves, the tool's length can be adjusted. The clamping process is easy since the chuck is heated as usual and the tool is inserted with a turning move. The balls or rods locate themselves into the grooves. A spring supports the accurate fitting of the tool. After a few seconds the holder gets cold, so that there is a friction- and form-closed connection.