The hole is the goal

Profound changes in aircraft design are triggering an increase in composite product quantities. The challenge for manufacturers is how best to integrate cutting tools into the equation and determine how to improve productivity.

If there are any disadvantages to composites then these are associated with machining. Producing holes in CFRP, for example, requires unique geometries to achieve hole tolerance and quality, while combining CFRP with a stacked material such as aluminium adds another factor as the two materials vary in machining characteristics.

There's little doubt that composites machining is already a significant technology area, and it's certain to grow even larger in coming years. With this in mind, Sandvik is committing considerable resources to developing new products and applications knowledge for the benefit of its customers.

As a company, Sandvik has already established an application centre for composites in Europe, a joint application centre with Precorp in the USA, and a third opening in Asia in June 2010. The application centres house teams of specialists dedicated to finding solutions and maximising savings for customers. Of course, there are many different applications. In the aerospace sector, around 70-75% of these currently centre on hole making. The remainder is largely related to milling, although this is anticipated to grow in coming years.

Hole making in composites is extremely demanding, with inherent delamination and splintering traits. However, there is already a genuine solution for reliable, efficient and high quality hole making in the form of CoroDrill 854 and CoroDrill 856 diamond coated solid carbide drills.

Correct drill selection is critical in order to achieve optimum hole quality, process security and cost-per-hole economy. With this in mind, CoroDrill 854 with its ‘spurred' geometry is preferred where splintering or fraying is the problem, while users will find greater benefit with CoroDrill 856 if delamination is proving to be the difficulty in resin-rich materials – this is primarily due to its double-angled geometry which allows soft entry and exit of the workpiece material.

CoroDrill 854 and 856 are standard stocked drills in diameters from 4mm up to 12.7mm (lengths up to 5xD), and it's certain that other products will follow soon. However, there's also considerable demand for custom made tools to suit specific customer applications and machines, which are often specialised.

The milling of composites also sees demand for customised tooling, although standard solutions are already available in the form of CoroMill 590 with PCD inserts for face milling, CoroMill 390 for 3D pocketing and CoroMill Plura for edging of composites using diamond coated or PCD tipped inserts.

The increasing capability of cutting tool solutions is helping to optimise the manufacture of a growing number of aircraft parts. Structural components such as wing boxes, spars, stringers and skins are made increasingly from various carbon fibre and matrix materials, while other structures, such as the central (fuselage) wing box, are manufactured from several types of composite material commonly stacked with alloys. Even turbine blades at the front end (cold end) of the engine are now being produced from CFRP.

The opportunity for both Sandvik and its customers is significant. Many of these large structural aircraft parts have thousands of holes and many pocket-type features. Sandvik's aim is to offer cutting tools that provide maximum productivity and extended tool life. Regarding the latter, this is often determined by the quality of the hole, its surface finish and edge quality. As a point of note, tolerances are generally getting tighter.

www.sandvik.coromant.com/composite