Cutting tool performance is constantly evolving as we gain a higher understanding of the relationships between tool geometry, material and surface finish. In this article, Steve Dowey, project leader of the DMTC Next Generation Cutting Tool Project and technical manager of Surface Technology Coatings, a Sutton Tools company discusses how Sutton Tools develop tools using state of the art technologies.

Sutton Tools was a founding member of the Defence Materials Technology Centre (DMTC) – a joint venture that brings together defence industry, universities and government research agencies to develop new materials and manufacturing technologies that will enhance Australia’s defence capability. Now in its third year, big improvements in cutting tool productivity have been demonstrated from small or ‘Tiny Design’ features.

When purchasing a cutting tool it’s vital to consider its application. It’s not only about the material and cutting process – the design of the component and the machine it is to be made on affect the cutting tool design and choice further. These factors not only influence the end users choice – they also influence the design of the cutting tool.

‘Tiny Design’ is a simple concept which includes micro-finishing techniques however the embodiment of Tiny Design was complex and difficult. Now, increasingly smaller and smaller features can be incorporated at the design stage, controlled in production and their influence on the performance of a cutting tool measured. Systems like the Alicona IFM (Fig. 1 and 2) allow the engineer to make measurements and see features that previously required laboratory equipment like SEMs (Scanning Electron Microscopes), which incidentally have shrunk to the point of straightforward desktop use, however sample preparation and manipulation in vacuo are still an issue for cutting tool makers.

The use of a cutting tool adds it as an influential component in a larger multi-component system together with the machine tool, workpiece and cutting tool holder. From the following case studies it is clear that the cutting tool itself has multiple components which when applied create a complex system.

Case study: Ti application drills

A drill specifically designed for titanium metals and in wide use amongst end users in Australia was investigated by drilling 3.5D holes in mill annealed Ti6Al4V on a machining centre with HP through spindle coolant. This drill is produced uncoated and therefore offered the potential for improvement by applying Tiny Design principles. It was coated at Surface Technology Coatings with an Aldura PVD coating and given a micro post coating treatment. Following testing at Sutton Tools’ cutting laboratory we found that not only could a productivity gain of around 47% be achieved over the standard drill but a lifetime improvement also resulted, with less wear on the coated tools compared to the uncoated tools.

This work also showed that for the uncoated tools the standard catalogue conditions could be accelerated and longer life and productivity gains made with no other changes except optimising the speeds and feeds.

However, in order to apply this to the drill it was necessary to use a dynamometer to make quantifiable measurements of torque and thrust. Sutton Tools uses piezoelectric dynamometers to validate and optimise tool design and process conditions. Note that HP coolant was used which does enable higher speeds, however using HP coolant without re-optimising the process can also lead to unexpected consequences.

An important factor in considering holemaking conditions for aircraft applications is hole quality. Consistently it was shown that the exit burr height and the entry hole diameter were influenced by the process parameters and that the best conditions (lowest burrs and controlled hole diameters) were achieved at the higher productivity levels when using HP coolant and the improved drill and the worst with the HP coolant and standard parameters.

Case study: Micro-finish and milling cutter performance

Tiny Design is not just applicable to drills. In this study the influence of the combined effects of a PVD coating and an edge micro finish treatment are shown. Alcrona, a high performance AlCrN monolayer coating with wide application on HSS and carbide cutting tools was compared to Futura Nano, an older generation but still leading TiN/TiAlN nano-structured bi-layer film.

The Futura Nano coating and the Alcrona coating were applied to untreated 10mm diameter four flute milling cutters and a further cutter was micro-finished and coated with Futura Nano. These tools were tested in the Sutton Tools cutting laboratory by milling a 1045 grade steel (Fig.4). Remarkably the performance of the Futura Nano can be increased almost to the level of the higher performance Alcrona coated tool by careful application of Tiny Design – notably micro edge finishing after grinding. Although not shown here, micro finishing boosts the performance of Alcrona too. This is a further example of the complex system that is created when a thin film coating is combined with a cutting tool and shows that ‘just’ coating a cutting tool can lead to limited benefits.

PVD coatings are thin, typically 3-4µm very hard and consequently, like the cutting tool substrate, very brittle. This hardness is also combined with large compressive stresses in the film, unlike CVD films which are typically much thicker and have tensile stresses (unless treated) in the coating.

Thick CVD films are ideal for turning applications but can have limitations in interrupted cutting applications like milling, where PVD coatings are in general often better. Being highly stressed, it is important that the coating adhesion is the best it can be. Certain steps can be taken to improve adhesion and they involve the application of Tiny Design, such as micro edge finishing. The overall application of Tiny Design is therefore really aimed at improving the surface integrity of the cutting tool system.

Milling is an application where the influences of the machine tool, cutting tool holder, workpiece fixturing and machining strategy have significant effect on the cutting tool life. For example, in certain circumstances, depending on the dynamics of the machine/workpiece/tool system, forced or unforced vibrations can build up, creating chatter which is both detrimental to finish and cutting tool life.

The Sutton Tool Harmony range of milling cutters is a family of cutting tools which embody all the design principles outlined so far, together with a variable pitch and helix, to reduce the potential for harmonic build up of vibrations in the system. This results in chatter-free milling in many applications, increasing both productivity and cutting tool life – a winning combination.

Sutton Tools
www.sutton.com.au