‘Tiny Design’ is a simple concept that has demonstrated significant improvements in cutting tool productivity.
Cutting tool design is influenced by factors such as the end application, material and cutting process, as well as the design of the component and the machine it is to be made on.
Tiny Design is a simple concept wherein increasingly smaller features can be incorporated at the design stage, controlled in production and their influence on the performance of a cutting tool measured. Systems such as the ALICONA IFM allow the engineer to make measurements and see features that previously required laboratory equipment like scanning electron microscopes.
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 widely used in Australia was investigated by drilling 3.5D holes in mill annealed Ti6Al4V on a machining centre with HP through spindle coolant. Produced uncoated, the drill offered the potential for improvement by applying Tiny Design principles.
The drill was coated at Surface Technology Coatings with an ALDURA PVD coating and given a micro post coating treatment. Testing in Sutton Tools Cutting Laboratory showed that the drill had a 47% productivity gain over the standard drill in addition to achieving lifetime improvement with less wear on the coated tools compared to 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 (~20%). However, in order to do this for 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. An important factor in considering hole-making 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 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
This case study shows the influence of the combined effects of a PVD coating and an edge micro finish treatment. 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 4 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 1045 grade steel.
The tests showed that the performance of the Futura Nano coated tool can be increased almost to the level of the higher performance ALCRONA coated tool by careful application of Tiny Design, specifically with micro edge finishing after grinding. Micro finishing also boosts the performance of ALCRONA coated tools.
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 such as milling where PVD coatings offer better performance. Coating adhesion is an important factor and can be improved with 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, work piece fixturing and machining strategy have significant effect on the cutting tool life. For example, depending on the dynamics of the machine/ workpiece/ tool system, forced or unforced vibrations can build up, creating chatter that can be detrimental to the finish and cutting tool life.
The Sutton Tools
Harmony range of milling cutters is a family of cutting tools, which incorporate all the design principles outlined here 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 milling applications, increasing both productivity and cutting tool life.