Christer Richt* looks at how using exchangeable-head end mills can fast track efficient cutting processes.
ENDMILLING operations are dominated by two overlapping end mill types: indexable insert cutters and solid carbide cutters. These tools have application areas largely determined by tool-diameter, operation type and the component finish required. Using the exchangeable head concept allows one tool to combine the best of both worlds – but ensure to check the coupling.
End mills that have indexable inserts have no upper size limit but, through practical reasons, have a lower one. The smallest diameters are usually around 12mm. End mills in solid carbide, on the other hand, can be a lot smaller, with diameters of tenths of a millimetre, but have an upper tool-economy limit up to about 25mm.
When it comes to application, indexable insert cutters are flexible, high-metal-removal-rate tools, well suited for most operations, while solid carbide cutters have close tool-tolerances and can provide high finishes and accuracy, especially at large axial depth of cut thanks to the long radial cutting edges.
In between these two cutting options, there is a potential for an alternative tool solution which overlaps both, providing both indexability and the benefits of solid carbide tooling for small to medium size end mill diameters. Up to now, marginal in-roads have been made in this area to point out potential benefits as well as shortcomings.
The concept of the exchangeable-head end mill provides a good combination of what both of the different end mill types have to offer without the ambition of making either type redundant. The tool-diameter area of 10 – 25mm lends itself well to an end mill based on a tool shank and a cutting-tool head that is exchangeable.
When it comes to heads made of solid carbide, both indexability and accuracy is achieved. The conventional solid carbide endmill remains the best choice where a long radial edge is needed for large axial depths of cut as in semi-finishing to super-finishing operations. The indexable insert end mill remains the best for versatile, high-productive roughing to semi-finishing.
Advantages of exchangeable-head end mills include: the benefits of solid carbide tooling without having long, spiral chip-channels which result in a relatively weak tool-core; the benefits of an indexable cutter without the need for the loose parts in a seat with clamping screw; reduced replacement cost compared with solid carbide end mills; elimination of re-grounding, avoiding tool diameter loss, position and costs as the small tool-head of the end mill is used only once, exchanged for a new one and recycled when worn out; increased versatility and easy tool changing; increased potential metal removal rates compared with solid carbide cutters; and enhanced precision and surface finish than with indexable insert cutters.
Many of these advantages however depend upon the design of the end mill, particularly the coupling between head and tool shank. Performance relies heavily on the strength, stability, accuracy, repeatability, ease of handling as well as the function of the coupling of head to shank.
The coupling for a new generation of exchangeable-head end mills has recently also been the subject of considerable development and has resulted in a unique, patented coupling, called EH.
This coupling has a unique interface between the head and shank which provides the stiffness for full-slot roughing to high accuracy for precision finishing operations. It provides an axial tool-length repeatability and radial tool run-out limited to within a few hundredths of a millimetre.
The concept of exchangeable-head end mills lends itself to almost any type of milling operation, though extensive side and face milling or super-finishing are exceptions. It offers users the ability to quickly, easily and accurately switch between various options such as cutter type, radius variation, number of teeth, geometry and grade.
*Christer Richt is the technical editorial manager at Sandvik Coromant, Sweden.