The geometry, substrate and coating of a tool determine its performance. An ideal cutting tool material should resist flank and point wear, as well as deformation, be tough to resist breakage, not interact chemically with the workpiece, resist oxidation and diffusion, and have good resistance to sudden thermal changes. Harder tool substrates last longer, but tend to be more brittle and so more likely to break under adverse operating conditions. Softer tool substrates are less likely to fracture, but operate at lower performance parameters and so don’t last as long.

Solid rotary tools consist of one entire piece made up of the cutting edge and shank. They are typically associated with drilling, threading and milling applications. In terms of material, high speed steel (HSS) is tough and cost-effective for many applications, but is not very wear resistant. High speed cobalt (HSCo or HSS-E) offers a good combination of toughness and hardness. Solid tungsten carbide is the most widely used and wear-resistant cutting tool material today and is suitable for both round tool and indexable applications.

Indexable tools consist of a tool body that holds replaceable inserts or tips. These are generally used for milling and drilling. Apart from carbide, other insert substrates include cermet – good flank and crater wear resistance and maintains its sharpness because not prone to built-up-edge; ceramics – good for cutting hard materials (45-55 HRc) and resistant to abrasive and thermal conditions; cubic boron nitride – extremely hard and highly thermally resistant for cutting hardened steels and cast iron; polycrystalline diamond – highly resistant to wear, so good for non-ferrous materials, such as high silicon aluminum, but too brittle for impacts.

Although requiring greater initial investment, indexable toolholders have the potential to last for longer than solid rotary cutters. On the other hand, tool replacement is simpler because the toolholder need not be removed from a collet or chuck; only the insert needs changing. Some toolholder systems allow the use of several types of inserts with different material properties. Indexable cutting tools can also perform multiple operations; such as milling, plunging, helical interpolation, profiling and enlarging a hole.

Solid tools are usually more expensive than the inserts for an indexable tool, but they may be able to be reground, which inserts cannot be. Also, solid tools can be supplied in much smaller diameters. In many materials, the solid tool point will also act as a chipbreaker. Application-specific tools have the potential to produce greater accuracy than general-purpose tools. For example, the four-facet split point geometry used on rotary drills was originally developed for making deep holes in automotive crankshafts. Today, this feature offers easier and more precise self-centring than other designs in many cases.

Both solid and indexable tools continue to develop and improve, in terms of geometries, coatings, substrates and manufacturing processes – such as edge preparations, surface finishing and other treatments. Dormer Pramet provides a range of support to help customers decide which tools best suit their needs, including a computer-based solid tool selector (https://is.gd/evisik).


TEXT BOX

Alternatives: a few other online product selectors

TEXT BOX

New solid and indexable rotary tools

  • Sandvik Coromant (www.sandvik.coromant.com/uk) – M612 face-mill for stainless steel turbo housing rough machining
  • Iscar (0121 422 8585) – solid carbide Chatterfree end-mill; three families expanded at the small diameter end of the range. www.machinery.co.uk/146342
  • Widia (ITC; 01827 304500) – indexable insert grade for milling titanium and other superalloys. www.machinery.co.uk/148289
  • WNT (UK) (0114 249 6249) – solid carbide step-drill system combines drill and countersink in a single rotary tool. www.machinery.co.uk/147339

This article was first published in the December 2016 issue of Machinery magazine.