The use of carbide tools has increased significantly in the last few years. Nowadays turning, drilling and milling operations are done, for the most part, with these kind of tools. The development of carbide tools, with better wear resistance and higher toughness compared to HSS tools, has been pushed forward by the evolution of CNC machines and the request for higher cutting speeds.

More specifically, in certain tapping applications, the use of carbide is either indispensable, such as in heat-treated steels or very
competitive, such as in abrasive materials.

Range

The Vergnano carbide tap range includes:

• Straight fluted taps with chamfer form C for blind and through holes, for machining abrasive materials such as grey cast iron and aluminium-silicon alloys; metric and metric fine threads (types HB43 and HB45)
• 15° spiral fluted taps for blind holes, for machining aluminium, copper, bronze and plastic materials; metric threads (type
  HB29)
• Straight fluted taps for blind and through holes, for machining heat-treated steel with hardness up to HRC 62; metric threads
  (type H130)
• Forming taps with radial through coolant for blind and through holes, for machining low/medium resistance steel, stainless steel, aluminium; metric threads (type HB80 NR)

A carbide twist drill has been included in the carbide product range (type HP900) for drilling holes in heat-treated steels with hardness up to HRC 62. The twist drill is oversize compared to normal twist drills in order to increase the toollife of the tap. The twist drill can be used to prepare the pre-hole before tapping with the H130 tap.

Advantages

The advantages of using carbide taps compared to standard HSS taps consist in a significant increase in tool life when machining
certain types of materials and the possibility to machine hard/heat-treated steels otherwise impossible to machine with HSS tools.
In particular, in the machining of abrasive materials such as cast iron or aluminium-silicon alloys (Si > 10%), the tool life can reach 8-10 times that of an equivalent tap in HSS. All taps for cast iron are equipted with through coolant channels to improve chip evacuation and to allow tapping of deep blind holes up to 3xD.

For aluminium and non-ferrous materials, HB29 type taps have through coolant channels for better chip evacuation and tapping of
deep blind holes up to 3xD. The advantages are an increased tool life and a reduction in cycle times.

Taps for hard steels (type H130) are the only solution for tapping heat-treated steels up to HRC 62. Taps in HSS are not capable of
machining materials with hardness above HRC 46.

Carbide forming taps (type HB80NR) can be used on all types of steels, including stainless steels, and on aluminium and aluminium
alloys. In addition to the well-known advantage common to all forming taps of not producing chips, carbide forming taps offer a higher tool life. For example, on steel the increase in tool life compared to HSS taps can reach up to 20 times.

It is important to use carbide taps in combination with quality tapping attachments with micro-compensation and no axial or radial play. The best solution is the use of tapping attachments for synchronised tapping, such as the new Vergnano Sincro attachment series. It is suggested to use the cutting speeds recommended in the catalogue, starting from the lowest value moving upwards.

Carbide

Carbide can be considered a metallic composite material consisting of a mixture of hard carbide particles, mainly tungsten carbide
(WC), in a metallic matrix of cobalt (Co). Other commonly used carbides are titanium carbide (TiC), niobiom carbide (NbC) and tantalum carbide (TaC).
The carbides, which confer hardness and compressive strength to the structure, are responsible for the wear resistance of the tool.
The binding element cobalt confers toughness.
The size of the carbide particles is also important since it balances the hardness and the toughness. In general, the mechanical properties of carbides depend on composition (type and concentration of carbides), percentage of binding material, size of carbides and fabrication process.

The main differences between carbides and high speed steels are summerised in the following table:

According to the IS0 513 standard, carbides are classified in function of properties and applications.

The ISO standard defines 3 groups of carbides: P (blue colour code), M (yellow colour code), K (red colour code). Subgroups are
indicated with a two-digit number which increases with increasing percentage of cobalt binder.

Vergnano carbide taps are produced in K grade carbide. The carbide grain size is “ultra-fine” (UF) which guarantees excellent hardness and toughness.

Applications

Carbide taps find numerous applications, both in the automotive and in the aeronautical industry. In the following case studies, the
difference in toollife and in cutting speed can be seen between carbide taps and high speed steel taps.