As a common tool for processing internal threads, taps can be divided into spiral flute taps, spiral pointed taps, pipe taps, forming taps, and more. Tap is also the main tool used in threading. So how to choose a thread tap? Let’s take a look at different types of tap materials and coatings.
Materials of Taps
Taps are highly dependent on materials. The selection of good materials can further optimize the structural parameters of taps, making them suitable for efficient and more demanding working conditions, while also having a higher life. At present, large tap manufacturers have their own material factories or material formulas. At the same time, due to the problems of cobalt resources and price, new cobalt-free high-performance high-speed steel has also been introduced.
1. Tool steel: it is mostly used for hand incisor taps, which is not common at present.
2. Cobalt-free high-speed steel: currently widely used as tap materials, such as M2 (W6Mo5Cr4V2, 6542), M3, etc., with the marking code of HSS.
3. Cobalt high-speed steel: currently widely used as tap materials, such as M35, M42, etc., with the marking code of HSS-E.
4. Powder metallurgy high-speed steel: as a high-performance tap material, its performance is greatly improved compared with the above two. The naming methods of each manufacturer are also different, and the marking code is HSS-E-PM.
5. Cemented carbide materials: usually choose the brand with ultra-fine particles and good toughness, which are mainly used for manufacturing straight groove tap processing short chip materials, such as gray cast iron, high silicon aluminum, etc.
Coatings of Taps
Coatings on threading taps provide the following advantages:
– Surface treatment: improve the appearance of the HSS tap without changing the tap size
– Improve the service life of tap: high wear resistance, reduce friction and power consumption, reduce blade breakage and fracture, and slightly improve surface hardness.
– Improve the surface quality and dimensional accuracy of the screw hole: the cutting edge is kept sharp, with lubrication, reducing load and abrasion, and minimizing chip buildup.
Types of Coatings:
1. Steam oxidation: put the tap into high-temperature steam to form an oxide film on its surface, which has good adsorption on the coolant, can reduce friction, and prevent the adhesion between the tap and the material being cut. It is suitable for processing mild steel.
2. Nitriding treatment: nitriding the surface of the tap to form a surface hardened layer, which is suitable for processing cast iron, cast aluminum and other materials with large tool wear.
3. Steam + nitriding: combine the advantages of the above two.
4. Tin: golden yellow coating, with good coating hardness and lubricity, and good coating adhesion, suitable for processing most materials.
5. TiCN: blue gray coating, hardness about 3000hv, heat resistance up to 400 ° C.
6. TiN+TiCN: dark yellow coating, with excellent coating hardness and lubricity, suitable for processing most materials.
7. TiAlN: blue gray coating, hardness 3300hv, heat resistance up to 900 ° C, can be used for high-speed processing.
8. CrN: silver gray coating, excellent lubrication performance, mainly used for processing non-ferrous metals.
The influence of tap coating on tap performance is very obvious, but at present, most manufacturers and coating manufacturers cooperate to study special coating alone.