Although coated tools have many advantages and the amount of use is increasing, they cannot completely replace ordinary uncoated tools:
(1) Since the toughness of cemented carbide tools decreases after coating, the coated tools are not suitable for rough machining under particularly heavy loads and interrupted cutting with high impact.
(2) In order to increase the edge strength of the coated tool, the tool should be treated with a blunt edge before coating. The radius of the blunt circle is generally 20~80um. The strength of the edge increases with the increase of the blunt circle radius, so it cannot keep up with the uncoated tool. The blade is sharp. The blunt radius r of the cutting edge of the carbide tool coated by CVD method. Generally, it is 0.02~0.07mm, and the blunt radius r of the cutting edge of the carbide tool coated by PVD method. Although small, it is generally not less than 0.02mm, and Kennametal's KC710-PVD coated tool r. It is estimated to be 0.01mm, which makes the coated tool unsuitable for finishing with a small feed amount, such as 0.015 mm, and not suitable for fine finishing.
(3) Coated tools are prone to peeling and chipping when cutting at low speeds, so they are not suitable for low-speed cutting.
(4) Coated tools are not recommended for the processing of the following materials: high-temperature alloys (such as nickel-based, cobalt-based, iron-based alloys), heat-resistant steel and titanium alloys, non-metallic materials (such as graphite, glass fiber, nylon and Plastics), non-ferrous metals and alloys (such as free-cutting brass, bronze, nickel, silver, pure copper, manganese, zinc and other alloys), and difficult-to-process non-ferrous alloys (such as aluminum bronze alloy, silicon aluminum alloy, manganese bronze alloy, Mongolian Nair alloy and nickel-copper alloy) and so on.
(5) Coated tools are also not suitable for processing high-hardness materials, such as steel materials above 300HB, chilled cast iron, and materials with hard inclusions.
(6) Deep hole drilling, cutting, threading, and cutting processing where the chips are difficult to discharge, the effect of using coated tools is not very good, and it is not suitable for processing blanks with sand and hard skin on the surface.