What are PVD and CVD coatings for cutting tools?

CVD can be coated with TiCN, which has excellent wear resistance, and Al2O3, a thick film with very good heat resistance, and therefore shows long life in high speed, high efficiency cutting operations that generate high temperatures.

PVD is generally used at the same or higher cutting speeds as uncoated carbide and HSS, with the goal of extending tool life. It is particularly suitable for tools that require wear resistance and chipping resistance, as well as for low feed and finish machining or threading tools where a sharp edge is required.

During cooling after coating, the difference in thermal contraction between the coating film and the substrate can lead to internal deformation within the coating film and consequently to residual stresses.

Coating of tools is one of the important ways to improve the performance of tools, the emergence of coated tools, so that the cutting performance of tools has been greatly improved, the field of application continues to expand, coated tools in the field of CNC machining has great potential, will be the most important tool varieties in the field of CNC machining in the future. At present, the coating ratio of foreign carbide indexable inserts is above 70%, and the coating ratio of European gear tools is as high as 90%. Coating technology has been applied to end mills, reamers, composite hole processing tools, gear hobs, shaving cutters, forming broaches and various machine clamping indexable inserts to meet the needs of high-speed cutting and processing of various steel and cast iron, heat-resistant alloys and non-ferrous metals and other materials.

The correct choice of coating is a prerequisite for the rational use of coated tools and for giving full play to the function of the coating. Here are three points on the basis of the selection of PVD coating. Firstly, it is still based on the classification and hardness of the workpiece material. Processing steel and cast iron generally use general TiN, TiCN, high hardness available TiAlN; processing stainless steel, choose anti-bonding, good thermal conductivity coating; processing titanium alloy, nickel-based alloys and other difficult to machine materials, high cutting temperature, to choose good heat resistance, high oxidation resistance TiAlN, AlTiN and other coatings; processing copper in addition to the general TiN can choose CrN coating; processing high silicon Aluminum alloy should be coated with wear-resistant grains such as TiCN; processing of synthetic materials should choose diamond coating or TiN, TiCN coating.

Secondly, according to the categories of processes such as turning, milling, drilling, tapping and hobbing. Continuous cutting processes such as turning and drilling are suitable for coatings with good heat resistance, while intermittent cutting processes such as milling and hobbing are suitable for coatings with good toughness, and drills and taps are suitable for coatings with small surface roughness values, which are less prone to bonding and beneficial to chip evacuation.

Finally, consider the cutting conditions. For low cutting speeds, choose coatings that are resistant to abrasion and bonding; for high cutting speeds, choose coatings that are heat-resistant and resistant to oxidation temperatures; for processing with cooling fluids, choose coatings with good toughness.