General knowledge of selecting and using diamond coated tools

Mon Jul 04 11:43:18 CST 2022

Before selecting and using diamond-coated cutting tools, we must know the following common knowledge about diamond-coated cutting tools:

1. The difference between CVD diamond coating and amorphous diamond coating

Amorphous diamond coating is a kind of carbon film deposited by PVD process. It has part of the SP3 bond of diamond and part of the SP2 bond of carbon. The hardness of film forming is very high, but lower than that of diamond film. It's also a little thinner than the diamond film we normally deposit. In the processing of graphite, the life of an amorphous diamond coated tool is 2-3 times longer than that of an uncoated carbide tool. In contrast, CVD diamond is pure diamond coating deposited by CVD process. The cutting tool life of graphite processing is 12-20 times that of cemented carbide cutting tool, so as to reduce the number of tool changes and improve the reliability and precision consistency of processing.

2. Hardened steel cannot be machined with diamond tools

Diamond is made of carbon atoms. Some materials, when heated, suck carbon atoms out of the diamond and form carbides in the workpiece. Iron is one such material. When diamond cutting tools are used to process iron materials, the heat generated by friction will cause the carbon atoms in diamond to diffuse into iron, resulting in the premature failure of diamond coating due to chemical wear.

3. The coating on the tool surface is pure diamond

It is difficult to guarantee the quality of diamond coated tools because the coating generated on the cutting tool surface is pure diamond, so it takes a long time to regrind the cutting tool with diamond grinding wheel. In addition, a tool used to grow a diamond. The preparation process alters the chemical properties of the tool surface, and because the coating requires very precise control of the chemical properties, it is difficult to guarantee the effectiveness of the tool recoating.

4. The life of diamond coated tools varies

Like any other tool, diamond-coated tools vary in life, depending on the material being cut, the feed rate and cutting speed chosen, and the geometry of the workpiece. In general, diamond-coated tools that process graphite last 10-20 times longer than uncoated carbide cutting tools, and in some cases even longer. In this way, almost any machining task can be completed with a single tool, without tool change due to tool wear, eliminating machining interruption and recalibration, making it possible to achieve unattended machining. It is also possible to obtain longer tool life in composite machining.

It has been reported that diamond-coated tools can last up to 70 times longer than uncoated carbide tools when processing hard-to-work composites such as high-density glass fiber, carbon fiber and GL0-FR4.

5. The spalling of diamond coating can prevent the spalling of coating

Spalling of diamond coatings to prevent spalling is a serious and common problem with diamond-coated tools (especially when working with materials such as carbon fiber), resulting in unpredictable cutting tool life. In the late 1990s, interface chemical properties were identified as an important factor affecting the adhesion properties of diamond coatings. It is possible to reduce or eliminate the spalling of diamond coating and achieve a stable wear pattern by selecting the chemical characteristics of cemented carbide with good compatibility, using appropriate pretreatment technology and reasonable deposition reaction conditions. Under the microscope, it can be found that the diamond is worn steadily to the carbide matrix without breaking or spalling.