In metal cutting, the cutting temperature is typically evaluated based on the cut of the steel.
Normally, during normal dry cutting, it is considered normal for iron chips cut into steel to have a purple appearance.
The change in chip color is indicative of the conversion of most of the energy consumed in the cutting process into cutting heat.
This process can also be thought of as the progression of tool degradation (sharpening → passive dulling → severe dulling → scrapping).
The term “cut-off temperature” typically refers to the average temperature.
During dry cutting, the temperature can vary from approximately 200°C to over 500°C.
The color changes of iron filings are as follows: silvery white → light yellow → dark yellow → crimson → dark blue → bluish gray → grayish white → purple black.
It is common practice for experienced technicians to determine cutting parameters based on the change in cutting color.
It is considered more efficient when the color of the cut is blue or bluish purple.
If the color is silver or yellow, the efficiency is not ideal.
If the color is gray blue, it indicates that the cutting amount is too large.
When using high-speed steel cutting tools, it is ideal to cut in silvery white or yellowish white.
If the cutting color is blue, you may need to reduce the cutting speed or feed.
The relationship between chip color and cutting temperature is as follows:
- Silver white: approximately <200℃;
- Light yellow: approximately 220 ℃;
- Dark blue: approximately 300 ℃;
- Light gray: approximately 400 ℃;
- Dark purple black: approximately >500 ℃.
