Mist collector technical information　1-2. Cutting oils and their effects

This section explains the role of cutting oils which serve as sources of oil mist.

(1) What is a cutting oil?

A cutting oil is applied to ensure cutting is smooth

If you wet the kitchen knife a little, sushi rolls, cheese and other foods can be cut smoothly.
This is because friction is reduced by the lubricating action of the moisture. The lubricating action also makes the road surface slippery on a rainy day.
The same thing can be said when cutting a metal, but by cutting the metal while pouring a liquid onto it, the friction between the workpiece and tool and between the tool and chips can be reduced, allowing cutting to proceed smoothly and the friction between the tool and work material to be reduced too.

At a high temperature of close to 1000 °C when cutting

The friction between the workpiece and tool makes it hot when cutting.
When the temperature gets high, the workpiece and tool expand and deform due to the heat, reducing the hardness of the tool and intensifying the wear.
This reduces the dimensional accuracy of the finished product.
Therefore, it is necessary to apply a liquid to cool it.

To put it simply, the principle is similar to an engine burning when there is no engine oil in the car.

Cutting oil is used for cutting

Cutting oil is the liquid which lubricates and cools the workpiece when cutting. In addition to these two actions, it also has anti-welding, penetration, rust prevention, and cleaning actions.
Three effects are especially important - lubrication, cooling and anti-welding. The anti-welding action prevents the workpiece and tool as well as the tool and chips from bonding due to the high temperature and high pressure during cutting.

Is the main purpose for lubrication or for cooling?

Cutting oils are roughly divided into water-soluble cutting oils that are used without diluting them in water and water-soluble cutting oils that are used by diluting them in water.
Water-insoluble cutting oils are mainly used for lubrication and anti-welding, and for cutting which require a high processing accuracy. Water-soluble cutting oils are mainly used for cooling and offer the advantage of a reduced risk of ignition.

(2) Effect of each action

Lubricating action improves the cutting tool sharpness

The lubricating action of the cutting oil reduces the wear of the tool and workpiece. I’ll explain this in detail then.
When the tool, workpiece and metal come into direct contact, the contact surface is actually slightly uneven and not in complete close contact, so a large force acts on the protruding parts of the unevenness, resulting in a large friction.
Therefore, cutting oil is supplied to the respective tool and workpiece to create an oil film on the metal surface to prevent direct contact between the metals and reduce friction and wear. This is the lubricating action of the cutting oil.

In addition, chips are generated during cutting, but the greater the friction between the surface (rake surface) on the chip side of the tool and the contact surface of the chip, reduced by the cutting oil, the smaller the radius of curvature of the chip.
The smaller the radius of curvature is, the smaller the contact area between the tool and the chip gets, and the better the sharpness becomes.
The friction during cutting that causes the tool to wear out is mainly due to the chips, so cutting oil plays an important role in protecting the tool.

Cooling action reduces tool wear

When cutting, the cutting temperature is 800 °C or as high as 1000 °C in some cases. Heat is mostly carried away by the chips, but some of it is also conducted to the tool, increasing the temperature of the cutting edge.
The cooling action of the cutting oil suppresses the temperature rise, protecting the tool from deformation and softening caused by the heat, thereby reducing wear and extending the life.
Although the workpiece also becomes very hot, the cooling action prevents expansion and deformation due to the heat, thereby maintaining machining processing accuracy.
In addition, hot chips are very dangerous as they may cause a fire or result in burns when touched. The cooling action also plays an important role in ensuring the safety of such a work environment.

 

Anti-welding action protects the cutting edge of the tool

A part of the chips melts and adheres to the cutting edge of the tool, becoming a hard, welded substance. This is called the built-up edge. As it is welded to the cutting edge, the finishing accuracy of the workpiece becomes rough, peeling off together with a part of the cutting edge when cutting, and the tool may be degraded too.
In particular, this tends to occur easily in aluminum alloys, stainless steel, heat-resistant alloys, etc.
Cutting oil has the effect of protecting the cutting edge with an oil film, preventing adhesion of the built-up edge.



 

Various effects are demonstrated by the permeating action

The reason why cutting oils can exhibit a variety of effects such as lubrication and cooling is due to the effect of the cutting oil flowing into the gaps between the tool and workpiece and between the chips.
Permeability varies depending on the type of cutting oil.




 

Anti-rust action protects the machine, tool and workpiece

After cutting, the workpiece reacts with water and oxygen to turn into a state which rusts easily.
By using a cutting oil, an oil film adheres to the surface to create a protective film which prevents contact with water and air. In addition, water-soluble cutting oils are becoming more and more commonly used as a result of environmental issues. Since they can easily affect not only the workpiece but also the tool and work machine, it is thus necessary to closely examine the types and properties of cutting oils available.



 

Cooling action reduces tool damage

When cutting, chips are caught between the tool and workpiece, so the cutting oil prevents adhesion by flushing them away.
In addition, it is also effective in keeping the work environment clean and safe because it prevents the fine chips generated during cutting from spattering.

 

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