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RY U - G I

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The 9th SEMI-DRY CUTTING INTRODUCTION CHAPTER 3

We have discussed semi-dry
cutting (MQL) several times
at TAKAMATSU RYU-GI.
In this article, we willfocus on two semi-dry cutting
methods:- Cutting with oil mist spray- Cutting with water oil
mist spray

Cutting That Requires Cooling
Compared with usual cutting, semi-dry cuttinguses only a very small quantity of coolant anddue to this feature the shop environment canbe kept clean and tool life can be extended
because high-performance oil can be used.
However, semi-dry cutting has a weak point as
well. That is, semi-dry cutting with oil mist
spray has no forced air-cooling effect. Ifcutting with large heat generation is continued
only with mist spray, heat will build up in
the workpiece, deteriorating accuracy andshortening tool life. Cutting that generates
large amount of heat requires cooling.

Cooling Performance of Water Oil Mist Spray
During cutting with water oil mist spray, unlike
the conventional cooling method, large amountsof coolant do not circulate. In addition, since
the sprayed water and oil evaporate, no waste
is generated. What we'd like to know is its cooling
performance. The graph below indicates the temperatureof a workpiece after being subjected to roughturning process for 3 minutes with different coolingmedia: air blow (dry), oil mist spray, water oil
mist spray, and coolant flow. As can be seen inthe graph, cutting with water oil mist spray has
a considerable cooling effect.

What are the Cuttings that Heavily
Generate Heat?
Heat is generated heavily during cuttings inwhich the contact area between a tool and aworkpiece is large or the contact duration islong. Cutting materials with low thermal
conductivity such as stainless steel also cause
heat generation problems since heat is concentrated
at the point of cutting. Among various cutting
kinds, turning is one of the cuttings in whichheat is likely to be generated since the tool
nose is constantly located in a workpiece,
although the degree of heat generation depends
on the depth of cut and cutting time.

Types of Cutting
Although water mist has an effective cooling
performance for the cutting explained above,
it does not have lubricity or anti-corrosive
properties and therefore a mixture of waterand oil will be more appropriate. Here, wecall the method that uses a mist of awater-oil mixture "cutting with water oil
mist spray" in contrast to "cutting with oil
mist spray" that uses only oil. Water oil mist
cutting has two coolant spraying methods:
spraying a water-soluble coolant and spraying
water and oil individually using a dedicatednozzle.

Coolant mist equipment Sprays mist of water-soluble coolant

Issues and Selection of Cutting Method
Although water oil mist spray has both good cooling
effect and lubricity, it still has a problem.
When compared with semi-dry cutting that uses
only oil, it uses more than 10 times (100 to 200 ccper hour) the fluid (especially, water) and canmake the workplace smoky. This must be taken
into consideration when introducing this method
to improve the workplace environment. When choosing
between cutting with oil mist spray and water
oil mist spray, we must study the advantages andproblems carefully to select the cutting methodthat best meets our purposes. The key factor for
selection is which is more important for yourapplication, cooling effect by water or lubricity
by oil. In continuous rough cutting on a lathe,water oil mist spray will be appropriate sinceheat tends to accumulate in the workpiece. Meanwhile,in finish cutting or near-net-shape cutting withsmall stock removal, oil mist is appropriate since
it provides good surface finish and extends toollife.