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3. Coolant and MQL |
|
| It is necessary, first of all, to verify the well-known triple role of
coolant: lubrication, cooling, and chip transfer, the priority of which
depends on the work piece material, the method of cutting and the machine.
For aluminum lubrication the most important priority is lubrication, whereas
cooling is more important for heavy cutting of steels. |
| When you cut aluminum with a diamond
coated tool, two materials having low affinity for each other, a complete
dry method is possible. For rough turnings, some factories have already
realized dry processes with air blowing only. To cut castings whose
chips are of flow type, whose solidity is low and whose precipitating
carbon is self-lubricating, most factories adopt complete dry methods.
Face milling or end milling are of interrupted cutting, chips are
easy to remove, hence dry cutting is possible. |
| For boring, which generates and accumulates considerable heat, coolant
is a must. Verifying the roles that coolant plays concerning work piece
materials or production mode show where MQL is relevant. MQL assumes only
one among three principal roles that coolant plays: the lubrication. It
somewhat suppresses heat generation because of higher lubricity of lubricant
than ordinary coolants, but has no property of forced cooling. MQL requires
a strict cutting condition that minimum area and time of touch between
tool and work piece prevent heat generation. Unlike coolant where volume
helps with chip removal, MQL, which utilizes air blowing appears mediocre
for chip removal. For this, additional air blowing or magnetic transfer
systems are recommended but the additional lines in operation may obstruct
performance. |
| Expectations for machine manufacturers
to develop corresponding models : horizontal machining center, tilting
trick on the upper surface of flat parts where chips tend to gather,
renovation of chip exit. |
As we have seen above, MQL meets with difficulty in many areas:
| 1. |
Boring |
| 2. |
Some aluminum having tendency towards deposition
(especially rolled materials like A5052) |
| 3. |
Some stainless steels which bear flow type
chips |
|
Trials were conducted on these angles. For turning, we laid stress on calculating
flank wears, because it is easy for MQL to hadle. We intended to classify
MQL cases into 3 categories comparing them to traditional high pressured
coolant:
| 1. |
more efficient than coolant |
| 2. |
as efficient as coolant |
| 3. |
less productive than coolant (tool life &
cutting condition) |
|
| However it is not so easy; many clients use many different types of coolants,
some of them are water soluble whereas others not, some contain chlorine
based extreme pressure additives others not - in different conditions -
equipment with or without high pressure coolant facility, spindle through
or external nozzles, etc. Comparing conditions varies and there are over
2000 brands of water-soluble lubricants in the market. For these reasons
it is difficult to make a strict comparison between MQL and coolant. Instead,
we chose to verify approximately the MQL cutting possibilities. Testing
using various methods and various materials developed data that appears
somewhat ambiguous. We hope that you can see the opportunities and possibilities
of MQL cutting based upon the principles
presented. |
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