How cutting fluid works (newbie question)

Daniel A. Mitchell wrote:

As anyone trying to TIG on one will quickly discover. :-(
Ted
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jim rozen wrote:

ONE purpose of cutting fluid is to assure that the tool and work are **NOT** "in perfect contact"!
Dan Mitchell ==========
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X-NO-Archive:Yes

day
easily,
((((((((((((((((((((((((((((((((((((()))))))))))))))))))))))))))))))))))))) Well there are lots of variations, mostly it adds sulpher to the mix. When sulpher is present in the steel it cuts easier, as in high sulpher steels. Chlorine is another additive that works at a lower temp than sulpher oils. However the job you described may have been helped better by a spray of cool mist. Bronze especially in deep hole drilling is very troublesome without the mist.
Chlorine oil... cut max 570 E.F Houghton Best for stainless and bronze Costs a little...does a lot... HTH BeeVee
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I've wondered about that too.

Logic says that it doesn't reach the very cutting point. It reaches just about everything else tough (including your clothes). The likely benefit is that it helps the chips/swarf slide against the surfaces above the cutting point easier, where it bends, thereby reducing pressure on the points. With deep holes, I find that the surface tension actually makes the chips stick in the flutes, but the advantages outweigh that disadvantage.
M.K.
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day
the
easily,
edge
But cutting-force analysis shows that lubricants sharply reduce cutting force in many cases.
This subject has been studied in some depth, beginning with research at Carnegie-Mellon Univ. around 50 years ago, and continuing with studies by Dr. Eugene Merchant at Tempe Univ., and elsewhere. If you talk to one of the top engineers at Sandvik, Kennametal, or one of the other biggies, they can direct you to the research info. There also are several knowledgable people at Univ. of Ohio, Perdue, and some other universities where they do academic research on metalworking manufacturing.
There are several mechanisms by which cutting lubricants lower cutting forces, alter the geometry of chip formation, improve finish, and so on.
Ed Huntress
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What logic? Remember all it takes is a monolayer to affect how the cutting happens. That's not much, and right near the cutting there's a storm at work all the time.
Also, when you say 'the very cutting point' you are missing the issue that cutting doesn't just happen at a single location in space. The deformation, chip separation, and chip flow really do occupy a larger volume than just a single point.
So the real question is, how much of the cutting process is devoid of even a monolayer of cutting fluid, if the entire rest of the tool is coated or flooded?
Consider that temperatures get hot enough to vaporize the oil - which means that now there is oil vapor permating the work as well.
Jim
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jim rozen wrote:

In many, if not most, cutting situations, the 'cutting point' doesn't actually do the cutting anyway. This is obviously true of negative rake or zero rake tools, which work more by fracturing the work in front of the tool, but is less obviously true of positive rake tools also. There, the tool acts more like a wedge, prying material out of the work. The fracture in the work still occurs some distance (a SMALL distance to be sure) in front of the cutting tool. The face of the cutting tool tip (point) may not even be in contact with the work (at a microscopic level), with the chip first contacting the tool part way up the rake slope. The chip is 'peeled' upward, tearing the material AHEAD of the so called 'point'. This is the region in which the cutting fluid may aid in material failure and separation.
The lower face of the cutting point will ride on the work behind the cut. Considerable friction (heating) can still occur there, as well as at the point of chip contact. As has been stated, even a thin layer of fluid at those points can substantially reduce friction, heating, and chip 'welding' problems.
Dan Mitchell ==========
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"Cutting fluids play a significant role in machining operations and impact shop productivity, tool life and quality of work. The primary function of cutting fluid is temperature control through cooling and lubrication [Aronson, et al., 1994]. A fluid's cooling and lubrication properties are critical in decreasing tool wear and extending tool life. Cooling and lubrication are also important in achieving the desired size, finish and shape of the workpiece [Sluhan, 1994]. A secondary function of cutting fluid is to flush away chips and metal fines from the tool/workpiece interface to prevent a finished surface from becoming marred and also to reduce the occurrence of built-up edge (BUE)."
http://www.mfg.mtu.edu/cyberman/metal_fluids/charact.html
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