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{{Short description|Coolants and lubricants used in metalworking}}
[[Image:Makino-S33-MachiningCenter-example.jpg|thumb|Thin-wall milling of [[aluminum]] using a water-based cutting fluid on the [[milling cutter]].]] '''Cutting fluid''' is a type of [[coolant]] and [[lubrication|lubricant]] [[designed]] specifically for [[metalworking]] processes, such as [[machining]] and [[Stamping (metalworking)|stamping]]. There are various kinds of cutting fluids, which include oils, oil-water [[emulsion]]s, pastes, gels, aerosols (mists), and air or other gases. Cutting fluids are made from petroleum distillates, [[animal fat]]s, [[plant oil]]s, water and air, or other raw ingredients. Depending on context and on which type of cutting fluid is being considered, it may be referred to as '''cutting fluid''', '''cutting oil''', '''cutting compound''', '''coolant''', or '''lubricant'''.
Most metalworking and machining processes can benefit from the use of cutting fluid, depending on workpiece material. Common exceptions to this are [[cast iron]] and [[brass]], which may be machined dry (though this is not true of all brasses, and any machining of brass will likely benefit from the presence of a cutting fluid).<ref name="Camm1949">{{cite book|author=Frederick James Camm|title=Newnes Engineer's Reference Book|url=https://books.google.com/books?id=iXxGAAAAMAAJ|year=1949|publisher=George Newnes|page=594}}</ref>
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==Function==
{{Unreferenced section|date=May 2023}}
=== Cooling ===
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== Delivery methods ==
{{Unreferenced section|date=May 2023}}
Every conceivable method of applying cutting fluid (e.g., flooding, spraying, dripping, misting, brushing) can be used, with the best choice depending on the application and the equipment available. For many metal cutting applications the ideal has long been high-pressure, high-volume pumping to force a stream of liquid (usually an oil-water emulsion) directly into the tool-chip interface, with walls around the machine to contain the splatter and a sump to catch, filter, and recirculate the fluid. This type of system is commonly employed, especially in manufacturing. It is often not a practical option for maintenance, repair and overhaul or hobbyist
As technology continually advances, the flooding paradigm is no longer always the clear winner. It has been complemented since the 2000s by new permutations of liquid, aerosol, and gas delivery, such as minimum quantity lubrication and through-the-tool-tip cryogenic cooling (detailed below).
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[[Mineral oil]]s, which are petroleum-based, first saw use in cutting applications in the late 19th century. These vary from the thick, dark, sulfur-rich cutting oils used in heavy industry to light, clear oils.
Semi-synthetic coolants, also called ''soluble oil'', are an emulsion or [[microemulsion]] of water with mineral oil. In workshops using British English, soluble oil is colloquially known as '''SUDS'''.<ref>{{Cite web | url=https://www.midlandslubricants.co.uk/metalworking/cutting-oils-suds/midlands-lubricants-general-soluble-cutting-oil-suds/ | title=General Soluble Cutting Oil – Water Soluble Cutting Oil – Midlands Lubricants Ltd}}</ref> These began to see use in the 1930s. A typical CNC machine tool usually uses emulsified coolant, which consists of a small amount of oil emulsified into a larger amount of water through the use of a detergent.
[[Synthetic chemical|Synthetic]] coolants originated in the late 1950s and are usually water-based.
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Some cutting fluids are used in [[aerosol]] (mist) form (air with tiny droplets of liquid scattered throughout). The main problems with mists have been that they are rather bad for the workers, who have to breathe the surrounding mist-tainted air, and that they sometimes don't even work very well. Both of those problems come from the imprecise delivery that often puts the mist everywhere and all the time except at the cutting interface, during the cut—the one place and time where it's wanted. However, a newer form of aerosol delivery, {{Visible anchor|MQL}} (minimum quantity of lubricant),<ref name="Z">{{Citation |last=Zelinski |first=Peter |date=2006-08-28 |title=Toward more seamless MQL |journal=Modern Machine Shop |url=http://www.mmsonline.com/articles/toward-more-seamless-mql }}</ref><ref name="K">{{Citation |last=Korn |first=Derek |date=2010-09-24 |title=The many ways Ford benefits from MQL |journal=Modern Machine Shop |url=http://www.mmsonline.com/articles/the-many-ways-ford-benefits-from-mql }}</ref> avoids both of those problems. The delivery of the aerosol is directly through the flutes of the tool (it arrives directly through or around the [[tipped tool|insert]] itself—an ideal type of cutting fluid delivery that traditionally has been unavailable outside of a few contexts such as [[gun drill]]ing or expensive, state-of-the-art liquid delivery in production milling). MQL's aerosol is delivered in such a precisely targeted way (with respect to both location and timing) that the net effect seems almost like dry machining from the operators' perspective.<ref name="Z"/><ref name="K"/> The chips generally seem like dry-machined chips, requiring no draining, and the air is so clean that machining cells can be stationed closer to inspection and assembly than before.<ref name="Z"/><ref name="K"/> MQL doesn't provide much cooling in the sense of heat transfer, but its well-targeted lubricating action prevents some of the heat from being generated in the first place, which helps to explain its success.
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[[Carbon dioxide]] (chemical formula CO<sub>2</sub>) is also used as a [[coolant]]. In this application pressurized liquid CO<sub>2</sub> is allowed to expand and this is accompanied by a drop in temperature, enough to cause a change of phase into a solid. These solid crystals are redirected into the cut zone by either external nozzles or through-the-spindle delivery, to provide temperature controlled cooling of the cutting tool and work piece.<ref>{{Citation |date=2011-09-26 |title=CO2 Cooling System reduces friction |journal=Modern Machine Shop Online |url=http://www.mmsonline.com/products/co2-cooling-system-reduces-friction}}</ref>
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Some of the diagnoses that can result from the mechanisms explained above include [[irritant contact dermatitis]]; [[allergic contact dermatitis]]; [[occupational acne]]; [[tracheitis]]; [[esophagitis]]; [[bronchitis]]; [[asthma]]; [[allergy]]; [[hypersensitivity pneumonitis]] (HP); and worsening of pre-existing respiratory problems.
Safer cutting fluid formulations provide a resistance to tramp oils, allowing improved filtration separation without removing the base additive package. [[HVAC|Room ventilation]], splash guards on machines, and [[personal protective equipment]] (PPE) (such as [[safety glasses]], [[respirator]] masks, and [[glove#Commercial and industrial|gloves]]) can mitigate hazards related to cutting fluids.<ref name=niosh>NIOSH (1998). [https://www.cdc.gov/niosh/98-102.html Criteria for a recommended standard: occupational exposure to metalworking fluids]. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. DHHS (NIOSH) Pub. No. 98-102.</ref> Additionally, Skimmers may be used to remove tramp oil from the surface of cutting fluid, which prevents the growth of micro-organisms.<ref>{{Cite web|url=https://oil-skimmers.co.uk/|title=Tramp Oil Skimmers {{!}} Belt, Disc Oil Skimmers {{!}} SKIM IT|website=Oil Skimmers|language=en-US|access-date=2018-10-17|archive-date=2023-04-17|archive-url=https://web.archive.org/web/20230417173918/https://oil-skimmers.co.uk/|url-status=dead}}</ref>
[[Bacteria]]l growth is predominant in petroleum-based cutting fluids. Tramp oil along with human hair or skin oil are some of the debris during cutting which accumulates and forms a layer on the top of the liquid; anaerobic bacteria proliferate due to a number of factors. An early sign of the need for replacement is the "Monday-morning smell" (due to lack of usage from Friday to Monday). [[Antiseptic]]s are sometimes added to the fluid to kill bacteria. Such use must be balanced against whether the antiseptics will harm the cutting performance, workers' health, or the environment. Maintaining as low a fluid temperature as practical will slow the growth of microorganisms.<ref name=niosh /> Some health and safety regulators (such as the HSE in the United Kingdom) require weekly testing of metal working fluids to help maintain the fluid's health. These tests involve checking the bacterial CFU/ml Level of the MWF (using [[Dipslide]]s) and the pH level by using either a pH meter or pH test strips (since a low pH can be caused by a high bacterial level).<ref>{{Cite web|url=https://dip-slides.com/home/31-metal-cutting-fluid-dipslides-box-of-10.html|title=Metal Cutting Fluid Dipslides (10 Pack)|website=dip-slides|language=en-US|access-date=2022-04-28}}</ref>
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Cutting fluids degrade over time due to contaminants entering the lubrication system. A common type of degradation is the formation of ''tramp oil'', also known as ''sump oil'', which is unwanted oil that has mixed with cutting fluid.<ref name="Smid2010p114">{{Harvnb|Smid|2010|p=114}}.</ref> It originates as [[lubrication]] oil that seeps out from the [[slideway]]s and washes into the coolant mixture, as the protective film with which a steel supplier coats [[bar stock]] to prevent rusting, or as [[hydraulic fluid|hydraulic]] oil leaks. In extreme cases it can be seen as a film or skin on the surface of the coolant or as floating drops of oil.
[[Skimmer (machine)|Skimmer]]s are used to separate the tramp oil from the coolant. These are typically slowly rotating vertical discs that are partially submerged below the coolant level in the main reservoir. As the disc rotates the tramp oil clings to each side of the disc to be scraped off by two wipers, before the disc passes back through the coolant. The wipers are in the form of a channel that then redirects the tramp oil to a container where it is collected for disposal. Floating [[weir]] skimmers are also used in these
Since the introduction of CNC additives, the tramp oil in these systems can be managed more effectively through a continuous separation effect. The tramp oil accumulation separates from the aqueous or oil based coolant and can be easily removed with an absorbent.
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==References==
{{Reflist|35em}}
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==External links==
*[https://www.cdc.gov/niosh/topics/metalworking/ Metalworking Fluids - NIOSH Workplace Safety and Health Topic] - National Institute for Occupational Safety and Health
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{{DEFAULTSORT:Cutting Fluid}}
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