coolant All about cutting fluid

Composition of coolant (COTS)
Additives in coolant for machine tools
Main functions of coolant
Coolant classification
Cutting fluids for cutting operations
How to properly use coolant for machine tools

When processing metals by cutting or plastic deformation, a large amount of heat is released. As a result of heating the working tool and the workpiece surface, the quality of processing deteriorates, the wear of expensive tools and equipment increases, and the structure of the surface layers of the workpiece metal changes. This, in turn, leads to a decrease in performance properties and quality of final products.

To prevent the listed manifestations and improve the quality of surface treatment of the workpiece, special cooling technical means are used - COTS.

According to their state of aggregation, COTS are divided into gaseous, liquid, and solid.

The most widely used liquid coolants are cutting fluids (cutting fluids).

Cutting fluid (coolant)

– a special substance used in the operation of metal processing machines. Each technological process of a turning or milling machine is accompanied by friction, which can lead to deformation of the workpiece, breakdown of an expensive machine or its part, and a change in the mechanical properties of the metal.

The main purpose of coolant for metalworking is to separate surfaces subject to friction and reduce the temperature of the tool. This fluid forms a lubricating film on the working surfaces, which reduces friction and the force required for cutting. The introduction of special additives into the composition of the product simplifies the cutting process - liquid molecules quickly penetrate microcracks on the metal surface and, as it were, drive a wedge between its particles.

Composition of coolant (COTS)

The composition of most metalworking coolants is approximately the same. In products of different manufacturers and names, only the concentration of a particular substance or additive needed by a specific process or metal changes.

Effective coolant for machine tools includes:

Lubricants made from natural or synthetic oils
Additives with various performance properties
Substances that prevent the separation of cutting fluids into fractions
Anti-corrosion and wear-reducing components
Additives that reduce foaming and aggressiveness towards processed metals

an engineer will help - The influence of coolant on aluminum processing

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Evaluate the Material
Manufacturers of parts such as automotive engine blocks and cylinder heads process a lot of aluminum. Typically, these operations involve aggressive cutting and feed rates.

The purpose of cutting mode adjustment is to increase the cutting speed sufficiently to improve productivity without exceeding the force and power limits of the machine and cutting tools.

The better the understanding of the interaction between cutting speed, tool edge wear, and cutting power required, and how the selected coolant affects all of these factors, the more successful the machining process.

To this end, Quaker Chemical Corp. conducted a series of end machining tests on aluminum workpieces to evaluate the effects of different cutting fluids on cutting power and cutting tool wear. When machining with a new cutting tool, the coolant had no effect on the machining forces generated at the same cutting speed. However, the more the tool processed the workpiece, the greater the difference in power required to effectively machine using different coolants.

These results show the following

The influence of metal fluid on cutting power is minimal when using new cutting tools. Thus, the difference between the effect of two different coolants on cutting power may not be noticeable until the cutting edges of the tool begin to wear.

The increase in power when milling aluminum is a direct result of cutting edge wear. The rate of this wear is directly affected by both the cutting speed and the metal cutting fluid used.

The relationship between these variables is linear (cutting speed, cutting edge wear and cutting power all increase together). Armed with this knowledge, manufacturers can potentially predict the condition of the cutting edge at any point in the milling process, as well as the required power at other, untested cutting speeds.

Getting into the laboratory

Testing focused primarily on two types of cutting fluids: microemulsion and macroemulsion, each diluted at a concentration of 5% in water. The main difference between the two is the size of the suspended oil droplets. Macroemulsion contains particles with a diameter of more than 0.4 microns, which give an opaque white appearance to the coolant. Microemulsion has a smaller particle diameter and has a translucent appearance.

The experiment was carried out on a Bridgeport GX-710 three-axis CNC machine. The blank was a block of 319-T6 aluminum alloy, 203.2 by 228.6 mm by 38.1 mm, cast, containing copper (Cu), magnesium (Mg), zinc (Zn), and silicon (Si). Machining was carried out with an 18 mm diameter end mill with eight inserts with 15-degree rake angles and 1.2 mm radii.

It machined with an axial depth of 2 mm and a radial depth of 50.8 mm. Each coolant composition was applied to the cutting zone for 28 milling passes at two different cutting speeds, 6,096 rpm (1,460 m/min) and 8,128 rpm (1,946 m/min), to remove 1,321.6 material cm3.

Feed rates at both speeds were 0.5 mm per revolution (0.0625 mm per insert per revolution).

Speed, wear and power

Power measurements for this study during processing were obtained using an instrumented monitoring and adaptive control system. The test results are shown in the charts in this article. As expected, higher cutting speeds resulted in higher machining speeds. However, as described above, the differences in cutting power between the two fluids were minimal when machining with the new cutters.

At the beginning of the process, the workpiece material properties and cutting edge geometry are the dominant factors affecting cutting power. Differences between the performance characteristics of the metal environment arose only after the geometry of the cutting edge changed during wear. The choice of metalworking fluid directly affected the rate at which this wear occurred, and therefore the cutting power required at any given point in the milling operation.

Assuming a certain baseline level of performance for the two fluids being compared, tests should be performed until the cutting inserts begin to wear to determine which coolant allows higher cutting speeds to be maintained for a longer period of time.

The plots made it possible to say that the rate of increase in power can be used to predict the condition of the insert at any given point in the milling operation. Likewise, power measurements taken at several cutting speeds can be used to obtain the required power at other, untested cutting speeds.

Proof

While the x-axis in Figure 1 consists of raw material removal volume data, Figure 2 uses the natural logarithm of this variable. Plotting the volume of material removed in this manner results in a slope, which represents the exact rate at which power increases with subsequent processing.

This measurable measure is necessary to predict tool wear and cutting performance at different cutting speeds. However, these data only indicate that cutting power and material removal volume increase together.

Confirmation of insert wear is especially important since the driving force behind the power increase requires additional testing (specifically, to correlate the slopes of the lines in Figure 2 directly with insert wear that occurs during processing).

These tests added two additional cutting fluids: another macroemulsion and another microemulsion. Each of the four fluids was applied at a cutting speed of 1.946 m/min. until 660 cm3 of material was removed. This provided sufficient time for abrasive wear and, in some cases, metal-to-metal adhesion to occur.

Flange wear measurements were then taken for the four fluids with respect to a parameter relating cutting power to metal slot volume (specifically, the slope of power compared to the natural volume of metal removed).

Additives in coolant for machine tools

Additives are an important component of metalworking coolants. Having a very small concentration, they can significantly improve the quality and efficiency of working with metal.

Additives for various purposes perform several important functions:

Increases the resistance of metals to corrosion
Anti-wear by reducing wear on tool working surfaces
do not allow scuff marks to form on the surface of the metal workpiece during processing,
Prevents the formation of foam, which reduces the quality of the coolant, and the appearance of oil mist, which is harmful to the skin and respiratory organs of working personnel

Lubricant for drilling stainless steel

The drilling operation also requires the application of a cooling lubricant. This is done more to preserve the instrument. In the process of continuously drilling a hole in metals of a strong composition, the drill often begins to overheat and subsequently become dull.

There are two known ways to solve this issue - periodic stops, during which the drill will cool, or the use of an emulsion for cooling. As a rule, the second option is preferable; it will save time and money on a new drill. To do this, use an oil-based lubricant for drilling stainless steel; as a home equivalent, it is fair to use regular machine oil.

After drilling a hole a little, add oil to it, or periodically lubricate the drill with the product using a brush.

Main functions of coolant

Lubricating and cooling fluids for metal-cutting machines perform the following main functions:

Cools cutting tools that get hot during operation and increases their service life
Improving the quality of metal surface treatment
Removing dust, dirt, metal shavings, etc. from working surfaces.
Lubrication of the friction zone to increase the service life of cutters, reduce the coefficient of friction and heat generation
Increasing machine productivity by increasing speed, improving quality and precision of processing

Emulsol for paving slabs

In this case, the lubricant serves to facilitate the process of creating tiles. A special form is lubricated with an emulsion, then a concrete solution is poured into it. After drying, the product is easily and simply removed from the mold due to the fact that the mold has been lubricated, this significantly speeds up the work process.

The following compounds can be used as lubricants: KSF-1, Nometal, AGAT-B9, Separen.

But no one cancels the use of improvised means, in the form of machine oil or soap solution. With their help, you can also prepare an emulsol for paving slabs with your own hands.

Source

Coolant classification

Each technological process requires a coolant, the properties of which will best meet the specifics of the material and the characteristics of the machine.

Typically, metalworking production uses several types of metalworking coolants:

Oil coolants.
Their base is mineral or synthetic oil. To obtain special properties of the liquid, additives are added to the composition. Such coolants perfectly lubricate surfaces, but do not reduce temperatures well, so they are used for soft metals for simple work.
Water-miscible coolants
– these liquids may contain alcohols, emulsifiers, oils, electrolytes, additives, etc. They cool tools and metals well, but have modest lubricating characteristics,
Mineral cutting fluids
– produced from petroleum products, used primarily for the operation of milling and lathes for cutting steel,
Synthetic and semi-synthetic coolants
– these types of cutting fluids are made on the basis of a mixture of water-soluble half-mirs with the addition of surfactants, inhibitors, biocides, etc.
Coolant emulsions
– compositions with a higher concentration of dispersed components compared to water-miscible ones. Such fluids have excellent lubricating and anti-wear characteristics.

In addition to composition, cutting fluids can be classified according to other criteria, for example:

Based on the method of preparation or composition of the working fluid, a distinction is made between emulsols - ready-made liquids that contain additives that prevent separation - and coolant concentrates, mixed with water before use to obtain coolant emulsions.
By viscosity, flash point, acid number, etc. (oil coolants)

Coolant for copper/wire drawing

When working with copper wire, emulsions of different compositions are used, in accordance with the stage of the work. The initial stage will be rough drawing, in this case, the first step is to use an oil-based composition. It will optimally cool the product and give the primary processing the desired properties.

The second step is to use exclusively coolant for wet wire drawing, in the form of an aqueous emulsion. This is a finishing version of processing, and the final stage of part formation.

Cutting fluids for cutting operations

Let us note which cutting fluids are most common when carrying out various cutting operations on lathes:

One and a half percent solution of soda ash in boiled water (for rough grinding)
Water, trisodium phosphate and sodium trinitrate – increases anti-corrosion resistance
Water, emulsol and soda - ensures high quality grinding
Oil (industrial and linseed) and kerosene - for high-precision work with expensive cutters
Sulfofresol and kerosene - for deep metal drilling
Kerosene – when working with aluminum and its alloys

Metal forming also requires the use of metalworking coolants, but such materials must have special properties. Metal forming is characterized by significant forces and low sliding speed between the workpiece and the tool, therefore the coolant must be sufficiently viscous and resistant to delamination at high temperatures. Often, such fluids contain fine-flaked graphite, which minimizes friction in the plastic deformation zone.

Special lubricants and cooling materials are also used when working with aluminum and its alloys. This metal tends to stick to the surfaces of the cutting tool with which it comes into contact. For this reason, cutting fluids for aluminum must provide high quality finishing of the workpiece. When working with aluminum, emulsions of coolant based on fatty acids and substances with ethylene glycol or glycerin are usually used.

Types of coolant for metal forming processes

Due to the significant specific forces, as well as the speeds of relative sliding of the workpiece material along the tool, grades for use in technological processes must have a significantly higher viscosity. In addition, at significant degrees of deformation, chemical-mechanical surface reactions begin on the contact surfaces, contributing to the deterioration of friction conditions. This reduces tool life, particularly when machining soft metals such as aluminum. It is unacceptable to use partially waste substances when processing aluminum. Therefore, the characteristic features of these compositions for Russian conditions are:

Quite high viscosity. In practice, it varies from 45 - 50 cSt for coolants based on mineral oils of type I20 (GOST 20799-88), to 75 - 80 cSt for coolants with sulfur compounds and animal fats (a typical representative is Ukrinol GOST 9.085-88);
Resistant to high temperature delamination or fracture. The composition necessarily contains sulfur additives and anionic emulsifiers. The most commonly used brands include ethanolamines and alkyl sulfates with additives in accordance with GOST 10534-88. In waste products, the concentration of such components decreases sharply;
Water-based graphite types, including an additive based on an oil suspension of fine-flaked graphite. Produced in accordance with GOST 5962-88.

A special group is represented by substances used in the processing of aluminum and its alloys. Aluminum is characterized by intense adhesion to the contact surfaces of the equipment, so it should be ensured not so much a decrease in temperature as a high cleanliness of the final surface of the product.

For example, when rolling aluminum sheets, the following are used:

Products based on 5 - 10% lubricant 59c (GOST 5702-85);
Emulsols based on synthetic fatty acids with the addition of triethanolamines (GOST 8622-85);
Substances containing high molecular weight synthetic alcohols: for example, ethylene glycol GOST 10136-97 or glycerin GOST 6823-97.

Quite a lot of coolant systems designed for working with aluminum are produced according to the specifications of Russia and other CIS countries. The viscosity of such compositions for processing aluminum is usually assumed to be minimal.

Lubricant for drilling stainless steel

After drilling a hole a little, add oil to it, or periodically lubricate the drill with the product using a brush.

Types of coolant for metal forming processes

Quite high viscosity. In practice, it varies from 45 - 50 cSt for coolants based on mineral oils of type I20 (GOST 20799-88), to 75 - 80 cSt for coolants with sulfur compounds and animal fats (a typical representative is Ukrinol GOST 9.085-88);
Resistant to high temperature delamination or fracture. The composition necessarily contains sulfur additives and anionic emulsifiers. The most commonly used brands include ethanolamines and alkyl sulfates with additives in accordance with GOST 10534-88. In waste products, the concentration of such components decreases sharply;
Water-based graphite types, including an additive based on an oil suspension of fine-flaked graphite. Produced in accordance with GOST 5962-88.

For example, when rolling aluminum sheets, the following are used:

Products based on 5 - 10% lubricant 59c (GOST 5702-85);
Emulsols based on synthetic fatty acids with the addition of triethanolamines (GOST 8622-85);
Substances containing high molecular weight synthetic alcohols: for example, ethylene glycol GOST 10136-97 or glycerin GOST 6823-97.

Why is it sometimes better to mill without coolant?

As the cutting edge enters or exits the cut, a sudden temperature change occurs. The cutting edge is subjected to thermal shock at this moment, which often leads to the appearance of thermal cracks, and then to breakage. It is believed that the higher the temperature in the cutting zone, the less the need to use cutting fluid. When finishing milling a material, the liquid does not cause harm, since the heat generated is much less.

The absence of lubrication during roughing increases the strength of the cutting edge. This does not cancel temperature fluctuations, but leaves them within acceptable limits. Thus, rough milling of AMG6 without coolant is quite possible and even desirable.

In the modes listed below, the use of liquid is permitted and does not pose a danger to the instrument:

Finishing of aluminum alloys (to protect against chip adhesion).
Milling of thin-walled parts (to maintain the specified geometry).
Working with heat-resistant materials (to reduce friction).

If chips are stuck in deep recesses on a machine or part, then the oil mist method described above will help eliminate them. It should also be understood that for the best quality of milling using lubricant, it is necessary to ensure its sufficient and continuous supply.

Our company offers to purchase any cutting fluids in St. Petersburg at a reasonable price. We are personally responsible for product quality.

Coolant for copper/wire drawing

The second step is to use exclusively coolant for wet wire drawing, in the form of an aqueous emulsion. This is a finishing version of processing, and the final stage of part formation.