Coolant for aluminum drawing. Selection of cutting fluid for machining aluminum alloys Coolant for aluminum alloys

Anyone, even a novice metalworking specialist, knows that when performing turning work on a machine, it is imperative to use cutting fluids (coolants). The use of such technical fluids (their composition may vary) allows you to solve several important problems at the same time:

cooling of the cutter, which is actively heated during processing (respectively, extending its service life);
improving the surface finish of the workpiece;
increasing the productivity of the metal cutting process.

Types of coolant used in turning

All types of coolant used for turning work on the machine are divided into two large categories.

Water based coolant
Oil-based coolant

Such liquids remove heat from the processing area much worse, but provide excellent lubrication of the surfaces of the workpiece and tool.

Among the most common coolants that are used when, the following can be noted.

A solution of soda ash (1.5%) in boiled water. Such a liquid is used when performing rough turning on a lathe.
An aqueous solution containing 0.8% soda and 0.25% sodium nitrite, which increases the anti-corrosion properties of the coolant. It is also used for rough turning on the machine.
A solution consisting of boiled water and trisodium phosphate (1.5%), almost identical in its cooling effect to liquids containing soda ash.
An aqueous solution containing trisodium phosphate (0.8%) and sodium nitrite (0.25%). It has improved anti-corrosion properties and is also used in rough turning on lathes.
A solution based on boiled water, containing in its composition a special potassium soap (0.5–1%), soda ash or trisodium phosphate (0.5–0.75%), sodium nitrite (0.25%).

Water-based solution containing 4% potassium soap and 1.5% soda ash. Coolants, which contain soap, are used when performing roughing, as well as shaped turning on a lathe. Potassium soap, if necessary, can be replaced by any other soap that does not contain chloride compounds.
A solution based on water, to which emulsol E-2 (2–3%) and technical soda ash (1.5%) are added. Coolant of this type is used when, to the cleanliness of the machined surface, which is not required high demands. With the use of such an emulsion, it is possible to process workpieces on the machine on high speeds.
An aqueous solution containing 5–8% emulsol E-2 (B) and 0.2% soda or trisodium phosphate. With the use of such a coolant, fine turning is performed on a lathe.
An aqueous solution containing emulsol based on oxidized petrolatum (5%), soda (0.3%) and sodium nitrite (0.2%). You can use such an emulsion when performing roughing, as well as finishing turning on the machine, it allows you to obtain surfaces of higher purity.
An oil-based fluid containing 70% industrial oil 20, 15% linseed oil of the 2nd grade, 15% kerosene. Coolant of this composition is used in cases where high-precision threads are cut and workpieces are processed with expensive shaped cutters.

Sulfofrezol is an oily cutting fluid activated with sulfur. This coolant is used when turning with a small cut section. When performing rough work, characterized by active and significant heating of the tool and workpiece, the use of such coolant can be harmful to the machine operator, as it emits volatile sulfur compounds.
A solution consisting of 90% sulfofresol and 10% kerosene. Such a liquid is used for threading, as well as for deep drilling and finishing workpieces.
Pure kerosene - is used when it is necessary to process workpieces made of aluminum and its alloys on a lathe, as well as when finishing using oscillating abrasive bars.

Features of the use of cutting fluids

For the use of coolant to be effective, a few simple rules should be considered. The flow rate of such a liquid (regardless of whether it is an emulsion or an aqueous solution) should be at least 10–15 l / min.

It is very important to direct the coolant flow to the place where the maximum amount of heat is generated. Such a place when performing turning is the area where the chips are separated from the workpiece.

From the very first moment when turning on the machine, the cutting tool begins to heat up actively, so coolant should be applied immediately, and not after some time. Otherwise, with a sharp cooling of a very heated one, cracks may form in it.

More recently, an advanced cooling method has been introduced, which involves the supply of a thin stream of coolant from the back of the cutter. This method of cooling demonstrates particular efficiency when, on a lathe, a tool made of high-speed alloys is required to process a workpiece made of hard-to-cut materials.

In the process of metalworking, there is always a strong friction between the workpiece and the tool. This is especially significant for lathes, where the cutter is very hot. Intense friction also causes premature wear of the tool for cold plastic deformation, especially for operations such as high-speed multi-position upsetting or cold extrusion. In all these cases, it is necessary to use special cutting fluids.

One of the latest domestic developments in the field of cutting fluids is the water-soluble universal coolant EFELE CF-621. Although this coolant is synthetic, it has the lowest cost associated with mineral products.
EFELE CF-621 is designed for cutting operations on metals such as steel, including stainless and alloyed, cast iron, titanium, aluminum and copper alloys.
This coolant is available in the form of a concentrate. It has an amber color and a pleasant caramel smell, does not contain formaldehyde, chlorine and secondary amines, therefore it does not have a harmful effect on health. Made from synthetic components with the addition (up to 15%) of a mineral oil composition, EFELE CF-621 coolant has good biostability and high performance properties. This allows the processing of metals at a lower concentration of the solution.

Cutting fluids: structure, mechanism of action

The widespread use of cutting fluids is due to the fact that they simultaneously perform effective separation of the rubbing surfaces of the workpiece and tool, and also reduce the temperature of the latter. At the same time, the composition of the components, which include the most effective cutting fluids, is presented:

Lubricants based on synthetic or animal oils.
Additives that provide substances with anti-friction, extreme pressure indicators.
Components that exclude the separation of compositions during long-term storage.
Substances that protect working tools from corrosion and destruction.
Additives that reduce aggressiveness.
Additives that improve wettability and reduce foaming during metalworking.

Waste products are subject to mandatory disposal.

The classification according to which cutting fluids (coolants) are produced is usually made according to the following parameters:

By origin of the main components. Thus, oil coolants are produced based on technical oils - petroleum products, as well as on the basis of fats of animal or vegetable origin.
According to the method of preparation, emulsols are distinguished - products with a long period of spontaneous exfoliation, or technical oil coolants, which are prepared immediately before their use. In the latter case, coolant concentrate is produced according to GOST.
According to the industry of their application, synthetic coolants are produced, designed for the conditions of plastic deformation operations, moreover, for lathes.
Oil coolants also differ in their physical and mechanical properties - acid number, viscosity, flash point. The latter characteristic determines whether oil coolants can be used in hot stamping operations or not.

Brands of the most common compounds for machining

For lathes, the following types are produced:

Emulsols, which are diluted conventional mineral oils (for example, I-12, I-20) Petroleum-based emulsols are produced according to technical requirements GOST 6243-75;
Emulsifiers that contain metallic soaps of synthetic fatty acids. Produced in accordance with GOST R 52128-2003;
Synthetic formulations based on high-atomic alcohols, tall oils, triethanolamine. They are produced in accordance with GOST 38.01445-88, and are intended for lathes that machine high-speed, stainless, alloy steels. It is not allowed to use them in a waste form;
Sulfofresols (GOST 122-94) are mixtures of highly purified oil and sulfur-containing compounds. Effectively reduce friction, do not have corrosive properties, since they do not contain water, acids, alkalis.

A common property that synthetic cutting fluids for lathes should have is reduced viscosity. Here, the main components of the coolant are easily distributed over the complex surface of the tool, cool it well, and do not allow chips to stick to the cutter. On average, the considered indicator for machining processes does not exceed 35 - 40 cSt.

In Russia, imported products are often used, for example, from trademark MobilCut. However, according to the principle of import substitution, which is now being widely introduced in Russia, imported brands are gradually being replaced by domestic types of similar products. In addition, the descriptions for such products often do not cover the types of steels or non-ferrous alloys (in particular, aluminum) that are used in Russia. There are specially equipped containers for used coolant.

Types of coolant for metal forming processes

Due to the significant specific efforts, as well as the relative sliding speeds of the workpiece material on the tool, the brand for use in technological processes should have a significantly higher viscosity. In addition, at significant extent deformations on the contact surfaces, chemical-mechanical surface reactions begin, contributing to the deterioration of friction conditions. This reduces tool life, particularly when machining soft metals, for example, aluminum. The use of partially spent substances in the processing of aluminum is unacceptable. That's why characteristic features these compositions for the conditions of Russia are:

Relatively 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, anionic emulsifiers. The most used brands include ethanolamines and alkyl sulfates with additives according to GOST 10534-88. In waste products, the concentration of such components is sharply reduced;
Water-based graphite types, including an additive based on an oil suspension of fine-flake graphite. Are issued 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 sticking to the contact surfaces of the tooling; therefore, not so much a decrease in temperature should be ensured as a high purity 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.

A lot of coolant systems designed to work with aluminum are produced according to the specifications of Russia and other CIS countries. The viscosity of such compositions for working aluminum is usually taken as a minimum.

Preparation, storage and disposal of cutting fluids

In Russia, both coolant concentrate and components for its preparation are produced for the conditions of a particular enterprise. Before being used for metalworking, they go through the following procedures:

Mixing the components at the right temperatures (at 60 - 110 ° C, which is determined by brand and composition).
Sampling for compliance analysis (GOST 2517-80 applies to Russia).
Storage in specialized containers that allow periodic mixing, heating, etc.
Refueling in devices and devices for continuous supply.

Additives may be added in preparation for coolant. For this, fine emulsification vibrators are often provided at the sites of Russian enterprises.

Over time, the compositions in question become contaminated, therefore, various systems, which clean the coolant from the remnants of chips, adhering metal, etc. Waste products, the effective cleaning of which is no longer possible, are disposed of.

Video how to weld cutting fluid with your own hands

Most machine tool operators find it difficult to imagine a machining process without the use of a cutting fluid (coolant). However, in some cases, there is a need for dry processing, which may be due to the lack of appropriate equipment preparation, or other conditions for the work. Analytical data from various sources indicate that the cost of providing workpiece cooling is 2-3 times higher than the cost of cutting tools. In addition, the world community is increasingly concerned about the protection of health and environment during the production work. Disposal of used cutting fluid is a major concern for most businesses, and inhalation of its fumes can cause significant harm to human health. Due to the high costs of coolant disposal, European manufacturing enterprises more and more often use dry or semi-dry (with a minimum amount of coolant) machining technologies, in contrast to enterprises in the United States. However, countries such as Germany still have to reckon with the current economic and working conditions and use coolant. However, new regulations have already been proposed that limit the use of coolant in machining.

Let's talk more about dry machining. Can materials be machined without coolant? In most cases it is possible, but this issue requires more detailed consideration.

First, the cutting fluid performs a number of tasks:

Cooling. That is why the liquid is called coolant.
Grease. Tough materials such as aluminium, build up on the cutting edge, so it is necessary to reduce friction and, consequently, their heating.
Chip cleaning. In many cases, this task is the most important. If chips hit the surface being machined, it will damage the surface and cause a much faster tool blunting. In the worst case, a cutter or cutter inserted into a slot or hole can become clogged with chips, causing them to overheat or even be damaged.

In dry machining, each of the above functions of the cutting fluid must be taken into account.

Lubrication and build-up on the cutting edge

Let's talk about lubrication. I paid the least attention to this topic, but this does not mean that lubrication is not important in processing. First of all, lubrication contributes to more effective work cutting tool with less heat. When the front edge of the cutter slides over the workpiece, it heats up due to friction. In addition, the chips also rub against the cutter, generating additional heat. Lubrication reduces friction and therefore heat. Thus, one of the functions of lubrication is to improve cooling efficiency by reducing heat generation. The main function of the lubricant is to prevent build-up on the cutting edge. Anyone who has seen how aluminum sticks to a cutter immediately understands the importance of this issue. Built-up edges can cause damage to the tool very quickly and thus delay work.

Fortunately, the presence or absence of build-ups mainly depends on the type of material being processed. Most often, build-up occurs when machining aluminum and steel with a low content of carbon or other alloying elements. AT this case very sharp cutters with large rake angles must be used (positive rake angle is your friend!). Also, spraying a small amount of coolant helps to cope with this problem, and the efficiency of this method is not inferior to the traditional method. Most importantly, do not forget to take these measures before the formation of adhesions between the chips and the surface being machined.

Chip cleaning

The next problem with dry machining is chip removal. Compressed air can be used for this purpose. However, this cleaning method may not be fully effective in some operations, such as drilling. Deep boring and drilling are two of the most problematic dry machining operations in terms of chip removal. To solve the problem, you can use process air supplied to the tool, but spraying a small amount of coolant is a better solution. Liquid coolant is better at this task, because it has a higher density, better transfers chips and cools the machined surface. But the correct application of spraying allows you to extend the life of the tool compared to the traditional method described above. It should be noted that natural chip removal is more effective on horizontal milling and turning machines than on vertical ones, especially in dry or semi-dry machining, due to the presence of gravity.

Cooling

Let's talk about cooling. Temperature is the most important factor affecting the life of a cutting tool. A slight heat softens the material, which has a positive effect on the processing. At the same time, strong heating softens the cutting tool and leads to its premature wear. Permissible temperature depends on the material and coating of the cutting tool. In particular, carbide withstands significantly higher temperatures than high speed steel. Some coatings such as TiAlN (titanium aluminum nitride) require high working temperature, so these tools are used without coolant. There are many examples where cutting out coolant while maintaining technology results in longer tool life. Carbide tools are susceptible to the formation of microcracks in the event of sudden temperature changes during uneven heating and cooling. Sandvik recommends in its educational course do not use coolant, at least in large quantities, in order to prevent the formation of microcracks. It should also be noted that high heat adversely affects the accuracy of processing, since as a result of heating, the size of the workpiece changes.

How can workpieces be cooled without coolant? First, let's look at the most common cooling methods. There are two types of coolants - water-based coolants and coolants based on oil. Water-based coolants are most effective for cooling. How much? Comparative data are shown in the following table:

coolant	Specific heat	Steel A (hardened) Decrease in temperature, %	Steel B (annealed) Decrease in temperature, %
Air	0.25
Oil with additives (low viscosity)	0.489	3.9	4.7
Oil with additives (high viscosity)	0.556	6	6
Aqueous moisturizer solution	0.872	14.8	8.4
Water-soda solution, 4%	0.923	-	13
Water	1.00	19	15

First, the data presented in the table indicate that the efficiency of various types of coolants directly depends on their specific heat capacity. Secondly, it should be noted that air is the worst refrigerant - its characteristics are 4 times inferior to those of water. Also interesting is the fact that oil coolants are almost 2 times inferior to water in terms of cooling properties. Given this fact, as well as safety issues, it is not surprising that many enterprises use water-based coolants - they are the best coolants. However, water-based coolants only work effectively up to a certain cutting speed, and the higher the speed becomes, the worse they cool the material and tool. One of the reasons for this phenomenon is that at a high cutting speed, the coolant does not have time to penetrate into all the recesses and cracks in the material. As a result, the cooling becomes less and less qualitative, resulting in a decrease in the cooling efficiency of the carbide tool at a cutting speed exceeding a certain value.

Heat-resistant coatings such as TiAlN that do not require cooling can be used, but it is possible to do without them. For example, compressed air can be used for cooling, but it must be remembered that large volumes of air will be required to achieve efficiency comparable to water cooling. In cases where cooling is required, it is much more efficient to use humidified air containing atomized liquid. Spraying also provides lubrication, which can be useful for materials such as aluminium. In addition, at high cutting speeds, humidified air penetrates into all cavities in the material better than water with water cooling.

Another method of cooling is the use of chilled air. There are many ways to cool the air, and it cools naturally as it exits the nozzle, but more effective solution is the application of a device called a vortex tube. The above data on various types of coolants, as well as detailed information on research related to the use of air and vortex tubes for cooling, can be found in scientific work Brian Boswell "The use of air cooling and its effectiveness in the dry processing of materials."

this work can be quite helpful if you want to get into the details. Boswell is considering equipping some lathe chucks with air channels, but concludes that the most effective option is to use vortex tubes. If you are going to use only air, it must be directed to the right places to ensure effective cooling. Boswell found that adjusting the vortex tube was much easier because the nozzle could be located farther away from the material being processed. At the same time, this device is able to cool the material as efficiently as a traditional water cooling system.

Parameters of dry machining of materials

Let's assume that you don't have accessories like a vortex tube, but you use dry or humidified compressed air for lubrication and chip removal. How does this affect the machining conditions (feed and cutting speed) compared to conventional wet machining?

Consider separately such a parameter as feed per tooth. The adjustable value, depending on the type of cooling, is the cutting speed. In this case, the feed rate for a given feed per tooth will decrease slightly.
If a certain cutting speed threshold is exceeded, the adjustment depending on the type of cooling does not work. In most cases, the cooling system will be turned off altogether. Let's call this threshold value the critical cutting speed. This speed will be slightly slower, but it can definitely be accepted as recommended for TiAlN-coated tools. TiN (titanium nitride) coated tools will still run more efficiently at these speeds with cooling, so the critical cutting speed is somewhere between the speeds recommended for TiN and TiAlN coated tools. Obviously, the critical speed will depend on the type of material being processed, so there is no universal value for all cases.
For cutting speeds below critical, a special correction factor is applied. Like the critical speed, the coefficient depends on the material being processed and takes values from 60% to 85%. In other words, for some materials a factor of 60% of the recommended speed is used (tool manufacturers' recommendations are based on the wet machining method), while for other materials the factor can be as high as 85%. The coefficient depends on the thermal conductivity of the material (heat-resistant alloys are quite difficult to process, since they conduct heat poorly, and a large amount of build-up is formed during cutting), the lubricating properties of the coolant, etc.

What about the quality of the surface treatment?

This is the last question regarding dry machining. Often, the quality of the dry finish is lower than with wet machining. There are many factors that affect quality, but in most cases it all comes down to a decrease in cutting speed. To maintain the quality of processing, it is important to compensate for the decrease in speed by using a tool with a larger radius (for example, a milling cutter). A secondary factor is lubrication, which reduces wear and ensures smooth cutting. In this case, humidified air will help you.

Results

So what are the conclusions?

It is clear that machining with the use of a cutting fluid is superior in parameters to dry or semi-dry machining, if you do not take into account the cost of coolant and have the appropriate equipment available. However, the effects are not as pronounced as it might seem. Humidified air can be used when machining viscous materials, and vortex tubes and other air cooling devices are no less effective than the traditional wet method. In this case, you will at least have a stream of compressed air to clean the workpiece from chips. It should be understood that dry machining leads to a change in cutting speed by 20-25%. Feed per tooth depends on the implementation of water cooling. Proper coolant nozzle orientation can increase feed per tooth by up to 5%, and delivering high pressure coolant through the spindle allows for even greater productivity gains.

In some cases, the refusal to use coolant is quite a challenge:

Heat resistant alloys and titanium should be machined with wet cutting, except when using tools where dry machining is recommended. The above materials have insufficient thermal conductivity to be used solely for air cooling.
Materials that build up on the cutting edge (some stainless alloys and aluminium) require the use of coolant or at least humidified air to provide lubrication.
Without coolant, it is very difficult to remove chips from deep holes. This problem can be solved by supplying humidified air under pressure.

Remember!

If your spindle is not the fastest in the world, you will most likely have to reduce the cutting speed due to its insufficient RPM. This is especially true when machining aluminum (or other soft materials such as brass), as well as when using small carbide cutters. However, in this case, the rejection of traditional liquid cooling is not critical.
It is often possible to increase the feed rate by reducing the chip thickness.

To the metalworking process aluminum alloys have the following requirements:

1) high accuracy processing and low roughness;

2) high productivity and exclusion of finishing work;

3) low sensitivity to the spread of mechanical properties and geometric dimensions (a variety of tool material grades);

4) relatively low cost of the tool.

However, the processing of these materials causes significant difficulties associated with their high viscosity, which leads to the formation of build-up, overheating and a decrease in the durability of the cutting tool, and a decrease in the quality of the machined part.

The use of modern machine tools, tools with wear-resistant coatings and the supply of cutting fluids (coolant) to the cutting zone does not always provide the required quality and productivity parameters. Nevertheless, today metal-cutting machines meet the requirements of accuracy. The offered range of tools and the results of numerous studies allow you to choose such cutting inserts, the use of which maximizes productivity and quality of processing.

At the same time, despite the development of a large number of coolant brands and tests in this area, there is no single methodology that ensures the choice of the most effective coolant. The selection of an efficient coolant brand, according to available data, can reduce cutting forces by 20%. Therefore, it is advisable to develop a methodology that ensures the choice of such a brand.

In general, coolants have lubricating, cooling, washing, dispersing, cutting, plasticizing and other effects on the cutting process. One of the main functional actions of the coolant is the lubricating effect, since the reduction of friction in the cutting zone leads to a decrease in the intensity of tool wear, to a decrease in cutting forces, average cutting temperature, and roughness of the workpiece. Therefore, it is necessary to investigate the lubricating action of the coolant in order to select a specific grade for processing these alloys.

Study of the lubricating effect of coolant

The lubricating effect is evaluated according to the test results both on the metal-cutting machines themselves in the process of processing, and on friction machines. The use of friction machines allows not only to reduce the consumption of materials, the coolant itself and the time spent, but also to eliminate the influence of other actions. Therefore, the lubricating effect of the coolant in this work was evaluated based on the results of tests on a friction machine. On fig. 1 shows the friction machine used for coolant research.

Since turning is the most common type of machining, for the research we used such a loading scheme for the friction machine, which made it possible to simulate this species processing, - the scheme "block - roller" (Fig. 2).

The block is made of the material of the processing tool - hard alloy T15K6. As a material for the manufacture of rollers, one of the most common representatives of aluminum alloys, D16 alloy, was chosen.

The research was carried out at a pressure force on the shoe P=400 N and a roller speed of n=500 rpm. The loading force is chosen in accordance with the cutting forces that arise during the metal processing of these alloys. The speed of the roller is obtained by calculation from its diameter and cutting speed recommendations.

The roller was mounted on the shaft and brought into contact with the block. The chamber was closed with a lid and filled with the tested coolant. Then the rotation of the roller was switched on with a frequency n, and by means of the loading mechanism, the load on the block was smoothly applied until its value was reached R.

According to the readings of the instruments, the maximum and minimum values of the friction moment were determined. The average value of the moment was obtained as the arithmetic mean of the results of five experiments. Based on the available data, the actual coefficient of friction was calculated f according to the formula:

For testing, 10% aqueous coolant solutions of several brands were used: Addinol WH430, Blasocut 4000, Sinertek ML, Ukrinol-1M, Rosoil-500, Akvol-6, Ekol-B2. In addition, the tests were carried out without the use of coolant.

The research results are given in table. one.

The results of the studies carried out make it possible to evaluate the lubricating effect of the tested coolants during the processing of the presented groups of materials. The data obtained provide the possibility of selecting the most technologically effective coolant for processing the given materials in terms of lubricating effect.

The effectiveness of each grade of coolant must be determined in comparison with the treatment without the use of coolant. The value of efficiency K cm for lubricating action when processing various materials is determined by the formula:

The lower the K cm value, the more effective this grade is in processing the tested material. In table. 2 shows the effectiveness of the tested coolant grades in terms of lubricating action.

It is known that when processing low speeds When the coolant reaches the cutting zone best, the lubricating action of the coolant has the greatest effect. Thus, the use of coolant with a high lubricating effect is advisable for roughing.

According to the table Table 2 shows that when processing aluminum alloy D16, the most effective lubricating fluids are Rosoil-500 (K cm = 0.089), Akvol-6 (K cm = 0.089) and Ekol-B2 (K cm = 0.096).

conclusions

1. In the work, experimental studies of the lubricating action of the tested coolants were carried out. The presented results make it possible to choose the most effective brand of coolant for rough machining of aluminum alloys.

2. The results of the work will be especially useful in the production of aircraft parts, as aircraft parts are subject to increased requirements for quality and processing accuracy.

3. The use of effective coolant provides the maximum possible reduction in friction and average cutting temperature, which leads to an extension of tool life, a decrease in cutting forces, a decrease in surface roughness, and an increase in machining accuracy.