Water spindle. Spindle cooling system as a tool to compensate for thermal deformation of the machine

Milling machines carry out contact machining by cutting. Under the action of cutting forces, the sharp wedge of the tool (cutter) separates the particles of the material with the formation of a new - machined - surface of the workpiece. To overcome the intermolecular attraction and separate the particles of the material, it is necessary to apply a sufficiently high energy. It is generated by the spindle - the main power element of the milling machine. It is designed to mount cutting tool, transferring torque to it, as well as moving over the workpiece in accordance with the processing program (route of the cutter).

Structurally, the spindle of the milling machine is a powerful asynchronous AC motor. The motor shaft is installed in angular contact bearings to compensate for the effects of axial loads during the vertical movement of the cutter, as well as to compensate for loads in the horizontal plane when the tool moves along the processing route. The end of the spindle shaft has a Morse taper for mounting a collet chuck. The latter serves to secure the cutter, previously installed in a collet of the corresponding diameter.

All spindle units are combined in a single non-separable housing with a built-in cooling system. For units of small power (up to 500 W), the system is mainly used air cooling. More powerful spindles (from 1 kW and above) are equipped with a water cooling system.

Spindle liquid cooling system

Any liquid (especially water) has a much higher heat capacity than air. Therefore, for powerful spindles that require intensive heat dissipation, a liquid cooling system is used. Its design is a special "jacket" (cavities inside the spindle housing for the passage of fluid), where the coolant is supplied under pressure. The base coolant is water, however antifreeze or other mixtures can be used to prevent corrosion (see below).

The greatest heating during the operation of the spindle is experienced by the winding asynchronous motor and shaft bearings. It is them that are “hugged” by the cooling jacket - excess heat is absorbed by the circulating liquid. For fluid supply/discharge, the spindle housing is equipped with special fittings (on this basis, it is easy to distinguish water-cooled spindles from "air-cooled" ones). Fittings connects flexible hoses with liquid pump and a heat exchanger. Another component of the system is a reservoir for storing a supply of liquid. In some cooling systems, the tank can also play the role of a heat exchanger.

Structural diagrams of heat exchangers

normal temperature regime operation of the CNC milling machine is the heating of the spindle no higher than 50 ° C (the spindle should be hot to the touch, but not scalding). In case of excessive heating of the spindle (especially during prolonged milling in forced modes), the heat exchange intensity of the cooling system has to be increased.

As noted above, the simplest heat exchanger can be a container for storing liquid. The metal walls of the tank dissipate the heat of heated water quite well. And if necessary, the efficiency of such a passive radiator can be increased by ensuring reliable contact of the metal container with the metal frame of the milling machine. The massive frame will provide excellent heat dissipation of the heated fluid draining from the spindle into the tank.

Another version of the heat exchanger is a tubular coil-radiator from household refrigerator. To intensify heat dissipation, the coil can also be mounted on the metal frame of the machine. A good example of an effective system is a design where a heater radiator from a VAZ-2106 car is used as a heat exchanger. Buy an electric fan for it. suitable diameter(designed for AC power, 220 V). The liquid pump in such a system would be an aquarium "pump" (also rated for 220 V). All components of the cooling system are assembled in a single housing that provides reliable fastening of the units. An important requirement to the system is its tightness, so the installation of components and all connections must be carried out very carefully.

Ready solutions

A good option for organizing a cooling system is to use ready-made solutions from adjacent areas. For example, for milling machines with relatively low-power spindles (up to 1 kW), a PC microprocessor cooling system can be used. Such a system is already equipped with a liquid pump (pump), a coolant reservoir, a radiator with a built-in fan and all connecting hoses.

Even more effective tool will use a special chiller for cooling systems of laser machines. The chiller is a single unit containing a tubular radiator, blowing fans, electronic thermostats and liquid container. The chiller has a high performance and allows you to flexibly adjust the temperature of the coolant. The only disadvantage of these systems is their high cost(compared to do-it-yourself solutions).

Types of coolants

The simplest (and in most cases recommended by machine tool builders) available and cheapest coolant is water. Distilled water should be used to prevent sedimentation inside the channels of the spindle cooling jacket. However, it should be borne in mind that over time, bacteria multiply in the water, and mucus forms in the cooling system (including inside the spindle). As a result, heat dissipation is significantly reduced. In addition, even distilled water causes corrosion of the metal elements of the spindle.

To simultaneously combat corrosion and microorganisms, antifreeze (an aqueous solution of ethylene glycol) should be used as a coolant. When using a sealed cooling system, liquid evaporation is practically excluded, so the cost of topping up / replacing antifreeze is not required. In principle, you can use automotive antifreeze (the same antifreeze, but with a package of special additives), but a branded mixture will be more expensive than a simple solution of ethylene glycol (alcohol) in water. In addition, a number of branded antifreeze additives form a whitish coating on pipelines, which also reduces heat dissipation and makes it difficult for fluid to circulate in the cooling system.

It should be remembered that ethylene glycol is the strongest poison! When operating a cooling system filled with antifreeze or antifreeze, extreme caution must be exercised!

It is more correct to ask this question as follows: what type of spindle cooling is more suitable for solving the problem? This question is usually asked by those who design a new machine or modify an existing one. In any case, the fact that both types of refrigeration exist means that each has its own advantages. The easiest way to draw the right conclusion is to familiarize yourself with all the advantages and disadvantages of both types of cooling.

Air cooled spindle:

Usually has an elongated design rectangular shape and light alloy. The case itself, together with the internal air channels, forms a cooling surface. For forced ventilation, an impeller is mounted on the upper shaft of the spindle, pulling air through the channels. The lower shaft is equipped with a collet for holding a tool.

Such spindles are often found on woodworking machines, and there are several reasons for this. Let's take a closer look at all the pros and cons of air-cooled spindles.

Advantages:

• The current design of such spindles is such that, with the same power compared to a water-cooled spindle, they have a much more massive and powerful design, which has a positive effect on the life of the spindle and the magnitude of the withstand loads. This is of particular importance in woodworking, since cutters for such types of work often do not have good balance, and can be quite large.
• Also with comparable power, these spindles have larger size collets, thus expanding the possibilities for the tool used.
• A huge plus is the great autonomy, the air-cooled spindle only needs to be connected to the power cable, unlike the water-cooled spindle, it does not have coolant pipes that need to be laid through all the flexible cable channels. This feature is especially noticeable when the spindle is installed on large machines, more than 3m.

Disadvantages:

• As we have already said, the design of the air-cooled spindle is more massive and designed for large loads, so this affects its cost. The price of air-cooled spindles is somewhat higher than that of water-cooled spindles.
• An air-cooled spindle has a risk of overheating when running at low speeds, and because the impeller is fixed to the shaft, the amount of cooling air decreases as the speed decreases. The situation is exacerbated if the spindle is operated at high outside temperatures.
• The spindle is mounted in such a way that it is impossible to adjust its position in height, if the machine does not have a special adapter plate, this can cause some difficulties with limited travel along the Z axis of the machine.
• The cooling air flow of an air-cooled spindle is strong enough to blow the cut material sideways, so a fairly powerful dust and chip removal system is required in this case.
• The cooling fan is quite noisy, so it is not advisable to use such a spindle on machines where a tool is used and material that does not give noise (engraving machines, cutting wax and modeling plastic).

Water cooled spindle:
Advantages:

• With comparable power compared to air, they have a significantly lower cost
• More compact dimensions spindle
• A water-cooled spindle is characterized by fairly quiet operation, provided that the cutter itself does not make much noise. This property allows you to create a machine that can be operated in non-specialized production facilities.
• The cylindrical shape of the spindle and fastening with a collar allows you to easily adjust the height of the spindle, and expand the capabilities of the machine when working with long cutters and high workpieces.

Disadvantages:

• The main disadvantage of the water-cooled spindle is all attachments. optional equipment for cooling: pipes, radiator, fan, pump and expansion tank. Although all of these components are not expensive, their placement on the machine and maintenance require time resources.
• A water-cooled spindle has a risk of corrosion inside the cooling jacket, which can cause coolant to enter the windings and eventually fail.

Important notes when operating spindles:

For air cooled spindles:

• try not to let the spindle run at low speeds, this can cause it to overheat and fail
• keep the cooling channels in good condition and that they are free for air flowing through them, as well as that the inlet is free of foreign objects.
• It is not recommended to use air-cooled spindles in an environment containing water or oil mist.

For water cooled spindles:

• if you want the spindle to last a long time, and there are no problems with its body and windings due to corrosion, in no case use ordinary water to cool the spindle. We recommend equipping the spindle completely closed system cooling filled with a special liquid. This liquid can be any compositions that are used for car cooling systems. It is permissible to dilute these liquids with clean distilled water, as there is no danger of freezing of the entire system. The meaning of using coolants lies in their anti-corrosion properties.
• often there are cases of operation of the spindle without a cooling system, due to the fact that the pump is powered independently of the spindle power, and the operator may forget to turn it on. We recommend connecting the pump so that it automatically turns on when the machine and spindle are running.
• use a suitable pump or pump to circulate the coolant. Common mistake is the use of a pump that is not designed for continuous continuous work or a pump with leaking electrical connections, such as some fuel pump models.
• for laying the lines of the cooling system in flexible cable channels, use pipes of sufficient rigidity to avoid their kinks when the machine is running. Also, some types of tubes can lose their shape already at temperatures above 40 ° C, so their use is also not recommended.

The phrase "spindle for a CNC milling machine" is usually taken to mean an engine with a collet self-tightening chuck installed on it (as on a manual milling machine), which serves to fix a cutting tool such as a milling cutter, grindstone, drill, etc., and transferring rotational motion to it at high speed.

Classification

They can be divided into 2 small groups - these are domestic and industrial:

1. Homemade include various drills, small household routers or drills.
2. Industrial motors include motors designed to withstand high loads during operation, having ceramic bearings and, often equipped with complex system liquid or air cooling and a lubrication system directly to areas with a high level of friction and heat.

When using a drill as a spindle in a home CNC machine, it must be understood that its bearings are not designed for high side load and will begin to “howl” very quickly, which can lead to high heating of the windings, a decrease in shaft power, and subsequently such a spindle will simply will burn.

In this case, cooling will not help, and it is necessary to refine the drill itself, namely: replace the ball bearing of the shaft with a roller bearing (preferably with ceramic rollers), fix it firmly in the housing and take care of the constant presence of lubrication in it.

Spindle features depending on the type

Basically, during the operation of milling machines, all loads are perpendicular to the spindle axis, and parallel loads appear only at the moment of insertion into the body of the workpiece. That is why it is necessary to choose an engine that can withstand such loads for a long period of time, since the operation of milling machines can be continuous for a day or even more.

Spindles designed for industrial purposes do not need constant cleaning and lubrication of bearings throughout their entire service life, but if you begin to notice extraneous sounds in its idling, it is still better to disassemble the motor housing, blow it out from the inside compressed air all impurities (if any) and lubricate the bearing well with a special grease that does not lose its properties at high temperatures.

In addition, the industrial spindle is equipped with a high-quality collet chuck that has minimal runout during operation, providing the necessary machining accuracy, the minimum difference between the actual and real size of the cutter and allowing clamping cutters with a conventional cylindrical shank.

Collets

Basically, the most common are collets of the ER11 and ER16 types, into which a drill or cutter with a tail diameter of 2.5 to 3.2 mm becomes, even if it is made with a cone. There are also cartridges designed for a larger tool diameter, but they are used for rough metalworking or steel milling and have a hole for a tool clamp of 6 or more millimeters.

Why can't I install it on my home CNC machine, you ask?

If you clamp a cutter with a diameter of 2 mm with a shank diameter of 3.2 mm into a collet chuck, then during processing you will hardly notice a difference, but if you install a cutter with a diameter of 10 mm and a shank of 3.2 mm on an amateur machine, you can easily deform the guides, since the load on them in this case increases significantly. In the machine, all parts must be perfectly combined with each other, otherwise it will be more problems than quality work. Therefore, we recommend that you opt for the EP-13 collet, it is quite enough for small amounts of work and is suitable for almost any working tool used in the processing of various materials.

Spindle power

When choosing spindle power, you must be guided by the golden rule - the more the better. Basic rules for choosing power:

1. If you plan to use milling machines only for drilling or engraving small parts, then a spindle with a power of up to 600 watts will be enough.
2. For milling hard wood and metal, you need to consider already an engine with a power of 600 to 1400 watts.
3. If further modernization of the machine is planned (there are machines with two or more spindles) or a large margin of power is needed, it is necessary to look towards spindles with a power of more than 1.6 kW, they will allow processing almost any materials, and the quality of work will depend only from the reliability of the mechanical part of CNC machines.

Milling methods

Let's clarify some subtleties. Milling can be done in two ways, either with fast feed and slow rotation of the cutter, or with slow feed, but with a high speed of rotation of the cutter. The first method is called speed, and the second - power.

In industry, power milling is commonly used to remove excess material from a workpiece as quickly as possible. Before that, it is necessary to study the description and passport data of a certain cutter and enter the necessary cutting conditions specifically for it into the machine, namely: rotation speed, penetration and feed. Thus, you can use the cutter, getting from it maximum performance without overloading it.

If the mechanical part of your machine does not allow you to get a good force and begins to deform, then it is better not to experiment, but to use the second milling method - high-speed, having developed the maximum speed of rotation of the cutter and setting the minimum feed rate.

Spindle Selection Criteria

After analyzing the above, it is necessary to decide what is more important to us, the speed of the spindle or its power. When buying a high-quality and expensive spindle, you can not ask such a question, because most of them have a fairly high power and high rotation speed at the same time.

To the maximum, such spindles are practically not used, but they are loaded by 60-80% of all power and use up to 90% of the maximum speed, which is undoubtedly a great advantage, since in such conditions the spindle for CNC milling the machine will not overheat and will not work for wear. A high rotation speed (18000-20000 rpm) is practically not used for the reason that when processing at such speeds, the tool and the workpiece begin to heat up and burn, ruining all the work.

Separately, it is worth considering spindles powered by a three-phase network. They are connected by five wires, three of which are linear, one is zero and one is for grounding. They cannot be connected to a household network without modifications.

Previously, starting capacitors were used for such purposes, which, according to the laws of electrical engineering, changed the phase angle and artificially created 3 phases from one. But a CNC milling machine for this method is unlikely to be relevant, since in this case the ability to control the speed of rotation of the spindles is lost. Therefore, in our time, electronic frequency converters (FCs) are used, the principle of operation of which is based on rectifying household voltage and generating 3-phase voltage from it with the possibility of smooth frequency adjustment.

The frequency converter or chastotnik, as it is popularly called, has many useful functions, among which are: temperature control of the spindles, smooth adjustment of their rotation speed, and the most useful feature is that it can be connected to the control unit of milling machines and software will automatically set the required tool rotation speed. In addition, the chastotnik makes it possible to smoothly start and brake the spindles, which significantly increases their life.

Cooling

As mentioned above, spindles can be equipped with both air and liquid cooling. Air is a conventional impeller mounted on the motor shaft and blowing around its windings.

The big disadvantage of this type of cooling is the fact that the impeller not only blows air into the hot motor, but also sucks chips, dust and everything that the cutter cuts out of the workpiece into its body. Also, when processing low speeds air cooling is ineffective, since it directly depends on the speed of rotation of the spindle shaft.

The water cooling system does not have such a drawback, but when using it, a separate place is required for the reservoir with coolant and the correct fixation of the tubes with it on the body of the milling machines, which greatly complicates the design if it is a two-spindle milling machine.

She is much more efficient system air cooling, since the speed of the fluid flow through the spindle is the same all the time due to the use of a special pump. The main condition that must be observed when having a water-cooled spindle is that you cannot turn on the engine without turning on the pump, because in this case it will not cool at all, it will overheat very quickly and, as a result, burn out.

Chinese liquid-cooled spindles involve the passage of a liquid coolant to cool the bearings and windings. Outwardly, such spindles are distinguished by the presence of fittings for connecting hoses. The hoses must connect the spindle to the pump and heat exchanger.

On the Internet you can find descriptions of the most different systems spindle cooling. In the simplest of them, a tubular radiator from an old refrigerator is used as a heat exchanger (such radiators are mounted on back side refrigerators). There are options when the coolant-water is simply supplied to plastic container with an open top (in other words, a pelvis). An open top is necessary for better heat dissipation. plastic somewhat impairs the heat exchange of water with the surrounding air.

This article will offer more serious options for cooling systems. The presentation is divided into the following topics:

• Water, antifreeze or antifreeze - what to use?

The use of a ready-made liquid system for cooling PC processors

by the most simple solution for spindles up to 1 kW can be used finished system for cooling PC processors. It should be borne in mind that such a system is not cheap, it costs about $200. But at the same time, in the kit you will already have mounted pumps with expansion tank and a heatsink with a cooling fan.

But the ethylene glycol-based coolant available in the kit (practically antifreeze) is most likely not enough, because. the spindle cooling system has a larger volume. So antifreeze will have to be bought in addition. And it remains only to add a 12 volt DC power supply (you can unstabilized). You can use an old computer or any transformer with suitable power.
Now you need to mount all the modules in a suitable case (or home-made, plywood), combine the system with hoses, fill it with antifreeze and expel air from it.

Be sure to remember that such a system is equipped with a small radiator and a weak pump. Their power may not be enough to cool the spindle. In this case, the degree of load on the spindle matters. That is, if the spindle is constantly working with large cutters, at high speeds, with a large number material in one pass, and even if the workpiece material is metal, and even steel. In such cases, it is better to provide a more powerful spindle cooling system (see below).

Cooling system based on an aquarium pump and a VAZ-2106 car heater radiator

The next version of the cooling system requires less investment, but more installation time.
The heater radiator of the VAZ-2106 car was used as a radiator (see photo below). It can be purchased at almost any auto shop. Buy a fan for the radiator right size at 220 volts. The cost of the heatsink and fan will be approximately $40 (~1200 rubles).

An aquarium pump is suitable as a pump. These can be purchased at pet stores. The photo below shows two options for pumps. The cost of the pump can be $50-$100 (up to 3000 rubles).

The photo shows that the supply voltage of the pump is 220 volts. Therefore, care must be taken during installation to ensure the safety of both the installation itself and the further operation of the cooling system.

When all the main components are purchased, you can begin to install them in a single case. The case can be made of plywood (see photo below) or you can purchase a suitable ready-made one.
In this solution, the radiator is attached using pieces of galvanized drywall profile. The width of the profile just fits the thickness of the radiator. The pump is immersed in an expansion tank.

It is highly desirable that the cooling system be sealed to eliminate the possibility of antifreeze evaporating. The reason for this is the harmfulness of ethylene glycol, on the basis of which antifreeze is made.
To solve this problem, the easiest way is to place the pump in a container with a wide neck and a hermetically sealed lid, and take the radiator with the fan into a separate case (see photo below).

It may be that the standard spindle fittings do not fit the existing hose. In this case, it is quite possible to make your own fittings right size similar to the photo below. Hose clamps are not conventionally shown, but they are necessary for their secure fixation.

Summary

Such a cooling system has been tested in real conditions in tandem with the ET80-2.2kW spindle from ET. At the same time, the processing modes are quite tough: the maximum diameter of the cutters is 6 mm, the material being processed is high-strength aluminum alloys, the speed is up to the maximum (24000 rpm). Maximum temperature never reached 50°C. After running the control program for 10-20 hours, you can feel the heat in the area of ​​the lower bearings with your hand. At the same time, the temperature around the machine is stabilized at about 20°C.

Water, antifreeze or antifreeze?

As a coolant in the spindle cooling system, it is cheapest to use water. It must be distilled water to prevent precipitation in the channels of the system. It should be borne in mind that after some time microorganisms develop in the water and mucus appears on the walls of the cooling system, and the water begins to stink. It is clear that such mucus also appears inside the spindle, which worsens heat dissipation. The use of bactericidal additives requires checking whether they will cause sediment or rust on the spindle walls. Also, the use of water itself can cause corrosion inside the spindle.

In connection with the foregoing, the use of antifreeze may become more reasonable. It is not as expensive as the use of antifreeze, but it also has its own characteristics. The fact is that low-quality antifreeze leaves white efflorescence on pipelines, which also worsens heat dissipation and patency of channels.

Almost ideal for the spindle cooling system is the use of antifreeze. In this case, there are only two drawbacks: the high cost and harmfulness of ethylene glycol, on the basis of which antifreeze is made.
However, the high cost of antifreeze is very arbitrary, because. antifreeze is purchased once for the entire period of operation, because it does not wear out.
And the use of a sealed cooling system ensures that antifreeze does not evaporate into the air, and these solve the issue of its harmfulness.