Do-it-yourself cooling of the spindle of a cnc machine. Structural diagrams of the water cooling system of the spindle

Milling machines carry out contact machining by cutting. Under the action of cutting forces, the sharp wedge of the tool (mill) 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 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 milling machine spindle is a powerful asynchronous electric motor alternating current. 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), an air cooling system is mainly used. 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 from 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. good example 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 manufacturers) 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 slime 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!

Milling machines carry out contact machining by cutting. Under the action of cutting forces, the sharp wedge of the tool (mill) 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 intended for fastening the 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), an air cooling system is mainly used. 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 of the asynchronous electric motor and the 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). The fittings are connected by flexible hoses to the liquid pump and 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

The normal temperature regime for the operation of a 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 option for a heat exchanger is a tubular radiator coil from a 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. You should purchase an electric fan of a suitable diameter for it (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 for 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 related 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.

An even more effective means would be to use a special chiller for cooling systems for laser machines. The chiller is a single unit containing a tubular radiator, blowers, electronic thermostats and a liquid tank. The chiller has a high performance and allows you to flexibly adjust the temperature of the coolant. The only drawback of these systems is their high cost (compared to home-made solutions).

Types of coolants

The simplest (and in most cases recommended by machine tool manufacturers) 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 slime 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.

Spindle with air-cooled:

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 noise-free material is not advisable (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.

Guys, we built a cooling system for our CNC and share all the documentation with you in case you want the same.

The day came when it became possible to put the spindle cooling in order: the Chinese pump failed. And we thought it was time to stop hiding the canister with antifreeze and the pump under the machine and do something that would not be embarrassing to put in a conspicuous place. We are a bureau industrial design, eventually!

This is what it looked like right after the crash:

Such a canister warmed up to 60C if the machine worked 5-6 hours in winter, and up to 70C in summer. At the same time, the temperature of the spindle housing, according to the indications of an infrared thermometer, had a temperature in a comparable range: from 60 to 75C. This was enough but in the next couple of weeks there was a fairly large order for processing, and we decided to make cooling with a margin.

We had some plumbing change in our bins and a couple of beautiful bimetal thermometers from one of the past projects that I wanted to attach somewhere. We also have quite expensive electricity and very cheap cold water, therefore, we decided to use the plumbing trifle to organize a second circuit, which would cool the antifreeze.

To the right of the machine we have a shield with an electrician: frequency converter, power supplies, damper and more. Everything is mounted on a sheet of laser-cut plexiglass, and we did not deviate from the given style.

After a couple of hours of modeling, I got this scheme:

• On the left wall are two "American" 1/2 "for connecting running water. Adapters with a collet for a 10mm silicone tube are attached to them, which is threaded into the holes of the cassette (the one with the handle) in a spiral.
• Running cold water will flow through the silicone tube and cool the antifreeze through the tube wall. Not super effective, but in our case it is enough.
• The whole structure is suspended from the wall, so a 1/2" tap is built into the bottom of the tank to drain in case everything needs to be removed for maintenance or simply re-hung.
• The bimetal thermometers on the right also have a 1/2" thread and are secured with a locknut through a silicone gasket. Warm refrigerant will flow onto the upper thermometer sleeve, and the thermometer will indicate its inlet temperature. The lower thermometer sleeve is located next to the inlet of the submersible pump and indicates the temperature outgoing stream.

There are 12 pieces in total. different thickness: it was decided to make the side parts and the bottom from a 10mm thick sheet to make it more convenient to drill and cut threads, and back wall and front panel - 6mm. We prepared contours for cutting in DXF, made a specification and sent it to our friends for laser cutting. The next day we received the parts and spent about half a day drilling edges, threading and chamfering.

Then we did a test build:

Everything came together perfectly, and the next day we went to pick up submersible pump from the point of issue of online orders. The pump for fountains ZUBR ZNFCH-20-1.6 was chosen. Quite compact and with characteristics just for our task.

It's time for the final assembly. All joints were glued, the screws were tightened and left to dry. You can watch the build video here:

Everything dried out, and we successfully installed the unit. Now it looks like this:

In total, it took:

• 12 plexiglass pieces
• 2 fittings "American" for 1/2"
• 2 bimetal thermometers
• 1 tap per 1/2"
• 5 silicone pads per 1/2"
• scattering of fasteners M4x0.5
• tube of silicone sealant
• 4 meters of silicone tube 10mm
• submersible pump ZUBR ZNFCH-20-1.6

Total cost: about 6 thousand rubles.

We have archived all the documentation, including the model and DXF scans for laser cutting, and posted it here.