Wood sanding machines are one of the main production mechanisms used in the woodworking industry. The equipment is intended for grinding wooden surfaces of blanks made in the production process, parts of wooden structures and finished products. Modern models presented in the catalog are powerful, compact and versatile devices capable of working in long-term modes. Depending on the terms of reference, mechanisms are capable of processing workpieces and products of any shape, including the performance of a number of other technological operations. On this technique, you can perform trimming and grinding the edges of finished products.

According to the nature of the operations performed and depending on the production need, all units can be divided into the following types:

surface grinding equipment, drum type;

aggregates for internal and external grinding, installations for working with edges;

machines for external grinding of spherical and round surfaces, belt and disc-belt machines.

Each type of technology is designed for a specific technological cycle. Changeover of mechanisms is carried out quickly and easily, thanks to a wide range of fixtures and equipment.

Features and specifics of the design of grinding machines for wood

In the catalog you can see a wide variety of models that differ in size, compactness of the mechanism, power of the electrical installation. The purpose of the mechanisms determines the location and type of installation. Large installations for mass production, have a massive base, installed on the floor. small items, desktop type designed for domestic use, work in workshops.

Most models are equipped with additional devices and devices that ensure the accuracy of grinding, compliance with the required dimensions. Angle stops, sanding belt or disc significantly increase the range of production use of this technique. equipped with powerful asynchronous motors with high torque, shaft speed control devices.

Each machine is covered by warranty service, which significantly increases the operational life of the mechanisms. All machines comply with electrical safety standards, have the necessary certificates of conformity.

A grinding machine is a device used to process workpieces from various materials with an abrasive tool and is capable of providing a surface roughness from 0.02 to 1.25 microns. Grinding machines, which can have a different design, allow you to effectively solve the problems associated with the processing of surfaces of parts made from different materials.

Application of grinding machines

With the help of a grinding machine, a number of technological operations can be carried out:

• grinding of internal as well as external surfaces of parts having different shapes and purposes;
• sharpening tools for various purposes;
• peeling, grinding, as well as cutting off metal castings, products with a complex profile;
• processing gear parts, as well as parts with threads;
• the formation of grooves of the key and spiral type on steel bars.

The grinding machine is almost indispensable when working with parts made of ceramic and magnetic materials and characterized by the complexity of processing and high fragility. In addition, grinding machines are capable of performing grinding and roughing operations at high speeds, which makes such equipment efficient and productive. On these machines, it is possible to remove from the surface of the workpiece during processing a large number of metal in a short period of time.

In the video below, the operation of a CNC circular grinding machine:

All grinding machines work on the same principle: metal processing is carried out by simultaneously rotating and moving or rotating the workpiece. The working surface is the periphery or end of the abrasive wheel, and the workpiece moves relative to it along a straight or arc path. Any grinding machine contains in its design several kinematic chains that provide:

• movement of the desktop in the longitudinal and transverse directions, which is possible due to the hydraulic drive;
• rotation of the working tool - a grinding wheel, carried out by an individual drive of the working tool;
• feed of a workpiece or tool in the transverse direction due to a hydraulic or electromechanical drive;
• wheel dressing, which can be done manually by using an electromechanical or hydraulic system;
• rotation of the workpiece or desktop;
• supply of a working tool to a depth, which can be performed by a hydraulic or mechanical drive.

Classification of grinding equipment

Grinding machines are divided into a number of types depending on the area of ​​application.

This equipment is designed for grinding cylindrical (Ø 25–600 mm) and conical workpieces. Such machines have in their design a spindle rotating in a horizontal plane, which can move on a special sled. The part to be machined can be clamped in the chuck or between the centers of the tailstock and headstock.

Such machines are used for grinding the outer and end surfaces of cylindrical workpieces (Ø 25–300 mm), as well as conical parts. To perform machining, workpieces can be fixed in centers or in a chuck.

Grinding machines of this type are used for processing cylindrical (Ø 150–400 mm), conical and profile workpieces, which are fixed in the centers of the equipment. Processing is carried out due to the transverse movement (plunging) of the abrasive wheel.

Processing on such equipment can be carried out according to two schemes: by pass (cylindrical surfaces (Ø 25–300 mm)) and by the plunge method (cylindrical, conical and profiled surfaces). Distinctive feature grinding machines of this type is that their design does not provide centers for fixing workpieces.

This includes machines for grinding cylindrical, conical and profile rolls. Fixation of workpieces on machines of this type is carried out using equipment centers.

For grinding crankshaft journals

On such machines, working according to the plunge method, simultaneous or sequential grinding of the connecting rod journals of the crankshafts is performed.

These devices allow processing cylindrical and conical holes in a wide range of sizes (diameter 1–10 cm on a bench grinder and up to 100 cm on a production grinder).

surface grinding

Processing on such equipment is performed by the end or periphery of the abrasive wheel. Grinding machines of this type can be equipped with additional devices, which makes it possible to process metal workpieces of complex configuration on them. Depending on the location of the spindle, they can be horizontal and vertical. The design of such devices can also be provided with one or two columns.

This equipment can simultaneously process two flat surfaces, which greatly increases its productivity. Such grinding machines, in which the workpieces are fixed on a special feeder, can be of a vertical or horizontal type.

The maximum length of rails that can be machined with these grinders is 1000-5000mm. Guides of these types are equipped with beds, work tables, sleds and other units of equipment for various purposes.

These grinders are used for sharpening various instrument with a maximum diameter of 100–300 mm (tappers, reamers, countersinks, cutters, etc.). The technical capabilities of this type of equipment allow it to be equipped with additional devices for processing cylindrical workpieces, as well as for internal and face grinding.

This grinding equipment is used for peeling and cleaning the surface of workpieces by grinding. These machines use abrasive wheels with a diameter of 100–800 mm.

This grinding equipment is used for lapping workpieces with flat and cylindrical surfaces. The diameter of the abrasive discs that are installed on such machines is 200–800 mm.

On this equipment, grinding of a calibration and measuring tool made of metal is performed. The maximum diameter of gauges and tools that can be processed on machines of this type is 50–200 mm.

With the help of such equipment, holes are lapped, the maximum diameter of which is 100–300 mm.

These are machines designed to perform finishing (lapping) operations. On such devices, various metal products are processed: crankshafts with a maximum diameter of 100–200 mm, equipment spindles, pistons, etc.

Such machines are used to polish metal parts. On this versatile equipment, you can polish flat, cylindrical, conical, internal surfaces, as well as workpieces of complex configuration. As a working tool on these machines, an endless belt with a width of 100–200 mm or a soft polishing wheel with a diameter of 100–200 mm can be used.

There are also honing machines that are used to perform fine grinding (0.04–0.08 mm per diameter).

We make the simplest do-it-yourself grinding machine

Given the fact that serial grinding equipment is not cheap, it makes sense to think about how to make such a machine with your own hands. Even the simplest home-made machine, which is not difficult to make, will allow you to grind workpieces of various configurations with high efficiency and quality.

The supporting element of a home-made machine for grinding work is a frame on which two drums and an electric motor are fixed. For the manufacture of the frame, you can use a thick steel sheet, from which a platform of the required size is cut.

With the engine, everything is much simpler: it can be removed from the old washing machine which has already served its time. Drums can be made stacked, for this it is convenient to use a chipboard plate, from which disks of the required diameter are cut.

Drive shaft mount Drive drum Motor mount

As an example, let's analyze the sequence of manufacturing steps, the bed of which has dimensions of 50x18 cm. First of all, the bed itself is cut out of the steel sheet, as well as the desktop on which the electric motor will be fixed. The dimensions of such a table will be approximately 18x16 cm.

It is important that the ends of the bed and the desktop that will be connected are cut as evenly as possible. The thick sheet of metal from which you will make the bed and desktop is difficult to cut by hand, so it is better to perform this procedure on milling machine. It is necessary to drill three holes in the bed and the desktop and securely connect them with bolts. Only after that, the engine is installed and securely connected to the surface of the working table so that the engine base fits snugly against the surface of the platform.

When choosing an electric motor for your homemade grinding equipment, it is important to pay attention to the power: it must be at least 2.5 kW, and the rotational speed should be about 1500 rpm. If you use a drive with more modest characteristics, then the machine will have low efficiency. You can avoid the need to use a gearbox if you correctly select the diameters of the drive and tension drum.

The diameters of the drums should be selected depending on the speed at which the abrasive belt will move. So, if the belt speed should be approximately 20 m / s, then it is necessary to make drums with a diameter of 20 cm. A fixed axle is used to install the tension drum, and the leading one is fixed directly on the motor shaft. To make the rotation of the tension drum easier, a bearing assembly is used. The platform on which the tension drum is installed is best done with some bevel, this will ensure smooth contact of the abrasive belt with the workpiece being processed.

It will not be particularly difficult to make drums for a homemade grinding machine. To do this, it is necessary to cut square blanks from chipboard measuring 20 by 20 cm, in the center of each of which a hole is drilled. These blanks are then assembled into a 24 cm thick bag, which is machined to form a cylindrical drum 20 cm in diameter.

To prevent the abrasive belt from slipping on the drums, wide rubber rings can be pulled onto their surface, which are usually cut from a bicycle or moped chamber. The width of the abrasive belt, which you can make yourself, should be about 20 cm.

Belts for belt grinders

Both in production and at home, grinding machines are often used, the working tool in which is a cloth tape with a layer of abrasive powder. The basis of such tapes is dense matter (coarse calico, twill) or special paper, and the abrasive layer on them is fixed with an adhesive composition.

The efficiency of using such a tape depends on a number of parameters: the density of application of the abrasive powder and the composition of its grains. Belts are more efficient if the powder on them occupies no more than 70% of their area. This is explained by the fact that the material being processed is not clogged between the abrasive grains of such a belt. As an abrasive powder applied to the working surface of the tape, both natural and artificial materials can be used, but all of them must have high hardness.

The belts mounted on the grinding machine are classified according to the number indicating the size of the abrasive grains, expressed in hundredths of a millimeter. The reliability and effectiveness of such a tape also depends on the type of adhesive that is used to fix the abrasive grains. To date, two types of such glue are used: mezdrovy and synthetic resin.

The processing of steel products can consist of several stages, which differ technological scheme and the equipment used. To give the product or workpiece the final shape, metal grinding machines are used. Despite structural differences, they have almost the same functions and parameters.

Scope of grinding machines

The grinding process is necessary to form the final dimensions and roughness parameters of the part. During this work, with the help of abrasive materials, the metal layers are gradually removed from the workpiece.

Additionally, the implementation of this procedure will allow you to get rid of minor defects, improve appearance product and increase its anti-corrosion properties. Grinding is the gradual removal of a thin layer of chips by contacting the material with an abrasive tool. The rotation of the cutting tool is the main movement in the equipment. Machining can be performed by the periphery of the abrasive component or its end face.

Depending on the configuration of the workpiece and the required parameters of its grinding, the following processing methods are distinguished:

• external. It is used to give the outer surface the required shape;
• internal. Actual for products with blind or through holes. The abrasive performs the processing of the inside;
• profile. Necessary for grinding products of complex shape.

To perform each type of work, it is necessary to choose the right equipment and its characteristics. The selection parameters are productivity, degree of automation and functionality of the machine. Also Special attention is given to abrasives, with the help of which the layers of material are removed. They must have the required grain size and have a large enough area for contact with the workpiece.

Some models of metal grinders are designed to perform several types of processing. But at the same time, they are characterized by high cost and complexity of operation.

Cylindrical grinding machines

These machines are designed for longitudinal and plunge grinding of metal workpieces of various shapes. They are characterized by high precision of the operation. To increase this indicator, it is recommended to choose models with an electronic control unit.

Structurally, the equipment consists of two working tables. On the main (horizontal) part is fixed in the centers (chuck) for further rotation. The vertical table contains a headstock with a mounted abrasive wheel. It can be controlled manually or by means of a CNC unit.

Stages of work of the internal grinding machine.

1. Fixing the part in the centers.
2. Setting the initial position of the abrasive relative to the workpiece.
3. Starting the rotation of the part with translational movement along the horizontal axis.
4. Surface treatment and further displacement of the abrasive to the depth of the removed layer of material.

Depending on the characteristics of the equipment, it can be used for rough or fine grinding. In the second case the best option will be the use of models with an automatic feed system. In this case, the determining parameter will be the speed of rotation of the abrasive wheel.

The defining parameters of the machine are the restrictions on the size and weight of the workpiece. Due to the wide setting range, all types of grinding can be performed on equipment of this class.

Changing the location of the abrasive wheel depends on the model of the machine. In some of them, it can move not only in the vertical plane, but also in the horizontal one. This greatly expands the range of applications.

Internal grinding equipment

They are designed for processing the inside of workpieces with through or blind holes. The main difference from the models described above is the immobility of the workpiece relative to the abrasive. This metal grinding machine is used for processing engine cylinders and similar structures.

Processing occurs due to the movable spindle on which the disk is mounted. It transmits to the abrasive not only rotational, but also translational motion. Due to this, the inner edges of the workpiece are ground.

Depending on the design and the required complexity of grinding, equipment of this type is conditionally divided into the following groups:

• with one spindle. With their help, the processing of conical and cylindrical products of the correct shape is performed. In this case, the hole does not have to be deaf;
• additional processing of edges. This function makes it possible to do face grinding simultaneously with internal grinding. To do this, the equipment must have an additional spindle;
• bilateral. This type of equipment is designed to perform double-sided grinding of through holes in parts.

Internal grinding machines are used for grinding massive products. Due to their design and wide functionality, they can perform all types of processing, including the final finishing of the internal surface.

Special technical specifications are the maximum length of processing, restrictions on the outer diameter of the workpiece and the values ​​of the maximum and minimum angle of rotation of the abrasive in conical products.

One of the problems in the operation of internal grinding machines is the timely removal of waste from the area of ​​work of the abrasive. For this, magnetic devices and special filters are used. Without them, it will be impossible to achieve the desired roughness index.

Honing

The final grinding step is best done on special honing equipment. Its design is in many ways similar to internal grinding models. The difference lies in the fact that the workpiece is not mounted on a special device. The spindle is also longer for more thorough grinding.

To fully perform their functions, nozzles with various configurations and sizes of abrasive grains can be installed on the spindle. The processing of the workpiece is carried out manually or with the help of automated system. In the first case, the spindle can be displaced relative to its axis. Automatic mode provides mechanisms for maximum finishing of the surface of the workpiece.

To select the optimal model, it is necessary to take into account the following design nuances:

• spindle parameters - its length and number of degrees of freedom;
• the ability to perform grinding in a horizontal and vertical plane;
• number of spindles. This affects not only the quality, but also the speed of grinding.

A blank mounted on a spindle is used as a processing tool. Its design provides connectors for attaching abrasive bars of various configurations.

In order to achieve an optimal result during the honing process, liquid is fed into the processing zone. It performs several functions: it prevents surface heating and removes abrasive particles that have broken off from the bars.

Centerless grinding models

The principle of operation of these machines is based on the transmission of torque from the driving circle to the workpiece. It is not fixed rigidly in the centers. The degree of pressing to the working abrasive is controlled by adjusting the position of the driving circle.

Most often, an abrasive belt is used as a processing material. It is installed on the surface of the working circle. This principle of operation allows you to quickly reconfigure the equipment to activate another mode.

Benefits of using centerless grinding units:

• high processing speed. Compared to the models described above, it increases by 1.5-2 times. This makes it possible to grind thin-walled products from soft grades of metals;
• for massive workpieces, you can use the method of fixing on rigid supports. In this case, the spindle drive has a cantilever design, and its rotation is carried out due to the influence of a magnetic chuck. Thus, the likelihood of beats is reduced. There is also practically no load on the walls of the workpiece, which is the main reason for its partial deformation along the edges, which is typical when using classic spindles;
• the possibility of using axial supports. They hold the structure along its axis of rotation. In this way, sanding can be performed on the entire outer surface.

Such equipment is equipped with an automated function control complex. This is a forced measure, since it is almost impossible to achieve a good fine grinding result using manual mechanisms for this method.

R.B. Margolit, E.V. Bliznyakov, O.M. Tabakov, V.S. Tsibikov

Scope of use of turning and grinding machines

In line with modern trends in the integration of processing, the demand for combined lathes has increased, on which, along with turning, grinding can be performed. We can say about the emergence of a special group of turning and grinding machines.

When quality issues come to the fore, grinding is usually preferred. Grinding (with the exception of deep grinding), by virtue of the very nature of the method, is based on multi-pass, at which the decrease in initial errors occurs to the greatest extent. Blade turning outperforms grinding in terms of productivity. However, it is difficult to perform the cutting process with a blade tool with shallow depths and low feeds. At small depths, the cutter, due to the rounding of the cutting edge, works with large negative rake angles y (Fig. 1), and at low feeds, the likelihood of vibrations sharply increases. It is for this reason that, despite the emergence of new types of cutting materials that work successfully on soft and hard surfaces, it should not be assumed that edge processing will significantly reduce the scope of grinding.

These features determine the delimitation of these two processing methods. Preliminary processing of bodies of revolution is usually performed by turning on lathes, and finishing of the same parts by grinding on circular grinding machines. The separation is also aggravated by the fact that, within the same accuracy class, grinding machines have a higher accuracy than lathes.
At the same time, there is a trend towards the integration of these types of processing, which has led to the emergence of combined turning and grinding machines.

1. A very time-consuming procedure for aligning massive large shafts and long sleeves before each new operation. Such parts do not have high rigidity and are deformed under the action of gravity and fastening forces. Reconciliation requires skills and abilities from the worker, and naturally the desire to reduce their number.

2. There is a general trend towards increasing the accuracy of lathes.

3. Attractive to carry on various surfaces one part turning or grinding, depending on the requirements for them in terms of accuracy and roughness

In this paper, the experience of the Ryazan Machine Tool Plant in creating combined turning and grinding machines is considered. The assumption turned out to be erroneous that such machines can be obtained from lathes by retrofitting the calipers with interchangeable grinding heads. I had to solve several rather difficult tasks.

1. The accuracy of the longitudinal movement of the grinding wheel is ensured, however, at a limited length.

2. The reach zone of the outer and end surfaces of parts has been increased, including on shafts with a large difference in the diameters of adjacent steps.

3. The rotation accuracy of the product is ensured.

4. Methods for aligning massive large-sized parts are proposed and structurally provided.

At present, when the plant has mastered the production of several models of machine tools of this group (1P693, RT248-8, RT318, RT958) of a sufficiently high technical level, the demand for them is growing. The most complete technological possibilities of combined processing were embodied in a special machine mod. RT958 (Fig. 2). At the request of the customer, the length of the machines can be changed from three to 12 meters, the number of turning and grinding calipers, supporting steady rests, supports that facilitate alignment.

Turning and grinding machines are effectively used in the repair of turbine rotors for various purposes, rolls of metallurgical and printing industries, spindles of heavy metal-cutting machines, propeller drive shafts and other large-sized parts. Since the maximum allowable amount of removal from the repaired surfaces is small, it is possible to increase the number of possible repairs and extend the service life of expensive products by switching from turning to grinding. There is a successful experience of using turning and grinding machines not only in repair, but also in the main production.

Ensuring the accuracy of the longitudinal movement of the grinding wheel

When grinding, the support carrying the grinding head must move smoothly, straight and without reorientation when changing the direction of feed movement. In the case of reorientation, the grinding wheel moves along one path in one direction, and along another path in the other direction. On lathes, the cutter almost never works on the same outside surface in two directions without traversing, so reorientation requirements are not as stringent as in grinding.

The supports of lathes, especially heavy ones, do not move in such a straight line, without undulating movements, as grinding tables. It depends on the following:

The carriages of lathes are inferior in length to the tables of grinding machines;

The mass of the apron, eccentrically attached to the caliper carriage, is large;

The feed drive is carried out from a rail placed outside the guides and at a great distance from them;

The radial runout of the drive shaft causes the caliper to wobble;

The rotating force of the feed drive (even with the absolute straightness of the drive shaft) swings the caliper, acting on it through the apron.

After a number of unsuccessful attempts to realize the required accuracy of the longitudinal movement of the grinding head along the entire length of the bed guides, it was decided to move not by the carriage, but by the upper longitudinal slide of a specially designed grinding caliper. This caliper is interchangeable and can be installed instead of the lathe (traditional design) on the cross slide of the machine.

Figure 2 shows a machine with two grinding supports (left and right). Each grinding caliper has a lower swivel part, a longitudinal grinding slide with an adjustable feed drive, a cross grinding slide with a manual micrometer cross feed mechanism, a grinding head with a rotation drive.

Grinding is performed on separate sections of limited length (300mm on a machine mod. RT958, 600mm on a machine mod. PT700). If it is necessary to carry out processing in another place, the grinding caliper is moved along the frame by the movement of the carriage. The analysis shows that for most parts the length of individual steps is small, which makes it possible to process a step in one carriage installation.

It turns out that the machine has two duplicate movements:

1) Longitudinal can be carried out by the machine carriage and longitudinal grinding slide, but the movement of the slide is more accurate;

2) Crosswise can be done by machine cross slide and cross grinder slide, but the second one has a finer count.

The rotations around the vertical axis are also duplicated, but each of the rotations fulfills its purpose. By turning the longitudinal grinding slide, the taper of the area to be ground is adjusted, and by turning the grinding head, its axis is set to the required position.

During the search, two different design designs of the guide rails of the longitudinal grinding sled were tested: dovetail and rectangular. Various materials of the friction pair were also tested: cast iron on cast iron; cast iron on hardened steel; bronze on hardened steel; filled with fluoroplast for cast iron and steel.

The results in terms of accuracy for all designs and combinations of materials cannot be considered satisfactory, which gave reason to give preference to the purchased Star ball rolling guides from Rexroth. Fears that such guides would dampen vibrations worse were not confirmed. The reorientation value practically reduced to zero, high processing accuracy and roughness in the range of Ra 0.1 - 0.16 μm were achieved.

The feed drive of the longitudinal grinding slide is carried out from an individual DC electric motor, which transmits rotation by a belt drive to a centrally located lead screw. The drive provides a wide range of stepless speed control, which is important for obtaining optimal grinding and wheel dressing modes.

The drive for moving the cross slide is manual with a micrometric feed device, similar to that used on cylindrical grinding machines. On the digital display, you can observe the position of the working edge of the cutting tool with a reading accuracy of 1 µm.

In order to reduce vibrations, the source of which can be the rapidly rotating elements of the grinding head, the slide, on which the grinding head and the drive motor for its rotation are fixed, must have increased rigidity and increased weight. All mating parts of the grinding caliper must be mutually adjusted by scraping to a tight joint. Fast rotating parts must not be unbalanced. This approach has proven itself well: in order to reduce imbalance, all working and non-working surfaces of pulleys, mandrels and faceplates are given a runout not exceeding 0.03 mm, which makes it unnecessary to carry out a special balancing operation.

Some features of circular surface grinding

On grinding machines, the processing of the outer and inner surfaces of bodies of revolution is usually performed by the periphery of the grinding wheel, and the processing of the ends of the part is done by both the periphery and the end.

However, if it is necessary to process recessed surfaces on part 1 (Fig. 3) (for example, bearing journals of turbine rotors for various purposes), then the processing zone (Fig. 3, a) may be inaccessible to the periphery of the grinding wheel 2. Structural elements of the faceplate 3, grinding head 4 and head body 5 interfere with approaching such recessed surfaces. The only way out is to work with large diameter wheels, which, in turn, require large-sized sections al heads, which are difficult to place on the calipers of lathes.

In order to radically solve this problem, a significant change in the traditional approach is proposed: to perform cylindrical grinding of the outer surfaces not only with the periphery, but also with the end of the circle (Fig. 3,b).

When grinding with the end face of the circle, the reach area expands significantly, because. the overhang of the working part of the circle 2 increases due to the length of the mandrel 3 and the part of the grinding head 4 protruding from the body 5. Practically, any recessed surfaces of the parts become accessible to the cutting tool.

The question arises: why the method, known for many years and having such a clear advantage over grinding the periphery of the circle, has not found wide use on cylindrical grinding machines? The explanation can be found in the fact that said advantage cylindrical grinding with the end of the circle has three characteristic features that reduce its effectiveness:

1) Productivity is lower than when grinding with the periphery;

2) There are two working sections of the grinding wheel to the left and to the right of the axis of its rotation, in contact with the surface to be machined, we will further call them the left and right sides of the wheel.

3) If, when machining closed surfaces, the length of the longitudinal movement L (Fig. 3, b) turns out to be less than two diameters of the inner part of the grinding wheel Dk, then grinding with the end of the wheel will become impossible, since part of the machined surface of the part lying inside the circle will not be overlapped, therefore, will remain unprocessed.

Reduced productivity is determined by the lower rigidity of the technological system and the shorter length of the two working sections of the circle compared to one working surface when grinding the periphery of the circle.

To understand the second feature of circular grinding with the end of a circle, let us dwell in more detail on the essence of this method. The decisive role is the accuracy of the location of the axis of rotation of the circle to the direction of movement of the feed. They (axis and direction) must be strictly mutually perpendicular.

The wheel is dressed with a diamond, which moves the feed along one of the working sections of the wheel to the left or right of the axis of its rotation. The feed motion in dressing and grinding is common. Figure 4 shows the case when the wheel was dressed to the left of the axis of rotation. If the axis of rotation is not perpendicular to the direction of movement of the feed, then the end of the circle during dressing will take on the shape of a cone.

On the left side of the wheel where dressing was performed, a line is formed that is parallel to the feed motion. Along this line, on the left, the circle contacts the surface to be machined, and on the opposite side, on the right, a point contacts the surface to be machined.

Depending on the deviation of the perpendicularity of the axis with respect to the feed direction, the line operates either on a smaller diameter of the part (Fig. 5a) or on a larger diameter (Fig. 5b). In addition, the left and right working sides of the wheel work with different depths of cut. With an increase in the deviation, a moment will come when the difference between the position of the left and right sides of the circle will exceed the cutting depth and then only one of the sides will start working: the left in case a), the right in case b).

If grinding is a pass, then the side of the wheel that works on a smaller diameter of the product determines the quality of the surface. Of the two cases shown in Fig. 4, the best indicators for the roughness of the machined surface will be obtained in case a), since a line works on a smaller diameter of the part, not a point.

The described leads to the fact that when grinding closed surfaces, which is not performed for a pass (Fig. 5), two sections of different diameters are formed on the machined surface. At the junction of these two sections, a step appears, the height of which h depends on the non-perpendicularity of the circle axis to the direction of feed movement.

where D is the diameter of the grinding wheel, d is the angular error of the wheel axis error relative to the feed direction.

By the direction of the step, one can judge the position of the axis of the circle: the smaller diameter of the machined surface is obtained from the side of an acute angle a between the axis of the circle and the direction of feed. When

a) smaller diameter on the left, in case b) - on the right.

The nature of the surface roughness of both parts of the part will also be different. The roughness will be better in the left section, where the wheel contacts the product along the line (editing was performed on this side of the circle). The roughness will be worse in the right section, where the circle works as a point.

where s is the grinding wheel feed, mm/rev.

It is possible to obtain the required roughness Ra 0.2 - 0.32 μm throughout the entire length of the ground surface by adding high precision perpendicularity of the axis of rotation of the circle to the direction of feed (Fig. 6). In this case, during grinding, sparks of the same intensity can be observed on the left and right working sides of the wheel. On the treated surface, not two, but three sections appear: the first section, processed by the left working side of the circle; the second, on which the circle worked on both sides; the third, processed by the right working side. There is no step at the junction, and the roughness in all three sections is approximately the same.

The design of the machine provides for the possibility of extremely fine adjustment of the position of the axis of the grinding spindle by turning the grinding head around the vertical axis. Using a pair of adjusting screws located to the left and right of the axis of rotation, you can finely turn the head, changing the position of the axis of rotation of the circle. You can determine the position of the axis by crossing the indicator, attached to the mandrel of the grinding wheel with a clamp, along the ground surface.

In order to reduce the effect of the previously discussed limitation 3), it is necessary to work with circles of small diameters of 80 - 100mm. Although a high wheel speed of 5000 - 7500 rpm is necessary to maintain a cutting speed of 25 - 32 m / s, small-sized lightweight grinding wheels, even at such speeds, can work successfully without balancing.

When grinding deep cylindrical surfaces with the butt end of a circle (see Fig. 3, b), one has to work with large overhangs of circles, due to which the rigidity of the technological system is reduced. Correct solution The problem lies in the combination of the optimal length of the conical mandrel and the increased overhang of the grinding head from the body. It is necessary to adhere to the rule: the maximum length of the mandrel should not exceed the distance between the bearings of the grinding head. Based on this, preference should be given to increasing the length of the grinding head, rather than the mandrel. An increase in the diameter of the grinding head also contributes to the increase in rigidity, but with a head diameter larger than the diameter of the grinding wheel, there are restrictions in reaching recessed surfaces.

Ensuring the accuracy of product rotation

The accuracy of product rotation is ensured by the accuracy of rotation of the spindles of the headstock and tailstock, the accuracy of rotation of the rollers of the supporting rests and the correctness of the initial alignment of the workpiece. The workpiece is clamped with the cams of two four-jaw chucks of the front and rear headstocks.

The experience of the plant has shown that the best results are achieved when the tailstock of the machine has a spindle assembly, which is not inferior to the front one in terms of rigidity and accuracy of spindle rotation. This is provided by:

1) the design and dimensions of the spindle assembly are identical to the headstock assembly;

2) the spindle has a flange for mounting the chuck;

3) bearings of the 3182000 series of the second accuracy class are used as radial spindle bearings;

4) by displacement during assembly of the inner rings in the bearings, an interference is created that provides high rigidity.

Verification of the accuracy of rotation of the spindles of lathes is usually carried out indirectly by identifying the radial and end runouts of the seating surfaces for the installation of chucks and centers. At the same time, the accuracy of axis rotation and the location accuracy of the spindle seating surfaces relative to this axis are evaluated simultaneously. However, the accuracy of machining on turning-grinding machines with fixing the workpiece in the jaws of clamping chucks is in no way related to the accuracy of the location of these surfaces. It is more expedient to use a special adjustable mandrel to control the accuracy of rotation of the spindle axis in accordance with the test 4.11.2. GOST 18097-93 “Screw-cutting and turning lathes. Main dimensions. Norms of accuracy.

The mandrel (Fig. 8) with body 1 is attached to the flange of the spindle end of the machine. The position of the rod 2 is adjusted by end screws 3 and radial screws 4 until the minimum possible runout is obtained at the end of the spindle and at a certain distance from the end. The plant has developed the design of adjustable mandrels and equipped the production for all used sizes of spindle ends.

The norms regulated by GOST are unjustifiably equalized with the requirements for the runout detected by conventional mandrels. Probably, the authors of GOST considered that the adjustment of adjustable mandrels to the minimum runout is a laborious procedure and left a margin for control error. Experience shows that with some skill, alignment can be carried out with a minimum error and judged by the readings of the measuring device about the true accuracy of spindle rotation. The factory set runout rate is 4 µm.

The design of the spindle unit uses adjustable roller bearings type 3182000 of the second accuracy class. Bearing clearances are reduced to zero. The rollers of the steady rests are also based on bearings of the second class of accuracy, the permissible runout of the working part of the rollers should not exceed 5 microns.

Alignment and fixing of workpieces

It is known that the alignment of a massive non-rigid workpiece is an extremely time-consuming procedure. If no constructive solutions are provided for in the machine, then the alignment and fixing of the workpiece will turn into an extremely difficult task, successful solution which even skilled craftsmen cannot afford.

The workpiece is deformed under the action of gravity and fastening forces, which forces us to overcome two difficulties.

1. The sagging of the central part of a long workpiece, fixed by the ends of the chuck jaws, is a few tenths of a millimeter. At the same time, at the turbine rotor, the allowable radial runout of most surfaces relative to the common axis of the working necks that need to be machined should not exceed 0.02 - 0.03 mm, i.e. should be 30 - 40 times smaller.

2. When clamping the workpiece with the jaws of the headstock chuck, its axis will certainly deviate from the axis of the machine. The actual value of the deviation is greater, the farther the distance from the cartridge. An attempt to fix the second end of the workpiece with the jaws of the tailstock chuck is associated with a curvature of the axis of the workpiece.

A technology for reliable alignment and fixing of large-sized non-rigid workpieces has been developed and implemented. This technology is feasible if the machine design has two headstocks (front and rear) equipped with four-jaw clamping chucks, two supports and supporting steady rests. The number of steady rests is chosen by the customer, depending on the length of the machine and the nature of the workpieces processed on the machine. Stands have prisms on which the workpiece is freely laid, their axes lie in the same plane with the axis of the machine. Prisms can be adjusted in height.

Both ends of the workpiece are initially aligned with the axis of the machine. Here are two possible options reconciliations.

1. Indicators are attached to each end of the workpiece and rolled over the outer surfaces of the chuck bodies. To eliminate the influence of the chuck body runout, the workpiece and the chuck are simultaneously rotated through the same angle.

2. A laser emitter and receiver are attached to the cartridge and the workpiece, respectively. The amount of misalignment is detected while turning the spindle and the workpiece. Laser devices for alignment control are manufactured by a number of foreign companies (Pergam, Germany; Fixturlaser and SKF, Sweden).

Only after both ends of the workpiece are coaxial with the axes of the spindles of the front and rear headstocks of the machine, you can begin to secure the workpiece with the cams of the cartridges. The clamp is combined with the final alignment, bringing the radial runout of the individual surfaces of the workpiece to the minimum allowable value (5 microns on the working surfaces, somewhat more on the rest). After alignment, the prisms of the supports are removed from the workpiece, and if the supports interfere with processing, they are removed from the machine.

The rollers of the steady rests must be installed on one or two surfaces that are not machined in this operation, which have a high shape accuracy (roundness). Otherwise, the workpiece error will be transferred to the machined surface.

Cutting tool, processing modes, achieved accuracy

As a cutting tool, it is possible to recommend the use of grinding wheels with a fairly large grain size, for example, 40. Wheels made of white electrocorundum with a hardness of CM2, which can be successfully grinded, have the greatest versatility. various materials different hardness.

Such characteristics of the wheels will allow to achieve high grinding performance with preliminary and good results in terms of roughness in finishing strokes made using the final dressing of the wheel. More on fine editing will be discussed in the next section.

Tab. 1 Wheel end grinding modes

A wheel dressed in the finishing mode does not have a high cutting ability, so they should be made no more than two working strokes at a shallow depth and one or two sparking-out strokes without transverse feed.

If it is necessary to increase productivity, the longitudinal feed can be raised to half the width of the working side of the circle when grinding with the end face and half the width of the circle when grinding the periphery.

Cross feed during pre-grinding can be carried out for each single stroke of the wheel, and for finishing work strokes - only once per double stroke. The machine has an automatic grinding cycle from stop to stop. Even more opportunities are revealed when equipping the machine with a CNC device with restoring the position of the cutting edge of the circle after dressing. A CNC device, or at least a digital display device, makes it possible to increase the productivity and accuracy of processing.

When grinding the necks of the rotors, performed during the tests of several machines mod. RT958, the following accuracy was achieved on a section 220 mm long:

1) Differentiation of diameters in the longitudinal section - 5 microns,

2) Different sizes of diameters in cross section- 10 microns,

3) Coaxiality with other surfaces - 20 microns.

Dimensional tolerance is 20 µm, alignment - 30 µm.

Dressing the grinding wheel

The grinding process requires systematic edits, because. the stability of the circle is small. Set diamonds are used as a ruling tool. New circle fill in order to eliminate the beating of its working surfaces.

The design of the machine must ensure the fulfillment of a number of conditions:

1. The dressing device must have high rigidity to avoid the appearance of diamond pressing and vibration during dressing.

2. Ease and convenience of placement of the dressing device in the working area of ​​the circle should be ensured.

3. The feed drive must provide the possibility of dressing in two modes (Table 2):

a) In the mode of accelerated feed and great depth for chipping blunt abrasive grains;

b) In the mode of finishing editing before the implementation of the finishing strokes. When finishing with low feeds (longitudinal and transverse), the diamond does not crumble the grains of the circle, but cuts. Even a coarse-grained grinding wheel becomes smooth, and regardless of its grit, a good roughness (Ra 0.1 to 0.32 µm) can be obtained, although the cutting ability of the wheel is degraded.

4. CNC or digital display devices significantly increase labor productivity, as it becomes possible to quickly exit the circle to the dressing position and return it to the meeting point with the workpiece after dressing, as well as compensation for the dressing amount.

Table 2 Editing modes

The option of fastening the ruling diamond directly to the workpiece has proven itself well. The removable dressing device covers one of the necks of the part with a tape or chain, fastening is carried out with a screw clamp. The top of the diamond is set in the plane in which the circle is in contact with the surface to be machined. For this purpose, a level can be set on the horizontal platform of the diamond holder. It is advisable for the diamond itself to be tilted to this plane by about 10 - 15 degrees. Such an arrangement provides, as it were, a self-sharpening of the diamond, since when it is turned in the holder, the blunting platform will also turn. The diamond will start working as a new peak.

Cooling system and protective screens

The coolant supply system is equipped with devices for cleaning both metal and non-metal particles - wear products and wheel dressing. It is not enough to limit ourselves to the use of magnetic separators.

Protective screens are designed to protect workers from splashes of cutting fluid and fragments of the grinding wheel in case of its destruction. At the same time, structural elements should not impair the view of the processing zone and wheel dressing and impede the approach of grinding wheels to the surfaces to be machined. Removable and adjustable shields and flexible hinged elements in the form of leather and rubber “noodles” performed well.

conclusions

1. Turning and grinding machines are a special class of machine tools, the scope of which will expand. These machines are indispensable for the repair of large-sized massive parts.

2. In the design of machine tools, it is necessary to have front and rear headstocks that have the same characteristics of accuracy and rigidity.

3. It is advisable to equip the machines with special interchangeable turning and grinding calipers, which are installed on the same cross slide of the machine. Grinding is performed on a limited length of the workpiece being processed.

4. In many cases, it is effective to grind the outer surfaces with the end face of the wheel. Such a circle can reach almost any deep surface of the workpiece, which is not always possible when grinding with the periphery of the circle.

5. The guides of the sanding caliper must ensure that the sled moves in a straight line over the entire stroke without reorientation. The best results are obtained when using rolling guides.

6. The holder of the ruling diamond must have increased rigidity; Noteworthy is the fastening of the diamond on the workpiece.

7. It should be possible to dress the wheel in two modes: with increased feed and with slow feed of the diamond relative to the wheel.

8. Equipping the machine with a CNC device or digital display allows you to increase labor productivity and processing accuracy.

9. The fixing of large-sized non-rigid parts must be preceded by the alignment of their position relative to the axes of both headstocks. A technology for aligning and fixing such parts has been developed.

10. A technique has been developed for grinding with the end of a wheel, which in some cases has an advantage over grinding with the periphery.

11. The coolant supply system must be equipped with devices for cleaning the liquid from metal and non-metal particles.

Bibliography

1. Certificate for utility model No. 17295 RF. The machine is a special lathe.

Modern trends in the field of integration of combined processing have led to the fact that grinding can also be carried out on lathes. When the quality problem comes to the fore, attention is always paid to the finishing process, which is called grinding - the implementation of mechanical action in several passes to reduce initial errors. It is impossible to finish with a turning tool with the same quality as when using grinding heads due to the rounding of the cutting edge. Also, do not forget that lathe at small feeds, vibration may occur, which will lead to an error. For this reason, even with the emergence of new materials that can withstand strong impact for a long time and not change their shape, grinding remains the main method used to obtain a surface of a high roughness class.

Need for grinding heads

The production of bodies of revolution on lathes has been carried out over the past few decades. As a rule, grinding was carried out on other equipment. This moment determined the next technological process:

1. performing rough turning to remove a large layer of metal;
2. performance of fine turning to prepare the part for the final stage of the technological process;
3. finishing on a circular grinding machine.

Such a technological process determines the increase in costs due to the installation of a special machine for finishing. When creating a large batch of products, the purchase of a grinding machine pays off, but in small-scale production, its purchase will lead to an increase in the cost of one product. The way out of the situation can be called the use of special grinding heads, which can also be used to obtain a surface with high class roughness.

Design features

Grinding heads are a special design that is used to significantly expand the capabilities of the turning group machine. This mechanism is conditionally related to equipment. Design features include:

1. the presence of its own electric motor, the power of which can be from 1 kW or more. this moment determines that the head can become a tool for various models of lathes. as a rule, turning equipment has a closed gearbox and does not have a separate drive for connecting the equipment in question;
2. the installed electric motor is connected to the circuit of the lathe, which determines the versatility of the whole structure. at the same time there is also a three-phase plug for inclusion in a separate power circuit;
3. the head has its own frame, which, when upgraded, can be fixed rigidly instead of the standard tool post. this moment determines that the equipment allows obtaining high-quality surfaces with high mechanization of the process. in the manufacture of the bed, steel is used, which helps to prevent vibration during operation by increasing the rigidity of the structure;
4. the transmission of rotation takes place using a belt drive to reduce speed.

The design is pretty simple. When considering it, you should pay attention to the type of bed. This is due to the fact that only a certain type of bed can fit a certain model of a lathe instead of a tool holder.

Steel and cast iron with the help of the equipment in question can go through the finishing process on a lathe. In this case, it is possible to achieve the same roughness index as when using cylindrical grinding equipment. Model 200 differs from the considered power of the installed electric motor and the maximum diametrical dimensions of the installed circles. Similarly, it is possible to reduce the cost of manufacturing parts by increasing the versatility of the equipment used. At the same time, we note that the equipment is suitable for old and new turning equipment, as it has a universal application.

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