Turning grinding machine. JET grinding machines. Design features of machines

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 performing 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. It is attractive to perform turning or grinding on different surfaces of the same part, 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 in the use of 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. Approach such recessed surfaces the structural elements of the faceplate 3, the grinding head 4 and the body of the head 5 interfere. The only way out is to work with circles of large diameters, which, in turn, require large-sized grinding heads that 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, in addition to the indicated advantage, circular 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 giving high accuracy to the perpendicularity of the rotation axis of the circle to the feed direction (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. The correct solution to 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, the successful solution of which is beyond the power of even qualified craftsmen.

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. We present two possible reconciliation options.

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 sufficiently large grain size, for example, 40. Wheels made of white electrocorundum with a hardness of CM2 have the greatest versatility, which can successfully grind various materials of 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. A new circle is filled 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.

findings

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.

Specialists of machine-building enterprises visiting foreign exhibitions of metalworking equipment are witnesses of the success of such a technical solution as the combination of several technological operations and even processes on one machine, and in various combinations. It seems that there are no operations left in the production, even the most difficult to combine, that would not be combined in an attempt to increase the accuracy and productivity of processing by reducing the number of resets.

This idea, which originated a long time ago and was really embodied in 1992 by Emag, which presented an inverted vertical lathe at the METAV92 exhibition, became a real material force a few years later. Evidence of this is over 5,000 machine tools of this configuration, sold to various factories, mainly automobile and tractor ones. On its basis, it became possible to combine turning, mainly hard, for hard-to-cut steels and alloys with a hardness of over 45HRC, with abrasive machining, also for the first time in the world carried out in 1998 by the same Emag company, but already together with Reinecker, which was part of it, on a machine Maud. VSC250DS (Fig. 1).

When the benefits are clear

Since then, the advantages of this arrangement have become apparent to many other German, Swiss and Italian firms producing both lathes and grinders. For turning centers, they consist in the possibility of using dry and hard turning, and in some cases, grinding in one set-up of parts of small diameter (up to 400 mm, only on the Index G 250 machine the machining diameter reaches 590 mm), but rather large length. There are many such parts such as gears, various disks in the automotive industry.
In addition, machining productivity is increased, since the grinding allowance after turning can be brought up to several hundredths of a millimeter (in reality, it usually reaches several tenths), and its accuracy, which is ultimately determined by grinding. To date, such combined machines are produced by several companies, mainly German, whose main field of activity is, as shown in Table 1, the production of not only turning centers (Emag, Index, Weisser), but also grinding machines (Junker, Buderus Schleifmaschinen, Schaudt Mikrosa BWF). Their cost fluctuates considerably and is determined primarily by the layout, design and equipment.

The exhibition EMO 2003 showed that interest in combined machines for hard turning and grinding is growing. Along with the companies Emag, Index, Weisser, Buderus, Schaudt Mikrosa BWF, which previously exhibited machines for combined turning and grinding, other manufacturers of machine tools also demonstrated similar products. For example, Tacchella (Italy) showed a prototype of a Concept cylindrical grinding machine equipped with an 8-position turret with stationary tools (Fig. 2), and Meccanodora (Italy) showed a serial Futura machine for hard turning and milling, as well as external and internal grinding transmission parts. The Stratos M, shown for the first time by Schaudt Mikrosa BWF at EMO 2001, was additionally equipped with an 8-station turret.

Combined processing

For parts passing through a turning and grinding center, for example, electric motor shafts, in most cases, grinding of all surfaces is not required - mainly only the supporting ones or the most worn ones. For the rest, turning is enough. In such cases, when tight dimensional tolerances and high surface quality are required only in certain parts of the part, the use of lathes with the possibility of grinding is fully justified, especially since they are machined in one setup. If the workpiece has many steps, most of which are subject to grinding, then it must be processed on a grinding machine with the possibility of turning.

Thus, on a grinding machine, processing is carried out if:

• workpieces are made of hard-to-cut materials that are not amenable or difficult to turn;
• the required tolerances exceed those achievable when turning;
• the required surface quality is so high that it cannot be achieved when turning, including hard turning.

The lathe is used for processing when:

• the complex geometry of the workpiece makes machining with a bladed tool with a point cutting edge (for example, a cutter) more efficient than a relatively wide grinding wheel;
• the volume of material removed is relatively large and exceeds the possibility of removal by grinding;
• processing of discontinuous surfaces is necessary.

For many parts, the requirements of both the first and second cases apply, so the combination of grinding with hard turning on the same machine increases its flexibility and allows you to optimize each operation.

Design features of machines

An analysis of the machines presented in Table 1 shows that the vast majority of them have a vertical layout, which for relatively short parts (with a diameter greater than the length), usually subjected to turning and grinding, turned out to be more effective than the horizontal one. The processing of sufficiently long shafts (from 600 mm for the HSC250DS model from Emag to 1400 mm for the G250 model from Index) remains an exception and is carried out only on machines with a horizontal layout. In addition, most machines, in order to increase their efficiency, are equipped with conveyors for feeding blanks and removing finished parts from the working area. One of the means of increasing the rigidity of machine tools subjected to increased loads during combined processing is the use (for machines from Emag, Schaudt BWF Mikrosa and some others) polymer concrete beds with good damping properties, as well as (for Buderus machines) natural granite beds.

Almost all machines are equipped as standard with more than one grinding spindle, in order to be able to perform both external and internal machining. In this case, the dressing mechanism is built directly into the machine. Note that almost all companies offer linear motors as options, not only along the longitudinal axis, along which the maximum movement occurs, but also along the transverse one. This means that the productivity of such machines can be further improved.

Of course, turning machine manufacturers such as Emag and Index, and grinding machine manufacturers such as Junker, with the common goal of achieving high flexibility, productivity and machining efficiency when choosing an approach to the design of their equipment that combines hard turning with grinding or vice versa, are guided by various considerations. As a rule, this design is made such that on the machine, in addition to turning and grinding, it is possible to perform other operations if necessary.
So, machine mod. Index's inverted V300 with vertical spindle (based on Emag) is designed to handle a wide range of workpieces of any type (castings, forgings, etc.). They are loaded and unloaded automatically. Thanks to the modular design, the machine, which is equipped with a large number of tool heads and blocks combined in any order (Fig. 3), designed to perform various turning, drilling and grinding operations, can work in both small and medium batch production. During processing, the spindle moves the workpiece, leading it to various tool blocks installed on the bed, which carry out the specified operations of turning, drilling, external and internal grinding. To perform combined hard turning and grinding, a turret with stationary and rotating tools is mounted on the bed. In the external grinding unit, grinding wheels with a diameter of 400 mm and a width of 40 mm are used from traditional and superhard materials, such as CBN, rotating at a frequency of up to 6000 min -1 from a drive with a power of 7.5 kW. They are edited automatically. The block has a built-in electromagnetic system for balancing the grinding wheel. Internal grinding is carried out with wheels made of the same materials, but mounted on HSK32 taper arbors for maximum precision and rigidity of the grinding spindle. The high-frequency spindle for their rotation has a power of 2 to 15 kW and is designed for a rotation speed in the range of 45,000-100,000 min -1 . Additional operations on this machine can be performed by means of a diode laser built into the production process to perform hardening of the outer surfaces on the workpiece clamped in the spindle chuck, as well as the ends and individual sections on the inner surfaces. An additional operation is also rolling, performed on a machine mod. CNC 435 from Buderus.
Multifunctional machines - the most successful type of equipment for blade processing today, and in many respects - are not something particularly new for abrasive. With the help of grinding wheels, built-in, for example, in the magazines of some milling machining centers, semi-finishing and finishing of complex surfaces of parts made of difficult-to-machine materials, such as turbine blades, has long been performed. The main technological advantages of such centers - a reduction in the amount of equipment required and, accordingly, the required production space and the number of operators, the ability to transfer finished parts directly to assembly - are also retained for multifunctional machines based on grinding. However, this equipment for combined grinding and turning has a number of differences and advantages. It should be noted, in particular, the significant predominance of his grinding operations over turning, milling and drilling, the obligatory cooling of the working area, the presence of a mechanism for changing wheels during grinding in some cases. As an advantage, it should also be considered that when turning, milling, threading and other blade operations are performed on grinding machines, greater accuracy is achieved than when they are performed on turning and / or milling machines, because in grinding machines that turn into multifunctional ones, more higher precision than, for example, in lathes, which are given the possibility of grinding. Such machines are produced by the Swiss company Magerle and the German Junker.
The modular MMS machine (Fig. 4), first shown by Magerle at the EMO2003 exhibition, has a symmetrical portal design, which, together with ball screws along the coordinate axes, ensures its static and dynamic rigidity and thermal stability. Movement along three coordinate axes (500x250x200 mm) through these gears is performed by a table, which allows you to install horizontal, vertical or inclined grinding heads on the machine and load it manually or automatically from four sides. At the exhibition, in particular, a version of the machine was shown with a vertical motor spindle with a power of 30 kW and a built-in tool changer (five grinding wheels with a diameter of 300 mm, a width of 60 mm and a weight of no more than 20 kg or 20 wheels with a diameter of no more than 130 mm), produced in 3 seconds. The frequency of rotation of circles is recommended in the range of 1000-8000 min -1 . Milling cutters, drills and other cutting tools can also be mounted in the HSK-A-100 spindle taper, which, when combined with an XY dividing head and pallet changer, allows processing small pump blades, turbine blades and other complex parts. This is facilitated by the possibility of supplying coolant through the center of the spindle at a pressure of 80 bar.
The prototype of the Concept multifunctional machine, which was also shown for the first time at this exhibition by the Italian company Tacchella Macchine, is a combination of a conventional cylindrical grinder with an eight-position turret in which stationary tools are mounted. Made of CBN, two circles of large diameter are rotated on the machine relative to each other by 180 degrees and can turn in turn into the working area. The machine bed is made in the form of a rigid ribbed iron casting. Movements along the X and Z axes can be performed by means of linear motors or ball screws. To move the working bodies are hydrostatic guides. Among the disadvantages of this machine can be attributed to the fact that it does not separate the working areas of turning and grinding. In the future, rotating tools will apparently also be installed in the turret, which will expand the technological capabilities of the machine, and the number of turrets can be increased to two.
On Junker's Modular 300 Series Hardpoint machine with slant bed, hardened and non-hardened parts such as bodies of revolution with a diameter of 80 mm and the same length (Fig. 5) in addition to grinding and honing with CBN wheels and heads, turning, drilling and reaming can be performed in one setup as well as cut threads and remove burrs. The machine is implemented in four versions with the number of spindles from two to four, in which up to four parts can be processed simultaneously with or without transfer from one spindle to another. The machine is controlled along six coordinate axes from the CNC Sinumerik 840D. The machine can be loaded manually or automatically.

High performance machine mod. The CNC235 from Buderus Scheiftechnik (Fig. 6) is achieved by installing two spindles on it, which allow external and internal grinding (with special heads) and hard turning (with separate cutters or a turret) of workpieces with a diameter and length up to 150 mm, as well as a conveyor belt.

Multifunctional machines designed for hard turning and grinding of heat-treated blanks are in high demand among consumers abroad and are gradually beginning to penetrate into Russia. There is information about the installation of one such machine (Buderus) at the Volgoburmash plant. Two machines mod. Stratos M was delivered in 2004 to VAZ. At the same time, there are already 60 such machines in operation in Europe, the USA and Southeast Asia. The reason for such a sharp difference lies in the insufficient level of development of most branches of our industry and the insufficient efficiency of such complex and expensive equipment in our economic conditions, and, consequently, the minimum demand for it. Therefore, in the near future, Russian factories should not expect the appearance of a large number of machines for dry turning and grinding, except perhaps at individual enterprises in the automotive industry and several enterprises producing equipment for the oil and gas industry.

Vladimir Potapov
Magazine "Equipment: market, offer, prices", No. 07, July 2004

According to their functionality, lathes can be conditionally divided into types: by groups, and by application features.

1. Screw-cutting group. Equipped with additional equipment for drilling and cutting a variety of threads. Such a machine allows you to give parts the shape of a cone, a cylinder and make complex combinations of these and other shapes. You can also use it to: drill and ream holes, make boring, countersink holes, cut threads, both internal and external.

2. Turning and milling machines are universal equipment, they make it possible to work with any material: plastic, iron, wood, etc. Functional work: turning, drilling, drilling, including deep holes, milling.

An excellent solution from PROMA will be a universal metal lathe. Suitable if the production requires a small amount of turning work without maintaining high levels of accuracy, or for home use.

The equipment allows you to perform the following types of operations:

• workpiece end processing;
• ream;
• drilling and reaming holes;
• cut thread.

CNC universal lathe is used in mass production enterprises. Multi-purpose lathes have the maximum functionality among such machines. It allows you to perform an extended range of work in addition to turning. With it, you can drill and mill after the primary processing of the workpiece has been completed.

The predetermined shape of the workpiece is given by means of a machining tool, in particular a cutter fixed in a tool holder. When it moves along a rotating workpiece along a perpendicular or at a given angle, metal layers of the required thickness are ground off. This operation gives the part a new shape.

Buy metal lathes

The universal lathe for metal is designed to shape workpieces from a variety of materials. They allow you to do the following:

• cut;
• sharpen;
• cut a thread;
• bore holes;
• perform deep drilling.

The processing of the workpiece on a lathe is carried out with its constant rotation.

The presence of a tool holder in the design of a lathe is the main difference between a machine for metal processing. The main task of this device is to hold the processing tool while working with metal.

The PROMA company on the site provides a catalog of screw-cutting lathes of European quality. Here you will find machines for domestic and industrial use.

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 on a lathe at low 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 following 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 a high roughness class.

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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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, the 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, differing in size, compactness of the mechanism, power of the electrical installation. The purpose of the mechanisms determines the location and type of installation. Large units designed for mass production have a massive base and are installed on the floor. Small products, desktop type are 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.