CNC grinding machines differ from devices with manual control in that ensuring the productivity of work on a CNC machine often does not depend on the grinding process itself. It largely depends on reducing the time spent on metal processing and programmed automatic control of the grinding process.
CNC grinding machines are usually suitable for final finishing of workpiece surfaces with various abrasives and diamond wheels. This treatment is carried out by removing the top layers of metal to give the surfaces the best possible cleanliness.
The following operations are performed with such grinding devices:
- stripping;
- cutting;
- cutting blanks;
- precision machining of rotary surfaces, gears, sharpening of various tools.
About the types of grinding devices
Typically, programmed numerical control systems are installed on devices of the following types:
- surface grinding for processing ordinary planes;
- cylindrical grinding devices for grinding crankshafts;
- internal grinding machines for profile grinding of holes;
- sharpening and grinding machines, for sharpening machine and manual tools, cleaning parts, processing welded or simple structures;
- contour grinding;
- sharpening, for metalwork work, such as chamfering, deburring, sharpening any tools, up to sharpening cutters of various types and drills;
- centerless grinding types of devices for plunge-cut and continuous-through grinding.
About the technical features of some CNC devices
The manufacture of such machines for grinding work is associated with certain difficulties, which are characterized by the following technical factors:
- on the one hand, it is necessary to achieve good quality and fairly high accuracy of grinding work, with the least dispersion in the size of the wheels;
- on the other hand, it is necessary to take into account the error in the exact dimensions of the grinding working wheel, depending on its wear.
In such cases, it is required that such a CNC grinding machine have special mechanisms to automatically compensate for the wear of this tool. Such mechanisms are designed to compensate (reimburse):
- some deformation;
- small error in temperature conditions;
- changes in allowances allowed on workpieces being processed;
- any errors of machine tools at given coordinates.
Important. For these types of cylindrical grinding devices, for example, these mechanisms can provide a constant ability to measure the diameter of the workpiece while it is being processed. Moreover, the measurement error will not exceed 2·10-5 mm. The longitudinal movement of such a table is controlled with an error of only 0.1 mm.
Usually, for grinding type devices, special CNC systems are used (from the English CNC), the control of which is implemented along ordinates from 3 to 4. And if several grinding wheels are used in the machines, then such control will be carried out along 5-6-8 different ordinates. Moreover, the operator’s interaction with the built-in CNC system is often carried out in dialogue mode using the display. In addition, to increase reliability, such systems are equipped with special diagnostic modules.
Russian-made CNC grinding machines
The Vladimir Machine Tool Plant Tehnika produces a universal CNC cylindrical grinding machine model KSh3 CNC , as well as a CNC grinding machine for processing rollers SWa AGL-125 CNC .
The machine is made on a modern element base, taking into account the latest trends in machine tool construction and has a number of fundamental features that allow it to compare favorably with the base model.
The machine is controlled by the Mikros-12Sh1 CNC system, which allows you to flexibly reconfigure the machine for various technological tasks:
- grinding of complex surfaces using the copying method with wheel dressing with one or two diamonds in two coordinates
- grinding of several surfaces according to a given program without operator participation
- grinding of eccentric surfaces by introducing a controlled coordinate for the rotation of the part (optional)
- maintaining a wide range of speeds of movement of the grinding headstock and table, including minimum ones - up to 0.002 mm/min
The presence of reading linear photopulse transducers in two coordinates makes it possible to control linear movements with an accuracy of 0.1 microns. Purified and dried compressed air is supplied to the converter housing, which eliminates the possibility of harmful substances entering and increases the reliability of its operation.
The use of two-axis synchronous linear electric motors complete with a variable-frequency drive produced by the Belarusian company Ruchservomotor ensures the exclusion of mechanical and hydraulic devices from the feed drive and, accordingly, high dynamics, rigidity, accuracy and reliability due to the elimination of intermediate elements of the classic drive, while reducing the number of required rigging.
The spindles of the product headstocks and the grinding head are mounted on hydrodynamic supports, which improves the accuracy of rotation of the spindles and increases the service life of the units. Spindles have the ability to smoothly change speeds.
The high positioning stability of the actuator units makes it possible to abandon the use of an active control device.
The main technical characteristics are as follows: the largest diameter of the installed product is 200 mm, the longest length of external grinding is 360 mm, the diameter of the grinding hole is no more than 50 mm, the height of the centers above the table is 125 mm, the distance between centers is 400 mm, non-roundness of the sample (d= 35) when processing in fixed centers - 0.2-0.3 µm, constancy of the sample diameter in the longitudinal section over a length of 300 mm - 1 µm, cleanliness of the processed cylindrical surface - Ra 0.04 µm.
The CNC grinding machine for processing rollers, model AGL125P CNC, is designed for high-speed grinding of “barrel-shaped” bearing rollers in serial, large-scale and mass production.
Mikros-12Sh2 CNC system and has the same design characteristics as the machine model KSh3 CNC .
Let us list the main parameters: the largest outer diameter of the workpieces processed is 180 mm (manual control) or 50 mm (automatic cycle), the smallest is 28 mm; the greatest length of the workpiece is 56 mm, the shortest is 12 mm; The minimum radius of the roller generatrix is 180 mm, the maximum is 280 mm.
The Moscow plant of grinding machines MSZ-Salyut CJSC offers CNC grinding machines:
- gear grinding machines models МШ395, МШ350С, МШ500С and МШ504С
- profile grinding machines model MSh397
- special semi-automatic machines models MSh475, MSh476
- internal grinding machine model MSh204
The MSh395 machine has an original layout with a horizontal axis of the product, which makes it possible in the future to easily automate the loading and unloading of products in mass production conditions.
The machine widely uses hydrostatic guides, as well as guides with fluoroplastic coating. The bed and main components have a special design to ensure high accuracy.
The machine is equipped with a six-axis CNC, providing electronic synchronous communication on three axes simultaneously. The ruling device consists of two sharp-angled diamond rollers.
The special design of the product rotation mechanism allows for high-performance power grinding with a worm abrasive wheel, as well as grinding of coarse-grained (modulus above 6 mm) gears with a profile wheel.
CNC gear grinding machines models МШ350С, МШ500С and МШ504С, working with a flat wheel using the rolling-in method, are designed for processing the involute profile of cutters, shaver and measuring gears.
The machines are equipped with a CNC system from Siemens, which performs the function of dividing and shaping the tooth profile and has stepless control of the grinding wheel rotation speed and dressing speed.
The productivity of the machine is increased by equipping it with adjustable drives for the main movement and straightening. It is envisaged to introduce a system for maintaining a constant cutting speed as the grinding wheel wears out. The machine is designed for the use of both electrocorundum and CBN wheels. The main characteristics of these machines are shown in Table 1.
Profile grinding machines model МШ397 (gamma) with CNC and drives. The range of profile grinding machines МШ397 provides processing of splined shafts and broaches with various real profiles - straight-sided, involute, sharp-splined, radius, as well as gears.
Flexibility of control provides not only the choice of optimal grinding modes, but also the ability to process broaches with specific features.
The flexible grinding wheel profiling capabilities provided by the CNC-controlled dressing mechanism allow simultaneous grinding of flanks, internal diameters, rounds and chamfers at the base and top of the spline.
Setting up the machine components and systems that provide the cycle and profile of the grinding wheel is carried out from the remote control. Entering data on the product and modes into the CNC system (directly from a drawing or technical card), as well as adjustments based on grinding results, are carried out in interactive mode. It is possible to independently adjust each profile element.
High quality of service is ensured by visual diagnostics of the entered parameters and the operation of individual machine systems. It is possible to simulate both the processing cycle and the grinding wheel profile on the display.
MSh475, MSh476 with CNC are special semi-automatic machines that operate using both plunge-cut and pendulum grinding methods. The MSh475 cylindrical grinding machine is designed for external grinding of cylindrical (conical) surfaces of rotating bodies. Face cylindrical grinding machine MSh476—for simultaneous external grinding of diameter and end.
Possible machine versions:
- in hard centers
- in moving centers with base stop
The internal grinding machine MSh204 is designed for grinding cylindrical and conical external and internal surfaces of rotating bodies; it can be produced in the following design:
- with automatic loading and unloading of parts
- with manual loading and unloading
The machine is equipped with two spindles and allows you to produce:
- simultaneous grinding of the hole and the end of the part
- sequential grinding of the hole and the end of the part
- sequential grinding of all external and internal surfaces
Dressing of grinding wheels is carried out along any trajectory specified by the CNC (undercut, bevel, barrel, etc.). All units are moved by Simodrive drives from Siemens. The machine is equipped with a Sinumerik 840D CNC system.
About CNC systems
In order to correctly control the straightening mechanisms in machines, the following software systems are used:
- are closed to compensate for temperature deformations and geometric inaccuracies;
- have the ability to measure with good resolution to ensure small tolerances for precise positioning;
- have the ability to automatically compensate for wheel wear;
- will be able to control the frequency of circular rotation and feed speed.
When controlling such CNC systems, it is possible to coordinate the functioning of multi-axis centerless cylindrical grinding devices. For this purpose, the embedded system uses special modules that calculate:
- any trajectories of grinding devices;
- necessary corrective actions;
- mutually agreed dialogue between the operator and the service device.
Important. The existence of multi-axis CNC systems gives these production devices more versatility and allows them to effectively influence any grinding process.
CNC grinding machines made in Belarus:
The Krasny Borets machine-tool plant in Orsha presents CNC grinding machines:
- surface grinder with a round table and a horizontal spindle, model OSH-641FZ
- semi-automatic deep-depth flat-profile grinding ORSHA-630FZ
- high precision semi-automatic cylindrical grinding machine ZV130F4
- semi-automatic profile grinding machine OSH-631FZ
- semi-automatic special internal grinding machine with a vertical spindle OSH-642FZ
The OSH-641FZ machine is designed for high-precision processing of both flat surfaces (for example: flat disks) and profiles, which are combinations of segments, straight lines, arcs, circles and other precisely defined curves in a rectangular coordinate system.
The rational design of the bed, column, table and grinding head, made of cast iron, ensures high rigidity and vibration resistance of the machines, which guarantees stable precision and cleanliness of processing.
The machine is equipped with a Sinumerik-802D CNC system with STEPDRIVE electric drives for control along the Y and Z coordinates.
The use of high-precision backlash-free ball screws in the feed units ensures smooth, high-precision backlash-free positioning. All working movements of the machines are automated.
There is an electronic handwheel for moving along the Y and Z coordinates with a resolution of 1 micron. The machine uses components from the world's leading manufacturers: Siemens, Baluff, FAG, Rexroth.
The ORSHA-630FZ semi-automatic machine is designed for high-performance and high-precision abrasive processing of flat surfaces (tenons, grooves) by creep-feed grinding of various products made of difficult-to-cut and heat-resistant materials. The ORSHA-630FZ semi-automatic machine, due to the CNC system, has the ability to process complex-profile surfaces.
Design Features:
- CNC system Sinumerik 840D from Siemens
- availability of mechanisms for contour and continuous dressing of the grinding wheel during the grinding process
- highly efficient coolant supply system with temperature stabilization
- hydraulic cleaning of the grinding wheel
- effective cleaning of coolant with automatic unloading and removal of sediment
- high-speed grinding
Components from the world's leading manufacturers were used: SIMODRIVE 611 drives, Hitachi frequency converter; Heidenhain linear converters; Rexroth linear guides, FAG spindle bearings.
The semi-automatic CNC cylindrical grinder ZV130F4 is designed for grinding surfaces of complex profiles in transverse and longitudinal sections. Equipped with a Sinumerik 840D CNC system. The main characteristics of this machine are shown in Table 2.
The OSH-631FZ semi-automatic machine is designed for processing high-precision two- and three-coordinate profiles using interpolation along two coordinates and programmable movement along the third coordinate using the creep-feed grinding method.
The semi-automatic machine can be used as flexible technological equipment, designed for straightening and grinding with contour control, and well meets the requirements of small- and medium-scale production with frequently changing profiles of workpieces.
Scope of application of the semi-automatic device:
- stamps and molds - production of complex-profile punches, matrices, design marks of molds
- copiers and templates - shaped grinding of copiers and templates is carried out easily and accurately
- cutting tool - successfully used for the manufacture of various cutter profiles
- grooves and tenons – grinding in one pass with a guarantee of high precision and quality
- Turbine blade locks - high rigidity and power of the main drive ensure optimal performance
- gear racks – we guarantee high step accuracy, both per pass and during positional grinding
The OSH-642FZ semi-automatic machine is designed for high-precision grinding of external and internal cylindrical surfaces, as well as ends in multi-stage parts such as a rotating body. The scope of application of the semi-automatic device is enterprises with large-scale and mass production. Processing of parts on a semi-automatic machine is carried out due to the vertical movement (feed) of the grinding wheel and the circular rotation of the part with oscillation or longitudinal feed. Machining of the ends can be carried out using a single-pass depth method with radial feed (removal of allowance in one pass) or as conventional face grinding with dressing and undercutting of the grinding wheel according to a CNC control program with compensation.
Vitebsk grinding machine plant Visas produces several models of CNC grinding and sharpening machines.
Vitebsk machine tool plant Vistan produces cylindrical grinding center and centerless machines, universal and CNC.
About cylindrical grinding devices
In any CNC grinding machines, the greatest effect produced is achieved when processing surfaces with one installation of special multi-stage parts, for example:
- spindles for securing workpieces;
- electric motor shafts;
- turbine elements;
- rotational frequency control gearboxes.
In such cases, productivity increases significantly by reducing the extra time that is allocated to:
- installation of the required blanks and removal of already processed finished products;
- reinstallation for the purpose of subsequent processing of the shaft journal;
- necessary measurements.
On these numerical cylindrical grinding machines, the programmed processing of various multi-stage shafts reaches the end with a reduction of time of almost 1.5-2 times when compared with a conventional control machine.
About the types of centerless grinding devices
Machines of this type are usually used for:
- processing of various parts, of any length, with large or small diameters;
- grinding parts with rather complex external profiles.
These machines usually have high productivity and very precise processing. But, unfortunately, for small-scale and small individual productions their use is difficult, since it is quite difficult to re-adjust these devices, since this will require significant time expenditure and highly qualified service personnel.
About CNC face-cylindrical grinding devices
Typically, program-controlled devices provide a large number of coordinates. For example, in a grinding device of this type there can be up to 10 controlled ordinates, of which three are main and at least six auxiliary for better positioning:
- axial orientation of the workpieces relative to the circle;
- shifting the tailstock for adjusting and processing workpieces;
- editing wheels to ensure the ability to process any profiles;
- device axes for active control;
- better rotation of tables for processing cones.
To process different types of geometric shapes of products with CNC grinding machines, special programs are installed:
- mode selection manager;
- a special module that controls the drive;
- An interpolator that determines the coordinates of points.
In mass production, such CNC grinding machines are used using software systems, which makes it possible to flexibly configure the dressing and grinding cycle, which significantly affects the speed of changeover of machines and processing of a wide variety of parts. In addition, such multi-axis systems give more versatility to machines and stable efficiency in managing all processes.
Manufacturers of grinding machines in the CIS
Currently, in the territory of the former Soviet Union, grinding machines are produced by Russian enterprises - manufacturers of grinding machines:
Voronezh Machine Tool Plant named after. The 50th anniversary of the Lenin Komsomol produces universal and special grinding machines. These are particularly high-precision internal grinding machines, models ZK228A and ZK229A, surface grinding machines mod. ZD725, ZL725VF10 with a rectangular table measuring 630×2000 mm, designed for grinding flat surfaces with the periphery of a grinding wheel. These are surface grinding machines mod. ZE756, ZE756L, ZE756L-1 with a retractable round electromagnetic table with a diameter of 800 and 1000 mm and a vertical spindle, designed for high-performance grinding of flat parts with the end of a grinding wheel. These are, finally, semi-automatic and automatic two-, three- and five-spindle surface grinders with round annular tables, designed for grinding the planes of various parts with the end of a grinding wheel in large-scale and mass production.
The Lipetsk Machine Tool Plant produces surface grinding machines with a rectangular table - the base model ZL722V and with a round table - the base model ZL741VF10, as well as spare parts for them (electromagnetic plates, spindle units, hydraulic cylinders, etc.).
The Derbent plant offers several models of belt polishing machines, a suspended roughing and grinding machine, machines for sharpening tools, semi-automatic machines for sharpening flat knives with a straight cutting edge, a semi-automatic machine for sharpening frame saws.
The plant of jig boring machines Stan-Samara, JSC produces a number of models of thread grinding machines.
Leningrad Machine Tool Plant named after Ilyich. The Precision Machine Tool Manufacturing Plant St. Petersburg ZPS produces a universal cylindrical grinding machine model LZ-269F10.
However, among the machines of these six companies, there is not a single CNC machine.
The production program of other enterprises to a greater or lesser extent includes machines equipped with CNC systems. Let's talk about them.
