Grinding machine can process high hardness materials, such as hardened steel, carbide, etc.; also can process brittle materials, such as glass, granite. Grinding machine can make high precision and surface roughness is very small grinding, but also can carry out high efficiency grinding, such as power grinding. Grinding processing, in the mechanical processing belongs to the finishing process (mechanical processing is divided into roughing, finishing, heat treatment and other processing methods), processing volume is small, high precision. In the machinery manufacturing industry is more widely used, the heat treatment of quenched carbon tool steel and carburized quenched steel parts, in the grinding and grinding direction of the basic perpendicular to the surface often appear a large number of more regular arrangement of cracks - grinding cracks, which not only affects the appearance of the parts, and more importantly, will also have a direct impact on the quality of the parts.
Grinding refers to the use of abrasive, abrasive removal of excess material on the workpiece processing methods, according to the process purpose and requirements of different, grinding process has a variety of forms, in order to adapt to the needs of the development of grinding technology toward precision, low roughness, high efficiency, high speed and automatic grinding direction. Grinding and other cutting methods, such as turning, milling, planing, etc., has the following characteristics:
(1) grinding speed is very high, up to 30m ~ 50m per second; grinding temperature is high, up to 1000 ℃ ~ 1500 ℃; the grinding process is very short, only one ten thousandth of a second or so.
(2) The grinding process can obtain high machining accuracy and small surface roughness value.
(3) grinding not only can process soft materials, such as unhardened steel, cast iron, etc., but also can process hardened steel and other tools can not be processed hard materials, such as ceramic parts, carbide, etc..
(4) The depth of cut in grinding is very small, and the metal layer that can be removed in one stroke is very thin.
(5) When grinding, a large number of fine abrasive chips fly out from the grinding wheel, while a large number of metal chips splash out from the workpiece. Both abrasive and metal shavings can be harmful to the operator's eyes, and dust inhaled into the lungs can also be harmful to the body.
(6) Due to the poor quality of grinding wheels, poor storage, improper selection of specifications, installation of eccentricity, or feed speed is too large, etc., grinding may cause the grinding wheel broken, which will lead to serious injuries to the workers.
(7) In the manual operation close to the rotating grinding wheel, such as grinding tools, cleaning workpieces or grinding wheel correction method is incorrect, the worker's hand may touch the grinding wheel or other moving parts of the grinder and get hurt.
(8) The noise generated during grinding processing can be up to 110dB or more, and if no noise reduction measures are taken, it will also affect health.
Grinding is used to process the internal and external cylindrical surfaces, conical surfaces and flat surfaces of various workpieces, as well as special, complex shaped surfaces such as threads, gears and splines. Due to the high hardness of the abrasive grains and the self-sharpening nature of the abrasives, grinding can be used to process a wide variety of materials, including hardened steel, high-strength alloy steel, cemented carbide, glass, ceramics and marble and other high hardness metal and non-metallic materials. Grinding speed refers to the grinding wheel line speed, generally 30 ~ 35 m / s, more than 45 m / s is called high-speed grinding.
Grinding is usually used for semi-finishing and finishing, the accuracy can be up to IT8 ~ 5 or even higher, the surface roughness of the general grinding Ra1.25 ~ 0.16 microns, precision grinding Ra0.16 ~ 0.04 microns, ultra-precision grinding Ra0.04 ~ 0.01 microns, mirror grinding can be up to Ra0.01 microns below. Grinding than the power (or than the energy consumption, that is, the removal of a unit volume of workpiece material consumed by the energy) than the general cutting, metal removal rate is smaller than the general cutting, so the workpiece in the grinding before the first usually through other cutting methods to remove most of the machining allowances, leaving only 0.1 ~ 1 millimeter or smaller grinding allowances. With the development of slow feed grinding, high-speed grinding and other high-efficiency grinding, has been able to grind parts directly from the blank into shape. There are also grinding as a desert processing, such as grinding castings pouring risers, forging edge and ingot skin, etc..
The main types of CNC grinding machine:
1, cylindrical grinding
Mainly on cylindrical grinding machine, used to grind the shaft type workpiece of the external cylindrical, external cone and shoulder end face. When grinding, the workpiece rotates at low speed, and if the workpiece moves longitudinally and reciprocally at the same time, and the grinding wheel is fed transversely relative to the workpiece after each single or double stroke of the longitudinal movement, it is called the longitudinal grinding method. If the width of the grinding wheel is greater than the length of the surface to be ground, the workpiece in the grinding process does not move in the longitudinal direction, but the grinding wheel relative to the workpiece continuous transverse feed, known as the plunge-cut grinding method. Generally, the efficiency of plunge-cut grinding method is higher than that of longitudinal grinding method. If the grinding wheel is trimmed into a molded surface, plunge-cut grinding method can process the outer surface of the molded.
2, internal grinding
Mainly used for internal grinding machine, universal cylindrical grinding machine and coordinate grinding machine on the cylindrical holes, conical holes and holes end face. Longitudinal grinding method is generally used. The plunge-cut grinding method can be used when grinding the shaped inner surface. When grinding internal holes on a coordinate grinding machine, the workpiece is fixed on the table, and the grinding wheel, in addition to high-speed rotation, also makes planetary motion around the centerline of the hole to be ground. Internal grinding, due to the small diameter of the grinding wheel, the grinding speed is often less than 30 meters / sec.
3, surface grinding
Mainly used in surface grinding machine grinding plane, groove, etc.. There are two kinds of surface grinding: grinding with the outer surface of the wheel is called peripheral grinding, generally use horizontal axis surface grinder, such as molding wheel can also process a variety of molding surface; grinding with the end of the wheel is called end face grinding, generally use vertical axis surface grinder.
4, centerless grinding
Generally in the centerless grinding machine, used to grind the outer circle of the workpiece. When grinding, the workpiece is not centered and supported by the top, but is placed between the grinding wheel and the guide wheel, supported by the pallet underneath, and rotated by the guide wheel. When the axis of the guide wheel is adjusted to intersect the grinding wheel axis diagonally by 1° to 6°, the workpiece can rotate and make longitudinal feeding movement in the axial direction automatically, which is called penetrating grinding. Throughfeed grinding can only be used for grinding external cylindrical surfaces. When plunge-cut centerless grinding is used, the axis of the guide wheel and the axis of the grinding wheel must be adjusted to be parallel to each other, so that the workpiece is supported on the pallet without axial movement, and the grinding wheel is continuously fed in the transverse direction relative to the guide wheel. Plunge-cut centerless grinding can be used to process shaped surfaces. Centerless grinding can also be used for internal grinding, when processing the workpiece outer circle supported on the roller or support block centering, and eccentric electromagnetic suction ring to drive the workpiece rotation, the grinding wheel into the hole for grinding, at this time, the outer circle as a positioning reference, to ensure that the inner circle and the outer circle concentric. Centerless internal grinding is often used to grind the inner groove of the bearing ring on special grinding machines for bearing rings.