Grinding is a method of cutting workpiece using a grinding wheel as a cutting tool on a grinding machine. The characteristics of this method are as follows:
(1) Because the abrasive particles of the grinding wheel have high hardness and heat resistance, the grinding can process materials with high hardness, such as hardened steel, hard alloy and so on.
(2) The characteristics of grinding wheel and grinding machine determine that the grinding process system can perform even micro-cutting, generally AP =0.001 ~ 0.005mm; High grinding speed, generally up to V =30 ~ 50m/s; Good rigidity of grinding machine; By using hydraulic transmission, grinding can achieve high machining accuracy (IT6 ~ IT5) and small surface roughness (Ra=0.8 ~ 0.2 m) economically. Grinding is one of the main methods of parts finishing.
(3) Due to the intense friction, the grinding area temperature is very high. This can cause stress and deformation and even surface burns on the workpiece. So a lot of coolant must be injected during grinding to reduce grinding temperature. The coolant can also be used for chip removal and lubrication.
(4) Great radial force in grinding. This will cause the machine tool - grinding wheel - workpiece system flexibility, so that the actual cutting depth is less than the nominal cutting depth. Therefore, the grinding will be completed, should not feed polishing, in order to eliminate errors.
(5) After the abrasive obtuse, the grinding force will also increase, resulting in the abrasive grains broken or fell off, re-exposed the sharp edge, this property is called "self-sharpening". Self-sharpening enables grinding to be carried out normally within a certain period of time, but after a certain working time, manual dressing should be carried out to avoid vibration, noise and damage to the surface quality of the workpiece caused by the increase of grinding force.
A grinding wheel is a cutting tool for grinding. It is a porous substance bonded by a number of small, hard abrasive particles and a binder. The abrasive particles are directly responsible for the cutting work and must be sharp and have high hardness, heat resistance and certain toughness. Common abrasives are alumina (also known as corundum) and silicon carbide. Alumina abrasive with high hardness and good toughness is suitable for grinding steel. Silicon carbide abrasive with higher hardness, sharper, good thermal conductivity, but more brittle, suitable for grinding cast iron and hard alloy.
The grinding wheel with the same abrasive, due to its different thickness, the surface roughness and processing efficiency of the workpiece after processing are not the same, the coarse abrasive is used for coarse grinding, the fine abrasive is suitable for fine grinding, the coarser abrasive, the smaller particle size.
The binder ACTS as a bond to the abrasive. Ceramic binder is commonly used, followed by resin binder. Different binder selection can affect the corrosion resistance, strength, heat resistance and toughness of grinding wheel.
The hardness of the grinding wheel refers to how hard it is for grinding grains to fall off under the action of external forces. Easy to fall off called soft, vice versa called hard. The hardness of grinding wheel and abrasive are two different concepts. The surface of the workpiece to be ground is soft, and the edge of the abrasive grain (edges and corners) is not easy to wear, so the abrasive grain can be used for a longer time, that is to say, you can choose to stick to a more firm grinding wheel (grinding wheel with higher hardness). On the contrary, the grinding wheel with low hardness is suitable for grinding the workpiece with high hardness.
The grinding wheel works under the condition of high speed. In order to ensure safety, it should be inspected before installation without defects such as cracks. In order to make the grinding wheel work smoothly, a balancing test should be carried out before use.
After working for a certain period of time, the surface gap of the grinding wheel will be blocked by the grinding chips, the sharp Angle of the abrasive will be blunt, and the original geometry will be distorted. It must therefore be trimmed to restore cutting power and correct geometry. The grinding wheel shall be dressed with a diamond pen.
The structure and grinding motion of surface grinding machine
There are many kinds of grinding machines, including surface grinder, cylindrical grinder, internal grinder, universal cylindrical grinder (also grinding internal hole), gear grinder, thread grinder, guide grinder, centerless grinder (grinding external grinder) and tool grinder (grinding tool), etc. The surface grinder and its motion are introduced here.
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