Grinding wheel is a cutting tool for grinding, which is a porous object made of many small and hard abrasive particles and bonding agents. The abrasive particles directly shoulder the cutting work and must be sharp and have high hardness, heat resistance and a certain toughness. Commonly used abrasives are alumina (also known as corundum) and silicon carbide. Alumina abrasives have high hardness and good toughness, suitable for grinding steel. Silicon carbide abrasive hardness is higher, sharper, good thermal conductivity, but more brittle, suitable for grinding cast iron and carbide.
The same abrasive grinding wheel, 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 the abrasive, the smaller the particle size.
The binder acts as a bond to the abrasive. Ceramic binder is commonly used, followed by resin binder. The different material selection of the bond affects the corrosion resistance, strength, heat resistance and toughness of the grinding wheel.
The stronger the abrasive bond, the less easy it is to fall off the grinding wheel, it is called the hardness of the grinding wheel, that is, the hardness of the grinding wheel refers to the difficulty of the abrasive particles on the surface of the grinding wheel falling off under the action of external forces. Easy to fall off is called soft, and vice versa is called hard. The hardness of grinding wheel and abrasive hardness are two different concepts. The surface of the grinding workpiece is softer, and the cutting edge (edge) of the abrasive particle is not easy to wear, so that the abrasive can be used for a longer time, that is to say, a solid grinding wheel (higher hardness grinding wheel) can be selected. Conversely, low hardness grinding wheels are suitable for grinding high hardness workpieces.
The grinding wheel works at high speed, in order to ensure safety, it should be checked before installation, and there should be no cracks and other defects; In order to make the grinding wheel work smoothly, the action balance test should be carried out before use.
After the grinding wheel works for a certain period of time, the surface gap will be blocked by grinding chips, the acute Angle of the abrasive will be blunted, and the original geometry will be distorted. It must therefore be trimmed to restore cutting power and correct geometry. The grinding wheel needs to be trimmed with a diamond pen.
Grinding is the method of cutting the workpiece with the grinding wheel as the cutting tool on the grinding machine. The characteristics of this method are:
(1) Because the grinding wheel itself has high hardness and heat resistance, it can process materials with high hardness, such as hardened steel and cemented carbide.
(2) The characteristics of the grinding wheel and grinder determine that the grinding process system can make uniform micro cutting, generally ap=0.001 ~ 0.005mm; Grinding speed is very high, generally up to v=30 ~ 50m/s; Grinding machine stiffness is good; Using hydraulic transmission, grinding can economically obtain high machining accuracy (IT6 ~ IT5) and small surface roughness (Ra=0.8 ~ 0.2μm). Grinding is one of the main methods of parts finishing.
(3) Due to intense friction, the temperature of the grinding area is very high. This will cause stress and deformation of the workpiece, and even cause burns on the surface of the workpiece. Therefore, a large amount of coolant must be injected during grinding to reduce the grinding temperature. The coolant can also play a chip removal and lubrication role.
(4) The radial force during grinding is very large. This causes the elasticity of the machine-grinding-workpiece system to give way, making the actual cutting depth less than the nominal cutting depth. Therefore, when grinding is to be completed, it should be polished without feeding to eliminate errors.
(5) After the abrasive is blunted, the grinding force also increases, causing the abrasive to break or fall off, and re-exposing the sharp edge, this characteristic is called "self-sharpness". The self-sharpness enables the grinding to be carried out normally within a certain period of time, but after a certain working time, it should be manually trimmed to avoid vibration, noise and damage to the surface quality of the workpiece caused by the increase of grinding force.
Structure and grinding motion of surface grinding machine
There are many types of grinding machines, mainly surface grinding machines, external grinding machines, internal grinding machines, universal external grinding machines (can also grind internal holes), gear grinding machines, thread grinding machines, guideway grinding machines, centerless grinding machines (grinding external) and tool grinding machines (grinding tools). The surface grinder and its motion are described here.
1. Structure of surface grinding machine (take M7120A as an example, wherein: M-- grinding machine tool; 71-- horizontal shaft rectangular table surface grinding machine; 20-- the width of the working table is 200mm; A-- First major improvement.
(1) Grinding wheel frame -- Install the grinding wheel and drive the grinding wheel to rotate at high speed, and the grinding wheel frame can make manual or hydraulic transverse clearance movement along the dovetail guide rail of the slide seat.
(2) Slide - Install the grinding wheel frame and drive the grinding wheel frame to move up and down along the guide rail of the column.
(3) Column - supporting slide and grinding wheel holder.
(4) Workbench - installation of the workpiece and driven by the hydraulic system for reciprocating linear movement.
(5) Bed - support table, install other components.
(6) Coolant system - provides coolant (saponified oil) to the grinding area.
(7) Hydraulic transmission system - its composition is:
a. Power components -- for the oil pump, supply hydraulic transmission system pressure oil;
b. Executive components -- for the cylinder, drive the table and other parts to move;
c. Control components - for various valves, control pressure, speed, direction, etc.;
d. Auxiliary components - such as fuel tank, pressure gauge, etc.
Compared with mechanical transmission, hydraulic transmission has the advantages of smooth transmission, overload protection, and stepless speed regulation in a large range.
2. Surface grinding movement
(1) Main movement - high-speed rotation of the grinding wheel.
(2) Feed movement
a. Longitudinal feed - the table drives the reciprocating linear motion of the workpiece;
b. Vertical feed - the movement of the grinding wheel to the depth of the workpiece;
c. Transverse feed - the movement of the wheel along its axis.
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