Grinding wheels are the grinding tools used for grinding and abrasive machining. Grinding can be referred to as abrasive cutting. To perform the abrasive machining operations, the grinding wheels will be mounted to the grinding machines. Surface grinding is a type of abrasive cutting that is performed to produce a smooth finish on the flat surfaces of the work pieces. The surface grinding wheels are the grinding tools that are used in a surface grinding operation. The surface grinding operation can be done manually with an electricity powered rotary hand tool or it can be done with a console style grinding machining in a modern manufacturing setting.
Either manually or mechanically, the surface grinding wheels are needed in the operations. The manually conducted surface grinding is included in the light duty machining works can conducted by a skilled operator. On the other hand, the surface grinding machine is used in the heavy duty industrial machining works, such as CNC machining. The process here is typically highly automated where the mechanist is less involved. As the key component in a surface grinding operation, the choice of surface grinding wheels is quite crucial.
To choose the best grinding wheel for certain abrasive cutting operation, there are five basic characteristics to look for. They are the material hardness, the grain size, the wheel grade, the grain spacing and the bond type. A grinding wheel can be made from several materials such as aluminum oxide, silicon carbide, ceramic, diamond, and cubic boron nitride (CBN). The surface grinding wheels that are made with diamond or cubic boron nitride are called the super-abrasives while the grinding wheels made with other materials are called conventional abrasives.
The grain size of a grinding wheel ranges from 10 to 600. The number is determined depending on the size of the grains. The coarsest grain size is rated 10, which means the greatest size; the finest grain size is rated 600 which means the smallest size. The grinding wheels with larger grains allow fast cutting but the surface finishing is less ideal. On the other hand, with the finest grain size, the grinding wheels can be used for precision finish works. According to the rating, the grinding wheels can be categorized into coarse, medium, fine, and extra fine.
The wheel grade is rated from letter A to letter Z, from the softest to the hardest. The wheel grade refers to how tight the bond is to hold the abrasive together. Grading from A to H, the grinding wheel has a softer structure; from I to P, moderately hard structure; from Q to Z, hard structure. The wheel grade of the surface grinding wheels is important since it affects the wheel speed, coolant flow, feed rates and grinding depth directly.
The grain spacing or the grain structure is rated from number 1 to number 17. The number represents the density of the grains on the grinding wheel. The smaller the number is, the denser the grain structure is. A grinding wheel with less density can take deeper or wider cuts with less coolant and greater chip clearance on the wheel. A less-dense grinding wheel tends to have a larger effect on surface finish.
There are quite a number of wheel bond types. By the material a grinding wheel uses to hold the abrasives together, the finish work, coolant, and wheel speed are affected. V represents glass-based bond such as clays. B represents the resin-based materials. There are also silicate-based (S), shellac-based (E) bonding materials too. Other materials that create the bond on the grinding wheels are rubber (R), metal alloys (M), oxychloride (O), and plated (P).
In an industrial manufacturing setting, a surface grinding machine, or a surface grinder, is used to grinds down uneven surfaces on a work piece so that the part can have a flat and even-level surface finish. During such abrasive cutting process, the surface grinding wheel will spin at high speed to remove the differences in height. Before the machining operation begins, the height of the work piece will be set to the level just below the grinding wheel. Once the grinding wheel comes into the predetermined speed, the table of the surface grinder begins to raise and move left and right so that the work piece can get contact with the wheel. When the grinding wheel touches the work piece, the surface differences will be grinded off.
The material of the work piece as well as the grinding wheel is important. Take cast iron or most steels for instance, the steel-based or iron-based work pieces can be grinded relatively well. Yet, the aluminum work pieces, the stainless steel work pieces, or the brass and plastic work pieces may easily get heated during the grinding operation. The excessive heat may start to corrode the grinding wheel at some point. As a result, the choice of the surface grinding wheel to certain types of work piece and the setting of grinding speed are very important.
Normally, a typical surface grinder has a precision to plus and minus 0.002 mm. The surface grinding process is a time intensive process and hand adjustment and setup are sometimes involved. Therefore, the surface grinding machines are sometimes considered semi-automated. However, when the adjustment and settings are done, very little human factor is included in the grinding operation in order to maintain the overall precision of the work.
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