What Is Grinding?
Grinding is the process of grinding the surface of a workpiece with a circular grinding wheel.
A grinding wheel rotating at high speed is pressed against the workpiece to grind the surface of the workpiece gradually to the desired shape. Grinding is similar to polishing, but in grinding, a certain amount of pressure is applied to the workpiece using a grinding wheel, file, buff, etc., to achieve a “flat and clean” surface.
Grinding, on the other hand, is performed with a certain amount of depth of cut in pursuit of “dimensional accuracy” of the finished product.
Uses of Grinding
Grinding is used for many industrial parts and products as a finishing process for cast, forged, and machined workpieces. Particularly in the automotive industry and industrial machinery, grinding is used for precision finishing of shafts, bearings, moving parts inside engines, and brake discs.
It is also used in the manufacture of furniture, bearings for household appliances, and circular saws. The ability to process extremely hard workpieces has led to widespread use in the semiconductor industry, including the processing of silicon wafers and minerals such as quartz and sapphire for use inside electronic components.
Principles of Grinding
1. Surface Grinding
Surface grinding uses a surface grinder to machine the flat surface of a workpiece. The workpiece is fixed to the table, and the table is moved back and forth, up and down, to grind. There are two types of grinding methods: vertical grinding with the wheel axis perpendicular to the table, and horizontal grinding with the wheel axis parallel to the table. There are various types of grinding methods depending on the combination of the table movement method and axis direction.
2. Cylindrical Grinding
Cylindrical grinding is the process of grinding the outer surface of a cylindrical workpiece using a cylindrical grinder. There are three types of grinding methods: traverse grinding, plunge grinding, and angular grinding.
In transverse grinding, the workpiece is ground by reciprocating it. Plunge grinding is performed by grinding the workpiece with the grinding wheel perpendicular to the workpiece while rotating the workpiece. Angular grinding is a method in which the grinding wheel is tilted to simultaneously grind the outer surface and the end face of the workpiece.
3. Internal Grinding
Internal grinding is a method of grinding the internal surface of a workpiece with a hole using an internal grinding machine. There are two types of internal grinding methods: the standard type and the planetary type.
In the standard type, a grinding wheel is inserted into the internal surface of the workpiece, and both the workpiece and the grinding wheel are rotated for machining. The planetary type is a method in which only the grinding wheel rotates and orbits on the inner surface of the workpiece.
4. Centerless Grinding
Centerless grinding is a method of grinding the outside of a cylinder in the same way as cylindrical grinding. However, the method of securing the workpiece differs between the two.
In centerless grinding, the workpiece is evenly supported at three points: the support blade, the regulating wheel, and the grinding wheel, and the rotating grinding wheel is placed against the workpiece so that the workpiece spins naturally. This allows the workpiece surface to be finished uniformly.
This type of grinding is suitable for machining thin or long cylinders such as cylinder rods. Since the workpiece does not need to be fixed in place, it is suitable for mass production and can achieve a uniform finish.
Characteristics of Grinding
1. High-Precision Machining
The small depth of cut in a single operation improves machining accuracy. Since each of the abrasive grains that make up the grinding wheel has a role as a blade and is rotated at high speed, chips are extremely small. Therefore, the roughness of the finished surface is much better than that of a cutting tool, and the dimensional accuracy is also excellent.
2. Capable of Machining High-Hardness Materials
Because the cutting edges of grinding wheels are made of extremely hard mineral particles, even cemented carbide and ceramics can be easily ground. The self-sharpening action of the grinding wheel allows gradual grinding while maintaining sharpness. Materials that cannot be ground with cutting tools can also be ground.
3. High Surface Roughness
Smooth surface finish is possible due to gradual grinding.
4. Self-Activation of Cutting Edges
When the cutting edge of a grinding wheel wears down during use, the abrasive grains fall off to form new cutting edges and pores. Therefore, there is no need for resharpening, as is the case with cutting tools.
5. High Productivity
Grinding requires only a small amount of cutting at a time, but the grinding wheel rotates at a high speed, and the peripheral speed is 10 times faster than other cutting processes, resulting in high productivity.
Other Information on Grinding
About Grinding Wheels
Grinding wheels used in the grinding process grind the workpiece using three elements: abrasive grains, bonding agent, and pores.
- Abrasive Grain
Each grain acts as a blade to grind the workpiece. When abrasive grains can no longer be ground after use, they drop off and new abrasive grains are formed to continue the work. - Bonding Material
The bonding material holds the abrasive grains and adjusts the performance depending on the type and amount of the bonding material. - Pores
Pores are gaps between abrasive grains where shavings enter and are discharged by the centrifugal force of rotation.
Another problem with grinding wheels is that they can become “ground up,” “clogged,” or “spilled.” When these occur, the workpiece cannot be ground.
- Blinding
When grinding conditions are poor, abrasive grains do not fall off and the surface of the grinding wheel becomes flat. - Clogging
This phenomenon occurs when shavings or abrasive grains get into the pores. - Spilling
The abrasive grains drop out of the workpiece before it is ground.