Internal grinding is very common machining in the grinding process. Internal grinding can process through holes, blind holes, step holes, etc. on the parts of the machine. Therefore, it is widely used in machining. The dimensional accuracy of the machining is usually up to the tolerance class IT6-IT7. If applied high precision grinding process, the dimensional accuracy can be controlled within 0.005mm. So, how to choose the internal grinding wheels?

1.Internal grinding Form

Internal grinding can be divided into the following three forms:

 1). Center type internal grinding

When grinding, the workpiece rotates around the centerline of the spindle box. Conventional internal grinding machines or universal cylindrical grinding machines are these types, which is suitable for grinding the inner holes of sleeves, gears, flanges and other parts.

2). Planetary internal grinding

When grinding, the workpiece is fixed and the grinding wheel rotates around its own axis at high speed, and also rotates around the hole center to be ground at a slower speed to achieve circumferential feed. In addition, the grinding wheel also performs longitudinal feed motion and periodic lateral feed. The lateral feed of the internal grinding wheel is achieved by increasing the radius of gyration of the planetary motion. Planetary internal grinding machines are mainly used for grinding the parts that are large and inconvenient to rotate.

3). Centerless internal grinding

The grinding method is suitable for the inner hole of the thin-walled ring part.

2.Features of internal grinding

Compared with cylindrical grinding, internal grinding has the following features.

1) When internal grinding, the diameter of the internal grinding wheel is small, and the rotation speed of the grinding wheel is limited by the rotation speed of the internal grinding tools. Therefore, the grinding speed is usually within 20-30m/s. Due to the low grinding speed, the surface roughness of the workpiece is not easily reduced.

2) When internal grinding, the grinding wheel is in contact with the workpiece in an inscribed circle. The contact arc of the grinding wheel and the workpiece is larger than the cylindrical grinding. Therefore, the grinding heat and the grinding force are relatively large, and the abrasive grains are easily blunt and the workpiece easily heats or burn.

3) When internal grinding, the cutting fluid is not easy to enter the grinding area, and the grinding debris is not easy to discharge. When the grinding debris accumulates in the inner hole of the workpiece, it is easy to cause the grinding wheel block and affect the surface quality of the workpiece. Especially when grinding brittle materials such as cast iron, the grinding debris and the cutting fluid are mixed into the paste, which makes the grinding wheel block and affects the grinding performance of the grinding wheel.

4) The rigidity of the long shaft of the grinding wheel is relatively poor, and it is easy to produce bending deformation and vibration, which has a great effect on the processing precision and surface roughness and also limits the improvement of the grinding amount.

3.Internal grinding method

Adjust the position of the grinding wheel before grinding. When the inner hole is ground on the universal cylindrical grinding machine, the grinding wheel is in contact with the front wall of the hole. At this time, the direction of the lateral feed of the grinding wheel is the same as cylindrical grinding. On the internal grinding machine, the internal grinding wheel in contact with the rear wall of the hole to facilitate the operator to observe the longitudinal grinding of the surface.

Longitudinal and cut-in method of internal grinding

1). Longitudinal grinding method

This grinding method is the same as the cylindrical longitudinal grinding method. When grinding through holes, first select the diameter and the shaft of the grinding wheel according to the hole diameter and length of the workpiece. The rigidity of the long shaft is better, and the length of the long shaft only needs to be slightly larger than that of the hole.

2). Cut-in grinding method

This grinding method is the same as the cylindrical cut-in grinding method and is suitable for grinding workpieces with short inner holes.

When grinding by the cut-in method, the rigidity of the long shaft is better, the grinding wheel is blocked easily and blunt when continuous feeding and the grinding wheel should be dressed in time. The lower cutting speed should be used for finish grinding.

4. Selection of internal grinding wheels

1.Selection of the diameter of internal grinding wheels

When the internal grinding is performed in the inner hole, and if the diameter of the grinding wheel is too large, the contact arc between the grinding wheel and the workpiece increases. It increases the grinding heat and is difficult to cool and remove the debris. If the diameter of the grinding wheel is small, it is difficult to achieve the ideal grinding speed(30m/s-50m/s), making the grinding thickness increased, the load of the abrasive grains increased, and it is easy to be blunt, and the surface roughness of the inner hole is increased.

In order to obtain a better grinding effect, should keep the appropriate ratio of the diameter and inner hole of the grinding wheel. This ratio is usually within 05-0.9. When the aperture is small, if the problem is the peripheral speed of the grinding wheel is low, should take the large ratio. When the pitch is small, and the problem is the difficulty of cooling and debris removal, should take the small ratio.

2. The width of the grinding wheel should not be too wide or too narrow when internal grinding.

When the internal grinding, if the width of the grinding wheel is too narrow, the grinding wheel is easy to wear, which is not good for improving production efficiency and reducing the surface roughness. If the grinding wheel is too wide, the grinding force is increased, which may cause the long shaft of the grinding wheel to deformation. Therefore, when grinding the inner hole, should choose the appropriate width of the grinding wheel.

3  Selection of abrasive of internal grinding wheels

Conventional abrasive grinding wheel: fused alumina abrasive

Superabrasive wheel: Diamond wheel and CBN wheel

4  Selection of the bond of the internal grinding wheels:

Conventional abrasive: resin bond and vitrified bond

Superabrasive: electroplated bond, vitrified bond, metal bond, resin bond

Remarks: Click here, you will learn the comprehensive knowledge of conventional abrasive wheels.

Remarks: Click here, you will learn the comprehensive knowledge of superabrasive grinding wheels.

Conclusion

In the process of choosing the internal grinding wheels, should choose suitable grinding wheel according to the actual situation to improve the production efficiency and ensure the production quality.