How do you decide the hardness of a diamond grinding wheel?

What is the hardness of a diamond grinding wheel?

The hardness of the grinding wheel refers to the difficulty of abrasive grains on the grinding wheel's surface falling off when subjected to external force. Soft diamond and CBN electroplated grinding wheels are easy to fall off, while hard diamond and CBN electroplated grinding wheels are. The same abrasive can be made into grinding wheels of varying hardness, which is determined primarily by the performance and proportion of the binder, as well as the manufacturing process of the grinding wheel.

In the grinding process, how do you select a diamond grinding wheel with a hardness diamond and a CBN electroplated grinding wheel?

When the grinding wheel's hardness is correctly selected, the diamond or CBN electroplated grinding wheel will automatically remove the blunt abrasive grains during the grinding process, exposing new sharp abrasive grains to continue grinding. If the grinding wheel is too soft, the abrasive grains will fall off prematurely before passivation, increasing not only the grinding wheel's consumption but also causing the grinding wheel to lose its correct shape and affecting machining accuracy. If the grinding wheel chosen is too hard, the abrasive grains will not fall off in time after passivation, resulting in damage. Grinding debris blocks the gap between the abrasives on the surface of the grinding wheel, resulting in increased grinding force, increased grinding heat, and increased grinding temperature, resulting in workpiece deformation or even burns, as well as increased surface roughness and reduced productivity.

The hardness of the grinding wheel should be lower when grinding hard materials with diamond and electroplated CBN grinding wheels; otherwise, it should be higher. Because non-ferrous metals have high toughness and the pores of the grinding wheel are easily clogged by grinding debris, they are generally unsuitable for grinding. If you intend to grind, use a softer grinding wheel. A harder grinding wheel should be used for form and precision grinding to maintain the shape accuracy of the grinding wheel. Grinding wheels ranging from medium-soft to medium-hard are commonly used.

Diamond and CBN electroplated grinding wheel grinding process characteristics

Grinding has the following properties:

1. Excellent processing precision and low surface roughness. Diamond and CBN electroplated grinding wheels can cut off a very thin layer of material due to the small cutting edge radius of abrasive grains; and because there are many abrasive grains on the surface of the grinding wheel, the grinding speed is high (30-35m/s), and it also participates in cutting. There are many abrasive grains, forming small and dense network wear marks on the workpiece's surface; when combined with the grinding machine's high precision, stable hydraulic transmission, and micro-feeding mechanism, the grinding processing accuracy is high (IT8IT5), and the surface roughness is low (Ra=1.60.2m).

2. The force with a radial component Fy is quite large. Because the grinding depth and cutting thickness of abrasive grains are small during grinding, Fz and Fx are smaller. However, because the contact width between the grinding wheel and the workpiece is wide, the abrasive grains' cutting ability is poor, so Fy is relatively large. In general, Fy = (1.5 3) Fz.

3. The grinding temperature is extremely high. The friction between the surface of the grinding wheel and the surface of the workpiece is very serious due to the abrasive grains with a large negative rake angle cutting, grooving, and sliding on the surface of the workpiece under high pressure and high speed, which consumes a lot of power and generates a lot of cutting heat. Because the thermal conductivity of the grinding wheel is poor, a large amount of grinding heat is not easily transmitted in a short period, so the temperature in the grinding area is extremely high, sometimes reaching 800-1000 degrees.

4. The grinding wheel sharpens itself. The self-sharpening of the grinding wheel allows for continuous grinding wheel processing. This is a feature that other knives do not have.

What are the advantages of internal grinding over external grinding?

Internal grinding differs from cylindrical grinding primarily in the following ways:

1. It is difficult to control the grinding accuracy. Because the contact area between the grinding wheel and the workpiece is large during grinding, heat generation is high, cooling conditions are poor, and the workpiece is prone to thermal deformation, particularly because the grinding wheel shaft is slender and rigid, resulting in cylindricity (inner cone) errors. As a result, it is common practice to reduce the grinding depth and increase the number of polishing times.

2. the roughness of the grinding surface Ra is quite large. During internal grinding, the speed of the grinding wheel should not exceed 20,000r/min. Because the diameter of the grinding wheel is small, it is difficult to achieve a linear speed of 30-50m/s during external grinding. Internal grinding roughness Ra values are typically 1.60.4m.

3. There is a lack of productivity. Because the grinding wheel's diameter is small, the wear is rapid, the coolant does not easily wash away the chips, and the grinding wheel is easily blocked, the grinding wheel must be trimmed or replaced regularly. Furthermore, to ensure accuracy and surface roughness, the grinding depth must be reduced and the number of grinding times must be increased, both of which will affect productivity.

Working principle and application of centerless cylindrical grinding

The workpiece is placed between two wheels with a supporting plate beneath it when centerless cylindrical grinding. The large wheel is a spinning grinding wheel that cuts when rotated. The small wheel is a guide wheel, which is a rubber-bonded grinding wheel with very fine abrasive grains. To support the workpiece, the two wheels and pallets form a V-shaped positioning surface. The guide wheel's speed v guide is very low, typically 20-30m/min, and its axis is oblique to the axis of the working grinding wheel at an angle of. The v guide can be divided into two parts: v work and v advance.

V is used to drive the workpiece to rotate, which is the workpiece's circumferential feed speed; v is used to drive the workpiece to move axially, which is the workpiece's longitudinal feed speed. The contact part between the guide wheel and the workpiece must be trimmed into a straight line to stabilize the positioning of the workpiece and have sufficient frictional torque with the guide wheel. As a result, the circumferential surface of the guide wheel is a hyperbolic revolution surface.

Centerless cylindrical grinding is primarily used for the production of slender optical shafts, shaft pins, small sleeves, and other components.