Common issues when using a grinding wheel

How can vibration be reduced during grinding?

Ripples on the surface of parts in production grinding operations are potential indicators of vibration problems in the machine or operating procedures. The ripples will be felt during the inspection, and if there are still grinding or polishing steps in the later stages, you will need to spend more time removing the ripples.

The workpiece's surface has ripples caused by vibration.

The wavelength of the peak (the distance between peaks) can reveal information about the cause of vibration.

On a surface grinder, for example, the vibration frequency (cycles per minute) equals the working speed (inches per minute) divided by the distance (inches) between two consecutive tremor marks. To determine the vibration frequency, use this formula. If it is the same as the rotation speed of the grinding wheel shaft, it indicates that the culprit could be the grinding wheel, the grinding wheel flange, or the grinding wheel shaft itself. It is sufficient to solve or control the vibration problem by changing the grinding wheel, tightening the flange bolts, or simply changing the speed. Related product: Grinding and Polishing Wheels.

In other cases (which may involve other parts of the machine or be limited by the system's fixed frequency), simple repairs are insufficient to adequately solve the problem. It is best to repair the machine and any machine parts that may cause vibration and affect the workpiece in these cases. However, maintenance takes time, which means the machine must be shut down. Even a short break is insufficient for factories that require continuous operation.

As a result, researchers have demonstrated a method for mitigating the effects of vibration without reducing productivity or stopping the machine for maintenance.

The contact length theory seeks to increase the contact length between the grinding wheel and the workpiece relative to the surface wavelength affected by vibration. When the former is larger than the latter, the grinding wheel can effectively remove the peaks and valleys caused by vibration on the workpiece, smoothing the surface even when the vibration is still present.

When the cutting depth increases, the feed speed decreases, and both are adjusted to the same multiple, the material removal rate (i.e., productivity) can remain constant. The depth of the undercut limits the contact length of the grinding wheel. Of course, to increase the contact length, other negative effects such as material burning and workpiece deformation must be avoided.

To achieve the effect, the grinding wheel's cutting depth must be increased to be deeper than the standard cutting conditions. However, this still avoids the unfavorable ripple effects. Simultaneously, the feed rate (or workpiece speed) influences the wavelength of some vibration traces. The shorter the wavelength, the slower the speed. The smooth surface can be measured using the contact length theory when the contact length between the grinding wheel and the workpiece is twice the tremor wavelength or the surface ripple.

Grinding Wheel Hardness Selection:

Grinding wheel hardness is an important index for determining the "self-sharpening" of a grinding wheel.

The abrasive gradually becomes blunt and sharp during the grinding process, while the partially passivated abrasive continues to work, and the pressure on the abrasive increases. When the pressure is high enough, some abrasive grains will break and form a new edge. When the pressure exceeds the binder's bonding force, the abrasive particles self-detach. "Self-sharpness" refers to the ability of passivated abrasive grains to collapse or fall off themselves, thereby keeping the wheel sharp. The hardness of the grinding wheel reflects the degree of difficulty with which abrasive particles fall off the surface of the grinding wheel when the grinding force is applied. If the grinding wheel is hard, the abrasive particles are difficult to remove; if the grinding wheel is soft, the abrasive grains are easily removed.

The hardness of a grinding wheel and the hardness of an abrasive grain are two distinct concepts: the hardness of a diamond grinding wheel does not have to be high, while the hardness of ordinary abrasive brown corundum must be low.

Grinding wheel hardness is high, blunt abrasive particles are difficult to fall off, the grinding wheel is easy to plug, grinding heat rises, the workpiece burns easily, and grinding efficiency is low, affecting workpiece surface quality.

The grinding wheel is too hard and soft, and the grinding grain will fall off while it is still sharp, increasing grinding wheel loss, easily losing correct geometry, and affecting workpiece accuracy.

As a result, the selection of grinding wheel hardness should be appropriate and comprehensive, taking into account the contact area between the grinding wheel and the workpiece, the workpiece shape, the grinding mode, the cooling mode, the grinding wheel bond type, and other factors.

The following principles can be used to select grinding wheel hardness:

1. Workpiece hardness

The harder the workpiece material, the softer the grinding wheel should be chosen, so that dull abrasive particles fall off quickly, the grinding wheel frequently keeps sharp abrasive particles working, and the workpiece is not burned due to the high grinding temperature. The softer the workpiece material, the harder the grinding wheel hardness should be chosen, so that the abrasive particles fall off slowly, allowing the abrasive particles to fully play their cutting role.

2. Contact surface for processing

When the grinding wheel has a large contact surface with the workpiece, a soft grinding wheel should be used to allow the abrasive particles to fall off more quickly, preventing workpiece surface burn caused by grinding dust blocking the grinding wheel surface. For inner and end grinding, the hardness of the grinding wheel should be lower than that of the outer grinding wheel. The hardness of the grinding wheel should be reduced when grinding thin-walled parts and workpieces with low thermal conductivity.

3. Forming and fine grinding

Workpiece hardness and harder grinding wheels should be used in fine and form grinding to maintain the grinding wheel's required shape accuracy.

4. Grinding wheel grain size

To avoid dust blocking the surface structure of the grinding wheel, the hardness should be lower as the grain size of the grinding wheel increases.

5. Workpiece Material Section

When grinding nonferrous metals, rubber, resin, and other soft materials, a soft grinding wheel should be used to avoid dust accumulation on the grinding wheel surface.

6. Under identical grinding conditions

Resin-bonded grinding wheels are 1-2 times harder than ceramic-bonded grinding wheels.

7. When the rotational speed of the grinding wheel is high

The grinding wheel's hardness can be 12 small grades soft.

8. Coolant grinding

The grinding wheel's hardness is 1-2 small grades higher than that of dry grinding.

The hardness of a grinding wheel ranges from K to N. When grinding steel ingots and castings, a Q grinding wheel can be used to grind stone and hard material. Soft grinding wheels self-sharpen better, which improves grinding performance while reducing grinding force and heat. k-L is commonly used. Because abrasive grains are easily passivated when grinding hard materials, a soft grinding wheel should be used to keep the grinding wheel sharp. Grinding wheels are difficult to passivate when grinding soft materials, so hard grinding wheels should be used to avoid premature shedding and abrasive particle loss. The grinding wheel is easily jammed when grinding soft and tough materials, so a soft grinding wheel can be used.