How to solve grinding vibration veins during hole grinding ?

CBN internal grinding wheel for grinding hole requires the machine to have enough rigidity and the grinding wheel to keep enough stable state, otherwise it is easy to produce grinding vibration veins, especially for processing thin-walled disc parts with inner holes.

Causes of grinding vibration veins:

The vibration of parts are generated from the vibration of machine. The vibration veins of parts are mainly reflected in the waviness measured on the roundness instrument of grinding surface. With a certain frequency, periodic vibration reflected in the surface of the machined parts will form a ripple. Further analysis shows that the vibration can be divided into machine tool resonance caused by high speed rotation of grinding wheel, including dynamic unbalance of grinding wheel shaft, eccentricity of parts shaft, etc. It may also be caused by the change of grinding force during grinding, which is mainly caused by the interaction between grinding wheel and workpiece, including the uneven wear and blockage of grinding wheel, which will form ripples on the workpiece surface, and the ripple on the workpiece surface will in turn worsen the wear and blockage of grinding wheel, and even form ripples on the workpiece surface.

Features of  grinding with CBN internal grinding wheel:

The hardness of CBN is higher than that of conventional abrasive, CBN can sharp cutting ability.  At the same time, CBN has high wear resistance, which is more difficult to wear than ordinary abrasives. The ability to keep the shape of abrasive grains is one of the main characteristics of CBN as a high performance abrasive. Because CBN grinding wheel can keep the sharpness of the micro-edge of abrasive grains for a long time, the processing accuracy and surface roughness of the processed workpiece can achieve relatively ideal results. Grinding wheel can obtain higher dimensional accuracy and lower surface roughness. Therefore, the durability of the workpiece can be increased by 10% ~ 30%. CBN grinding wheel has a long dressing cycle, less dressing amount, long replacement time and no need to change and dress grinding wheel frequently, so it can save man-hours, high work efficiency and good comprehensive economic benefits. But at the same time, the linear speed of CBN grinding wheel is very fast, which can reach 45 ~ 100 m/s. In this case, the whole system of grinding wheel, workpiece and machine tool is easy to produce vibration, especially when processing thin-wall parts, because of its poor rigidity, it is easier to produce vibration veins.

How to solve the grinding veins?

1. Resonance problems caused by high-speed rotation of internal grinding wheel
Before the machine leaves the factory, the natural frequency of the lathe body and its main castings has been analyzed and resonance test, so that it avoids the resonance area of the high-speed grinding wheel rotation and the spindle of the parts. Therefore, if vibration marks appear in production and processing, we mainly solve the vibration caused by high-speed rotation of grinding wheel, including grinding wheel installation clearance and installation accuracy, dynamic unbalance of grinding wheel, etc.

2. Vibration caused by rotation unbalance of internal grinding wheel
The maximum speed of CBN grinding wheel is 10000 r/min, and the very small dynamic unbalance of grinding wheel will cause great vibration when rotating at high speed, so it is necessary to strictly control its dynamic unbalance.
Therefore, it is necessary to check the dynamic unbalance of grinding wheel after the grinding wheel is manufactured, which is a key index to measure the accuracy of grinding wheel.

3. Vibration caused by changes in grinding force

In high-speed rotary grinding of CBN internal grinding wheel, the interaction between grinding wheel and workpiece will cause uneven wear and blockage of grinding wheel, which will form ripple on the workpiece surface, and the ripple on the workpiece surface will in turn aggravate the wear and blockage of grinding wheel, and lead to the formation of ripple on the workpiece surface.

In the grinding process of CBN internal grinding wheel, diamond wheel is needed to dress the grinding wheel for every certain number of parts processed by the grinding wheel. The purpose of rest is to ensure the grinding quality of the workpiece and prevent uneven surface of grinding wheel caused by improper surface dressing of grinding wheel during dressing process. Therefore, the roughness of workpiece surface can not be satisfied, and the uneven surface of grinding wheel will even cause vibration veins of parts. Therefore, the grinding wheel dressing quality needs to be monitored.

CBN has high wear resistance, meaning it is harder to wear than ordinary abrasives. The ability to maintain the shape of abrasive grains is one of the main characteristics of CBN as a high performance abrasive. The high compressive strength of CBN means that it can keep the particles intact and not easily broken when used in harsh conditions. CBN has good thermal conductivity and can achieve cold cutting during grinding.

Moresuperhard vitrified CBN grinding wheel for internal grinding, used for internal grinding of hydraulic tappets, universal joint, stator and rotor. Moresuperhard can offer: abrasive internal grinding wheel (PA, SG), CBN internal grinding wheel(  reisn CBN internal grinding wheel, electroplated CBN internal grinding wheel)  for high precision hole processing.

The efficiency of internal grinding is always low, the main reasons are grinding speed, grinding wheel material and grinding rod rigidity. The time spent in dressing and replacing grinding wheels in the production process almost accounts for 1/3 to 1/5 of the working hours of a single piece. If within the circle or groove grinding with CBN internal grinding wheel, and increase the grinding wheel speed, increase the stem diameter, can be appropriately raise the workpiece speed and feed rate, not only can guarantee the hole (arc) diameter, groove width size and shape accuracy, surface roughness and avoid burns, but also improve the machining efficiency will be multiplied, reduce the processing cost.

Because the cubic boron nitride abrasive (CBN) can keep the sharpness of the grain micro edge for a long time, the machining accuracy and surface roughness value of the processed workpiece can reach a relatively ideal effect, so the durability of the workpiece can be increased by 10%-30%. So even if the batch processing of the workpiece, will always obtain a higher shape, accuracy and consistency. CBN internal grinding wheel can obtain high dimensional accuracy and low surface roughness, the machined surface is not easy to crack and burn, and the residual stress is small. Processing surface quality is improved, generally no crack, not easy to burn, and can obtain residual compressive stress, significantly improve the fatigue strength of the workpiece, usually, the durability of the grinding parts can be improved by 30-50%.

—EDITOR: Doris Hu

—POST: Doris Hu