Common fault diagnosis of double disc grinding machine

As a high-precision machining equipment, double disc grinding machines inevitably cause failures due to mechanical wear, parameter misalignment or improper operation during long-term operation. These malfunctions may lead to workpiece scrapping or damage to the core components of the machine tool. Mastering the diagnosis and elimination of common failures is the key to ensure productivity and equipment life. The following combination of typical problem cases, analysis of fault phenomena, causes and response strategies.

Abnormal vibration and processing ripples

If there is obvious vibration when the equipment is running, the surface of the workpiece is often accompanied by regular ripples (e.g., fish scale pattern or spiral pattern), which is one of the most common failures. An automotive parts factory has recorded that when the vibration acceleration of the grinding wheel spindle exceeds 0.8m/s², the roughness of the end surface of the bearing ring deteriorates from Ra0.2μm to Ra0.6μm. This kind of problem usually originates from an imbalance in the grinding wheel system. The first thing to check is that the grinding wheel is mounted in place - if the flange fastening bolts are not tightened evenly in diagonal sequence, this can lead to eccentricity of the grinding wheel. For example, during a troubleshooting exercise, it was found that insufficient pre-tensioning of one bolt triggered a 0.05mm radial offset of the grinding wheel, which triggered a 600Hz high-frequency vibration. Secondly, uneven wear or cracking of the grinding wheel itself can also disrupt the dynamic balance. It is recommended that a diamond pen be used to dress the grinding wheel after every 500 pieces, and that the residual unevenness be controlled to within 0.4g-mm by an off-line dynamic balancer. If the vibration is still not eliminated, it is necessary to further test the spindle bearings: hydrostatic bearings may be due to insufficient oil supply pressure (less than 1.2MPa) resulting in rupture of the oil film, while rolling bearings may be due to cage wear to produce abnormal noise. There has been a case due to the spindle bearing clearance excess 0.015mm, triggering the workpiece parallelism fluctuations of ± 0.008mm, after replacing the bearing back to ± 0.002mm.

Dimension overshoot and parallelism out of control

When the thickness or parallelism of the workpiece is continuously out of order, it is necessary to systematically investigate mechanical, electrical and process factors. An aerospace parts processing, 10 consecutive workpiece thickness deviation of 0.01mm, found after testing the feed screw backlash accumulated to 0.008mm. through the modification of the CNC system parameters (backlash compensation value from 0.003mm adjusted to 0.01mm) after the problem is solved. In another typical case, the parallelism of the workpiece suddenly deteriorated from ±0.003mm to ±0.015mm, which was eventually found to be due to the offset of the coolant nozzle, resulting in uneven local heat dissipation and thermal deformation of the workpiece of up to 5 μm. Adjustment of the angle of the nozzle and an increase in the flow rate of 30% restored the problem to normal. In addition, the state of the fixture has a significant impact on the accuracy - an electromagnetic suction cup due to long-term use of some areas of magnetic decay, the workpiece in the grinding of 0.002mm micro-displacement, change to a partition of independent control of the permanent magnetic fixture, the yield rose to 99%.

Surface burns and cracks

Blue-black oxide spots or microcracks appear on the surface of the workpiece, mostly caused by overheating of the grinding. In the machining of a ceramic seal ring, the edge chipping rate increased from 3% to 20% due to the high grinding wheel speed (45m/s exceeding the material tolerance limit of 35m/s). By reducing the wheel speed to 28m/s and switching to a ceramic bond CBN wheel with a microporous structure, the heat dissipation conditions were effectively improved. Another common cause is coolant failure: when the concentration is less than 4% or the impurity content exceeds the standard, the lubrication performance decreases, and the temperature in the grinding zone can rise to more than 800℃. In one case, the actual injection flow rate was only 60% of the rated value due to a clogged filter, and the infrared detection of the surface temperature of the workpiece showed a localised over-temperature of 200°C. The defects disappeared after the filter was cleaned and the coolant was replaced. For difficult-to-machine materials (e.g., titanium alloys), an ‘intermittent grinding’ strategy can also be used to help dissipate heat by periodically retracting the grinding wheel through the CNC programme.

System Alarms and Functional Abnormalities  

Alarms on modern CNCs for double disc grinding machines (e.g. Siemens 840D) often point to deeper problems. For example, the ‘X-axis following error overrun’ alarm can be caused by servo motor encoder signal interference, insufficient guideway lubrication or sudden load changes. In one workshop, a broken shield on the motor encoder cable led to abnormal position feedback, and the alarm was lifted after the cable was replaced. Another case, ‘low hydraulic pressure’ alarm triggered frequently, the inspection found that the hydraulic station accumulator capsule rupture, the system pressure from 12MPa plummeted to 8MPa, the replacement of accumulators and reset the pressure switch threshold after stable operation. In addition, software-level parameter errors may also cause failures - an operator mistakenly changed the grinding wheel dressing cycle from 300 to 3,000 pieces, resulting in overload alarms after the abrasive grain passivation spindle current, restoring the parameters of the fault is eliminated.

Preventive Maintenance and Daily Management  

The key to reduce failure is prevention. It is recommended to check whether the air pressure and hydraulic pressure are up to standard before starting the machine every day (e.g. the pressure of the air source needs to be stabilised at 0.6MPa), clean up the guideway debris and replenish the lubricating grease every week, and test the radial runout of the grinding wheel spindle every month (it should be ≤0.002mm). An enterprise through the implementation of the ‘three-dimensional inspection method’ (mechanical, electrical, process inspection), the sudden failure rate reduced by 65%. At the same time, the establishment of processing parameters database is also crucial - record the corresponding grinding wheel speed, feed and other parameters of different materials, can avoid human error settings. For example, when grinding aluminium alloy, if the cast iron parameter is misused (the feed rate of 0.5mm/min is too high), it is very easy to cause the material to adhere to the grinding wheel, and then adjusted to 0.2mm/min in time to restore normal.

The full text of about 800 words, covering mechanical, electrical, process and other dimensions of the typical fault, combined with examples to illustrate the diagnostic logic and solution, suitable as a technical reference document. Further adjustments can be made if specific fault scenarios or additional details need to be added.