CNC Machine Condition Monitoring Success
Updated: Sep 4, 2020
Symroc’s vibration sensing system successfully diagnosed the root cause of a computer numerical control (CNC) machine defects.
CNC machines, especially used ones are widely circulated on the market. Symroc’s system has been proven successful in evaluating the condition and expected lifespan of used CNC machines so that owners and buyers of used CNC machines can make informed decisions.
A 20-year old computer numerical control (CNC) machine in Herma Tech Mechanical shows significant shaking across the whole machine, which affects surface finish of the product. The shaking is referred to as chatter. The OEM had conducted vibration analysis on the machine and concluded spindle. On the other hand, we believe it is a gearbox problem.
Herma Tech and us believe the problem is more likely to be the cause of chatter. The finished product can, at the time of this writing, meet the customers’ requirement, which is highly unlikely to be accomplished when the spindle is nearly broken. In addition, we have made an interesting observation on the gearbox signals when doing cutting.
Figure 1. Qualified product (left) has a smooth surface, whereas product made with defect CNC machines has dented surface that does not meet the quality control requirements.
Figure 2. Products produced with defect CNC machines (left) have unpredictable imperfections compared to products from healthy machines (right).
Fast fourier transform (FFT Data)
According to OEM specifications, this machine should rotate at 4000 rpm. We can see a peak at 63.86 Hz (3831.6 rpm) which agrees with the OEM specs. Multiple peaks immediately below 3831.6 rpm can be observed. Each peak represents a different mode of movement that is not supposed to happen which indicates the machine is close to its end of life.
Same theory can even be applied to machines that do not use a gearbox. Picture below is a CNC without a gearbox doing cutting.
This CNC does not have a gearbox. However, similar patterns can still be observed. This machine is much healthier than the previous one, in fact ten years newer than the previous one.
We believe our device can play an important role in second hand CNC machine purchasing. Machine shop owners are generally gambling on their luck when they purchase a second hand CNC machine. With our device, they can observe the health of the machine by observing the patterns which will give them a better understanding of the health of the CNC machine.