Vibration-Based Condition Monitoring for CNC Milling

Choong, Wei Hong (2024) Vibration-Based Condition Monitoring for CNC Milling. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

CNC milling is a subtractive machining process to machine a custom-designed product or component by removing material from a workpiece. CNC machine is still commonly utilized in the machining manufacturing business for machine parts or components, ranging from small-scale to big-scale, such as instrumentation components, tooling and dies, medical implants, engine and transmission components, oil and gas components, aerospace components, and automotive parts. However, it is inevitable that machine breakdowns can occur due to many factors such as tool breakage and tool wear, despite efforts to prevent them. In this paper, a vibration response measurement and tool wear measurement on the cutting between the carbide ball mill tool and STAVAX stainless steel with a 90 degree and a 65 degree of machining angle is carried out. Time domain analysis revealed that machining at 90 degrees resulted in highly unstable and chaotic vibrations due to pronounced rubbing between the ball mill tool and the workpiece surface. In contrast, machining at 65 degrees exhibited greater vibration stability until tool holder imbalance occurred, indicating its potential for effective vibration monitoring. Frequency domain analysis demonstrated that peak vibration amplitudes at 1TPF (Tooth Passing Frequency) could predict tool flank wear during 90-degree machining, though with limited efficiency due to relatively insignificant changes in peak amplitude along flank wear progression. Conversely, at the 65- degree angle, changes in peak amplitude with flank wear were more substantial, offering a more reliable basis for early-stage tool wear prediction. Furthermore, the study found that the ball mill tool’s lifespan was significantly longer when machining at a 65-degree angle, primarily attributed to the increased cutting radius generating higher cutting forces for material removal. During 90-degree machining, the tool experienced significant flank wear (0.0605mm) at a cutting length of 36 meters. In contrast, at a 65-degree angle, the flank wear was substantially less, measuring only 0.0305mm for the same cutting length. Lastly, machining at 65 degree consistently yielded a smoother surface finishes, as it involved actual material cutting rather than surface rubbing during machining at 90 degree.