Abstract
In thread milling, there exists a trade-off between thread manufacturing efficiency and thread quality. In this study, an integrated design of spindle speed modulation (SSM) and cutting vibration suppression (CVS) controls using a disturbance observer were developed to simultaneously ensure superior quality and high manufacturing efficiency. The proposed integrated design not only controls the cutting torque while suppressing cutting vibrations but also ensures cost-effectiveness and mitigates the installation problems prevalent in existing sensor-based methods. The SSM control uses a disturbance observer to estimate the cutting torque required on the spindle during thread milling. The estimated cutting torque is used as a feedback signal so that the SSM control can modulate the spindle speed to make the cutting torque achieve a preset torque command. To further avoid cutting vibrations in thread milling, the CVS control analyzes the estimated cutting torque, detects the occurrence of cutting vibrations, and then adjusts the torque command of the SSM control to suppress the cutting vibrations. In this study, thread milling experiments were performed on a computer numerical control milling machine using the workpiece with stacked materials. The feasibility and performance of the proposed integrated design were validated by experiments.
Highlights
The thread manufacturing method of thread milling has been in practice for a long time and is used to manufacture high-strength and high-accuracy threads with good surface characteristics [1,2,3,4]
This study developed an integrated design of spindle speed modulation (SSM) and cutting vibration suppression (CVS) controls using a disturbance observer (DOB), to automatically modulate the spindle motion characteristics for controlling the cutting torque while avoiding the cutting vibration during thread milling
The proposed SSM control utilized a DOB to estimate the cutting torque on the spindle during thread milling, and the estimated cutting torque was used as the feedback signal for the SSM control to modulate the spindle speed so that the cutting torque during thread milling was maintained at the preset torque command
Summary
The thread manufacturing method of thread milling has been in practice for a long time and is used to manufacture high-strength and high-accuracy threads with good surface characteristics [1,2,3,4]. The existing methods for milling use different sensors to achieve precise cutting force control, accurate cutting torque control, and efficient cutting vibration suppression. Even though some sensorless methods have been developed to avoid the aforementioned problems, cutting force control, cutting torque control, and cutting vibration suppression were studied individually and independently. The integrated design ensures high thread manufacturing efficiency and superior thread quality without using additional sensors and thereby avoids the problems present in sensor-based methods. A computer numerical control (CNC) milling machine was used to perform the thread milling experiments using workpieces with stacked materials and the experimental results were used to validate the feasibility and performance of the proposed integrated design.
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