Machining vibration is one of the most important constraints on productivity. This vibration may cause increase in machining costs, lower accuracy of products, and decrease tool life. Active control is one of the conventional methods for dealing with vibration in machining, but designing an optimized controller for machining process due to unknown parameters in the system is challenging. DVF control method with low computational costs and high capability in increasing the performance of the cutting tool is an effective method, but due to increasing in actuator control input, it can cause actuator saturation; thus, it is not an efficient control method. The aim of this research is implementation of a nonlinear fractional PID controller for increasing effectiveness and improving performance of active vibration control on a boring bar. The results of impact control tests indicate that nonlinear PID control algorithm has good performance in reducing vibrations and increasing the damping of the structure. Using the controller performance criteria, the optimal fractional can be chosen for the nonlinear PID controller, which in addition to increasing the damping of the tool, can reduce the power consumption and, thus, prevent the actuator saturation. The results of the cutting tests also show that the nonlinear PID controller reduces control voltage and actuator power with respect to the DVF controller, which results in improving the boundaries of stable machining. Moreover, during impacts in machining process, such as the initial engagement of the tool, the proposed controller results in a significant reduction in the control voltage peak.

Although there have been several research work  published in the field of simulating and predicting the surface roughness of machining processes, most of them are limited to turning and milling operations.  A few number of studies concerning the internal turning processes is very limited. Furthermore, the existing publications in this field have implemented statistical approaches which not only clearly lack in generality, but also require a huge amount of experiments. In the current research, the simulation of surface roughness has been investigated by using kinematics and dynamics of the process. Despite the numerous applications of this approach in turning operations, this approach has not applied in the internal turning processes. In order to implement the proposed approach, firstly the insert nose profile of the tool has been measured. Then, the surface profile consisting the periodical component of feed marks has been constructed. In the next step, excessive amount of vibrations imposed by the long boring bar have been measured by an accelerometer, which are then converted to displacements and added to the periodical component of the roughness profile. Results obtained from internal turning experiments show that the developed simulation approach has a maximum error of 19.3% in estimating roughness parameters which can be considered as a reasonably accurate results due to the complicated nature of surface roughness.