The system for adaptive control of axial tool oscillations in vibratory drilling: description and experimental study

Reliable segmentation and evacuation of chips from the cutting zone are essential for effective deep hole drilling. Drilling with low-frequency axial vibrations ensures these useful effects because cutting edges periodically leave the cutting zone. Useful tool vibrations can be maintained by using a special self-vibratory drilling head. The drilling head has an elastic element and ensures the self-excitation of vibrations due to the regenerative effect. However, high damping in the cutting zone suppresses axial self-vibrations and renders such a drilling head inexpedient for the industry. In this study, a novel system of adaptive control of the vibration drilling process was developed. The control objective is to maintain a specified peak-to-peak (PTP) value of vibration displacements. Due to in-process adaptation of the feedback gain, the control system supplies additional energy if vibrations are not self-excited and removes energy if the PTP vibration displacements are greater than the specified value. To test the workability of the system, an experimental setup was made. In the setup, the actuator force acts on an elastically fixed workpiece. The dynamic properties of the setup are equivalent to those of the vibration drilling head. The algorithm of feedback gain adaptation was implemented with a microcontroller. A number of experiments for different drilling regimes revealed that the control system successfully maintains the specified PTP value of displacements. The developed control system can be implemented on a vibration drilling head because only an accelerometer is required for control and the required actuator force is under 100 N.

Wear Identification of Vibration Drilling Bit Based on Improved LMD and BP Neural Network

In view of the low accuracy of single signal monitoring for the wear state of vibration drilling bit, a multisignal acquisition system for the wear state of ultrasonic axial vibration drilling bit is built to collect the drilling force, vibration, and acoustic emission signals under three different wear states. The drilling force, vibration and acoustic emission signals of the bit in the drilling process are processed by using wavelet decomposition technology, and the signals are extracted from the wear state of the bit, The wavelet energy coefficient with high state correlation is used as the feature parameter to identify the bit wear state. The feature parameter is trained by the combination of noise assisted LMD method and BP neural network. The experiment of single signal and multisignal fusion monitoring bit wear state is carried out, and the neural network structure is optimized according to the error. The results show that the accuracy of monitoring bit wear with a single signal of drilling force is 83.3%, the accuracy of monitoring bit wear with a single signal of vibration is 91.6%, the accuracy of monitoring bit wear with a single signal of acoustic emission is 91.6%, and the accuracy of monitoring bit wear with multisignal fusion is 95.8%; when the number of network layer is 4, the vibration is monitored with the fusion of force signal, acoustic emission signal, and vibration signal The accuracy of the state of drilling tool is up to 100%. The structure model of neural network is optimized reasonably to improve the recognition rate of bit wear in vibration drilling.

Removal Mechanism of Titanium Alloy Material in Ultrasound Vibration Drilling

In drilling the ultra-slim small diameter deep hole of titanium alloy, the problem of chip breaking and chip removal is common. When the drill is working normally, the ultrasonic vibration can be applied for the drill bit to cut the bit in the vibration to form a pulse. The cutting force waveform in drilling, should select the reasonable vibration frequency, amplitude, feed amount, workpiece rotation and other parameters to match, control the size and shape of the chip, get satisfactory chips, and avoid chip clogging. In this study, the ANSYS finite element simulation software was used to simulate the TC4 drilling process, and the difference between ultrasonic vibration drilling and ordinary drilling was analyzed. Drilling experiments were carried out. The experimental results show that compared with conventional drilling, ultrasonic vibration drilling has better surface quality, reduced tool wear and increased material removal rate.

Simulating the dynamics of vibration drilling featuring chip control driven by peak-to-peak vibration displacement

Chip control is one of the most important problems in deep hole machining. A special self-vibratory drilling head may be used to implement chip control. However, chip control via a self-vibratory head is only possible for specific manufacturing parameters, which limits the use of this method. This paper presents an algorithm for adaptive control of vibration drilling dynamics intended to facilitate chip control and driven by peak-to-peak vibration displacement. We provide a mathematical model of drilling using a self-vibratory head, taking into account the facts that the cutting force is a non-linear function of the chip thickness and that there is additional non-linearity introduced when the drill is exiting the material. In order to validate the efficiency of the algorithm proposed, we performed numerical simulations for a wide range of variable processing parameters. The simulation results obtained confirm that the strategy proposed is efficient for chip control.

Formation of Feed-Direction Burr in Axial Vibration Drilling

Based on the fundamental theory of axial vibration drilling, the influence of vibration drilling on the feed-exit burr has been analyzed. The result shows that, due to axial vibration,vibration drilling has some unique characteristics, such as variable-thickness cutting and impulse cutting,which not only improve the chip-breaking conditions and working angle of the drill,but reduce the thrust force.Therefore, the plastic deformation of workpiece material and the exit burr are restrained and decreased effectively.