In-process monitoring and characterization of arc welding

Inspection of weld quality is critical because it ensures the integrity of structures. There are many available methods for monitoring and diagnosis of the weld quality. However, most of them are off-line and thus make the quality monitoring and remedial measures difficulty and costly. In this research, a real-time quality monitoring and diagnosis method based on the input electrical impedance of the arc welding is proposed. It is obtained by taking the quotient of input voltage to current which both signals are measured simultaneously at the output terminal of welding machine. Two time record data, real part and imaginary part, or the resistance and reactance of impedance reflect the system property of arc welding which is represented by an equivalent circuit. This equivalent circuit consists of resistor, inductor and capacitor connected in series. Therefore, any abnormal change of arc welding will be reflected by the time variation of these components. Several major findings were obtained from this research. The mean and standard deviation of resistance and reactance of impedance are affected by the operating parameters such as welding voltage, current, welding speed, free wire length and leading angle of welding torch. Further investigation of impedance also leads to have a more accurate heat input per unit length by including the resistance of impedance. The implementation of Taguchi Method and Macro Testing shows that the proposed method can achieve 95% accuracy of detecting weld defects. Furthermore, the proposed method is also capable to diagnose the weld defect as result of abrupt change of arc length or wrong welding speed. The capability of proposed method is further extended to provide real-time and in-situ information of metal transfer. The time varying resistance and reactance curves reflect the dynamic change of metal transfer like the formation and detachment of droplet to the weld pool. This in-situ information helps to develop a new classification method of metal transfer which the metal transfer modes are quantified in percent weightage. Furthermore, the study of welding metallurgy indicates that the metal transfer mode shown in percent weightage is correlated with the macro structural change of weld but not the micro structural change of weld.DOCTOR OF PHILOSOPHY (MAE

Development of a real time quality monitoring device for resistance spot welding

Electrical input impedance is used as a new monitoring signature to study its correlation between RSW process and micro structural changes of RSW so that a real time quality monitoring device can be achieved with help of automated tools such as Artificial Neural Network.MASTER OF ENGINEERING (MPE

A new characterization approach of weld nugget growth by real-time input electrical impedance

The in-process changes of weld nugget growth during the Resistance Spot Welding were investigated based on the resistance of input electrical impedance. To compute the time varying resistance of input electrical impedance, the welding voltage and current signals are measured simultaneously and then converted into complex-valued signals by using Hilbert transform. Comparing with the dynamic contact resistance as reported in literature, it showed that the time varying resistance of input electrical impedance can be accurately correlated with the physical changes of weld nugget growth. Therefore, it can be used to characterize the in-process changes of weld nugget growth. Several new findings were reported based on the investigation of spot welds under no weld, with and without weld expulsion conditions.Published versio

A New Characterization Approach of Weld Nugget Growth by Real-Time Input Electrical Impedance

The in-process changes of weld nugget growth during the Resistance Spot Welding were investi-gated based on the resistance of input electrical impedance. To compute the time varying resis-tance of input electrical impedance, the welding voltage and current signals are measured simul-taneously and then converted into complex-valued signals by using Hilbert transform. Comparing with the dynamic contact resistance as reported in literature, it showed that the time varying re-sistance of input electrical impedance can be accurately correlated with the physical changes of weld nugget growth. Therefore, it can be used to characterize the in-process changes of weld nug-get growth. Several new findings were reported based on the investigation of spot welds under no weld, with and without weld expulsion conditions

Improved measurement of resistance and calculation of arc power in fusion welding

We reported a new method based on the input electrical impedance of a welding system to measure the resistance of the welding system for the arc power calculation in fusion welding. This impedance can be obtained by dividing the measured voltage to current in their analytic form. Two time recorded waveforms, namely, resistance and reactance of impedance, are therefore calculated. Theoretically, the resistance used for arc power calculation is obtained by dividing measured voltage to current directly without considering the influence of inductance. Through experimental studies, we confirm that the error of arc power calculation incurred by the influence of inductance can range from 2 to 10% depending on the welding voltage and current setting. Since the proposed method can obtain the resistance of the welding system without the influence of inductance, it is a better approach as compared with the current method to obtain the accurate resistance and then arc power.Accepted versio

An investigation of dynamical metal transfer in GMAW : effects of argon shielding gas

The unbalance radial electromagnetic force was firstly obtained by measuring the real-time input electrical impedance of GMAW. This force acts as an attaching force because it pushes the droplet aside of the welding wire and sticks on the tip of welding wire as result of surface tension force. In spray transfer mode, lower unbalance radial electromagnetic force was observed when argon shielding gas was used. The finding presented in this paper is contrary to the literature which reported that higher electromagnetic force is desirable for faster transfer rate of droplets in spray transfer mode.Accepted versio

Fabrication and Characterization of Smart Sliders with Integrated ZnO Thin-Film Sensors and Actuators

To realize higher areal densities in hard disk drive (HDD), it is necessary to decrease distance between slider and disk, i.e. flying height. The low flying height may result in severe damage occurring on the head-disk interface. Therefore, it is essential to monitor head-disk interactions to prevent instability and damage. In this paper, a smart slider integrated with micro-sensor and micro-actuator is proposed. The fabrication and characterization of the smart slider with integrated zinc oxide (ZnO) thin-film sensor and actuator is presented here. A possible 3D printing manufacturing approach is also proposed to replace the current complex MEMS fabrication processes for producing the smart slider.Published versio

Analytical solutions to flexural vibration of slender piezoelectric multilayer cantilevers

The modeling of vibration of piezoelectric cantilevers has often been based on passive cantilevers of a homogeneous material. Although piezoelectric cantilevers and passive cantilevers share certain characteristics, this method has caused confusion in incorporating the piezoelectric moment into the differential equation of motion. The extended Hamilton's principle is a fundamental approach to modeling flexural vibration of multilayer piezoelectric cantilevers. Previous works demonstrated derivation of the differential equation of motion using this approach; however, proper analytical solutions were not reported. This was partly due to the fact that the differential equation derived by the extended Hamilton's principle is a boundary-value problem with nonhomogeneous boundary conditions which cannot be solved by modal analysis. In the present study, an analytical solution to the boundary-value problem was obtained by transforming it into a new problem with homogeneous boundary conditions. After the transformation, modal analysis was used to solve the new boundary-value problem. The analytical solutions for unimorphs and bimorphs were verified with three-dimensional finite element analysis (FEA). Deflection profiles and frequency response functions under voltage, uniform pressure and tip force were compared. Discrepancies between the analytical results and FEA results were within 3.5%. Following model validation, parametric studies were conducted to investigate the effects of thickness of electrodes and piezoelectric layers, and the piezoelectric coupling coefficient d 31 on the performance of piezoelectric cantilever actuators.Accepted versio

Design and Evaluation of a Novel Hybrid Soft Surgical Gripper for Safe Digital Nerve Manipulation

Forceps are essential tools for digital nerve manipulation during digital nerve repair surgery. However, surgeons have to operate forceps with extreme caution to prevent detrimental post-operative complications caused by over-gripping force. Their intrinsically safe characteristics have led to the increasing adoption of soft robotics in various biomedical applications. In this paper, a miniaturized hybrid soft surgical gripper is proposed for safe nerve manipulation in digital nerve repair surgery. This new surgical gripper includes a soft inflatable actuator and a gripper shell with a hook-shaped structure. The ability to achieve a compliant grip and safe interaction with digital nerves is provided by the inflated soft pneumatic actuator, while the rigid hook retractor still allows surgeons to scoop up the nerve from its surrounding tissues during surgery. The performance of the proposed surgical gripper was evaluated by the contact/pulling force sensing experiments and deformation measurement experiments. In the cadaver experiments, this new surgical gripper was able to complete the required nerve manipulation within the limited working space. The average deformation of the digital nerve with an average diameter of 1.45 mm gripped by the proposed surgical gripper is less than 0.22 mm. The average deformity is less than 15% of its original diameter

A fluid-structure interaction investigation of intra-articular pressure and ligament in wrist joint

10.1080/10255842.2022.2106133Computer Methods in Biomechanics and Biomedical Engineering2691077-108