12th Week
1-Trace element method for welding: In trace element method, prior to the start of the welding process, tracers are attached to the back face of the weld piece. When full penetration reaches the traces, they are melted and mixed with the weld pool and transferred by convection to the surface of the weld pool, where they are detected by a spectral emission collector and processed by a computer for data analysis. With partial penetration, the tracers are not melted and hence are not detected. The choice of the tracer is an important factor in this technique
(Modeling, Sensing and Control of Gas Metal Arc Welding,Desineni Subbaram Naidu, S. Ozcelik, K. Moore D. S. Naidu-1st edition, (2003),P.109)
2-Weld Pool Oscillation: Weld pool oscillations are caused by high frequency external forces on the weld pool. It was first suggested that the ripple formation in solidified welds is explained by the oscillatory behavior of the weld pool. It is worth noting that the weld pool oscillation frequency will be influenced by the droplet frequency. Weld pool oscillations can also be induced by current pulsing and monitored using optical sensing. This approach is applied for the GTAW process in. In particular, the oscillations are induced by a phase-locked loop (PLL) which consists of a phase detector, low-pass filter, and oscillator
(Modeling, Sensing and Control of Gas Metal Arc Welding,Desineni Subbaram Naidu, S. Ozcelik, K. Moore D. S. Naidu-1st edition, (2003),P.110)
3-Iterative learning control (ILC): Iterative learning control (ILC), a relatively a new technique within the arsenal of the control engineer, is a technique for improving the transient response and tracking performance of any physical system that is required to execute a particular operation repeatedly (such as a manipulator that might be programmed to do spot welding in an automobile manufacturing assembly line). By observing the error in the output response after each operation and using the error to modify the input signal to the system, ILC attempts to improve the system performance. In other words, ILC is a technique for systems with repetitive or iterative operations, which are modified based on the observed error (or are programmed to learn) to control the input signal at each repetitive operation
(Modeling, Sensing and Control of Gas Metal Arc Welding,Desineni Subbaram Naidu, S. Ozcelik, K. Moore D. S. Naidu-1st edition, (2003),P.179)
4-Relative Gain Array (RGA): The relative gain array (RGA) technique of process control is applied to the empirical model to design a multi-loop proportional integral controller for the process. The resulting controller pairs wire-feed speed with current and opencircuit voltage with arc voltage to regulate current and arc voltage to desired set points. Using the error between the measured values of current and arc voltage and the desired values of these variables, the controller simultaneously adjusts the wire-feed speed and the opencircuit voltage of the power supply, espectively. The basic benefit that is derived at this stage is the ability to reduce variability in the measured signals combined with the ability to force the measured outputs to their desired values. One of the distinguishing features of much of the work has been the model-based approach to the design of the controllers for the process. Also, the use of the RGA method to select controller loop pairings is unique and offers interesting insight into the best ways to control the process. A quantitative measure of interaction is needed to apply a multiloop controller and the relative gain array (RGA) is a useful technique for determining the appropriate loop pairing.It was found that the correct pairing is that wire feed speed should be used to control the current and the open-circuit voltage should be used to control the arc voltage. Based on these loop pairings, several multiloop controllers were designed.
(Modeling, Sensing and Control of Gas Metal Arc Welding,Desineni Subbaram Naidu, S. Ozcelik, K. Moore D. S. Naidu-1st edition, (2003),P.180,222)
5-Multivariable feedback control system: Hardt in [560] addressed the multivariable feedback control system to control the five output variables: weld geometry variables (width, depth and height) and thermal properties (CR and HZ), for a presentation of a multivariable linear controller designed to regulate the width and throat thickness of filet welds during a GMAW process by simultaneously manipulating torch travel speed, power supply voltage, and wire-feed rate to achieve desired weld geometry. In this work the controller was designed using an empirically-derived linearized model of the welding process operating at a pre-selected operating point and using optimal control theory to ensure reference tracking, disturbance rejection, and robustness.
(Modeling, Sensing and Control of Gas Metal Arc Welding,Desineni Subbaram Naidu, S. Ozcelik, K. Moore D. S. Naidu-1st edition, (2003),P.161)
6-Control of arc length (in the welding process): Control of arc length in the welding process is important to ensure consistent heat input, constant melting rate, and stable performance of the process. In particular, arc length determines the transfer mode, arc stability, and the deposition rate.In GMAW, one simple way of controlling the arc length is to control the arc voltage. With a constant-current power source and variable wire-feed speed (WFS), the arc voltage (i.e., the process voltage) is used to drive the wire feed motor which in turn changes the arc length.On the other hand, with a constant-voltage power source and constant WFS, the changes in current are such as to provide a constant arc voltage (i.e., arc length).
(Modeling, Sensing and Control of Gas Metal Arc Welding,Desineni Subbaram Naidu, S. Ozcelik, K. Moore D. S. Naidu-1st edition, (2003),P.150)
Ertan TOPARLAK
503091329
No comments:
Post a Comment