L.J. Yang

Linear regression equations for modeling the submerged-arc welding process

Abstract Traditionally, curvilinear regression equations have been used for modeling the geometrical features of the submerged-arc welding process. However, recent investigation has shown that, due to low tolerance in some cases, it is not possible to include all variables in the regression analysis. This investigation was therefore carried out to study the feasibility of using linear regression equations instead of curvilinear techniques to model the weld features. The linear regression equations are found to give correlation coefficients similar to those obtainable from curvilinear regression equations. The average mean, standard deviation, minimum value and maximum value of the deviations between the measured features and those computed by use of the linear regression equations are only slightly (1.38–5.40%) higher. Linear regression equations are equally suitable, therefore, for modeling the sub-merged-arc welding process.

Optimization of laser deep-hole drilling of Inconel 718 using the Taguchi method

Abstract The use of a Nd:YAG laser to drill deep cooling holes in aerospace components is a stringent operation. Various characteristics pertaining to the input beam, focussing lens, and assist gas have to be optimized in order to produce a hole economically and of sufficiently good quality. This paper reports the use of the Taguchi technique of experimental design in optimizing the process parameters for drilling deep-holes in nickel-based superalloy, Inconel 718. The thickness of the material is 25.0 mm. Oxygen is the assist gas andthe focal length of the focussing lens is 300 mm. The effects of five process parameters — pulse energy, pulse duration, pulse shape, focal position, and assist gas pressure — have been explored. The various parameters are assigned to an L18 orthogonal array. The primary response under study is the drilling time. It is predicted that a minimum drilling time of 31.51 s is needed to drill a hole with a pulse energy of 30.0 J, a pulse duration of 1.8 ms, a “treble” pulse shape, a focal position of 0.0 mm into the material, and an oxygen pressure of 0.35 MPa. Confirmatory experiments have produced results that lay within the 95% confidence interval.

An analysis of curvilinear regression equations for modeling the submerged-arc welding process

Abstract Curvilinear regression equations have traditionally been used for modeling the weld bead geometrical features of the submerged-arc welding process, but, however, only the correlation coefficients have been reported. This investigation was carried out to study the relationship, if any, between the correlation coefficient and the standard deviation of the deviations between the predicted and measured values, with respect to melting rate, total fusion area, penetration, deposit area, bead height and bead width. It is found that there is no strong relationship between the correlation coefficient of a correlation equation and the standard deviation of the deviations between the predicted and measured values. A low correlation coefficient does not necessarily mean that there are standard-deviation consequences for weld-bead features. The statistical analysis has provided other useful information also. It is found that the mean deposit area obtained directly from the melting rate is higher, since it is assumed that all the melted metal goes into the weld deposit without any losses. It is estimated that the metal loss through vaporization is about 4% and 8% for positive electrode polarity and negative electrode polarity, respectively.

The effects of process variables on the bead width of submerged-arc weld deposits

Abstract The results of bead-on-plate weld measurements are presented to determine the effects of the process variables on the bead width for the submerged-arc welding process, at a heat input of 3 kJ/mm. It is found that bead width is affected by the electrode polarity, electrode diameter, electrode extension, welding current, welding voltage and welding speed. A positive electrode polarity, a large electrode diameter, a small electrode extension and a high welding voltage encourages a large bead width in most cases. For a particular electrode diameter and extension, it is found that the bead width initially increases as the current and the welding speed increase. The bead width reaches a peak value, and then decrease as the welding current and speed are further increased. It has been suggested in a recent tungsten-inert-gas welding investigation that heat input could be used as an independent parameter for predicting bead width. However, the present work suggests that heat input alone is not sufficient for predicting bead width in submerged-arc welding. The bead width is not affected significantly by the power source, constant voltage or constant current, when an acidic fused flux is used. However, when a basic fused flux is used, constant-current operation gives somewhat larger bead widths. It is found also that basic fused flux welds have a somewhat larger bead width than acidic fused flux welds. Regression equations are presented for computing bead width from the welding parameters, the analysis including both linear and curvilinear multiple-regression analysis techniques. Surprisingly, the correlation coefficients of the linear multiple-regression equations were found to be somewhat better than those of the curvilinear analysis.

A review of the laser processing of aircraft components

Abstract Composite materials and some exotic alloys have been used in the fabrication of both structural and non-structural members of the air-frames and engines of aircrafts. Different machining processes, such as the use of traditional solid tools with modified cutters, ultrasonic cutting and drilling, water-jet cutting, abrasive water-jet cutting, electron beam welding, and various laser processes have been applied successfully to the processing of these materials. In this paper, the physical mechanisms, the advantages as well as the limitations, and examples of application of the laser processes that are used to machine aircraft components are reviewed.

Elastic-plastic modelling of the residual stress caused by welding

Abstract An investigation was carried out to find an analytical model to examine the residual stress distribution across the weld of the panels welded with mechanical constraints. The panels to be welded were considered to be cantilever bars and the stress caused by the heat source during the welding process was assumed to have a parabolic distribution along the plate thickness. An ideal elastic-plastic material curve was assumed. It was found that for a weld with full penetration, no yielding would occur if the ratio of the maximum thermal stress to the yield stress was less than 0.938. Full yielding across the weld would take place if the ratio exceeded 1.246. For a weld without a full penetration, this ratio could be increased further before full yielding was achieved. It was also found that the surface residual stress increased as the depth of the yield zone increased. However, the maximum residual stress did not always occur at the surface. As the depth of the yield zone was increased, the position of the maximum stress was shifted towards the bottom of the panel. Furthermore, the maximum thermal stress to cause yielding was found to increase as the depth of weld penetration was reduced.

A software system for anticipating the size and shape of submerged arc welds

Abstract A software system for computing the size and shape of bead-on-plate submerged arc (SA) welds is described in this presentation. The system is based on algorithms originated by McGlone et al., Chandel et al. and Yang et al. Essentially the system consists of a specially designed interface for welding/materials/design/fabrication engineers, automated plotting for parametric studies, a simplified data base for storing/editing/retrieving frequently used welding parameters and pictorial graphics for displaying weld size and shape. The use of the system in engineering practice is discussed at some length.

The Effects of Process Variables on the Case Depth of Laser Transformation Hardened AISI 01 Tool Steel Specimens

Abstract An investigation was carried out to study the effects of speed, nozzle gap and power input on the case depth of laser transformation hardened ASSAB DF2 (equivalent to AISI 01) tool steel specimens. The specimens, used were 5 and 10 mm thick and 10 and 25 mm in diameter. A defocussed beam from a fast axial flow C02 laser was used with continuous-wave power inputs of 0.4 to 0.6 kW. The traversing speeds used were 5, 10 and 15 mm/s. The nozzle gaps were 5, 10 and 15 mm which gave calculated beam diameters of 0.129, 1.174 and 2.276 mm respectively. It is found that, the case depth increases as either the specimen thickness or power input is increased, but decreases as the: traversing speed is increased. The beam diameter, however, does not seem to have a significant influence on the case depth.