This paper introduces the application of neural networks to modeling cut surface quality for plasma arc cutting process. The neuro-model of cut surface quality consists of three parallel neural networks, respectively, called the cut shape neuro-predictor, and dross attached level and cut surface roughness neuro-estimators. A modified BP learning algorithm was used to train the neural networks. Implementation of the neural networks in the modeling is discussed in detail. Prediction applications of the neuro-model are described for various cutting conditions.
Tested and estimated results show the effectiveness and acceptable estimation accuracy of the modeling approach proposed. The neuro-model developed is applicable to the base metal of mild steel and the cutting conditions described. By using additional training data at any time, fine tuning and enlarging applicable scope can be done for the neuro-model.

View full abstract

A commercially pure titanium has been liquid phase diffusion bonded to pure nickel by using amorphous alloy filler metal.
The dissolution phenomenon of the base metals into the liquid filler metal and the isothermal solidification process during bonding was investigated. Main experimental results obtained in this reserch are as follows;
(1) The dissolution phenomenon of the base metals into the liquid filler metal was completed rapidly, its time was about 60 sec at 1125 and 1150 K, and about 120 sec at 1200 K.
(2) The dissolution of titanium base metal shown a value three times as much the dissolution of nickel base metal into the liquid filler metal. The maximum dissolution width of the base metals were related to the boning temperature by the following equations.
W_DTi=(1.78×10^-6×T)-(1.99×10^-3), W_DNi=(4.85×10^-7×T)-(5.37×10^-4)
(3) The relation between dissolution parameter P of the base metals and bonding time dose not shown by the straight line relation, the dissolution process was divided into three stage according to the dissolution rate constant K. therefor, the dissolution phenomenon does not conformed to the Nernst-Brunner's theory.
(4) The concentration of each elements were distributed itself uninformly throughout the bonded interlayer after the dissolution phenomenon of the base metals was completed.
(5) The maximum width of the bonded interlayer was related to the boning temperature by the following equation.
W_BImax=(2.32×10^-6×T)-(2.55×10^-3)
(6) The Ti-Cu and Ti-Ni system intermetallic compound layers formed on the interface of titanium base metal to the bonded interlayer. The Ti-Ni system intermetallic compound layer formed on the interface of nickel base metal to the bonded interlaver.

View full abstract

The effect of aluminum content on the penetration behavior in stainless steel tube welded by tungsten inert gas arc welding was investigated from a point of view of the effective oxygen content in molten pool. Girth welding tests were carried out on 18%Cr-9%Ni stainless steel tubes with 0.006-0.030% aluminum and 0.003-0.004% oxygen. The penetration depth, the bead width and the root bead length were measured to evaluate the formability of root bead. Then the aluminum content in weld metal was analyzed. The formability of root bead was deteriorated in proportion to the decrease of penetration depth and the increase of bead width caused by the addition of aluminum to the base metal. The aluminum content in weld metal analyzed was inconsistent with the content estimated from the dilution law but that agree with the content calculated from the solubility of Al₂O₃. The deterioration of the root bead formability by the increase of aluminum is thought to be caused by the molten metal flow to the molten pool edge induced by the decrease of the soluble oxygen content in molten pool.

View full abstract

Conventionally, the site welding of large diameter natural gas line pipes have been performed by using arc welding processes, including shielded metal arc welding and. gas metal arc welding. In order to achieve a drastic improvement of the productivity, authors have executed fundamental study on the application of the electron beam welding process to the site welding of line pipes.
This paper, as the first report, describes the influence of the welding position to the proper electron beam welding parameters in API-5L X65 line pipe steel of 19 mm thick. As a result of welding trials in various welding positions, it was clarified that the beam focusing condition and the welding speed should be properly controlled according to the welding position to obtain satisfactory weld bead shape. In the flat position, to prevent the under-fill on the surface, the beam focus had to be located under the plate surface. On the contrary, in the over-head position, the proper weld bead was obtained by positioning the beam focus outside the plate surface. In the vertical upward position, welding speed had to be kept lower to prevent the humping bead formation.
On the basis of above investigation, it has been basically confirmed that the all-position circumferential welding of large diameter line pipes can be performed with the electron beam welding process.

View full abstract

To establish all-position electron beam welding conditions for 19 mm thick API 5L-X65 pipe, in the previous report, appropriate welding parameters to obtain acceptable weld bead quality were clarified in eight representative welding positions.
Based on that result, all-position continuous welding trials were carried out by turning an electron gun inside the test pipe to be welded. Welding parameters such as the welding speed and the beam focusing condition were continuously changed, by tracing proper conditions at eight positions located by 45 degrees' interval. By using that method, all position welding has been completed successfully, and acceptable weld bead quality was obtained throughout the circumference.
Dimensional tolerances of the pipe setting for the acceptable weld bead formation was investigated by welding test pipes with various gap and mismatch values. Subsidence of weld metal, called under-fill, was observed, when the gap exceeded 0.2 mm. On the other hand, the mismatch up to 2.5 mm did not cause a surface defect of the weld bead.

View full abstract

GHTA (Gas Hollow Tungsten Arc) welding experiments were performed in a simulated space environment using aircraft. A vacuum chamber for GHTA welding test was placed in the cabin of the aircraft and the microgravity environment was produced by a parabolic flight of the aircraft.
Spot welding tests on stainless steel plates and girth welding tests of stainless steel pipes were performed in the vacuum chamber under microgravity condition.
The results are summarized as follows,
(1) GHTA method makes it possible 'to form a stable arc and weld stainless plates and pipes in the simulated space environment.
(2) Experimental results show that the arc configuration and the melting characteristics of GHTA are insensitive to the gravity.
(3) The weld bead formation is affected significantly by the gravity. The flat weld with full penetration, as is expected, is formed both in the spot welding and the girth welding under the microgravity condition.
(4) The butt joints of pipes welded by GHTA process in the simulated space environment have no defect good joint strength and the bead appearances is quite satisfactory.

View full abstract

To clarify the formation mechanism of the reaction layer, the behaviour of elements composing Si₃N₄ and brazing filler at the brazed interface was examined by SEM observation and EPMA analysis. The erosion depth of the brazed ceramic surface was also evaluated by surface roughness measurement, in order to examine the relation between the erosion depth and the brazing condition. The results of EPMA analysis suggested that Si₃N₄ was eroded with diffusion of Si and N to reaction layer. According to the erosion test using Ag-Cu-4 mass%Ti, the isothermal erosion depth of Si₃N₄ increased proportional to square root of brazing time in the temperature range of 1123 K to 1223 K. The temperature dependence of the rate constants fits an Arrhenius equation yielding activation energies of 127.5 kJ/mol.

View full abstract

It is well known that a lot of porosity is liable to be formed in high power CO₂ laser welding of aluminum alloys. At present, the formation causes and mechanisms of such porosity have not been satisfactorily understood. In this study, therefore, a microfocused X-ray transmission in-situ observation system was developed and utilized to observe the keyhole behavior and the formation situations of bubbles and pores during laser welding. It was observed that a keyhole fluctuated unstably in geometry and vibrated up and down dynamically, and accordingly many bubbles were frequently generated in the bottom part of the keyhole front wall. Bubbles were pushed into the liquid pool, and floated up quickly in a complex manner. Some bubbles disappeared into the keyhole or from the molten pool surface. However, most of bubbles were captured at the solidifying wall in the rear part of the weld pool to form pores in the spherical or elongated shapes. Moreover, it was revealed that partial penetration welding with a proper pulse modulation power input, a forward inclination of a laser beam or in N₂ shielding gas, and full penetration welding in any shielding gas were beneficial to the reduction and prevention of porosity.

View full abstract

Diffusion bonding process was carried out to make a joint of copper and molybdenum at 700 to 900°C, and the effect of oxygen content in copper and post heating treatment on the tensile strength of the joint was investigated. Additionally, the oxide product formed at the bonding interface was observed by SEM and identified by XRD.
It was found that the tensile strength increases with increase in bonding temperature for the joint of molybdenum to oxygen-free high conductivity copper. On the other hand, the tensile strength of the joint of molybdenum to tough pitch copper is low because of the formation of brittle oxide, MoO₂, at the bonding interface.
To clarify the formation of the oxide at the bonding interface, change of the composition at the copper surface were measured using Auger electron spectroscopy. On oxygen-free high conductivity copper, sulfur segregates to the surface at high temperature. While, on tough pitch copper, oxygen increases on the surface at high temperature.

View full abstract

Flattening ratio of thermal sprayed particle on a flat substrate has been of great concern in the thermal spraying research. To clarify the flattening ratio experimentally, accurate information on the flying particle, such as velocity and temperature, is essential. In flight measured values for the thermal sprayed particles will play a significant role to understand the flattening behavior of the particle on a substrate. Most of the studies relating to the particle's flattening, however, has applied some assumed values as for the particle's characters in flying, because in-situ measurement for them is somewhat difficult at the present condition.
In this study, DPV-2000 system, which is a revolutionary optical sensing device with on-line monitoring of the individual particle in thermal spray flame, was introduced to establish the in flight measurement of the particle's characters. The purpose of the study is to investigate the relationship between spraying parameters and particle's characters, and clarify the flattening behavior of the particle on a substrate based on the measured data.
From the measurement results of the particle's characters obtained by changing each spraying parameter, i.e. spray distance, arc current and operating gas flow rate, it was found that the spray distance had the strongest effect on the particle's character. The flattening ratio based on the measured data increased with the particle's Re number. In comparison with experimental flattening ratio and theoretical values, Mostaghimi's curve agreed well to the experimental data.

View full abstract

In this work, a feasibility study has been conducted to determine if gas-hollow-tungsten-arc (GHTA) can be used for welding purposes in space.
As described in the previous paper, the GHTA-method has been tested in a simulated space environment using aircraft. The test result shows that the method is very promising as a welding process in space.
In this paper, some fundamental characteristics of GHTA in vacuum chamber, such as ignition voltage and arc voltagecurrent characteristic, have been made clear and the results of melting test on stainless steel plate by GHTA-method have been compared with the case by a conventional GTA (gas tungsten arc)-method under atmospheric pressure.
The results are summarized as follows,
(1) The ignition voltage of GHTA depends on the ambient pressure : P, and the voltage is minimized under condition of P=26.6 [Pa]
(2) The arc voltage-current characteristic of GHTA is nearly equal to that of GTA under atmospheric pressure.
(3) The penetration shape by GHTA-method is quite different from that by GTA-method under atmospheric pressure. The GHTA method is characterized by shallow and wide penetration.
(4) The current distribution on anode surface of GHTA is extremely diffused, and the anode area increases with the arc-length.
(5) The diffused anode, which means diffused heat source, gives a satisfactory explanation for the shallow penetration in the GHTA-method.

View full abstract

To determine the correct welding current as function of the geometrical condition of groove incorporating deviations from prescribed standard groove shape, a quantity termed "joint capacity" was introduced, using which, linear expressions have been established relating the groove geometry to welding current and speed. The empirical relation thus derived gave results agreeing well with the expression given by A.A. Wells relating total heat input to quantity of electrode melting. These simple linear expressions enable active control of welding parameters for maintaining uniform reverse bead in automated welding process which produce defect free weld.

View full abstract

A laser diode beam detector system has been devised to detect the position of groove axis and to discern the groove geometry. The signals from this sensor are fed into an automated control system incorporating micro-computer storing the expressions which calculate correct welding parameters for deviating weld groove. And relating the input from monitoring sensor, the control system gives commands for automated operations to the welding unit.
A prototype machine has been utilized for actual welding work, and has proved to ensure weldments requiring no remedial operation.

View full abstract

Weld bead shape control is necessary for adequate welded structure performance when used under repetitive load. Bead shape occasionally deviates even when using automatic welding equipment because of changes in welding conditions such as the shape of the weld groove. A system for measuring the bead shape and controlling welding conditions during welding is thus required. Such a system will further upgrade the weld quality and welding efficiency. The effect of the root gap, a weld groove shape factor, on welding conditions and the bead shape were studied to work out a suitable bead shape control algorithm for an automatic bead shape control system to be used aluminium alloy butt welding.

View full abstract

Effects of oxygen on microstructure, shape recovery behavior and tensile properties were investigated for Ti-Ni shape memory alloy weldments. Gas tungsten arc (GTA) welding technique was applied for the alloy under controlled Ar-O₂ welding atmospheres. The oxygen content in the weld metal increased with rising oxygen partial pressure and welding current. Many second phase particles were observed in the weld metal which had absorbed oxygen. The second phase was identified as Ti, Ni₂O by transmission electron microscopy. Shape recovery behavior was measured for the temperature range of 283 to 372 K. The shape recovery stress of weldment at the 372 K gave equivalent value to that of the base material, however, As temperature of the weld metal decreased with increasing oxygen content. Tensile strength and elongation of the weldment decreased by welding and with increasing oxygen content.

View full abstract

Effects of nitrogen on microstructure, shape recovery behavior and tensile property of Ti-Ni alloy weldments were investigated. A near-equiatomic Ti-Ni shape memory alloy was welded by a gas tungsten arc (GTA) welding technique under Ar-N₂ welding atmosphere. The nitrogen absorbed into the weld metal increased with rising nitrogen partial pressure and welding current. Second phase particles were observed in the weld metal containing nitrogen. The second phase was identified as TiN by transmission electron microscopy. The shape recovery stress of the weldment was equivalent to that of the base material. As temperature of the weld metal decreased with increasing nitrogen content. Tensile strength of the alloy decreased by welding process, and the further reduction was observed for the weld metal absorbed nitrogen. Elongation also decreased by welding and rising nitrogen content.

View full abstract

The aim of this study is to investigate the effect of misorientation angle at bonded boundary on the tensile properties and the interface energy at the bonded boundary. The interface energy was evaluated with an observation of dihedral angle of the groove with a free surface which was achieved by thermal etching. The misorientation angle at the bonded boundary was measured by the electron channelling pattern method. The results obtained are as follows. (1) The interface energy at the bonded boundary depends on the misorientation angle at the bonded boundary, the bonding temperature and the thickness of surface oxide film. But the fracture strength does not depend on the misorientation angle. (2) The interface energy at the low angle bonded boundary below 5° is lower than that at the grain boundary in the base metal. The interface energy at the high angle bonded boundary at 18 up to 30° is higher than that in the base metal. (3) The interface energy of bonded boundary decreases with an increase in bonding temperature and a decrease in thickness of surface oxide film. (4) The number of void at the low angle bonded boundary is fewer than that at the high angle bonded boundary after the thermal etching, the size of the void is smaller than that at the high angle bonded boundary. The number and size decrease with an increase in the bonding temperature.

View full abstract