Dominic Cuiuri

Characterization of in-situ alloyed and additively manufactured titanium aluminides

Titanium aluminide components were fabricated using in-situ alloying and layer additive manufacturing based on the gas tungsten arc welding process combined with separate wire feeding of titanium and aluminum elements. The new fabrication process promises significant time and cost saving in comparison to traditional methods. In the present study, issues such as processing parameters, microstructure, and properties are discussed. The results presented here demonstrate the potential to produce full density titanium aluminide components directly using the new technique.

Measurement of residual stresses in titanium aerospace components formed via additive manufacturing

In the present study gas tungsten arc welding (GTAW) with automated wire addition was used to additively manufacture (AM) a representative thin-walled aerospace component from Ti-6Al-4V in a layer-wise manner. Residual strains, and hence stresses, were analysed quantitatively using neutron diffraction techniques on the KOWARI strain scanner at the OPAL research facility operated by the Australian Nuclear Science and Technology Organisation (ANSTO). Results showed that residual strains within such an AM sample could be measured with relative ease using the neutron diffraction method. Residual stress levels were found to be greatest in the longitudinal direction and concentrated at the interface between the base plate and deposited wall. Difficulties in measurement of lattice strains in some discrete locations were ascribed to the formation of the formation of localised texturing where α-Ti laths form in aligned colonies within prior β-Ti grain boundaries upon cooling. Observations of microstructure reveal basket-weave morphology typical of welds in Ti-6Al-4V. Microhardness measurements show a drop in hardness in the top region of the deposit, indicating a dependence on thermal cycling from sequential welds.

Investigation on Welding Arc Interruptions in the Presence of Magnetic Fields: Welding Current Influence

Arc interruptions and, therefore, oscillation in the amount of energy and molten wire delivered to the plate have been observed during tandem pulsed gas metal arc welding (GMAW). It appears that these instabilities are related to the magnetic interaction between the arcs. In order to clarify the possible mechanisms involved, this paper tries to mimic the tandem GMAW arc interruptions. External magnetic fields were dynamically applied to GTAW arcs in constant current mode to verify their resistance to extinction as a function of current level and direction of deflection. High-speed filming was carried out as an additional tool to understand the extinction mechanism. The influence of the welding current level on the arc resistance to extinction was established: The higher the welding current, the more the arc resists to the extinction. The arc deflection direction has minor effect, but arcs deflected backward have more resistance to extinction.

Investigation on Welding Arc Interruptions in the Presence of Magnetic Fields: Arc Length, Torch Angle and Current Pulsing Frequency Influence

Arc interruptions have been observed in tandem pulsed gas metal arc welding (GMAW). This fact, which is likely related to magnetic interaction between the arcs, motivated previous study concerning the influence of the welding current on this phenomenon. In order to promote further understanding, this paper investigates the effects of arc length, torch angle, and high-frequency current pulsing on the arc resistance to extinction. To mimic the situation found in tandem GMAW (magnetic field induced by one arc acting on the other arc), external magnetic fields were applied to gas tungsten arc welding arcs. It was verified that short arc lengths and torch angles set to push the weld pool increase the arc resistance to extinction, whereas the utilization of high-frequency current pulsing tends to weaken the arc resistance to extinction. According to a model devised from the results, the arc extinction takes place if the heat generated inside and the heat transferred into the arc column become insufficient to counterbalance the total heat loss in this arc region.

Preliminary evaluations on laser - Tandem GMAW

Recently there has been considerable research and development activity in the use of lasers for welding operations, turning this process into an important tool for a variety of applications. Although it is possible to use lasers as a unique source of heat to promote union of materials, the combination of the beam provided by a laser system with an arc welding process has been studied widely and applied in the so-called hybrid welding systems. Generally, the final result of such a combination is an increase in the weld penetration depth, width and welding travel speed. Despite these advantages, there are many issues still requiring further research and development concerning the use of hybrid welding using laser and arc welding, including a more comprehensive understanding of the various welding phenomena involved and the exploitation of new combinations. This paper describes an approach for hybrid welding combining a laser with tandem G MAW, in particular placing the laser beam between the tandem GMAW wires. This hybrid process variation is described and some basic aspects regarding its performance are discussed. The laser beam was found to have a positive effect on the appearance of the weld beads produced and best results are obtained if the laser is located halfway between the leading and trailing wires. A 10 mm inter-wire distance was found to be the most appropriate of the separation distances tried. The hybrid process approach was able to increase the welding travel speed or penetration depth significantly in comparison with tandem GMAW (operating in pulsed mode).

Arc Welding Processes for Additive Manufacturing: A Review

Arc-welding based additive manufacturing techniques are attracting interest from the manufacturing industry because of their potential to fabricate large metal components with low cost and short production lead time. This paper introduces wire arc additive manufacturing (WAAM) techniques, reviews mechanical properties of additively manufactured metallic components, summarises the development in process planning, sensing and control of WAAM, and finally provides recommendations for future work. Research indicates that the mechanical properties of additively manufactured materials, such as titanium alloy, are comparable to cast or wrought material. It has also been found that twin-wire WAAM has the capability to fabricate intermetallic alloys and functional graded materials. The paper concludes that WAAM is a promising alternative to traditional subtractive manufacturing for fabricating large expensive metal components. On the basis of current trends, the future outlook will include automated process planning, monitoring, and control for WAAM process.

Process planning for robotic wire and arc additive manufacturing

This study presents a process planning system, which directly generates manufacturing code from CAD models for robotic wire and arc additive manufacturing (WAAM). A variety of modules are developed for this system with special considerations on slicing and path planning. Multi-direction slicing methodology is developed to allow the WAAM system to deposit material along multiple directions and eliminate the need for supporting structure. MAT-based path planning method is proposed for void-free deposition of layers with any complex geometry. The proposed automatic process planning system is an important tool for the development of mature WAAM technology.

Characterisation and Control of a Prototype HTS SMES Device

A 2.79 kJ prototype high transition temperature Superconducting Magnetic Energy Storage (SMES) device has been constructed. The coil for the prototype has been wound using High Temperature Superconducting (HTS) BSCCO-2223 tape. The refrigeration system is a gaseous helium cold head cryocooler used to maintain the SMES coil at a temperature of 30 K, improving the Ic characteristic of the coil by a factor of 4.7 compared to that at 77 K. The SMES device is capable of supplying a 3-phase load during power interruptions, and has been constructed during a program to develop a larger 20 kJ system aimed at industrial applications.

Advanced Design for Additive Manufacturing: 3D Slicing and 2D Path Planning

Commercial 3D printers have been increasingly implemented in a variety of fields due to their quick production, simplicity of use, and cheap manufacturing. Soft‐ ware installed in these machines allows automatic production of components from computer-aided design (CAD) models with minimal human intervention. However, there are fewer options provided, with a limited range of materials, limited path patterns, and layer thicknesses. For fabricating metal functional parts, such as laserbased, electron beam-based, and arc-welding-based additive manufacturing (AM) machines, usually more careful process design requires in order to obtain compo‐ nents with the desired mechanical and material properties. Therefore, advanced design for additive manufacturing, particularly slicing and path planning, is necessary for AM experts. This chapter introduces recent achievements in slicing and path planning for AM process.

Optimising the welding conditions to determine the influence of shielding gas on fume formation rate and particle size distribution for gas metal arc welding

An automatic voltage control technique, to optimise gas metal arc welding (GMAW) conditions for minimised fume generation, was compared to conventional constant-voltage operation on the influence of shielding gas on fume formation rate (FFR) and particle size distribution. Significant reductions in FFR were attributed to reductions in the arc length and current and to improved metal transfer stability, achieved by promoting the ‘drop-spray’ transfer condition and reducing repelled globular transfer. A general decrease in average particle size was observed when using the automatic control technique for the O2-bearing shielding gases, which is significant, as finer particulates are more likely to be inhaled into the lungs. The proposed mechanism to explain this behaviour was lower arc temperatures combined with an increase in the availability of oxygen, leading to nucleation of large amounts of extremely fine fume particles when the supercooling of the vapour was large. FFR increased as CO2 content increased due mainly to the dominant influence of CO2 on metal transfer and arc characteristics. It is recommended that the influence of shielding gas on FFR should be investigated using optimised welding conditions for each shielding gas composition for GMAW, especially when operating in the spray regime.