Characterisation of the cold metal transfer (CMT) process and its application for low dilution cladding

The process characteristics of the synergic cold metal transfer (CMT) process have been examined for welding aluminium alloy. Utilising a simple backlighting system and through the arc monitoring the droplet transfer modes were identified. Whilst the modified short circuit mode was evident for the lower parameter range, a two part transfer mode based upon a combination of spray and short circuit transfer was observed for the mid to upper parameter range. The technology was also explored as a cladding process for applying to ternary alloyed (Al–Cu–Mg) aluminium plate. This alloy system is known to be susceptible to solidification cracking when MIG welded using the binary Al-2319 (Al–Cu) filler wire, this being due to the wide element freezing range of the weld resulting from mixing with the base material. Utilising this filler, weld dilution ratios for both CMT and pulsed welding were identified across the examined parameter range. The CMT process exhibited greater control of dilution that enabled deposition of a quasi-binary (Al–Cu) layer exhibiting a less crack susceptible composition. Onto this layer conventional MIG welding could be applied which could potentially eradicate cracking using a binary fi

Self-piercing riveting-a review

© The Author(s) 2017. This article is published with open access at Springerlink.com.Self-piercing riveting (SPR) is a cold mechanical joining process used to join two or more sheets of materials by driving a rivet piercing through the top sheet or the top and middle sheets and subsequently lock into the bottom sheet under the guidance of a suitable die. SPR is currently the main joining method for aluminium and mixed-material lightweight automotive structures. SPR was originated half century ago, but it only had significant progress in the last 25 years due to the requirement of joining lightweight materials, such as aluminium alloy structures, aluminium-steel structures and other mixed-material structures, from the automotive industry. Compared with other conventional joining methods, SPR has many advantages including no pre-drilled holes required, no fume, no spark and low noise, no surface treatment required, ability to join multi-layer materials and mixed materials and ability to produce joints with high static and fatigue strengths. In this paper, research investigations that have been conducted on self-piercing riveting will be extensively reviewed. The current state and development of SPR process is reviewed and the influence of the key process parameters on joint quality is discussed. The mechanical properties of SPR joints, the corrosion behaviour of SPR joints, the distortion of SPR joints and the simulation of SPR process and joint performance are reviewed. Developing reliable simulation methods for SPR process and joint performance to reduce the need of physical testing has been identified as one of the main challenges.Peer reviewe

Control of weld composition when arc welding high strength aluminium alloys using multiple filler wires

An experimental method of controlling weld composition when welding Al2024 has been explored. Utilising the tandem process and a cold wire feed unit, two and three commercially available filler wires were mixed in a single weld pool to control composition. Thermodynamic modelling was used to provide optimum weld compositions for the eradication of solidification cracking. Validation showed that by controlling the principal elements, not only was cracking eliminated, the mechanical properties of the weld could be varied. In particular, a composition was identified, which offered adequate joint strength and ductility. Exceeding this composition resulted in a corresponding increase in weld hardness at the expense of joint ductility