Page 24 - ITAtube Journal 2/2019

Technical Papers
Figure 6. Small exible system. The robot/ enclosure interface is effectively sealed against leaks using an adaptable occlu- sion. Enclosures up to 27 m3 volume have been manufactured to accommodate large systems
stainless steels is in the region of $400/kg. Few problems remain when it comes to fusion welding and consequently an extensive variety of wire electrodes is available, most of which can be used for arc depo- sition. Because of the quantity of wire manufactured the cost is not high. Typically, stainless steel ller wire is readily available for $30/kg.
Deposition Rate
Powder deposition rates are very low and average 0.1 kg/hr. With advancing technology this may well increase but at the present time this severely restricts applications. The wire arc process is capable of laying down 10 kg/hr of a wide range of metal alloys. [Table 1.]
Figure 7. Small exible system. Advanced oxygen monitor includes full colour touch screen control. The instrument supports data logging and weld certi cation. Readings are accurate down to 10 ppm.
PROCESS LIMITATIONS
Many alloys may be used during the WAAM process simply by using the welding torch inert gas shroud as protection. However, some materials are much more prone to reaction with residual oxygen and this can lead to fusion zone and surface oxidation. Titanium alloys are particularly sensitive but stainless steels. and many low alloy steels also demand additional inert protection.
With the electron beam process, protection is assured since operations are carried out in a vacuum. Nevertheless, this is an expensive alterna- tive to arc welding.
Overcoming the Problem of
Oxygen Contamination
The issue of adequate protection has been resolved by developing ex- ible enclosures that can be purged with inert gas, usually argon. These can accommodate the entire welding equipment and robot and provide inert gas protection throughout the deposition process.
Flexible Enclosure Technology
There have been considerable advances in enclosure development since the concept was introduced over two decades ago. Huntingdon Fusion Techniques Ltd [10] for example has spearheaded a drive to design systems speci cally for the welding industry. These innovative products offer signi cant attractions over both vacuum and glove box alterna- tives not least a signi cant reduction in cost.
ITAtube Journal No2/May 2019
24