a b s t r a c tThe 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 filler wire.
Cold metal transfer (CMT) is an automated welding process based on dip transfer welding, characterised by controlled material deposition during the short circuit of the wire electrode to the workpiece. Preliminary results are presented examining the suitability of this process for welding aluminium alloy. Trials show that in comparison with pulsed metal inert gas (MIG) welding, CMT exhibits a higher electrode melting coefficient. By adjusting the short circuit duration penetration can be controlled with only a small change in electrode deposition. Furthermore, by mixing pulsed MIG welding with CMT welding the working envelope of the process is greatly extended allowing thicker material sections to be welded with improved weld bead aesthetics.
The main drawback to programming robots offline lies in the poor accuracy of the robot. Robots are mainly programmed using the traditional teach and repeat method of programming which requires only good repeatability. As a result robots are manufactured with this in mind. Little is done to improve or even quote figures for the accuracy, which is generally regarded as being poor. A trial has been conducted on three modern serial linkage robots to assess and compare robot accuracy. Using a laser interferometry measurement system each robot has been measured in a similar area of its working envelope. The results and conclusions from this trial show that compared to older robots the accuracy can be remarkably good though it is dependent on a calibration process which is far from robust.
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