Vehicle Window Manufacturer Expands Robotic Welding with UK's first Cold Metal Transfer System

Motoman

Aluminium window frames for off-road vehicles are being welded faster and to the same high quality at the Birmingham factory of Widney UK, following the installation in January 2006 of a Motoman ArcSystem 6000 robotic welding cell comprising a 6-axes robot working with a servo controlled twin station positioner.

Motoman Robotics is the first robot company in the UK to integrate the new CMT (cold metal transfer) process developed by the Austrian company, Fronius. Some of the major advantages over conventional MIG welding are reduced cycle times, improved cosmetic appearance of the weld bead, virtually no spatter and very low heat input, keeping weld distortion to an absolute minimum. Post-weld dressing and scrap are virtually eliminated.

A key factor for making the investment was the fact that Widney UK required additional robotic welding capacity to satisfy new contracts for their glazed window business and Motoman Robotics proved to be a competent partner to supply this type of system.

Motoman Robotics successfully integrated the new CMT process into one of their standard range of ArcSystem welding cells utilising a highly accurate and fast HP20-6 long reach robot in order to provide full cover over the relatively large window assembly. These cells are supplied with all auxiliary equipment such as guarding, electrical safety etc.

The new Motoman cell is up to twice as fast as other robot cells in the Widney factory, six times more productive than a manual welder, and delivers an important extra benefit. As CMT weld quality is so good, the process is able to match the quality of TIG welds and get closer to the finish of a brazed weld. CMT welding of a window joint takes typically three minutes, representing a 10-fold time saving over the 30 minutes required for manually brazing the joint. Small wonder, then, that the original 11 manual brazing stations at Birmingham have been cut to three.

According to Widney UK production engineer, Anne Seeley, Motoman Robotics was the only company able to offer a high specification cell at an attractive level of investment. The system features a servo controlled, twin station rotary positioner that allows fixtures to be loaded during the weld cycle. All three servo axes and the robot's six axes are controlled from the Motoman NX100 robot controller, with its unique ability to control up to 36 axes.

In practice, to take advantage of the ArcSystem 6000's fast set-up time, jobs for two different customers are generally produced sequentially using different fixtures at each station. If component dimensions allow, two window frames are clamped on each of the two fixtures at either of the stations, which is ideal for setting up 'handed' window frames. In this way, production flexibility is balanced with maximising output over two shifts from 7.30 am to 3.00 am. Aluminium welded by Widney UK is mainly from 1.5 to 3.0 mm thick, which is the upper limit for pure CMT.

CMT derives its ability to create high quality welds from a modified dip-transfer technique whereby the arc is deliberately discontinued and resumed at up to 70 times per second. Accurate control is maintained over the mechanical motion of the wire as well as over the electrical and electronic parameters, leading to greater uniformity of the weld bead and enhanced reproducibility over a batch of components, and from one batch to the next. As the temperature of the base metal does not rise as high as with conventional MIG, there is less tendency for cracking to occur in the heat affected zone around the weld.

Currently, there are very few off-road vehicles built on which the welds of Widney's window frames are visible. However, the higher quality of the CMT weld will allow Widney UK greater flexibility in that additional products may be designed so that the welds do show, so good is their appearance.

Three photographs herewith, captioned:

1. Anne Seeley programming the Motoman robot to weld an aluminium window frame at Widney UK. Programs for all jobs are held within the extensive memory of the NX100 robot controller.

2. Robotic welding at Widney UK of an aluminium window frame for a Volvo off-road vehicle. Symmetrically opposite frames are mounted on the same fixture on this station.

3. Close-up showing the quality and minimal spatter of a Cold Metal Transfer weld.