SmartDress

Introduction
High volume automotive production (such as body-in-white construction) operations rely heavily on RSW (resistance spot welding), and suffer significant losses of output (and resulting revenue) as a consequence of frequent production line stoppages. These stoppages are predominantly caused by weld quality issues, which in turn arise from poor maintenance of consumable ‘tips’ on RSW guns.
SmartDress is a fully automated adaptive control system that will optimise, monitor and maintain electrode tip quality in these applications. This will improve weld quality and reliability and minimise line stoppages.
Another key feature of the SmartDress system will be that it will allow cost-competitive spot welding of aluminium, which is not currently commercially viable. As a result production of lower cost light weight vehicles would become possible leading to a significant reduction of CO2 emissions.
The Solution
Resistance spot welding is the most commonly applied process for joining thin metal sheet in automotive body structures, with a typical family car containing up to 5000 spot welds. The spot welding process offers a high level of reliability with modern welding systems able to accurately control and monitor spot welding process times, currents and forces.
However one aspect of the spot welding process that is not tightly controlled is the wear of the welding electrode tips. Zinc coated steels are the most popular car body material, but zinc rapidly degrades the electrode to the point where maintenance is required to ensure an adequate weld quality is produced. Electrode wear can be repaired by a technique known as ‘tip dressing’ where a mechanical cutter removes material from the tip face repairing any damage and returns the tip to its optimum geometry. Today nearly all modern automotive spot welding lines run production with automated tip dressing, but even these systems do not offer a complete solution:

• Problems with electrode tip maintenance remain the number one cause of stoppages on car production lines
• Conventional electrode tip dressers use mechanical ‘cutters’ that remove a large quantity of copper, resulting in rapid consumption of expensive copper electrodes
•  In the production line start-up phase all tip dressing schedules must be manually programmed, tested and iteratively optimised. This operation is labour intensive and the optimisation phase can take several months before the line is ready to run at full production output

SmartDress is a novel new approach to electrode tip dressing comprising a complete automated solution to all the challenges faced when setting up and maintaining a resistance spot welding process. The SmartDress system comprises five elements, including 3 totally new innovations:

1. A new approach to electrode tip dressing using an abrasive to clean electrode faces with a minimal removal of copper, greatly extending electrode production lives
2.  An optical sensor able to monitor the electrode condition providing vital data concerning the state of wear
3.  A computerised control system able to process data from the optical sensor to determine the level of electrode cleaning required. The control system can also optimise dressing schedules adaptively controlling electrode maintenance frequency
4.  A mechanical dresser designed to minimise copper removal during tip dressing
5.  An automated tip changer able to replace worn tips during production without the need for a line stop and manual intervention

Technical Objectives

• Address the need of several SME companies to maintain their position within an already fiercely competitive sector by introducing a new product with associated economic gains (projected as 65M over the first 5 years of product launch).
• Eliminate the main cause of weld failures and associated production stoppages in automotive BIW production, bringing with it a cost saving in the order of 7M per line per annum.
• Reduce the use of consumable copper electrodes, and more importantly, the use of large amounts of steel self-piercing rivets (on aluminium vehicles) – which are in the order of 2000 per vehicle; accounting for a consumable cost in the order of 90 per BIW.
• Extending the application of RSW in aluminium vehicle BIW construction, lowering production costs, and promoting the uptake of light-weight environmentally friendly vehicles.

Impacts of the SmartDress system:
Introduction of the SmartDress system into a production line can have significant impact on the resistance spot welding process:

•  Increased production life of electrodes achieved by minimal material removal using the abrasive dresser development. Initial results show an increase of 3 x the production life when welding zinc coated steel
•  Regular electrode maintenance using abrasive dressing allows for economical spot welding of aluminium as copper consumption is dramatically decreased
•  Automated optimisation of electrode tip dressing frequency during production line start-up phase
•  Monitoring and adaptive control of the electrode during spot welding production, able to adapt electrode maintenance schedules to compensate for unexpected electrode damage

Control of spot weld quality through monitoring and maintaining welding electrodes improving quality assurance of the production line