Crane Systems Keep Eaton Production In Gear

July 1997
Torque sensing and monitoring equipment supplied by Crane Electronics has provided a complete solution to a quality control conundrum faced by Eaton Limited (Transmissions) UK at its Newton Aycliffe factory.

By permanently equipping nut runners used on two safety and performance critical assembly tasks with Crane CheckStar torque sensors and feeding back to Crane TMAC programmable torque controllers, Eaton is able to monitor every assembly.

As well as providing the line operator with a go/no-go signal the TMAC also logs the torque and tightening angle for every assembly operation. This allows the information to be archived, and has also allowed analysis of trends to facilitate preventive maintenance of the nut runner tooling.

Eaton is one of the world's leading manufacturers of transmissions for heavy goods vehicles. The Newton Aycliffe factory concentrates on assembly of six- and nine-speed transmissions.

Though the basic design is consistent there are hundreds of customer variations. Prior to installing the Crane monitoring system, the company relied on the pre-set torque limits on the nut runner, combined with random quality checks using a manual dial type wrench. The problem with this method was that, if the random check registered a failure, a whole batch of gearboxes would be quarantined for manual checking.

Two stations on the gearbox assembly line are critical. Firstly, tightening of a gear onto the main shaft, and, secondly, tightening of the output shaft to provide the necessary pre-load on the gearbox bearings. In either case variance could result in poor performance and/or premature failure of the entire assembly. Difficulty arose from the failure mode of the nut runners and associated torque multiplier gearboxes, which was gradual rather than instantaneous.

The company therefore set about finding an independent means of monitoring the applied torque. The solution provided by Crane entailed introduction of a CheckStar rotary transducer between the output shaft of the right angle nutrunner / gearbox assembly and the driven socket. The connecting cable from the transducer to the Crane TMAC tool monitoring and control unit is clipped to the nut runner's pneumatic hose, providing a neat installation.

The TMAC itself is programmed to register and archive applied torque and tightening angle, and provide a high/OK/low torque visual signal via three LED's. Trevor Hugill, Eaton Quality Control Engineer confirmed.

“The system provides a fully fail safe means of monitoring torque on the production line. In the event of a low or high reading the assembly worker contacts his supervisor and the tool is exchanged. As a result we are 100 per cent confident of shipping good product only and we have traceability on these parameters”�

A secondary benefit of logging the torque readings has been early identification of the need for preventive lubrication maintenance on the nut runners themselves. Mr Hugill concluded. “From the quality stand-point the Crane equipment has proved to be highly cost effective and contributed to the smooth running of the assembly process.”�