Nissan Uses Tool Controllers From Crane Electronics To Ensure That Important Safety Related Fasteners Are Tightened Correctly

April 1997
Japanese car manufacturers have worked hard to establish a justifiably strong reputation for the quality of their products, including all cars manufactured in plants outside Japan. The factory in Sunderland, which builds Nissan Micras, Primeras and the new Almeras, has always put a heavy emphasis on quality issues, and this has been reinforced by the purchase of 25 TMAC3 controllers from Crane Electronics. These are being used on the production line for the installation of threaded fasteners that are considered to be important, such as those on the seats, seat belts wheel hubs, suspension and rear axles.

The TMAC3 (third-generation Tool Monitor And Control) controllers are used in conjunction with various types of transducerised powered fastening tools to ensure that the correct torque is applied every time. Furthermore, these units record the torque and can raise an alarm if any fastener is under or over-torqued. In the Nissan factory. The result is, this facility ensures that no car leaves the factory with any of the monitored fasteners outside the specification, thereby helping to safeguard that the cars meet not only safety standards but also customers’ high expectations.

Nissan's Sunderland factory is unusual in that the two production lines are used for assembling more than one type of car each: one line is used for both Micras and Primeras concurrently; the other line for Micras and Almeras. One of the advantages of using the Crane TMAC3 is that the controller strategy can be easily switched to tighten the fixings of which ever vehicle or variant, is on station at that time. This avoids Nissan either having to increase the number of tools and controllers or slow down production to allow the tools to be reset.

One of the main reasons why Nissan chose the Crane TMAC controllers originally was that one controller (the then-current TMAC2 model) could be used to control powered tools supplied by several different manufactures (such as Stanley, Uryu, Yokota and Ingersoll Rand) - an unusual feature for tool controllers. When Crane started to develop the TMAC3, Nissan were able to request certain features should be included because of the close working relationship between the two companies. One of the facilities included on the TMAC3 is the ability to install, with the same tool, fasteners with differing characteristics. For example, a seat may be held in place with four fasteners, but some of the joints may be ‘hard’, while others are ‘soft’, even though the target torques and ranges are identical. Whereas this would traditionally mean the use of more than one tool and controller - or the use of ‘break-back’ torque wrenches - all four fasteners can now be installed successfully with the same tool and TMAC3.

Crane's relationship with Nissan extends well beyond the supply of equipment; training for operators, maintenance, repair and calibration technicians has been provided on an on-going basis to ensure that the equipment performs at its best, and that Nissan is making the best possible use of the equipment. Because two shifts are worked at Nissan, and task-rotation is used to ensure that operators work on two or three tasks per day, it is easily possible for the 25 TMAC3 instruments to be used by 200 different operators. Moreover, there are still over 50 TMAC2 instruments in use, making a total of around 600 operators who use the Crane controllers!

Although the TMAC controllers are not networked for data collection, the ‘pass/fail’ information is continuously fed to the zone controller. If any joints have not been torqued correctly, the car is therefore prevented from leaving the controlled zone until the fault has been rectified.

Another important use for the internal data collection facility is when new processes are being commissioned and the process capability needs to be established. To do this, readings are taken during each of the two shifts, then the cPk value is calculated complete with a histogram from the data stored on the TMAC3. This data is then printed and issued to the quality department. Because the data is collected and recorded automatically, the process capability is far easier to measure than if the procedure was undertaken manually.

Using the TMAC3 controllers allows a small amount of time to be saved from many of the assembly operations, but, more importantly, there is an improvement in overall product quality. Roger Bradfield at Nissan explains: “In many cases the versatility of the TMAC3 means that we are now able to use a controller where, previously, we might only have been able to justify using a break-back tool in a checking operation. Furthermore, using a break-back tool only ensures that a minimum torque is applied - the joint can easily be over-torqued - but the TMAC3 ensures that the torque is within a specified range. In addition, we have the data available for traceability should we ever experience a problem with any of the fasteners. All in all, we are utterly convinced of the benefits of the TMAC3.”�