On a truck there are thousands of bolted joints. Most of the time, operators use pneumatic assembly tools to tighten them with the pre-defined torque. But for the most critical bolted joints the operators since some years use electric assembly tools.
“It is the clamping force that decides if the bolted joint is tightened enough, says Filip Bergman, bolted joint specialist at Volvo Group Trucks Technology. “But the clamping force can’t be measured directly in production, only in laboratories where we perform tests to decide suitable assembly torque for each joint.”
The problem is that the clamping force is very much dependent on the assembly friction. And the friction can vary for different reasons, for example between different batches of screws and depending on what parts are joined together.
“With the introduction of electric assembly tools it was possible to pre-define not only the target torque but also the angle of rotation for the screw during tightening”, says Thomas Norberg who works with maintenance in the Tuve plant. “By monitoring two parameters instead of only one we can be sure that we reach the needed clamping force most of the time.”
The target torque and angle limits are set for each joint. The operator gets a green light from the when the operation is within the pre-defined limits and a red light when it is outside. Most of the time it is easy for the operator to understand why something is wrong and how to fix it, but not always.
“This is where Big Data are becoming very useful”, says Filip Bergman.
All operations with every electric screwdriver are logged and stored. Earlier it was not possible to handle and analyze this huge amount of data in a practical way. Today the tool supplier also provides software making it possible to quickly analyze large amount of data.
“It is now possible to save and analyze complete torque-angle curves from every tool and tightening, says Thomas Norberg. “ It is possible to go back and see if the tightening behavior suddenly looks different. It makes it much easier to analyze what could be the problem and how to fix it.”
“We today also use the historic data to update the pre-defined torque and angle limits in the tools to secure that we are always within the right span to secure the correct clamping force.
The new possibilities are not only used in the day to day operations in the plant. It can also be used if something happens with one of the trucks on the road.
If a bolted joint unexpectedly comes loose on a customer truck, Filip Bergman and his colleagues try to find the reason for this. One thing that can be done is to use the analyzing tool to look for any abnormal assembly behavior not previously detected in the factory for that specific joint.
“Earlier we sometimes had to recall thousands of trucks, says Filip Bergman. But with the analyzing tool, we can go back and study the curves in detail and see that this problem perhaps only affected a couple of trucks”.
This way the company can limit a possible recall to trucks that show similar abnormal behavior but not trucks with joints that behaved normally during installation.
“Thanks to Big Data thousands of our customers can then continue to safely use their trucks as planned, instead of visiting a workshop.”