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Scania Słupsk — a leader in bus production technology

Assembly line Scania - Photo: Scania

As the first bus producer in Poland, Scania Słupsk has integrated electrically controlled nutrunners into their production. This is the same technology that car and bus producers use, and it has brought Scania flexibility, ergonomic improvements and time savings. The precision of electrically controlled tools offers future possibilities for reducing the bolt sizes and thereby saving up to 200 kg of weight per bus.

Poland is one of Europe’s largest bus-producing nations. Including Scania, the country has a total of seven bus brands. Traditionally, bus assembly is low-volume production, involving a great deal of manual labour. It does not involve conveyor assembly, as seen in car and truck plants. Buses are built at a series of workstations and moved from one to the other by cranes or manual trolleys. 

Most bus assembly plants are still far behind the car and truck industry, when it comes to fastener tightening technology. In Polish car and truck plants today, as in the rest of Europe, joints are assembled with electrically controlled nutrunners that are connected to general computerized networks. The tools are highly accurate, monitor the tightening process, and validate the installation torque. In most cases, the resultant tightening is automatically stored for analysis in a database linked to the vehicle or part identification number. This provides full traceability in the event of a recall. This is a great contrast to traditional bus production in Poland, where pneumatic tools — like big, heavy impact wrenches and pulse tools — are still most commonly used. These tools are highly inaccurate, and process control is completely in the hands of the operator. Due to the size of buses, very long air hoses must be used, which cause pressure drops and reduce the air tool’s performance.

Scania goes cordless
Polish bus plants rarely use electrically controlled nutrunners like the ones used in car and truck production — the Scania plant in Słupsk is the exception. When the Słupsk plant was opened in 1999, Scania buses already had a few sets of electrical nutrunners for critical joints. Today they run more than 12 systems, and when Scania’s long-time partner Atlas Copco introduced the Tensor STB battery-operated nutrunner with cordless communication, Scania immediately saw its advantages. They became the first Polish bus producer to use the new technology.

Robert Tyrka, operator at Scania buses Photo: Scania

“With the Tensor STB, we get full flexibility on applications inside the cabin without compromising the quality of the operation,” says station manager Pawel Chuchla. By not compromising on quality, he means that when using an electrically controlled tool like the Tensor STB, the process control is integrated into the system. The tightening data for every joint is stored in the controller and can be extracted and analysed. Not only is quality improved but using the Tensor STB instead of air tools also saves time. There is no longer any need to verify the torque with click wrenches after tightening with an air tool. This is because an electrically controlled nutrunner accurately measures both torque and angle during the rundown. 

“Now, using the new cordless tool, I can cut the process time in half,” says Robert Tyrka, an operator at Scania. He uses the new cordless tool for assembling the wall-to-roof and accessories inside the bus. This involves a total of more than 100 screws per coach, and on the double-decker model, they also use the tool for assembling the second-floor frame. “We used to need two tools, one on each side of the bus. But since this tool is cordless and we don’t have to consider handling the cable, now we only need one tool.” continues Tyrka.

Noise reduction project
Scania not only works to improve the quality of their products, they also want to improve quality for their workers. Scania is recognized in the industry for its continuous work in developing proper ergonomics in production. Using the cordless nutrunner instead of dealing with cables or hoses is one ergonomic improvement. Another is the Noise reduction project with the goal to reduce production noise levels to below 75 dB. Noise reduction solutions include performing tasks in a different sequence, switching from air tools to electric ones, and training operators to avoid loud behaviours.

How to lose weight
Initially, large European truck and bus manufacturers like Scania used electric tools to minimize sound and vibration. Quality was monitored, and precision control was possible. However, in recent years, the weight savings from using smaller bolts and screws have drawn more attention.

“Using an electric nutrunner and advanced fastening technology, the weight of a truck or bus can be reduced by up to 200 kilos,” says Scania’s fastening technology expert Lars Oxelmark in an interview with a Swedish magazine (Ny Teknik, 13 May, 2009).

It is calculated that the weight of a truck or bus can be reduced significantly if it is fastened together using electric tools instead of pneumatic ones. An electric nutrunner is more precise and gives you better control over what actually happens to the screw and the entire joint as it is tightened. This reduces uncertainty:  The designer and the operator are willing and able to use the entire strength of each screw, and the margin of safety can be decreased. This means that smaller, lighter screws can be used.  

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