- Impeccable build quality, despite large number of model versions
Nearly every second truck built in Germany is a Mercedes-Benz model from the Wörth plant. Trucks from Wörth are exported to more than 150 countries. The Mercedes-Benz trucks being built today in Wörth already have the makings of classics of the future. No one can say today which trucks out of the 100,000 or so built here every year will be showing up as sprightly "senior citizens" at classic commercial vehicle meetings a few decades from now – but potentially it could be any of them, since long-term durability is built into every vehicle that leaves Wörth
Impeccable build quality despite large number of model versions
"The foundations for quality are laid at the development stage", says Ernst Wünstel, Head of Production in Wörth. All systems at the plant are geared to ensuring impeccable build quality. And that's no mean task for a truck plant, since every vehicle has to be built precisely to customer specifications. The Actros, Axor and Atego can be built in 331 different model versions, plus over 1600 special versions. The Actros, construction Actros, Axor and Atego are each available with a choice of four basic cab types and are based on different frames ranging from 3.5 to eleven metres in length. The engine range extends from four-cylinder to V8 units, which can be combined with a variety of auxiliaries and attachments, and there is a wide range of transmissions, axles and suspensions.
There's plenty of variety as far as wiring and pneumatic lines are concerned, too. These parts of the vehicle are pre-assembled individually while the frame is being built, then assigned to the relevant vehicle. On top of this, 11,400 of the trucks built last year included optional equipment specifically requested by customers.
In other words, apart from fleet orders, no two trucks built in Wörth are exactly the same.
It helps, therefore, if major suppliers build their components as close to the factory as possible. An on-site supplier park has been set up in Wörth, covering an area of 5000 m², at which six suppliers build components such as seats, bunks and other interior fittings, which are then delivered direct to the assembly line.
The plant has more than 1,000 suppliers on its books, and around half the required parts are delivered "just-in-time" or "just-in-sequence" to the assembly line. Some 550 trucks deliver parts to the Wörth plant every day.
All this variety must not get in the way of quality. After all, DaimlerChrysler truck plants operate to the same quality standards as the passenger car plants. The ambitious goal, therefore, is zero-defect production. With the huge complexity involved in Wörth, that's no easy task.
The all-important art of joining – for example bolting and screwing
Joining is an all-important part of vehicle production. "Bolting, screwing, riveting, welding, bonding" are the possibilities enumerated by Ernst Wünstel. Tightening a bolted connection can be quite an art – as a glance around the Wörth plant makes clear. Screws and bolts are specially coated for corrosion resistance and critical bolting and screwing operations, for example to connect the steering bracket or steering shaft to the frame, must conform to precisely laid down specifications: tool speed and torque are precisely defined, as are the angle of the tool and variations in tool speed at different stages of the tightening process.
For each truck, all significant production details, for example about critical screwing and bolting operations, are recorded on a vehicle card. Tightening torques are stated to within one tenth of a Newton metre, and tightening angles to within one degree. This checklist accompanies the truck through the factory, from the frame production stage through to final inspection.
Gradually, the checklist becomes a fat wad, in which each employee personally signs off his or her particular task. Any time a problem crops up on a Mercedes-Benz truck, anywhere in the world, it is possible to see from the card, even many years later, what jobs were carried out by whom on the day the vehicle was built. This system applies to all 100,000 or so trucks which come off the line in Wörth every year.
Quality – every employee plays their part
On the production line, precision is everything. Since precision can only be achieved by highly trained, highly motivated employees, most of the production line workers in Wörth have trade proficiency certificates or are otherwise highly qualified. This is particularly important in a truck plant, given the demanding nature of the work. Cycle times here range from 2.5 to ten minutes, depending on the assembly line concerned, whereas in car production even 60 seconds would be considered a lot. Every employee has to be fluent in a wide range of operations and a wide range of vehicles, since Actros, Axor and Atego models can come down the line in any order.
There's a good reason for this sequencing: a functional cab for a distribution truck, say, entails a significantly different workload from, say, a large, lavishly equipped long-distance haulage cab. Intricate coordination prevents several cabs with complicated workloads from being scheduled consecutively, thus causing a logjam on the production line. Conversely, it also prevents capacity underutilisation due to consecutive sequencing of several more basic cabs.
Employees organise their own shifts
Motivation is a number one priority in Wörth. The production line teams are free to organise their own work schedules and even to plan their own holidays. All shifts participate in the scheduling of individual working times. As well as individual responsibility, the employees also enjoy individual support, for example with regard to their personal fitness.
A mobile physical training device travels to the employee's work station on which, during his or her working time, the employee can perform individually prescribed muscle-strengthening exercises to get their fitness back up to par.
Successful delegation of responsibility requires clear, transparent information about objectives and results. On large, continuously updated displays, each team is informed about agreed targets, key quality indicators, audit results and absenteeism – so everyone knows exactly where they stand.
Robots build cabs in any sequence
It's not only the human personnel who work flexibly on the Wörth production lines. The robots, as used in cab body construction, operate on exactly the same principle. In the various production cells the robots can weld any of the many different cab versions in any order, while the individual components are transported on driverless conveyor systems. This overall system is unique worldwide in the automotive industry. It makes for the high standard of precision and the unsurpassed flexibility for which the Wörth plant has already won critical acclaim from international experts.
Quality is continuously monitored and tested. In addition to the continuous routine measurements, twelve cabs are singled out every day for particularly close scrutiny. This intensive inspection by a five-axis measuring system takes between 20 and 90 minutes, depending on the cab.
Parts production: accuracy and flexibility
In parts production too, accuracy and flexibility are the all-important basis for long-term durability.
Every month 3,000 forming tools produce some 2.9 million parts, such as brackets for attachments, or steel tubing for pneumatic lines. 6,400 different types of part are produced here.
The parts production sector also produces the tubular supporting structure, complete with a dozen brackets, for the driver's cockpit as used in every Mercedes-Benz truck. All components of the cockpit, including the panelling, instruments, push buttons and stowage trays, are pre-assembled separately in the cockpit pre-assembly section. The finished article, which in the case of an Actros can weigh anything up to 120 kg, is then installed in the prepared cab as a unit, fixed in place and connected. The door trim too is pre-assembled on a just-in-sequence basis.
Elaborate pre-treatment provides long-lasting corrosion protection
Elaborate production methods also provide the basis for long-lasting corrosion protection. The more at-risk parts at the front end of the cab, for example, are made from sheet metal which has been galvanised on both sides, or from plastic. Both the extensive pre-treatment and the subsequent painting of the cab are carried out in accordance with strictly defined procedures. After cleaning and degreasing, a protective coating of zinc phosphate is applied, prior to cataphoretic immersion priming. All seams and overlaps are then sealed and the filler is applied. The entire pre-treatment sector in Wörth was refurbished just last year.
260 different paint colours available
Pre-treatment is followed by application of the topcoat, which is available in 260 different colours. Following a thorough surface inspection, a wax preservative is then sprayed into the cavities. Thanks to these elaborate measures, trucks from Wörth keep corrosion firmly at bay. Long-term durability is ensured even under harsh operating conditions.
Trucks are test-driven on a defined trial course every day
The quality produced in Wörth is strictly monitored. Each truck goes through numerous quality control processes followed by a dynamometer test. To ensure consistently high standards, one finished vehicle per day is also put under the microscope for a detailed "audit", while a number of vehicles per day are test-driven on a defined trial course which includes sections with poor road conditions. If ever a problem comes to light, this particular point is then included in the pre-delivery inspection for each individual truck.
It's hardly surprising therefore that Ernst Wünstel, Head of Production, should have this to say: "Theoretically, there's nothing to stop our trucks going on and on for ever." That just about sums it up. Thanks to long-term durability made in Wörth, future years will see no let-up in the numbers of Mercedes-Benz trucks maturing into classics.