If you wish to buy a new car nowadays, you can choose from thousands of different models. The options are endless, ranging from the type of vehicle to its engine performance, cubic capacity and the number of cylinders, its colour, safety and comfort features and even extras like the radio, charging points and navigation. Variety and individual production make manufacturing cars an extremely complex business. This is why vehicle manufacturers rely on experienced logistics specialists when making their cars.
The latter fill the gap between the classic first-tier parts producer and the vehicle manufacturer, also known as an original equipment manufacturer or OEM. ‘Automotive logistics experts form the perfect interface and assemble the work output that the customer requires within a modular system: purchasing individual parts, transporting the components, managing the warehouse and sequencing as well as assembling components and even manufacturing a complete truck,’ says Florian Karlstedt, Project Manager at Rhenus Automotive.
One of the main areas of business for automotive logistics specialists involves pre-assembling modules that are then inserted into cars. They include, for example, axles, cooling systems, control units, chassis components and interior fittings. The complexity of the assembly work depends on various factors – such as the number of parts within a module and the options, but also the sensitivity of the component.
Florian Karlstedt quickly dismisses any false idea that one axle is like any other, and it takes him several minutes to list various types and shapes for different manufacturers and models. There are not only simple rigid axles and complex multi-link axles, but there can even be huge variety in axles from the same manufacturer and the same vehicle model.
‘The axles differ, for example, for left- and right-hand drive vehicles, the type of engine and the car’s size. There are large and small brake discs – and therefore you need different brake callipers for them, too. We install 100 different drive shafts alone in Wang, depending on which equipment the buyer has selected,’ he explains.
The automotive business site in Wang is a prime example of the complexity of module assembly work, not just because of the enormous number of components, but also the high rate of production. Two production lines operate in parallel at Wang because of the high speed that is required. They produce a finished corner module every 30 seconds. This involves pivot bearings and wheel mounts, which are later attached to the axle at the front and rear.
The number of components is so large that the parts cannot be directly taken to the assembly line. An additional sequencing area between the warehouse and the line has therefore been set up in Wang.
‘We can’t have 100 different drive shafts close at hand next to the line. One employee therefore walks to the shelf just like in a supermarket, takes the necessary parts and puts them in a frame in the correct sequence. The employee working on the line picks them off one after the other like beads from a necklace,’ Florian Karlstedt explains. Each employee has exactly thirty seconds to complete his or her work step and a small buffer of extra time has been included between the various workstations.
‘Once a customer has placed an order, we have to supply the goods quickly. Depending on what’s required, the module reaches the manufacturer within two or three hours.’ In terms of Wang, this means the BMW Group’s factory in Dingolfing. The variety of the components is slightly less at the production facility in China because more fully-equipped cars are sold in the market there. The complete axle is manufactured for them there and it consists of numerous parts overall. ‘Our task involves the planning work, stock controls and management as well as maintaining the supply chain. This means that we take over some of the work from the manufacturer and it can then focus on its core activities.’
‘The art of planning consists in standardising processes,’ Florian Karlstedt reports. The individual components pass through a large number of workstations. Each employee is able to work at a minimum of three places. A rotation principle brings with it variety, flexibility and experience. The distances walked, however, must not be too far for each working stage and the variability must not be too great. A pre-sequencing stage is therefore normally introduced if there are more than four variants.
But what happens if an incorrect part reaches the line from the shelf? In order to prevent any errors, the employees are supported via electronic displays in their work.
The working stages are specified on monitors at the relevant workstations. If there is more than one variant, a light signal, a scanner or both guarantee additional reliability. Before the employee makes use of a screw, he or she is directed and guided to the right position. There is also a special training zone to learn the necessary hand movements. A new employee can only start working on the line after he or she has been trained for several weeks. Very experienced assembly workers monitor the processes and intervene if anything goes wrong.
Depending on the quality required, components are either inserted by machine or by hand with the help of electronically supported screwdrivers. In contrast to torque screwdrivers, they not only tighten the screw, but record the precise pressure that has been exerted. As a result, it is possible to generate screw graphs and therefore track processes. If a screw graph is outside the target thresholds, there could be a material error. Checks are also made to ensure that the correct screw has been used.
‘If it’s necessary to turn the screw six instead of five times as specified, the wrong screw has probably been used. However, we can also recognise if a screw possibly has the correct length, but is of the wrong class. We can also see whether the component has been correctly tightened. Very detailed electronic documentation takes place for each screwing procedure,’ assures Florian Karlstedt.
The long preparation time for projects proves how important quality is in automobile production and for module assembly. Before a new factory is opened, pre-series models are first tried out and numerous tests are conducted. Once the manufacturer has checked the quality and capacity and a successful stress test has taken place at full capacity, the logistics specialist can then put the pedal to the metal – just as the car drivers will certainly do on the road.
Project Manager, Florian Karlstedt, describes the work at the 22 workstations, through which a rear axle passes until it has been completed at the assembly site in Shenyang. As soon as an order is received from a manufacturer, a sophisticated warehouse management process starts, which can be prepared and verified down to the smallest detail.
First or all, the order is checked: are we familiar with the axle and the components required, such as the specific suspension strut? Does the size of the brake disc fit? Does the combination make sense, do the types of bearings match and is the data correct? The automatic system checks the combination that is required and makes a note of it for future orders, too. If it does not recognise the procedure, further checks are performed by an engineer.
If the ordering procedure has been carried out correctly, the sequence, i.e. the chain, is determined for the production work. The warehouse management system reviews how many of the components that are required are already located on the line. If some parts are still missing, they are displayed on the employees’ mobile terminals; they then take a pallet and move the other parts to the relevant workstation along the production line.
Each line is different. In the case of the axles manufactured in Shenyang, the transmission is first connected, then the chassis cross member. The axle lies on a conveyor system and may only be supported at particular points so as not to damage it. The workpiece carrier is therefore moved along the complete assembly line. The drive shafts are inserted on both sides of the transmission and they have to snap into place firmly. A set amount of force has to be used for this and a small robot performs and checks this work automatically.
The next stage involves pre-assembling two bearings, which are to be attached at the chassis cross member. As they have to be attached at a position that is hard to reach, a workplace has been set up where the chassis cross member is turned. This makes it easier to screw in the bearings and the pre-assembled chassis cross member can be placed onto the line and attached to the transmission.
Swivel bearings are located on the sides of the axle and they are already prepared on a special pre-assembly line with six workstations because of their complexity. The pre-assembled module, the wheel mount, is also inserted and screwed into the chassis subframe. After several more screwing procedures, the axle arrives at a fairly large robot workstation.
The robot workstation consists of four robots because it is necessary to tighten a large number of screws here with very high levels of torque. Our employees initially tighten the screws slightly and the robots then handle the remaining work right round the axle – as in a ballet. A crane raises the axle into the air from the workpiece carrier so that the robots can reach the right places.
Following an intermediate workstation, the unit then passes to the axle setting bench. The axle is raised there and pressure is simulated, as if the axle was already in the vehicle. If this was not performed, the wheels would later be crooked. We measure the tracking and camber along the direction of travel, i.e. how the axle is aligned and what tilt angle it has. The robot then adjusts everything so that it fits perfectly.
The module passes through a camera cell during the following stage. The suspension struts are pre-assembled, clamped in an enormous press and screwed on. A final camera check takes place after the assembly work. A fairly small robot travels to critical positions on the axle. The target and actual values are compared using camera technology. If everything fits well, the finished axle travels to the end of the line. An employee then places it in a transport frame. That’s it!
Positioning a windscreen in a car seems simple. But that is far from the being the case. It requires special pins to align the windscreen in the vehicle so that it can be correctly inserted by the manufacturer. The challenge involves accurately attaching them to the smooth surface at the same position every time. Precision robots are therefore used for this, too.
Radiator modules have to be handled with particular care as the cooling fins can be easily crushed.
The engine is the driving force and the heart of any vehicle. The complete engine also includes control units, diesel and petrol pumps, a radiator and air-conditioning equipment.
Even the production of individual components is complex. Building a complete axle is based on a large number of possible combinations. Highly automated equipment combines Industry 4.0 and smart manufacturing.
Assembling interior elements like the central console or the cockpit may be less complex to organise, but the modules are particularly sensitive to scratches and dirt. There is also an enormous amount of variety here, e.g. USB connections or mobile phone charging points.
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