The assembly line has set the pace in car production for more than a century. Now it is increasingly reaching its limits. Numerous derivatives and customisation options are making vehicles more and more diverse. The process and component variance in the assembly systems is increasing. This complexity is becoming increasingly difficult to manage in a rigid, sequential process. Audi is therefore the first manufacturer in the world to introduce modular assembly as a new and additional form of organisation. In this process, employees assemble components in a non-cyclical manner at so-called production islands. In addition, automated guided vehicles (AGVs) transport the required material to the stations according to the goods-to-person principle with high component variance.
The complexity of specific customer requirements is becoming more and more difficult to map with the classic assembly line. Its principle: a uniform cycle time for each product at each workstation in a fixed sequence. In contrast, modular assembly works without a conveyor belt and a uniform work cycle.
The rigid assembly line is replaced by dynamic processes with a variable sequence of stations and variant-dependent processing times (“virtual assembly line”). In preparation for later use in series production, the team led by project manager Wolfgang Kern from Audi’s Production Lab is implementing the concept in the pre-assembly of interior door panels at the Ingolstadt plant. “Modular assembly is one of our answers to the future demands on production,” says Gerd Walker, Audi Board Member for Production and Logistics. “We are using digital technologies here specifically for the benefit of the employees, while at the same time obtaining more flexible and efficient assembly,” adds Walker. “In addition, this project is a prime example of our open innovation culture, in which we develop networked production in agile teams.” In the pilot project, the experts confirm both the feasibility and the potential of modular assembly and at the same time build up further know-how. A major advantage of the flexible system: the company can employ people who can no longer be used in the production line due to physical limitations. “We can thus adapt the working environment to their conditions, which is only possible to a very limited extent on the assembly line,” says Kern. “We use more flexible automation in the production process to relieve the people.” Thus, all employees benefit from the even workload due to variant-dependent processing time instead of uniform cycle times. Ergonomic adaptation to individual needs is thus possible.
In the test operation, the orders no longer follow a uniform sequence, but rather the respective demand. Automated guided vehicles (AGVs) transport the door panels to the exact station where the component requires assembly. For example, the light package with cables and lighting elements is assembled at one station. Orders without a light package make a circuit around this station. In another station, an employee installs the complete sunblind, which is available for the rear doors depending on the equipment. At the assembly line, the volume would have to be divided between two or three employees due to the given cycle, which is not efficient and can lead to quality risks. If the orders pile up at a station, the AGVs drive the product to the required station with the shortest waiting time.
The positioning is accurate to the centimetre via a radio network. A central computer controls the AGVs. Quality processes can also be integrated with a camera inspection. Compared to the assembly line, it is easier and faster to react to irregularities. Consequential costs can thus be avoided. “We combine the high division of labour of the assembly line with a holistic approach according to lean principles and the new possibilities of cyber-physical production systems,” Kern explains.
Through the series pilot, the experts gather valuable knowledge and make deductions for series use. “By reducing the production time thanks to value-added orientation and self-control, productivity can be increased by around 20 per cent,” Kern calculates. In the next step, project manager Kern and his team want to integrate modular assembly into larger pre-assembly. Exactly where high variance and dynamics are present, in order to deal with them more efficiently than is possible today. “Decoupling the stations enables rescheduling with less effort,” says Kern. The flexible hardware with the automated guided vehicles often only requires adjustments to the software. The stations can be adjusted to supply and demand more easily than in the interlinked assembly line.