The demand for aircraft with fuselage diameters between three and four meters continues unabated: Two thirds of all civil aircraft currently in use are so-called single-aisle standard fuselage aircraft with only one aisle. These models, also known as narrow-body aircraft, are mainly used on short and medium-haul routes. Airbus' share of this market has also risen continuously since the introduction of the single-aisle program: An A320 takes off or lands somewhere in the world every two seconds. With almost 7000 aircraft in service and more than 13,000 orders, this program family is one of Airbus' most successful models.

In order to meet this demand, structural suppliers such as Premium Aerotec are required to significantly increase the number of units and at the same time reduce production costs. In addition to shells and structural parts, the Tier 1 supplier also manufactures entire fuselage sections such as 'Section 19' for the Airbus 320 family at its Augsburg plant. Over the past two years, a partial shell production and longitudinal joint assembly line has been set up for this purpose, which, according to site manager Ulrich Amersdorffer, is currently the most modern aircraft assembly line in the world. Here, the partial shells are riveted and pre-assembled into half-sections.

The assemblies manually placed in component carriers are transferred to the automated area. For this purpose, a handling robot takes the component carrier and distributes it to one of the available transfer stations as required.

© Premium Aerotec

The centrepiece is an 80-metre-long system with three robots and three 'All Electric drilling/riveting machines', which was implemented entirely by Kuka Systems in collaboration with various subcontractors - such as the US company Gemcor. The team from the Augsburg-based robotics and automation specialist took the lead in planning and development, manufactured and procured all components and system parts, integrated control systems and, last but not least, coordinated all subcontractors.

The 'Section 19' in question is located in the aircraft fuselage between the end of the cabin and the last segment, the seat of the auxiliary power unit. This is where the pressure bulkhead is located, followed by the turbine for the auxiliary power units and the auxiliary connection points for the vertical and horizontal stabilizers. This part of the aircraft must be able to withstand high forces. Unlike the rest of the fuselage, which is conical, the section consisting of six partial shells tapers towards the rear - its special shape makes the individual segments more challenging to assemble.

In the first phase of the production process, the individual partial shells (skin panel) of the section must be connected. For this purpose, stiffening elements (stringers) and connecting brackets (clips) are fitted to the skin panels. The worker inserts the skin panel in a manual station, where it also receives an RFID chip for identification. Using this chip, the handling robots and riveting systems at the individual stations can recognize which component is involved and switch to the corresponding tool. Each component can thus be tracked seamlessly throughout the entire production process. In addition, the process information generated at the assembly stations is collected for each component, supplemented with additional information and then stored in the database. In the long term, this should minimize manual inspection and documentation work in the riveting process and replace it with automated documentation. The production process can also be monitored more efficiently: If a process or quality-relevant value is outside the defined tolerance, the corresponding machines stop.

"We use the performance data not only for documentation and to visualize the progress of the system, but also to optimise production processes," explains Thomas Vogt, Head of Shell Assembly. This makes it possible to identify bottlenecks in production, but also to support preventive maintenance. This allows for transparent production - fully in line with Industry 4.0. Premium Aerotec's goal is to eventually reach the point where every single component is equipped with such a chip from the outset. This would allow them to be tracked not only during production, but over their entire service life.

Component carriers converted to lightweight construction

Once the part shells have been provided with a chip and the assemblies have been inserted into the component carriers by the worker, automated processing begins. The handling robot picks up the component carriers on a linear axis and transfers them as required to one of the transfer stations, each of which is located within the two riveting stations. Previously, the component carriers were modular pallets made of steel. Together with the two partial shells attached to them, this added up to over 1000 kg - too heavy to be moved by articulated robots in the planned cycle production.

Together with Premium Aerotec, Kuka therefore developed a solution based on weight-reduced aluminum profiles. The result: a lightweight construction as a gripper on the robot and a component carrier that only weighs around 400 kg including the partial shell. The industrial robots - a total of three 'KR 1000 Titan' with a maximum payload of 1000 kg each - can move the load quickly and precisely, which significantly reduces production and assembly costs.

Parallel to the development of the component carrier, tests were carried out to measure how quickly and precisely a robot can position the partial shells on the component carrier. The results provided information about the rigidity of the overall system - important information, because before a riveting cycle is started in the automated cell, the positioning cycle must be completed without significant oscillation.

The components from the first automatic area are clocked out and transferred to the following manual station. This is where the half-shell assembly takes place.

© Rebecca Weingarten, B4BSchwaben.de

The automatic drilling/riveting machines are permanently stationed in the cell. This is where stringers, clips and edge beams are connected to the outer skin of the partial shells. Drilling, countersinking and rivet setting are fully automated: an image processing system takes over the local referencing using the tack rivets, then drills the hole and sets the rivet. Rivets of different lengths and diameters are automatically fed and processed - up to 1800 per part shell.

The component carrier and component are then transferred to a finishing station. The assembly is manually unclamped and transported to the next station using an overhead crane track system, where the partial shells are pre-assembled into half sections in further component carriers and then transported to the final drilling/riveting center using a rail-mounted floor conveyor. There, the outstanding connectors are placed and the half-section is completed.

Various controls integrated

A 'Sinumerik 840D' acts as the higher-level machine controller. Using the interface defined and implemented by Kuka between the Siemens controller and the 'KRC4' robot controller, workers can operate all machines via a single, familiar interface. It makes no difference whether they are handling robots or machines such as the automatic riveting machines from a US manufacturer, which are seamlessly integrated into the system.

All assembly stations are digitally networked and the entire process is controlled by a line control PC. Kuka's own control standard 'miKuka' is used to collect information, visualize it on the line and make it available to the customer systems (MES, SCADA, ERP). This means that the information from the various stations is clearly displayed at a central location and can be further distributed via network communication. The advantage: different user and station levels as well as different levels of granularity can be distinguished. The robot movement for the drilling/riveting process was programmed entirely using offline programming based on 'Cenit FastSuite' and a specially developed PIK (process-specific implementation kit).

According to Premium Aerotec, the new system, which will produce up to 50 sections per month in future, has significantly reduced waiting times, throughput times and logistics costs. In addition, arduous manual work steps, such as assembly or employee-guided transportation, could be made more ergonomic. In addition to a considerable reduction in workload, this also means new work processes with technically more complex tasks for employees. Last but not least, the experience gained with the new system should also pay off in the long term: In a further expansion stage, a similar concept is to be implemented with an automation solution for the assembly of half shells into complete sections.

Author: Josephin Della Rovere works in the Corporate Communications department at Kuka.