Since the beginning of 2016, Trepte Metall- und Fahrzeugbau GmbH has been welding some of its aluminium assemblies with a "PA-ET-2PD-XL" welding robot system from ERL Automation GmbH. Previously, the company carried out all welding work manually, which took a lot of time due to the complexity of the products and the number of components to be welded. Thanks to the new system concept, the user benefits from a consistently high weld seam quality and shorter production times.
Trepte GmbH, based in Hartmannsdorf near Chemnitz, is active in the field of metal and sheet metal processing, manufactures individual fittings for special vehicles and offers high-quality aluminium composite panels and their processing. Founded in 1979, the company now employs around 25 people and manufactures its products using a wide range of processes on a production area of 2000 m² - from sheet metal to assemblies. For this purpose, the company has modern machinery at its disposal: Laser systems for cutting the blanks, bending machines for edging the sheets and, more recently, a welding robot system from ERL Automation GmbH for welding the assemblies.
Initial contact with welding robots
Although Trepte already had experience with automated production processes, the specialist for metal and vehicle construction entered new territory with the automation of welding production, as all welding work had previously been carried out manually. Due to the complexity of the products and the number of components to be welded, this had taken a lot of time: The aluminium constructions consist of a large number of individual parts - a welder needed up to 45 min. to complete such an assembly manually, for example, and possibly a little longer if reworking was required. "So far, we have produced at the limits of our capacity," reports plant manager Peter Hake. In order to create capacity for further orders and to achieve consistently high quality, the company decided to largely automate welding production with a compact robot cell from ERL Automation. Trepte's main requirements when considering the purchase of a new machine were high weld seam quality, short processing times and easy handling.
ERL Automation designed a system for the metal and vehicle manufacturer from Saxony that exactly met the requirements: a compact welding cell of the type "PA-ET-2PD-XL", consisting of a Panasonic welding robot with two work stations. The project also included installing an extraction system, enclosing the work area with a protective fence and providing fixtures to hold the components to be welded. The programming of the components and training for the future robot operators ensured an optimal production start-up.
Six-axis robot for aluminium welding
ERL Automation provided a complete solution for fully mechanical MIG/MAG welding of large and small series. The system is equipped with a compactly designed welding robot from Panasonic, which is characterized by high torsion resistance and works with the latest servo technology. This makes it possible to achieve high speeds in the positioning of the welding torch while at the same time using smooth motion sequences. "It feels as if the robot is welding continuously. The positioning times are so short that you hardly notice them," explains Managing Director Jörg Trepte.
The robot processes the components at two stations, which are brought alternately into the robot's working area by an electrically operated 180° transfer table. The stations are separated from each other by an anti-dazzle device - while the robot is welding on one side, the finished component can be removed and the fixture can be reloaded on the other side. This way, the robot is almost permanently in operation and the system is optimally utilized. In addition, the stations are each equipped with an additional axis that enables the welding seams to be applied to each side of the component without reclamping.
The robot meets the high quality requirements by being equipped with the "Active Wire Process (AWP)" for aluminium welding. The advantage of the "AWP" technology lies - as the name suggests - in the active wire feed. A constant arc is generated by a permanent forward and backward movement of the welding wire electrode and the number and size of weld spatters is reduced. The process variant is suitable for thin sheets as well as for those with medium thickness and achieves high-quality weld seams almost without splashes due to the pulsating wire even in forced positions. The optimum welding wire supply is ensured by the "Wire Booster" - a wire feeding system to support the conveying of the welding wire electrode in unfavourable conditions. When traction is exerted on the welding wire by the wire feed unit on the robot, the "Wire Booster" intervenes and the wire is then conveyed in a supportive manner, ensuring a stable arc.
The welding robot is equipped with the "Panasonic WG3" robot control, which is also suitable for beginners due to its ease of operation. A simple and well-structured programming interface and a 7" colour display make the user's work easier. In addition, the "WG3" control system has a welding navigator that assists in selecting the optimum welding parameters based on the component data. In order to ensure an optimal production start-up, the future plant operators were able to familiarize themselves with both the control system and the entire system in a training course lasting several days.
To protect the system operators, both the welding work area and the insertion area are surrounded by a protective fence. The insertion area is entered through a safety gate protected by a light barrier - for service or maintenance work, operators can access the robot via a built-in service door. In addition, a TCP (Tool Center Point) checking station is integrated into the safety fence, which allows wearing parts to be replaced and the TCP to be checked without having to enter the system. For process visualization, a control unit with touch display is attached to the front of the safety fence, which saves Trepte's system operators time when operating the system. It enables convenient programme selection per table without having to resort to the hand-held programming device, as well as an automatic query of the service status. In addition, fault messages are automatically determined and displayed - they can thus be remedied immediately without the need for a time-consuming cause research.
The component programming was carried out by ERL Automation using the offline programming software "Panasonic DTPS". The software enables the complete programming and simulation of the robot's movements as well as the calculation of the cycle times. The offline programming allowed ERL Automation to programme the robot on the personal computer, optimize programming sequences and thus allow it to be put into service quickly.
The ultimate discipline of fixture construction
Probably the biggest challenge for the engineers at ERL Automation was the development of the fixture for holding the welding components - it is not for nothing that fixture construction is considered the supreme discipline in automated welding. "The art is to place the fixtures in such a way that the individual parts are optimally fixed, all weld seams can be applied by the robot without reclamping and at the same time the positioning times are kept as short as possible," explains Michael Saxstetter, Head of Project Management at ERL. Trepte's aluminium assemblies are complex products with many angles and different dimensions. Depending on the variant, up to 90 welding seams have to be applied. "This was a challenging task - but definitely solvable. We measured the components precisely and simulated various clamping points and ultimately came up with a solution that allows Trepte to load the robot system easily, precisely and efficiently. Of course, the know-how that Trepte's employees have gained from manual welding of the component has also been incorporated," he explains. While the robot welds on one side of the table, the fixture is loaded on the other side by the respective system operator. All they have to do is place the individual parts in the right place and close the clamping handles. All parts are fixed in place in just a few steps.
The new system has been in operation since the beginning of 2016. Only two and a half weeks after commissioning, the user was already welding various aluminium assemblies completely with the robot. Works manager Peter Hake is confident that more aluminium products will be converted for welding with the robot in the future.
