Welding roof profile struts in robot cells - Processing a wide variety of variants with short cycle times
Whether passenger cars or commercial vehicles - structural components for vehicles must be manufactured to the highest quality standards, otherwise the consequences for stability and safety can quickly become fatal. At the same time, however, suppliers are under enormous pressure to reduce costs in order to remain competitive. Automated processes are often the preferred solution here to increase quality as well as to produce more efficiently and economically. DALEX Schweißmaschinen GmbH & Co. KG optimized a supplier's production with two robot welding cells. Different variants of roof profile struts for truck cabs are automatically fitted with nuts and sheet metal parts and welded - and all that in the shortest possible time.
Rising quality requirements, shorter delivery times, falling prices, growing competitive pressure - these are the challenges that suppliers to the automotive and commercial vehicle industries in particular have to face. An efficient and economical solution often lies in automated production processes. In addition to the proven standard machines, DALEX also develops robot cells, automated systems and interlinked complete solutions for all processes involved in resistance welding. A manufacturer of roof profile struts for truck driver cabs also used the expertise of the traditional company located in Wissen to rationalise production.
Challenge: huge variety
DALEX designed two robot cells for this purpose, in which nuts and sheet metal parts are automatically welded to the roof profile struts. "The special feature of the two robot cells is the processing of different roof profile geometries. To handle the unwieldy components, the robots require a type-specific gripper system. That is why we have designed a vertically arranged gripper station for the adaptation and storage of the respective grippers. The change is made online without stopping the system," says graduate engineer Hans-Werner Chwalisz, Sales and Marketing Manager at DALEX.
The robots handle the different roof profiles and bring them to the stationary projection welding machines. The welding stations are used, among other things, in C- construction. In contrast to conventional resistance welding systems, they have a narrow design so that they can still find space in tight robot lines or have reduced geometric interference contours, especially when working with unwieldy and large components. Welding nuts are then placed in various positions in the machines and welded to the profiles. In addition, the system attaches sheet metal parts such as angles to the roof profile struts. For this purpose, the roof profile struts are mounted in multifunctional workpiece carriers, where the additional sheet metal parts are then positioned and welded using robot-guided spot welding guns.
If such cells have manual input stations, these are usually duplicated. This way, the operator can supply the cells online while welding is in progress. The small parts - nuts and sheet metal parts - are transported to the right place via a magazine chain conveyor.
Ensuring production and quality
Since the supplier always produces all types of roof profiles required for a truck cab as a set, the two systems work in parallel in order to produce a certain number of profiles each. Hans-Werner Chwalisz: "In an emergency, for example in the event of a failure, one cell can partly take over the tasks of the others. This is not optimal, since the workpiece carriers have to be moved from one cell to the other, but it is still better than production downtime".
“The good into the pot, the bad into the crop" - DALEX's robot cells also follow the Cinderella principle. Sensors check the finished parts for incorrect insertion positions or welding forces. The so-called NOK parts (Not Okay parts) are then deposited in a defined sequence within the system, and the good parts leave the system via conveyor belts. This ensures that no faulty part gets into further processing and the high quality standards are maintained.
The enhancement: very short cycle times
Despite the unwieldy geometry of the different roof profile struts, processing should be very fast. DALEX also uses robot simulation for cycle time analysis to find out whether implementation is possible within a certain time window. "In simple operations, experience tells us how much time is needed for a particular task, such as opening and closing the gripper or handling movements," says Hans-Werner Chwalisz. "In the case of complex processes, however, these empirical values are not sufficient and lead to inaccurate results. This is where robot simulation comes into play. We simulate the real process with all movements and welding times. We then determine the possible cycle time from the sum of the input times and movement speeds.”
In this project, the cycle times were profile-dependent. In other words, there was an assigned cycle time for each profile. What was important here was not the individual cycle time, but that the annual quantities were achieved in the combination of the individual times. Previous cycle time analysis and simulation help DALEX to define what is feasible at an early stage.