Complex system for cooking pot production - Fully automatic processing of a wide variety of variants
Every pot has a matching ... handle. Although the proverb is somewhat different, the automated welding system DALEX Schweißmaschinen GmbH & Co. KG has developed and built for a well-known German manufacturer of cooking equipment reflects the premise quite well. The system fully automatically connects different pot and pan models with their corresponding numerous handle variants and welds them at the correct angle - high-end technology with maximum precision.
Whether large or small, cylindrical or bulbous, with high or low edges, pans, saucepans, roasting pots, asparagus or stews - in order to further automate the processing of the numerous pot models, the manufacturer of kitchen equipment was looking for a partner to develop a welding system that would weld the various pot designs with the appropriate handles. "That was no easy task with the large number of variants. The system had to be able to accommodate six pot families with different diameters - a total of 46 variants - and twelve different handle types, such as U-handles and shaft handles or even both in combination. It then has to weld these to the corresponding diameter at the correct welding angles. All this happens in one product family fully automatically and of course with the highest quality. The operator only has to intervene during the filling of the system and during type-related set-up processes. Reproducible quality is a must, because especially with high-quality cooking utensils for high demands such as those manufactured by our customer, the user does not forgive any mistakes", says Hans-Werner Chwalisz, Sales and Marketing Manager at DALEX Schweißmaschinen GmbH & Co. KG. The solution is a complex high-tech welding system linking six robots and five camera systems.
(Almost) everything fully automatic
The system always processes a family of pots, for example cylindrical pots with diameters of 160, 200 and 240 mm, together with one type of handle. The allocation of the pot to the handle is managed via the system control. So the operator calls up a recipe on the control panel, and the system automatically adjusts itself to the pot diameter, angular position of the handle and camera presets for recognition of the handles. In addition, the robots automatically retrieve the corresponding grippers from the gripper station and park the gripper systems that are no longer required there. Merely certain welding tools have to be retrofitted by the operator before the start of production.
Regarding personnel requirements, the decisive operator intervention is found when equipping the rotary indexing magazine. Here the handles are filled into the magazine compartments in unstable deep-drawn films. Since each of these so-called "trays" holds up to twelve handles and the magazine can hold 80 trays, a capacity of 960 handles is created. The magazine is deliberately integrated into the corner area of the system. As a result, approximately one quarter is in the protected area of the system, and approximately three quarters of the storage volume can be refilled online by the operator.
A servo axis pushes the trays into the gripper chamber of the first robot. The robot clamps the tray, turns it around and places the gripper chamber on one of the belts. By pulling on the base plate, the handles together with the tray now lie turned on the belt. A second gripping system on the robot removes the tray packaging from the handles and disposes of it.
Camera monitoring ensures process reliability
"At this point it got tricky as the handles, when emptied from an unstable tray, never lie properly in the same position. In order to be able to weld them correctly to the pots, however, the handles must always be inserted into the welding station in a reproducible manner and accordingly gripped on the belts with the same accuracy," Hans-Werner Chwalisz describes one of the challenges. "That is why we are using two cameras at this point to detect the position of the handles on the belt. If the angle differences are narrow, even a third camera on another robot can refine the analysis." Once the exact position has been determined, Robots 3 and 4 take the handles and insert them into the lateral welding carriages of the welding station. These welding carriages can be adjusted in the approach path and angle so that different pot diameters and handle angles can be processed.
Since the pots also have geometrical constraints - it would be useless if the spout of a pot were in the same position as the handle - the pots must also be precisely defined with two additional cameras. Once the type and position of the relevant feature have been determined, the fifth robot places the pot in the welding station on a central mounting plate. Multiple steps allow different diameters to be placed. The pot is clamped with a vacuum gripper to ensure reproducible positioning.
Once the individual parts have been positioned, the handles are precisely welded to the various pots at the correct angle using resistance projection welding. Finally, the sixth robot removes the finished part and places it on the discharge conveyor. Alternatively, the robot brings the pot to a test station for quality assurance in a defined cycle, where the desired strength values are destructively tested.
Quality assurance and resource conservation included
Of course, a system with such complex processes also automatically detects if an incorrect handle or pot enters a recipe cycle: Here, the system goes to STOP with a predefined shutdown routine. Incorrect grips first run into the rejects box because they have been detected as missing parts. The fault memory then switches off the system after a defined quantity of missing parts has been detected.
"We are particularly proud of the outstanding performance of our employees, because the variety of variants meant that automation of the process in this complexity was previously considered almost impossible. We have succeeded - and with excellent results: an average cycle time of 8 seconds, a staff requirement of 7 to 8 percent and an autonomous running time of 100 minutes until the trays are refilled make the system a technical highlight," says Hans-Werner Chwalisz, proud of the potential of the DALEX specialists.