Order based variant manufacturing of a modular mounting box series, batch size 1 – how Striebel & John GmbH & Co. KG safeguards the flexibility and high efficiency of its mounting box production with a high degree of automation and a KASTO sheet metal storage system
Processing about 9,500 tonnes of steel sheets a year in a range of qualities and with various surfaces (black, galvanised) as coils or plates for power distribution systems – a complicated task for the ABB Group company Striebel & John GmbH & Co. KG based in Sasbach, Baden-Württemberg. Founded in 1958 by Franz Striebel, this company has evolved into a specialist in the development and production of mounting box and power distribution systems, in which the ABB Group participated in 1993 with 51 % and employs today a workforce of about 450. Above all, the ABB management were highly impressed by the high innovativeness of Striebel & John that had found and still finds testimony in its great many pioneering products and system developments. It goes without saying that Striebel & John sees itself today as a leading manufacturer and supplier of power distribution systems for the electrical trade and switchgear production. Divided into consumer units; compact distribution boards; and wall mounting, meter, floor standing, and switchgear cabinets, the product portfolio covers every conceivable application in both commercial and industrial environments. The electrical system planners and designers receive sound support in the form of services like, for instance, the software package StriePlan, and the fitters and system builders benefit from the fast availability of the mounting boxes, cabinets, and accessories for the internal configurations. In turn, the fast availability and the renowned high quality of Streibel & John products are due to a very high level of inhouse production, an output that can be regulated with the corresponding flexibility, and – of course – the appropriate machinery and indispensable expertise.
The objective: consistent automation from sheet metal storage system to final mounting box production
Roland Schnurr, Head of Production at Striebel & John, expresses the production philosophy as follows: “At our sheet metal parts production and assembly lines, we have to manage four series, namely compact distribution boards, meter and other cabinets, and the TwinLine and TriLine series. Our customers in the electrical systems wholesale and switchgear production sectors no longer manage storage systems, so we are forced to provide a highly flexible job controlled manufacturing of batch sizes from single batch. This is economically viable only with a certain, very high, yet practical degree of automation. For this reason, automation extends to a great many of the processes in the preproduction of parts, like punching, bending, and shaping, and in the final production involving welding and bonding. In addition, we also apply powder coatings in the standard colours on site, whereas special colours are handled by external providers. In addition to the product variants in size, width and depth as well as technical function, also the type of interior design distinguishes in different regions, from which the customers are also the kind of interior finishes, so that the assembly is primarily manual work. ”
When a modular system now needed new products, the following specifications were formulated for their production: Delivery time 48 h, batch size 1 in sheet metal parts production and assembly welding, inline setups, continuous component provision, production stock from ongoing orders for no-break final production through welding, access to all preproduced and order relevant components. The last of these are standardised rear panels in a range of sizes that are welded to other components to form complete mounting boxes or cabinets in final production. This takes place in a robot system that consists essentially of welding and spot-welding robots with glue application, two changeover table served by a gantry robot system and an automatic sheet metal storage system of the type UNITOWER B 3.0 from KASTO Maschinenbau GmbH & Co. KG of D-77855 Achern-Gamshurst.
Reality: Batch size 1 in the many variants of mounting box production
The task of the automatic inline storage system is to supply the welding cell with the various rear panels mentioned above. It therefore functions as a buffer and interim storage system that can be supplied externally and inline with parts that are needed either immediately or at a later time. The sheet metal storage system presents a total of 35 pallet storage locations arranged in two blocks that then provide the required quantities of the various rear panel geometries. The pallets are designed for payloads up to 2500 mm long, 1545 mm wide, 130 mm high, and 3 t in weight. The operating gantry crane traverses between the two shelf blocks and handles all of the storage and removal operations. Outside of the cell area downstream of the transverse storage station, it utilises the carriage for the removal and return storage systems. Inside the welding/gantry robot cell, it utilises the carriage for the longitudinal transfer system. The pallet changeover time from the transfer station to the gantry robot system is just 135 seconds, starting from the carriage’s parked position. This 135 second cycle includes the carriage’s traverse into the shelf block, the return of the pallet no longer needed, the retrieval of the requested pallet, and finally the traverse to the position for transfer to the gantry robot system and automatic loading on the changeover table. The 135 second cycle runs parallel to the welding cycles of the robots.To minimise storage and removal times, the operating gantry crane traverses in the hoist at speeds up to 16 m/min, and the push/pull mechanism for the pallets up to 20 m/min. When asked about the particular features of this custom storage and material flow solution, Martin Stöckle, Head of Sales Team 1 at KASTO Maschinenbau GmbH & Co. KG, answered as follows: “We’re working here with two pallet carriages that operate independently of each other. The storage/removal carriage for transverse station I features a hydraulic lifter with pistons for the crane or side loader provision and removal of the pallets as well as an optical contour monitor. The carriage for transporting the sheet metal into the transfer station for the gantry robot system also has, of course, an optical contour monitor and, in addition, a fanning magnet for the reliable separation of the stacked metal sheets. The controller for the KASTO storage system UNITOWER 3.0 and for the two carriages is responsible for all storage and material flow operations, and it interfaces with the controller for the gantry and welding robot cells. In practice, it’s possible to switch in auto or manual mode. The system is therefore available at all times for the constant supply of material.”
The success: 50% growth in capacity with 40% fewer personnel hours
According to Roland Schnurr, this works so well that the worker at the setup station need only insert the side panel elements, secure these in the clamps, and then release auto mode initiation. “The gantry robot retrieves a rear panel on the carriage in the transfer station and places it precisely in the receivers for the spot-welding operations and glue application. The robot system tools itself according to the mounting box type and signals to the storage system controller which of the stored rear panel variants must be provided next. Afterwards, everything proceeds automatically. After the boxes are welded and glued, they are placed on a pallet by the robot. The operator removes only the pallet loaded with cabinets.
“Aided by the robot system and the automated material supply, we were able to increase our capacity by about 50%, and that with 40% fewer personnel hours compared with the costly manual operations earlier. This growth in capacity allowed us to master with ease the sudden increases following the start-up phase for the new product line, and that without additional personnel. This, of course, had a very encouraging effect on our ability to deliver in time,” summarised the Production Manager at Striebel & John GmbH & Co. KG. “At the same time we are capable to flexibly provide our customers with batch size 1 in a very short time”, was the conclusion of Roland Schnurr.