By investing in a press line for truck wheel hubs, in which ten KUKA robots handle drop forged parts at a temperature of 1,250 degrees Celsius, Buderus Edelstahlwerke has achieved a lasting increase in cost-effectiveness. In their “hot job”, these six-axis jointed-arm robots are above all impressive for their high availability, flexibility and repeatability. Proof of their high performance is the fact that output has doubled.
Edelstahlwerke Buderus AG was founded in 1920 as Stahlwerke Röchling-Buderus in Wetzlar, Germany. Today the company is one of Europe’s leading producers of stainless steel for strip products, semi-finished products, drop forged and hammer-forged items and for forged bar stock in tool steel and structural steel grades.
Enhancing competitivenessBuderus Edelstahlwerke employs 1,650 people in various branches, one of which is the drop forging shop. About two thirds of the parts manufactured there are produced for the commercial vehicles industry and its components suppliers, and the remaining third for manufacturers of special machines and agricultural machinery, and customers in the process technology field. In 2004 the drop forging shop alone sold products weighing about 50,000 tonnes. Since all of the manufacturing steps, from the melt-down of the raw material to the final product, are carried out by Buderus itself, its customers all over the world benefit from quick and flexible order processing and high quality.
To enhance the competitiveness of its drop forging shop, Buderus Edelstahl invested an eight-figure euro sum in a fully-automatic press line with a press force of 8000 tones. The greatest single purchase in the history of the company, this investment replaced the old line and increased capacity. “On our new press line 1 we produce forgings with sophisticated forming requirements weighing from 20 to 70 kilograms per piece, with a maximum length of 600 millimeters and a diameter up to 450 millimeters”, explains Dipl.-Ing. Hans-Wilhelm Giese, Branch Manager for drop forged products at Buderus Edelstahl. On regular workdays, the line operates in three shifts. There is also an early shift on Saturdays and a night shift on Sundays.
A wide range of requirements
For the handling of the forgings, the user had KUKA Roboter GmbH, Augsburg, install ten six-axis jointed-arm robots of type KR 210, Series 2000. The old press line still used manipulators which had to be operated manually. Nine of the new robots were supplied in the version for foundry applications, developed by KUKA for operation in the harsh environments present in forge shops and foundries. For one thing, these robots have special paintwork and special seals at their motor and gear unit flanges. This makes them resistant to the very high temperatures of the forgings, as well as to moisture and dirt. The robots’ foundry wrists are painted aluminum white; their purpose is to hold gripper tooling made of special heat-resistant steel. The result: even more heat resistance for this particularly critical area.
The tenth robot used in press line 1 carries out spraying tasks. It is fitted with a protective suit to guard it against excessive fouling, and has a number of article-specific spraying programs.
In addition to heat resistance, Buderus Edelstahl has other requirements with regard to the KR 210s. “The robots must provide nearly continuous availability and high repeatability, despite their inhospitable environment”, says Hans-Wilhelm Giese. “High flexibility is also important, so that we can produce different product families in the line. The robots meet this need thanks to the manoeuvrability of their six axes – the possible alternative, a walking beam unit, could never provide this manoeuvrability.”
Another aspect of the KUKA robots’ flexibility is the ability to implement semiautomatic sequences for forging and trimming; an advantage derived from a control concept developed jointly with SMS Eumuco. In some cases, these operations are carried out manually and supported by the robots. Here the KR 210 concerned carries out the rough handling, thus reducing the physical strain for the operator. This method is useful for specimen forging, when starting production of new articles and for forging tests, for example.
Robots work hand in hand
The production sequence for press line 1 begins when a transfer system brings so-called billets from a warehouse to two high-performance circular saws. After the billets are cut into sections, the robot located downstream of the saw places them in forging containers or on an underfloor conveyor. After that, they are transported into the production shop itself, where they are transferred to a spiral conveyor. There the billet sections are moved to the elevated pick-up position of the second KR 210, which picks up the blank parts one by one and places them on the conveyor which moves through the induction heating unit. This furnace system heats the material continuously to a forging temperature of 1,250 degrees Celsius.
After the furnace, a robot picks up the red-hot billet section and transfers it to a hydraulic preforming press. A further KUKA robot places the preformed blank onto an intermediate support. The next two robots place the blank in the blocking die and then in the finishing die of the main forging press, since each part must pass through the two different recesses of this press in order to get its final form.
Normally, such presses use only one die per press stroke. Because, however, the two KR 210s installed at this 8,000 tonne main forging press can work in parallel, two dies are used for part of the product range. At the main forging press, the spraying robot is also in operation, blow-drying the recesses and spraying them with cooling lubricant.
An additional robot fetches the drop-forged part from the main forging press and places it once again on an intermediate support. After that, one of the KR 210s places in a trimming press, which removes the excess material. The robot which unloads the press is mounted in an inverted position. It sets the finished forging down on a cooling line. The same robot also places the forging burrs on a separate conveyor, which leads back to the user’s own steel mill.
Even more flexible thanks to tool changes
“Because we use the line to produce shafts, crown wheels, steering knuckles and gears, we have to exchange the press dies after batch sizes from 2,000 to 10,000” says Hans-Wilhelm Giese. “We can produce cost-effectively from a quantity of 2,000 units.” In the event of a tool change, Buderus Edelstahl either changes over from one family of parts to another, or within a particular family. A changeover between families means that the pincers and grippers for five or six KUKA robots have to be exchanged, taking up to two hours. Within a particular family it takes about 50 minutes. As end-effectors for the KR 210, the company uses two hydraulic gripper types, which are exchanged when switching to a new product family. Within families, only the gripper jaws are exchanged.
Well-trained operators program the robot and monitor the entire system. The robot controllers communicate with the higher-level central controller via Profibus. It is possible to modify individual parameters of the system, such as press forces and temperatures, without interrupting production.
Output doubled
By using robots it was possible to nearly double the output of the fully-automatic press line 1 compared to a similar line with three operators per shift, which achieves an average hourly production of 1.5 tonnes. At present Buderus Edelstahl achieves a throughput of 2.8 tonnes per hour with two persons who supervise and tend the system. The company plans an output of 3.5 tonnes of forgings per hour.
Also of note is the availability of the robots; despite the very harsh conditions, availability has exceeded expectations. A service agreement specifying a response time of two hours further ensures the availability of the system. In addition, the automation solution enables the user to manufacture parts which could not be produced manually. Moreover, thanks to the extended product range the user has been able to acquire orders which he would not have obtained previously. The automation solution has also secured jobs in Germany and improved working conditions.
Furthermore, Hans-Wilhelm Giese emphasizes the excellent working relationship between Buderus Edelstahl, KUKA Roboter and the press supplier SMS Eumuco: “Due to the close, constructive cooperation, we did not need any general contractor, but could take on this role ourselves.”
One of the advantages which helped KUKA to win the contract was the fact that KUKA robots can be operated in an inverted position – even in the size required for this application. This was not possible with the robots offered by the competitors. KUKA’s expert consulting services were also a major favorable factor, as was the geographical proximity of KUKA’s Branch Office West, whose prompt service contributes to the production reliability of press line 1.
This article was published in part in the July 2009 issue of CFN. To have your case history, product development, corporate news, etc, included in CFN’s newspaper and website, please submit to:
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