In the press hardening method, parts are heated to 930°C (1706°F) and then simultaneously cooled and hardened in the subsequent forming process, which gives the parts their extremely high rigidity. At its Waghäusel, Germany site, Schuler recently presented its new PCHflex technology, which has been under development for about two years and is a further development of the company’s “pressure controlled hardening” process.
The new process allows flexible and economical production of hot stamped parts with high output performance and consistently high quality, according to Schuler Managing Director Dr. Martin Habert. It also allows maximum process reliability and availability. “More performance pays off,” he said. “In this way, costs and energy consumption per part are reduced.”
PCHflex uses what Schuler claims are the fastest hydraulic presses with Dynamic Force Control and RingValve technology. With four parts per stroke (4-out mode), up to four million parts per year can be produced on one line.
By controlling pressure during hardening, the necessary press force can be distributed evenly over the part. The flexible bed cushion ensures—within the part and distributed over several parts—a uniformly high contact pressure, resulting in faster cooling, according to Jens Aspacher, Sales Manager Hot Forming at Schuler. “This ensures a reliable and optimized metallurgical transformation process,” he stated. The cooling time is claimed to be half that of conventional methods, while productivity and part quality are increased.
“The material properties are the same [as with other hot-stamping processes], but the martensitic transformation becomes more reliable within the part, which leads to higher content of martensite and higher part quality,” Aspacher added.
What makes the PCHflex technology unique, according to Aspacher, is that automotive manufacturers and suppliers are more independent of die and material fluctuations for process reasons; different manufacturing tolerances and sheet thicknesses can be compensated for more easily. “This reduces scrap as well as downtime and idle losses that would otherwise occur due to the reworking of dies, for instance,” he shared.
An additional benefit of the new PCHflex technology is that existing conventional press hardening dies can be used on these lines, he noted. And conversely, dies designed for PCHflex technology can be used on conventional lines.
A U.S. car manufacturer has placed an order with Schuler for four production lines to manufacture lightweight parts using PCHflex technology. Options have been agreed upon for four further lines. The supplier expects PCHflex to be in operation by the beginning of 2017.
“As a systems supplier, Schuler will not only be providing hydraulic presses and automation equipment, but also the roller hearth ovens and dies,” explained Habert. “Our employees will also be helping launch production in the first few months.”
Is the pressure-controlled process suitable for applications on on- and off-highway heavy-duty vehicles? “Absolutely,” said Aspacher. “Commercial-vehicle manufacturers are also affected by the need to reduce CO2 emissions, which is why they, too, have to make use of lightweight parts with extremely high rigidity. And hot stamping is the most economical way to produce lightweight parts.”
Paired parts such as left and right of the rocker, A-, B- and C-pillars, or the roof frame are typical applications for the process. “Now, there are more and more roof bows or connector plates under the back seat, for example. More or less all structural parts which do not need to absorb energy in crash situations [are possible],” Aspacher said. “Outer skin parts are not possible because of the rough surface.”
The press-hardening equipment supplier expects demand for such technology to grow in the coming years due to requirements for passenger protection and emissions reduction. In response, the company is planning to open a new Hot Stamping TechCenter at the Group’s main site in Göppingen, Germany, in early 2016. The technical center will serve both as a demonstration center as well as a location for training and research on press hardening.