Schuler Group, Canton, Mich., offers a heat-treating technology called press-hardening to increase the strength of steel parts. In this technology, blanks or pre-formed parts are heated in a furnace to a temperature of 930°C, then placed into the press as quickly as possible, within just 10-12 seconds. The press remains closed for a few additional seconds during the forming process. During this time, the parts are cooled and hardened.
The cycle times range from 8 to 30 seconds. In combination with a two-slide press and Schuler’s fast feeder solutions, however, the productivity of the PCH concept can be significantly enhanced. “A key factor in determining high quality and short cycle times is the fast heat transfer from hot part to cooling water,” stresses Schuler’s expert. “The weakest link in this chain sets the speed.”
“The determinants of the part’s cooling period include the transferred energy, which depends heavily on the thickness of the blank, as well as the heat transfer between blank and die,” adds Dr. Dirk Haller. “Further factors are the die’s thermal conductivity and energy dissipation, i.e. the number of cooling channels, the temperature of the cooling medium, and the flow in the cooling channels.”
The benefits have led to a dramatic increase in the number of press-hardened parts produced around the world – including bumper supports, roof frames, sills, B-columns and tunnels: compared to around eight million pieces in 1997, the figure reached 124 million by 2010, and growth is expected to continue in the next few years.
