Page 42 - MetalForming April 2012

Tooling Technology
In-Die Fastening
Along aTandem Press Line
...tells a value-added success story of increased throughput, reduced floor space and significant cost reduction.
This is a success story of the value of partnership and technology occurring at the BMW main stamping facility in Dingolfing, Ger- many. The technology employed is in- die fastening; the value is in the elimi- nation of secondary operations.
For high-volume production of wheelhouse reinforcements, BMW had been stamping the reinforcement one- out, in a line-die process with robotic station transferring. Then, during a secondary operation eight rivet nuts were inserted into each stamped part. In 2008 the plant initiated a project with the following goals:
• Increase stamping throughput; and • Reduce semifinished parts inventory Specifically, it hoped to double pro-
duction output by producing the rein- forcements complete in a 2500-ton tan- dem press at maximum press speed of 25 strokes/min. Additionally, the spec- ification stated that downtime due to the integration of the fastener-joining technology should be “negligible,” and not require press modification. The die was to be reconfigured for two-out pro- duction, designed to deliver—in the die—the 16 rivet nuts simultaneously to the parts.
One of the fundamental challenges of integrating fastener insertion into the stamping process was locating the sorting and feeding (S-F) equipment on the press bolster, to minimize die- change time. Also, fastener insertion required an additional die station— the last station.
Project Engineering
Tackling the project, a tool layout was first created to determine the space
available for the S-F equipment in the insertion station with the insertion die. Then the electrical and pneumatic scheme was planned, including the infrastructure needed to foster com- munication between the in-die tooling (piercing heads), S-F equipment and press control. Key was ensuring that the press only receives an enable signal when the nuts are correctly positioned in the pierce heads, achieved by locat- ing sensors in the pierce heads and die.
In the specified solution, the nuts were required to feed from two sides. Accordingly, two S-F units are located on the bolster, one on each side of the insertion die. Each unit provides the required air and electrical connectors. Also, the S-F equipment connects through a data bus line so they can communicate with each other and the press control. The connection with the press control initiates automatically at
press startup.
With the support of stamping-
sequence simulation software, the cus- tomer viewed how the die-protection system would function, ensuring that nuts would only feed when sensors sig- naled the presence of a stamped panel in the correct position in the insertion station. Also, no parts can leave the press without nuts properly inserted. Through sensors in the pierce heads, only after nuts are positioned and inserted correctly is the press-enable communication signal sent. The system ensures the avoidance of scrap and tool breakage.
Custom Sort-Feed Equipment
With little space available around the press, the S-F equipment had to be customized based on standardized modules. The magazine for the nuts was integrated into the S-F equipment and sized to supply enough nuts for a
40 MetalForming/April 2012
www.metalformingmagazine.com
BMW doubled production output of
wheelhouse reinforcements by pro- ducing the reinforcements complete in this 2500-ton tandem press, includ- ing in-die fastener insertion, at maxi- mum press speed of 25 strokes/min.