Page 18 - MetalForming February 2020

Better Process Monitoring via In-Press Detection
move out of spec. Other parts, coined or with critical angles, are susceptible to changes in die condition and sharp- ness, temperature, the amount of oil, or material thickness. There are many variables to control, which makes improved process monitoring an excel- lent tool.”
Depending on the application, sen- sors placed either on the machine, in the tooling or in the dies connect the press to a Brankamp X-series unit, enabling users to assess in real time process performance via an HMI.
Force sensors, placed in specific positions, monitor tool and machine performance related to the forces applied, according to Marposs officials. From these sensors, the systems learn the normal limits of the process. The control unit then observes the signals of each cycle and compares it with the stored limit curve. Sensing the move- ment of a signal outside of the envelope curve, the formed part is sorted out or the machine is stopped.
Throughout the process, the control panel shows force measurements and identifies the wheres and whats of parameters that are approaching or surpassing range limits.
“In simple terms, it’s like the picture game from when you were a kid,” Tucker says. “You have two pictures and have to find the differences between them. The X-series handles all sensor moni- toring with output to our presses. Should stoppage result, operators can evaluate the problem within the system.”
Especially in high-speed stamping, precise process monitoring can pay big dividends.
“Bruderer has machines that run 2300 strokes/min.,” Tucker says. “An out-of-spec condition may result in thousands of bad parts before a quali- ty-control check identifies a problem. A press working at 23 strokes/sec. to produce two-off parts takes perhaps 130 milliseconds to stop. That means six bad parts. Compare that to an oper- ation where parts are checked every few minutes at the minimum. Bad parts can add up very quickly when operat- ing at these high press speeds.”
An errant slug, a blob of oil...the slightest problems in a die can spell doom for intri- cate, small parts. The ability to detect and act upon such problems quickly saves tooling and minimizes the chances of producing bad parts.
16 MetalForming/February 2020
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For typical high-speed applications such as small electrical or connector parts, “standard die protection fea- tures can perform double-thickness and misfeed detection,” Tucker says, “but won’t detect a coin that’s out of tolerance or an incorrect angle. Sen- sitive monitoring can do that. For example, one stamping customer of ours placed a small piece of paper on the material strip going into the tool- ing and the monitoring system caught it at the first station and stopped the press.”
On-the-Fly Adjustment Keeps Presses Running
To this point, the discussion has revolved around detection of a bad process or a bad part. What’s the next logical step? Ideal is the ability to mon- itor the process and then make adjust- ments prior to making bad parts.
Servo feeds now dynamically com- pensate to ensure a match to forming speeds, so that’s not really an issue, according to Tucker. But monitoring the forces created during stamping provides real opportunities to adjust on the fly. Sensing and process moni- toring capability, such as that available with the Brankamp X series, enables sensors to measure precise stamping forces. Sensors placed on press columns can measure the full tonnage,
but acting on that information results in a coarse adjustment, according to Tucker. Sensors mounted on the die right next to a punch or a forming tool responsible for coining, however, pro- vides much-improved and precise ton- nage monitoring and control.
“The user can improve tonnage- monitoring resolution and then be more specific in controlling and adjusting based on the feedback from the process control system,” says Tucker. “The oper- ator can set a window to maintain a range of correct tonnage to produce good parts. Should tonnage approach range limits, the press control, when integrated with a system such as the X series, can adjust the ram shut height as the press runs to increase or decrease the tonnage and bring it back into range. The system essentially allows a metal former to zoom in on specific areas of the die to monitor and control.”
X-series systems offer various analy- sis functions as well as different coun- ters and storage media to ensure repeatability of various processes. The X3, representing the majority of sys- tems employed in Bruderer’s presses, provides this type of monitoring, along with eight channels for sensor signals and four others as zoom channels for detailed monitoring of specific, sensi- tive process areas. X5 and X7 models offer additional capabilities.