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Higher and higher speeds and increasingly complex production proceduresmake process monitoring for stamping applications indispensable. GermanBaumann GmbH utilizes force-acoustic emission technology and existingeddy-current technology which are both integrated into a press monitoringsystem by Schwer + Kopka.

Combined force and acoustic sensorssafegard stamping processes

Miro Ribaric, Production Manager at,Baumann GmbH

Lichtenstein (Reutlingen)

One of the production halls of Baumann GmbH in Lichtenstein near Reutlingen inSouthern Germany, smells of fresh paint. The company, headquartered in Switz-erland, is sprucing itself up. There is reason to celebrate: the 50th anniversary ofthe company is just ahead and enough reason for Miro Ribaric, production mana-ger at Baumann, to have the painters drop by to put a new coat of paint on the wallsin the production halls. With eleven sites on three continents, and about 1400employees world-wide, Baumann is a leading manufacturer of springs andstamped parts. In Lichtenstein, the focus is on three areas of production: stampingtechnology on Bruderer presses, stamping and forming technology on Bihlermachines and classic spring production of wire, e.g. on Wafios machines.Baumann develops and produces all stamping tools used in-house depending onthe product and the customer's wishes.

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Examining the process during production

If you develop, build and use tools to form parts, you also have to ensure that theparts are definitely okay. This is where Schwer + Kopka comes in. The effectivemonitoring of tools and production machines, as well as the objective recording ofmachine and operating data, are focus areas of the medium-sized owner-managedcompany from Weingarten and Hilden. Until now, Baumann has relied on “classic

Left:Baumann GmbHproduces manymillions of smalland very smallstamped parts,mostly for theautomotiveindustry.

A state-of-the-art machinerycomplex withBruderer andBihler stampingdepartmentsis maintainedin Lichtenstein.

In Lichtenstein, most automotive parts, including springs for seat adjustment, areproduced in three shifts. Miro Ribaric considers his facility a tier 2 supplier, sinceBaumann supplies, e.g., seat manufacturers who supply only the OEMs. In stripprocessing, stamped parts range in material thickness from 0.1 mm and go up to 3mm; the maximum diameters of the parts can reach 50 mm. Ribaric states thatthere are currently about 500 active parts being produced in his facility.

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controls” such as the worker himself. "Now we want to look into the process duringproduction, listen into the tool and map the condition of the tool," says Ribaric.

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On the left: Wolfgang Faul-haber, managing directorof Schwer + Kopka GmbHin Weingarten and Hilden.He supplies the measuringand inspection technology,as well as a hybrid solutionwith which signals fromdifferent systems can beprocessed.On the right: Miro Ribaric,production manager atBaumann GmbH. For him,quality assurance for thehigh-quality and precisestamped parts is indispen-sable. Therefore, he relieson the SK combination boxas well as the SK processmonitor and sensors.

The Bruderer stampingmachines are nearly allequipped with a processmonitoring solution bySchwer + Kopka.

The sensors are practi-cally integrated into thestamping die, in thisexample, a progressiontool.

The monitoring terminalis placed next to the stam-ping press. The sensorcables plug into the SKterminal. The followingsignals are measured:stamping forces andbinary signals, such asfeed, stock progressions,and part ejection. Thein-die force-acousticemission sensors areparticularly effective, per-mitting individual forming,piercing, blanking, andbending operations to bemonitored.

All photographs (10) by: D. Kuhn, BLECHNET magazine

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Up to now, the conventional eddy-current technology has been used to recognizeprocess issues caused by slugs, chips or scrap while the press was in productionmode. However, defective forming, cutting and embossing processes, as well assmaller stamping slugs that are formed into the material, cannot be recognized withthe eddy-current method. The eddy-current sensors measure the “tipping” of thestripper plate. When tiny stamped slugs are struck by the tooling, the stripper platehardly tips and the sensors will not see any deflection. Modern monitoring systemsuse hybrid force-acoustic emission sensors to sense different forming forces or torecognize very small foreign bodies. "The sound of the stripper plate is differentwhen it moves properly than when it contacts something foreign when closing. TheSK sensors “listen” and check whether the acoustic signals are correct. In short:The SK system verifies if the acoustic signals and forming forces are as they shouldbe." explains Wolfgang Faulhaber, managing director at Schwer + Kopka. Force-acoustic emission sensors measure, as their name says, force and acousticemission at the same time.

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Special pockets are milled into the plate to accommodate the sensors

Force and acoustic emission sensors notice even the smallest slugs

This figure shows a classic analogproximity sensor (eddy-currentsensor) with its’ sensor cable. Bothsensor and cable are protected by therecessed installation. SK's state-of-the-art evaluation software significant-ly increases the monitoring results ofthe existing sensors as well.

The monitoring system from SKmonitors older proximity sensorsand hybrid force-acoustic emissionsensors in parallel. Thanks to modernmonitoring software, the sensitivityof the proximity sensors has beenim-proved as well. For old and new tointeract, Schwer + Kopka has develo-ped a unique sensor combination box.

This tool uses both sensing systemsin parallel: eddy current and forceacoustic emission. The right cablecomes from the eddy current sensor,the left one connects to the forceand acoustic emission sensormounted in the top stripper plate.

With each stroke, the deflection of the plate is measured in the time and acousticdomains. In typical progression tools, there are several sensors in various stationsthat each record different data, e.g. the forming forces associated with the punchesor the coining process where the sensor is located above the embossing tool. Thehybrid sensors are not attached to the tool, but glued into a pocket in the tool with aspecial two-component adhesive. Faulhaber explains that the excellent sensingresults from the integrated tool sensors are achieved because of the uniqueinstallation process. This way, part of the tool “becomes” the sensor. Installed on thestripper plate, it can recognize stamping slugs, chips, or even small scrap pieces.

Baumann has also equipped their presses with force-acoustic emission sensors bySchwer + Kopka. A technician from Schwer + Kopka came to Baumann and dis-

cussed implementation with the toolmaker on site to determine where thesensors were to be inserted into theplate. The pockets for the sensorswere then milled, and on the next visitby the Schwer + Kopka technician,the sensors were epoxied into theplate using a two-component epoxyconsisting of an epoxy and a curingagent. During this same visit,Schwer + Kopka taught the sensorinstallation techniques to Baumannpersonnel so that the tool makerscould install the sensors themselves.The sensor wireways are alsointegrated into the plate.

Left: in this case, the monitoring systemby Schwer + Kopka is attached belowthe press controls. The combination boxwith the eddy current and force-acoustic-emission-signal processing optionshelps ensure that the millions of verysmall precision stamped parts that areproduced on the press are all of thehighest possible quality.

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The solution: the combination boxfrom Schwer + Kopka. This uniquehardware allows the force-acousticemission sensors and the eddy-current sensors to be monitored witha single device. The combination boxallows older eddy-current sensors tobe used until they are ready to bereplaced.

Due to the great number of tool sets in use, many of which have been equipped witheddy-current sensors, a huge investment would be needed for Baumann tocompletely switch to force and acoustic emission technology. To overcome thisobstacle, Schwer + Kopka has developed the SK combination box. It can be con-nected to stamping tools with eddy-current sensors and tools with integrated forceand acoustic emission sensors. Dynamic signal processing also automates theconstant adjustment of the monitoring limits in the eddy-current sensors.

Ribaric praises the idea: "The smart combination box automatically recognizes theconnected sensor. Is it a classic eddy-current sensor that measures the deflectionof the plate or is it the new sensor with force-acoustic emission technology?Depending on the sensor recognized, the system switches to force-acousticemission or eddy current analysis, saving our employees time and effort." The boxis designed to combine sensors by Schwer + Kopka with sensors from otherproviders.Ascreen displays the process data: the employee is able to compare theenveloping curve for the eddy current sensor signal to the acoustic emission signal.

The monitoring system is also intelligent: when a machine is retrofitted andequipped with a new stripper plate, the box can be made to load the newparameters with the push of a button and to learn the new correct signals resultingfrom this. This dynamic saves time and effort: when a machine, e.g. a fast pressstarts, it will first run “cold,” i.e. it will run a bit unstable, and show the same stripperplate variation, but eventually, will display more stable results once it warms up.Ribaric sees only benefits in this for its project: "The fact is, a temperature increasewill always occur when machines and tools are running quickly, requiring manualcorrections to the monitoring system much more often. Corrections are automatedin the Schwer + Kopka system today and performed automatically. This clearlyreduces process interruptions and unnecessary downtime."

The part data memory of the combination box can store parameter settings for up to3000 tool set I.D.s. The target curve of each individual tool can be recalledwhenever necessary. For example, the condition of a tool can be reviewed bychecking whether the current curve matches the target curve stored.

Combination box combines old and new sensor technology for best results

The future belongs to the system providers

Baumann GmbH sees its future as a provider of entire assemblies. "We want topush the envelope when it comes to technology," Ribaric explains. This requireswell-working process monitoring systems that are adaptable to our productionneeds. With the force-acoustic emission technology and the combination box bySchwer + Kopka, you feel well prepared to achieve this goal. For example, theBaumann site in Asia is equipped with the same process monitoring technology bythe Asian branch of Schwer + Kopka, strictly according to the motto of "globalizeand standardize".