When German physicist AlexanderBehm was granted a patent onthe invention of the depth
sounder in 1913, certainly no one wouldhave imagined that, sixty years later, thisinvention would form the basis of aprocess for joining thermoplastic parts.
After the sinking of the Titanic, Behmattempted to develop an iceberg position-ing system based on the reflection ofsound waves.Although the depth sounderthat he invented was not suitable fortracking down icebergs, it was nonethe-less able to detect the position of theseabed and the distance and direction ofships. As we now know, whether the ul-trasonic waves that are emitted are reflect-ed, absorbed or transmitted depends onthe nature of the material that the wavesare aimed at.
During the Second World War, the navyneeded exceedingly large numbers of ul-trasonic generators.After the war, surplusstocks of magnetorestrictive oscillatorsand short-wave transmitters were lookingfor new uses, which were then found inultrasonic cleaning systems for the metaland jewelry industry. The small town ofPforzheim on the edge of the Black For-est blossomed into the “Gold Town”of theGerman state of Baden-Württemberg.When the sound generated by the clean-ing systems oscillated, however, thiscaused problems with television recep-tion. The Post Office Headquarters sentout its radio-interference measurementteam, which had also the ancillary task oftracking down viewers without licenses.The very young electrician, Walter Herr-mann, was amongst them.
From Cleaning to Welding
Having caught the ultrasonic virus, Wal-ter Herrmann, took up a position in theindustry in 1958 with the task of further
developing generators for ultrasoniccleaning, with a tube anode voltage of10,000 volts (Fig. 1). Up until then, the ul-trasonic frequency had been generatedby a self-oscillating final stage with ahigh-voltage tube (diode). One problemwas that the tube was air-cooled, and thefactory air which contained dirt andmetal repeatedly caused short-circuits,
Black Magic Rendered Reproducible
1 00 Y EARS O F KUNST S TOFFE
Looking Back. At the start of its industrial use, ultrasound was employed for
cleaning systems in the metal and jewelry industry. In the Sixties, a new
technology for joining thermoplastic parts then developed out of this. Walter
Herrmann is one of the pioneers.
Fig. 1. HF ultrasound generator from 1957 Fig. 2. Walter Herrmann (on the far right) with his first employees in 1961
Fig. 3. The first generation of ultrasonic welding machines
Translated from Kunststoffe 6/2010, pp. 18–20Article as PDF-File at www.kunststoffe-international.com; Document Number: PE110421
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which meant that the units frequentlycaught fire.
Walter Herrmann then went intobusiness on his own (Fig. 2) with the ideaof generating the ultrasonic frequencyvia a machine generator, employing thedynamo principle, with a low operatingvoltage of 200–300 volts. Alongside thenew machine generator, which was mar-keted in the electroplating sector, his ac-tivities also included the construction ofthe first cleaning units. When semicon-ductors began to gain ground at the endof the Sixties, the young company im-mediately recognized their potential forthe construction of ultrasonic genera-tors. A definitive switch to low-voltageoperation at between 100 and 300 voltswas now technically possible. The com-pany built semiconductor generatorswhich worked exceedingly well and pro-vided a suitably high performance. Atthe same time, the first ultrasonic weld-ing machines for plastics arrived in Ger-many from the USA. They only had alow output, however, and no applicationadvice was given on how to use them.Walter Herrmann saw good prospectsfor his generator and commenced devel-opment work on his own ultrasonicwelding machine (Fig. 3).
Pioneers in the “Ultrasonic Forum”
The industry pricked up its ears and tookan interest in this rapid and cost-efficientmethod of joining plastics, which addi-tionally only required a small amount ofenergy. There were, however, no scientif-ic findings on the joining process at thattime, or indeed on the process parame-ters, which meant that ultrasonic weldinghad an air of black magic about it, since
the technology operated perfectly well onsome occasions and then, at other times,would not work at all. The machine tech-nicians could only adjust parameters onan empirical basis at the customers’ butcould not set the machine for permanentoperation. There was no explanation asto why black plastic parts should requiredifferent parameters from white ones inthe same thermoplastic. Even identical
plastics in the same color produced dif-ferent results. But the raw material pro-ducers’ interest had been aroused, andeminent companies such as Siemens,Bosch, BASF, Bayer and Hoechst set upthe legendary first “Ultrasonic Forum”under the auspices of the Central Associ-ation of Electrical Engineering and Elec-tronics Industries (Zentralverband Elek-trotechnik und Elektronikindustrie –ZVEI), together with the ultrasonic ma-chine manufacturers Branson, HerrmannUltraschall and Dr. Lehfeld (now KLN).The aim was to jointly research the ultra-sonic joining process and to make it trans-parent.
An industry had been born, and it hadenormous potential. As the quantity ofplastic used increased, there was a simul-taneous increase in the demand for so-phisticated joining applications (Fig. 4).
Soundproofing and ProcessVisualization
The first machine to be serially producedwith soundproofing (type: Ultrasafe) at-tracted a great deal of attention at the “K”Plastics Fair in 1980 (Fig. 5). The reason for
Fig. 4. Rotaryindexingtable machinefrom 1977
Fig. 5. Advert forsoundproofing from1979 which boasted:“Not hearing, justseeing!“
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the success of this soundproofed machinewas the ancillary frequencies, which, at 20kHz, caused loud acoustic emissions andwere already a cause of concern for the oc-cupational health and safety associationsin the Seventies. A large number of cus-tomers thus constructed their own sound-
proofing around the machine which wasmade of plywood in some cases.
The next milestone to be reached wasthe visualization of the welding process.Only if the process was visible would itbe possible to influence it. The first im-ages of the welding process were createdwith a combination of an oscilloscopeand a Polaroid camera. By developing acontrol system that incorporated screencommunication and additionally inte-grating a linear encoder in the weldingmachine, it proved possible to display thejoining velocity on a graph. The blackmagic had given way to a visible andphysically comprehensible process. Withtheir competitors laughing at them,Herrmann Ultraschall, in 1989, broughtout the first dialogue-based series weld-ing machine that incorporated screencommunication (Fig. 6).
And it was precisely this transparencyprovided by the monitor that made it pos-sible to specify and adjust the welding pa-rameters.Test series showed that the qual-
ity was a function of a uniform, linear in-crease in the joining velocity. It provedpossible to reduce what, at times,were un-avoidable, high reject rates – in some cas-es, from 30 % to less than 1 %. This wasachieved through the welding machine’srefined process control system which in-
corporated comprehensive data acquisi-tion features. That meant the rapid detec-tion of errors and further process opti-mization.
These developments were only possi-ble because the proceeds were reinvest-ed as a matter of course. Then, in theEighties already, the first CAD work-places were set up. From that time on-wards, expensive high-performancecomputers with customized softwarehelped to make the oscillation behaviorof the sonotrodes perceptible and visi-ble on the basis of finite element analy-sis (Fig. 7). The amplitude distributionand stress distribution in the materialwere now depicted in color, and it provedpossible to reduce the high-level andcostly titanium waste incurred insonotrode production.
The company was then the first man-ufacturer to replace manual pressurecontrol valves by an advanced propor-tional pressure control system at thestart of the Nineties already, and the ul-
trasonic welding machine with all-nu-meric controls had been born. It wasnow feasible to modify all the parame-ters on a digitally reproducible basis.Since then, it has been possible to pre-cisely program and visualize both thecontact pressure – the so-called trigger
force – and the welding forces, employ-ing the dialogue technique in a weldingprogram. The next milestone involvedthe development of digital ultrasonicgenerators with the same high level ofefficiency, irrespective of temperaturefluctuations and the influence of com-ponent aging.
In recent times, ultrasonic technologyhas made its way into new fields of ap-plication, such as the sealing of packag-ing and the lamination and embossing ofweb goods, especially nonwovens.
Ultrasonic technology is thus con-stantly developing and it will be inter-esting to see what is on display at K 2010this autumn. One product can alreadybe hinted at here. It marks the outcomeof more than ten years’ developmentwork (Fig. 8). �
THE AUTHOR
THOMAS HERRMANN, born in 1963, is amechanical engineer and managing director of Herrmann Ultraschall, Karlsbad, Germany.
Fig. 6. The first machine with a screen from 1989 Fig. 7. FEA amplitude distribution Fig. 8. New development HiQ evolution
