FOR 702

The idea of using ultrasound in the production of micro-moulded parts was formulated against the background that up to now there has been no optimally suitable injection moulding machine concept for the production of individual plastic parts with shot weights (including sprue) of less than 0.01 g. The ultrasound is used in the production of micro-moulded parts. The effect known from welding plastics is used to supply materials with the energy required for melting by means of ultrasound.

Integrated into the micro injection moulding process, the sonotrode can be integrated as a vibration-generating component of the ultrasonic system in the following ways: Either it is arranged in a separate plasticising chamber, from which the prepared melt is transferred to the injection cylinder, or it simultaneously serves as an injection piston that presses the melt into a cavity.

Objectives of the sub-project

In the project, the process idea of ultrasonic plasticising, whose feasibility in principle was already proven some time ago, was to be analysed for various unfilled and filled moulding compounds. Furthermore, it was to be examined to what extent findings already known from ultrasonic welding can be transferred to ultrasonic plasticising and what parallels can be drawn with regard to the processing limits of both methods.

The goals in the further course of the project were to fundamentally work out and model the physical relationships during heating, as well as to build up a broad process knowledge through the processing of different polymer materials. The advantages of the process as well as its restrictions were to be demonstrated for various questions regarding the process such as material damage or moulded part homogeneity.

Essential results of the 1^st funding period

In the first project phase, an approach for process modelling was developed and fundamental interrelationships of ultrasonic plastification were systematically worked out against the background of material behaviour and plant technology, including the parameters that can be changed. The interactions of the physical variables were presented in a comprehensive effect matrix. In practical tests, the amount of material to be melted, the material used, the selected excitation amplitude and the design of the plasticising chamber initially proved to be decisive for the plasticising result. This was particularly evident when granulate was used as the starting semi-finished product, as in this case external friction losses contribute to a large part of the dissipated energy and melt is increasingly formed in the contact surfaces.

With the process variant of direct injection, ultrasonic plastification was also used at an early stage to produce test components in small batches. In the course of this, the test stand was adapted and expanded in several stages so that it could be used to determine process windows, component production via direct injection, for investigations into material degradation and for analysing melting behaviour. The moulding of microcavities was also possible in detail, but there were limitations with regard to the flow lengths that could be achieved. In some cases, no molecular degradation at all could be determined via measurements of material degradation; in others, it was in the order of magnitude of conventionally injection-moulded parts.

Essential results of the 2^nd funding period

In the second project phase, the two heating mechanisms (contact surface friction and volumetric damping) were comprehensively analysed. The investigations were designed in such a way that both effects could be considered separately. The volumetric heating was carried out with geometrically defined plate material that exactly filled the volume of the plasticising chamber. Thus, the lateral movements and the associated contact surface friction could be minimised. The heating curves were documented with an IR mould internal thermometer and an infrared camera.

The temperature curve during plasticisation can be divided into two sub-areas, which are characterised by different heating rates. In the first phase of the process, moderate heating of the sample takes place. In the second sub-area, the temperature rises much faster due to the higher damping capacity in the area of the glass transition of the plastic. Heating rates of 1500-2000 K/s are possible here. After the short heating phases, the temperature stagnates at a level in the range of the processing temperature of the materials. Temperatures above this level are difficult to realise. The experimental investigations can also be represented well in a first approximation with the help of an analytical process model. Assuming an adiabatic plasticising chamber and isotropic heating in the plastic, the sample temperature can be calculated iteratively using extrapolated material parameters.

In addition to the analyses of the different plasticising mechanisms, the homogenisation potential of the process was also analysed. In the process, only a low mixing effect was found for ultrasonic plasticising, irrespective of the starting semi-finished product used. The achievable material homogeneity can only be slightly influenced by the process parameters and is primarily dependent on the semi-finished product used. For the production of high-quality micro components, it is therefore advisable to select powdered starting materials.

In order to demonstrate the potential industrial benefits of the process, ultrasonic plasticisation was integrated into micro injection moulding machine technology. By coupling it with a highly dynamic injection plunger, significantly higher injection pressures (of up to 2000 bar) can be realised. In addition, a dynamic mould temperature control was integrated in order to achieve a higher moulding accuracy. First analyses with this new process were carried out using a micro screw.

Publications

2012

Analysis and comparative assessment of different process technologies for manufacturing polymer micro-elements
Drummer, D.; Ehrenstein, G.W.; Hopmann, C.; Vetter, K.; Meister, S.; Fischer, T.; Piotter, V.; Prokop, J.
J. Mat. Sc. Eng. A, in press.

Expansion-injection-molding (EIM) by cavity near melt compression - about the process characteristic
Drummer, D.; Vetter, K.
CIRP Journal of Manufacturing Science and Technology

Long Term Properties of Injection Moulded Micro-Parts: Influence of Part Dimensions and Cooling Conditions on Ageing Behaviour
Drummer, D.; Meister, S.; Jungmeier, A.
Macromolecular Materials and Engineering (2012) (DOI: 10.1002/mame.201100379)

Präzise Abformung von Mikrostrukturen mittels Expansionsspritzgießen
Drummer, D.; Vetter, K.
Mikroproduktion 10 (2012) 3

Ultraschallplastifizieren kleinster Schmelzemengen
Hopmann, Ch.; Fischer, T.
Mikroproduktion 10 (2012) 2, S. 46-50

Galvanoformung in partiell leitfähigen Kunststoffformen
Prokop, J.; Lorenz, J.; Piotter, V.; H.-J. Ritzhaupt-Kleissl
Mikroproduktion 10 (2012) 2, S. 51-55

Orientierungsarme Mikrobauteile durch langsame Abkühlung
Drummer, D.; Meister, S.
Mikroproduktion 10 (2012) 4

Oberflächenveredlung von Mikrobauteilen mittels Metall-Kapillardruckgießens
Bach, Fr.-W.; Prehm, J.; Dellinger, U.; Holländer, K.; Möhwald, K.
Mikroproduktion

Innovative Prozesstechnologien für die Mikrofertigung
Drummer, D.; Bach, F.-W.; Hopmann, Ch.; Möhwald, K.; Piotter, V.; Fischer, T.; Meister, S.; Prehm, J.; Prokop, J.; Vetter, K.
Mikroproduktion 10 (2012) 1, S. 50-57

2011

Wechseltemperierung steuert Bauteileigenschaften
Drummer, D.; Gruber, K.; Meister, S.
Kunststoffe 101 (2011) 4, S. 46-49

Manufacturing of polymer micro parts by ultrasonic plasticization and direct injection
Michaeli, W.; Kamps, T.; Hopmann, Ch.
Microsystem Technologies, 17 (2011) 2, S. 243-249

Mechanical testing of micro samples produced by a novel LIGA related process chain
Prokop, J.; Eberl, C.; Funk, M.; Prüfe, P.; Lorenz, J.; Piotter, V.; Welz, M.; Ritzhaupt-Kleissl, H.J.
Microsystem Technologies, 17(2011), S. 281-288 (DOI:10.1007/s00542-011-1256-4)

Alternating Temperature Technology Controls Parts Properties
Drummer, D.; Gruber, K.; Meister, S.
Kunststoffe International 101 (2011) 4, S. 25-27

Expansion-injection-molding (EIM) by cavity near melt compression - about the process characteristic
Drummer, D.; Vetter, K.
CIRP Journal of Manufacturing Science and Technology 4 (2011) 4, S. 376-381

2010

Manufacturing of polymer micro parts by ultrasonic plasticization and direct injection
Michaeli, W. Kamps, T., Hopmann, Ch.
Microsystem Technologies 17 (2010) 2, S. 243-249

Tiniest parts, greatest benefit
Michaeli, W. Kamps, T.
German Research (2010) 2, S. 25-26

Mechanical testing of micro samples produced by a novel LIGA related process chain
J. Prokop, C. Eberl, M. Funk, P. Prüfe, J. Lorenz, V. Piotter, M. Welz, H.-J. Ritzhaupt-Kleissl
Microsystem Technologies Volume 17 (2010) 2, S. 281-288

New Aspects of Process-Induced Properties of Micro Injection Molded Parts
Jungmeier, A.; Ehrenstein, G.W.; Drummer, D.
Plastics, Rubber and Composites: Macromolecular Engineering 39 (2010) 7, S. 308-314

How mold inserts influence the replication of metallic microparts produced by electroplating into two-component templates
Prokop, J., Heneka, J., Lorenz, J., Moehwald, K., Piotter, V., Ritzhaupt-Kleissl, H.J., Vetter, K., Hausselt, J.
Microsystem Technologies, 16 (2010) S. 13-18

Multi-component microinjection moulding - trends and developments
Piotter, V., Prokop, J., Ritzhaupt-Kleissl, H.J., Ruh, A., Haußelt, J.
International Journal of Advanced Manufacturing Technology, 47 (2010) S. 63-71

2009

Manufacturing of nickel, copper, and ceramic micro parts through the MSG/MSE process
Prokop, J., Lorenz, J., Elsenheimer, H., Piotter, V., Ritzhaupt-Kleissl, H.J., Haußelt, J.
Saile, V. [Hrsg.]. 4M/ICOMM 2009 : The Global Conf.on Micro Manufacture, Karlsruhe, September 23-25, 2009. London : Professional Engineering Publ., 2009 S. 107-09. Engineering Conferences Online

Improving properties of microparts by slow cooling
Jungmeier, A.; Ehrenstein, G.W.; Drummer, D.
SPE Plastics Research Online. DOI: 10.1002/spepro.4038

Durchschaut - Strukturanalyse von spritzgegossenen Mikroteilen
Jungmeier, A.; Hülder, G.; Schmachtenberg, E.
Plastverarbeiter 60 (2009) 7, S. 36-38

Gießformen mit Kapillareffekt: Neuartiges Gießverfahren für Mikrokomponenten
Bach, Fr.-W. ; Möhwald, K.; Prehm, J.; Hartz-Behrend, K.; Roxlau, C.
Giesserei Erfahrungsaustausch, Heft 3 2009, S. 22-23

Prozessinnovationen mit Potenzial
Michaeli, W.; Hessner, S.; Kamps, T.; Klaiber, F.; Michaelis, I.; Schreiber, A.
Kunststoffe 99 (2009) 2, S. 93-97

Temperaturänderung bei der Kompression und Expansion von Kunststoffschmelzen
Rudolph, N.; Vetter, K.; Kühnert, I.
Kunststofftechnik 6 (2009) 4, S. 249-277

Charakterisierung der Struktur teilkristalliner Thermoplaste mittels Kleinwinkellichtstreuung
Jungmeier, A.; Vetter, M.; Schmachtenberg, E.
Praktische Metallographie, 46 (2009) 4, S. 173-193

2008

Manufacturing process for high aspect ratio metallic micro parts made by electroplating on partial conductive templates
Prokop, J.; Finnah, G.; Lorenz, J.; Piotter, V.; Ruprecht, R.; Haußelt, J.
Microsystem Technologies 14 (2008), S. 1669-1674

Mikrospritzgussteile langsam abkühlen
Lurz, A.; Schmiederer, D.; Kühnert, I.; Schmachtenberg, E.:
Mikroproduktion 6 (2008) 3, S. 46-50

Local Thermo-Oxidative Degradation in Injection Molding
Schmiederer, D.; Gardocki, A.; Kühnert, I.; Schmachtenberg, E.
Journal of Polymer Engineering and Science 48 (2008) 4

Schonende Spritzgießverarbeitung durch lokalen Ausschluss von Sauerstoff
Schmiederer, D.; Kühnert, I.; Schmachtenberg, E.
Zeitschrift Kunststofftechnik 4 (2008) 2

Einflüsse auf die Eigenschaften kleiner und dünnwandiger Spritzgussteile – Teil 2: Bedeutung der Wärmeleitfähigkeit des Werkzeugwerkstoffs
Lurz, A.; Kuehnert, I.; Schmachtenberg, E.
Zeitschrift Kunststofftechnik 4 (2008)

2007

Mehr Vielfalt in der Mikroformgebung
Piotter, V.; Plewa, K.; Prokop, J.; Hausselt, J.
Mikroproduktion 3/2007, Carl Hanser Verlag, München, S. 52-55

Mit neuen Prozessketten zu wirtschaftlicher Mikrofertigung
Michaeli, W.; Kamps, T.; Schmachtenberg, E.; Lurz, A.; Vetter, K.; Schmiederer, D.; Bach, F.-W.; Möhwald, K; Hartz, K.; Piotter, V.; Prokop, J.
Mikroproduktion 4/2007, Carl Hanser Verlag, München

2006

Einflüsse auf die Eigenschaften kleiner und dünnwandiger Spritzgussteile
Schmiederer, D.; Schmachtenberg E.
WAK Kunststofftechnik 2 (2006) 5