Demolding of micro-structured surfaces in the injection molding process

Tobias Struklec

Research output: ThesisDoctoral Thesis

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Abstract

Modern medical applications attempt to scale down entire diagnostic laboratories to a single polymer chip the size of a credit card. This is an enormous challenge for the manufacturing process because very small structures have to be realized. The demolding of the polymer part containing these structures in the injection molding is often the bottle neck for the part quality. Structures can be damaged and in some cases even the continuous manufacturing process can be disturbed. Understanding the demolding is therefore essential for the final part quality. To analyze this step, a special measurement device has been developed. Using this measurement tool, demolding forces can be measured in a reproducible way under process conditions. Demolding energies are calculated from this force. The demolding energy is shown to be an important indicator for the demolding step where lower energies mean better demolding and therefore less risk of damage to the part. The measurement device was used to investigate four influencing factors that affect the demolding step: a) polymer, b) geometry, c) mold surface and d) process conditions. Concerning a) the polymer, three thermoplastic polymers, one thermoplastic elastomere and two polymer blends were tested. To investigate b) the geometry, four different micro-structures in six configurations were tested. To look into c) the injection mold unit, several different coatings were tested to look into how different surface properties affect demolding. Finally, for d) the injection molding process, specifically the temperature management for the demolding step was emphasized. The investigations showed that there is not one coating ideal for all polymers but different suitable coatings for each investigated polymer. PMMA works well with TiN while TiN does not improve the demolding of COP. The placement of the micro-structure is also important, especially in combination with the process settings. High mold temperatures increase the demolding energy which can add to the effect of an unsuitable structure placement. Due to the complexity of the interactions improving the demoldability is not a straight forward process. Using this measurement device, suitable coatings for the application and polymer can be found easily. Additionally, an optimization of the processing parameters can be performed, reducing the number of substandard goods.
Translated title of the contributionEntformung von mikrostrukturierten Oberflächen im Spritzgussverfahren
Original languageEnglish
QualificationDr.mont.
Supervisors/Advisors
  • Holzer, Clemens, Assessor A (internal)
  • Lucyshyn, Thomas, Supervisor (internal)
  • Gobrecht, Jens, Assessor B (external), External person
Publication statusPublished - 2015

Bibliographical note

embargoed until 13-05-2020

Keywords

  • injection molding
  • micro-structures
  • demolding

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