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Modeling of molecular healing for micro-laser welding of plastics with diffractive optical elements as spatial modulators

Grewell, David
http://rave.ohiolink.edu/etdc/view?acc_num=osu1123082743

Abstract Details

2005, Doctor of Philosophy, Ohio State University, Welding Engineering.
This work demonstrated, developed and characterized a new and novel technique for plastics welding using diffractive optics. Using diffractive elements laser beams were reshaped into various geometries that could be used for simultaneous welding of plastic in through transmission infrared welding. This novel technique also included the use of standard optics for resizing diffractive images for microwelding of complex geometries. In addition, new molecular healing models that accurately predict weld size and quality (degree of healing) were developed. The ability to quickly and economically form microwelds is critical to the development and commercialization of polymer-based MEMS and micro-fluidic devices. Thermoplastics offer significant advantages in the fields of biomedical engineering, communications, and in particular applications related to Micro Electro Mechanical Systems (MEMS). For example, the low manufacturing costs of polymers may allow industry to fabricate disposable MEMS. Rapid, consistent, and inexpensive assembly or packaging is critical to the commercialization of polymer-based MEMS. One method of joining that offers great promise of success for MEMS devices is Through Transmission Infrared (TTIr) welding. In the following studies, diffractive optics were used to reshape a laser beam into complex shapes for TTIr welding of plastics. These complex image shapes were then resized to micron-scale for micro-welding of plastics. In this portion of the study, the major findings included but are not limited to the following: 1. The diffractive optical elements could withstand as much as 80W of laser power 2. The efficiencies of the diffractive optics was greater than 55% 3. Micro-weld features as small as 300 microns with weld lines as thin as 75 microns could be produced 4. Cycle times as short as 50 ms are possible with TTIr welding with beam shaping diffractive optics 5. It is possible to produce hermetic welds that can sustain 0.7 MPa of burst pressure, which based on the weld geometry (average weld stress of 16 MPa). Another task of this work was to gain a better understanding of molecular healing so that micro-welds could be better understood. Because minimum weld size is affected by competing driving forces, namely thermal conductivity and molecular diffusion, these forces were studied. For example, as time increases heat conduction results in an increase in weld size, thus minimum heating time is desired to produce small welds. In contrast, molecular healing is also proportional to time, thus increasing the heating time increases weld strength. In addition, these two mechanisms are limited by maximum allowable temperatures, where the base material can degrade or ablate. Thus, increasing the temperatures (power) is also limited. In this study, it was found that the activation energy for molecular diffusion is temperature dependent. In addition, it was found that by considering the temperature cycle of a weld cycle, better models for predicting the degree of healing can be produced compared to traditional models that rely on a single peak temperature.
Avraham Benatar (Advisor)
247 p.
MEMS; Welding; Plastics; Micro-welding; Diffractive optics; Holograms; Molecular healing

Recommended Citations

Citations

  • Grewell, D. (2005). Modeling of molecular healing for micro-laser welding of plastics with diffractive optical elements as spatial modulators [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1123082743

    APA Style (7th edition)

  • Grewell, David. Modeling of molecular healing for micro-laser welding of plastics with diffractive optical elements as spatial modulators. 2005. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1123082743.

    MLA Style (8th edition)

  • Grewell, David. "Modeling of molecular healing for micro-laser welding of plastics with diffractive optical elements as spatial modulators." Doctoral dissertation, Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=osu1123082743

    Chicago Manual of Style (17th edition)

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This open access ETD is published by The Ohio State University and OhioLINK.