Date of Award
Doctor of Philosophy (PhD)
Dr. Srikanth Pilla, Committee Chair
Dr. Craig Clemons
Dr. Gang Li
Dr. Hongseok Choi
Due to global competition, manufacturing firms in high-wage countries must target innovation in production processes and technologies that allow the mass manufacturing of customized products through highly efficient processes. Motivated by the concept of the integrative production systems, hybrid process of polymer injection molding and sheet metal forming, known as polymer injection forming (PIF), has been introduced to manufacture sheet metal-polymer components using a single tooling, machinery, and operating system. During this process, the sheet metal blank inside the injection mold is deformed by means of tool movement and/or by pressure of the polymer melt. As the melt cools, the injected polymer is permanently bonded to the deformed sheet metal depending upon the existence/use of any bonding agents.
Despite the wide application potential of the PIF process in the manufacturing of sheet metal-polymer hybrid structures, its scientific knowledge is still premature, and several challenges have prevented the implementation of this technology. From the experimental point of view, the lack of special tool design for PIF process and limitations of injection molding machines have confined previous work to stretch forming of sheet metal with no draw-in allowance. In addition, previous studies have mostly focused on the effect of injection parameters on deformation of sheet metal, thereby overlooking the specification of injected moiety as part of the final hybrid component. In theoretical studies, PIF process has been mostly compared with the hydroforming process and investigation was limited to only understanding the effect of rheological characterization of the polymer melt on pressure distribution and sheet metal deformation. Hence, the effect of coupled filling/forming condition of this process on melt flow pattern and modeling of PIF process, based on the particular behavior of polymer melt flow, was missed in previous studies. Finally, no applied solution has been so far suggested to mitigate the practical issues ahead of implementing PIF technology in actual industrial applications.
It is these issues that this dissertation addresses. Hence, the first part of this study is to conduct a holistic experimental investigation using a specialized setup and a new design concept of PIF mold for the purpose of applying the blank holder force (BHF) independently from the preset clamping force on injection machine. Moreover, a set of sensors and a data acquisition system are integrated to capture online in-mold process parameters as well as transient variables on the injection machine.
Using the proposed mold design, the interaction of BHF and injection rate is studied experimentally and compared with the results of a novel analytical-numerical simulation. Besides the successful conduction of this modeling approach, the superposition of draw-in value calculated from this analysis with pressure profiles captured by the sensor revealed that the drawing of sheet metal into the cavity happens mostly during the initial stages of PIF process, whereas wrinkling and flashing occurred afterward.
Using the specialized setup, the PIF process was investigated and compared with regular injection molding in terms of online process parameters, cross-sectional morphology and degree of crystallinity. The most important finding to emerge out of this study is that the polymer melt is packed to a much greater extent in filling/forming phase of PIF process and its flow pattern follows sheet deformation mostly in the axial direction which directly influences the distribution of pressure, temperature, crystallinity and the solidified layer.
Based on the aforementioned flow pattern, a general approach to modeling the PIF process is developed in this work. Regardless of the quick and reasonably accurate performance of this modelling approach to predict the pressure distribution of the melt flow and deformation of the sheet metal, the results of this study clearly showed the dependence of the pressure profile and deformation characterization to the shot volume and the blank material.
As mentioned earlier, there are several challenges ahead of using PIF technology in the actual industrial production; thick layer of polymer when there is deep deformation, nonuniform deformation due to pressure loss and the effect of shrinkage vs. springback. To mitigate these issues, the final part of this dissertation focused on a feasibility study integrating PIF process with Sc.F. technology. The results of this feasibility study clearly demonstrated that the capability of this integration concept in ensuring weight reduction and achieving microcellular structure while eliminating the issues related to shrinkage.
Farahani, Saeed, "Polymer Injection Forming: A New Age Technology for Manufacturing Polymer-Metal Hybrids" (2018). All Dissertations. 2482.