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Title: Fundamental studies on the blow forming of polymeric micro-tubes and components
Author: Anyasodor, Gerald Njiribeako
ISNI:       0000 0004 5359 1668
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2014
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There is increasing demand for micro components in large quantities for medical as well as non-medical applications. To a large extent, the required component are hollowed shaped made from polymers such as micro-needles for drug infusion, microfluidic systems for the life-sciences, micro-pumps and fluidic connectors in micro-heat exchanger. However the manufacture of polymeric micro hollow (tubular) components requires innovative and economically competitive micro manufacturing processes. Blow forming processes are based on internal pressurization of an extrusion shaped polymer micro tube could provide an economic and reliable micro manufacturing process to the mass production of precise complex-shaped hollow micro parts. Despite the advantages of blow forming process in conventional polymeric tubes expansion, the application to micro manufacturing has not been investigated to date. This work represents therefore a systematic investigation of the polymeric micro tube blow forming process aimed at providing fundamentals for micro manufacturing applications. Based on reviews of micro forming, conventional stretch blow forming of polymers and other forming processes such as hydroforming, process configuration and machine and, tools design consideration were defined. Investigations to miniaturize the design consideration concepts were conducted, which focused on the influences of tube dimensions (handling, flow stress, materials forming limit, instabilities, and friction), quality of extruded polymer micro-tubes, complexity of polymeric material properties, heat distribution and heat transfer in the mold insert, new sealing, and pressurization technique and process cycle-time variations. Practical experiments supported by numerical analysis formed the basis of the investigations. Experimental investigations were conducted with a flexible-custom designed pneumatic-electric hybrid device, while numerical analyses were FE program based. For systematic blow forming processing tests, process parameters were varied systematically to analyze their influence. The parameters were: temperature (cavity temperature), pressure, elongation compensation force (axial tension), and cycle time. Dimensions of micro tubes used were: initial outer diameter dα₀ between 630 μm and 1300 μm and initial inner diameter di₀ between 500 μm and 1000 μm. Customized software was developed in-house, to implement the expansion process configuration defined. The process software was written in LabVIEW, although data acquisition and control were possible via appropriate hardware interface. In the experiments, the mould was first heated to a polymer processing temperature and other parameters were varied systematically to analyze their influences and interrelations in the process. The research objectives of a functional demonstrator as shown in the Figure on page II, were achieved through application of precise control of the process parameters. The manufactured machine specifications are: maximum internal pressure of 50 bar, sealing force 120 N, closing force 132 N and local heating temperature up to 600 °C (heating cartridge 100 Wcm-²) and a cycle times variation from 30 to 40 ms (without handling time). Machine design specifications supports processing of polymeric micro tubes with dα₀ below 1340 μm and di₀ below 1000 μm and a tube length of 60 mm. Operation on industrial automation control environment such as programmable logic controllers (PLC) was also supported, to enable integration on micro manufacturing platform for volume manufacture of hollow polymer components Experimental results conducted with the developed machine showed significant process temperature deviation for a failure free process and part compared to results from the literature for PA 6 and PC micro-tube materials. PET showed less deviation. Achieved suitable process parameters for PET were a maximum internal pressure of 18 bar and working temperature Tf of 90 °C, while optimal parameters to form PA 6 are maximum internal pressure, 15 bars and process temperature of 190 °C. Tube outer diameter of 1300 μm and inner diameter of 1000 μm was used in both cases to achieve maximum formed hoop ratio of 2. Cooling and handling were conducted manually and will require more investigations and refinement to enable integration in a full automated system.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available