Thesis
Manufacturing of silk particles using diamond turning
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2022
- Thesis identifier
- T16270
- Person Identifier (Local)
- 201782248
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- Silk fibroin has robust mechanical properties with superior biocompatibility and biodegradability. Therefore, it has great potential as surgical sutures and scaffolds for cartilage reconstruction. In addition, silk fibroin particles (hereinafter referred to as silk particles) have shown significant capability as ideal drug carriers for anti-tumour and intra-articular agents. However, most manufacturing methods for silk particles are chemical-based or instrument-based, which requires chemical agents or costly instruments. Some mechanical manufacturing techniques, such as ball milling and bead milling, have been used to fabricate silk particles. However, the dimensional consistency of the fabricated silk particles is often poor, not to mention the low productivity of these techniques. More importantly, most manufacturing approaches can only make spherical silk particles and lack the ability to fabricate particles with helical or filamentous shapes and specified sizes that are believed to have better drug delivery efficacy. Therefore, this thesis aims to develop a new low-cost, chemical-free manufacturing process using diamond turning to obtain silk particles in the form of cutting chips whose geometries can be tailored by processing parameters. The machinability of silk fibroin in diamond turning was first investigated through cutting experiments from the aspects of specific cutting force and chip morphology. The ductile mode cutting of silk fibroin was achieved. Moreover, long helical silk particles with a tunable radius of curvature were manufactured using a sharp point tool with a feed rate of less than 2.5 μm/rev. The feed rate can be used to customise the radius of curvature of helical particles. Long ribbon silk particles were also generated using a round nose tool. The folding wavelength of the ribbon particles can be tailored by tuning the cutting speed and depth of cut. All experimental results demonstrated the feasibility of manufacturing geometry-controllable silk particles using diamond turning. A chip chart for diamond turning of silk fibroin was created, indicating that the breakability of silk chips increases at a reduced feed rate and depth of cut. This tendency is opposite to what is commonly observed on metallic materials due to the soft but highly tough property of silk fibroin. Although short and discontinuous folded particles were also manufactured, the dimensional consistency of the particles is extremely low, demonstrating the low chip-breaking efficiency when simply changing the processing parameters due to the ductility of silk fibroin.The serrated chip formation mechanism in diamond turning of silk fibroin was then studied using hybrid finite element and smoothed particle hydrodynamics (FE-SPH) numerical simulations. The Cowper-Symonds material parameters for silk fibroin were preliminarily determined to be p = 7 and D = 1140 s-1. The specific cutting force obtained by this model was 49.0% smaller than the experimental value. Nevertheless, good prediction accuracy regarding chip morphology was achieved. The simulation results revealed that the shear band formation was ascribed to the conjunction of two parts of the plastic deformation localized at the cutting zone. Specifically, one part propagates from the cutting edge to the free surface, while the other part initiates on the free surface and propagates towards the cutting edge. The link between the serrated chip formation and the hierarchical structure of silk fibroin was also revealed with the aid of this hybrid FE-SPH model. A high-frequency elliptical vibrator for diamond turning with tunable operational frequency and amplitude was developed as a chip breaker to obtain filamentous silk particles. The designed elliptical vibrator adopts a flexure-hinge structure that IV combines the leaf spring flexure hinge (LSFH) and the notch hinge prismatic joint (NHPJ). This configuration can not only transmit and connect the reciprocating displacements of the diamond tool but also offer an improved operational frequency. The finite element analysis (FEA) results indicate that a decrease in the neck thickness of the NHPJ can reduce the cross-axis coupling ratio. Meanwhile, a reduction in the thickness of the LSFH can reduce the first natural frequency of this vibrator and change the sequence of its vibrational mode shapes. A series of performance evaluation tests was conducted on a prototype of the designed elliptical vibrator. The test results show that this elliptical vibrator can achieve a high-frequency and non-resonant working mode with an acceptable cross-axis coupling ratio and thermal generation. Moreover, the elliptical tool trajectories with different amplitudes were generated by tuning the operational frequency, input voltage and phase angle. This elliptical vibrator can work at an operational frequency of up to 5 kHz. Its vibration amplitude can reach 2 μm. Preliminary diamond turning experiments were conducted on a copper workpiece to verify its chip-breaking effectiveness. Finally, the manufacturing of filamentous silk particles was studied through elliptical vibration diamond turning experiments and hybrid FE-SPH numerical simulations. The influence of processing parameters such as horizontal speed ratio (HSR) and depth ratio on chip breakability was thoroughly studied in cutting experiments and simulations. It was found that a large HSR and a small depth ratio can help to achieve effective chip breaking and obtain filamentous silk particles due to the reduced average tool velocity angle θa. The simulation results show that a decrease in the average tool velocity angle can decrease the ductility of silk fibroin and make the chip easy to break due to the reduced hydrostatic pressure and enhanced shearing action of the diamond tool. The critical average tool velocity angle θc was confirmed to be 22.6° for elliptical vibration diamond turning of silk fibroin. The average tool velocity angle should always be kept below this critical value to obtain filamentous silk particles.
- Advisor / supervisor
- Qin, Yi
- Luo, Xichun (Manufacturing teacher)
- Resource Type
- Note
- This thesis was previously held under moratorium from 31st May 2022 until 31st May 2024.
- DOI
Beziehungen
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PDF of thesis T16270 | 2022-06-08 | Öffentlich | Herunterladen |