Extrusion Die Swell Deformation Mechanism and Control of Medical Heteromorphosis Double⁃Cavitiy Catheter

doi:10.19491/j.issn.1001-9278.2020.06.009

Abstract

Abstract:

The accurate prediction and precise control are two key technologies for the extrusion die swell deformation of medical heteromorphosis double?cavity catheter to realize the precision forming. A comparative analysis was performed for the traditional and gas?assisted precision extrusion forming. The results indicated that the extrusion die swell deformation was induced by the secondary flow driven by the second normal stress difference of the viscoelastic melt. On the other hand, a large second normal stress difference was generated during the traditional extrusion forming, and the secondary radial flow induced by the second normal stress difference was the direct driving force of the deformation caused by extrusion die swell. This led to the extrusion die swell and ellipticity error of the medical heteromorphosis double?cavity catheter obtained by traditional extrusion forming, and its maximum die swell ratio and ellipticity error were 1.86 and 6.3 %, respectively. The second normal stress difference of the viscoelastic melt could be basically eliminated by the gas assisted precision extrusion forming of the medical heteromorphosis double?cavity catheter, which eliminated the secondary flow in the extrusion process. Therefore, the high?precision shape control could be realized for the medical heteromorphosis double?cavity catheter.

Key words: heteromorphosis, medical part, double?cavity catheter, die swell, mechanism, precision shape control

CLC Number:

TQ 320.66⁺3

Fucheng LI, Guofa ZHOU. Extrusion Die Swell Deformation Mechanism and Control of Medical Heteromorphosis Double⁃Cavitiy Catheter[J]. China Plastics, 2020, 34(6): 52-59.

Figures/Tables 23

Fig.1. Solid model and finite element model

η₀/

Pa?s

λ/ s

η_r

ρ/

kg·m^-3

J·mol^-1

T₀/℃

Tab.1. Material property and PTT model parameters

Fig.2. Relaxation time vs. morphology of die swell

Fig.3. Melt inlet volumetric flow rate vs. morphology of die swell

Fig.4. Die swell ratio vs. relaxation time

Fig.5. Die swell ratio vs. inlet volumetric flow rate

Fig.6. Maximum secondary flow vs. relaxation time

Fig.7. Maximum secondary flow vs. inlet volumetric flow rate

Fig.8. Influence of relaxation time on displacement distribution along the meridian

Fig.9. Influence of inlet volumetric flow rate on displacement distribution along the meridian

Fig.10. Influence of relaxation time on secondary flow intensity distribution along the meridian

Fig.11. Influence of inlet volumetric flow rate on secondary flow intensity distribution along the meridian

Fig.12. Influence of relaxation time on second normal stress difference distribution along the meridian

Fig.13. Influence of inlet volumetric flow rate on second normal stress difference distribution along the meridian

Fig.14. Influence of relaxation time on the distribution of displacements along hoop direction

Fig.15. Influence of inlet volumetric flow rate on the distribution of displacement along hoop direction

Fig.16. Influence of relaxation time on distribution of secondary flow intensity along hoop direction

Fig.17. Influence of inlet volumetric flow rate on distribution of secondary flow intensity along hoop direction

Fig. 18. Second normal stress difference vs. relaxation time

Fig.19. Second normal stress difference vs. inlet volumetric flow rate

Fig.20. Comparison curve of the second normal stress difference between traditional and gas?assisted molding

Fig.21. Comparison curve of secondary flow strength between traditional and gas?assisted molding

Fig. 22. Comparison of the final cross?sectional shape of gas?assisted and traditional extrusion molding

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