Extrusion of nickel–titanium alloys Nitinol to hollow shapes

Author: K. MüllerPresenter: Joshua FurnerDate: 16 September 2009

Function of Paper

• Describe results of hot extrusion of NiTi alloys• Development of extrusion principles for NiTi

alloys

References• 1. D. Stöckel, et al., Legierungen mit Formgedächtnis: Grundlagen-Werkstoffe-Anwendungen,

Kontakt & Studium, Band 259, Expert Verlag Renningen Malmsheim, 1988.• 2. D. Stöckel, Formgedächtnis und Pseudoelastizität von Nickel–Titan-Legierungen. Metall. 41

(1987), p. 5. • 3. H.-P. Kehrer and H. Nußkern, Erhöhung der umwandlungstemperatur von formgedächtnis-

elementen durch konstruktive maßnahmen. Metall. 46 (1992), p. 7. • 4. T.W. Duerig, A.R. Pelton and D. Stöckel, The use of superelasticity in medicine. Metall. 50

(1996), p. 9. • 5. W. Thedja and K. Müller, Strangpressen von superelastischen NiTi-Legierungen. Metall. 52

(1998), p. 12. • 6. K. Mueller, Grundlagen des Strangpressens, Expert Verlag Renningen Malmsheim, 1995.

ISBN 3-8169-1071-8.• 7. K. Mueller, E. Hellum, Indirect tube extrusion of dispersion strengthened aluminum, in:

Proceedings of the Third World Congress on Aluminum, Aluminum 2000, Limassol, Cyprus, April 15–19, 1997.

• 8. L. Tillmann, K. Müller, W. Thedja, H. Nußkern, Massivumformung von Nickel–Titan, ein Werkstoff mit außergewöhnlichen Eigenschaften, in: Neuere Entwicklungen in der Massivumformung, 1999, MAT INFO Werkstoff-Informations-Gesellschaft. ISBN 3-88355-282-8.

Technical details

• This paper discusses the extrusion process of a material with high deformation resistance

• Consideration is taken in material selection for die design

• Comparison of Direct and Indirect methods

Parameters• Friction force• Die force• Ram displacement• Extrusion ratio• Deformation resistance• Temperature

• Deformation resistance

• Specific Extrusion Pressure

• Extrusion Ratio

Design Principle• Indirect extrusion used because of reduced

friction forces• High affinity between NiTi and steel results in

welding• Cu canning of NiTi billet protects against this• Copper chosen because of its similar

deformation properties at high temperature

Indirect extrusion

Billet Preparation

Design Principles applied

• Extrusion of composite billet results in 2 nested tubes when copper is chemically removed

Data/tables/design discussed

Fig. 4. Force–displacement diagrams with — FG: total force; indirect extrusion (right); FM: die force; direct extrusion (left); FR: friction force.

Fig. 5. Deformation resistance kW of NiTi as a function of the billet temperature TB.

Fig. 6. Specific extrusion pressure Pspec of NiTi in relation to the extrusion ratio ln V.

Fig. 7. Deformation resistance kWC of NiTi/CuCr versus core fraction Vcore of CuCr.

Fig. 9. Limits for indirect tube extrusion with a moving mandrel.

Other design consideration

Technical Advancement and industrial impact

• Innovative solution to shaping NiTi alloys