PSI - Issue 69

Roman Karelin et al. / Procedia Structural Integrity 69 (2025) 35–40

37

a

b

Fig. 1. (a) general view of the NiTi rod cross-section after cutting; (b) a shell for screw rolling, a shell for rotary forging and a rod with a diameter of 5 mm.

As a result of the above technological operations, nickel-titanium sleeves with an external diameter of 40.0 mm and a wall thickness of 10.0 mm for rolling on screw rolling mills, sleeves with an external diameter of 15 mm and a wall thickness of 5 mm for rotary forging and rods with a diameter of 5 mm, suitable both for subsequent metal pressure treatment and for the manufacture of functional elements by turning or erosion processing, were obtained. In the present paper only results of experimental screw rolling will be performed, since it is the first stage of the developed technological scheme. Experimental screw rolling of the obtained shell with an external diameter of 40 mm and a wall thickness of 10 mm was carried out on a three-high screw rolling mill SVP 70. Deformation was carried out at a temperature of 1000 °C. A rod made of stainless steel with a diameter of 18.5 mm was used as a mandrel, and laundry soap was used as a lubricant for the mandrel. The rolling process route and the dimensions of the shell before and after each pass are given in Table 1.

Table 1. Rolling route of a NiTi SMA shell.

D/H/L * before rolling, mm 40,0/10,0/250 37,0/9,0/215 35,5/8,2/240 34,1/7,3/253 34,5/7,3/223 31,0/5,3/180

d/h/l * after rolling, mm 36,7/8,9/295 35,3/7,8/270 34,1/7,1/253 33,5/6,8/253 30,5/5,3/300 27,5/4,0/218

Pass No

Treatment designation

Heating time, min

Relative strain ε , %

1 2 3 4 5 6

35 35 35 35 35 35

18 13 11

1

- -

5

2 3 4

26 30

Rolling was carried out to a tube schedule of 4 mm, since for the applied rolling mill, this thickness is critical for the stability of the rolling process. As a result of rolling, a defect-free NiTi tube with an external diameter of 27.5 mm and a tube schedule of 4.0 mm was obtained.