Cutting titanium and titanium alloys

In general, titanium and titanium alloys can be cut by any of the three thermal cutting methods - flame cutting, plasma cutting and laser cutting - and by abrasive waterjet cutting.

Whereas material thicknesses up to 50 mm can be cut satisfactorily by flame and plasma cutting, laser cutting is restricted to max. thicknesses of 10 mm. It is essential that the heat-affected zones on the cut faces be machined off prior to further processing - in particular before welding.

The depth of the heat-affected zones is approx. 1 mm with plasma cutting, 0.5 mm with flame cutting (depending on surface condition) and 0.1 - 0.2 mm with laser cutting. For this reason, sheets and plates must be dimensioned with an appropriate cutting allowance so that the damaged microstructure zone can be removed afterwards.

Thermal cutting speeds for titanium alloys must be reduced by anything up to 50% versus those for CP titanium, depending on composition.

Please note that the figures provided in the following relate to individual test results. They are intended as a guide and as an aid to setting existing cutting equipment.

The results of comparative flame and plasma cutting tests on 50 and 100 mm thick plates of titanium alloy TiAl6V4 are described in the following report.

• J. Schutz, C. Boucher, D. Georgeault, F. Gaillard "Thermal Cutting of Thick TA6V4 Products² Sociéte Française de Métallurgie, Vol. 3, p. 1257/62 Proceedings of the Sixth International Conference on Titanium (1988) Published by les éditions de physique

1. Flame cutting

In contrast to steel, very short pre-heating times are required due to titanium 's low thermal conductivity and low ignition temperature. A narrow heat-affected zone adjacent to the cut is achieved using a severely choked neutral preheating flame and with the cutting oxygen flowing - i.e. preheating and cutting virtually simultaneously.

A suitable fuel gas is acetylene/oxygen with iron powder additives.

The quality of the cut faces depends primarily on the cutting speed. For example, tests on 4 mm thick titanium sheets at cutting speeds of 6 m/min. resulted in cut faces with a maximum surface roughness of 30 µm. The same surface quality was achieved cutting 10 mm thick sheets at a speed of 5 m/min. Success at these high speeds is conditional on a fault-free, smooth surface and perfect cutting machine guidance.

Torch tips should be one to two sizes smaller than those used for steel. In the aforementioned tests, the heat-affected zone was less than 1 mm deep.

2. Plasma cutting

Two tables are attached showing the results of plasma cutting tests on titanium performed on cutting equipment at the company Messer Griesheim GmbH. Table 1 provides information on cutting 12-58 mm thick unalloyed titanium, while the figures in table 2 relate to 17-61 mm thick alloyed titanium.

These tests included both underwater and water shield cutting using nitrogen/hydrogen as the plasma gas. However, a mixture of argon/hydrogen or argon/nitrogen has proved more suitable for titanium.

Underwater cutting may provide lower cutting quality than water shield cutting, although noise levels are considerably higher with the water shield technique.

The hydrogen generated during cutting burns above the surface of the water, with the flame column increasing significantly as cutting speed increases. The same is true of smoke formation.

3. Laser cutting

The following publication describes the results of laser cutting tests:

• H. W. Bergmann, M. Geiger, R. Nuss, B. Juckenath, S. Biermann Å’Laser Cutting of Aluminium and Titanium Alloys for Aerospace Applications¹ Opto Elektronik Magazin, Vol. 5, No. 2 (1989), p. 186/200

The cutting tests described were carried out on 2.5 mm thick CP titanium sheets (material no. 3.7025) and 1 and 2.5 mm thick sheets of titanium alloy TiAl6V4 (material no. 3.7165). Air, nitrogen, argon, helium and a mixture of Ar + 20% O2 were used as cutting gases; the impact of these different cutting gases on cutting speed and cut quality are presented.

4. Abrasive waterjet cutting

Test results are available on the abrasive waterjet cutting of 26 mm thick plates of our titanium alloy TIKRUTAN LT 34 (TiAl4Mo4Sn2Si) in age-hardened condition and 110 mm thick plates of our alloy TIKRUTAN LT 31 (TiAl6V4). In both cases water cutting pressure was 3,000 bar. Good cut qualities were achieved at the following cutting speeds:

• LT 34 (plate thickness 26 mm): 50 mm/min - straight-line cut
• LT 31 (plate thickness 110 mm): 7 mm/min - straight-line cut
• 1 mm/min - cutting radii

The major advantage of abrasive waterjet cutting over thermal cutting methods is that there are no heat-affected zones and thus no edge hardening. This eliminates the need for subsequent machining of the cut edges.

Deutsche Titan, Nov. 2000

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