Machining of Tantalum – Technical Challenges

Machining of tantalum is difficult. It has been described as “kind of like machining copper with the hardness of titanium”1. Especially annealed tantalum may cause problems, being ‘sticky’, as well as having a strong tendency to seize, tear and gall2. Unannealed tantalum material is in general more suitable for machining than annealed. Medical grade tantalum is unalloyed and has a tendency to harden during processing and can be difficult to machine. Copper or soft aluminium would be good examples to compare it to 1,4. Lubrication is therefore essential to avoiding the development of too much heat during tantalum machining, as tantalum may ignite at elevated temperatures. Flaming during machining of tantalum should, however, not be an issue as long as the tantalum is well lubricated during the machining 1.

Lubrication of tantalum during machining
Lubrication medium is required when machining tantalum and the work must be well flooded at all times. Conventional coolant does not work1. Perchloroethylene 2, trichloroethane 2 or Moly-Dee 1 has been reported as suitable as a cutting medium for tantalum. WD-40 has been used but washes away quickly 1.

Turning tantalum
When maching  tantalum by turning it is generally recommended to use ceramic tooling, e.g. uncoated cemented carbide1-4. Very sharp inserts with a high positive (as much as possible) rake are suggested for turning1. Turning speeds in the range 100-175 SFM (surface feet per minute) have been reported suitable1-3. Slower speeds may cause tantalum to tear. Lubrication medium is required for turning tantalum and the work must be well flooded at all times. (See paragraph above).

Drilling tantalum
Drilling tantalum is in general difficult. A carbide drill at 80 SFM (0.025 pecks at 0.002 per rev) with Moly-Dee as lubricant has been reported suitable for drilling tantalum 1.

Grinding tantalum
Grinding tantalum has been reported to be extremely difficult and grinding annealed tantalum is almost impossible4. However, cold worked (unannealed) tantalum can be ground with limited success using aluminium oxide4. Lubrication medium is required for grinding tantalum (see paragraph on lubrication), as tantalum dust may have a risk of causing fire upon reaction with oxygen.


References
1) Integrex Machinist Forum: integrexmachinist.com
2) Espi Metals: www.espimetals.com
3) Thomas Net: www.thomasnet.com
4) Eagle Metals: www.eaglealloys.com

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