Strange "hammered" surface while turning Titanium grade 5 Ti6Al-4V (annealed)
A subsupplier is currently experiencing a strange phenomenon while turning a workpiece for my company. Serial production. CNC-lathes. We start with a forged blank approx. Ø 100 mm by 1000 mm long, with a bore hole Ø 80 mm. A forged and annealed tube actually. Ti6Al-4V. The blank is in step 1 turned from the inside. In step 2 the workpiece is put on a rather tight mandrel and we turn the outside and most of the material is cut away. The remaining wall thickness of the tube, in finished condition, is only approx. 0,5-0,8 mm.
In both step 1 and step 2 we sometimes observe a strange surface. The Surface appears to be hammered. This happens more often on the outside (step 2) than on the inside. This hammered surface is not all over the cylindrical Surfaces, mostly partially only and it is not present on all pieces. Some looks "normal".
The Surface roughness is the same on the hammered and on the regular Surface. Within spec.
I realise there is a problem with the thin-walled machining and I understand that it is a challange, but what causes this? Vibrations? Heat? Material variation/structure?
We're Clueless and we've tested lots of different Tools and cutting parameters.
A subsupplier is currently experiencing a strange phenomenon while turning a workpiece for my company. Serial production. CNC-lathes. We start with a forged blank approx. Ø 100 mm by 1000 mm long, with a bore hole Ø 80 mm. A forged and annealed tube actually. Ti6Al-4V. The blank is in step 1 turned from the inside. In step 2 the workpiece is put on a rather tight mandrel and we turn the outside and most of the material is cut away. The remaining wall thickness of the tube, in finished condition, is only approx. 0,5-0,8 mm.
In both step 1 and step 2 we sometimes observe a strange surface. The Surface appears to be hammered. This happens more often on the outside (step 2) than on the inside. This hammered surface is not all over the cylindrical Surfaces, mostly partially only and it is not present on all pieces. Some looks "normal".
The Surface roughness is the same on the hammered and on the regular Surface. Within spec.
I realise there is a problem with the thin-walled machining and I understand that it is a challange, but what causes this? Vibrations? Heat? Material variation/structure?
We're Clueless and we've tested lots of different Tools and cutting parameters.