FINITE ELEMENT ANALYSIS OF CENTRELESS-LUNETTE TURNING OF HEAVY SHAFT

Dynamics of huge renovated lathe is simulated. Turning scheme concerns to heavy rotor shaft finishing. Lofty parts and milling head may create dynamic problems. Static, modal and harmonic frequency response function simulations were provided. Bearing system consists of bed, support, tool, lunettes, tailstock. Headstock didn’t take part in shaft holding. Static and dynamic rigidities founded 3–4 times less for support than for shaft. Tool rigidity lessens from 186.5 to 11.9 N/µm for speeding from slow to near resonance turning. Twelve lathe eigenmodes were evaluated. Two eigenmodes are most dangerous. It is “shaft swinging on lunettes” (M1, 26.7 Hz) and “support pecking” (M3, 54.4 Hz). Bed has excessive flexibility due to through holes and lack of inner ribbing. Polymer concrete filling is moderately effective. Changing two-lunette (2L) scheme to three-lunette (3L) increases rigidity of shaft at 2.09 times at statics but gives limited action in dynamics. Resonant peaks on frequency response function are lowered only at 1.32 times for M1, M3. Effect of dynamic damping is revealed under condition of proximity middle lunette to lofty support. Support serves as tuned mass damper. Measures of machine tool reinforcement are simulated. Shaft swinging according to M1 may hardly be blocked by passive means. It would be better to bypass it. “Support pecking” resonance (M3) succumbs to only full set of measures. Small effect of partial reinforcement is predicted. Three frequency intervals are recommended for turn-milling at huge lathe: pre-resonant (<20 Hz), inter-resonant (35–45 Hz) and post-resonant (>65 Hz). The last one is more suited. Next design step is to create triangle inner ribbing system or caissons inside of bed.

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