Machining an alternator end casting was producing A-weighted noise levels of 104 dB, principally in a high pitched 'squeal' radiating from the casting. Overlapping hanging strips had been fitted around each machine to form a partial acoustic screen. However, these had been cut away at the operator position to improve access.
The noise arose from resonant vibration of the casting, excited by cutting forces, with evidence of chatter marks on some of the machine surfaces. The mounted casting exhibited very low damping characteristics during machining.
The solution was to apply a simple damping treatment to reduce the casting's vibration.
To test the method, an inexpensive rubber bungee was wrapped around a casting during machining. Subsequently a pair of damping straps were designed to provide a more durable solution. These were easily fitted to the casting by the operator while the preceding casting was being machined.
An overall noise reduction of 16 dB with the 'squealing' component being reduced by 30 dB. In addition, the quality of the cut improved and the machining time for each cycle was reduced.
Photographs courtesy of Industrial Noise and Vibration Centre. Consultants were Industrial Noise and Vibration Centre.