A 40 ton press was being used for a pierce and blank operation generating 98dB at the operator's position at 60 strokes/minute. Very high forces are generated in press frames during piercing and blanking operations. These generate vibration that is radiated as noise by the frame and associated steelwork. The highest level of noise is caused by the almost instantaneous release of press frame strain at break-through (brittle fracture).
Large noise reductions can be achieved by introducing carefully designed tooling modifications that can also produce parallel benefits by reducing peak press loads. This reduces wear and therefore maintenance down-time. For complex, multi-stage tools, the options may be limited as the increased break-through required may be unacceptable. However, the dominant noise is often generated by only one or two stages, simplifying the problem. Often, the only real difficulty for a particular job lies in ensuring that the modifications are not removed during subsequent regrinds.
The effect of these measures at 60 strokes/minute was to reduce both the noise and the load as follows:
Not only was the noise substantially reduced, but the press loading was halved. In this particular case, it allowed the job to be run on four other presses rather than being confined to the 40 ton machine. This introduced much more flexibility into the departmental work planning.
The main cost of introducing sheared and staggered tooling lies in the increased time required for tool regrinding. In this case, the tool was relatively simple and the costs involved very low.
Industrial Noise and Vibration Centre Ltd.