Punch press noise control through partial acoustic enclosure: A Field Study

Punch press is contributed as one of the major industrial machines to produce metal objects, which typically propagates hazardous noise. Acoustic enclosure is the most common method to mitigate noise transmitted from industrial equipment. This study aimed to assess the role of opening dimension and location in a partial acoustic enclosure on occupational noise exposure of punch press’s operator.

A punch press with the capacity of 60 tons in an automotive manufacturing company was considered as a real noise source. Equivalent noise exposure level was measured with reference to ISO 9612 using Cassella Cell-450 sound meter, before and after noise control intervention. Rubber sheet and mineral wool as insulation and absorption acoustical material with the thickness of 2 and 50 mm, respectively, applied to build acoustic enclosure. Rubber sheet sound transmission loss was measured using BSAW SW 477 acoustic impedance tube to predict acoustic performance of enclosure. In addition, Partial acoustic enclosure with the dimensions of 1.4 by 1.2 by 3 meter was constructed and opening areas which was equal to 2, 3, 5 and 7 percentage of total area of enclosure was created in front of punch press operator. Finally, an opening equals to 2 percentage of total area of enclosure was created on the left sidewall of enclosure to assess the location of opening on noise level.

Punch press operator noise exposure level was measured to be 89 and 67 dBA before and after using full acoustic enclosure respectively.  After using partial acoustic enclosure with open area percentage of 2, 3.5 and 7 on the front side of press, operator noise exposure level was measured 78, 79, 78 dBA, respectively which was a little bit more than predicted noise. As the opening position was relocated from the front wall to the sidewall of the enclosure, operator noise exposure was reduced from 78 to 69 dBA respectively. Although, there was not significant differences between mean sound level of the punch press after relocation of opening. 

Utilizing full acoustic enclosure constructed from insulation material recommended in this study, reduced punch press operator noise exposure remarkably. Although, opening area of partial acoustic enclosure was increased to some general extent to feed punch press, there was a slight change in noise exposure of press operator. On the other hand, press operator noise exposure was plummeted with the relocation of opening. Therefore, front opening dimension could be chosen fairly wide to access and feed operation zone of punch press without exposing operator with more noise level. Furthermore, repositioning the opening from the front wall to the side wall of the enclosure and automatically feeding the press through side opening could substantially reduce the operator noise exposure.