ANALYSIS OF VIBRATORY NOISE IN THE SAWING OF ALUMINUM EXTRUSIONS

High speed cutting of aluminum extrusions by circular saws generates sound pressure levels causing considerable concern relative to OSHA regulations. Aluminum sawing noise resulting from the saw blade and workpieces is categorized into two types: (1) "Acceleration" noise due to the mass-like vibration of the air near the blade tooth impact area and (2) "Ringing" noise resulting from workpiece and blade flexure at normal modes of vibration. A technique using laboratory impact tests provides a convenient evaluation of the relative contributions of these types of noise. It is shown that these tests reflect actual sawing conditions. Results presented demonstrate that reduction of "acceleration" noise can be achieved by using sound barriers while "ringing" noise can be reduced by surface damping, using constrainted- layer damping concepts in clamping devices. Surface damping is also shown to decrease "acceleration" noise--by increasing the mass effect of the vibrating workpiece. Based on laboratory findings, prototypes of acoustical treatments in the form of saw modifications can reduce L(,OSHA) of actual sawing noise by 10 to 13 dBA. The modifications to a commercial saw demonstrate the laboratory feasibility of decreasing sawing noise levels such that the amount of sawing per day can be planned to be within the constraints of OSHA regulations. The concept of L-equivalent noise exposure evaluation of cyclic sound sources is developed in this work and used to assess noise reduction requirements.