Identification of noise sources of forge hammers during production: An application of residual spectrum techniques to transients

Abstract

Three gravity-drop, four-piece forge hammers are analyzed to determine the principal structural sources of impulsive noise radiation during production forging. A three-input single-output model is used to describe the hammer system, based on “input” signals taken from one column, the anvil and the ram accelerations, and one “output” signal taken from the sound pressure at the operator's position. The frequency response functions between the elemental vibrations and the sound pressure signal are determined from these signals by residual spectrum techniques. For the three hammers studied, the analysis shows that the ram is a major source of acoustic energy radiated to the oeprator's position, while the columns and anvil radiate between 1 and 4 dB less energy. The three-input model is then used to estimate the effect of acoustic shrouds on the sound energy radiation. The results indicate that it may be necessary to treat all the structural elements before significant reductions can be achieved, due mainly to the high degree of interaction between the components. The residual spectrum derived from this model indicates that the three input model may not be totally adequate for all production hammers; it may be necessary to develop higher-input models, with use of data from more transducers located to sense a higher number of contributing vibration modes. However, in this study the three-input model accounted for 73–82% of the sound energy density at the operator's position.