Acoustic performance of countersunk micro-perforated panel in multilayer porous material

This study investigates the acoustic performance of a countersunk micro-perforated panel, along with two distinct porous materials used in a multilayer porous absorber configuration. Additive manufacturing is applied to create sub-millimeter perforation with different hole spacings on polymer micro-perforated panels. Experiments are conducted in an impedance tube, in which the effects of the perforation ratio, air gap, and varying porous layer configurations on the sound absorption capabilities are investigated. For validation, considering the converging hole profile in the micro-perforated panel, an integration method with end correction is used to calculate the tapered section impedance, and the traditional Maa theory is used for the uniform hole. The theoretical impedance of the multilayer absorber is calculated using the transfer matrix method and subsequently compared to the experimental results. The results demonstrate that the countersunk hole micro-perforated panel exhibits a significant improvement in sound absorption, and the introduction of porous materials extends the sound absorption bandwidth. Furthermore, the results indicate that the sound absorption capability depends on the porous material placement in the multilayer absorber configuration.

Extrusion of Circular Billet through Circular, Triangular and Square Multi-Hole Dies

In extrusion with multi-hole dies, more than one product is produced from the same billet and quite suitable for improving the productivity and to produce small dimensioned products. Many operating parameters like number of holes present on die, hole profile, length of die land, die pockets, extrusion speed and friction condition affect the surface finish, bending and mechanical property of the products get extruded. The equivalent size of products produced by multi-hole extrusion process does not exist in literature. The objective of this research work is to produce the products of equivalent dimension from different profile holes by multi-hole extrusion. In this experimental study, the products of circular, triangular ads square profiles have been produced. The dies of 2-hole, 3-hole and 4 holes have been used. The extrusion load requirement, hardness of the final products and the change in length of parts extruded are investigated. The extrusion with squared holed dies needs more extrusion load than circular and triangular holed dies. The hardness value varies along the extruded product length. The variation in length of the extruded parts is more for the products obtained from dies with squared hole dies.