405 Cellular Polymers, Vol. 28, No. 6, 2009 Experimental Study on Microstructural, Surface Hardness and Flexural Strength of Injection Molded Microcellular Foamed Parts © Smithers Rapra Technology, 2009 Experimental Study on Microstructural, Surface Hardness and Flexural Strength of Injection Molded Microcellular Foamed Parts Seyed Abdol Mohammad Rezavand, Amir Hossein Behravesh*, Mehdi Mahmoodi, Peyman Shahi Dept. of Mechanical Engineering, Tarbiat Modares University, Tehran, Iran, P.O. Box: 14115/143 Received: 26 August 2009, Accepted: 26 November 2009 ABSTRACT This paper presents an experimental study on microstructural and mechanical properties of injection molded microcellular foamed parts. The effects of shot size, injection pressure and mold temperature on the relative density, unfoamed skin thickness, cell population density, surface hardness and flexural strength of various regions of the injected parts were investigated. A conventional injection molding machine was modified to produce microcellular acrylonitrile butadiene styrene (ABS) foamed plates. Nitrogen gas was used as the blowing agent. The results showed that surface hardness of microcellular foamed parts are higher and their flexural strength is lower than those of the unfoamed parts. Examining the properties throughout the parts confirmed distinct variations. 1. INTRODUCTION Usage of thermoplastic foams provides reduction in part weight, manufacturing and transportation costs. Thermoplastic foams can be categorized as conventional and microcellular foams. In conventional foams, cell population density is in the order of 10 6 cells/cm 3 and the cell size is in the order of 100 microns. However, cell population density in microcellular foams is about 10 9 cells/cm 3 and higher and cell size is in the order of 10 microns. The main advantages of microcellular foams are claimed to be that their relative mechanical properties (property-to density) ratio are higher than or at least comparable to those of the unfoamed samples. The proposed reason was that the microcells are smaller than critical natural flaw (crack) (1,2) . In microcellular foaming, usage of small molecular size * The author to whom the correspondence should be addressed: amirhb@modares.ac.ir, Tel.: + 98 21 8288 3392