1. Introduction
The past century has observed the rapid increase of plastics and their proliferation into all markets. According to world consumption of raw materials by weight, plastic is the highest in comparison with other old materials such as aluminum, steel, rubber, copper, and zinc, resulting from its properties and lower production cost [1, 2]. Injection molding is one of the most significant processes for manufacturing of plastic products and approximately one-third of all plastics are converted into parts using injection molding processes [3]. The application of injection molding processes is increasing significantly in many industries like packaging, aerospace and aviation, building and construction, automotive parts and household articles [1, 3, 4] . the final quality of injected parts in injection molding depends on the material characteristics, the mold design and the process conditions [4-6]. There are three fundamental operations in injection molding. First, the Plastic granules will be converted into a melt. Then, the molten plastic will be injected into the mold cavity or cavities under pressure via sprue, runner and gate systems and finally, the mold tools will be opened to eject the part from the cavities [1, 7, 8].