Abstract—This paper presents a review on the effect of friction during forging operation; must especially the double cup extrusion process. The metal forming process, such as forging, is one of the manufacturing processes where metal is pressed or forced under great pressure into high strength parts. Before the process, lubricant is applied to the dies in operation to promote the flow of metal, to reduce friction and wear, and to aid in the release of the finished part. Interfacial friction between the forgings dies and the work piece such as billet has a significant effect on the forging applications, forming quality, and deformation loads. The most commonly used lubricant is liquid based lubricant, such as water-based graphite, synthetic oils, liquid soap, shear butter etc. Under the high pressure condition and reductions of the lubricant film often breaks down the operation and caused poor metal flow and wears. High interface friction is a primary cause for adhesive pickup in cold forging. Keywords—Double cup extrusion, forging, friction factor, lubrication I. INTRODUCTION ORGING is a process in which metal is plastically deformed under the application of temperature and pressure. This is deformed with the help of a compressive load. This new formation has a significant change in the properties of the deformed metal and as well as the shape. However, the grain size structure is refined and improved. Frequently, in producing discrete parts, several preformed forging operations are required to transform simple sample into a complex component, without causing any degradation to the deformed material. For a given operation, either preforming or finish forging operation, such design output basically consists of: (a) Predicting the material flow between the deformed and undeformed element such as the shape, velocities and strain rates, strains, (b) Determining whether it is possible to form the elemental part without surface or internal defect, (c) Predicting the forces and stresses required to accomplish the forging operation in order to facilitate the appropriate selection of tool and equipment [1]. Manuscript received March 18, 2016; revised April 02, 2016. This work was supported by the Mechanical Engineering Department, University of Johannesburg, South Africa. M. F. Erinosho is a post-doctoral fellow in the Department of Mechanical Engineering Science, University of Johannesburg, Auckland Park Kingsway Campus, Johannesburg, South Africa, 2006. (Phone- +27747425924; E-mail: mutiuerinosho@yahoo.com). E. T. Akinlabi is an Associate Professor in the Department of Mechanical Engineering Science, University of Johannesburg, Auckland Park Kingsway Campus, Johannesburg, South Africa, 2006. (E-mail: etakinlabi@uj.ac.za). In the 20 th century, a physical explanation for the law of friction called “Adhesive Theory” was described. This theory states that the true area of contact is a very small percentage of the apparent contact area. The true contact area is formed by the roughness, thus, as the normal force increases; more roughness comes into contact [2]. Studies on friction have been varied and detailed in past few decades. Different friction models have been proposed for different applications and researches are going on uninterruptedly [3] [4]. In metal forming operations; friction has great importance since it affects the forming force (or energy), material flow inside the die, and as well as the product quality and tool life. In addition to the operations, a finite element simulation of friction model is one of the key input boundary conditions. It was reported that the higher accuracy of friction models is still unknown and also difficult to establish a unique friction model that includes all forming parameters for all metal forming operations. However, the total contact area for both immigrated and expanded original contact area obtained in friction is always smaller than the area deformed without friction. The friction area ratio was introduced to reveal the effect of friction in contact area expansion [5]. A cylindrical compression test is a wide accepted method for determining the flow stress data for metals at various temperatures and strain rates. In this test, flat platens and cylindrical specimen are maintained at the same temperature so that the die chilling and its influence on metal flow are prevented. For this system to be applicable without corrections or errors, the specimen must be upset without any barreling. In other word, the state of uniform stress in the sample must be maintained. Adequate lubricant such as Teflon or machine oil at room temperature is applied to prevent barreling. It was reported that the load and displacement were measured and the flow stress was also calculated at every stage of deformation for strain increment [6]. The primitive objective of this research is to enable engineers to select the lubrication strategies in metal forming to achieve the best friction and also minimize the consumption of lubricant. II. STATEMENT OF THE PROBLEM Two surfaces in sliding contact produce friction, which is normally characterized by coefficient of friction. This is defined as the ratio of the resisting force to the normal force or load. Under dry conditions, the coefficient of friction is usually a constant and independent of the sliding speed and load known as Amonton‟s Law of dry friction. In metal forming processes however the situation is quite different. Study of Friction during Forging Operation Mutiu F Erinosho, Member, IAENG, and Esther T Akinlabi, Member, IAENG F Proceedings of the World Congress on Engineering 2016 Vol II WCE 2016, June 29 - July 1, 2016, London, U.K. ISBN: 978-988-14048-0-0 ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online) WCE 2016