Indian Journal of Science and Technology Vol. 4 No. 6 (June 2011) ISSN: 0974- 6846 Research article “Aluminium alloy” Velu & M.R.Cecil ©Indian Society for Education and Environment (iSee) http://www.indjst.org Indian J.Sci.Technol. 652 Spike and disc forming test for friction measurement in cold forming of aluminium alloys R. Velu 1 and Moses Raja Cecil 2 1 Mechanical Department, Dr.M.G.R. University, E.V.R.Salai, Chennai-600095, India 2 Design and Development Division, Integral Coach Factory, Chennai-600038, India veluramasamy@yahoo.co.in; rajacecil@yahoo.com Abstract Interfacial friction plays a vital role in cold forming and forging. Since this shear force, if uncontrolled, would lead to many defects and problems, it is essential to measure this entity and to overcome it. Using spike and disc forming test, this interfacial friction is measured. A circular billet is extruded to form a spike on one side and upset to form a disc on the other. Aluminium alloy 6063 is used as the material. Simulation is carried out for various combinations of height/ diameter of the billet and for different spike diameters. The ratio of the height of the spike to the disc diameter is a measure of the friction force. This ratio is plotted to form calibration curves. Using these curves, the friction present during the cold forming process is quantified. Keywords: Aluminium, friction measurement, interface friction, spike extrusion, calibration curves, lubricants Introduction Cold forming is a fast, effective and efficient metal forming processes employed to manufacture a part with less material wastage. Parts with intricate features can be produced in a minimum time using cold forming process than any other processes. The effectiveness of this process has enabled it to retain an edge over others and the progress in various fields could not have been possible without the advancement in cold forming. The soundness of the formed part depends upon many characteristics like the ability of the metal to flow and to fill up the die cavities. During forming, there exists relative movement between the tooling setup, and the billet being worked upon; hence, there arises friction in the interface between them. This interfacial friction, if uncontrolled can cause many defects like inadequate die filling, cracks and discontinuities, porous surfaces and subsurface defects in the formed part, premature wear and tear of the tool and die setup, increased energy requirements, stalling of the press/forge (Gopal, 2001). Therefore, if a quality part is to be made, this interface friction has to be controlled and kept within limits. The first step in controlling this friction is to quantify the same that arises, and then accordingly select a suitable lubricant and apply it during the forming process. In a metal forming operation, the lubricating characteristic of a lubricant influences the interfacial friction. It is generally expressed in two terms, co-efficient of friction, µ and shear friction factor, m. In metal forming analysis, frictional shear stress, τ is expressed as follows: τ = µ σ n (1) where σ n is the normal stress or pressure that acts perpendicular to the surface and µ constant co-efficient of friction (Schey J.A, 1970). This constant co-efficient of friction theory could not truly represent the bulk forming operation (DePierrie V., 1974). Hence, constant shear friction factor, m as given below, is used for analysis. τ = m σ o /√3 (2) where σ o is the flow stress of the billet material. The flow stress again depends upon strain, strain rate and temperature. The value of m varies from 0 to 1 where m=0 represents frictionless interface and m=1 represents sticking friction. Studies indicate (Altan et al., 1983) that equation (2) represents the frictional shear stress to a greater extent in metal forming than equation (1). Usage of the shear friction factor offers a distinct advantage in evaluating friction and load calculation. Hence, to find this shear friction factor, many tribo-tests have been conducted. During mass manufacturing in a production unit, it is impractical to quantify the interfacial friction since this would affect the regular production (Henry S. Valberg, 2010). Tribological tests like Ring Compression Test, Simple Upsetting test, Spike Forging Test (Moses R. Cecil, 2003), Double Cup Extrusion (DCE) (Gopal, 2001) Test, Compression and Twist Test (Hansen & Bay, 1986) have been conducted in laboratory conditions to measure the interfacial friction. These tests differ in their aspects of the complexity of the setup and their aptness to simulate the exact production conditions. The simplest of the tests is ring compression test (Abdul, 1981) and a comparatively complex test is Compression and Twist test. It has been tried to measure the interfacial friction of Magnesium alloys using Forward Rod Backward Cup Extrusion (FRBCE) test (Hu Yamin et al., 2007). The Spike and Disc Forming (SDF) test has been devised to eliminate the difficulty faced in conducting the test and extracting the tested specimen. Extraction in DCE test or FRBCE test is extremely difficult. SDF test is simple but as effective as both the tests. The principle of SDF test in measuring the interfacial friction during cold forming of aluminium alloy and its effectiveness is brought out in this paper. Spike and disc forming test Two types of tests are employed in friction measurement; 1) direct measurement techniques,