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Process parameters influence on friction coefficient in sheet formingoperationsE. Ceretti 1 , A. Fiorentino 1 , C. Giardini 21 University of Brescia, Dept. of Mechanical and Industrial Engineering - Via Branze 38, 25123 Brescia, ItalyURL: www.ing.unibs.it/tecmece-mail: elisabetta.ceretti@unibs.it; antonio.fiorentino@unibs.it2 University of Bergamo, Dept. of Design & Technologies - Viale Marconi 5, 20044 Dalmine (BG), Italye-mail: claudio.giardini@unibg.itABSTRACT: In conventional sheet forming processes, such as stamping or drawing, significant contactphenomena take place between workpiece and die surfaces. Especially, relative motion and normal loadsgenerate friction which influences some aspects of processes such as material flow, tools wear and life andtotal force needed to complete the process. In the current paper an experimental test campaign has beencarried out using a large scale pin-on-disk device designed and realized by the Authors to investigate theinfluence of pressure, sliding velocity and temperature. The purpose is to test the developed device and to findwhich and how these parameters mostly affect friction. The pin-on-disk test consists of two specimens, a pinand a plate representing respectively die and workpiece, which are compressed by means of a known forceand then moved one over the other. Compression and friction forces are sampled during the tests and thefriction coefficient is estimated as the ratio of these two forces. The tested materials are H13 die steel onFeP04 and AZ31 sheets.Keywords: sheet forming, friction, contact problems, temperature, pressure, velocity.1 INTRODUCTIONIn conventional manufacturing operation significantcontact phenomena take place between tool andworkpiece. Due to this contact and the resultingsurface interactions, friction is generated. Frictionknowledge is very important because it affects manyaspects of manufacturing processes, such as therequired force, the die wear and in some cases theprocess feasibility.To investigate and to determine the friction valueseveral tests, such as ring test [1] and strip test [2],and the Pin-on-Disk [3] have been introduced. Inrecent years many Authors have proposed newmethods to evaluate friction, for example themodified LDH [4], the Twist Compression Test [5].Among these tests Pin-on-Disk (PoD) allows todirectly measure the compression (F) and friction(T) forces and to estimate the friction coefficient(µ=T/F) using one single couple of surfaces incontact.In previous works the Authors studied the influenceof contact pressure, sliding velocity and materialroughness on friction coefficient by using a selfdesignedPin-on-Disk equipment [6, 7, 8]. In theseworks, the H13 steel and different die coatings weretested on AISI 5115 and on Series 1 Aluminiumpainted sheets. The idea was to identify thedependence of friction on the process parametersand to implement it in FE codes.The aim of the present work is to study the influenceof contact pressure, sliding velocity and temperatureon friction while forming different materials, namelydeep drawing steel FeP04 and AZ31 Magnesiumalloy sheets. Since this latter is characterized by ahigh formability in warm forming [9], thetemperature influence was studied too.2 EXPERIMENTAL EQUIPMENTThe experimental device (Fig. 1 left) is a large scalePin-on-Disk tribometer designed by the Authors [7].The friction coefficient is evaluated by pushing intocontact two components called Pin and Plate. ThePin (a cylinder with a diameter of 12 mm and acorner radius of 2 mm) stands for the die (or more ingeneral the tool) and is mounted on a carriage whichcan move orthogonally with respect to the platesurface. The Plate (flat) represents the workpieceand it is mounted on a disk that rotates so