Study And Application Of Friction And Lubrication Characteristics Of Graphite Lubricant During Cold Extrusion Processing

Friction and wear of cold extrusion processing is an important factor affecting the products quality and the dies using life.This problem is solved mainly by using lubricants.At present,the traditional phosphorus-saponification process still occupies the main lubricants market,but it can’t meet the requirements of environmental protection now.In order to solve the above problem,a new lubricant of cold extrusion has been prepared,and its friction and lubrication characteristics has been studied in this paper.It is applied in cold extrusion forming of spline shaft parts.The specific contents of this paper are as follows:1.The influence of single factor on the lubrication performance of lubricants is analyzed.It is found that the friction coefficient of lubricants decreased first and then increased with the increase of the mass fraction of graphite,S₂Mo and CMC,the minimum average friction coefficients were 0.109,0.18 and 0.2 at 9wt%,10wt%and 0.4wt%respectively.The friction coefficient of graphite lubricant decreases with the increase of the mass fraction of NNO.With the increase of the mass fraction of Mg O,the friction coefficient decreases first and then remains unchanged.2.Graphite,S₂Mo,tackifier and dispersant are selected as the factors of orthogonal test,which are recorded as A,B,C and D respectively.The orthogonal test results show that under the condition of confidenceα=0.01,the influence of C is highly significant,the influence of A is second,and the influence of B and D is not significant.The optimal combination obtained by orthogonal experiment is A₁B₃C₁D₂ with the ratio of 10:15:0.3:3.3.The optimum lubricant ratio obtained by orthogonal test is compared with the lubricating properties of phosphorus-saponification,polymer lubricant and dry friction,which are respectively recorded as C,P,G and N respectively.The average friction coefficients of different lubricants measured by friction and wear tests respectively are 0.11,0.125,0.143 and 0.39 in 15 minutes.The order of average friction coefficients is C<P<G<N.Using ring upsetting to measuring the friction coefficients,the friction coefficients of C is in 0.058-0.115,the friction coefficients of G and P are in 0.115-0.173and the friction coefficients of N is close to 0.231.The order of friction coefficients is C<G<P<N.4.The SEM and EDS analysis of the worn scars show that there are active groups in graphite lubricant,which can effectively cover the surface of friction pairs to form a good anti-wear lubrication film,avoid direct contact with the surface of friction pairs,and reduce the friction coefficient.The surface of the worn scars treated with graphite lubricant is smooth and sparse,and the width of the worn scars is about 200μm.The surface of samples treated with phosphorus-saponification has more adherents,deeper and dense grooves,and the width of the worn scars is about 300μm.Graphite lubricant has better anti-wear effect than phosphorus-saponification.5.The surface of parts with graphite lubricant forming is smooth,only slight scratches and furrows exist and its surface forming quality is very good.There are obvious scratches and furrows on the surface of parts by phosphorus-saponification treatment,and there are a lot of micro-cracks in most areas.Comprehensive analysis shows that graphite lubricant has better surface morphology than phosphorus-saponification process,and it can improve the surface quality of formed parts and reduce the die wear.