H. Hamdi et al. / Wear 254 (2003) 1294–1298 1295 Fig. 1. High-speed scratch test. Fig. 4. Scratch morphology. is clear that the lateral rolls are virtually non-existent for the whole length of the scratch. Moreover MS1 is manufac- tured by the highest cutting edge of the grain (Fig. 2). This shows that for this cutting edge it seems that metal cutting occurs while for the other one abrasive wear and plowing seems to have happened. In fact, the study of the physical phenomena of the metal cutting must take into account the grain topography (Fig. 2) and an abrasive grain has sev- eral cutting edges and not only one as it was suggested in the literature . From the scratch analysis (Fig. 4) and the phenomena interpretations, the concept of minimum chip as it is widely explained for other machining process like turning or milling could be introduced in the abrasive grain scale. The study of the shape of the scratch gives some other interesting information. In fact, if the theoretical trajectory of the grain  and the experimental measurement of the scratch shape are compared, the way the material move in the Fig. 2. Grain topography. vertical direction could be qualitatively understood (Fig. 6). The theoretical depth of the scratch is greater than the ex- perimental one like it could be observed in Fig. 6. So, during The frontal roll present at the end of the scratch (Fig. 4) the scratch test there is probably an elastic strain of the ma-is in fact a chip which is not ejected from the workpiece.Moreover, lateral rolls are observed in some area of thescratch. So, during the scratch test there is a lateral ﬂowof the material as it could be expected. This lateral ﬂow ofthe material is more important in some area of the scratchand in some other it is unobserved as it is illustrated onthe extracted transversal proﬁle (Fig. 5). If the manufactur-ing scratch MS1 is particularly studied (Figs. 4 and 5), it Fig. 3. Succession of scratches on the workpiece. Fig. 5. Transversal proﬁle extracted from the scratch (Fig. 4).
1296 H. Hamdi et al. / Wear 254 (2003) 1294–1298 Fig. 9. The principle of the sclerometer. a numerical integration must be performed to compute the speciﬁc abrasive energy. Let W denote the mechanical energy given by the follow- Fig. 6. Superposition of the theoretical and experimental trajectory. ing equation: 1 W= Ft (x) dx (2) 0 The scratch length l is equal to 5 mm in our case (Fig. 4). So 5 W= Ft (x) dx = 85.34 × 10−3 J (3) 0 And ﬁnally the speciﬁc abrasive energy is equal to W Es = = 15.86 J mm−3 (4) Fig. 7. Background of the chip. Ve The present result must be confronted to the result obtainedterial in front of the cutting edge. Then when the mechani- with the sclerometer exposed in the sequel.cal stresses are higher, a part of the material gets round thegrain in the lateral (lateral roll, Fig. 4) and/or vertical way,the rest results in a chip (Fig. 7) . 3. Standard scratch test: sclerometer2.3. Speciﬁc abrasive energy 3.1. Principle The speciﬁc abrasive energy Es is the energy needed to The sclerometer principle [6,7] is illustrated in Fig. 9. Theremoved a volume of material. This quantity is widely used aim is to score a surface with an indenter. A normal forceby abrasive manufacture to qualify the grain behavior. It is Fn = 20 N and a displacement are imposed to the indenter.computed using Eq. (1) [6,7]: The tangential force Ft is measured by a piezoelectric sensor l during the test. The scratch velocity in this case is equal to 0 Ft (x) dx 0.3 mm s−1 while for the high-speed scratch test it is equalEs = (1) Ve to 37.3 m s−1 . So, the inﬂuence of the scratch velocity could be studied.where Ft is the tangential force (N), Ve the material volume Like for the high-speed scratch test the indenter is a blueremoved (m3 ), and l the length of the scratch (m). corundum grain and the workpiece is a quench bearing steel In the case of this present study the material volume re- (AISI 52100).moved Ve , in the above experimental condition, is estab-lished using the TopoSurf image processing software and is 3.2. Scratch analysisequal to Ve = 5.38 × 10−3 mm3 (Fig. 4). The acquired tangential force (Fig. 8) is not constant. So, Figs. 10 and 11 show that in the case of the standard scratch test the lateral rolls are less marked as compared to those obtained in a high-speed scratch test. The differences between the two experiments is ﬁrst the velocity and second the trajectory. Do those differences inﬂuence the metal cut- ting physic? Any response could be given with the present scratch analysis. Like it is previously noticed, the scratch in the sclerometer test is constituted by several manufacturing scratches too. Fig. 8. Tangential force for the high-speed scratch test. So, the grain have several cutting edges.
H. Hamdi et al. / Wear 254 (2003) 1294–1298 1297 Fig. 12. Tangential force in the sclerometer test. The volume of the material removed is equal to Ve = 1.34× 10−4 mm3 , so the speciﬁc abrasive energy is equal to Es = 52.23 J mm−3 . 4. Discussion Fig. 10. Sclerometer scratch morphology. In Table 1, it is observed that the speciﬁc abrasion en- ergy decreases when the scratch speed increases. Such anal- ysis could involve some mistakes and could lead to some conclusions like the scratch velocity inﬂuence the physical phenomena as the metal cutting, the wear mechanisms, the plowing, etc. The greatest care must be taken, and an anal- ysis of the two above experiments must be done. First, the experimental conditions are different. In the standard scratch test case a normal force Fn is imposed and in the high-speed scratch test the cutting depth is imposed. Such differences give a ﬁrst incidence on the maximum nor- mal force measured and cutting depth. Secondly, a physic analysis of the two experiences shows that the trajectories of the two grains are different from one Fig. 11. Transversal proﬁle extracted from the scratch (Fig. 10). process to another. In one case, the trajectory is linear and in the other one it is circular. This observation has an impor- tant consequence on the forces distribution (Figs. 8 and 12)3.3. Speciﬁc abrasive energy and may have an incidence on the way the material is re- moved. In fact, during the high-speed scratch test the depth The speciﬁc abrasive energy is computed using Eq. (1). of scratch varies theoretically from 0 up to 20 m. This isThe analysis of the scratch represented in Fig. 10 by means why the tangential force distribution is not constant (Fig. 8).of TopoSurf gives the volume Ve = 1.34 × 10−4 mm3 of the Moreover, the cutting angle varies too during the high-speedmaterial removed. scratch test which may affect the speciﬁc abrasive energy. The acquired tangential force represented in Fig. 12 could The sclerometer experiment gives some advantages. Itbe considered as constant. In the steady state, the mean of is easy to make use of this way of investigation for sev-the tangential force Ft is equal to 10 N for a scratch length eral reasons. First, the low velocity of the grain during theequal to 0.7 mm (Fig. 12). So the speciﬁc abrasive energy is scratch test make the acquirement of the forces more easier.computed as follows: Secondly, the grain could be easily replaced on the indenter l l (Fig. 9), which is a great advantage when the life time and the 0.3 Ft (x) dx Ft (x) 0.3 dx Ft (x)(l − 0.3)Es = = = (5) wear mechanisms of a grain population are studied. Finally, Ve Ve Ve the sclerometer is useful when an abrasive manufactureTable 1Recapitulative table Ft,max (N) Fn,max (N) Depth of the scratch (m) Vs Ve (mm3 ) Es (J mm−3 )Sclerometer 10 20 5 0.3 mm s−1 1.34 × 10−4 52.23High-speed scratch test 7 67 20 37 m s−1 5.38 × 10−3 15.86
1298 H. Hamdi et al. / Wear 254 (2003) 1294–1298will study the inﬂuence of the shape and the cutting angles ﬂuence of the velocity on the grain behavior in the case ofof the grain on the speciﬁc abrasion energy. This could be a high-speed scratch test. Moreover, the experimental resultsfast way to classify a population of grain and extract those of the grain behavior presented in this paper must be con-presenting the best abrasive behavior. fronted to some numerical simulation of the scratch test. The high-speed scratch test gives some advantages too. At last, if the behavior of the grain on the metal cuttingIt allows to study the grain abrasive behavior in the case characteristics and physics will be understood, the grindingof grinding conditions which impose the trajectories, the process and its effects on the workpiece will be better un-velocity and the depth of cut. The main drawback is to derstood too.hold the grain in position on the disk (Fig. 1) whichmake the experiment heavy when several grains must becompared. References The comparison of the two experiments is critical in term  E. Minke, E. Brinksmeier, The use of conventional grinding wheelsof the effect of the velocity on the grain behavior and the in high-performance grinding processes, in: Proceedings of theabrasive phenomena. The experiment conditions are differ- First International Machining and Grinding Conference (SME), SMEent and induce two types of trajectories which may have an Identiﬁcation, Product ID MR95-199, Paper No. MR95-199, Dearborn,inﬂuence on the expected results. At last, the two experi- USA, 1995, 12 pp.ments are complementary because one (the sclerometer) al-  J.W. Kim, H. Gupta, High speed grinding: evaluation of wheel performance and surface integrity, J. Mater. Process. Manuf. Sci. 5 (2)lows an easy classiﬁcation of an abrasive grain population (1996) 115–126.in terms of life time, wear resistance and speciﬁc abrasive  F. Klock, E. Brinksmeier, C. Evans, T. Howes, I. Inasaki, E.energy, and the other permits a second selection when good Minke, H.K. Toenshoff, J.A. Webster, D. Stuff, High-speed grinding:mechanical behavior is expected in the grinding process fundamentals and state of the art in Europe, Japan, and the USA,condition. CIRP Ann. Manuf. Technol. 46 (2) (1997) 715–724.  B.N. Colding, A wear relationship for turning, milling and grinding— machining economics, Ph.D. Thesis, Stockholm, 1959.  J. Verkerk, Final report concerning CIRP cooperative work in the5. Conclusion characterisation of grinding wheel topography, Ann. CIRP 26 (2) (1977) 385–395. In this paper two experiments which give some interest-  H. Hamdi, Contribution to the study of the physical phenomena in theing information on the grain behavior are presented. The wheel–workpiece interface in the case of traditional and high speedhigh-speed scratch test for the study of the grain behavior is grinding, Ph.D. Thesis, Ecole Central de Lyon, 2000, 170 pp.  V. Jardret, H. Zahouani, T.G. Mathia, Technique for analysis ofthe nearest of the real process and give more qualitatively scratch genesis: morphological and rheological point of view, in: T.S.physics information of the grinding process. In further in- Sudarshan, M. Jeandin (Eds.), Surface Modiﬁcation Technologies VIII,vestigations, it seems that it is interesting to study the in- The Institute of Materials, 1995, pp. 222–228.