Researches concerning the influence of the technological parameters on 42MoCr11 surface roughness.

Negoescu, Florin ; Nagit, Gheorghe ; Iosub, Adrian 等

1. INTRODUCTION

The cold superficial plastic deformation of the metals is a chipless shaping method. One or more tools, without cutting edges, perform a movement and a pressing action on the workpiece surface. Between the workpiece and the tool there is a relative translation or rotation motion (Nagit, 1997). The cold plastic deformation process can be applied to metallic materials and has the following effects: superficial layer hardening, obtaining of new texture, inside of the workpiece there appears a remnant stress, modification of the temperature in the workpiece, transformation of the phase and modification of the material properties (Nagit et al., 1998).

The superficial plastic deformation by vibro-hardening as a superficial treatment contributes to the improvement of the physical and mechanical properties of the workpiece depending on the material nature and structural modifications (Kvackaj, 2006). For the experiments it is used a steel-42MoCr11 with the following chemical composition: 42MoCr11-0.4%C, 0.2%Si, 0.6%Mn, 1%Cr, 0.2%Mo.

2. PRESENTATION OF THE EXPERIMENTAL EQUIPMENT

The experimental equipment is consisted of machine tool, devices used to measure the process forces, roughness parameters and hardness of the workpiece after the vibro-hardening process (fig. 1).

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

The objectives armed at this experiment are:

* To establish the technological parameters on the roughness surface.

* To establish the interactions among factors.

* To develop a mathematical model, in a matrix form, able to describe the process.

The tool used in the experiments is presented in fIgure 2. The bearing 6 is fixed in the tool body 1 by bolt 5. The ball 7 is maintained and fixed in bush 3 by the bearing 6. The bush can be changed according to ball diameter. A stable position during the process can be ensured by the clutch 2 (Nagit et al., 2003).

The device is designed so as to bear a force between 20 and 1000 N. The working stroke can be adjusted between 0.3 and 0.7 mm. The roughness of the samples used in the experiments was 6 urn. The experiment is a complete orthogonal factorial experiment [2.sup.n] ([2.sup.4] = 16 attempts), the Yates algorithm is used in order to establish the research points.

[paragraph] The interpretation of the factor effects can be done easier if the model, which characterizes the process, is expressed in a matrix form (Braha et al., 2003). One may express opinions and observations on the influence of the input parameters among the process.

[FIGURE 3 OMITTED]

[Ra.sub.T] = M + l + n + f + P + l* n + l* f + l* P + n* f + n* P + f* P (1)

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (2)

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (3)

Interpretation of the results is facile if it is transferred into a diagram which illustrates the effects and the interactions of the factors mentioned in table 1.

Analyzing figure 3 one may observe that the factors "f" and "P" presente the most important effects.

3. RESULTS AND CONCLUSIONS

Taking into account Fisher criterion, the influence of factors can be illustrated, as can be observed in table 2.

As one may observe from Fisher test, the revolution of the workpiece has a significant importance, with big influences on the surface quality. When it comes to the interactions between the factors, one may notice that l*n, l*f, l*P and n*P are playing a very important role. Experimental determination of the roughness in case of vibro-hardening process, taking into account process parameters, shows that the roughness decreases significantly after vibro-hardening process [4].

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

Increase of pressing force has a good influence on the geometric parameters and the quality of the workpiece up to a limit value. After this limit value, the influences are negatives.

Increase of workpiece rotational speed and of feed, usually, has a negative influence on the surface quality. It is necessary to limit the rotational speed in accordance with the frequency of oscillations. The oscillations amplitude is described as having a positive influence regarding quality surface, when its value increases, but only in accordance with the other parameters of the process. If oscillations amplitude increases, many zones of workpiece material may remain unprocessed and, therefore, the surface quality decreases.

As a final conclusion, it is recommended to use small feeds in order to obtain an optimal number of tool crossings on the workpiece surface, decreasing roughness parameter. The feed used has to be optimally chosen in order to ensure at the same time a good productivity.

4. ACKNOWLEDGEMENT

The authors gratefully acknowledge the financial support offered to researchers of this paper by Romanian Ministry of Education, Research and Youth, through CNCSIS Grant no. 28, AT type.

5. REFERENCES

Braha, V., Nagit, Gh. & Negoescu, F. (2003). Cold plastic deformation technology (in Romanian), Technical and scientific publishing house CERMI, ISBN 973-667-025-2, Iasi-Romania

Kvackaj, I. (2006). Development of bake hardening effect by plastic deformation and annealing conditions. Availble from:http://public.carnet.hr/metalurg/Metalurgija/2006_vol _45/No_1/MET_45_1_051_055_Kvackaj.pdf Accesed: 2008-05-16

Nagit, Gh., (1997). Theoretical and experimental contributions on vibrorolling process (in Romanian), PhD thesis, Technical University Gheorghe Asachi of Iasi

Nagit, Gh., Braha, V., Slatineanu, L. & Musca, G. (1998). Experimental researches concerning pressure force influence and lubrication on roughness at vibrorolling. Technical Institut's Bulletin of Iasi, Vol. XLIV (2003), pp. 391-396, ISBN 1011-2855

Nagit, Gh., Dodun, O., Negoescu, F. & Ignatescu, E.(2003). Cold superficial plastic deformation-a solution to replace heat treatment in small laboratory, Proceedings of Baia Mare-North University, Vol. XVII, pp. 227-231, ISSN 1224-3264, Baia Mare-Romania

Tab 1. The factors and level of tests.

The code Level Level
 of the Test factor 1 2
parameter Unit of
 -1 +1 gauge

 v The
 l amplitude of 0.65 3 mm
 the
 oscillations

 n Rotations per 80 315 rot/min
 minute

 f Feed 0.024 0.132 mm/rot

 P Deformation 10 30 daN
 force

Tab 2. The aria of analyses for 42MoCr11.

 8 Variable F [alpha]=99% [alpha]=85%
 [f.sub.[alpha]] [f.sub.[alpha]]

 l [S.sub.1]=0,0052 0,07 16,26 3,16
 n [S.sub.n]=2,6163 37,19 16,26 3,16
 f [S.sub.f]=0,1173 1,66 16,26 3,16
 P [S.sub.P]=0,0095 0,13 16,26 3,16
l * n [S.sub.1*n]=0,3220 4,57 16,26 3,16
l * f [S.sub.1*f]=0,3108 4,41 16,26 3,16
l * P [S.sub.1*P]=0,2328 3,30 16,26 3,16
n * f [S.sub.n*f]=0,0162 0,23 16,26 3,16
n * P [S.sub.n*P]=0,2889 4,10 16,26 3,16
F * P [S.sub.f*P]=0,0060 0,08 16,26 3,16