Experimental research regarding electromagnetic field deformation.

Sindila, Gheorghe ; Ocnarescu, Constantin

1. INTRODUCTION

The electromagnetic field deformation, as a non-conventional process of manufacturing, enables the practical achievement of all classical cold-working procedures. Taking into account its relatively low efficiency (< 30%), the process applies only when the classical cold deformation procedures do not meet certain technical and economical requirements. Threading (fig. 1) and even assembling metallic parts with non-metallic ones (fig.2) represent the domains that the electromagnetic field deformation procedure is mostly applied to. In order for a good assembling to take place, it should be performed a rigorous check of the battery's of condensers charging degree, according to the required level of deformation (Balaban, 1993).

This is the reason why this paper establishes the influence of the main constructional and functional parameters (which characterize the deformation process in electromagnetic field), upon cylindrical parts' degree of deformation. (Ciocardia &al., 1992)

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

2. EXPERIMENTAL ESTABLISHING OF THE DEFORMATION DEGREE

The experience in applying the deformation process in electromagnetic field emphasizes that, for the deformation of the same material by means of the same deformation device, the main parameters that influence the deformation degree are: the energy level charged in the condensers battery U, the diameter of the part subject to deformation D, the thickness of the material g, the diameter of the coil's wire d, the total number of coil's wires N, the clearance between the coil and the blank j. The determination of a dependency function between the diameter of the deformed part [D.sub.f] and the abovementioned parameters is experimentally performed by employing the method of response surfaces:

[D.sub.f] = f (U, D, g, d, N, j) (1)

Because most of the multi-variable dependency functions (determined practically by means of different experimental methods) are found in a polytrophic form, , we propose the following dependency function (Sindila & al., 2003):

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (2)

Choosing the domains where the parameters vary is performed according to their frequency of appearance in experimental research studies, the technological limitations of the material, the constructional characteristics of the experimental device, etc. Thus, relation (2) leads to:

ln [D.sub.f] = ln [a.sub.0] + [a.sub.1] x ln U + [a.sub.2] x ln N +

+ [a.sub.3] x ln d + [a.sub.4] x ln D + [a.sub.5] x ln j + [a.sub.6] x ln g (3)

In order to simplify the computations, the parameters' values were established in geometrical progression and were encrypted in accordance with those displayed in tabel 1. There were manufactured tool-coils and tubular parts whose diameters, respectively thickness of material, have values according to those stated in table 1.

There were also observed the values of the charging tension of the condensers battery as well as the values of the clearance between the tool-coil and the tubular part (Mihail, 1976).

Employing the established methodology for an entire eXperimental factorial program with central points, there were performed 16 different experiments and 4 within the centre of the experiment, as a result of which there were determined the [a.sub.ir] values of the parameters under study (Sindila, 1976).

[FIGURE 3 OMITTED]

The experiments were run on a DEMARO-type installation of deformation in electromagnetic field, employing the set of coils displayed in fig.3 and tubular parts made of aluminium alloys (fig.4).

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

The analysis of the experimentally-obtained values revealed the model's adequacy and enabled the determination of the independent variables' significance, as well as the importance of reliance/trust intervals, statistic errors and the required dependency function. It was concluded that not all the variables under study (such as the number of wires and the clearance between the coil and the part) have an important significance on the deformation and thus, they were dropped out (table 2).

The statistical errors lower than 5% emphasize the fact that the theoretical results and the practical ones (obtained in a real case of deformation) are conveniently close.

Replacing the values thus determined in relation 2, it was established the computation formula of the deformed part's diameter, taking into account only the significant parameters:

Independent variable Fisher function Meaning

Coefficient [a.sub.0] 46376,45 >> 1 significant
Tension, U 1,53 > 1 significant
No. of wires, N 0,00 insignificant
Conductor's diameter, D 4,40 >1 significant
Coil's wire diameter, d 316,21 >1 significant
Clearance, j 0,64 < 1 insignificant

[D.sub.f] = 0,345 x [U.sup.0,130] x [D.sup.1,018]/[d.sup.0,113] x [g.sup.0,091] (4)

In order to determine the energy level charged in the condensers battery needed to obtain a certain diameter [D.sub.f] of the deformed final part, it's recommended to use the following relation:

U = 3582 x [D.sup.7,692].sub.f] x [d.sup.0,869] x [g.sup.0,699]/[D.sup.7,83] (5)

3. CONCLUSIONS

The specialty literature offers, in general, few data regarding the deformation process in electromagnetic field and the main parameters that are involved in the process. The data derived from the experimental method offer the opportunity of estimating the way the main constructional (D, d, n, U) and functional (j) parameters influence the degree of deformation of cylindrical aluminium parts under the bloating process in electromagnetic field. The energy level charged in the condensers battery in order to obtain a certain diameter of the deformed part, can also be estimated. The same methodology can be extended as well to parts made of different materials. The graphic representation of the experimentally-obtained relations enables, in practical situations, the rapid determination of the way in which the parameters under consideration influence the purpose function.

4. REFERENCES

Balaban, C.--Strategia experimentarii si analiza datelor experimentale, E.A.R. Bucuresti, 1993.

Ciocardia, C., Draganescu, Fl ., Sindila, Gh., Carp C ., Parvu C .--Tehnologiapresarii la rece, E. D. P., Bucuresti , 1992.

Mihail, R.--Introducere in strategia experimentarii, cu aplicafii din tehnologia chimica, E.S.E., Bucuresti, 1976.

Sindila, Gh.-Cercetari teoretice si experimentale privind deformarea plastica in camp electromagnetic. Teza de doctorat. Bucuresti, 1985.

Sindila Gh., Rohan R., Sindila G.--Deformation of metals in electromagnetic field. Proceedings. International conference on manufacturing science and education challenges of the European integration. 6-7 Nov., 2003, Sibiu.

Table 1

 Encrypted level values

Natural variables Encrypted -1 0 +1
 variables
 Natural level values

 Tension, U [V] [x.sub.1] 4000 4475 5000

 No. of wires, N [x.sub.2] 5 8 13

Coil's wire diameter, [x.sub.3] 1,1 1,6 2,3
 d [mm]

 Conductor's [x.sub.4] 30 40 60
 diameter,
 D [mm]

 Clearance, j [mm] [x.sub.5] 0,7 1,0 1,5

Material's thickness, [x.sub.6] 0,5 0,7 1,0
 g [mm]