Comparison of numeric simulated and experimental measured results of setting deformation.

Martinkovic, Maros ; Sobota, Robert ; Kapustova, Maria 等

1. INTRODUCTION

Macroscopic effects of deformation in the volume forming are not corresponding fully with microscopic structural chances. Different degree of deformation depending on the area of specimen was observed (Martinkovic 2005). Degree of deformation heavily influences the materials properties due to deformation strengthening and materials behaviour during forming depends on the materials properties. Finite elements methods can lead to excellent results of deformation in each place of deformed parts, but it is necessary to verify them (their parameters) by experimental results. There are several microscopic methods (Forejt 2006) to obtain degree of strain in material structure, but measurement of grain boundaries deformation by means of grain boundaries orientation measurement was not used to recent time. The grain boundaries orientation direct depend on the grain deformation.

2. EXPERIMENTS

The verification of numerical model of bulk forming was made on two types of materials: steel S235JRG1 (1.0036) and aluminium alloy AW-6063A (6063A) and two types of forming: cold and warm bulk forming. For numeric simulation MSC.SuperForge simulation software was used (http:// www.mscsoftware.com).

2.1 Numeric simulation

The parameters of numeric simulation for steel specimen was: forging on crank press, tool temperature 20[degrees]C, friction coefficient 0,4, cylindrical bar from steel 1.0036 with diameter 14 mm and high 29 mm, temperature 20[degrees]C in basic state, high 16,7 mm after deformation. The results of numeric simulation of deformation--effective plastic strain in longitudinal section in the middle of cylindrical bar was observed.

The parameters of numeric simulation for aluminium alloy specimen was: forging on crank press, tool temperature 20[degrees]C, friction coefficient 0,4, cylindrical bar from aluminium alloy 6063A with diameter 25 mm and high 49 mm, temperature 240[degrees]C in basic state, high 30 mm after deformation. The results of numeric simulation of the process--effective plastic strain re in longitudinal section in the middle of cylindrical bar was observed. In this case the temperature in longitudinal section in the middle of cylindrical bar was observed too, because increasing temperature within process can lead to recrystallization effect.

2.2 Setting

Cold forming of the real part from steel was realized at the same basic parameters as are described hereinbefore (see chapter 2.1). Eccentric press LEXN 100 was used.

Warm forming of the real part from aluminium alloy was realized at the same basic parameters as are described hereinbefore (see chapter 2.1). Eccentric press LEXN 100 was used.

3. MICROSTRUCTURE ANALYSIS

The structure of steel material was observed with about 200x magnification of light microscope on metallographic cut of longitudinal section in the middle of cylindrical bar. The metallographic cut was mechanical grinded and polished, chemical etched in 3% HNO3 alcohol solution. An example of steel structure in basic state is on Fig. 1, an example of steel structure after deformation is on Fig. 2.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

The structure of aluminium alloy material was observed with about 50x magnification of light microscope on metallographic cut of longitudinal section in the middle of cylindrical bar. The metallographic cut was mechanical grinded and polished, chemical etched in Keller etcher (1,5 ml HF, 3 ml HN[O.sub.3], 100 ml [H.sub.2]O). An example of aluminium alloy structure in basic state is on Fig. 3, an example of aluminium alloy structure after deformation is on Fig. 4.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

3.1 Quantitative analysis

The strain of probes on their sections was obtained by stereological measured by measurement of degree grain boundaries deformation--degree of grain boundaries orientation (Saltykov 1970; Underwood 1970). The method of oriented test lines was used. Test lines were placed perpendicular and parallel to the grain boundaries orientation direction effected by straining (Russ & Dehoff 2000). From the relative number (number to unit of length) of parallel test lines intersections with grain boundaries [([P.sub.L]).sub.P] and perpendicular lines ones [([P.sub.L]).sub.O] was total relative surface area (area to unit test volume) [([S.sub.V]).sub.TOT] of grains estimated according equation (1) and planar oriented part of relative surface area [([S.sub.V]).sub.OR] of grains estimated according equation (2). The relative measure precision was always smaller then 10% with reliability 90%. Degree of grain boundaries orientation was estimated as [([S.sub.V]).sub.OR] to [([S.sub.V]).sub.TOT] ratio.

[([S.sub.V]).sub.TOT] = [([P.sub.L]).sub.O] + [([P.sub.L]).sub.P (1)

[([S.sub.V]).sub.OR] = [([P.sub.L]).sub.O] - [([P.sub.L]).sub.P] (2)

[FIGURE 5 OMITTED]

The results of grain boundaries orientation measurement in different places (see Fig. 5.) of deformed bulk of steel specimens are in Table 1, the ones of deformed bulk of aluminium alloys specimens are in Table 2.

4. CONCLUSION

The effective strain in each places of steel specimen obtained by numeric simulation was in very good coincidence with the experimental results (Table 1.). The effective strain obtained by numeric simulation of aluminium alloy specimen in the middle of specimen bulk was greater then experimental ones (Table 2.). In these places the temperature of the material during deformation increased over the recrystallization temperature 250[degrees]C and recrystallization was passed and the deformation of grain boundaries was decreased. In other places the coincidence was observed. The results of numeric simulation are valid. The utilization of stereology metallography allow very simple and effective experimental estimation of plastic deformation degree in various places of bulk formed parts and to verify numerical model by comparing this results with numeric simulated ones.

This work was supported by Slovak Republic Ministry of Education VEGA Grant No. 1/3192/06.

5. REFERENCES

Forejt, M. & Piska, M. (2006). Teorie obrabeni, tvareni a nastroje, Theory of machining, forming and tools, CERM, 80-214-2374-9, Brno

Martinkovic, M. (2005) Quantitative analysis of plastic deformed material structure, Proceedings of Forming 2005, pp. 175-180, 80-248-0888-9, Lednice, 14.-17.9.2005, VSB-Technicka univerzita, Ostrava

Russ, J., C. & Dehoff, R., T. (2000). Practical stereology, Plenum Press, 0-306-46476-4, New York

Saltykov, S., A. (1970). Stereometriceskaja metallografia, Stereometric metallography, Metallurgia, 3-11-1 88-70, Moskva

Underwood, E., E. (1970) Quantitative stereology, Addison-Wesley Pub., Mass

Tab. 1. Measured grain boundaries orientation in different
places of steel specimen

 Orientation [%]

Position 1 2 3

C 30 23 40
B 42 40 35
A 62 44 43

Tab. 2. Measured grain boundaries orientation in different
places of aluminium alloy specimen

 Orientation [%]

Position 1 2 3

C 19 27 40
B 18 28 33
A 0 20 32