Optimalization of technological parameters of flow forming process.

Malina, Jiri ; Jirkova, Hana ; Masek, Bohuslav 等

1. INTRODUCTION

Flow forming (Awiszus et al. 2005, Awiszus et al. 2005, Ufer et al. 2006) uses three rollers for the reduction to final diameters. These three rollers are not driving and their rotation is attained through the friction between the wrought rotating semi-product and the shaping rollers Fig. 1.

The optional parameters for this forming technique are, apart from material, the size of reduction and speed of feed. During the experiment, the influence of the forming parameters on the quality of the final product was obtained.

2. THE INITIAL SEMI-PRODUCT

A semi product made of hot rolled thin-walled 16MnCrS5 steel tube was used with an initial diameter of 60 mm and wall thickness of 6 mm (Table 1).

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

The 16MnCrS5 steel is low alloyed manganese-chromic steel with good hardening capacity for cementation. It is primarily used for medium stressed motor vehicle components. The initial ferrite pearlite microstructure had an average grain size of about 10 [+ or -] 5 [micro]m (Fig. 2)

3. EXPERIMENT

Firstly the initial formability of the material without heat treatment was tested. The material had the following mechanical properties (Table 2).

The material in this state was found to be unsuitable for this forming technology. It was impossible to use the material in this state for production and it was necessary to use soft annealing.

The initial material was soft annealed at 700[degrees]C for 30 to 180 min (Fig. 3).

[FIGURE 3 OMITTED]

On the basis of the resulting relationship between micro-hardness and annealing time and the metallographic analysis, the initial material was annealed at 700[degrees]C for time 60 and 180 min.

The annealing time of 60 minutes was chosen, because after this time the lamellar pearlite can transform to globular, leading to increased formability of the material.

The annealing time of 180 min provided the possibility of comparing the forming process on the material with inferior mechanical properties (Table 3) with globular pearlite structure. Mechanical properties were measured on the micro tensile specimens.

Annealing for 180 minutes led to the steep reduction of yield and ultimate strength, and increasing ductility [A.sub.5mm] to 44%.

While forming to the required size, the feed speed was varied and its influence on the surface quality was observed. In this case the surface of the material was not turned before forming. The feed speed was 1, 2 and 3 mm/rev.

On the basis of the surface analysis, a feed speed of 2 mm/rev was chosen as the optimal speed. This feed led to the most balanced surface quality ( Fig. 4)

Both variants of the heat treated materials were reduced to the same dimensions (Fig.5). The size of reduction and speed of feed (2 mm/rev) were also the same. The forming process was successful for the first material variant (annealed for 60 min), and for the second variant (annealed for 180 min). The materials and technological properties were found to be suitable for reaching the required goal, which was the production of a hollow shaft (Fig.6).

The final product was cut into sections. The structure, micro hardness and mechanical properties were found for the smallest and middle diameters, which were where the material was reduced. The results of the microstructure analysis did not prove the structure refinement in the first or the second material variant.

The mechanical properties were relatively similar for the smallest diameter 0 37 mm and the middle diameter 0 42 mm, but there were big differences between materials (Table 4).

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

4. CONCLUSION

The results of the experiment verified that an experimental machine developed primarily for spin extrusion is suitable for the flow forming process, and that it is possible to produce a viable product with this technology. This product has many potential uses in the construction area. It can, because of the minimal amount of scrap created during production, contribute to the reduction of material costs.

On the material annealed at 700[degrees]C/60 min an increase of ultimate strength by about 29% and yield strength by about 96% was obtained. For the forming material annealed at 700[degrees]C/180 min, a 36% increase of [R.sub.m] and 106 % of [R.sub.p02] was achieved. All with residual ductility [A.sub.5mm] higher than 25 %.

In the future, the fatigue properties of the whole semi-product will be tested.

ACKNOWLEDGEMENTS

This paper includes results obtained within the project 1M06032 Research Centre of Forming Technology.

5. REFERENCES

Awiszus, B. (2005) Erweiterung der Formgebungsgrenzen durch inkrementelle zyklische Umformung am Beispiel des Druckwalzens. (The extension of the forming limits with use incremental cyclical forming on the example of flow forming). The conference transcript for the final colloquium of DFG (German Research Council) main theme 1074 "Extension of formings' limits in the forming process.", Aachen

Awiszus, B. & Meyer, F. (2004) Der Einfluss technologischer Kenn-grdfien und Parameter auf den quasistationdren Zustand beim Druckwalzen -Beschleunigung der FEM durch modifizierte Anfangswerte. (The influence of the technological parameters on the quasistatic state in Flow forming described with FEM with help of modified beginning conditions). Progress report for DFG (German Research Council) main theme: Modeling of the incremental forming. Technical University Chemnitz.

Neugebauer R.; Glass R.; Kolbe M. & Hoffmann M. (2002) Optimisation of processing routes for cross rolling and spin extrusion. Journal of Materials Processing Technology, Volumes 125-126, Pages 856-862

Neugebauer R.; M. Kolbe & R. Glass (2001). New warm forming processes to produce hollow shafts. Journal of Materials Processing Technology, Volume 119, Issues 1-3, Pages 277-282

Ufer R., (2006). Modellierung und Simulation von Druckwalzprozessen, (Modelling and Simulation of Flow forming process) ISBN 3-937524-43-6, Zwickau

Table 1. Chemical composition of 16MnCrS5 steel.

element C Si Mn Cr S P

% 0.16 0.4 1.2 1 0.03 0.03

Tab. 2. The micro-hardness and mechanical properties of the
initial material.

HV 0.2 [R.sub.m] [MPa] [R.sub.p02] [A.sub.5mm] [%]
 [MPa]

 238 687 680 23

Tab. 3. The micro-hardness and mechanical properties of the
initial material, after soft annealing.

Annealing HV 0.2 [R.sub.m] [R.sub.p02] [A.sub.5mm]
time [min] [MPa] [MPa] [%]

60 184 582 375 41
180 157 476 312 44

Tab. 4. The micro-hardness and the mechanical properties in
relation to size of reduction and annealing time.

Diameter Annealing HV 0.2 [R.sub.m]
 time [min] [MPa]

[empty set] 37 60 248 750
 180 230 647
[empty set] 42 60 245 739
 180 221 624

Diameter Annealing [R.sub.p02] [A.sub.5mm]
 time [min] [MPa] [%]

[empty set] 37 60 736 27
 180 645 26
[empty set] 42 60 716 27
 180 622 26