Abstract
In this study, an experimental, metallographic method for determining strain distribution in a cold extruded aluminum gear-like element, based on the dependence of recrystallized grain size on prior deformation, was devised in order to overcome design problems in manufacturing of complex parts where critical values of strain and stress could cause a fracture. The method was applied on a 99.5% aluminum bar subjected to cold, radial extrusion, in order to produce complex gear-like element. To reveal the strain and stress distribution in specimens, the calibration and flow curves were first obtained by uniaxial compression (Rastegaev test). Afterwards, the grain size in different parts of the gear section was examined, the strain and stress distributions were calculated, and the results were confirmed by microhardness measurements. It was found that grain size, strain, stress, and microhardness considerably differed throughout the cross-section of the gear. The coarsest grain, and thus the lowest strain zone, was obtained in the central part of the tooth and in the zone between teeth. Conversely, the finest grains appeared in the highest strain zone at the specimen surface, particularly in the root of the teeth. Furthermore, results were supported by microhardness measurements, i.e., microhardness corresponded to grain size and strain hardening. Finally, the real view of material flow in the complex extruded part was successfully obtained by the metallographic method.
Highlights
Cold extrusion of gear-like elements is a forming process which has many advantages compared to other manufacturing processes, such as machining or casting
That that material is only and slightly that is almost to the die cavity. Another only slightly deformed, thatdeformed, is almostand translated to thetranslated die cavity. Another zone wherezone relatively where relatively low deformation is observed is the area between the teeth, close to the surface
The microhardness measurement, used in Reference [14], as well in this paper shows that deformation zones could be determined, but with lower precision, as the microhardness measurement was more dependent on the place of indentation, while the metallographic method gave the mean grain diameter in the field of view and gave direct visualization of the deformation zones
Summary
Cold extrusion of gear-like elements is a forming process which has many advantages compared to other manufacturing processes, such as machining or casting Parts obtained in this process have higher mechanical properties, due to strain hardening, than those made by machining or casting, while, production time could be shorter, and less material is lost compared to machining [1]. Application of this process is limited, due to the high values of required forming load, which affects the size of the parts that can be produced, as well as part accuracy and tooling life. Expected values of forming load and punch pressure help define the number of process stages, as well as the design of the tool, while values of stress and strain could indicate the location of potential critical fracture zones within the workpiece [1].
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