Evaluation of the level of hardening of aluminum alloy chips intended for subsequent pressure treatment

OBRABOTKAMETALLOV Vol. 23 No. 1 2021 TECHNOLOGY The experiments demonstrated that to ensure the briquettes’ relative integral density of 70...80 %, briquetting pressure should not be lower than 80...100 MPa. The use of the stated pressures is common for compacting installations; usually, this level is not exceeded to avoid the danger of increased wear of the tool working surfaces. In the case of aluminum alloys, tool wear is caused by a thin protective fi lm of aluminum oxide surrounding each chip fragment. The hardness of aluminum oxide is very high; the edges of its protruding parts continuously scratch the tool and cause wear. The danger of aluminum sticking to these surfaces aggravates the situation. An important factor in thedisposal of aluminumchips isknown tobe thedevelopment of sheardeformations that allow crushing the oxide fi lm surrounding each metal fragment, which enables consolidating the metal [11, 12]. Therefore, for the further processing of the obtained briquettes, a combined rolling-pressing unit (CRP) was used (Fig. 1, b ). The rolls of the unit were heated to a temperature of 80...100 o C. The briquettes were set into rolls and deformed to obtain a rod with a fi nal size of 7 and 9 mm, which corresponded to the values of the reduction ratios during pressing 8 and 5. Studies of the obtained rods microstructure led to the conclusion that in some cases the chip elements do not form a continuous connection, despite certain conditions created for this, such as high temperature and signi fi cant shear deformations. The reason for this phenomenon could be that after removal by the cutter the chips have increased strength properties, which prevents the process of their consolidation during cold briquetting. A low level of compaction at this stage leads to a high level of residual porosity after hot deformation. Mathematical simulation of the cutting process is proposed to apply for assessing the level of chip hardening. It is carried out in the next part of the work. The methodology of the computational experiment To estimate the deformed state, we used the fi nite element method implemented in the RAPID 2D software package (  E.G. Polishchuk, D.S. Zhirov); the description and application of the software product are given in the book [13]. The sequence of actions included the creation of the initial shape of the deformation focus and the con fi guration of the tool (Fig. 2). The scheme of the deformed state is fl at. Thus, only the near-surface layer of the material is considered. This layer experiences the cutting stresses. The physical and mechanical properties of the deformable material correspond to the AMg1 alloy and are taken from the library of the program module. The presence of viscous properties of aluminum alloys in the cold state was proved in [14–16]. The cutter is presented as an absolutely rigid body, so the characteristics of the material from which it is made were not taken into account. The mutual movement of the tool and the deformable material is set using the appropriate boundary conditions. The deformable medium is viscoplastic with power-law hardening. The speed of mutual displacement of the workpiece and the cutter is set at 2 m/s. Usually, the Siebel law of friction is set in Fig. 2. Boundary conditions in the formulation of the problem and the coordinate system,  – tool rake angle