Abstract
In a study with an undergraduate student, supported by Fapesp (2008/50918-6) and concluded, it was developed the first prototype of a toolholder internally cooled using a fluid in phase change. The basic concept of this system is originated in the more efficient heat removal during the fluid change in steam, promoted at the region below of cutting tool, where the highest machining temperature are present. For this phenomenon to easily occur, it is used a refrigerant fluid as CFC or HCFC type, which the tipping points are closed to the room temperature, like is the case of Freon 11 (R-11) and Suva 123 (R-123). The toolhoder proposed has a cavity below of the insert, which is filled with a refrigerant fluid passing through within of the toolholder body. The cavity and the insert are separated by a cooper plate for better heat dissipation. The vaporized fluid is transported to a condenser, where the fluid is liquefied and return to the toolholder in closed cycle. As result, in the turning of an austenitic steel with chromium carbide, it was obtained promising results in relation to the tool life, which reached seemed values to the machining with semi-synthetic cutting fluid and clearly superior to the dry machining. However, significant problems related to the toolholder design and characteristic of the machine tool were detected, which limited the capacity of the study. Specifically, it was observed that the deficiencies are in the low dynamic stiffness of the machine tool, which in higher rotations used to maintenance of cutting speed produce damages in the insert due to excessive vibrations of the machine tool. Another restraint treats of the project and manufacture of the toolholder, once it was not have financial support. This way, it was chosen a simple configuration, but the cavity had poor geometry hindering the good fluid flow and possibly forming steam at the interface between the cooper plate and the fluid in liquid state, especially in the corners. According to the problems reported, and in the attempt to rescind the use of cutting fluid, even if in some specific machining conditions, in this Project is proposed the optimization of the toolholder by mean of more adequated solutions to heat change in the cavity region below the insert, now using a CNC machine, obtained in a Project of same subject, able to utilize the specimens in constant cutting speed and no dynamic disturbances due to low stiffness of the machine tool.
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