The production of components by machining remains a relevant application within manufacturing. From a commercial point of view, the aim is manufacture accurate parts within a time that maximise the profit. Unfortunately, there are a number of factors that influence the ability to achieve this goal.
One of the main factors that leads to a decrease in the machining capacity of a machining process is the vibrations that are generated during the process. This decrease in the material removal rate capabilities leads to an increase in cycle time that has not been foreseen in the design phase of the process, directly affecting the company's commercial margins.
Knowledge of the mechanics of the machining process and the vibrations generated is essential to prevent negative consequences.
These vibrations can be caused by the excitation produced by an external force or disturbance that causes a vibration of the same frequency as the exciting force (forced vibration). In milling operations, this frequency is usually the tooth passing frequency. However, vibrations can also be caused by self-regeneration which continuously amplifies the generated disturbances. The consequence of this continuous amplification of the disturbances is self-excited vibrations or chatter.
In the case of forced vibrations, the objective is to keep the amplitude of these vibrations below a range considered admissible that ensures a good surface finish, small dimensional errors and does not adversely affect either the life of the tool or the machine. In the case of chatter, the objective is to work in conditions in which chatter does not appear.
In both cases, a thorough knowledge of the mechanical system used in machining is essential. This knowledge includes above all the stiffness, damping and natural frequencies of the mechanical assembly consisting of the machine, tool, tooling and workpiece. The way to synthesise all this information is through Frequency Response Function (FRF).
By using mathematical models that use the FRF of the mechanical system, the geometry of the cutting tool, the working conditions (speed of rotation, depth of cut, ...), and the tool paths, it is possible to predict the dynamic behaviour (vibrations) and therefore find the best conditions to reduce cycle times.
Likewise, finite element programmes will be used to optimise the design of certain components of the mechanical assembly made up of the machine, tool, tooling and part.
The goal is to have a software that allows the prediction of stable cutting conditions in order to design machining processes where the predicted cycle times do not suffer alterations/modifications due to the need to modify the cutting conditions in order to ensure the quality of the part.
The PhD student will have to develop analytical models for predicting stable machining conditions, combining analysis with finite element analysis and validation with experimental machining tests.
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