Composites for machine tool beds

Abstract

In general, machine tool structures like lathe, milling, broaching, and grinding machines, etc. are subjected to regular unwanted vibrations. These machine tool vibrations or chatter are deleterious to machining operations. It results in degraded quality on the machined parts, shorter tool life, and unpleasant noise, hence are to be necessarily damped out. The important characteristics of the machine tool structures for metal cutting are high damping and static stiffness which ensure manufacture of work pieces of the required geometries with acceptable surface finish at the required rate of production in the most economical way. The unwanted vibrations must be arrested in ordet to ensure higher accuracy along with productivity.

In the present work, the chatter vibrations on a slotted table Horizontal Milling Machine have been damped out using composite structure as a substitute for the base of the work piece. Glass Fiber Polyester and Glass Fiber Epoxy plates are fixed on to the slotted table as a secondary bed material and the workpiece is mounted on this bed for feeding to the rotating milling cutter. Initially four holes are drilled on each plate of the composite and a set of five plates of each type of composite are mounted for conducting the experiments. A mild steel specimen of similar dimension of the composite plate is placed on the pile of the composites and the setup is fixed to the slotted table using bolts and nuts. An up milling operation is carried out and the vibration signal is recorded on the screen of the digital phosphorus storage oscilloscope. The signal and RMS amplitude, frequency and time period of vibrations are recorded. The experiment is repeated for different sets of composite plates by decreasing the number and the corresponding readings are recorded and tabulated. Moreover, experiments are also conducted without any composite material below the mild steel specimen. It is observed that the vibration amplitude decreases with increase in number of layers of sheets of composites and then increases with increase in number of plates. Moreover, the optimum number of composites are also experimentally determined. The design of the experimental setup has been modeled using CatiaV5R15.

Apart from total damping of the system, emphasis has also been focused to find out the material damping of the composite materials so as to select the same for effective damping of the structures. An energy balance approach has been used for calculating the material damping of the fiber reinforced composites used in the experiment.