Novel Auxiliary Fixture System to Enhance Milled Thin-Walled Parts Quality

Al Zubaidi, Nihad
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University of Guelph

Due to the high flexibility of thin-walled workpieces, vibrations are a common problem when milling thin-walled workpieces. Vibrations lead to poor surface finish and reduced machining efficiency. Employing multi-pin fixtures to increase the damping and stiffness of the vibration modes of the workpieces is one of the best methods to suppress vibrations. The performance of multi-pin fixtures depends on the efficiency of their pin’s mechanism. In this study, a novel pin mechanism was developed based on the application of meteorological elastomer (MRE) Nine pins were used in building a new fixture. Hammer test results showed that the mechanism provided adjustable damping and stiffness, and with increasing the electric current, the damping and stiffness increased. Based on contact force measurements, it was found that the pin contact force is soft and can be adjusted. For the fixture with a single pin, results of hammer tests showed an increase in the dynamic properties of vibration modes of workpieces. The properties further increased with increased electrical current. For the single-pin fixtures, four locations (1, 2, 4 or 5) were tested. It was found that Location 5 had the best vibration suppression and the lowest surface roughness combined with the lowest cutting force value.
Fixtures were also tested with more than one pin, which resulted in increased properties compared to fixtures with single pins. A multi-pocked industrial workpiece was milled in order to evaluate the performance of a six-pin fixture. The results showed that the stiffness increased by 90%, and the damping ratio was increased tenfold. The cutting force decreased by 70% for milling a slot in the bottom floor of the workpiece and by 40% for milling a sidewall of the workpiece. The surface roughness of the bottom floor decreased from 2.5 μm to about 0.4 μm. However, cutting the sidewall decreased the surface roughness from 2.3 to 0.3 μm. Here, we show that it is possible to design a fixture with adjustable dynamic properties. for milling thin-walled workpieces with complex geometric shapes. Due to the use of MR elastomer, this design is cost-effective, easy to assemble, and provides high vibration suppression performance.

Milling Process, Vibration suppression, Robot, Fixtures, Multi pin fixture, MR Elastomers, Frequency Response Function (FRF), Surface quality, Cutting force